Finixa

Logging an expense in under five seconds from your phone — the one constraint that drove every decision in Finixa, from the PostgreSQL schema down to the input gesture.

What's the context behind Finixa?

Finixa is a personal finance SaaS MVP built around one hard UX constraint: add an expense as fast as possible from a mobile device. It covers expense and income tracking, per-category and per-subcategory budgeting, envelope budgeting (50/30/20), virtual recurring transactions, and monthly statistics backed by PostgreSQL RPCs. The app is packaged for iOS/Android via Capacitor in addition to the web deployment.

What's the tech stack?

• Nuxt 4 + Vue 3 (SPA, hash routing) — SSR is intentionally disabled: hash-based routing is required for Capacitor compatibility, as the capacitor:// scheme does not support push-state routing.
• Strict TypeScript — Amounts are signed at the database level (-50 = expense, +1000 = income). The central discriminant is TransactionType ('depense' | 'revenu' | 'epargne'), used consistently from the database schema up to UI components.
• Pinia (15 stores) — Three-layer architecture: app/services/ isolates all Supabase calls, stores hold state and expose mutations, pages and components consume stores. No direct Supabase calls in components.
• Supabase (PostgreSQL + Auth + RLS) — Row Level Security on every table. Computed views (stats, virtual recurrences) are PostgreSQL RPCs called directly from the service layer.
• Edge Functions (Deno) — Four serverless functions for external integrations: quick transaction insertion via API key, daily digest, push notifications, category listing endpoint.
• Custom SCSS (token-based design system) — No Tailwind. Design tokens are auto-injected into every component via additionalData in nuxt.config. Components use only semantic CSS custom properties.
• Capacitor 8 — iOS/Android packaging, @capacitor/preferences for secure local storage (PIN, theme, onboarding state).
• @nuxtjs/i18n — Full FR/EN localization, no_prefix strategy compatible with hash routing.

Global architecture

Notable Technical Points

1 · Transaction add flow

The full sequence from button tap to reactive UI update — the layer separation in action. add.vue only knows the store, the store only knows the service, the service only knows Supabase.

Transaction add flow

2 · Operation date vs accounting date

Each transaction has a date (when the operation occurs) and a nullable accounting_date (when it is attributed to the budget). For recurring transactions with accounting_offset: 'next_month', the accounting date is set to the 1st of the following month at materialization time. Concrete use case: a subscription debited on December 28th but counted against January's budget.

Operation date vs accounting date

3 · Subcategory budget versioning

Editing a budget does not rewrite history: a new row is created with valid_from, the old one is closed with valid_to. Stats queries use the date to find the budget that was in effect at that point in time — January statistics remain accurate even if the budget changed in May.

Subcategory budget versioning

4 · Virtual recurrences and lazy materialization

Recurring transactions are not persisted in the database by default. On every load, getDatesInRange() computes occurrences for the current period and getOccurrenceKey() generates a stable identifier. Only unmatched occurrences are shown as "virtual" rows. Persistence only happens when the user checks off an occurrence.

getDatesInRange() handles day-of-month clamping (e.g., monthly on the 31st → Feb 28/29) and all edge cases for weekly, quarterly, and yearly frequencies.

Virtual recurrences and lazy materialization

5 · PostgreSQL RPCs for all aggregations

No stats logic on the frontend. All computed views are SQL functions: get_subcategory_stats, get_variable_daily_remaining, recurring_virtual_for_month, etc. Called via supabase.rpc() from the service layer.

6 · API key system for external integrations

Deno Edge Functions expose endpoints authenticated via a SHA-256 hash of a user-generated key. This allows adding a transaction from an iOS Shortcuts automation without exposing Supabase credentials.

API key authentication flow

SCSS Design System

Tokens are defined in two layers: a primitive palette (never referenced directly in components) and semantic CSS custom properties (the only layer components may use). The token file is auto-injected into every <style lang="scss"> block via additionalData in nuxt.config.ts — no manual imports needed.

SCSS design system — tokens and injection

What I Learned / Contributed

The most challenging part was the recurring transactions engine: computing stable virtual occurrences over any arbitrary time window, with day-of-month clamping (e.g., monthly on the 31st → Feb 28/29), while cleanly handling the split between operation date and accounting date. Budget versioning required rethinking the schema so that stats queries are deterministic regardless of which historical period is queried.