Rate Limiting & Response Headers

async function fetchWithRetry(url, options, maxRetries = 3) {
  for (let i = 0; i < maxRetries; i++) {
    const response = await fetch(url, options);

    // Check rate limit headers
    const remaining = response.headers.get('X-RateLimit-Remaining');
    const resetAfter = response.headers.get('X-RateLimit-Reset-After');

    console.log(`Remaining requests: ${remaining}`);

    if (response.status === 429) {
      // Rate limited - wait and retry
      const waitTime = parseInt(resetAfter || '60') * 1000;
      console.log(`Rate limited. Waiting ${waitTime}ms...`);
      await new Promise(resolve => setTimeout(resolve, waitTime));
      continue;
    }

    if (response.ok) {
      return response;
    }

    // Exponential backoff for other errors
    const delay = Math.min(1000 * Math.pow(2, i), 10000);
    await new Promise(resolve => setTimeout(resolve, delay));
  }

  throw new Error('Max retries exceeded');
}

class CachedAPIClient {
  constructor(apiKey, cacheTTL = 300000) { // 5 minutes default
    this.apiKey = apiKey;
    this.cache = new Map();
    this.cacheTTL = cacheTTL;
  }

  async fetch(endpoint, params = {}) {
    const cacheKey = `${endpoint}:${JSON.stringify(params)}`;
    const cached = this.cache.get(cacheKey);

    if (cached && Date.now() - cached.timestamp < this.cacheTTL) {
      console.log('Cache hit');
      return cached.data;
    }

    const response = await fetch(
      `https://api.oilpriceapi.com/v1${endpoint}?${new URLSearchParams(params)}`,
      { headers: { 'Authorization': `Token ${this.apiKey}` } }
    );

    const data = await response.json();

    this.cache.set(cacheKey, {
      data,
      timestamp: Date.now()
    });

    return data;
  }
}

class RequestQueue {
  constructor(apiKey, requestsPerMinute = 100) {
    this.apiKey = apiKey;
    this.queue = [];
    this.interval = 60000 / requestsPerMinute;
    this.processing = false;
  }

  async add(endpoint, params) {
    return new Promise((resolve, reject) => {
      this.queue.push({ endpoint, params, resolve, reject });
      if (!this.processing) {
        this.process();
      }
    });
  }

  async process() {
    this.processing = true;

    while (this.queue.length > 0) {
      const { endpoint, params, resolve, reject } = this.queue.shift();

      try {
        const response = await fetch(
          `https://api.oilpriceapi.com/v1${endpoint}`,
          {
            headers: { 'Authorization': `Token ${this.apiKey}` },
            params
          }
        );
        resolve(await response.json());
      } catch (error) {
        reject(error);
      }

      // Wait before next request
      await new Promise(r => setTimeout(r, this.interval));
    }

    this.processing = false;
  }
}