QR Code Generator

Promptfree, for everyone, and the only version there is

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Build me a QR code service that replaces the paid generators: codes I own, that keep working when a poster is already printed, with scans I can count.

STACK
- Node 20+ with Fastify
- SQLite through better-sqlite3, WAL mode
- A QR library for the matrix, and my own SVG renderer on top of it so the styling is mine
- Caddy in front

THE DATA MODEL
- codes: id, slug, kind, destination, title, tags_json, style_json, is_dynamic, created_by, created_at, archived_at, expires_at, password_hash
- code_versions: id, code_id, destination, changed_by, changed_at — a dynamic code's destination is appended, never overwritten
- scans: id, code_id, created_at, referrer_host, country, city, device, os, ip_hash, bot
- batches: id, name, template_json, created_at — a thousand codes generated at once with a counter or from a CSV
- Kinds: url, wifi, vcard, email, sms, geo, text, event. Each has its own encoded payload format, and the formats are exactly per specification — a vCard that Android reads and iOS does not is a wasted print run

STATIC AND DYNAMIC, WHICH IS THE WHOLE DECISION
- A static code encodes the destination itself: it works forever, needs no server, and can never be changed
- A dynamic code encodes a short link on my own domain: it can be re-pointed after printing, and it stops working the day the service does
- The interface makes the reader choose deliberately and states the trade-off in one sentence, because this is the choice people regret
- Dynamic codes redirect through /q/:slug with a 302, never a 301 — a permanent redirect cached in a phone can never be re-pointed

RENDERING
- SVG first, PNG rendered from it, and a PDF with crop marks for print
- Error correction level chosen by intent: L for screens, Q or H when a logo is placed in the middle, and the interface refuses a logo larger than the correction level can survive
- Quiet zone of four modules, always. Most unscannable codes in the world are missing it
- Styling: module shape, eye shape, foreground and background colour, and a logo. Contrast between foreground and background is checked and a low-contrast code is refused with an explanation
- Test render at the size it will be printed, with a note of the minimum physical size for the amount of data: a URL of ninety characters on a business card does not scan

BATCHES
- Generate from a CSV, or from a template with a counter
- Every code in a batch gets its own slug and its own scan counter
- Export as a zip of SVG and PNG, plus a CSV of slug to destination
- A print sheet: N codes to a page with labels, as a PDF

COUNTING SCANS
- Only dynamic codes can be counted, and the interface says so where the number would be
- Scans, unique scanners, by day, by country, by device
- A unique scanner is a distinct salted hash of address and user agent within the window, and the page says so
- Bots and preview fetchers flagged and excluded — a link preview in a messaging app is not a scan
- Export to CSV

CARE OF PRINTED THINGS
- A dynamic code can expire, and an expired code lands on a page that says what it was and where to go instead — never a 404, because the poster is still on the wall
- A code can be password-protected, showing a form before the destination
- Archiving keeps the history and stops the redirect, with the same explanatory page

THE INTERFACE
- One screen: kind, content, style, preview at three sizes, download
- The preview is the real code, scannable from the screen, updating as you type
- A list with scan counts, searchable by title and tag
- Dark and light, one accent

OPERATIONS
- .env: DATABASE_PATH, BASE_URL, HASH_SALT, GEOIP_DB_PATH, SESSION_SECRET
- Migrations on boot, each once
- The redirect answers from one prepared statement and records the scan after responding
- Nightly backup off the machine, restore script
- Health endpoint that renders one code and resolves one redirect

WHAT MATTERS MOST
Scannability and the static-versus-dynamic decision. Build the renderer with correct quiet zones and error correction first, print a page of codes at real sizes and scan them with three phones in bad light. A code that looks beautiful and does not scan is a poster nobody can use.

Give me the repository, migrations, .env.example, a seed with codes of every kind, and a README with deploy steps behind Caddy and a table of minimum print sizes.