import type { H3Event } from 'h3';

interface ServiceCheckResult {
  status: 'up' | 'down' | 'slow';
  responseTime?: number;
  error?: string;
}

class HealthChecker {
  private static instance: HealthChecker;
  private isReady: boolean = false;
  private startupChecks: Map<string, boolean> = new Map();
  private requiredServices = ['nocodb', 'directus', 'minio'];
  
  private constructor() {
    this.initializeStartupChecks();
  }
  
  static getInstance(): HealthChecker {
    if (!HealthChecker.instance) {
      HealthChecker.instance = new HealthChecker();
    }
    return HealthChecker.instance;
  }
  
  private initializeStartupChecks() {
    this.requiredServices.forEach(service => {
      this.startupChecks.set(service, false);
    });
  }
  
  async checkServiceWithRetry(
    serviceName: string,
    checkFunction: () => Promise<ServiceCheckResult>,
    maxRetries: number = 3,
    retryDelay: number = 1000
  ): Promise<ServiceCheckResult> {
    let lastError: string | undefined;
    
    for (let attempt = 0; attempt < maxRetries; attempt++) {
      try {
        const result = await checkFunction();
        
        if (result.status === 'up' || result.status === 'slow') {
          this.startupChecks.set(serviceName, true);
          return result;
        }
        
        lastError = result.error;
      } catch (error) {
        lastError = error instanceof Error ? error.message : 'Unknown error';
      }
      
      if (attempt < maxRetries - 1) {
        await new Promise(resolve => setTimeout(resolve, retryDelay * Math.pow(2, attempt)));
      }
    }
    
    return {
      status: 'down',
      error: lastError || 'Max retries exceeded'
    };
  }
  
  markServiceReady(serviceName: string) {
    this.startupChecks.set(serviceName, true);
    this.checkOverallReadiness();
  }
  
  markServiceDown(serviceName: string) {
    this.startupChecks.set(serviceName, false);
    this.isReady = false;
  }
  
  private checkOverallReadiness() {
    const allRequired = this.requiredServices.every(service => 
      this.startupChecks.get(service) === true
    );
    
    if (allRequired) {
      this.isReady = true;
      console.log('[HealthChecker] All required services are ready');
    }
  }
  
  isApplicationReady(): boolean {
    return this.isReady;
  }
  
  getStartupStatus(): { [key: string]: boolean } {
    const status: { [key: string]: boolean } = {};
    this.startupChecks.forEach((value, key) => {
      status[key] = value;
    });
    return status;
  }
  
  async performStartupHealthChecks(): Promise<boolean> {
    console.log('[HealthChecker] Performing startup health checks...');
    
    // Import check functions dynamically to avoid circular dependencies
    const { checkNocoDB, checkDirectus, checkMinIO } = await import('./service-checks');
    
    // Check all services in parallel
    const checks = await Promise.all([
      this.checkServiceWithRetry('nocodb', checkNocoDB, 5, 2000),
      this.checkServiceWithRetry('directus', checkDirectus, 5, 2000),
      this.checkServiceWithRetry('minio', checkMinIO, 5, 2000)
    ]);
    
    // Log results
    checks.forEach((result, index) => {
      const serviceName = ['nocodb', 'directus', 'minio'][index];
      console.log(`[HealthChecker] ${serviceName}: ${result.status}${result.error ? ` - ${result.error}` : ''}`);
    });
    
    this.checkOverallReadiness();
    return this.isReady;
  }
}

export const healthChecker = HealthChecker.getInstance();

// Middleware to check if app is ready
export function createReadinessMiddleware() {
  return defineEventHandler(async (event: H3Event) => {
    // Skip health check endpoint itself
    if (event.node.req.url === '/api/health') {
      return;
    }
    
    // During startup, return 503 for all requests except health
    if (!healthChecker.isApplicationReady()) {
      const startupStatus = healthChecker.getStartupStatus();
      
      setResponseStatus(event, 503);
      return {
        error: 'Service Unavailable',
        message: 'Application is starting up. Please wait...',
        startupStatus
      };
    }
  });
}