Goddii/DAI

**Dai** ("owe" in Swahili) is a mobile-first credit ledger for informal and semi-formal market traders in Kenya. It replaces the trader's memory or notebook, answering one question instantly: **"Who owes me money, and how much?"** # Dai — Market Trader Credit Ledger **Dai** ("owe" in Swahili) is a mobile-first credit ledger for informal and semi-formal market traders in Kenya. It replaces the trader's memory or notebook, answering one question instantly: **"Who owes me money, and how much?"** - Record credit and payments in seconds - See each customer's current balance and full history - Works offline; transactions sync safely and exactly once when connectivity returns - Individual trader accounts with strict data isolation ## Stack | Layer | Technology | |---|---| | Frontend | React, TypeScript, Vite, Tailwind CSS v4, PWA (`vite-plugin-pwa`) | | Backend | Flask, SQLAlchemy, PostgreSQL, Flask-Migrate (Alembic) | | Offline | IndexedDB (`idb`) + idempotent sync with client-generated UUIDs | | Money | Integer minor units (1 KSh = 100 cents), balance always derived from the ledger | ## Repository layout ``` backend/ Flask API (app factory, blueprints, models, tests) frontend/ React + Vite PWA ``` ## Backend quick start ```bash cd backend python3 -m venv .venv && source .venv/bin/activate pip install -r requirements.txt -r requirements-dev.txt cp .env.example .env # adjust DATABASE_URL flask --app run.py db upgrade # or: flask db upgrade (migrations dir) flask --app run.py seed # optional demo data flask --app run.py run --debug ``` Tests (SQLite in-memory by default, no database needed): ```bash cd backend && source .venv/bin/activate pytest ``` ### PostgreSQL parity run The suite runs unmodified against PostgreSQL and is the release gate. It verifies eight ledger invariants, including the concurrency guards that rely on real row locking (`WITH FOR UPDATE` — a no-op on SQLite): 1. customer data isolation between traders 2. exact derived ledger balance 3. payments never exceed the outstanding balance 4. idempotent client-UUID sync 5. duplicate sync batches never double-post 6. voiding reverses the balance without mutating history 7. concurrent payments on one custome …