API Error Recovery Patterns

class CircuitBreaker {
  constructor(threshold = 5, timeout = 60000) {
    this.failureCount = 0;
    this.threshold = threshold;
    this.timeout = timeout;
    this.state = 'CLOSED'; // CLOSED, OPEN, HALF_OPEN
    this.nextAttempt = Date.now();
  }

  async execute(fn) {
    if (this.state === 'OPEN') {
      if (Date.now() < this.nextAttempt) {
        throw new Error('Circuit breaker is OPEN');
      }
      this.state = 'HALF_OPEN';
    }

    try {
      const result = await fn();
      this.onSuccess();
      return result;
    } catch (error) {
      this.onFailure();
      throw error;
    }
  }

  onSuccess() {
    this.failureCount = 0;
    this.state = 'CLOSED';
  }

  onFailure() {
    this.failureCount++;
    if (this.failureCount >= this.threshold) {
      this.state = 'OPEN';
      this.nextAttempt = Date.now() + this.timeout;
    }
  }
}

const breaker = new CircuitBreaker();

async function makeRequest(url, options) {
  return breaker.execute(() => fetch(url, options));
}

async function getUserData(userId) {
  try {
    return await apiRequest(`/api/service/users/${userId}`);
  } catch (error) {
    if (error.status >= 500) {
      // Server error - use cached data if available
      const cached = localStorage.getItem(`user_${userId}`);
      if (cached) {
        console.warn('Using cached user data due to server error');
        return JSON.parse(cached);
      }
    }
    throw error;
  }
}