interface QueuedRequest<T> {
  id: string;
  priority: 'high' | 'normal' | 'low';
  execute: () => Promise<T>;
  resolve: (value: T) => void;
  reject: (error: any) => void;
  timestamp: number;
  retries: number;
}

interface QueueOptions {
  maxConcurrent: number;
  maxQueueSize: number;
  requestTimeout: number;
  maxRetries: number;
}

class RequestQueue {
  private static instances: Map<string, RequestQueue> = new Map();
  private queue: QueuedRequest<any>[] = [];
  private activeRequests: number = 0;
  private requestId: number = 0;
  
  constructor(private name: string, private options: QueueOptions) {
    this.options = {
      maxConcurrent: 5,
      maxQueueSize: 100,
      requestTimeout: 30000,
      maxRetries: 2,
      ...options
    };
  }
  
  static getInstance(name: string, options?: Partial<QueueOptions>): RequestQueue {
    if (!RequestQueue.instances.has(name)) {
      RequestQueue.instances.set(name, new RequestQueue(name, options as QueueOptions));
    }
    return RequestQueue.instances.get(name)!;
  }
  
  async add<T>(
    execute: () => Promise<T>,
    priority: 'high' | 'normal' | 'low' = 'normal'
  ): Promise<T> {
    if (this.queue.length >= this.options.maxQueueSize) {
      throw new Error(`Queue ${this.name} is full (${this.queue.length} items)`);
    }
    
    return new Promise<T>((resolve, reject) => {
      const request: QueuedRequest<T> = {
        id: `${this.name}-${++this.requestId}`,
        priority,
        execute,
        resolve,
        reject,
        timestamp: Date.now(),
        retries: 0
      };
      
      // Insert based on priority
      if (priority === 'high') {
        // Find the first non-high priority item
        const index = this.queue.findIndex(item => item.priority !== 'high');
        if (index === -1) {
          this.queue.push(request);
        } else {
          this.queue.splice(index, 0, request);
        }
      } else if (priority === 'low') {
        this.queue.push(request);
      } else {
        // Normal priority - insert before low priority items
        const index = this.queue.findIndex(item => item.priority === 'low');
        if (index === -1) {
          this.queue.push(request);
        } else {
          this.queue.splice(index, 0, request);
        }
      }
      
      console.log(`[Queue ${this.name}] Added request ${request.id} (priority: ${priority}, queue size: ${this.queue.length})`);
      
      // Process queue
      this.processQueue();
    });
  }
  
  private async processQueue() {
    while (this.queue.length > 0 && this.activeRequests < this.options.maxConcurrent) {
      const request = this.queue.shift();
      if (!request) continue;
      
      this.activeRequests++;
      
      // Process request with timeout
      const timeoutPromise = new Promise<never>((_, reject) => {
        setTimeout(() => reject(new Error('Request timeout')), this.options.requestTimeout);
      });
      
      try {
        console.log(`[Queue ${this.name}] Processing request ${request.id} (active: ${this.activeRequests}/${this.options.maxConcurrent})`);
        
        const result = await Promise.race([
          request.execute(),
          timeoutPromise
        ]);
        
        request.resolve(result);
        console.log(`[Queue ${this.name}] Request ${request.id} completed successfully`);
      } catch (error) {
        console.error(`[Queue ${this.name}] Request ${request.id} failed:`, error);
        
        // Retry logic
        if (request.retries < this.options.maxRetries) {
          request.retries++;
          console.log(`[Queue ${this.name}] Retrying request ${request.id} (attempt ${request.retries + 1}/${this.options.maxRetries + 1})`);
          
          // Re-queue with same priority
          this.queue.unshift(request);
        } else {
          request.reject(error);
        }
      } finally {
        this.activeRequests--;
        
        // Continue processing
        if (this.queue.length > 0) {
          setImmediate(() => this.processQueue());
        }
      }
    }
  }
  
  getStatus() {
    return {
      name: this.name,
      queueLength: this.queue.length,
      activeRequests: this.activeRequests,
      maxConcurrent: this.options.maxConcurrent,
      queueByPriority: {
        high: this.queue.filter(r => r.priority === 'high').length,
        normal: this.queue.filter(r => r.priority === 'normal').length,
        low: this.queue.filter(r => r.priority === 'low').length
      }
    };
  }
  
  clear() {
    const cleared = this.queue.length;
    this.queue.forEach(request => {
      request.reject(new Error('Queue cleared'));
    });
    this.queue = [];
    console.log(`[Queue ${this.name}] Cleared ${cleared} requests`);
    return cleared;
  }
}

// Pre-configured queues for different operations
export const queues = {
  documenso: RequestQueue.getInstance('documenso', {
    maxConcurrent: 3,
    maxQueueSize: 50,
    requestTimeout: 45000,
    maxRetries: 2
  }),
  
  email: RequestQueue.getInstance('email', {
    maxConcurrent: 2,
    maxQueueSize: 30,
    requestTimeout: 60000,
    maxRetries: 1
  }),
  
  nocodb: RequestQueue.getInstance('nocodb', {
    maxConcurrent: 5,
    maxQueueSize: 100,
    requestTimeout: 20000,
    maxRetries: 3
  })
};

// Utility function to get all queue statuses
export function getAllQueueStatuses() {
  return {
    documenso: queues.documenso.getStatus(),
    email: queues.email.getStatus(),
    nocodb: queues.nocodb.getStatus()
  };
}