Spendcap

iOS app that links your bank through Plaid and pushes you a notification the moment the day's spending crosses your cap.

Most budgeting apps tell you what you overspent on last month. Spendcap tells you at 3pm today, while you can still do something about it.

You set one number — a daily spending cap. Spendcap mirrors your bank transactions in the background and sends a push at 80% ("getting close") and again at 100% ("over cap"), one of each per day, no nagging.

Platform	iOS 17+, SwiftUI, Swift 5.10
Backend	Supabase — Auth, Postgres (RLS on every table), Edge Functions
Bank data	Plaid transactions product
Push	APNs via a Supabase edge function
Status	TestFlight, Plaid sandbox

How it works

1. Sign up with email/password and set a daily cap (defaults to $50).
2. Connect a bank with Plaid Link. The public token is exchanged server-side by an edge function — the Plaid access token is written to a table only the service role can read, and never returned to the client.
3. Transactions sync. Plaid fires a SYNC_UPDATES_AVAILABLE webhook, which runs /transactions/sync and upserts the delta. An hourly pg_cron job is the fallback for missed webhooks.
4. Overspend check. After every sync, check_overspend totals the day's outflows in the user's own timezone (pending transactions included) and compares against the cap. Crossing a threshold sends one push, deduped per user/day/kind in spend_alerts.
5. The app shows what's left of today's cap, month-to-date pacing, and a twelve-month view of monthly totals with the bank statement behind each month.

Plaid Link (LinkKit)
  ├─> plaid_create_link_token ────────── JWT-gated ──> link token
  └─> plaid_exchange_public_token ────── JWT-gated ──> access token
                                                       (service-role only)

Plaid webhook ─────> plaid_webhook ────┐
pg_cron (hourly) ──> sync_transactions ─┴─> /transactions/sync ──> upsert
                                             └─> check_overspend ──> APNs

Security notes

This app touches bank data, so a few things are deliberate:

• Plaid access tokens never reach the client. They live in plaid_item_secrets, which has no anon or authenticated grants at all — only the service role, used by edge functions.
• RLS on every table, self-only, with explicit grants rather than inherited ones.
• Threshold math is duplicated on purpose. The server decides when to push; BudgetMath mirrors the same integer comparison client-side so the screen and the notification can never disagree. Unit tests pin them together, and the monthly_spend() rollup reuses the same outflow filter.
• Financial data is redacted in the app-switcher snapshot, so balances don't leak into the multitasking view.
• No secrets in this repo. Credentials come from Secrets.xcconfig (gitignored) and the macOS keychain; Plaid keys are Supabase function secrets.

Project layout

Spendcap/
  App/            app entry, settings
  Auth/           Supabase email auth
  Budget/         cap editing
  Dashboard/      Home, Trends, Months
  Link/           Plaid Link (LinkKit) wrapper
  Notifications/  APNs registration + token upload
  Services/       spend queries, BudgetMath
  Supabase/       client
supabase/
  functions/      5 edge functions (Deno)
  migrations/     numbered SQL
  schema.sql      canonical schema
scripts/          generate, test, ship

Building it yourself

Requires Xcode 16+, XcodeGen, a Supabase project, and Plaid API keys.

cp Secrets.xcconfig.example Secrets.xcconfig   # add your Supabase URL + anon key
./scripts/generate.sh                          # generate the .xcodeproj
./scripts/run_tests.sh                         # unit + UI sweep

Apply supabase/schema.sql to your project, deploy the functions in supabase/functions/, then store your Plaid keys in the keychain and run ./scripts/set_plaid_keys.sh to push them to Supabase.

./scripts/ship.sh bumps the build, archives, and uploads to TestFlight.

See CLAUDE.md for full architecture notes and working rules.

License

No license — all rights reserved. Public for reading, not for reuse.