Operational Redundancy and Fail-Safe Engineering Principles

export class CircuitBreaker {
  private failures = 0;
  private state: 'CLOSED' | 'OPEN' | 'HALF_OPEN' = 'CLOSED';
  private lastStateChange = Date.now();

  constructor(
    private readonly threshold = 5,
    private readonly resetTimeoutMs = 30000
  ) {}

  async execute<T>(fn: () => Promise<T>): Promise<T> {
    if (this.state === 'OPEN') {
      if (Date.now() - this.lastStateChange > this.resetTimeoutMs) {
        this.state = 'HALF_OPEN';
      } else {
        throw new Error('Circuit breaker is OPEN. Fast failing request.');
      }
    }

    try {
      const result = await fn();
      if (this.state === 'HALF_OPEN') {
        this.state = 'CLOSED';
        this.failures = 0;
      }
      return result;
    } catch (err) {
      this.failures++;
      if (this.failures >= this.threshold) {
        this.state = 'OPEN';
        this.lastStateChange = Date.now();
      }
      throw err;
    }
  }
}