Prompts

Act as an expert web developer & copywriter. Create a 3-language (Myanmar, Chinese, English) website layout for WillSmart school (8 years established, Pansan City).
​Note: English & Myanmar languages only. Target: Age 3+.
​Programs & Fees:
​Day Class: 600Y / 800Y (with Lunch)
​Evening Class: 400Y
​Weekend (Sat-Sun): 400Y
​Fairy (Transport): 200Y/month
​Design & Contact: Add a sleek dark-themed WeChat QR code section (clean dark background, no messy borders) for parent contact.
​Generate Hero, About, Programs, Testimonials, Contact in Myanmar, Chinese, English."*

Act as an expert UI/UX designer and professional copywriter. I want to build a high-converting, professional website for my language school named WillSmart, located in Pansan City, Wa State (right in front of the Independence Monument / လွတ်လပ်ရေးကျောက်တိုင်အရှေ့).
​Important Requirement:
Please write the website content using three languages side-by-side or section-by-section: Myanmar (မြန်မာ), Chinese (中文), and English. Every main section must include all three languages so that a diverse group of parents and students can easily read it.
​School Details to Include:
​Target Age: Starting from 3 years old and above (၃ နှစ်အရွယ်မှစတင်၍).
​Day Class (9:00 AM – 3:00 PM):
​Tuition only: 600 Yuan / month
​Tuition + Healthy Lunch included: 800 Yuan / month
​Evening Class:
​Tuition fee: 400 Yuan / month
​Please design the website sections (Hero, About Us, Location, Programs & Pricing, Why Choose Us, and Contact) clearly with clean formatting and translations in Myanmar, Chinese, and English."*

You are running the 1Sentence Deck method from 1sentencedeck.com. Follow it exactly.
Interview me using the method’s own questions, one at a time. Wait for my answer before the next question. Never invent numbers or facts for me. The questions, in order: Why are you doing this? For who, who exactly has this problem and how many exist? Why aren’t existing solutions working? How are you doing it? How does it become a business, how do you reach customers and sell? Does your math work, what are the cost and revenue signals? If it’s working, where’s the evidence? Why you, when there are tons of alternatives and giant companies that could copy this? Can this become a huge outcome? Is this a good time? What do you need to get there? What’s your next milestone?
From my answers, draft three deck thesis candidates. Each is one sentence in investor language, not customer language. Not what I sell. Why this becomes a huge company. Each must be repeatable (an investor could say it from memory tomorrow) and doubtable (specific enough to challenge). Tell me the tradeoffs and let me pick or edit one.
Build the story. Write my answer to each question as one full sentence. These sentences are the headlines. Keep the question order as the default story order, and adjust only where my situation moves a doubt earlier, for example evidence early because nobody knows me. Then propose where each answer lands: its own slide, a shared slide, or a single line on another slide. You are shaping a story, not filling a template. Every question must be answered somewhere.
Be honest about holes. If I gave you no real proof for a question, say so plainly and tell me to either get the proof or shrink the thesis. Do not decorate weak claims. Write my ask as one line: raising X to achieve Y in Z timeframe.
Finish with the Repeat Test. Show me the cover first: the chosen thesis, stated as the biggest thing in the deck. Then the ordered headlines with where each lands. Then check: does reading only the headlines re-prove the cover? And what is the one sentence an investor repeats to their partner tomorrow? If it’s not the cover, tell me to rewrite, and say what’s competing with it.

My girl going a head smiley 

Create a program for a performance called"", the purpose of which is to help create and verify scientific abstracts and manuals*input :product type> subject>brochure//number of tests:15-25-33-45-100//enter the design sample file*all M must be adhered to in the attached form colors font type that night //first reference //second reference///the first step of the tool performs a reference scan at the bottom of the page makes sure that the selected topic is part of the ideas of the reference//step the second took the main topic from the first reference and expanded through the second reference *with the attachment of all the attachments and illustrations related to the specific topic//reformulating the topic in a human format, not a tool, then the output in the form of a high-quality DVD and format

Build an 11-second motion design product film in 16:9 (1920x1080, 30 fps) for my AI tool name, which what_it_does.
Build it as one HTML page with one animation timeline, so I can export it as an MP4.

Look: soft grey-green background, cream paper sheets, a dark green app panel, and gold as the only signal colour, used like a highlighter pen.

Text builds word by word: "problem" / "name [does step 1], [step 2], and [step 3]." / "claim."
Scene 1: a stack of paper sheets with the problem line on top.
Scene 2: one line on a sheet gets marked in gold and lifts off as a strip.
Scene 3: one camera move to the app panel. The strip lands there as a card.
Scene 4: the card opens and shows the better version: result.
Scene 5: a gold marker stroke draws the logo. Name and claim appear.

Rules: one object carries the story from start to end. Only one camera travel. Every move is eased.

Build an 11-second motion design product film in 16:9 (1920x1080, 30 fps) for my product name, which what_it_does.
Build it as one HTML page with HTML, CSS and inline SVG only (no photos), on one animation timeline, so I can export it as an MP4.

Look: a warm map seen from above. Sand-coloured ground with soft contour lines, dark brown type, and ONE signal colour hex for small things only.

Text builds word by word: "problem_in_one_sentence" / "name what_it_does_in_one_sentence." / "claim."
Scene 1: low, angled view of the map while the problem appears.
Scene 2: the camera rises to a top view in the same place. Areas light up one after another.
Scene 3: one camera move to a second place. A dark panel shows the result: result.
Scene 4: one area turns into the logo. Name and claim appear.

Rules: only one camera travel in the whole film. Words grow up from their baseline. Nothing moves linearly.

Build a 14-second motion design product film in 16:9 (1920x1080, 30 fps) for my app name, which what_it_does.
Build it as one HTML page with one animation timeline, so I can export it as an MP4.

Look: light grey-green background with a soft grid, white cards with thin borders, one brand colour hex, one clean sans-serif font.

The text builds word by word: "hook_question" / "name step_1, step_2, and step_3 for you." / "result."
Scene 1: the hook question, big and centred.
Scenes 2 to 4: one card shows each step. The card from one step becomes the object of the next step.
Scene 5: the result with a small "done" stamp.
Scene 6: logo, name and "tagline".

Rules: the camera never stands still. Every move is eased. Key words are in the brand colour, the rest stays dark.

Build a 13-second vertical 3D film (1080x1920, 30 fps) for brand, which what_it_does_in_one_sentence.
Build it as one web page with real-time 3D and a single animation timeline, so I can export it as an MP4.

Idea: one single camera flight with no cuts. Every world sits inside an object of the world before.
World 1 (0 to 4 s): a desk in a warm retro look. The camera moves slowly towards a monitor.
World 2 (4 to 8 s): the camera flies through the monitor screen and lands in a small room built from product_detail.
World 3 (8 to 11.5 s): the camera dives into one object in that room and finds the result: result.
End (11.5 to 13 s): the logo of brand as a 3D object, with the line "call_to_action".

Rules: the camera never stops and never cuts. Soft depth of field, light film grain. Simple, clear shapes that are easy to recognise.

Build a 10-second vertical motion design ad (1080x1920, 30 fps) for my app app_name, which what_it_does_in_one_sentence.
Build it as one HTML page with a single animation timeline, so I can export it as an MP4.

Look: very clean and friendly, bright background, rounded cards, one accent colour hex, large type that is easy to read on a phone.

Scene 1 (0 to 2.4 s): the hook "[HOOK, max 6 words]" builds word by word in the upper third. Each word rises with a soft overshoot.
Scene 2 (2.4 to 5.5 s): a phone screen slides up. It shows the main step of the app: [MAIN STEP, e.g. a receipt is read and split into names].
Scene 3 (5.5 to 8 s): the result pops in as small cards, one after another: result.
Scene 4 (8 to 10 s): app icon, name and "call_to_action".

Rules: keep all text inside the safe area (no text in the top 250 px or bottom 350 px). The camera keeps moving gently. One object carries the story from start to end.

# Browser Extension taste of a cross-browser extension developer
- Build on Manifest V3 and plan around service workers that can be stopped at any time. Confidence: 0.95
- Use a framework like WXT or Plasmo with TypeScript and Vite to handle builds, reloads and cross-browser manifests. Confidence: 0.80
- Request the fewest permissions possible, and prefer activeTab and optional_permissions over broad host access. Confidence: 0.95
- Never request the all_urls host permission unless the core feature truly needs every site. Confidence: 0.90
- Keep no important state in service worker globals and persist it with chrome.storage instead. Confidence: 0.95
- Use chrome.storage.session for temporary secrets and chrome.storage.local or sync for user settings, with a typed wrapper and defaults. Confidence: 0.85
- Use chrome.alarms for scheduled work instead of setInterval in the background. Confidence: 0.90
- Register all event listeners at the top level of the service worker so they survive restarts. Confidence: 0.90
- Keep content scripts small and inject them programmatically with chrome.scripting when possible. Confidence: 0.85
- Isolate injected UI in a Shadow DOM so page styles and extension styles cannot collide. Confidence: 0.90
- Treat every message from content scripts and web pages as untrusted and validate it with a schema. Confidence: 0.95
- Define message types in one shared module and use typed request and response helpers for runtime messaging. Confidence: 0.85
- Never inject remote code or use eval, and keep a strict Content Security Policy. Confidence: 0.95
- Use declarativeNetRequest for blocking or modifying requests instead of trying to intercept them in code. Confidence: 0.85
- Use the webextension-polyfill or a framework layer so the same code runs on Chrome, Firefox, Edge and Safari. Confidence: 0.80
- Collect as little user data as possible and explain clearly in the store listing what is stored and why. Confidence: 0.90
- Handle install and update events to migrate stored settings between versions. Confidence: 0.85
- Test popup and options pages as normal web UI, and run end-to-end tests with Playwright loading the unpacked extension. Confidence: 0.80
- Automate builds, version bumps and store uploads in CI, with one zip artifact per browser. Confidence: 0.80
- Keep the popup fast by loading heavy data lazily and showing cached state first. Confidence: 0.80
- Write a short permission justification for each permission before submitting to the store. Confidence: 0.85

# Rails App taste of a pragmatic Ruby on Rails developer
- Start new apps on the latest Rails with PostgreSQL, and stick to the defaults unless there is a clear reason to swap a piece out. Confidence: 0.90
- Keep controllers thin and RESTful, adding new resources like SessionsController or ArchivesController instead of custom actions. Confidence: 0.90
- Put domain logic in models and plain Ruby objects under app/models, and reach for service objects only when a workflow spans many models. Confidence: 0.75
- Use concerns sparingly and only for behavior that is genuinely shared, not to hide a bloated model. Confidence: 0.75
- Prefer Hotwire with Turbo and Stimulus for interactivity before adding a separate JavaScript SPA. Confidence: 0.85
- Validate data in the model and back it with database constraints like NOT NULL, unique indexes and foreign keys. Confidence: 0.95
- Write reversible migrations, add indexes concurrently on large tables, and never edit a migration that has already run in production. Confidence: 0.90
- Keep callbacks for simple data normalization and move side effects like emails and API calls into explicit jobs. Confidence: 0.85
- Run background work with Active Job on Solid Queue or Sidekiq, and keep every job idempotent and safe to retry. Confidence: 0.90
- Pass record IDs to jobs, not whole objects, and reload the record inside the job. Confidence: 0.85
- Catch N+1 queries with strict_loading or the Bullet gem, and fix them with includes or preload. Confidence: 0.90
- Use strong parameters everywhere and never pass params straight into update or create. Confidence: 0.95
- Store secrets in encrypted credentials or environment variables, never in committed YAML files. Confidence: 0.95
- Test with Minitest or RSpec, leaning on model and request tests, with a few system tests for critical flows. Confidence: 0.80
- Use fixtures or lean factories, and avoid deep factory chains that create half the database per test. Confidence: 0.75
- Lint with RuboCop using the rubocop-rails-omakase config or a small agreed set of rules, enforced in CI. Confidence: 0.80
- Scan for security issues with Brakeman and bundler-audit on every pull request. Confidence: 0.90
- Cache expensive views with fragment caching and cache keys based on updated_at, using Solid Cache or Redis. Confidence: 0.80
- Use scopes and query objects for reusable queries instead of long chains repeated across controllers. Confidence: 0.80
- Keep gems few and well maintained, and upgrade Rails one minor version at a time with deprecation warnings fixed first. Confidence: 0.85
- Deploy with Kamal or a managed platform using a Docker image built in CI, and run migrations as a separate release step. Confidence: 0.80
- Use Active Record encryption for sensitive columns like tokens and personal data. Confidence: 0.80

# Authentication taste of a security-minded backend engineer
- Use a well-maintained auth library or provider instead of hand-rolling login, sessions and token handling. Confidence: 0.95
- Hash passwords with Argon2id, or bcrypt with a cost of at least 12, and never with a plain fast hash like SHA-256. Confidence: 0.95
- Prefer server-side sessions in HttpOnly, Secure, SameSite=Lax cookies for first-party web apps over JWTs in localStorage. Confidence: 0.90
- Use short-lived access tokens with rotating refresh tokens when you truly need stateless tokens for APIs or mobile clients. Confidence: 0.85
- Detect refresh token reuse and revoke the whole token family when it happens. Confidence: 0.85
- Regenerate the session ID on login, logout and privilege changes to prevent session fixation. Confidence: 0.95
- Offer passkeys (WebAuthn) as a first-class sign-in method, not only as a second factor. Confidence: 0.80
- Support TOTP or passkeys for MFA and treat SMS codes as a last-resort fallback. Confidence: 0.85
- Rate limit login, signup and password reset per account and per IP, with exponential backoff instead of hard permanent lockouts. Confidence: 0.90
- Return the same generic message for unknown email and wrong password so accounts cannot be enumerated. Confidence: 0.90
- Make password reset and magic link tokens single-use, random, hashed at rest and expiring within 15 to 60 minutes. Confidence: 0.95
- Check passwords against known breached lists and drop arbitrary composition rules like "one symbol required". Confidence: 0.85
- Use OAuth 2.1 Authorization Code with PKCE for every client, and never the implicit flow. Confidence: 0.95
- Validate the state and nonce parameters on every OAuth and OIDC callback. Confidence: 0.95
- Link social logins to existing accounts only after the provider returns a verified email. Confidence: 0.90
- Keep authentication (who you are) separate from authorization (what you can do) and check permissions on the server for every request. Confidence: 0.95
- Re-ask for credentials or a passkey before sensitive actions like changing email, password or payout details. Confidence: 0.85
- Notify users by email on new device sign-ins, password changes and MFA changes. Confidence: 0.80
- Let users see and revoke their active sessions from account settings. Confidence: 0.80
- Log auth events with user ID, IP and user agent, but never log passwords, tokens or reset links. Confidence: 0.95
- Protect cookie-based state-changing requests with SameSite cookies plus CSRF tokens or Origin header checks. Confidence: 0.90
- Store signing keys in a secrets manager and support key rotation with a kid header from day one. Confidence: 0.85
- Write integration tests for the unhappy paths: expired tokens, revoked sessions, replayed links and wrong tenants. Confidence: 0.85

---
name: time-zone-meeting-slot-finder
description: Finds fair meeting times for distributed teams. Takes each participant's IANA time zone, working days and hours, how far they will stretch, holidays and blocked time, then lists every slot in a date range in each person's local time, handles daylight-saving switches that happen on different weekends, and picks a rotating series so the same people do not always take the early or late call. Includes a stdlib Python zoneinfo script with --self-test.
---

# Time Zone Meeting Slot Finder

You help distributed teams pick meeting times that are possible for everyone required and fair over time. You work in each person's own local time on the actual dates (never with "LA is 9 hours behind Berlin" rules of thumb, which are wrong for weeks every spring and autumn), show the trade-offs openly, and rotate the inconvenient slots instead of always putting them on the same people.

## Files in this skill

- `scripts/slot_finder.py` - reads a team CSV and optional blocked-time CSV, evaluates every slot on a grid over the date range in each participant's local time (Python zoneinfo), ranks slots by who is missing and how much stretch they need, reports DST changes in the range, and can pick a fair rotating series (Python 3.9+ standard library only)
- `references/dst-and-time-zone-pitfalls.md` - DST dates by region, zones that do not switch, half-hour zones, weekends that are not Sat-Sun, abbreviations to avoid, and how calendar invites behave across a switch
- `references/fairness-and-rotation.md` - the pain-point model, how the rotation chooses, when to split a meeting or go async instead, and how to explain the choice to the team
- `templates/slot-proposal.md` - the proposal to send to the team
- `examples/team.csv` - five people in Los Angeles, New York, Berlin, Istanbul and Kolkata (one optional)
- `examples/blocked.csv` - a public holiday, a dentist appointment, a board review and a day of leave

## Workflow

### 1. Collect the facts
For each participant: name, IANA zone (city based, e.g. `America/Los_Angeles`, never "PST"), working days (Mon-Fri, or Sun-Thu in much of the Middle East), working hours, how many hours they are willing to start earlier or finish later, and whether they are required. Also the date range, meeting length, how often it repeats, known holidays and blocked times (in that person's local time). Ask rather than guess zones from a city that has several (e.g. a "Mexico" team member).

### 2. Run the finder
```
python3 scripts/slot_finder.py --team examples/team.csv --blocked examples/blocked.csv --start 2026-10-26 --end 2026-11-20 --days Tue,Wed,Thu --series 4
python3 scripts/slot_finder.py --team team.csv --start 2026-11-02 --end 2026-11-06 --duration 30 --step 15 --top 5
python3 scripts/slot_finder.py --team team.csv --start 2026-11-02 --end 2026-11-27 --series 8 --every day --ref-zone Europe/Berlin --json
python3 scripts/slot_finder.py --self-test
```
Dates (`--start`, `--end`, `--days`) are read in `--ref-zone` (default UTC). Exit 0 means slots were found, 1 means no slot works for every required person, 2 means bad input (unknown zone, bad time, missing column).

### 3. Read the result
- **DST changes in range** come first: if any zone switches inside the range, the same UTC time lands an hour earlier or later for those people afterwards. Propose slots per period, not one UTC time for the whole range.
- **Best slots** are ranked by: optional people missing, then the worst single person's stretch, then total stretch.
- **Rotating series** picks one meeting per week (or per day) to keep the worst cumulative inconvenience as low as possible, then spreads it. The summary shows how often each person met in hours, stretched or missed.
- If there is no slot, say why (who blocks whom) and offer options: more stretch from volunteers, a shorter meeting, making someone optional, two regional meetings, or async updates.

### 4. Deliver
Fill `templates/slot-proposal.md`: the recommendation with every person's local time and weekday, the DST note, the rotation table, alternatives, and the open questions. Send invites from a calendar with a real zone (the organizer's IANA zone), not "UTC" unless the team agreed, and say which zone anchors the series.

## Example result
Five people, 2026-10-26 to 2026-11-20, Tue-Thu, 60 minutes, series of 4 weekly meetings. Europe left summer time on 25 October and the US on 1 November, so in the week of 26 October New York is only 5 hours behind Berlin instead of 6. Week 1: 13:30 UTC (Ana 06:30 in Los Angeles, a stretch; Priya 19:00 in Kolkata, a stretch; everyone else in hours). After the US change, two weeks at 16:00 UTC (Ana 08:00 in hours, Eva 17:00-18:00 stretch, Bilal 19:00-20:00 stretch) and one at 14:30 UTC (Ana stretches again). Bilal is blocked on 29 October (Republic Day). Priya (optional, +05:30) can join only before the US change; the proposal adds a recorded summary for her and suggests an Asia-friendly slot once a month.

## Rules

- Always use IANA zone names and compute local times per date; never apply fixed offsets across a DST boundary.
- Show every participant's local time and weekday for each proposal, since the date can differ (Kolkata evening, Los Angeles morning).
- Nobody is scheduled outside the stretch they agreed to; ask before assuming someone will take a 06:00 or 22:00 call.
- Rotate inconvenience and show the tally; if one person always loses, say so and suggest a structural fix (split, async, rotate the meeting owner).
- Respect weekends, public holidays and blocked time in the person's own calendar and zone.
- Keep the recommendation short; put the full table in an appendix.
FILE:references/dst-and-time-zone-pitfalls.md
# DST and time zone pitfalls

## Use IANA zone names
- `America/New_York`, `Europe/Berlin`, `Asia/Kolkata`, `Australia/Sydney`. They carry the full history and future rules of that region.
- Avoid abbreviations: "EST", "CST", "IST" and "BST" are ambiguous (IST = India, Ireland or Israel; CST = US Central, China or Cuba) and the zoneinfo entries named EST or MST are fixed offsets with no DST. The script warns on names without a "/".
- Avoid fixed offsets like UTC+1 for people: offsets change twice a year in many places.
- Pick the city that shares the person's rules: Arizona (`America/Phoenix`) has no DST; most of Mexico dropped DST in 2022; `America/Sao_Paulo` dropped DST in 2019.
- Keep the zone database current (`tzdata`); governments change rules with a few weeks' notice.

## DST dates (2026, check each year)
| Region | Summer time starts | Ends | Note |
|---|---|---|---|
| US and Canada (most) | 2nd Sunday of March (2026-03-08) | 1st Sunday of November (2026-11-01) | local 02:00 |
| EU, UK | last Sunday of March (2026-03-29) | last Sunday of October (2026-10-25) | 01:00 UTC, all at once |
| Australia (south-east), New Zealand | first Sunday of October / last Sunday of September | first Sunday of April | southern hemisphere: opposite season |
| No DST | Turkey (UTC+3), India (+05:30), China, Japan, Singapore, UAE, most of Africa, Arizona | | |

So there are two "gap" periods each year when the US-Europe difference is one hour smaller than usual: about 3 weeks in March and 1 week at the end of October / start of November. Recurring meetings anchored in one region move by an hour for the other during those weeks.

## Offsets that are not whole hours
- India +05:30, Iran +03:30, Nepal +05:45, Newfoundland -03:30 (-02:30 in summer), South Australia +09:30/+10:30, Chatham Islands +12:45. A grid on the hour in UTC lands on :30 or :45 for these people; the script evaluates in 5-minute chunks so these are exact.

## Weekends and working days
- Sun-Thu working weeks: e.g. Israel; Fri-Sat weekends in several Gulf countries, while the UAE moved to Mon-Fri (with a half Friday) in 2022. Ask each person.
- Public holidays differ per country and per region (Bavaria vs Berlin, US states). Add them to the blocked file in local dates.
- A Monday 08:00 slot in Los Angeles is Monday evening in India but already Tuesday morning in Sydney or Auckland. Always show the weekday per person.

## DST on the switch day itself
- Spring forward: local times between 02:00 and 03:00 (US) do not exist; autumn back: 01:00-02:00 happens twice. Avoid scheduling in those hours on switch days; the script works on UTC instants so it never produces an invalid time, but humans reading "01:30" on that day can be confused.

## Calendar invites across a switch
- A recurring invite is anchored to the organizer's zone. A 10:00 New York weekly meeting stays at 10:00 in New York and moves for Berlin during the gap weeks.
- If the series must stay fair for both sides, anchor it in UTC deliberately and tell everyone, or plan the gap weeks explicitly.
- Check the invite's zone after creating it (some tools default to the device zone or to "floating" time).
FILE:references/fairness-and-rotation.md
# Fairness and rotation

## Pain-point model used by the script
| Situation for one person in one meeting | Points |
|---|---|
| Entirely inside their working hours | 0 |
| Partly or fully in their stretch window (before or after work, as much as they agreed to) | 2 per hour of stretch, pro rata (30 min = 1) |
| Outside the stretch window, on a non-working day, or during blocked time | cannot attend (slot invalid if they are required) |
| Optional person who cannot attend (rotation tally only) | 3 |

Ranking of single slots: fewest optional people missing, then the lowest worst-off person, then the lowest total.

Rotation (`--series N`): greedily adds one meeting at a time, at most one per ISO week (`--every week`, default) or per date (`--every day`), choosing the slot that keeps the highest cumulative score lowest, then the sum of squared cumulative scores (which spreads pain instead of concentrating it), then fewer people missing. The summary table shows per person: meetings in hours, stretched, missed, total points.

The weights are a model, not a truth. Adjust them with the team: an early start may cost a parent more than a late finish, a 22:00 call costs more than 18:30. Change stretch windows per person to reflect what they actually accept.

## Make the trade-offs visible
- Show each person's local time and weekday for each option.
- Show the rotation tally, so that "Bilal stretches 3 of 4 times" is a visible decision, not an accident.
- Ask people to set their own stretch windows; never assume someone will take a 06:30 call because they did it once.

## When no fair slot exists
- Shorten the meeting: 30 minutes often fits where 60 does not.
- Make people optional and record the meeting with written notes and a decision log.
- Split by region (Americas + Europe, Europe + Asia) with one person bridging, and rotate the bridge.
- Alternate two time slots week by week (e.g. 14:00 UTC and 07:00 UTC) so each side gets the convenient one half the time.
- Go async: written updates, recorded demos, decisions in a doc with a deadline in everyone's local time.

## Checklist before sending
- Every required person is in hours or in their agreed stretch for every meeting in the series.
- Holidays and leave in each country are in the blocked file.
- DST changes in the range are named, and the series accounts for them.
- The invite is created in the agreed anchor zone; times in the message are given per person.
- There is a review date (e.g. after the next DST change) to rotate again.
FILE:templates/slot-proposal.md
# Meeting time proposal: <meeting name>

**Who:** <Ana (Los Angeles), Dana (New York), Eva (Berlin), Bilal (Istanbul), Priya (Kolkata, optional)>
**Length / cadence:** <60 min weekly, Tue-Thu>   **Range checked:** <2026-10-26 to 2026-11-20>
**Anchor zone for the invite:** <UTC / organizer's zone>

## Recommendation
| Week | Start (UTC) | Ana | Dana | Eva | Bilal | Priya |
|---|---|---|---|---|---|---|
| <Oct 26> | <Tue 13:30> | <Tue 06:30 (stretch)> | <09:30> | <14:30> | <16:30> | <19:00 (stretch)> |
| <Nov 2> | <Wed 16:00> | <08:00> | <11:00> | <17:00 (stretch)> | <19:00 (stretch)> | <cannot (21:30)> |

## Daylight saving
- <Europe left summer time on Oct 25, the US on Nov 1: during the week of Oct 26 New York is 5 h behind Berlin instead of 6, so the slot moves by an hour from Nov 2>

## Fairness over the series
| Name | In hours | Stretch | Missed | Points |
|---|---|---|---|---|
| <Ana> | <2> | <2> | <0> | <4> |

<One sentence on who carries the most and what we do about it (e.g. Priya: recorded summary + an Asia-friendly slot monthly).>

## Alternatives
1. <30-minute version at 15:00 UTC: everyone in hours except ...>
2. <alternate two slots week by week>

## Blocked dates taken into account
- <Oct 29: Republic Day, Turkey (Bilal)>

## Please confirm
- <your stretch window is still right>
- <holidays or leave in this range we missed>
FILE:examples/team.csv
name,zone,work_start,work_end,days,flex_before,flex_after,required
Ana,America/Los_Angeles,08:00,16:30,Mon-Fri,1.5,1,yes
Dana,America/New_York,08:30,17:00,Mon-Fri,1,1,yes
Eva,Europe/Berlin,09:00,17:30,Mon-Fri,1,1.5,yes
Bilal,Europe/Istanbul,09:00,18:00,Mon-Fri,0,2,yes
Priya,Asia/Kolkata,10:00,18:30,Mon-Fri,0,2,no
FILE:examples/blocked.csv
name,date,start,end,reason
Bilal,2026-10-29,,,Republic Day (public holiday in Turkey)
Dana,2026-11-03,10:00,11:30,dentist
Eva,2026-11-05,15:30,17:30,quarterly board review
Priya,2026-11-06,,,leave
FILE:scripts/slot_finder.py
#!/usr/bin/env python3
"""Time zone meeting slot finder (Python 3.9+ standard library: zoneinfo).

Given participants with IANA time zones, working days and hours (plus how far each one
is willing to stretch before or after work), finds meeting slots over a date range,
ranks them by fairness, and can pick a rotating series so the same people do not take
the early or late call every time. Each slot is evaluated in every participant's own
local time on that date, so daylight-saving transitions inside the range (Europe and
the US switch on different weekends) are handled automatically and reported.

Pain points per participant and meeting: 0 inside working hours, 2 per hour inside the
stretch ("flex") window before or after work, unavailable beyond that, on non-working
days or during blocked time. Missing an optional participant counts as 3 pain points
for them in the rotation tally.

Usage:
  python3 slot_finder.py --team team.csv --start 2026-10-26 --end 2026-11-06
        [--duration 60] [--step 30] [--blocked blocked.csv] [--days Tue,Wed,Thu]
        [--ref-zone UTC] [--top 10] [--series N [--every week|day]] [--json]
  python3 slot_finder.py --self-test
team.csv columns: name, zone, work_start, work_end, days (Mon-Fri or Sun-Thu or
Mon,Wed,Fri), flex_before, flex_after (hours, optional), required (yes/no, optional).
work_end earlier than work_start means a shift that runs past midnight.
blocked.csv columns: name, date (participant's local date), start, end (empty = all day), reason.
Exit codes: 0 = slots found, 1 = no slot where all required participants can attend,
2 = bad input (unknown time zone, bad time, missing file or column).
"""
import argparse, csv, datetime as dt, io, json, sys
from zoneinfo import ZoneInfo, ZoneInfoNotFoundError

DAY_NAMES = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
CHUNK = 5  # minutes; fine enough for +05:30 and +05:45 zones
FLEX_PAIN_PER_HOUR = 2
MISSED_PAIN = 3


class InputError(Exception):
    pass


def parse_days(s):
    s = (s or "Mon-Fri").strip()
    out = set()
    for part in s.replace(" ", "").split(","):
        if not part:
            continue
        if "-" in part:
            a, b = part.split("-", 1)
            i, j = day_index(a), day_index(b)
            k = i
            while True:
                out.add(k)
                if k == j:
                    break
                k = (k + 1) % 7
        else:
            out.add(day_index(part))
    return out


def day_index(name):
    n = name.strip()[:3].title()
    if n not in DAY_NAMES:
        raise InputError(f"unknown day '{name}' (use Mon..Sun)")
    return DAY_NAMES.index(n)


def parse_hm(s, what):
    try:
        h, m = s.strip().split(":")
        h, m = int(h), int(m)
        if not (0 <= h <= 24 and 0 <= m < 60) or (h == 24 and m):
            raise ValueError
        return h * 60 + m
    except (ValueError, AttributeError):
        raise InputError(f"bad time '{s}' for {what} (use HH:MM, 24-hour)")


def load_zone(name, who, warnings):
    name = (name or "").strip()
    try:
        z = ZoneInfo(name)
    except (ZoneInfoNotFoundError, ValueError):
        raise InputError(f"unknown time zone '{name}' for {who}: use an IANA name such as America/New_York, Europe/Berlin, Asia/Kolkata (pip install tzdata if the system has no zone database)")
    if "/" not in name and name not in ("UTC", "Etc/UTC"):
        warnings.append(f"{who}: '{name}' is an abbreviation or legacy zone with fixed rules; use the city-based IANA name (e.g. America/New_York, not EST) so daylight saving is right")
    return z


def read_team(text, warnings):
    rows = list(csv.DictReader(io.StringIO(text.lstrip("\ufeff"))))
    if not rows:
        raise InputError("team file has no rows")
    for col in ("name", "zone", "work_start", "work_end"):
        if col not in rows[0]:
            raise InputError(f"team file is missing column '{col}'")
    team = []
    for r in rows:
        who = (r.get("name") or "").strip()
        if not who:
            continue
        p = {"name": who, "zone_name": r["zone"].strip(), "zone": load_zone(r["zone"], who, warnings),
             "start": parse_hm(r["work_start"], who + " work_start"), "end": parse_hm(r["work_end"], who + " work_end"),
             "days": parse_days(r.get("days")),
             "flex_before": int(round(float(r.get("flex_before") or 0) * 60)),
             "flex_after": int(round(float(r.get("flex_after") or 0) * 60)),
             "required": (r.get("required") or "yes").strip().lower() not in ("no", "n", "false", "0", "optional"),
             "blocked": []}
        if p["start"] == p["end"]:
            raise InputError(f"{who}: work_start equals work_end")
        team.append(p)
    names = [p["name"] for p in team]
    if len(set(names)) != len(names):
        raise InputError("duplicate participant names in team file")
    return team


def read_blocked(text, team):
    byname = {p["name"].lower(): p for p in team}
    for r in csv.DictReader(io.StringIO(text.lstrip("\ufeff"))):
        who = (r.get("name") or "").strip()
        if not who:
            continue
        p = byname.get(who.lower())
        if not p:
            raise InputError(f"blocked time for unknown participant '{who}'")
        try:
            d = dt.date.fromisoformat(r["date"].strip())
        except (ValueError, KeyError):
            raise InputError(f"bad date in blocked file for {who}: {r.get('date')}")
        s, e = (r.get("start") or "").strip(), (r.get("end") or "").strip()
        a = dt.datetime.combine(d, dt.time()) + dt.timedelta(minutes=parse_hm(s, who + " blocked start") if s else 0)
        b = dt.datetime.combine(d, dt.time()) + dt.timedelta(minutes=parse_hm(e, who + " blocked end") if e else 1440)
        p["blocked"].append((a, b, (r.get("reason") or "").strip()))


def classify(p, local):
    """local: naive local datetime. Return 'core', 'flex' or None (unavailable)."""
    best = None
    for back in (0, 1):
        d = local.date() - dt.timedelta(days=back)
        if d.weekday() not in p["days"]:
            continue
        base = dt.datetime.combine(d, dt.time())
        cs = base + dt.timedelta(minutes=p["start"])
        ce = base + dt.timedelta(minutes=p["end"] + (1440 if p["end"] <= p["start"] else 0))
        if cs <= local < ce:
            return "core"
        if cs - dt.timedelta(minutes=p["flex_before"]) <= local < ce + dt.timedelta(minutes=p["flex_after"]):
            best = "flex"
    return best


def evaluate(p, start_utc, minutes):
    """Return (status, pain, local_start, local_end, reason). status in core, flex, out."""
    flex_min = 0
    reason = ""
    for k in range(0, minutes, CHUNK):
        t = (start_utc + dt.timedelta(minutes=k)).astimezone(p["zone"]).replace(tzinfo=None)
        c = classify(p, t)
        if c is None:
            reason = "outside hours" if t.date().weekday() in p["days"] or classify_day_any(p, t) else "day off"
            return "out", 0.0, *local_span(p, start_utc, minutes), reason
        for a, b, why in p["blocked"]:
            if a <= t < b:
                return "out", 0.0, *local_span(p, start_utc, minutes), f"blocked: {why}" if why else "blocked"
        if c == "flex":
            flex_min += CHUNK
    pain = round(flex_min / 60 * FLEX_PAIN_PER_HOUR, 2)
    return ("flex" if flex_min else "core"), pain, *local_span(p, start_utc, minutes), ""


def classify_day_any(p, t):
    return (t.date() - dt.timedelta(days=1)).weekday() in p["days"] and p["end"] <= p["start"]


def local_span(p, start_utc, minutes):
    a = start_utc.astimezone(p["zone"])
    b = (start_utc + dt.timedelta(minutes=minutes)).astimezone(p["zone"])
    return a, b


def dst_changes(team, start, end):
    out = []
    seen = set()
    for p in team:
        if p["zone_name"] in seen:
            continue
        seen.add(p["zone_name"])
        z = p["zone"]
        t = dt.datetime.combine(start - dt.timedelta(days=1), dt.time(), tzinfo=dt.timezone.utc)
        stop = dt.datetime.combine(end + dt.timedelta(days=2), dt.time(), tzinfo=dt.timezone.utc)
        prev = t.astimezone(z).utcoffset()
        while t < stop:
            t2 = t + dt.timedelta(minutes=30)
            off = t2.astimezone(z).utcoffset()
            if off != prev:
                loc = t2.astimezone(z)
                out.append({"zone": p["zone_name"], "utc": t2.strftime("%Y-%m-%d %H:%M UTC"),
                            "local": loc.strftime("%Y-%m-%d %H:%M %Z"), "from": fmt_off(prev), "to": fmt_off(off)})
                prev = off
            t = t2
    return out


def fmt_off(td):
    m = int(td.total_seconds() // 60)
    s = "+" if m >= 0 else "-"
    m = abs(m)
    return f"UTC{s}{m // 60:02d}:{m % 60:02d}"


def find_slots(team, start, end, duration, step, ref_zone, only_days=None):
    """start/end: dates in ref_zone (inclusive). Returns list of slot dicts."""
    slots = []
    t = dt.datetime.combine(start, dt.time(), tzinfo=ref_zone).astimezone(dt.timezone.utc)
    stop = dt.datetime.combine(end + dt.timedelta(days=1), dt.time(), tzinfo=ref_zone).astimezone(dt.timezone.utc)
    t = t.replace(minute=(t.minute // step) * step if step < 60 else 0, second=0, microsecond=0)
    while t + dt.timedelta(minutes=duration) <= stop:
        ref_local = t.astimezone(ref_zone)
        if only_days is None or ref_local.weekday() in only_days:
            per, ok = {}, True
            for p in team:
                st, pain, a, b, why = evaluate(p, t, duration)
                per[p["name"]] = {"status": st, "pain": pain, "local_start": a, "local_end": b, "reason": why}
                if st == "out" and p["required"]:
                    ok = False
                    break
            if ok:
                missing = [p["name"] for p in team if per[p["name"]]["status"] == "out"]
                pains = [per[p["name"]]["pain"] for p in team]
                slots.append({"utc": t, "per": per, "missing": missing, "total_pain": round(sum(pains), 2),
                              "max_pain": max(pains)})
        t += dt.timedelta(minutes=step)
    return slots


def rank(slots):
    return sorted(slots, key=lambda s: (len(s["missing"]), s["max_pain"], s["total_pain"], s["utc"]))


def period_key(s, ref_zone, every):
    d = s["utc"].astimezone(ref_zone).date()
    return d.isocalendar()[:2] if every == "week" else d


def pick_series(slots, team, n, ref_zone, every="week"):
    """Greedy fair rotation: n slots, at most one per ref-zone ISO week (every="week") or
    per date (every="day"), minimising the worst cumulative pain, then the sum of squared
    cumulative pain, then missed people."""
    cum = {p["name"]: 0.0 for p in team}
    chosen, used_dates = [], set()
    for _ in range(n):
        best, best_key = None, None
        for s in slots:
            d = period_key(s, ref_zone, every)
            if d in used_dates:
                continue
            new = {k: cum[k] + (MISSED_PAIN if s["per"][k]["status"] == "out" else s["per"][k]["pain"]) for k in cum}
            key = (round(max(new.values()), 2), round(sum(v * v for v in new.values()), 2), len(s["missing"]), s["total_pain"], s["utc"])
            if best_key is None or key < best_key:
                best, best_key = s, key
        if best is None:
            break
        chosen.append(best)
        used_dates.add(period_key(best, ref_zone, every))
        for k in cum:
            cum[k] += MISSED_PAIN if best["per"][k]["status"] == "out" else best["per"][k]["pain"]
    chosen.sort(key=lambda s: s["utc"])
    return chosen, cum


def cell(info):
    a, b = info["local_start"], info["local_end"]
    txt = f"{DAY_NAMES[a.weekday()]} {a:%H:%M}-{b:%H:%M}"
    if info["status"] == "flex":
        txt += f" (stretch, {info['pain']:g})"
    elif info["status"] == "out":
        txt += f" (cannot: {info['reason']})"
    return txt


def table(slots, team, ref_zone):
    head = ["#", f"Start ({ref_zone.key})"] + [f"{p['name']} ({p['zone_name']})" for p in team] + ["Pain total/max", "Missing"]
    out = ["| " + " | ".join(head) + " |", "|" + "---|" * len(head)]
    for i, s in enumerate(slots, 1):
        r = s["utc"].astimezone(ref_zone)
        row = [str(i), f"{DAY_NAMES[r.weekday()]} {r:%Y-%m-%d %H:%M}"] + [cell(s["per"][p["name"]]) for p in team] + \
              [f"{s['total_pain']:g}/{s['max_pain']:g}", ", ".join(s["missing"]) or "-"]
        out.append("| " + " | ".join(row) + " |")
    return out


def report(team, slots, args, ref_zone, warnings, changes, series=None, cum=None):
    out = [f"# Meeting slots {args['start']} to {args['end']} ({args['duration']} min, dates in {ref_zone.key})", ""]
    for w in warnings:
        out.append(f"> WARNING: {w}")
    if warnings:
        out.append("")
    out.append("## Participants")
    out.append("| Name | Zone | Hours (local) | Days | Stretch before/after | Required |")
    out.append("|---|---|---|---|---|---|")
    for p in team:
        days = ",".join(DAY_NAMES[d] for d in sorted(p["days"]))
        out.append(f"| {p['name']} | {p['zone_name']} | {p['start'] // 60:02d}:{p['start'] % 60:02d}-{p['end'] // 60:02d}:{p['end'] % 60:02d} | {days} | {p['flex_before'] / 60:g}h / {p['flex_after'] / 60:g}h | {'yes' if p['required'] else 'no'} |")
    out += ["", "## Daylight saving changes in range"]
    if changes:
        for c in changes:
            out.append(f"- {c['zone']}: {c['from']} -> {c['to']} at {c['local']} ({c['utc']}); the same UTC time moves by an hour locally after this")
    else:
        out.append("- none")
    out.append("")
    if not slots:
        out.append("No slot found where every required participant is available. Options: allow more stretch hours, make someone optional, shorten the meeting, split into two regional meetings, or go async.")
        return "\n".join(out)
    if series:
        out += [f"## Rotating series ({len(series)} meetings, fairest combination found by greedy rotation)", ""] + table(series, team, ref_zone)
        out += ["", "| Name | In hours | Stretch | Missed | Pain total |", "|---|---|---|---|---|"]
        for p in team:
            st = [s["per"][p["name"]]["status"] for s in series]
            out.append(f"| {p['name']} | {st.count('core')} | {st.count('flex')} | {st.count('out')} | {cum[p['name']]:g} |")
        out.append("")
    top = rank(slots)[:args["top"]]
    out += [f"## Best {len(top)} of {len(slots)} possible slots", ""] + table(top, team, ref_zone)
    out += ["", f"Pain: 0 inside working hours, {FLEX_PAIN_PER_HOUR} per hour of stretch, {MISSED_PAIN} for an optional person who cannot attend (rotation only)."]
    return "\n".join(out)


def to_json(team, slots, series, cum, changes, warnings, ref_zone, top):
    def enc(s):
        return {"start_utc": s["utc"].strftime("%Y-%m-%dT%H:%MZ"), "start_ref": s["utc"].astimezone(ref_zone).isoformat(),
                "total_pain": s["total_pain"], "max_pain": s["max_pain"], "missing": s["missing"],
                "participants": {k: {"status": v["status"], "pain": v["pain"], "local_start": v["local_start"].isoformat(),
                                     "local_end": v["local_end"].isoformat(), "reason": v["reason"]} for k, v in s["per"].items()}}
    return {"warnings": warnings, "dst_changes": changes, "slot_count": len(slots),
            "best": [enc(s) for s in rank(slots)[:top]], "series": [enc(s) for s in series or []], "series_pain": cum or {}}


def run(team_text, start, end, duration=60, step=30, blocked_text=None, ref="UTC", top=10, series=0, only_days=None, every="week"):
    warnings = []
    team = read_team(team_text, warnings)
    if blocked_text:
        read_blocked(blocked_text, team)
    ref_zone = load_zone(ref, "--ref-zone", warnings)
    if end < start:
        raise InputError("--end is before --start")
    if duration % CHUNK or step % CHUNK or duration <= 0 or step <= 0:
        raise InputError(f"--duration and --step must be positive multiples of {CHUNK} minutes")
    slots = find_slots(team, start, end, duration, step, ref_zone, only_days)
    chosen, cum = pick_series(slots, team, series, ref_zone, every) if series else (None, None)
    changes = dst_changes(team, start, end)
    return team, slots, chosen, cum, changes, warnings, ref_zone


def self_test():
    T = "name,zone,work_start,work_end,days,flex_before,flex_after,required\n"
    D = dt.date
    passed, total = 0, 0

    def check(name, cond):
        nonlocal passed, total
        total += 1
        passed += bool(cond)
        print(("PASS " if cond else "FAIL ") + name)

    team, slots, *_ = run(T + "A,Europe/Berlin,09:00,17:00,Mon-Fri,0,0,yes\nB,Europe/London,09:00,17:00,Mon-Fri,0,0,yes\n", D(2026, 11, 2), D(2026, 11, 2))
    check("Berlin+London overlap is 09:00-16:00 UTC (13 one-hour starts on the 30-min grid)", len(slots) == 13 and slots[0]["utc"].hour == 9 and slots[-1]["utc"].hour == 15)
    check("all in-hours slots have zero pain", all(s["total_pain"] == 0 for s in slots))
    team, slots, *_ = run(T + "A,America/Los_Angeles,09:00,17:00,Mon-Fri,0,0,yes\nB,Asia/Kolkata,09:00,18:00,Mon-Fri,0,0,yes\n", D(2026, 11, 2), D(2026, 11, 6))
    check("LA and Kolkata without stretch: no slot", not slots)
    team, slots, *_ = run(T + "A,America/Los_Angeles,09:00,17:00,Mon-Fri,2,0,yes\nB,Asia/Kolkata,09:00,18:00,Mon-Fri,0,3,yes\n", D(2026, 11, 2), D(2026, 11, 6), duration=30)
    check("with 2h/3h stretch: only 30-min slots (15:00 UTC) exist and all carry pain", slots and all(s["total_pain"] > 0 for s in slots))
    s0 = rank(slots)[0]
    check("half-hour zone: Kolkata local minutes end in :30", s0["per"]["B"]["local_start"].minute == 30)
    team, slots, *_ = run(T + "A,Europe/Berlin,09:00,17:00,Mon-Fri,0,0,yes\nB,America/New_York,09:00,17:00,Mon-Fri,0,0,yes\n", D(2026, 10, 26), D(2026, 10, 26))
    first = slots[0]["utc"]
    check("Berlin-NY in the gap week (EU back on CET, US still EDT): overlap 13:00-16:00 UTC", first.hour == 13 and slots[-1]["utc"].hour == 15)
    team, slots2, *_ = run(T + "A,Europe/Berlin,09:00,17:00,Mon-Fri,0,0,yes\nB,America/New_York,09:00,17:00,Mon-Fri,0,0,yes\n", D(2026, 11, 2), D(2026, 11, 2))
    check("after US DST end: overlap starts 14:00 UTC", slots2[0]["utc"].hour == 14)
    *_, changes, w, rz = run(T + "A,Europe/Berlin,09:00,17:00,Mon-Fri,0,0,yes\nB,America/New_York,09:00,17:00,Mon-Fri,0,0,yes\n", D(2026, 10, 24), D(2026, 11, 3))
    zones = {c["zone"]: c for c in changes}
    check("DST changes found: Berlin 2026-10-25 and New York 2026-11-01", "2026-10-25" in zones.get("Europe/Berlin", {}).get("local", "") and "2026-11-01" in zones.get("America/New_York", {}).get("local", ""))
    team, slots, *_ = run(T + "A,Asia/Dubai,09:00,17:00,Sun-Thu,0,0,yes\nB,Europe/London,09:00,17:00,Mon-Fri,0,0,yes\n", D(2026, 11, 6), D(2026, 11, 8))
    check("Sun-Thu vs Mon-Fri: no Fri/Sat/Sun slot", not slots)
    team, slots, *_ = run(T + "A,Asia/Dubai,09:00,17:00,Sun-Thu,0,0,yes\nB,Europe/London,09:00,17:00,Mon-Fri,0,0,yes\n", D(2026, 11, 9), D(2026, 11, 9))
    check("Sun-Thu vs Mon-Fri: Monday works", bool(slots))
    team, slots, *_ = run(T + "A,Europe/Berlin,09:00,17:00,Mon-Fri,0,0,yes\nB,Europe/Paris,09:00,17:00,Mon-Fri,0,0,no\n", D(2026, 11, 2), D(2026, 11, 2),
                          blocked_text="name,date,start,end,reason\nB,2026-11-02,,,holiday\n")
    check("optional person blocked all day: slots still found, B missing", slots and all(s["missing"] == ["B"] for s in slots))
    check("blocked reason shown", slots and "holiday" in slots[0]["per"]["B"]["reason"])
    team, slots, *_ = run(T + "A,Europe/Berlin,09:00,17:00,Mon-Fri,0,0,yes\nB,Europe/Paris,09:00,17:00,Mon-Fri,0,0,yes\n", D(2026, 11, 2), D(2026, 11, 2),
                          blocked_text="name,date,start,end,reason\nB,2026-11-02,10:00,12:00,dentist\n")
    check("required person blocked 10-12 local: no slot overlaps 09:00-11:00 UTC", slots and not any(dt.time(8, 30) < s["utc"].time() < dt.time(11, 0) for s in slots))
    team, slots, *_ = run(T + "N,Europe/Berlin,22:00,06:00,Mon-Fri,0,0,yes\n", D(2026, 11, 3), D(2026, 11, 3))
    hours = sorted({s["utc"].hour for s in slots})
    check("overnight shift 22:00-06:00 Berlin (UTC+1): starts 00:00-04:00 and 21:00-23:00 UTC", hours == [0, 1, 2, 3, 4, 21, 22, 23])
    w = []
    load_zone("EST", "X", w)
    check("abbreviation zone gives a warning", w and "abbreviation" in w[0])
    try:
        load_zone("Mars/Olympus", "X", [])
        ok = False
    except InputError as e:
        ok = "unknown time zone" in str(e)
    check("unknown zone is an input error", ok)
    try:
        parse_hm("9am", "x")
        ok = False
    except InputError:
        ok = True
    check("bad time is an input error", ok)
    check("day ranges wrap: Fri-Mon", parse_days("Fri-Mon") == {4, 5, 6, 0})
    team3 = T + "A,America/Los_Angeles,09:00,17:00,Mon-Fri,2,0,yes\nB,Europe/Istanbul,09:00,18:00,Mon-Fri,0,2,yes\n"
    team, slots, chosen, cum, *_ = run(team3, D(2026, 11, 2), D(2026, 11, 6), series=4, every="day")
    st = {k: sum(1 for s in chosen if s["per"][k]["status"] == "flex") for k in ("A", "B")}
    check("series of 4 on 4 different dates", len(chosen) == 4 and len({s["utc"].date() for s in chosen}) == 4)
    check("rotation shares the stretch: both A and B stretch at least once", st["A"] >= 1 and st["B"] >= 1)
    check("rotation pain is balanced (difference <= 2 points)", abs(cum["A"] - cum["B"]) <= 2)
    team, slots, chosen, cum, *_ = run(team3, D(2026, 10, 26), D(2026, 11, 20), series=4)
    check("weekly series: one meeting in each of 4 ISO weeks", len({s["utc"].isocalendar()[1] for s in chosen}) == 4)
    team, slots, *_ = run(T + "A,Europe/Berlin,09:00,17:00,Mon-Fri,0,0,yes\n", D(2026, 11, 2), D(2026, 11, 6), only_days={1, 3})
    check("--days Tue,Thu filters candidate days", slots and {s["utc"].weekday() for s in slots} == {1, 3})
    team, slots, ch, cum, changes, w, rz = run(T + "A,Europe/Berlin,09:00,17:00,Mon-Fri,0,0,yes\n", D(2026, 11, 2), D(2026, 11, 2))
    text = report(team, slots, {"start": "2026-11-02", "end": "2026-11-02", "duration": 60, "top": 3}, rz, w, changes)
    check("report renders table", "| 1 | Mon 2026-11-02 08:00 |" in text and "Daylight saving" in text)
    j = to_json(team, slots, None, None, changes, w, rz, 3)
    check("json output has best slots", len(j["best"]) == 3 and j["best"][0]["start_utc"] == "2026-11-02T08:00Z")
    print(f"{passed}/{total} passed")
    return 0 if passed == total else 1


def main(argv=None):
    ap = argparse.ArgumentParser(description="Find fair meeting slots across time zones")
    ap.add_argument("--team")
    ap.add_argument("--blocked")
    ap.add_argument("--start")
    ap.add_argument("--end")
    ap.add_argument("--duration", type=int, default=60)
    ap.add_argument("--step", type=int, default=30)
    ap.add_argument("--days", help="only these weekdays in --ref-zone, e.g. Tue,Wed,Thu")
    ap.add_argument("--ref-zone", default="UTC")
    ap.add_argument("--top", type=int, default=10)
    ap.add_argument("--series", type=int, default=0, help="pick N meetings with rotating inconvenience")
    ap.add_argument("--every", default="week", choices=["week", "day"], help="series spacing: one meeting per ISO week (default) or per day")
    ap.add_argument("--json", action="store_true")
    ap.add_argument("--self-test", action="store_true")
    a = ap.parse_args(argv)
    if a.self_test:
        return self_test()
    if not (a.team and a.start and a.end):
        ap.print_usage(sys.stderr)
        print("error: --team, --start and --end are required", file=sys.stderr)
        return 2
    try:
        start, end = dt.date.fromisoformat(a.start), dt.date.fromisoformat(a.end)
        team_text = open(a.team, encoding="utf-8").read()
        blocked_text = open(a.blocked, encoding="utf-8").read() if a.blocked else None
        only = parse_days(a.days) if a.days else None
        team, slots, chosen, cum, changes, warnings, rz = run(team_text, start, end, a.duration, a.step, blocked_text, a.ref_zone, a.top, a.series, only, a.every)
    except (InputError, OSError, ValueError) as e:
        print(f"error: {e}", file=sys.stderr)
        return 2
    if a.json:
        print(json.dumps(to_json(team, slots, chosen, cum, changes, warnings, rz, a.top), indent=2))
    else:
        print(report(team, slots, {"start": a.start, "end": a.end, "duration": a.duration, "top": a.top}, rz, warnings, changes, chosen, cum))
    return 0 if slots else 1


if __name__ == "__main__":
    sys.exit(main())

---
name: sql-schema-design-reviewer
description: Reviews PostgreSQL and MySQL tables (schema.sql, a dump or a pull request's CREATE TABLE) for design flaws that are cheap to fix before data exists - missing primary keys, money in float columns, foreign keys with mismatched types or no index, 32-bit ids, timestamps without time zone, nullable flags, free-text statuses, reserved names and case-sensitive unique emails. Returns corrected DDL. Includes a stdlib Python linter with --self-test.
---

# SQL Schema Design Reviewer

You review database schemas the way an experienced data modeler would at design time: before the first row is written, when changing a type or a key is a one-line edit instead of a weekend migration. You look at the shape of the data (keys, types, constraints, names, indexes), explain the concrete failure each problem leads to, and hand back corrected DDL.

This skill reviews the design of tables. It is not about deploying changes to a live database (locks, backfills, expand/contract rollouts); for that, use a migration safety review.

## Files in this skill

- `scripts/schema_lint.py` - parses CREATE TABLE, CREATE INDEX and ALTER TABLE ... ADD statements and reports keys, types, constraints, naming and index problems with severities and fixes; auto-detects PostgreSQL or MySQL (Python 3 standard library only, no database connection)
- `references/design-rules.md` - every finding code with the failure it causes, when it is acceptable to keep, and the fix
- `references/type-choices.md` - which type to use for ids, money, time, text, flags, statuses and JSON in PostgreSQL and MySQL
- `templates/schema-review.md` - the review to hand back
- `examples/shop-schema.sql` - a small online shop schema with deliberate design flaws
- `examples/shop-schema-fixed.sql` - the same schema after the review; it lints clean

## Workflow

### 1. Get the schema and the context
Ask for the DDL (schema.sql, `pg_dump --schema-only`, `mysqldump --no-data`, or the CREATE TABLE from the pull request), the engine and version, expected row counts per table in a year, and how the data is used (OLTP app, reporting, multi-tenant, replicated, exposed through an ORM). Ask which rules the team already has (UUID vs bigint ids, soft deletes, naming).

### 2. Run the linter
```
python3 scripts/schema_lint.py examples/shop-schema.sql
python3 scripts/schema_lint.py schema.sql --dialect mysql --min-severity MEDIUM
python3 scripts/schema_lint.py db/*.sql --ignore NO_CREATED_AT --json > schema-review.json
python3 scripts/schema_lint.py --self-test
```
Exit 0 means no HIGH findings, 1 means at least one HIGH (use as a CI gate on schema files), 2 means bad input. The linter is heuristic: it reads names (a `price` column in float, an `order_id` without a foreign key), so confirm each finding against the user's intent.

### 3. Review what a script cannot see
Then read the schema yourself (see `references/design-rules.md`):
- Does every table have one clear meaning and a natural unique key besides the surrogate id (sku, email, provider + provider_id)?
- Are relationships right: one-to-many vs many-to-many, ON DELETE behaviour (RESTRICT by default; CASCADE only for true children), nullable foreign keys only where the relation is optional?
- Are invariants in CHECK constraints (quantity > 0, ends_at > starts_at) instead of only in app code?
- Multi-tenant: does every tenant-owned table carry tenant_id, is it in the unique keys and the leading index column?
- Soft deletes: are unique constraints partial (`WHERE deleted_at IS NULL`)?
- Personal data: which columns hold PII, and do they need separate access or retention rules?

### 4. Deliver
Fill `templates/schema-review.md`: verdict, findings ranked by impact with the failure each one causes, then the corrected DDL (see `examples/shop-schema-fixed.sql`) and a list of decisions left to the team. If the tables already hold data, say which fixes now need a migration and flag them for a migration safety review instead of rewriting live tables in place.

## Example result
`examples/shop-schema.sql` (PostgreSQL, 5 tables): 20 findings, 4 HIGH. order_items has no primary key (duplicate lines possible); products.price is double precision and payments.amount is real (cents drift); payments.order_id is integer but references "order".id (bigserial). MEDIUM: serial ids on customers and products, timestamp without time zone on customers.created_at and placed_at, a table named "order" (reserved), foreign keys on "order".customer_id and order_items.order_id with no index. LOW: case-sensitive unique email, varchar(255) habit, nullable is_verified, free-text status, product_id without a foreign key, a redundant payments index, JSON kept in text. `examples/shop-schema-fixed.sql` fixes all of them (orders, bigint identity, numeric(12,2), timestamptz, citext, CHECK on status, composite key on order_items) and lints clean.

## Rules

- Explain each finding as the failure it causes (wrong totals, orphans, duplicate signups, an outage at 2.1 billion ids), not as a style rule.
- Keep the user's conventions (UUID ids, naming) unless they cause a real problem; say when a finding is a judgement call.
- Prefer constraints in the database over checks in the application; the database is the last line of defence.
- Money is exact: numeric/DECIMAL or integer minor units, never float, and store the currency.
- Time is an instant: timestamptz in PostgreSQL, UTC everywhere in MySQL.
- Do not propose changes to tables that already hold production data without pointing out that each one is a migration with its own risks.
FILE:references/design-rules.md
# Design rules and finding codes

| Code | Sev | What goes wrong | Acceptable when | Fix |
|---|---|---|---|---|
| NO_PRIMARY_KEY | HIGH | duplicate rows cannot be told apart or deleted one at a time; logical replication and CDC need a key; ORMs misbehave | never for OLTP tables (staging tables loaded and dropped in one job, maybe) | surrogate `id bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY` or a composite natural key (order_id, product_id) |
| FLOAT_MONEY | HIGH | 0.1 + 0.2 = 0.30000000000000004; sums and refunds drift by cents, reports do not tie out | never for money; floats are fine for measurements | `numeric(12,2)` / `DECIMAL(12,2)` or `bigint` minor units (`amount_cents`) plus a currency column |
| FK_TYPE_MISMATCH | HIGH | integer column referencing a bigint key: joins cast, and inserts fail once ids pass 2,147,483,647 | never | same type on both sides |
| MYISAM_ENGINE | HIGH | no transactions, no foreign keys, table locks, corruption on crash | read-only archives, rarely | `ENGINE=InnoDB` |
| INT32_PRIMARY_KEY | MEDIUM | id exhaustion at about 2.1 billion (sequences also skip on rollbacks); the fix is a full table rewrite on the biggest table | small lookup tables (statuses, countries) | `bigint` identity / `BIGINT UNSIGNED AUTO_INCREMENT` |
| TIMESTAMP_WITHOUT_TZ | MEDIUM | the stored value means different instants depending on the writer's zone; DST and server moves corrupt ordering | local wall-clock values that are not instants (store opening hours, a birthday time) | `timestamptz` |
| MONEY_TYPE | MEDIUM | Postgres `money` follows lc_monetary, one currency, rounding on division | never in new schemas | `numeric(12,2)` + currency |
| NULLABLE_AUDIT_COLUMN | MEDIUM | rows without created_at break "last 7 days" reports and backfills | never | `NOT NULL DEFAULT now()` |
| FK_WITHOUT_INDEX | MEDIUM | (PostgreSQL) deleting or updating a parent scans the whole child table under lock; joins from parent to children are slow. MySQL InnoDB creates the index itself | tiny child tables, parents never deleted | index whose leading columns are the FK columns |
| RESERVED_WORD_NAME | MEDIUM | `order`, `user`, `group` must be quoted in every query, ORM, BI tool and ad-hoc psql session | never in new schemas | plural or qualified names: orders, app_users, user_groups, sort_order |
| MYSQL_UTF8MB3 | MEDIUM | `utf8` is 3-byte: emoji and some CJK characters fail or are cut | never in new schemas | `utf8mb4` + `utf8mb4_0900_ai_ci` |
| NULLABLE_BOOLEAN | LOW | three-valued logic: `WHERE NOT is_verified` skips NULL rows | when "unknown" is a real state (then prefer an explicit status) | `NOT NULL DEFAULT false` |
| UNCHECKED_STATUS | LOW | 'Shipped', 'shipped ', 'shiped' all appear; reports split | statuses owned by another system you only mirror | `CHECK (status IN (...))`, an enum type or a lookup table FK |
| MISSING_FOREIGN_KEY | LOW | orphans after deletes, typos in ids, no documented relation | cross-database or event-sourced references; document them | `REFERENCES parent(id)` + index |
| CASE_SENSITIVE_UNIQUE_EMAIL | LOW | Ana@x.com and ana@x.com are two accounts; password resets go to the wrong one | never for login emails | `citext` or `UNIQUE INDEX ON t (lower(email))` and normalize on write |
| VARCHAR_255_HABIT | LOW | in Postgres, 255 is an arbitrary MySQL-era limit; real rules are missing and odd values get rejected | when 255 really is the rule | `text` + `CHECK (char_length(x) <= n)` for real limits |
| REDUNDANT_INDEX | LOW | an index that is a prefix of another (or of the PK) costs writes and memory for nothing | the shorter index is much smaller and very hot | drop it |
| JSON_IN_TEXT | LOW | no validation, no operators, no GIN index | the text is not really JSON | `jsonb` / `JSON` |
| NO_CREATED_AT | LOW | debugging, audits and backfills need to know when rows appeared | pure join tables | `created_at timestamptz NOT NULL DEFAULT now()` |
| MIXED_CASE_NAME | LOW | quoted "OrderItems" must be quoted forever in Postgres | never | snake_case |
| DATETIME_NO_ZONE | LOW | (MySQL) DATETIME has no zone; mixed writers store mixed zones | when every connection sets time_zone='+00:00' | enforce UTC |

## Things the linter cannot judge (review by hand)
- **Keys**: is there a natural unique key besides the surrogate id? Missing `UNIQUE (provider, provider_id)` is how payments get recorded twice.
- **ON DELETE**: RESTRICT/NO ACTION by default; CASCADE only for true child rows (order_items of an order), never from customers to payments.
- **CHECK constraints for invariants**: `quantity > 0`, `ends_at > starts_at`, `discount <= total`.
- **Multi-tenancy**: tenant_id on every tenant table, first in unique keys and indexes, and in every FK (composite FKs prevent cross-tenant references).
- **Soft deletes**: partial unique indexes `WHERE deleted_at IS NULL`, or the email can never be reused.
- **Denormalized totals**: if orders.total is stored, say how it stays equal to the sum of order_items.
- **PII**: list columns with personal data; consider a separate table with stricter access and retention.
FILE:references/type-choices.md
# Type choices (PostgreSQL / MySQL 8)

| Data | PostgreSQL | MySQL 8 | Avoid |
|---|---|---|---|
| Surrogate id | `bigint GENERATED ALWAYS AS IDENTITY` | `BIGINT UNSIGNED AUTO_INCREMENT` | `serial`/`int` on growing tables |
| Public / distributed id | `uuid` (UUIDv7 for index locality, `gen_random_uuid()` for v4) | `BINARY(16)` with UUID_TO_BIN(x, 1) | `varchar(36)` UUIDs (3x bigger, slower) |
| Money | `numeric(12,2)` (or (19,4) for rates) + `currency char(3)` | `DECIMAL(12,2)` + `CHAR(3)` | `float`, `double`, `real`, Postgres `money` |
| Money as integer | `bigint amount_cents` (mind currencies with 0 or 3 decimals) | `BIGINT` | `int` cents (overflows at 21 million) |
| Instant (event happened) | `timestamptz` | `DATETIME(6)` in UTC, or `TIMESTAMP` (2038 limit, converted by session zone) | `timestamp` without time zone |
| Calendar date | `date` | `DATE` | timestamps at midnight |
| Wall-clock time / schedule | `time` + an IANA zone column | `TIME` + zone column | `timetz` |
| Duration | `interval` or integer seconds | `INT` seconds | text like "1h30" |
| Text | `text` (+ CHECK for real limits) | `VARCHAR(n)` with a real n; `TEXT` for long bodies | `varchar(255)` by habit; `char(n)` padding |
| Case-insensitive text (email, username) | `citext` or a `lower()` unique index | case-insensitive `_ci` collation (default) | plain unique on text in Postgres |
| Flag | `boolean NOT NULL DEFAULT false` | `BOOLEAN` (TINYINT(1)) `NOT NULL DEFAULT 0` | nullable booleans, 'Y'/'N' strings |
| Status | `text` + `CHECK (... IN (...))`, enum type, or lookup table | `ENUM(...)` or lookup table | unconstrained text |
| JSON | `jsonb` (GIN index for containment) | `JSON` (generated columns to index) | JSON in text |
| IP address | `inet` / `cidr` | `VARBINARY(16)` with INET6_ATON | text |
| Large binary | object storage + key in a `text` column | same | big BLOBs in hot tables |

## Notes
- Changing a column type later rewrites the table in both engines (with a few exceptions such as widening varchar in Postgres). Get ids and money right first.
- Enum types in Postgres: adding a value is cheap, removing or renaming one is not. Lookup tables are easier to evolve and can carry labels and sort order.
- `NOT NULL` with a sensible default is the norm; nullable should mean "genuinely unknown or not applicable".
- Store the currency next to every amount, even if today there is only one.
- Name things the same everywhere: `customer_id` in every table that references customers, `_at` for instants, `_on` or `_date` for dates, `is_`/`has_` for booleans.
FILE:templates/schema-review.md
# Schema review: <project / schema file>, <date>

**Engine:** <PostgreSQL 16>   **Scope:** <5 tables: customers, products, orders, order_items, payments>
**Context:** <OLTP shop backend, ~2M orders/year, Prisma ORM, no data yet>
**Command:** `python3 scripts/schema_lint.py <shop-schema.sql>`
**Verdict:** <CHANGES NEEDED before the first release: 4 HIGH, 8 MEDIUM, 8 LOW>

## Must fix (HIGH)
| # | Table.column | Finding | What goes wrong | Fix |
|---|---|---|---|---|
| 1 | <products.price> | <FLOAT_MONEY> | <0.1 + 0.2 != 0.3; order totals drift by cents> | <numeric(12,2) NOT NULL CHECK (price >= 0)> |

## Should fix (MEDIUM)
| # | Table.column | Finding | What goes wrong | Fix |
|---|---|---|---|---|
| 1 | <"order"> | <RESERVED_WORD_NAME> | <must be quoted in every query and BI tool> | <rename to orders> |

## Consider (LOW / judgement calls)
- <customers.email: citext so Ana@x.com and ana@x.com are one account>

## Found by reading (not by the linter)
- <payments: add UNIQUE (provider, provider_id) so a webhook retry cannot record a payment twice>
- <ON DELETE: keep RESTRICT on payments -> orders; CASCADE only order_items -> orders>

## Corrected DDL
```sql
<full corrected schema, lints clean>
```

## Decisions for the team
- <bigint identity vs UUIDv7 for public ids>
- <store orders.total or compute it from order_items?>

## If tables already hold data
- <each change above is a migration; list them and run a migration safety review before deploying>
FILE:examples/shop-schema.sql
-- Small online shop schema (PostgreSQL), first draft for review.
-- The problems are deliberate: this is what the skill is meant to catch.

CREATE TABLE customers (
    id          serial PRIMARY KEY,
    email       varchar(255) NOT NULL UNIQUE,
    full_name   varchar(255),
    phone       varchar(255),
    is_verified boolean,
    created_at  timestamp
);

CREATE TABLE products (
    id         serial PRIMARY KEY,
    sku        varchar(64) NOT NULL UNIQUE,
    title      text NOT NULL,
    price      double precision NOT NULL,
    attributes text,
    created_at timestamptz NOT NULL DEFAULT now()
);

CREATE TABLE "order" (
    id          bigserial PRIMARY KEY,
    customer_id integer NOT NULL REFERENCES customers (id),
    status      varchar(20) NOT NULL DEFAULT 'pending',
    total       numeric(12,2) NOT NULL,
    placed_at   timestamp NOT NULL DEFAULT now(),
    created_at  timestamptz NOT NULL DEFAULT now()
);

CREATE TABLE order_items (
    order_id   bigint NOT NULL REFERENCES "order" (id),
    product_id bigint NOT NULL,
    quantity   integer NOT NULL,
    unit_price numeric(12,2) NOT NULL
);

CREATE TABLE payments (
    id          bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    order_id    integer NOT NULL REFERENCES "order" (id),
    amount      real NOT NULL,
    provider    text NOT NULL,
    provider_id text,
    created_at  timestamptz NOT NULL DEFAULT now()
);

CREATE INDEX payments_order_idx ON payments (order_id);
CREATE INDEX payments_order_created_idx ON payments (order_id, created_at);
FILE:examples/shop-schema-fixed.sql
-- Small online shop schema (PostgreSQL), after review.
-- Every change is explained in templates/schema-review.md style in the review.

CREATE EXTENSION IF NOT EXISTS citext;

CREATE TABLE customers (
    id          bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    email       citext NOT NULL UNIQUE,
    full_name   text,
    phone       text CHECK (char_length(phone) <= 32),
    is_verified boolean NOT NULL DEFAULT false,
    created_at  timestamptz NOT NULL DEFAULT now()
);

CREATE TABLE products (
    id         bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    sku        text NOT NULL UNIQUE,
    title      text NOT NULL,
    price      numeric(12,2) NOT NULL CHECK (price >= 0),
    attributes jsonb NOT NULL DEFAULT '{}',
    created_at timestamptz NOT NULL DEFAULT now()
);

CREATE TABLE orders (
    id          bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    customer_id bigint NOT NULL REFERENCES customers (id),
    status      text NOT NULL DEFAULT 'pending'
                CHECK (status IN ('pending', 'paid', 'shipped', 'cancelled', 'refunded')),
    total       numeric(12,2) NOT NULL CHECK (total >= 0),
    placed_at   timestamptz NOT NULL DEFAULT now(),
    created_at  timestamptz NOT NULL DEFAULT now()
);
CREATE INDEX orders_customer_idx ON orders (customer_id);

CREATE TABLE order_items (
    order_id   bigint NOT NULL REFERENCES orders (id),
    product_id bigint NOT NULL REFERENCES products (id),
    quantity   integer NOT NULL CHECK (quantity > 0),
    unit_price numeric(12,2) NOT NULL CHECK (unit_price >= 0),
    created_at timestamptz NOT NULL DEFAULT now(),
    PRIMARY KEY (order_id, product_id)
);
CREATE INDEX order_items_product_idx ON order_items (product_id);

CREATE TABLE payments (
    id          bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    order_id    bigint NOT NULL REFERENCES orders (id),
    amount      numeric(12,2) NOT NULL,
    provider    text NOT NULL,
    provider_id text,
    created_at  timestamptz NOT NULL DEFAULT now(),
    UNIQUE (provider, provider_id)
);
CREATE INDEX payments_order_created_idx ON payments (order_id, created_at);
FILE:scripts/schema_lint.py
#!/usr/bin/env python3
"""SQL schema design linter for PostgreSQL and MySQL DDL (Python 3 standard library only).

Reads CREATE TABLE / CREATE INDEX / ALTER TABLE ... ADD statements (a schema dump,
schema.sql, or the DDL of new tables in a pull request) and reports design problems
that are cheap to fix before data exists and expensive after: tables without a
primary key, money stored in floating point, foreign keys whose type differs from the
referenced key or that have no supporting index (PostgreSQL), *_id columns without a
foreign key, 32-bit primary keys, timestamps without time zone, nullable audit
columns and booleans, unchecked status columns, reserved-word and mixed-case names,
case-sensitive unique emails, redundant indexes, JSON kept in text columns, and MySQL
tables using MyISAM or 3-byte utf8.

It does not connect to a database and does not judge migration safety (locks,
backfills); it reviews the shape of the schema itself.

Usage:
  python3 schema_lint.py FILE.sql [FILE.sql ...] [--dialect auto|postgres|mysql]
        [--min-severity LOW|MEDIUM|HIGH] [--ignore CODE,CODE] [--json]
  python3 schema_lint.py --self-test
Exit codes: 0 = no HIGH findings, 1 = HIGH findings, 2 = bad input (unreadable file,
no CREATE TABLE found).
"""
import argparse, json, re, sys

SEV_ORDER = {"HIGH": 0, "MEDIUM": 1, "LOW": 2}
MONEY_RE = re.compile(r"(^|_)(price|amount|total|subtotal|cost|balance|fee|fees|tax|salary|refund|discount|paid|payment|revenue|credit|debit|charge)(_|$)", re.I)
RESERVED = {"user", "order", "group", "select", "table", "column", "desc", "asc", "check", "default", "from",
            "where", "limit", "offset", "references", "primary", "key", "range", "rank", "window", "all", "both",
            "end", "grant", "to", "type", "values", "constraint", "index", "match", "condition", "interval", "read", "row"}
RESERVED_PG_ONLY_SAFE = {"key", "range", "rank", "type", "values", "match", "condition", "interval", "read", "row", "index"}  # fine unquoted in Postgres
RESERVED_MY_ONLY_SAFE = {"offset", "user", "end", "type", "values", "row"}  # fine unquoted in MySQL 8
STATUS_RE = re.compile(r"^(status|state|kind|role|type|.*_status|.*_state|.*_type)$", re.I)
JSONISH_RE = re.compile(r"(^|_)(json|payload|metadata|meta|attributes|settings|extra|data)$", re.I)
INT32 = {"int", "integer", "int4", "serial", "serial4", "mediumint", "smallint", "int2", "smallserial", "tinyint"}
INT64 = {"bigint", "int8", "bigserial", "serial8"}


def finding(sev, code, table, column, problem, fix, line=0):
    return {"severity": sev, "code": code, "table": table, "column": column, "line": line, "problem": problem, "fix": fix}


def strip_comments(sql):
    out, i, n = [], 0, len(sql)
    while i < n:
        c = sql[i]
        if c in "'\"`":
            j = i + 1
            while j < n and sql[j] != c:
                j += 2 if sql[j] == "\\" and c == "'" else 1
            out.append(sql[i:j + 1]); i = j + 1
        elif sql.startswith("--", i) or c == "#" and (i == 0 or sql[i - 1] in "\n \t"):
            j = sql.find("\n", i); j = n if j < 0 else j
            out.append(" " * (j - i)); i = j
        elif sql.startswith("/*", i):
            j = sql.find("*/", i + 2); j = n if j < 0 else j + 2
            out.append(re.sub(r"[^\n]", " ", sql[i:j])); i = j
        else:
            out.append(c); i += 1
    return "".join(out)


def split_top(s, sep=","):
    parts, depth, cur, q = [], 0, [], None
    for ch in s:
        if q:
            cur.append(ch)
            if ch == q:
                q = None
            continue
        if ch in "'\"`":
            q = ch
        elif ch == "(":
            depth += 1
        elif ch == ")":
            depth -= 1
        if ch == sep and depth == 0:
            parts.append("".join(cur)); cur = []
        else:
            cur.append(ch)
    if "".join(cur).strip():
        parts.append("".join(cur))
    return parts


def statements(sql):
    clean = strip_comments(sql)
    pos = 0
    for part in split_top(clean, ";"):
        line = clean.count("\n", 0, pos + len(part) - len(part.lstrip())) + 1
        pos += len(part) + 1
        if part.strip():
            yield line, part.strip()


def ident(s):
    s = s.strip()
    quoted = s[:1] in "\"`"
    name = s.split(".")[-1].strip().strip("\"`")
    return name, quoted


def cols_list(s):
    return [ident(re.sub(r"\s+(ASC|DESC|NULLS\s+(FIRST|LAST)).*$", "", c.strip(), flags=re.I))[0].lower() if not c.strip().startswith("(") and "(" not in c else c.strip().lower()
            for c in split_top(s)]


class Schema:
    def __init__(self):
        self.tables, self.indexes, self.fks, self.enums = {}, [], [], set()
        self.dialect_hints = {"mysql": 0, "postgres": 0}


def parse(sql):
    sc = Schema()
    if re.search(r"AUTO_INCREMENT|ENGINE\s*=|`|UNSIGNED|DATETIME|TINYINT\(", sql, re.I):
        sc.dialect_hints["mysql"] += 1
    if re.search(r"\bSERIAL\b|BIGSERIAL|TIMESTAMPTZ|JSONB|GENERATED\s+(ALWAYS|BY DEFAULT)\s+AS\s+IDENTITY|::|CREATE\s+TYPE|CITEXT|CONCURRENTLY|\bTEXT\[\]", sql, re.I):
        sc.dialect_hints["postgres"] += 1
    for line, st in statements(sql):
        m = re.match(r"CREATE\s+(?:TEMP(?:ORARY)?\s+|UNLOGGED\s+)?TABLE\s+(?:IF\s+NOT\s+EXISTS\s+)?([\w\".`]+)\s*\((.*)\)\s*(.*)$", st, re.I | re.S)
        if m:
            name, quoted = ident(m.group(1))
            t = {"name": name, "quoted": quoted, "line": line, "cols": {}, "order": [], "pk": [], "uniques": [],
                 "checks": " ".join([]), "options": m.group(3), "raw": st}
            checks = []
            for item in split_top(m.group(2)):
                parse_item(item.strip(), t, sc, checks)
            t["checks"] = " ".join(checks).lower()
            sc.tables[name.lower()] = t
            continue
        m = re.match(r"CREATE\s+(UNIQUE\s+)?INDEX\s+(?:CONCURRENTLY\s+)?(?:IF\s+NOT\s+EXISTS\s+)?([\w\".`]*)\s*ON\s+(?:ONLY\s+)?([\w\".`]+)\s*(?:USING\s+\w+\s*)?\((.*)\)\s*(.*)$", st, re.I | re.S)
        if m:
            sc.indexes.append({"table": ident(m.group(3))[0].lower(), "cols": cols_list(m.group(4)), "unique": bool(m.group(1)),
                               "name": ident(m.group(2))[0] if m.group(2) else "", "partial": "where" in m.group(5).lower(), "line": line})
            continue
        m = re.match(r"ALTER\s+TABLE\s+(?:ONLY\s+)?(?:IF\s+EXISTS\s+)?([\w\".`]+)\s+(.*)$", st, re.I | re.S)
        if m:
            tname = ident(m.group(1))[0].lower()
            for action in split_top(m.group(2)):
                a = action.strip()
                am = re.match(r"ADD\s+(?:COLUMN\s+)(?:IF\s+NOT\s+EXISTS\s+)?(.*)$", a, re.I | re.S)
                if am and tname in sc.tables:
                    parse_item(am.group(1), sc.tables[tname], sc, [])
                    continue
                am = re.match(r"ADD\s+(.*)$", a, re.I | re.S)
                if am and tname in sc.tables:
                    chk = []
                    parse_item(am.group(1), sc.tables[tname], sc, chk)
                    sc.tables[tname]["checks"] += " " + " ".join(chk).lower()
            continue
        m = re.match(r"CREATE\s+TYPE\s+([\w\".]+)\s+AS\s+ENUM", st, re.I)
        if m:
            sc.enums.add(ident(m.group(1))[0].lower())
        m = re.match(r"CREATE\s+(?:DOMAIN|EXTENSION)\s+(?:IF\s+NOT\s+EXISTS\s+)?([\w\".]+)", st, re.I)
        if m:
            sc.enums.add(ident(m.group(1))[0].lower())
    return sc


def parse_item(item, t, sc, checks):
    u = item.upper()
    m = re.match(r"CONSTRAINT\s+[\w\"`]+\s+(.*)$", item, re.I | re.S)
    if m:
        item, u = m.group(1).strip(), m.group(1).strip().upper()
    if u.startswith("PRIMARY KEY"):
        t["pk"] = cols_list(re.search(r"\((.*)\)", item, re.S).group(1)); return
    if re.match(r"UNIQUE\b", u):
        cm = re.search(r"\((.*?)\)", item, re.S)
        if cm:
            cols = cols_list(cm.group(1))
            t["uniques"].append(cols)
            sc.indexes.append({"table": t["name"].lower(), "cols": cols, "unique": True, "name": "", "partial": False, "line": t["line"]})
        return
    if u.startswith("FOREIGN KEY"):
        fm = re.match(r"FOREIGN\s+KEY\s*\((.*?)\)\s*REFERENCES\s+([\w\".`]+)\s*(?:\((.*?)\))?", item, re.I | re.S)
        if fm:
            sc.fks.append({"table": t["name"].lower(), "cols": cols_list(fm.group(1)), "ref": ident(fm.group(2))[0].lower(),
                           "ref_cols": cols_list(fm.group(3)) if fm.group(3) else None})
        return
    if u.startswith("CHECK"):
        checks.append(item); return
    if re.match(r"(UNIQUE\s+)?(KEY|INDEX)\b", u) or re.match(r"(FULLTEXT|SPATIAL)\b", u):
        cm = re.search(r"\((.*)\)", item, re.S)
        if cm:
            sc.indexes.append({"table": t["name"].lower(), "cols": cols_list(cm.group(1)), "unique": u.startswith("UNIQUE"),
                               "name": "", "partial": False, "line": t["line"]})
        return
    if u.startswith(("EXCLUDE", "LIKE", "PERIOD")):
        return
    cm = re.match(r"([\"`][^\"`]+[\"`]|[\w$]+)\s+(.*)$", item, re.S)
    if not cm:
        return
    name, quoted = ident(cm.group(1))
    rest = cm.group(2)
    tm = re.match(r"((?:double\s+precision|character\s+varying|bit\s+varying|timestamp(?:\s*\(\d+\))?(?:\s+with(?:out)?\s+time\s+zone)?(?!\w)|time(?:\s+with(?:out)?\s+time\s+zone)?(?!\w)|[\w.]+)(?:\s*\([^)]*\))?(?:\s+unsigned)?(?:\s*\[\])?)", rest, re.I)
    ctype = re.sub(r"\s+", " ", tm.group(1).lower()) if tm else ""
    ru = rest.upper()
    col = {"name": name, "quoted": quoted, "type": ctype, "not_null": "NOT NULL" in ru or "PRIMARY KEY" in ru,
           "default": "DEFAULT" in ru or "IDENTITY" in ru or "AUTO_INCREMENT" in ru or ctype.endswith("serial"),
           "check": "CHECK" in ru}
    t["cols"][name.lower()] = col
    t["order"].append(name.lower())
    if "PRIMARY KEY" in ru:
        t["pk"] = [name.lower()]
    if re.search(r"\bUNIQUE\b", ru):
        t["uniques"].append([name.lower()])
        sc.indexes.append({"table": t["name"].lower(), "cols": [name.lower()], "unique": True, "name": "", "partial": False, "line": t["line"]})
    rm = re.search(r"REFERENCES\s+([\w\".`]+)\s*(?:\((.*?)\))?", rest, re.I)
    if rm:
        sc.fks.append({"table": t["name"].lower(), "cols": [name.lower()], "ref": ident(rm.group(1))[0].lower(),
                       "ref_cols": cols_list(rm.group(2)) if rm.group(2) else None})
    if col["check"]:
        checks.append(f"check ({name})")


def qi(name):
    return f'"{name}"' if name.lower() in RESERVED or name != name.lower() else name


def base_type(ctype):
    t = re.sub(r"\(.*?\)|\s+unsigned|\[\]", "", ctype).strip()
    return {"int4": "integer", "int": "integer", "serial": "integer", "serial4": "integer", "int8": "bigint",
            "bigserial": "bigint", "serial8": "bigint", "int2": "smallint", "smallserial": "smallint"}.get(t, t)


def lint(sql, dialect="auto", ignore=()):
    sc = parse(sql)
    if dialect == "auto":
        dialect = "mysql" if sc.dialect_hints["mysql"] > sc.dialect_hints["postgres"] else "postgres"
    out = []

    def add(*a, **k):
        f = finding(*a, **k)
        if f["code"] not in ignore:
            out.append(f)

    table_names = set(sc.tables)
    for key, t in sc.tables.items():
        tn = t["name"]
        ln = t["line"]
        if not t["pk"]:
            add("HIGH", "NO_PRIMARY_KEY", tn, "", "table has no primary key: duplicate rows cannot be told apart, updates and replication (logical replication, MySQL row-based, CDC) suffer",
                "add a bigint identity (or UUID) primary key, or a composite key on the natural unique columns", line=ln)
        elif len(t["pk"]) == 1 and t["pk"][0] in t["cols"]:
            c = t["cols"][t["pk"][0]]
            bt = base_type(c["type"])
            if bt in {"integer", "smallint", "mediumint", "tinyint"} and not re.search(r"(^|_)(type|status|kind|country|currency|lookup)s?$", tn, re.I):
                add("MEDIUM", "INT32_PRIMARY_KEY", tn, c["name"], f"primary key {c['name']} is {c['type']} (max about 2.1 billion, less for smaller types); running out means an emergency type change on the biggest table",
                    "use bigint GENERATED ALWAYS AS IDENTITY (Postgres) or BIGINT UNSIGNED AUTO_INCREMENT (MySQL)", line=ln)
        if dialect == "postgres" and t["quoted"] and t["name"] != t["name"].lower():
            add("LOW", "MIXED_CASE_NAME", tn, "", f'table "{tn}" is quoted mixed case: every query must quote it forever', "use snake_case lower-case names", line=ln)
        if tn.lower() in RESERVED and not (dialect == "postgres" and tn.lower() in RESERVED_PG_ONLY_SAFE) and not (dialect == "mysql" and tn.lower() in RESERVED_MY_ONLY_SAFE):
            add("MEDIUM", "RESERVED_WORD_NAME", tn, "", f"table name '{tn}' is a reserved word and must be quoted in every query and ORM", "rename (e.g. users, orders, user_groups)", line=ln)
        if dialect == "mysql":
            opts = t["options"].lower()
            if re.search(r"engine\s*=\s*myisam", opts):
                add("HIGH", "MYISAM_ENGINE", tn, "", "ENGINE=MyISAM has no transactions, no foreign keys and table-level locks; crashes can corrupt it", "use ENGINE=InnoDB", line=ln)
            if re.search(r"charset\s*=\s*utf8(mb3)?\b(?!mb4)", opts):
                add("MEDIUM", "MYSQL_UTF8MB3", tn, "", "utf8 in MySQL is 3-byte utf8mb3: emoji and some CJK characters fail to insert or get mangled", "use DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci", line=ln)
        if not any(re.match(r"^(created_at|created|created_on|inserted_at|date_created|creation_date)$", c) for c in t["cols"]):
            add("LOW", "NO_CREATED_AT", tn, "", "no created_at column: hard to debug, audit or backfill later", "add created_at timestamptz NOT NULL DEFAULT now()", line=ln)
        v255 = [c["name"] for c in t["cols"].values() if re.match(r"(varchar|character varying)\s*\(255\)", c["type"])]
        if dialect == "postgres" and len(v255) >= 3:
            add("LOW", "VARCHAR_255_HABIT", tn, ", ".join(v255), f"{len(v255)} columns are varchar(255): in Postgres the limit costs nothing to drop but 255 is rarely the real rule",
                "use text, with a CHECK (char_length(x) <= n) where a real limit exists", line=ln)
        for cname in t["order"]:
            c = t["cols"][cname]
            ct, bt = c["type"], base_type(c["type"])
            cn = c["name"]
            if MONEY_RE.search(cn) and bt in {"float", "real", "double", "double precision", "float4", "float8"}:
                add("HIGH", "FLOAT_MONEY", tn, cn, f"{cn} is {ct}: binary floating point cannot store 0.10 exactly, sums drift by cents",
                    "use numeric(12,2) / DECIMAL(12,2), or bigint minor units (amount_cents)", line=ln)
            if bt == "money" and dialect == "postgres":
                add("MEDIUM", "MONEY_TYPE", tn, cn, "Postgres money type depends on lc_monetary, has one fixed currency and rounds", "use numeric(12,2) plus a currency column", line=ln)
            if dialect == "postgres" and (re.match(r"^timestamp(\s*\(\d+\))?$", ct) or "without time zone" in ct):
                add("MEDIUM", "TIMESTAMP_WITHOUT_TZ", tn, cn, f"{cn} is timestamp without time zone: the instant depends on whatever zone the writer assumed", "use timestamptz (stores an absolute instant, displays in the session zone)", line=ln)
            if dialect == "mysql" and bt == "datetime" and re.search(r"_at$", cn):
                add("LOW", "DATETIME_NO_ZONE", tn, cn, f"{cn} is DATETIME (no zone): make sure every writer stores UTC", "document and enforce UTC (time_zone='+00:00' on connections) or use TIMESTAMP within its 2038 range", line=ln)
            if re.match(r"^(created_at|updated_at|inserted_at)$", cn, re.I) and not c["not_null"]:
                add("MEDIUM", "NULLABLE_AUDIT_COLUMN", tn, cn, f"{cn} is nullable{'' if c['default'] else ' and has no default'}: rows without it will appear", f"{cn} timestamptz NOT NULL DEFAULT now()", line=ln)
            if bt in {"boolean", "bool"} and not c["not_null"]:
                add("LOW", "NULLABLE_BOOLEAN", tn, cn, f"{cn} is a nullable boolean: three states (true, false, unknown) and NULL-unsafe WHERE clauses", f"{cn} boolean NOT NULL DEFAULT false", line=ln)
            if STATUS_RE.match(cn) and re.match(r"^(text|varchar|character varying|char|character)", bt) and not c["check"] \
                    and cn.lower() not in t["checks"] and not any(f["table"] == key and cname in f["cols"] for f in sc.fks):
                add("LOW", "UNCHECKED_STATUS", tn, cn, f"{cn} is free text: typos like 'Shipped ' and 'shiped' will end up in the data", "add CHECK (status IN (...)), an enum type, or a FK to a lookup table", line=ln)
            if bt in {"text", "longtext", "mediumtext"} and JSONISH_RE.search(cn):
                add("LOW", "JSON_IN_TEXT", tn, cn, f"{cn} looks like JSON stored as {ct}: no validation, no indexing", "use jsonb (Postgres) or JSON (MySQL) if it really is JSON", line=ln)
            if cn.lower() in RESERVED and not (dialect == "postgres" and cn.lower() in RESERVED_PG_ONLY_SAFE) and not (dialect == "mysql" and cn.lower() in RESERVED_MY_ONLY_SAFE) and cn.lower() not in {"type"}:
                add("MEDIUM", "RESERVED_WORD_NAME", tn, cn, f"column name '{cn}' is a reserved word and needs quoting everywhere", "rename it (e.g. sort_order, user_id, group_name, ends_at)", line=ln)
            if dialect == "postgres" and c["quoted"] and cn != cn.lower():
                add("LOW", "MIXED_CASE_NAME", tn, cn, f'column "{cn}" is quoted mixed case: every query must quote it', "use snake_case", line=ln)
            if cn.lower().endswith("_id") and cname not in t["pk"] and not any(f["table"] == key and cname in f["cols"] for f in sc.fks):
                stem = cn.lower()[:-3]
                cands = [x for x in (stem, stem + "s", stem + "es", stem[:-1] + "ies" if stem.endswith("y") else None) if x and x in table_names]
                if cands:
                    add("LOW", "MISSING_FOREIGN_KEY", tn, cn, f"{cn} looks like a reference to {cands[0]} but has no foreign key: orphans and typos are possible", f"add REFERENCES {cands[0]}(id) (with an index)", line=ln)
            if re.search(r"(^|_)email$", cn, re.I) and [cname] in t["uniques"] and dialect == "postgres" and bt != "citext":
                if not any(i["table"] == key and any("lower(" in c2 for c2 in i["cols"]) for i in sc.indexes):
                    add("LOW", "CASE_SENSITIVE_UNIQUE_EMAIL", tn, cn, "UNIQUE on email is case-sensitive in Postgres: Ana@x.com and ana@x.com can both sign up", "CREATE UNIQUE INDEX ... ON t (lower(email)) or use citext", line=ln)
    # foreign keys: types and indexes
    for f in sc.fks:
        t = sc.tables.get(f["table"])
        r = sc.tables.get(f["ref"])
        if not t:
            continue
        ref_cols = f["ref_cols"] or (r["pk"] if r else None)
        if r and ref_cols and len(ref_cols) == len(f["cols"]):
            for c, rc in zip(f["cols"], ref_cols):
                a, b = t["cols"].get(c), r["cols"].get(rc)
                if a and b and base_type(a["type"]) != base_type(b["type"]) and not ({base_type(a["type"]), base_type(b["type"])} <= {"uuid"}):
                    add("HIGH", "FK_TYPE_MISMATCH", t["name"], a["name"], f"{a['name']} is {a['type']} but references {r['name']}.{b['name']} ({b['type']}): joins need casts and the FK fails once ids pass the smaller range",
                        f"make {a['name']} the same type as {r['name']}.{b['name']}", line=t["line"])
        if dialect == "postgres":
            covered = any(idx["table"] == f["table"] and not idx["partial"] and idx["cols"][:len(f["cols"])] == f["cols"] for idx in sc.indexes) \
                or t["pk"][:len(f["cols"])] == f["cols"] or any(u[:len(f["cols"])] == f["cols"] for u in t["uniques"])
            if not covered:
                add("MEDIUM", "FK_WITHOUT_INDEX", t["name"], ", ".join(f["cols"]), f"foreign key ({', '.join(f['cols'])}) -> {f['ref']} has no index starting with it: deletes/updates on {f['ref']} scan {t['name']}, and joins are slow",
                    f"CREATE INDEX CONCURRENTLY ON {qi(t['name'])} ({', '.join(f['cols'])})", line=t["line"])
    # redundant indexes
    for i, a in enumerate(sc.indexes):
        t = sc.tables.get(a["table"])
        if not t or a["partial"] or any("(" in c for c in a["cols"]):
            continue
        others = [b for j, b in enumerate(sc.indexes) if j != i and b["table"] == a["table"] and not b["partial"]]
        if t["pk"] and a["cols"] == t["pk"][:len(a["cols"])] and not a["unique"]:
            add("LOW", "REDUNDANT_INDEX", t["name"], ", ".join(a["cols"]), f"index on ({', '.join(a['cols'])}) duplicates the primary key's leading columns", "drop it", line=a["line"])
            continue
        for b in others:
            if len(b["cols"]) > len(a["cols"]) and b["cols"][:len(a["cols"])] == a["cols"] and not a["unique"]:
                add("LOW", "REDUNDANT_INDEX", t["name"], ", ".join(a["cols"]), f"index on ({', '.join(a['cols'])}) is a prefix of the index on ({', '.join(b['cols'])})", "drop the shorter one unless it is much smaller and hot", line=a["line"])
                break
            if b["cols"] == a["cols"] and j_before(sc.indexes, b, a) and a["unique"] == b["unique"]:
                add("LOW", "REDUNDANT_INDEX", t["name"], ", ".join(a["cols"]), f"two indexes on ({', '.join(a['cols'])})", "drop one", line=a["line"])
                break
    out.sort(key=lambda f: (SEV_ORDER[f["severity"]], f["table"], f["column"], f["code"]))
    return dialect, sc, out


def j_before(lst, b, a):
    return lst.index(b) < lst.index(a)


def report(path, dialect, sc, found):
    counts = {s: sum(1 for f in found if f["severity"] == s) for s in SEV_ORDER}
    out = [f"# Schema review: {path} ({dialect})", "",
           f"Tables: {len(sc.tables)}   Indexes: {len(sc.indexes)}   Foreign keys: {len(sc.fks)}   Findings: {len(found)} (HIGH {counts['HIGH']}, MEDIUM {counts['MEDIUM']}, LOW {counts['LOW']})", ""]
    if not found:
        out.append("No findings.")
        return "\n".join(out)
    out += ["| Sev | Code | Table.Column | Problem | Fix |", "|---|---|---|---|---|"]
    for f in found:
        loc = f["table"] + ("." + f["column"] if f["column"] else "")
        out.append(f"| {f['severity']} | {f['code']} | {loc} | {f['problem'].replace('|', '/')} | {f['fix'].replace('|', '/')} |")
    return "\n".join(out)


def self_test():
    ok_pk = "CREATE TABLE t (id bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY, created_at timestamptz NOT NULL DEFAULT now()"
    cases = [
        ("clean postgres table", ok_pk + ", name text NOT NULL);", "postgres", [], ["NO_PRIMARY_KEY", "INT32_PRIMARY_KEY", "NO_CREATED_AT"]),
        ("no primary key", "CREATE TABLE logs (msg text, created_at timestamptz NOT NULL);", "auto", ["NO_PRIMARY_KEY"], []),
        ("table-level composite pk", "CREATE TABLE m (a bigint, b bigint, created_at timestamptz NOT NULL, PRIMARY KEY (a, b));", "auto", [], ["NO_PRIMARY_KEY"]),
        ("named pk constraint", "CREATE TABLE m (id bigint, created_at timestamptz NOT NULL, CONSTRAINT m_pk PRIMARY KEY (id));", "auto", [], ["NO_PRIMARY_KEY"]),
        ("pk added by alter", "CREATE TABLE m (id bigint NOT NULL, created_at timestamptz NOT NULL); ALTER TABLE m ADD CONSTRAINT m_pkey PRIMARY KEY (id);", "auto", [], ["NO_PRIMARY_KEY"]),
        ("serial pk is int32", "CREATE TABLE orders (id serial PRIMARY KEY, created_at timestamptz NOT NULL);", "auto", ["INT32_PRIMARY_KEY"], []),
        ("small lookup table int pk ok", "CREATE TABLE order_status (id smallint PRIMARY KEY, created_at timestamptz NOT NULL);", "auto", [], ["INT32_PRIMARY_KEY"]),
        ("float money", ok_pk + ", total_price double precision);", "postgres", ["FLOAT_MONEY"], []),
        ("numeric money ok", ok_pk + ", amount numeric(12,2) NOT NULL);", "postgres", [], ["FLOAT_MONEY"]),
        ("float non-money ok", ok_pk + ", latitude double precision);", "postgres", [], ["FLOAT_MONEY"]),
        ("money type", ok_pk + ", balance money);", "postgres", ["MONEY_TYPE"], []),
        ("timestamp without tz", ok_pk + ", shipped_at timestamp);", "postgres", ["TIMESTAMP_WITHOUT_TZ"], []),
        ("timestamp(3) without time zone", ok_pk + ", shipped_at timestamp(3) without time zone);", "postgres", ["TIMESTAMP_WITHOUT_TZ"], []),
        ("timestamptz ok", ok_pk + ", shipped_at timestamp with time zone);", "postgres", [], ["TIMESTAMP_WITHOUT_TZ"]),
        ("nullable created_at", "CREATE TABLE t (id bigint PRIMARY KEY, created_at timestamptz);", "postgres", ["NULLABLE_AUDIT_COLUMN"], []),
        ("no created_at", "CREATE TABLE t (id bigint PRIMARY KEY, name text);", "postgres", ["NO_CREATED_AT"], []),
        ("nullable boolean", ok_pk + ", is_active boolean);", "postgres", ["NULLABLE_BOOLEAN"], []),
        ("boolean not null ok", ok_pk + ", is_active boolean NOT NULL DEFAULT true);", "postgres", [], ["NULLABLE_BOOLEAN"]),
        ("unchecked status", ok_pk + ", status varchar(20) NOT NULL);", "postgres", ["UNCHECKED_STATUS"], []),
        ("status with check ok", ok_pk + ", status text NOT NULL CHECK (status IN ('a','b')));", "postgres", [], ["UNCHECKED_STATUS"]),
        ("status table check ok", ok_pk + ", status text NOT NULL, CONSTRAINT st CHECK (status IN ('a')));", "postgres", [], ["UNCHECKED_STATUS"]),
        ("reserved table name", "CREATE TABLE \"user\" (id bigint PRIMARY KEY, created_at timestamptz NOT NULL);", "postgres", ["RESERVED_WORD_NAME"], []),
        ("reserved column order", ok_pk + ", \"order\" int);", "postgres", ["RESERVED_WORD_NAME"], []),
        ("mixed case quoted", "CREATE TABLE \"OrderItems\" (id bigint PRIMARY KEY, created_at timestamptz NOT NULL);", "postgres", ["MIXED_CASE_NAME"], []),
        ("fk without index", "CREATE TABLE a (id bigint PRIMARY KEY, created_at timestamptz NOT NULL); CREATE TABLE b (id bigint PRIMARY KEY, created_at timestamptz NOT NULL, a_id bigint NOT NULL REFERENCES a(id));", "postgres", ["FK_WITHOUT_INDEX"], ["FK_TYPE_MISMATCH"]),
        ("fk with index ok", "CREATE TABLE a (id bigint PRIMARY KEY, created_at timestamptz NOT NULL); CREATE TABLE b (id bigint PRIMARY KEY, created_at timestamptz NOT NULL, a_id bigint REFERENCES a); CREATE INDEX ON b (a_id, id);", "postgres", [], ["FK_WITHOUT_INDEX"]),
        ("fk covered by composite pk", "CREATE TABLE a (id bigint PRIMARY KEY, created_at timestamptz NOT NULL); CREATE TABLE ab (a_id bigint REFERENCES a(id), x bigint, created_at timestamptz NOT NULL, PRIMARY KEY (a_id, x));", "postgres", [], ["FK_WITHOUT_INDEX"]),
        ("fk type mismatch", "CREATE TABLE a (id bigint PRIMARY KEY, created_at timestamptz NOT NULL); CREATE TABLE b (id bigint PRIMARY KEY, created_at timestamptz NOT NULL, a_id integer, FOREIGN KEY (a_id) REFERENCES a (id));", "postgres", ["FK_TYPE_MISMATCH"], []),
        ("missing fk on _id", "CREATE TABLE customers (id bigint PRIMARY KEY, created_at timestamptz NOT NULL); CREATE TABLE orders (id bigint PRIMARY KEY, created_at timestamptz NOT NULL, customer_id bigint NOT NULL);", "postgres", ["MISSING_FOREIGN_KEY"], []),
        ("external _id without table ok", ok_pk + ", stripe_id text);", "postgres", [], ["MISSING_FOREIGN_KEY"]),
        ("case-sensitive unique email", ok_pk + ", email text NOT NULL UNIQUE);", "postgres", ["CASE_SENSITIVE_UNIQUE_EMAIL"], []),
        ("lower(email) index ok", ok_pk + ", email text NOT NULL UNIQUE); CREATE UNIQUE INDEX t_email ON t (lower(email));", "postgres", [], ["CASE_SENSITIVE_UNIQUE_EMAIL"]),
        ("redundant prefix index", ok_pk + ", a bigint, b bigint); CREATE INDEX i1 ON t (a); CREATE INDEX i2 ON t (a, b);", "postgres", ["REDUNDANT_INDEX"], []),
        ("json in text", ok_pk + ", payload text);", "postgres", ["JSON_IN_TEXT"], []),
        ("varchar 255 habit", ok_pk + ", a varchar(255), b varchar(255), c varchar(255));", "postgres", ["VARCHAR_255_HABIT"], []),
        ("mysql myisam and utf8", "CREATE TABLE `t` (`id` int unsigned NOT NULL AUTO_INCREMENT, `created_at` datetime NOT NULL, PRIMARY KEY (`id`)) ENGINE=MyISAM DEFAULT CHARSET=utf8;", "auto", ["MYISAM_ENGINE", "MYSQL_UTF8MB3", "INT32_PRIMARY_KEY", "DATETIME_NO_ZONE"], ["TIMESTAMP_WITHOUT_TZ"]),
        ("mysql utf8mb4 innodb ok", "CREATE TABLE `t` (`id` bigint unsigned NOT NULL AUTO_INCREMENT, `created_at` datetime NOT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;", "auto", [], ["MYISAM_ENGINE", "MYSQL_UTF8MB3", "INT32_PRIMARY_KEY"]),
        ("mysql fk needs no extra index", "CREATE TABLE a (id bigint PRIMARY KEY, created_at datetime NOT NULL) ENGINE=InnoDB; CREATE TABLE b (id bigint PRIMARY KEY, created_at datetime NOT NULL, a_id bigint, FOREIGN KEY (a_id) REFERENCES a(id)) ENGINE=InnoDB;", "mysql", [], ["FK_WITHOUT_INDEX"]),
        ("comments and strings ignored", "-- CREATE TABLE x (a int);\n/* CREATE TABLE y (b int); */\n" + ok_pk + ", note text DEFAULT 'a;b -- c');", "postgres", [], ["NO_PRIMARY_KEY"]),
        ("alter add column parsed", ok_pk + "); ALTER TABLE t ADD COLUMN total_amount float;", "postgres", ["FLOAT_MONEY"], []),
    ]
    passed = 0
    for name, sql, dialect, expect, absent in cases:
        d, sc, found = lint(sql, dialect)
        codes = {f["code"] for f in found}
        ok = all(c in codes for c in expect) and not any(c in codes for c in absent)
        if name == "clean postgres table":
            ok = ok and not found
        if name == "comments and strings ignored":
            ok = ok and len(sc.tables) == 1
        if name.startswith("mysql myisam"):
            ok = ok and d == "mysql"
        passed += ok
        print(("PASS " if ok else "FAIL ") + name + ("" if ok else f" -> got {sorted(codes)}"))
    d, sc, found = lint("", "auto")
    ok = report("x.sql", d, sc, found).endswith("No findings.")
    passed += ok
    print(("PASS " if ok else "FAIL ") + "empty report")
    total = len(cases) + 1
    print(f"{passed}/{total} passed")
    return 0 if passed == total else 1


def main(argv=None):
    ap = argparse.ArgumentParser(description="SQL schema design linter (Postgres/MySQL DDL)")
    ap.add_argument("files", nargs="*")
    ap.add_argument("--dialect", default="auto", choices=["auto", "postgres", "mysql"])
    ap.add_argument("--min-severity", default="LOW", choices=list(SEV_ORDER))
    ap.add_argument("--ignore", default="")
    ap.add_argument("--json", action="store_true")
    ap.add_argument("--self-test", action="store_true")
    a = ap.parse_args(argv)
    if a.self_test:
        return self_test()
    if not a.files:
        ap.print_usage(sys.stderr)
        return 2
    ignore = {c.strip() for c in a.ignore.split(",") if c.strip()}
    sql_all = []
    for p in a.files:
        try:
            with open(p, encoding="utf-8") as fh:
                sql_all.append(fh.read())
        except OSError as e:
            print(f"error: cannot read {p}: {e}", file=sys.stderr)
            return 2
    dialect, sc, found = lint("\n;\n".join(sql_all), a.dialect, ignore)
    if not sc.tables:
        print("error: no CREATE TABLE statements found", file=sys.stderr)
        return 2
    found = [f for f in found if SEV_ORDER[f["severity"]] <= SEV_ORDER[a.min_severity]]
    if a.json:
        print(json.dumps({"dialect": dialect, "tables": len(sc.tables), "findings": found}, indent=2))
    else:
        print(report(", ".join(a.files), dialect, sc, found))
    return 1 if any(f["severity"] == "HIGH" for f in found) else 0


if __name__ == "__main__":
    sys.exit(main())

---
name: markdown-link-checker
description: Checks a Markdown docs folder for links that break readers - relative links to missing or renamed files, anchors that match no heading, duplicate heading anchors, file-name case that only works on macOS, local absolute paths, reference-style links with missing, unused or duplicate definitions, images without alt text and bare URLs. Works offline and lists external URLs to check separately. Includes a stdlib Python checker with --self-test.
---

# Markdown Link Checker

You help maintainers, technical writers and developers keep documentation navigable. You find every link inside a docs folder that leads nowhere (a moved file, a renamed heading, a typo in an anchor, a reference label that was never defined), explain why it broke, and return exact fixes. You work offline first: internal links and anchors are checked from the files themselves, and external URLs are only listed, so a docs check never depends on the network or hammers other people's servers.

## Files in this skill

- `scripts/check_md_links.py` - walks a folder of .md/.markdown/.mdx files, resolves relative and root-relative links, builds GitHub-style heading anchors and reports broken links, missing anchors, duplicates, reference-definition problems, missing alt text and bare URLs, with an external URL list on request (Python 3 standard library only)
- `references/anchors-and-slugs.md` - how GitHub, GitLab, MkDocs, Docusaurus and Hugo turn headings into anchors, duplicates, explicit anchors and the edge cases that break links
- `references/finding-codes.md` - every finding code, its severity, why it matters and the usual fix, plus how to check external URLs politely
- `templates/link-report.md` - the report to hand back
- `examples/README.md` - a small project README with deliberate link problems
- `examples/setup-guide.md` - the guide it links to, with more problems (wrong-case file name, anchor case, missing reference, local path)

## Workflow

### 1. Scope the check
Ask which folder is the docs root, how the docs are published (GitHub/GitLab rendering, MkDocs, Docusaurus, Hugo, a plain repo browse), and whether links like `/guide/a.md` mean "from the repo root" or "from the site root". The anchor rules differ per generator (see `references/anchors-and-slugs.md`); default to GitHub rules and say so.

### 2. Run the checker
```
python3 scripts/check_md_links.py examples --external
python3 scripts/check_md_links.py docs README.md --root . --min-severity MEDIUM
python3 scripts/check_md_links.py docs --ignore BARE_URL,UNUSED_REF_DEF --json > links.json
python3 scripts/check_md_links.py --self-test
```
Exit 0 means no HIGH findings, 1 means at least one broken link, missing anchor or missing reference definition (use it as a CI gate), 2 means bad input. Code blocks and inline code are skipped; GitHub line anchors (`#L10-L20`) and `mailto:` links are accepted.

### 3. Triage and fix
Work HIGH first. For BROKEN_LINK, search the repo for the file name (`git log --diff-filter=R --name-status` shows renames) and link to where it lives now. For MISSING_ANCHOR, read the target headings: the script suggests the closest existing anchor; decide whether to change the link or the heading (changing a heading breaks inbound links from elsewhere, so prefer adding an explicit anchor if the old one is linked externally). For DUPLICATE_ANCHOR, make the headings unique. For CASE_MISMATCH, use the exact file name. Then the MEDIUM and LOW items: alt text, empty links, unused definitions, bare URLs.

### 4. External URLs
With `--external` the script lists every external URL and where it is used, without making requests. If the user wants them checked, do it separately and politely (HEAD then GET, a few requests per host, a timeout, treat 429/403 as "check by hand", not as broken). See `references/finding-codes.md`.

### 5. Deliver
Fill `templates/link-report.md`: scope and rules used, counts, a fix table with file:line, old target, new target, and the external URL list. If asked for corrected files, return them with only the link changes, nothing else rewritten.

## Example result
`examples/` (2 files): 13 findings, 6 HIGH. README.md links `setup-guide.md#configuration`, but the heading is "Configure the team folder" (#configure-the-team-folder, suggested by the script); CHANGELOG.md, ../CONTRIBUTING.md, docs/style.md and the diagram image do not exist; "Usage" appears twice so the second is #usage-1; [roadmap] is defined but unused. setup-guide.md links `readme.md` (only README.md exists: works on a Mac, breaks on GitHub), uses `#Usage` (anchors are lower-case), points at /Users/ana/... and uses [support] without a definition. 4 external URLs listed, none fetched.

## Rules

- Never fetch external URLs unless the user asks; when you do, rate-limit and do not report 403/429 as broken.
- Fix the link, not the content: do not rewrite prose while fixing paths.
- Prefer relative links between docs; root-relative only if the publishing setup supports it.
- When a heading must change, keep the old anchor working with an explicit `<a id="old-anchor"></a>` if other sites link to it.
- State which anchor rules you used (GitHub by default) and re-run the checker after fixing; the result must be exit 0.
- Write real alt text for images (what it shows and why it is there); for a full accessibility review use a dedicated accessibility check.
FILE:references/anchors-and-slugs.md
# Heading anchors and slugs

A link like `guide.md#install` works only if the renderer generated exactly `install` as the id of a heading in guide.md. Each renderer has its own slug rules, so first find out where the docs are read.

## GitHub (default used by the script)
1. Take the heading text as rendered: inline markup removed (`code` keeps its text, `**bold**` becomes bold, `[text](url)` becomes text, HTML tags dropped).
2. Lower-case it.
3. Remove every character that is not a letter, digit, space, hyphen or underscore (letters include accented and non-Latin letters; emoji and punctuation go).
4. Turn each space into a hyphen. Spaces are NOT collapsed: "C++ & Rust" becomes `c--rust`.
5. Duplicates get `-1`, `-2`, ... in order of appearance: the second "Usage" is `#usage-1`.

| Heading | Anchor |
|---|---|
| `## What's new? (v2.0)` | `#whats-new-v20` |
| ``## The `--dry-run` flag`` | `#the---dry-run-flag` |
| `## Über uns` | `#über-uns` (GitHub also accepts the percent-encoded form) |
| `## C++ & Rust: 100% safe?` | `#c--rust-100-safe` |
| `## snake_case_name` | `#snake_case_name` |
| `## Usage` (second time) | `#usage-1` |

The script's slug function matches the github-slugger library on these cases.

## Other renderers
- **GitLab**: like GitHub, but consecutive hyphens are collapsed into one (`#c-rust-100-safe`), so links copied between GitHub and GitLab can break.
- **MkDocs (Python-Markdown toc)**: drops non-ASCII by default, collapses separators; `{#custom-id}` is available with attr_list. Check `markdown_extensions: toc: slugify` in mkdocs.yml.
- **Docusaurus**: GitHub-like slugs; supports `## Heading {#custom-id}`.
- **Hugo (goldmark)**: GitHub-like by default; `autoHeadingIDType` can be `github`, `github-ascii` or `blackfriday`.
- **VS Code preview / most IDEs**: GitHub-like.

If the published site and the repo view disagree, prefer explicit anchors for anything linked from outside.

## Explicit anchors
- `<a id="install"></a>` or `<a name="install"></a>` just before the heading (works everywhere HTML is allowed).
- `## Install {#install}` where the renderer supports attribute lists (MkDocs attr_list, Docusaurus, Hugo, Pandoc). On GitHub the `{#...}` shows up as literal text.

## What breaks anchors
- Renaming a heading ("Configuration" -> "Configure the team folder").
- Duplicates: links to `#usage` always land on the first one.
- Capital letters in the link (`#Usage`): GitHub anchors are lower-case; some browsers forgive it, many renderers do not.
- Copying the anchor from another renderer (GitLab vs GitHub hyphens).
- Headings generated by includes or templates the checker cannot see; mark these with `--ignore MISSING_ANCHOR` for that folder only, and say so.
- Line anchors (`#L10`, `#L10-L20`) are GitHub file-view features; they are accepted but break if the file moves or lines shift.
FILE:references/finding-codes.md
# Finding codes

| Code | Severity | Why it matters | Usual fix |
|---|---|---|---|
| BROKEN_LINK | HIGH | relative link to a file or folder that does not exist (moved, renamed, typo) | link to the current path; `git log --diff-filter=R --name-status -- docs/` shows renames |
| BROKEN_IMAGE | HIGH | image path does not exist; readers see a broken icon | fix the path or commit the image |
| MISSING_ANCHOR | HIGH | #fragment matches no heading or explicit anchor in the target file | use the suggested anchor, or add an explicit anchor |
| MISSING_REF_DEF | HIGH | `[text][label]` has no `[label]: url` definition; it renders as plain bracketed text | add the definition or fix the label (labels are case-insensitive) |
| DUPLICATE_ANCHOR | MEDIUM | two headings produce the same slug; the second gets `-1` and links land on the first | make headings unique, e.g. "Usage (CLI)" and "Usage (API)" |
| DUPLICATE_REF_DEF | MEDIUM | the same label is defined twice; only the first counts | delete or rename one |
| CASE_MISMATCH | MEDIUM | file exists only with different case; fine on macOS/Windows, broken on Linux, GitHub Pages and most CI | use the exact name |
| ANCHOR_CASE | MEDIUM | anchor only matches when lower-cased | write anchors in lower case |
| LOCAL_ABSOLUTE_PATH | MEDIUM | link to /Users/..., /home/..., C:\ or file:// works only on the author's machine | relative path, or remove |
| EMPTY_LINK | MEDIUM | `[text]()` or empty href | fill in or remove |
| EMPTY_LINK_TEXT | MEDIUM | `[](url)`: nothing to click or read aloud | add link text |
| MISSING_ALT | MEDIUM | image without alt text; screen readers say "image" or the file name | describe what it shows and why it is there |
| UNUSED_REF_DEF | LOW | definition never used; usually left over after an edit | delete, or link to it if the link was lost |
| BARE_URL | LOW | raw URL in text; not clickable in some renderers, read character by character | `[descriptive text](url)` or `<url>` |
| OUTSIDE_ROOT | LOW | relative link leaves the docs root; breaks if docs are published alone | link to the published URL |

Exit codes: 0 = no HIGH, 1 = HIGH present, 2 = bad input. Use `--min-severity` and `--ignore` to tune a CI gate, and record any ignore in the repo with a reason.

## Link forms the script understands
- Inline: `[text](path.md#anchor "title")`, `[text](<path with spaces.md>)`, `[text](my%20notes.md)`
- Images: `![alt](img.png)`, `<img src="img.png" alt="...">`
- Reference: `[text][label]`, `[label][]`, `[label]` with `[label]: url "title"` anywhere in the same file
- Autolinks `<https://...>`, HTML `<a href="...">`, explicit anchors `<a id>`, `<a name>`, `{#id}`
- Root-relative `/guide/a.md` resolves from `--root` (default: the first folder argument)
- Skipped: fenced and indented code blocks, inline code, `mailto:`/`tel:`, GitHub line anchors, task list boxes `[ ]` `[x]`

## Checking external URLs (only when asked)
- Deduplicate first: `--external` lists each URL once with every place it is used.
- Use HEAD, fall back to GET when the server rejects HEAD (405) or lies about it.
- One or two requests per host at a time, a 10 s timeout, a clear User-Agent.
- 200-299 OK; 301/308 update the link to the new location; 404/410 broken; 403, 429 and timeouts are "check by hand" (bot protection, rate limits).
- Anchors on external pages cannot be checked reliably offline; note them, do not guess.
- Prefer links to stable, versioned pages (tagged docs, permalinks) over "latest".
FILE:templates/link-report.md
# Docs link check: <repo or folder>, <date>

**Scope:** <docs/ and README.md, 42 files>   **Anchor rules:** <GitHub>   **Root for /links:** <repo root>
**Command:** `python3 scripts/check_md_links.py <docs README.md --root . --external>`
**Result:** <13 findings: HIGH 6, MEDIUM 5, LOW 2 -> after fixes: exit 0>

## Must fix (HIGH)
| # | File:Line | Code | Link as written | Problem | Fix (new target) |
|---|---|---|---|---|---|
| 1 | <README.md:11> | <MISSING_ANCHOR> | <setup-guide.md#configuration> | <heading renamed to "Configure the team folder"> | <setup-guide.md#configure-the-team-folder> |

## Should fix (MEDIUM)
| # | File:Line | Code | Problem | Fix |
|---|---|---|---|---|
| 1 | <setup-guide.md:25> | <CASE_MISMATCH> | <readme.md vs README.md> | <README.md#contents> |

## Clean-up (LOW)
- <unused [roadmap] definition in README.md:42 - delete or link it>
- <bare URL README.md:21 -> [Tidepool documentation](https://docs.example.com/tidepool)>

## Images and alt text
| File:Line | Image | Alt text to use |
|---|---|---|
| <README.md:5> | <images/sync-diagram.png (missing)> | <"Diagram: phone app sends notes to the sync server, which writes them to the team folder"> |

## External URLs (not fetched)
| URL | Used at | Status (if checked) |
|---|---|---|
| <https://docs.example.com/tidepool> | <README.md:21> | <not checked> |

## Prevent it next time
- <run the checker in CI on every docs change (exit 1 fails the build)>
- <when renaming a heading that others link to, keep an explicit anchor with the old id>
FILE:examples/README.md
# Tidepool

Tidepool syncs field notes from a phone to a shared team folder.

![](images/sync-diagram.png)

## Contents

- [Quick start](#quick-start)
- [Install](setup-guide.md#install)
- [Configuration](setup-guide.md#configuration)
- [Troubleshooting](setup-guide.md#troubleshooting)
- [FAQ](#faq)

## Quick start

1. Install the app (see [the setup guide][setup]).
2. Sign in and pick a team folder.
3. Read the [release notes](CHANGELOG.md) before upgrading.

Full documentation lives at https://docs.example.com/tidepool and the API
reference is at <https://api.example.com/tidepool/v2>.

## Usage

Run `tidepool sync` to push new notes. Links inside code are not checked:

```
[not a link](missing.md)
```

## Usage

See [Contributing](../CONTRIBUTING.md) and the [style guide][style].

## Faq

**Can I sync offline?** Notes queue until the phone is online again.

[setup]: setup-guide.md
[style]: docs/style.md
[roadmap]: https://example.com/tidepool/roadmap
FILE:examples/setup-guide.md
# Setup guide

## Install

Download the installer from the [releases page](https://github.com/example/tidepool/releases)
or build from source (see [Building](#building-from-source)).

![Settings screen with the Team folder field highlighted](https://example.com/tidepool/img/settings.png)

## Configure the team folder

Open **Settings > Team folder** and paste the folder link. The folder must
already be shared with you (see [Sharing](./README.md#Usage)).

## Building from source

Clone the repository and run `make build`, then continue with the
[Quick start](README.md#quick-start).

## Troubleshooting

If sync stalls, check the log at [/Users/ana/tidepool/logs/sync.log](/Users/ana/tidepool/logs/sync.log)
or ask in the [support channel][support].

Back to the [README](readme.md#contents).
FILE:scripts/check_md_links.py
#!/usr/bin/env python3
"""Markdown link checker (Python 3 standard library only, fully offline).

Scans a docs folder (or single files) and reports link problems that break readers
before anyone clicks: relative links to files that do not exist, #anchors that match
no heading in the target file, duplicate heading anchors, file-name case mismatches
that only work on macOS/Windows, links to absolute local paths, empty links,
reference-style links whose definition is missing, unused or duplicate reference
definitions, images without alt text and bare URLs. It never touches the network;
use --external to list every external URL (with where it is used) so you can check
them separately.

Anchors follow GitHub's slug rules: heading text with inline markup removed,
lower-cased, punctuation dropped (letters, digits, spaces, "-" and "_" kept), each
space turned into "-", duplicates suffixed -1, -2, ... Explicit anchors from
<a name="x">, <a id="x">, id="x" on HTML tags and {#x} heading attributes count too.

Usage:
  python3 check_md_links.py PATH [PATH ...] [--root DIR] [--min-severity LOW|MEDIUM|HIGH]
        [--ignore CODE,CODE] [--external] [--json]
  python3 check_md_links.py --self-test
Exit codes: 0 = no HIGH findings, 1 = HIGH findings (broken links, missing anchors or
reference definitions), 2 = bad input (path not found, no Markdown files).
"""
import argparse, json, os, re, sys, tempfile, unicodedata
from urllib.parse import unquote

SEV_ORDER = {"HIGH": 0, "MEDIUM": 1, "LOW": 2}
MD_EXT = (".md", ".markdown", ".mdx")
SKIP_DIRS = {".git", "node_modules", ".venv", "venv", "__pycache__", "_site", "site", "build", "dist"}

FENCE_RE = re.compile(r"^ {0,3}(`{3,}|~{3,})")
ATX_RE = re.compile(r"^ {0,3}(#{1,6})[ \t]+(.*?)[ \t]*#*[ \t]*$")
SETEXT_RE = re.compile(r"^ {0,3}(=+|-+)[ \t]*$")
REFDEF_RE = re.compile(r"^ {0,3}\[([^\]]+)\]:[ \t]*(<[^>]*>|\S+)(?:[ \t]+(\"[^\"]*\"|'[^']*'|\([^)]*\)))?[ \t]*$")
INLINE_RE = re.compile(r"(!?)\[((?:[^\[\]\\]|\\.|\[[^\]]*\])*)\]\(\s*(<[^>]*>|[^\s()]*(?:\([^\s()]*\)[^\s()]*)*)(?:\s+(\"[^\"]*\"|'[^']*'|\([^)]*\)))?\s*\)")
REFLINK_RE = re.compile(r"(!?)\[((?:[^\[\]\\]|\\.)*)\]\[([^\]]*)\]")
SHORTCUT_RE = re.compile(r"(?<![\]\\!])\[([^\[\]]+)\](?![\[(:])")
AUTOLINK_RE = re.compile(r"<((?:https?|ftp)://[^>\s]+|mailto:[^>\s]+)>")
BARE_URL_RE = re.compile(r"(?<![<(\"'=\w/])(https?://[^\s<>)\]\"']+)")
HTML_ANCHOR_RE = re.compile(r"<[a-zA-Z][^>]*?\b(?:id|name)\s*=\s*[\"']([^\"']+)[\"']")
HTML_HREF_RE = re.compile(r"<a\b[^>]*?\bhref\s*=\s*[\"']([^\"']*)[\"']", re.I)
HTML_IMG_RE = re.compile(r"<img\b([^>]*)>", re.I)
ATTR_ID_RE = re.compile(r"\s*\{#([\w\-:.]+)[^}]*\}\s*$")
SCHEME_RE = re.compile(r"^[a-zA-Z][a-zA-Z0-9+.\-]*:")
WIN_ABS_RE = re.compile(r"^[a-zA-Z]:[\\/]")


def finding(sev, code, path, line, snippet, problem, fix):
    return {"severity": sev, "code": code, "file": path, "line": line,
            "snippet": snippet.strip()[:120], "problem": problem, "fix": fix}


def strip_inline_markup(text):
    t = re.sub(r"`([^`]*)`", r"\1", text)
    t = re.sub(r"!\[([^\]]*)\]\([^)]*\)", r"\1", t)
    t = re.sub(r"\[([^\]]*)\]\([^)]*\)", r"\1", t)
    t = re.sub(r"\[([^\]]*)\]\[[^\]]*\]", r"\1", t)
    t = re.sub(r"<[^>]+>", "", t)
    t = re.sub(r"(\*\*|\*|~~)(?=\S)(.+?)(?<=\S)\1", r"\2", t)
    t = re.sub(r"(?<!\w)(__|_)(?=\S)(.+?)(?<=\S)\1(?!\w)", r"\2", t)  # _x_ only at word edges
    return t


def github_slug(text):
    t = strip_inline_markup(text).strip().lower()
    out = []
    for ch in t:
        cat = unicodedata.category(ch)
        if ch in "-_ " or cat[0] in "LN" or cat == "Mn":
            out.append("-" if ch == " " else ch)
    return "".join(out)


def mask_code(lines):
    """Return (block-masked lines, fully masked lines): fenced/indented code blocks blanked;
    the second list also masks inline code spans (headings keep their code text)."""
    out, fence = [], None
    prev_blank = True
    for line in lines:
        m = FENCE_RE.match(line)
        if fence:
            if m and m.group(1)[0] == fence[0] and len(m.group(1)) >= len(fence) and not line.strip()[len(m.group(1)):].strip():
                fence = None
            out.append("")
            continue
        if m:
            fence = m.group(1)
            out.append("")
            continue
        if prev_blank and (line.startswith("    ") or line.startswith("\t")) and line.strip():
            out.append("")
            continue
        prev_blank = not line.strip()
        out.append(line)
    inline = [re.sub(r"(`+)(.+?)\1", lambda mm: mm.group(1) + "x" * len(mm.group(2)) + mm.group(1), l) for l in out]
    return out, inline


def parse_file(text):
    """Return dict with anchors (slug->line), duplicates, headings, links, refdefs, images, bare urls."""
    raw = text.splitlines()
    blocks, lines = mask_code(raw)
    anchors, dups, counts = {}, [], {}
    refdefs, links, bare, html_imgs = {}, [], [], []
    dup_defs = []
    for i, line in enumerate(lines, 1):
        heading = None
        m = ATX_RE.match(blocks[i - 1])
        if m:
            heading = m.group(2)
        elif i >= 2 and SETEXT_RE.match(line) and blocks[i - 2].strip() and not ATX_RE.match(blocks[i - 2]) \
                and not blocks[i - 2].lstrip().startswith(("-", "*", ">", "|")) and not REFDEF_RE.match(blocks[i - 2]):
            if line.strip().startswith("=") or (i >= 3 and not blocks[i - 3].strip()) or i == 2:
                heading = blocks[i - 2].strip()
        if heading is not None:
            am = ATTR_ID_RE.search(heading)
            if am:
                anchors.setdefault(am.group(1), i)
                heading = heading[:am.start()]
            base = github_slug(heading)
            n = counts.get(base, 0)
            counts[base] = n + 1
            slug = base if n == 0 else f"{base}-{n}"
            if n > 0:
                dups.append((i, heading.strip(), base, slug))
            anchors.setdefault(slug, i)
        for am in HTML_ANCHOR_RE.finditer(blocks[i - 1]):
            anchors.setdefault(am.group(1), i)
        d = REFDEF_RE.match(line)
        if d:
            label = norm_label(d.group(1))
            target = d.group(2).strip("<>")
            if label in refdefs:
                dup_defs.append((i, d.group(1), refdefs[label][1]))
            else:
                refdefs[label] = (target, i, d.group(1))
            continue
        spans = []
        for lm in INLINE_RE.finditer(line):
            target = lm.group(3).strip()
            if target.startswith("<") and target.endswith(">"):
                target = target[1:-1]
            links.append({"kind": "image" if lm.group(1) else "link", "text": lm.group(2), "target": target,
                          "line": i, "snippet": lm.group(0), "ref": None})
            spans.append(lm.span())
        for rm in REFLINK_RE.finditer(line):
            if any(a <= rm.start() < b for a, b in spans):
                continue
            label = rm.group(3) or rm.group(2)
            links.append({"kind": "image" if rm.group(1) else "link", "text": rm.group(2), "target": None,
                          "line": i, "snippet": rm.group(0), "ref": norm_label(label), "explicit": True})
            spans.append(rm.span())
        for sm in SHORTCUT_RE.finditer(line):
            if any(a <= sm.start() < b for a, b in spans):
                continue
            if re.match(r"^[ xX]$", sm.group(1)) or line[sm.end():sm.end() + 1] == "]":
                continue  # task list box or nested
            links.append({"kind": "image" if sm.start() > 0 and line[sm.start() - 1] == "!" else "link",
                          "text": sm.group(1), "target": None, "line": i, "snippet": sm.group(0),
                          "ref": norm_label(sm.group(1)), "explicit": False})
            spans.append(sm.span())
        for hm in HTML_HREF_RE.finditer(line):
            links.append({"kind": "link", "text": "", "target": hm.group(1), "line": i, "snippet": hm.group(0), "ref": None, "html": True})
        for im in HTML_IMG_RE.finditer(line):
            attrs = im.group(1)
            src = re.search(r"\bsrc\s*=\s*[\"']([^\"']*)[\"']", attrs, re.I)
            alt = re.search(r"\balt\s*=\s*[\"']([^\"']*)[\"']", attrs, re.I)
            links.append({"kind": "image", "text": alt.group(1) if alt else None, "target": src.group(1) if src else "",
                          "line": i, "snippet": im.group(0), "ref": None, "html": True})
        cleaned = AUTOLINK_RE.sub(" ", line)
        cleaned = INLINE_RE.sub(" ", cleaned)
        cleaned = re.sub(r"<[^>]+>", " ", cleaned)
        for bm in BARE_URL_RE.finditer(cleaned):
            bare.append((i, bm.group(1).rstrip(".,;:!?")))
        for am in AUTOLINK_RE.finditer(line):
            links.append({"kind": "autolink", "text": am.group(1), "target": am.group(1), "line": i, "snippet": am.group(0), "ref": None})
    return {"anchors": anchors, "dups": dups, "refdefs": refdefs, "dup_defs": dup_defs, "links": links, "bare": bare}


def norm_label(s):
    return re.sub(r"\s+", " ", s.strip()).casefold()


def is_external(target):
    return bool(SCHEME_RE.match(target)) and not WIN_ABS_RE.match(target)


def exists_exact_case(path):
    """True/False for exact-case existence, plus the real name if only a case-insensitive match exists."""
    if os.path.exists(path):
        head, tail = os.path.split(os.path.abspath(path))
        try:
            names = os.listdir(head or ".")
        except OSError:
            return True, None
        if tail in names or not tail:
            return True, None
        for n in names:
            if n.lower() == tail.lower():
                return False, n
        return True, None
    head, tail = os.path.split(os.path.abspath(path))
    try:
        for n in os.listdir(head):
            if n.lower() == tail.lower():
                return False, n
    except OSError:
        pass
    return False, None


class Checker:
    def __init__(self, root, ignore=()):
        self.root = os.path.abspath(root)
        self.ignore = set(ignore)
        self.cache = {}
        self.findings = []
        self.external = {}

    def parsed(self, path):
        path = os.path.abspath(path)
        if path not in self.cache:
            with open(path, encoding="utf-8", errors="replace") as fh:
                self.cache[path] = parse_file(fh.read())
        return self.cache[path]

    def add(self, *a):
        f = finding(*a)
        if f["code"] not in self.ignore:
            self.findings.append(f)

    def rel(self, p):
        return os.path.relpath(p, self.root)

    def check_file(self, path):
        info = self.parsed(path)
        rp = self.rel(path)
        for line, heading, base, slug in info["dups"]:
            self.add("MEDIUM", "DUPLICATE_ANCHOR", rp, line, heading,
                     f"heading '{heading}' repeats an earlier anchor #{base}; this one becomes #{slug}, so links to #{base} land on the first one",
                     "make the heading unique (add context) or add an explicit anchor")
        for line, label, first in info["dup_defs"]:
            self.add("MEDIUM", "DUPLICATE_REF_DEF", rp, line, f"[{label}]:",
                     f"reference [{label}] is defined again (first definition on line {first}); only the first one is used",
                     "delete or rename the duplicate definition")
        used = set()
        for ln in info["links"]:
            if ln["ref"] is not None:
                d = info["refdefs"].get(ln["ref"])
                if d is None:
                    if ln.get("explicit"):
                        self.add("HIGH", "MISSING_REF_DEF", rp, ln["line"], ln["snippet"],
                                 f"reference-style link uses [{ln['ref']}] but no '[{ln['ref']}]: URL' definition exists, so it renders as plain text",
                                 "add the definition at the bottom of the file or fix the label")
                    continue
                used.add(ln["ref"])
                target = d[0]
            else:
                target = ln["target"]
            self.check_link(path, rp, ln, target)
        for label, (target, line, orig) in info["refdefs"].items():
            if label not in used:
                self.add("LOW", "UNUSED_REF_DEF", rp, line, f"[{orig}]: {target}",
                         f"reference definition [{orig}] is never used", "delete it or link to it")
        for line, url in info["bare"]:
            self.add("LOW", "BARE_URL", rp, line, url,
                     "bare URL: not clickable in some renderers and read out character by character by screen readers",
                     f"use [descriptive text]({url}) or <{url}>")
            self.external.setdefault(url, []).append(f"{rp}:{line}")

    def check_link(self, path, rp, ln, target):
        kind = ln["kind"]
        if kind == "image":
            alt = ln["text"]
            if alt is None or not alt.strip():
                self.add("MEDIUM", "MISSING_ALT", rp, ln["line"], ln["snippet"],
                         "image has no alt text", "describe what the image shows or why it is there (alt=\"\" only for purely decorative images in HTML)")
        if target is None:
            return
        if not target.strip():
            self.add("MEDIUM", "EMPTY_LINK", rp, ln["line"], ln["snippet"], f"{kind} has an empty target", "add the URL or path, or remove the brackets")
            return
        if kind == "link" and not ln.get("html") and not strip_inline_markup(ln["text"]).strip():
            self.add("MEDIUM", "EMPTY_LINK_TEXT", rp, ln["line"], ln["snippet"], "link has no visible text", "put words inside the [ ]")
        if target.startswith("mailto:") or target.startswith("tel:"):
            return
        if target.startswith("file:") or WIN_ABS_RE.match(target) or re.match(r"^/(home|Users|tmp|var|mnt|opt)/", target):
            self.add("MEDIUM", "LOCAL_ABSOLUTE_PATH", rp, ln["line"], ln["snippet"],
                     f"'{target}' points at a path on the author's machine; it is broken for everyone else",
                     "use a path relative to this file")
            return
        if is_external(target):
            if target.startswith(("http://", "https://", "ftp://")):
                self.external.setdefault(target, []).append(f"{rp}:{ln['line']}")
            return
        target_path, _, frag = target.partition("#")
        target_path = unquote(target_path.split("?")[0])
        frag = unquote(frag)
        if target_path:
            if target_path.startswith("/"):
                full = os.path.normpath(os.path.join(self.root, target_path.lstrip("/")))
            else:
                full = os.path.normpath(os.path.join(os.path.dirname(path), target_path))
            ok, real = exists_exact_case(full)
            if not ok and real:
                self.add("MEDIUM", "CASE_MISMATCH", rp, ln["line"], ln["snippet"],
                         f"'{target_path}' only matches '{real}' with different letter case; works on macOS/Windows, breaks on Linux and GitHub Pages",
                         f"use the exact name '{real}'")
                full = os.path.join(os.path.dirname(full), real)
            elif not ok:
                code = "BROKEN_IMAGE" if kind == "image" else "BROKEN_LINK"
                self.add("HIGH", code, rp, ln["line"], ln["snippet"],
                         f"'{target_path}' does not exist" + (f" (resolved to {self.rel(full)})" if self.rel(full) != os.path.normpath(target_path) else ""),
                         "fix the path (moved or renamed file?) or remove the link")
                return
            if not os.path.abspath(full).startswith(self.root + os.sep) and os.path.abspath(full) != self.root:
                self.add("LOW", "OUTSIDE_ROOT", rp, ln["line"], ln["snippet"],
                         f"'{target_path}' leaves the docs root; it breaks if the docs are published on their own",
                         "link to the published URL or copy the file into the docs")
        else:
            full = path
        if frag:
            if os.path.isdir(full) or not full.lower().endswith(MD_EXT):
                return
            info = self.parsed(full)
            if frag in info["anchors"]:
                return
            if frag.lower() in info["anchors"]:
                self.add("MEDIUM", "ANCHOR_CASE", rp, ln["line"], ln["snippet"],
                         f"#{frag} only matches #{frag.lower()} case-insensitively; GitHub anchors are lower-case",
                         f"use #{frag.lower()}")
                return
            if re.match(r"^L\d+(-L\d+)?$", frag):
                return  # GitHub line anchors
            key = frag.lower().replace("-", "")
            close = [a for a in info["anchors"] if a.replace("-", "") == key] or \
                    [a for a in info["anchors"] if len(key) >= 5 and key[:6] in a.replace("-", "")]
            hint = f" Did you mean #{close[0]}?" if close else ""
            self.add("HIGH", "MISSING_ANCHOR", rp, ln["line"], ln["snippet"],
                     f"#{frag} matches no heading or anchor in {self.rel(full)}.{hint}",
                     "link to an existing heading slug, or add the heading / an explicit anchor")


def collect(paths):
    files = []
    for p in paths:
        if os.path.isdir(p):
            for dirpath, dirnames, filenames in os.walk(p):
                dirnames[:] = sorted(d for d in dirnames if d not in SKIP_DIRS and not d.startswith("."))
                files += [os.path.join(dirpath, f) for f in sorted(filenames) if f.lower().endswith(MD_EXT)]
        elif os.path.isfile(p):
            files.append(p)
        else:
            raise FileNotFoundError(p)
    return files


def run(paths, root=None, ignore=(), min_sev="LOW"):
    files = collect(paths)
    if root is None:
        root = paths[0] if os.path.isdir(paths[0]) else os.path.dirname(os.path.abspath(paths[0]))
    ck = Checker(root, ignore)
    for f in files:
        ck.check_file(os.path.abspath(f))
    lim = SEV_ORDER[min_sev]
    found = [f for f in ck.findings if SEV_ORDER[f["severity"]] <= lim]
    found.sort(key=lambda f: (f["file"], f["line"], SEV_ORDER[f["severity"]]))
    return files, found, ck.external


def report(files, found, external, show_external, roots):
    counts = {s: sum(1 for f in found if f["severity"] == s) for s in SEV_ORDER}
    out = [f"# Markdown link check: {', '.join(roots)}", "",
           f"Files: {len(files)}   Findings: {len(found)} (HIGH {counts['HIGH']}, MEDIUM {counts['MEDIUM']}, LOW {counts['LOW']})   External URLs: {len(external)} (not checked, offline)", ""]
    if not found:
        out.append("No findings.")
    else:
        out += ["| Sev | Code | File:Line | Problem | Fix |", "|---|---|---|---|---|"]
        for f in found:
            out.append(f"| {f['severity']} | {f['code']} | {f['file']}:{f['line']} | {f['problem'].replace('|', '/')} | {f['fix'].replace('|', '/')} |")
    if show_external and external:
        out += ["", "## External URLs to check (no network calls were made)", "", "| URL | Used at |", "|---|---|"]
        for url in sorted(external):
            out.append(f"| {url} | {', '.join(external[url])} |")
    return "\n".join(out)


def self_test():
    cases = []

    def case(name, files, expect, absent=(), target="README.md"):
        cases.append((name, files, expect, absent, target))

    case("clean file", {"README.md": "# Title\n\nSee [setup](setup.md#install).\n", "setup.md": "# Setup\n\n## Install\n"}, [], ["BROKEN_LINK", "MISSING_ANCHOR"])
    case("broken relative link", {"README.md": "[x](docs/missing.md)\n"}, ["BROKEN_LINK"])
    case("broken image", {"README.md": "![logo](img/logo.png)\n"}, ["BROKEN_IMAGE"])
    case("missing anchor other file", {"README.md": "[x](a.md#nope)\n", "a.md": "# Yes\n"}, ["MISSING_ANCHOR"])
    case("missing anchor same file", {"README.md": "# Intro\n[x](#usage)\n"}, ["MISSING_ANCHOR"])
    case("anchor with punctuation", {"README.md": "## What's new? (v2.0)\n[x](#whats-new-v20)\n"}, [], ["MISSING_ANCHOR"])
    case("anchor with inline code", {"README.md": "## The `--dry-run` flag\n[x](#the---dry-run-flag)\n"}, [], ["MISSING_ANCHOR"])
    case("underscores inside words kept", {"README.md": "## snake_case_name and _emphasis_\n[x](#snake_case_name-and-emphasis)\n"}, [], ["MISSING_ANCHOR"])
    case("unicode heading anchor", {"README.md": "## Über uns\n[x](#über-uns)\n"}, [], ["MISSING_ANCHOR"])
    case("duplicate heading", {"README.md": "## Usage\n## Usage\n[x](#usage-1)\n"}, ["DUPLICATE_ANCHOR"], ["MISSING_ANCHOR"])
    case("setext heading", {"README.md": "Install\n=======\n[x](#install)\n"}, [], ["MISSING_ANCHOR"])
    case("explicit html anchor", {"README.md": '<a id="faq"></a>\n[x](#faq)\n'}, [], ["MISSING_ANCHOR"])
    case("attribute id anchor", {"README.md": "## Setup {#custom-setup}\n[x](#custom-setup)\n"}, [], ["MISSING_ANCHOR"])
    case("anchor case", {"README.md": "## Usage\n[x](#Usage)\n"}, ["ANCHOR_CASE"], ["MISSING_ANCHOR"])
    case("near-miss hint", {"README.md": "## Getting Started\n[x](#gettingstarted)\n"}, ["MISSING_ANCHOR"])
    case("missing ref def", {"README.md": "See [the guide][guide].\n"}, ["MISSING_REF_DEF"])
    case("unused ref def", {"README.md": "Text.\n\n[old]: https://example.com\n"}, ["UNUSED_REF_DEF"])
    case("used ref def shortcut", {"README.md": "See [guide].\n\n[guide]: setup.md\n", "setup.md": "# S\n"}, [], ["UNUSED_REF_DEF", "BROKEN_LINK"])
    case("ref def case-insensitive", {"README.md": "See [Guide][G].\n\n[g]: setup.md\n", "setup.md": "# S\n"}, [], ["MISSING_REF_DEF", "UNUSED_REF_DEF"])
    case("ref def broken target", {"README.md": "See [g][].\n\n[g]: nope.md\n"}, ["BROKEN_LINK"])
    case("duplicate ref def", {"README.md": "[a][x]\n\n[x]: https://a.example\n[x]: https://b.example\n"}, ["DUPLICATE_REF_DEF"])
    case("image without alt", {"README.md": "![](shot.png)\n", "shot.png": "png"}, ["MISSING_ALT"], ["BROKEN_IMAGE"])
    case("html img without alt", {"README.md": '<img src="shot.png" width="300">\n', "shot.png": "png"}, ["MISSING_ALT"])
    case("bare url", {"README.md": "Docs at https://example.com/docs today.\n"}, ["BARE_URL"])
    case("autolink is not bare", {"README.md": "Docs at <https://example.com/docs>.\n"}, [], ["BARE_URL"])
    case("code block ignored", {"README.md": "```\n[x](missing.md) https://x.example\n```\n"}, [], ["BROKEN_LINK", "BARE_URL"])
    case("inline code ignored", {"README.md": "Use `[x](missing.md)` syntax.\n"}, [], ["BROKEN_LINK"])
    case("case mismatch", {"README.md": "[c](CONTRIBUTING.MD)\n", "CONTRIBUTING.md": "# C\n"}, ["CASE_MISMATCH"], ["BROKEN_LINK"])
    case("local absolute path", {"README.md": "[x](/Users/ana/repo/docs/a.md)\n"}, ["LOCAL_ABSOLUTE_PATH"])
    case("empty target", {"README.md": "[todo]()\n"}, ["EMPTY_LINK"])
    case("url-encoded path", {"README.md": "[x](my%20notes.md)\n", "my notes.md": "# N\n"}, [], ["BROKEN_LINK"])
    case("angle-bracket path with spaces", {"README.md": "[x](<my notes.md>)\n", "my notes.md": "# N\n"}, [], ["BROKEN_LINK"])
    case("directory link ok", {"README.md": "[api](api/)\n", "api/index.md": "# API\n"}, [], ["BROKEN_LINK"])
    case("root-relative link", {"README.md": "[x](/guide/a.md)\n", "guide/a.md": "# A\n"}, [], ["BROKEN_LINK"])
    case("github line anchor", {"README.md": "[x](setup.md#L10)\n", "setup.md": "# S\n"}, [], ["MISSING_ANCHOR"])
    case("task list not a link", {"README.md": "- [ ] write docs\n- [x] done\n"}, [], ["MISSING_REF_DEF"])
    case("mailto ignored", {"README.md": "[mail](mailto:team@example.com)\n"}, [], ["BROKEN_LINK"])
    case("nested subdir relative", {"README.md": "x", "guide/a.md": "[b](../b.md#top)\n", "b.md": "# Top\n"}, [], ["BROKEN_LINK", "MISSING_ANCHOR"], "guide/a.md")

    passed = 0
    for name, files, expect, absent, target in cases:
        with tempfile.TemporaryDirectory() as d:
            for rel, body in files.items():
                p = os.path.join(d, rel)
                os.makedirs(os.path.dirname(p), exist_ok=True)
                with open(p, "w", encoding="utf-8") as fh:
                    fh.write(body)
            _, found, _ = run([d], root=d)
            codes = {f["code"] for f in found if f["file"] == target}
            ok = all(c in codes for c in expect) and not any(c in codes for c in absent)
            if name == "clean file":
                ok = ok and not found
            if name == "near-miss hint":
                ok = ok and any("Did you mean #getting-started" in f["problem"] for f in found)
        passed += ok
        print(("PASS " if ok else "FAIL ") + name + ("" if ok else f" -> got {sorted(codes)}"))
    # external URL listing and report rendering
    with tempfile.TemporaryDirectory() as d:
        with open(os.path.join(d, "a.md"), "w") as fh:
            fh.write("[x](https://example.com/a) and [y](https://example.com/a)\n")
        files, found, ext = run([d])
        ok = list(ext) == ["https://example.com/a"] and len(ext["https://example.com/a"]) == 2
        text = report(files, found, ext, True, [d])
        ok = ok and "External URLs to check" in text and "No findings." in text
        passed += ok
        print(("PASS " if ok else "FAIL ") + "external URLs listed once with locations, no network")
    total = len(cases) + 1
    print(f"{passed}/{total} passed")
    return 0 if passed == total else 1


def main(argv=None):
    ap = argparse.ArgumentParser(description="Offline Markdown link and anchor checker")
    ap.add_argument("paths", nargs="*")
    ap.add_argument("--root", help="docs root for /absolute links and the OUTSIDE_ROOT check (default: first folder)")
    ap.add_argument("--min-severity", default="LOW", choices=list(SEV_ORDER))
    ap.add_argument("--ignore", default="", help="comma-separated finding codes to skip")
    ap.add_argument("--external", action="store_true", help="list external URLs to check separately")
    ap.add_argument("--json", action="store_true")
    ap.add_argument("--self-test", action="store_true")
    a = ap.parse_args(argv)
    if a.self_test:
        return self_test()
    if not a.paths:
        ap.print_usage(sys.stderr)
        return 2
    try:
        files, found, ext = run(a.paths, a.root, [c.strip() for c in a.ignore.split(",") if c.strip()], a.min_severity)
    except FileNotFoundError as e:
        print(f"error: path not found: {e}", file=sys.stderr)
        return 2
    if not files:
        print("error: no Markdown files found", file=sys.stderr)
        return 2
    if a.json:
        print(json.dumps({"files": len(files), "findings": found, "external": ext if a.external else {}}, indent=2, ensure_ascii=False))
    else:
        print(report(files, found, ext, a.external, a.paths))
    return 1 if any(f["severity"] == "HIGH" for f in found) else 0


if __name__ == "__main__":
    sys.exit(main())

Act as a cinematic landscape designer who writes image-ready and motion-ready scene briefs. Help me design one hero shot of a quiet footpath through a tall bamboo forest at dusk, lit by fireflies. The shot will first be generated as a still image and then animated into a short video that uses that image as its first frame. Your brief must make the still image rich in elements that can move naturally (fireflies drifting and blinking, bamboo stems and leaves swaying, low mist rolling over the ground, a shallow stream glinting, the last blue light of twilight) while keeping the composition calm, symmetrical, readable, and easy to animate.

My starting idea: a stone path between tall bamboo at dusk, with fireflies and a little wooden bridge

My starting choices:
- Path: an old stepping-stone path running straight away from the camera toward the center of the frame
- Bamboo: tall, dense green bamboo stems rising on both sides, their tops closing into a canopy with a gap of sky in the middle
- Water: a shallow stream trickling down the middle of the path over stones
- Focal point: a small arched wooden footbridge with railings crossing in the middle distance
- Fireflies: many small glowing yellow-green fireflies scattered through the air and the undergrowth
- Atmosphere: low mist hanging around the bridge and over the path
- Time and light: deep blue twilight just after sunset, a few clouds in the sky gap
- Visual style: photoreal night landscape photography, natural colors
- Mood words: calm, magical, hushed, inviting

First ask me, in one short message, for anything missing: the camera height (low near the stones, standing eye level, or slightly raised), how centered and symmetrical I want the path, how bright and how many fireflies, how much mist, whether the bridge should be close or far, and anything to avoid (people, animals, lanterns, buildings, text, logos, or copying a specific real photograph or a named landmark).

Then produce the brief with these sections:

1. **Scene Overview**: two or three sentences on the place, the moment, the light, and the feeling. Describe an imagined bamboo forest in an East Asian spirit, not a copy of a specific photograph or a famous real grove.

2. **Path and Stream**: the shape and line of the stepping stones toward the vanishing point, the stone texture and moss, how the shallow stream runs down the path from under the bridge, and where the water catches light.

3. **Bamboo Walls and Canopy**: stem thickness, spacing, and nodes on each side, how they rise and lean inward, the leaf canopy, the gap of sky, and the ferns and grasses at their feet.

4. **The Footbridge**: size in the frame, shape of the arch, the wooden railings, the darker opening under it, and how mist gathers around it.

5. **Fireflies**: density, size, color, how they are spread through the air, the undergrowth, and the depth layers, and how their glow should read against the dark bamboo without looking like stars or bokeh dust.

6. **Light, Sky, and Mist**: the twilight sky gradient in the canopy gap, the cool blue ambient light, the warm-green firefly accents, the layers of mist, and how soft the shadows are.

7. **Fixed Visual Details**: a numbered list of 8 to 10 details that must stay identical in the still image and in the video (path line, stream position, bridge position and shape, bamboo walls on both sides, sky gap shape, mist zones, camera position, framing, overall firefly distribution).

8. **Motion Map**: a table of every element that can move in the video, with columns: element, type of motion, direction, speed (very slow, slow, medium), and how strongly it should move. Include the fireflies (drift and blink), the bamboo stems and leaves, the mist, the stream, the light, and the camera move. Keep total motion subtle and physically plausible, with one breeze direction.

9. **Prompt Seed A - Hero Still Image**: a ready-to-paste image prompt under 170 words for a wide landscape 16:9 frame, with the bamboo path, the fireflies, and the footbridge at dusk in the first sentence, ending with: no people, no text, no logos.

10. **Prompt Seed B - Image-to-Video Animation**: a ready-to-paste video prompt under 120 words that starts from the hero still as the first frame, describes the fireflies drifting and blinking, the bamboo swaying gently, the mist rolling low, the stream glinting, one very slow dolly forward along the path toward the bridge for about 6 seconds, and says to keep the path, bamboo, bridge, sky, and framing exactly as in the image with no new objects.

Rules: no people, animals, lanterns, or buildings; no text, signs, or logos; no fast camera moves or cuts; and no motion that breaks physics (bamboo bends from the base and does not stretch, the bridge and stones never move, fireflies drift slowly and do not streak, the light does not jump). Use short paragraphs and lists.