const Queue = require('bull');
const logger = require('./logger');
const metrics = require('./metrics');
const emailService = require('../services/email');

// Configure Redis connection for Bull
const redisConfig = {
  host: process.env.REDIS_HOST || 'localhost',
  port: parseInt(process.env.REDIS_PORT || '6379'),
  password: process.env.REDIS_PASSWORD || undefined,
  db: parseInt(process.env.REDIS_DB || '0'),
  // Retry strategy for connection failures
  retryStrategy: (times) => {
    const delay = Math.min(times * 50, 2000);
    return delay;
  },
  // Enable offline queue
  enableOfflineQueue: true,
  maxRetriesPerRequest: 3
};

// Create email queue
const emailQueue = new Queue('email-queue', {
  redis: redisConfig,
  defaultJobOptions: {
    attempts: 3,
    backoff: {
      type: 'exponential',
      delay: 2000 // Start with 2 seconds, then 4, 8, etc.
    },
    removeOnComplete: {
      age: 24 * 3600, // Keep completed jobs for 24 hours
      count: 1000 // Keep last 1000 completed jobs
    },
    removeOnFail: {
      age: 7 * 24 * 3600 // Keep failed jobs for 7 days
    },
    timeout: 30000 // 30 seconds timeout per job
  }
});

// Process email jobs
emailQueue.process(async (job) => {
  const { type, data } = job.data;
  const start = Date.now();
  
  logger.info('Processing email job', {
    jobId: job.id,
    type,
    attempt: job.attemptsMade + 1,
    maxAttempts: job.opts.attempts
  });

  try {
    let result;

    switch (type) {
      case 'campaign':
        result = await emailService.sendCampaignEmail(data);
        break;
      
      case 'verification':
        result = await emailService.sendVerificationEmail(data);
        break;
      
      case 'login-details':
        result = await emailService.sendLoginDetails(data);
        break;
      
      case 'broadcast':
        result = await emailService.sendBroadcast(data);
        break;
      
      case 'response-verification':
        result = await emailService.sendResponseVerificationEmail(data);
        break;
      
      default:
        throw new Error(`Unknown email type: ${type}`);
    }

    const duration = (Date.now() - start) / 1000;
    
    // Record metrics
    metrics.recordEmailSent(
      data.campaignId || 'system',
      data.representativeLevel || 'unknown'
    );
    metrics.observeEmailSendDuration(
      data.campaignId || 'system',
      duration
    );

    logger.logEmailSent(
      data.to || data.email,
      data.campaignId || type,
      'success'
    );

    return result;
  } catch (error) {
    const duration = (Date.now() - start) / 1000;
    
    // Record failure metrics
    metrics.recordEmailFailed(
      data.campaignId || 'system',
      error.code || 'unknown'
    );

    logger.logEmailFailed(
      data.to || data.email,
      data.campaignId || type,
      error
    );

    // Throw error to trigger retry
    throw error;
  }
});

// Queue event handlers
emailQueue.on('completed', (job, result) => {
  logger.info('Email job completed', {
    jobId: job.id,
    type: job.data.type,
    duration: Date.now() - job.timestamp
  });
});

emailQueue.on('failed', (job, err) => {
  logger.error('Email job failed', {
    jobId: job.id,
    type: job.data.type,
    attempt: job.attemptsMade,
    maxAttempts: job.opts.attempts,
    error: err.message,
    willRetry: job.attemptsMade < job.opts.attempts
  });
});

emailQueue.on('stalled', (job) => {
  logger.warn('Email job stalled', {
    jobId: job.id,
    type: job.data.type
  });
});

emailQueue.on('error', (error) => {
  logger.error('Email queue error', { error: error.message });
});

// Update queue size metric every 10 seconds
setInterval(async () => {
  try {
    const counts = await emailQueue.getJobCounts();
    const queueSize = counts.waiting + counts.active;
    metrics.setEmailQueueSize(queueSize);
  } catch (error) {
    logger.warn('Failed to update queue metrics', { error: error.message });
  }
}, 10000);

/**
 * Email Queue Service
 * Provides methods to enqueue different types of emails
 */
class EmailQueueService {
  /**
   * Send campaign email (to representative)
   */
  async sendCampaignEmail(emailData) {
    const job = await emailQueue.add(
      {
        type: 'campaign',
        data: emailData
      },
      {
        priority: 2, // Normal priority
        jobId: `campaign-${emailData.campaignId}-${Date.now()}`
      }
    );

    logger.info('Campaign email queued', {
      jobId: job.id,
      campaignId: emailData.campaignId,
      recipient: emailData.to
    });

    return { jobId: job.id, queued: true };
  }

  /**
   * Send email verification
   */
  async sendVerificationEmail(emailData) {
    const job = await emailQueue.add(
      {
        type: 'verification',
        data: emailData
      },
      {
        priority: 1, // High priority - user waiting
        jobId: `verification-${emailData.email}-${Date.now()}`
      }
    );

    logger.info('Verification email queued', {
      jobId: job.id,
      email: emailData.email
    });

    return { jobId: job.id, queued: true };
  }

  /**
   * Send login details
   */
  async sendLoginDetails(emailData) {
    const job = await emailQueue.add(
      {
        type: 'login-details',
        data: emailData
      },
      {
        priority: 1, // High priority
        jobId: `login-${emailData.email}-${Date.now()}`
      }
    );

    logger.info('Login details email queued', {
      jobId: job.id,
      email: emailData.email
    });

    return { jobId: job.id, queued: true };
  }

  /**
   * Send broadcast to users
   */
  async sendBroadcast(emailData) {
    const job = await emailQueue.add(
      {
        type: 'broadcast',
        data: emailData
      },
      {
        priority: 3, // Lower priority - batch operation
        jobId: `broadcast-${Date.now()}-${Math.random().toString(36).substr(2, 9)}`
      }
    );

    logger.info('Broadcast email queued', {
      jobId: job.id,
      recipientCount: emailData.recipients?.length || 1
    });

    return { jobId: job.id, queued: true };
  }

  /**
   * Send response verification email
   */
  async sendResponseVerificationEmail(emailData) {
    const job = await emailQueue.add(
      {
        type: 'response-verification',
        data: emailData
      },
      {
        priority: 2,
        jobId: `response-verification-${emailData.email}-${Date.now()}`
      }
    );

    logger.info('Response verification email queued', {
      jobId: job.id,
      email: emailData.email
    });

    return { jobId: job.id, queued: true };
  }

  /**
   * Get job status
   */
  async getJobStatus(jobId) {
    const job = await emailQueue.getJob(jobId);
    
    if (!job) {
      return { status: 'not_found' };
    }

    const state = await job.getState();
    const progress = job.progress();

    return {
      jobId: job.id,
      status: state,
      progress,
      attempts: job.attemptsMade,
      data: job.data,
      createdAt: job.timestamp,
      processedAt: job.processedOn,
      finishedAt: job.finishedOn,
      failedReason: job.failedReason
    };
  }

  /**
   * Get queue statistics
   */
  async getQueueStats() {
    const counts = await emailQueue.getJobCounts();
    const jobs = {
      waiting: await emailQueue.getWaiting(0, 10),
      active: await emailQueue.getActive(0, 10),
      completed: await emailQueue.getCompleted(0, 10),
      failed: await emailQueue.getFailed(0, 10)
    };

    return {
      counts,
      samples: {
        waiting: jobs.waiting.map(j => ({ id: j.id, type: j.data.type })),
        active: jobs.active.map(j => ({ id: j.id, type: j.data.type })),
        completed: jobs.completed.slice(0, 5).map(j => ({ id: j.id, type: j.data.type })),
        failed: jobs.failed.slice(0, 5).map(j => ({ id: j.id, type: j.data.type, reason: j.failedReason }))
      }
    };
  }

  /**
   * Clean old jobs
   */
  async cleanQueue(grace = 24 * 3600 * 1000) {
    const cleaned = await emailQueue.clean(grace, 'completed');
    logger.info('Queue cleaned', { removedJobs: cleaned.length });
    return { cleaned: cleaned.length };
  }

  /**
   * Pause queue
   */
  async pauseQueue() {
    await emailQueue.pause();
    logger.warn('Email queue paused');
    return { paused: true };
  }

  /**
   * Resume queue
   */
  async resumeQueue() {
    await emailQueue.resume();
    logger.info('Email queue resumed');
    return { resumed: true };
  }

  /**
   * Get queue instance (for advanced operations)
   */
  getQueue() {
    return emailQueue;
  }
}

module.exports = new EmailQueueService();