opendata/readme.hints.md

# OpenData Project Hints

## Stocks Module

### Overview
The stocks module provides real-time stock price data and cryptocurrency prices through various provider implementations. Currently supports Yahoo Finance, Marketstack, and CoinGecko with an extensible architecture for additional providers.

### Architecture
- **Provider Pattern**: Each stock data source implements the `IStockProvider` interface
- **Service Registry**: `StockPriceService` manages providers with priority-based selection
- **Caching**: Built-in cache with configurable TTL to reduce API calls
- **Fallback Logic**: Automatic failover between providers if one fails

### Yahoo Finance Provider Notes
- Uses public API endpoints (no authentication required)
- Two main endpoints:
  - `/v8/finance/chart/{ticker}` - Single ticker with full data
  - `/v8/finance/spark?symbols={tickers}` - Multiple tickers with basic data
- Response data is in `response.body` when using smartrequest
- Requires User-Agent header to avoid rate limiting

### Usage Example
```typescript
import { StockPriceService, YahooFinanceProvider } from '@fin.cx/opendata';

const stockService = new StockPriceService({ ttl: 60000 });
const yahooProvider = new YahooFinanceProvider();
stockService.register(yahooProvider);

const price = await stockService.getPrice({ ticker: 'AAPL' });
console.log(`${price.ticker}: $${price.price}`);
```

### CoinGecko Provider Notes
- Cryptocurrency price provider supporting 13M+ tokens
- Three main endpoints:
  - `/simple/price` - Current prices with market data (batch supported)
  - `/coins/{id}/market_chart` - Historical and intraday prices with OHLCV
  - `/coins/list` - Complete coin list for ticker-to-ID mapping
- **Rate Limiting**:
  - Free tier: 5-15 calls/minute (no registration)
  - Demo plan: 30 calls/minute, 10,000/month (free with registration)
  - Custom rate limiter tracks requests per minute
- **Ticker Resolution**:
  - Accepts both ticker symbols (BTC, ETH) and CoinGecko IDs (bitcoin, ethereum)
  - Lazy-loads coin list on first ticker resolution
  - Caches coin mappings for 24 hours
  - IDs with hyphens (wrapped-bitcoin) assumed to be CoinGecko IDs
- **24/7 Markets**: Crypto markets always return `marketState: 'REGULAR'`
- **Optional API Key**: Pass key to constructor for higher rate limits
  - Demo plan: `x-cg-demo-api-key` header
  - Paid plans: `x-cg-pro-api-key` header
- **Data Granularity**:
  - Historical: Daily data for date ranges
  - Intraday: Hourly data only (1-90 days based on `days` param)
  - Current: Real-time prices with 24h change and volume

### Usage Example (Crypto)
```typescript
import { StockPriceService, CoinGeckoProvider } from '@fin.cx/opendata';

const stockService = new StockPriceService({ ttl: 30000 });
const coingeckoProvider = new CoinGeckoProvider(); // or new CoinGeckoProvider('api-key')
stockService.register(coingeckoProvider);

// Using ticker symbol
const btc = await stockService.getPrice({ ticker: 'BTC' });
console.log(`${btc.ticker}: $${btc.price}`);

// Using CoinGecko ID
const ethereum = await stockService.getPrice({ ticker: 'ethereum' });

// Batch fetch
const cryptos = await stockService.getPrices({ tickers: ['BTC', 'ETH', 'USDT'] });
```

### Testing
- Tests use real API calls (be mindful of rate limits)
- Mock invalid ticker 'INVALID_TICKER_XYZ' for error testing
- Clear cache between tests to ensure fresh data
- The spark endpoint may return fewer results than requested
- CoinGecko tests may take longer due to rate limiting (wait between requests)

### Future Providers
To add a new provider:
1. Create `ts/stocks/providers/provider.{name}.ts`
2. Implement the `IStockProvider` interface
3. Register with `StockPriceService`
4. No changes needed to existing code