market_screener/src/api/BenchmarkProvider.js

import { YahooClient } from './YahooClient.js';

export class BenchmarkProvider {
  constructor() {
    this.client = new YahooClient();
    this.cache = { data: null, expiresAt: 0 };
    this.TTL_MS = 60 * 60 * 1000; // Cache for 1 hour
  }

  async getMarketContext() {
    // 1. Return cached data if still valid
    if (this.cache.data && Date.now() < this.cache.expiresAt) {
      return this.cache.data;
    }

    try {
      const [sp500, tn10y] = await Promise.all([
        this.client.fetchSummary('^GSPC'),
        this.client.fetchSummary('^TNX'),
      ]);

      const context = {
        sp500Price: sp500.price?.regularMarketPrice ?? 0,
        riskFreeRate: tn10y.price?.regularMarketPrice ?? 0,
        timestamp: new Date().toISOString(),
      };

      // 2. Validate data sanity (prevent 0-value errors)
      if (context.sp500Price === 0 || context.riskFreeRate === 0) {
        throw new Error('Invalid market data received (zero values)');
      }

      // 3. Update cache
      this.cache = { data: context, expiresAt: Date.now() + this.TTL_MS };
      return context;
    } catch (error) {
      console.error(
        'Market data fetch failed, using last known or empty state:',
        error,
      );
      // If we have stale cache, use it even if expired, otherwise return safe defaults
      return this.cache.data || { sp500Price: 4500, riskFreeRate: 4.0 };
    }
  }
}