import type { Client as ElasticClient } from '@elastic/elasticsearch';

/**
 * Health status
 */
export enum HealthStatus {
  HEALTHY = 'healthy',
  DEGRADED = 'degraded',
  UNHEALTHY = 'unhealthy',
  UNKNOWN = 'unknown',
}

/**
 * Cluster health status from Elasticsearch
 */
export enum ClusterHealth {
  GREEN = 'green',
  YELLOW = 'yellow',
  RED = 'red',
}

/**
 * Health check result
 */
export interface HealthCheckResult {
  /** Overall health status */
  status: HealthStatus;

  /** Cluster health from Elasticsearch */
  clusterHealth?: ClusterHealth;

  /** Whether the cluster is available */
  available: boolean;

  /** Response time in milliseconds */
  responseTimeMs?: number;

  /** Number of active nodes */
  activeNodes?: number;

  /** Error if health check failed */
  error?: Error;

  /** Timestamp of health check */
  timestamp: Date;

  /** Additional details */
  details?: Record<string, unknown>;
}

/**
 * Health check configuration
 */
export interface HealthCheckConfig {
  /** Interval between health checks in milliseconds */
  interval: number;

  /** Timeout for health check requests */
  timeout: number;

  /** Number of consecutive failures before marking unhealthy */
  unhealthyThreshold: number;

  /** Number of consecutive successes before marking healthy */
  healthyThreshold: number;

  /** Whether to check cluster health */
  checkClusterHealth: boolean;
}

/**
 * Default health check configuration
 */
export const DEFAULT_HEALTH_CHECK_CONFIG: HealthCheckConfig = {
  interval: 30000, // 30 seconds
  timeout: 5000, // 5 seconds
  unhealthyThreshold: 3,
  healthyThreshold: 2,
  checkClusterHealth: true,
};

/**
 * Health checker for Elasticsearch cluster
 */
export class HealthChecker {
  private config: HealthCheckConfig;
  private consecutiveFailures = 0;
  private consecutiveSuccesses = 0;
  private currentStatus: HealthStatus = HealthStatus.UNKNOWN;
  private lastCheckResult?: HealthCheckResult;
  private checkInterval?: NodeJS.Timeout;
  private isChecking = false;

  constructor(
    private client: ElasticClient,
    config: Partial<HealthCheckConfig> = {}
  ) {
    this.config = { ...DEFAULT_HEALTH_CHECK_CONFIG, ...config };
  }

  /**
   * Perform a single health check
   */
  async check(): Promise<HealthCheckResult> {
    const startTime = Date.now();

    try {
      // Ping the cluster
      const pingResponse = await Promise.race([
        this.client.ping(),
        this.timeout(this.config.timeout),
      ]);

      const responseTime = Date.now() - startTime;
      const available = pingResponse === true || (pingResponse as any).statusCode === 200;

      if (!available) {
        throw new Error('Cluster ping failed');
      }

      // Check cluster health if enabled
      let clusterHealth: ClusterHealth | undefined;
      let activeNodes: number | undefined;

      if (this.config.checkClusterHealth) {
        try {
          const healthResponse = await this.client.cluster.health({
            timeout: `${this.config.timeout}ms`,
          });

          clusterHealth = healthResponse.status as ClusterHealth;
          activeNodes = healthResponse.number_of_nodes;
        } catch (error) {
          // Cluster health check failed, but ping succeeded
          // Mark as degraded
          this.consecutiveSuccesses = 0;
          this.consecutiveFailures++;

          const result: HealthCheckResult = {
            status: HealthStatus.DEGRADED,
            available: true,
            responseTimeMs: responseTime,
            error: error as Error,
            timestamp: new Date(),
          };

          this.lastCheckResult = result;
          return result;
        }
      }

      // Success!
      this.consecutiveFailures = 0;
      this.consecutiveSuccesses++;

      // Determine status based on cluster health
      let status: HealthStatus;
      if (clusterHealth === ClusterHealth.GREEN) {
        status = HealthStatus.HEALTHY;
      } else if (clusterHealth === ClusterHealth.YELLOW) {
        status = HealthStatus.DEGRADED;
      } else if (clusterHealth === ClusterHealth.RED) {
        status = HealthStatus.UNHEALTHY;
      } else {
        // No cluster health, but ping succeeded
        status =
          this.consecutiveSuccesses >= this.config.healthyThreshold
            ? HealthStatus.HEALTHY
            : HealthStatus.DEGRADED;
      }

      this.currentStatus = status;

      const result: HealthCheckResult = {
        status,
        clusterHealth,
        available: true,
        responseTimeMs: responseTime,
        activeNodes,
        timestamp: new Date(),
      };

      this.lastCheckResult = result;
      return result;
    } catch (error) {
      this.consecutiveSuccesses = 0;
      this.consecutiveFailures++;

      const status =
        this.consecutiveFailures >= this.config.unhealthyThreshold
          ? HealthStatus.UNHEALTHY
          : HealthStatus.DEGRADED;

      this.currentStatus = status;

      const result: HealthCheckResult = {
        status,
        available: false,
        error: error as Error,
        timestamp: new Date(),
      };

      this.lastCheckResult = result;
      return result;
    }
  }

  /**
   * Start periodic health checks
   */
  startPeriodicChecks(onHealthChange?: (result: HealthCheckResult) => void): void {
    if (this.checkInterval) {
      return; // Already running
    }

    const performCheck = async () => {
      if (this.isChecking) return;

      this.isChecking = true;
      try {
        const previousStatus = this.currentStatus;
        const result = await this.check();

        if (onHealthChange && result.status !== previousStatus) {
          onHealthChange(result);
        }
      } catch (error) {
        // Error already handled in check()
      } finally {
        this.isChecking = false;
      }
    };

    // Perform initial check
    performCheck();

    // Schedule periodic checks
    this.checkInterval = setInterval(performCheck, this.config.interval);
  }

  /**
   * Stop periodic health checks
   */
  stopPeriodicChecks(): void {
    if (this.checkInterval) {
      clearInterval(this.checkInterval);
      this.checkInterval = undefined;
    }
  }

  /**
   * Get current health status
   */
  getStatus(): HealthStatus {
    return this.currentStatus;
  }

  /**
   * Get last health check result
   */
  getLastCheckResult(): HealthCheckResult | undefined {
    return this.lastCheckResult;
  }

  /**
   * Check if cluster is healthy
   */
  isHealthy(): boolean {
    return this.currentStatus === HealthStatus.HEALTHY;
  }

  /**
   * Check if cluster is available
   */
  isAvailable(): boolean {
    return this.lastCheckResult?.available ?? false;
  }

  /**
   * Reset health check state
   */
  reset(): void {
    this.consecutiveFailures = 0;
    this.consecutiveSuccesses = 0;
    this.currentStatus = HealthStatus.UNKNOWN;
    this.lastCheckResult = undefined;
  }

  /**
   * Helper to create a timeout promise
   */
  private timeout(ms: number): Promise<never> {
    return new Promise((_, reject) => {
      setTimeout(() => reject(new Error(`Health check timeout after ${ms}ms`)), ms);
    });
  }

  /**
   * Cleanup resources
   */
  destroy(): void {
    this.stopPeriodicChecks();
  }
}