import { Logger } from '../../utils/logger';

/**
 * @interface ReliabilityConfig
 * @description Configuration for System Reliability.
 */
export interface ReliabilityConfig {
  enableCircuitBreaker: boolean;
  defaultRetries: number;
  defaultBackoffMs: number;
  // Add configuration for failover regions, backup schedules, SLA targets
}

/**
 * @interface ReliabilityOperations
 * @description Defines operations for ensuring enterprise-grade reliability and resilience.
 */
export interface ReliabilityOperations {
  executeWithCircuitBreaker<T>(operation: () => Promise<T>, serviceName: string): Promise<T>;
  executeWithRetry<T>(operation: () => Promise<T>, retries?: number, backoffMs?: number): Promise<T>;
  triggerGracefulDegradation(componentName: string, reason: string): Promise<void>;
  initiateFailover(serviceName: string, targetRegion: string): Promise<void>;
  performBackup(dataScope: string): Promise<string>; // Returns backup ID/location
  monitorSLA(serviceName: string, currentMetrics: any): Promise<boolean>;
}

/**
 * @class SystemReliability
 * @description Implements features for ensuring system reliability and resilience, including circuit breakers, retries, and failover.
 */
export class SystemReliability implements ReliabilityOperations {
  private config: ReliabilityConfig;
  private logger: Logger;

  constructor(config: ReliabilityConfig) {
    this.config = config;
    this.logger = new Logger('SystemReliability');
    this.logger.info('System Reliability initialized.');
  }

  /**
   * Executes an operation with a circuit breaker pattern (conceptual).
   * @param {() => Promise<T>} operation The function to execute.
   * @param {string} serviceName The name of the service this operation interacts with.
   * @returns {Promise<T>} The result of the operation.
   */
  public async executeWithCircuitBreaker<T>(operation: () => Promise<T>, serviceName: string): Promise<T> {
    if (!this.config.enableCircuitBreaker) {
      return operation();
    }
    this.logger.info(`Executing operation for ${serviceName} with circuit breaker (conceptual)...`);
    // Placeholder for actual circuit breaker logic (e.g., using a library like 'opossum')
    try {
      const result = await operation();
      this.logger.debug(`Operation for ${serviceName} successful.`);
      return result;
    } catch (error: any) {
      this.logger.warn(`Circuit breaker for ${serviceName} caught error: ${error.message}`);
      // Simulate opening circuit if too many failures
      throw error;
    }
  }

  /**
   * Executes an operation with retry mechanisms and exponential backoff.
   * @param {() => Promise<T>} operation The function to execute.
   * @param {number} [retries] Number of retry attempts. Defaults to config.defaultRetries.
   * @param {number} [backoffMs] Initial backoff delay in milliseconds. Defaults to config.defaultBackoffMs.
   * @returns {Promise<T>} The result of the operation.
   */
  public async executeWithRetry<T>(operation: () => Promise<T>, retries?: number, backoffMs?: number): Promise<T> {
    const maxRetries = retries !== undefined ? retries : this.config.defaultRetries;
    const initialBackoff = backoffMs !== undefined ? backoffMs : this.config.defaultBackoffMs;

    for (let attempt = 1; attempt <= maxRetries + 1; attempt++) {
      try {
        this.logger.info(`Executing operation (Attempt ${attempt}/${maxRetries + 1})...`);
        const result = await operation();
        return result;
      } catch (error: any) {
        this.logger.warn(`Operation failed (Attempt ${attempt}/${maxRetries + 1}): ${error.message}`);
        if (attempt <= maxRetries) {
          const delay = initialBackoff * Math.pow(2, attempt - 1) + Math.random() * 100; // Add jitter
          this.logger.info(`Retrying in ${delay.toFixed(0)}ms...`);
          await new Promise((resolve) => setTimeout(resolve, delay));
        } else {
          throw new Error(`Operation failed after ${maxRetries + 1} attempts: ${error.message}`);
        }
      }
    }
    throw new Error('Unexpected error: Should not reach here.');
  }

  /**
   * Triggers graceful degradation for a failing component or service (conceptual).
   * @param {string} componentName The name of the component to degrade.
   * @param {string} reason The reason for degradation.
   * @returns {Promise<void>}
   */
  public async triggerGracefulDegradation(componentName: string, reason: string): Promise<void> {
    this.logger.warn(`Triggering graceful degradation for ${componentName} due to: ${reason} (conceptual)...`);
    // This would involve:
    // - Disabling non-essential features.
    // - Serving cached data instead of live data.
    // - Redirecting traffic to a static error page.
    await new Promise(resolve => setTimeout(resolve, 100));
  }

  /**
   * Initiates an automatic failover to a redundant service or region (conceptual).
   * @param {string} serviceName The name of the service to failover.
   * @param {string} targetRegion The target region for failover.
   * @returns {Promise<void>}
   */
  public async initiateFailover(serviceName: string, targetRegion: string): Promise<void> {
    this.logger.critical(`Initiating failover for ${serviceName} to ${targetRegion} (conceptual)...`);
    // This would involve DNS changes, load balancer reconfigurations, or active-passive/active-active setups.
    await new Promise(resolve => setTimeout(resolve, 500));
    this.logger.info(`Failover for ${serviceName} to ${targetRegion} completed.`);
  }

  /**
   * Performs a data backup operation (conceptual).
   * @param {string} dataScope The scope of data to backup (e.g., 'all', 'memory_db', 'configs').
   * @returns {Promise<string>} The ID or location of the backup.
   */
  public async performBackup(dataScope: string): Promise<string> {
    this.logger.info(`Performing backup for ${dataScope} (conceptual)...`);
    // This would involve Cloud Storage, Cloud SQL backups, etc.
    await new Promise(resolve => setTimeout(resolve, 300));
    const backupId = `backup-${Date.now()}`; 
    this.logger.info(`Backup completed: ${backupId}`);
    return backupId;
  }

  /**
   * Monitors Service Level Agreements (SLAs) and triggers alerts if violated (conceptual).
   * @param {string} serviceName The name of the service.
   * @param {any} currentMetrics Current performance metrics for the service.
   * @returns {Promise<boolean>} True if SLA is met, false otherwise.
   */
  public async monitorSLA(serviceName: string, currentMetrics: any): Promise<boolean> {
    this.logger.info(`Monitoring SLA for ${serviceName} (conceptual)...`, currentMetrics);
    // This would involve comparing current metrics (latency, error rate) against defined SLA targets.
    const slaMet = currentMetrics.latency < 100 && currentMetrics.errorRate < 0.01; // Example SLA
    if (!slaMet) {
      this.logger.warn(`SLA violation detected for ${serviceName}!`);
      // Trigger alert
    }
    return slaMet;
  }
}