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Architecture — Dabba: The Tiffin Tracker

A deliberately small system: one React PWA, one Postgres (Supabase), zero servers of our own, ₹0/month.

┌──────────────────────┐     HTTPS / WebSocket      ┌─────────────────────────┐
│  React PWA (Vite)    │ ◄────────────────────────► │  Supabase (Mumbai)      │
│  Vercel static CDN   │   supabase-js + Realtime   │  Postgres + Auth + RLS  │
└──────────────────────┘                            └─────────────────────────┘

Stack

  • Frontend: React 18 + TypeScript + Vite 6, plain CSS, vite-plugin-pwa (service worker, installable). No state library — server state is refetched on every mutation and on Realtime/visibility signals.
  • Backend: Supabase free tier — Postgres, GoTrue auth, PostgREST API, Realtime. No custom server. The browser talks straight to Postgres through row-level security.
  • Hosting: Vercel Hobby (static build). getdabba.vercel.app.

Key decisions

Phone + PIN auth without SMS cost

SMS OTP costs money. Instead a phone number maps to a synthetic email (p<10digits>@tiffin-tracker.app) and the 6-digit PIN is the password, using stock Supabase email/password auth with "Confirm email" disabled. PIN resets are a dashboard operation (documented in README) — acceptable for trusted friend groups, ₹0 forever. The synthetic domain is identity plumbing; renaming it would orphan accounts, so it survives rebrands.

Trust = transparency, enforced server-side

The product's core promise is "nobody can cheat":

  • Every entry/payment shows who created it; edits show edited by; deletes are soft tombstones ("deleted by X"), restorable for entries, immutable-once-recorded for payments.
  • These stamps are written by BEFORE INSERT/UPDATE Postgres triggers (stamp_entry_attribution, stamp_settlement_attribution) that overwrite whatever the client sends with auth.uid() — attribution can't be faked even with hand-crafted API calls.
  • RLS policies deliberately have no DELETE on entries/settlements, so the tombstone trail can't be bypassed.

Row-level security model

  • is_group_member(gid) — SECURITY DEFINER helper, avoids policy recursion.
  • Groups, entries, items, settlements: visible/writable only to group members.
  • profiles: visible via profile_visible(id) — yourself, current groupmates, and people referenced in your groups' records (names survive member removal). Strangers who sign up see nobody.
  • Invite-only joining via SECURITY DEFINER RPCs (create_group, join_group, regenerate_invite) with 6-char rotating codes.
  • leads / feedback / events: write-only via API (insert-only policies), read in the dashboard. Powers the marketing site forms + install counter.

Money math

Prices live on the group but are snapshotted onto each entry, so editing rates never rewrites history. An entry has individual items (per-person tiffin/roti/extras) plus a shared pool split equally among ticked members, exact to the paisa. All math is derived at read time (src/lib/balance.ts, src/lib/types.ts) and covered by vitest (npm test).

Live sync

Supabase Realtime (postgres_changes on entries/settlements/members/groups) plus a refetch on visibilitychange — phones see each other's changes instantly without polling.

Demo mode

src/lib/demo.ts is a localStorage mock of the Supabase client with seeded sample data — the full app runs without any backend ("Try the demo" on the welcome screen). Great for demos and for development without keys.

Repo map

src/
  lib/        supabase client, demo mock, money math, types, install prompt
  screens/    Welcome, Auth, Onboarding, MainShell + Add/History/Balances/Settings
supabase/
  schema.sql                      full schema — run once on a fresh project
  migration-*.sql                 changes applied to prod after first deploy
marketing/    carousel + capture/render scripts (screenshots/PDF gitignored)
scripts/      icon + OG image generators

Deploy

See DEPLOY.md. Short version: static build on Vercel, schema on Supabase, two VITE_* env vars connect them.