Forex API daily

Daily European Central Bank web‑scraper that extracts FX rates, computes cross rates, and stores them in Firestore. Exposed as an HTTP Cloud Function (main).

Requirements

• Node.js 22 (see .nvmrc). If your shell selects a different version, run nvm use.
• PNPM as the package manager (recommend corepack enable && corepack install).

Setup

pnpm install

Common Commands

• Build: pnpm compile (TypeScript → index.js).
• Lint/format: pnpm lint, pnpm format (use pnpm lint --fix to auto‑fix).
• Start locally: GCP_PROJECT_ID=forex-api-daily pnpm start (Functions Framework on http://localhost:8081/main).
• Test: pnpm test (runs Vitest; may use Firestore emulator if configured). If you hit PNPM migration issues with lifecycle scripts, run build/lint directly and let us know to update scripts.
• Start Firestore emulator: pnpm start-db (runs on http://localhost:8080).

How It Works

• Fetch: Scrapes ECB RSS endpoints to gather daily EUR base rates.
• Process: Combines latest day’s rates and derives cross rates for other bases.
• Store: Writes documents to the exchange_rates collection; periodically removes stale dates. After storing new rates, writes the list of available currency symbols to per-date documents under the symbols collection (e.g. symbols/2025-12-05) for efficient client lookups.

Querying Available Symbols

Each run stores a symbols/{YYYY-MM-DD} document (e.g. symbols/2025-12-05) containing the base currency codes available for that date:

{ "date": "2025-12-05", "symbols": ["AUD", "BGN", "BRL", "..."] }

To retrieve the latest available symbols, query the symbols collection ordered by date descending and take the first document:

const snapshot = await db.collection('symbols').orderBy('date', 'desc').limit(1).get();
if (!snapshot.empty) {
  const { date, symbols } = snapshot.docs[0].data();
}

CI/CD

• GitHub Actions (.github/workflows/ci.yml) runs tests on push. Deploys from main to Cloud Functions using repo secrets for GCP.

Notes

• Do not commit credentials. Files like .env and service-account.json are ignored by Git.
• The compiled index.js is generated; avoid committing build artifacts.