Re_Backend/src/services/gmail.service.ts

import { google } from 'googleapis';
import fs from 'fs/promises';
import path from 'path';
import { gmailConfig } from '../config/gmail.config';
import { IncomingEmail } from '../models/IncomingEmail';
import { WorkflowRequest } from '../models/WorkflowRequest';
import { ApprovalLevel } from '../models/ApprovalLevel';
import { User } from '../models/User';
import { ApprovalService } from './approval.service';
import { parseEmailAction } from '../utils/gmailParser';
import { ApprovalAction } from '../types/approval.types';
import logger from '../utils/logger';

const approvalService = new ApprovalService();

export class GmailService {
  private auth: any;
  private gmail: any;

  constructor() {
    this.initAuth();
  }

  private initAuth() {
    try {
      const keyPath = path.resolve(gmailConfig.serviceAccountPath);
      
      // Use Service Account with Domain-Wide Delegation to impersonate the approval mailbox
      this.auth = new google.auth.JWT({
        keyFile: keyPath,
        scopes: ['https://www.googleapis.com/auth/gmail.modify', 'https://www.googleapis.com/auth/gmail.settings.basic'],
        subject: gmailConfig.impersonateEmail
      });

      this.gmail = google.gmail({ version: 'v1', auth: this.auth });
      logger.info(`[GmailService] Initialized for ${gmailConfig.impersonateEmail}`);
    } catch (error) {
      logger.error(`[GmailService] Failed to initialize Google Auth:`, error);
    }
  }

  /**
   * Setup Gmail Watch for Pub/Sub notifications
   */
  async setupWatch() {
    try {
      const res = await this.gmail.users.watch({
        userId: 'me',
        requestBody: {
          labelIds: ['INBOX'],
          topicName: `projects/${process.env.GCP_PROJECT_ID}/topics/${gmailConfig.pubsubTopic}`
        }
      });
      logger.info(`[GmailService] Watch setup successfully:`, res.data);
      return res.data;
    } catch (error) {
      logger.error(`[GmailService] Failed to setup watch:`, error);
      throw error;
    }
  }

  /**
   * Process notification from Pub/Sub
   */
  async processNotification(notificationData: any) {
    try {
      const { emailAddress, historyId } = notificationData;
      logger.info(`[GmailService] Received notification for ${emailAddress}, historyId: ${historyId}`);

      // In a production environment, you might want to store the last processed historyId
      // and only fetch changes since then using users.history.list.
      // For simplicity in this requirement, we'll list the latest messages.
      
      const res = await this.gmail.users.messages.list({
        userId: 'me',
        maxResults: 10,
        q: 'label:INBOX is:unread'
      });

      const messages = res.data.messages || [];
      for (const msg of messages) {
        await this.processMessage(msg.id);
      }
    } catch (error) {
      logger.error(`[GmailService] Error processing notification:`, error);
    }
  }

  /**
   * Fetch and process a single message
   */
  private async processMessage(messageId: string) {
    try {
      // 1. Check if already processed
      const existing = await IncomingEmail.findOne({ where: { messageId } });
      if (existing && existing.processed) return;

      // 2. Fetch full message
      const res = await this.gmail.users.messages.get({
        userId: 'me',
        id: messageId,
        format: 'full'
      });

      const message = res.data;
      const headers = message.payload?.headers || [];
      const from = headers.find((h: any) => h.name?.toLowerCase() === 'from')?.value || '';
      const to = headers.find((h: any) => h.name?.toLowerCase() === 'to')?.value || '';
      const subject = headers.find((h: any) => h.name?.toLowerCase() === 'subject')?.value || '';
      
      // Extract body
      let body = '';
      if (message.payload?.parts) {
        const textPart = message.payload.parts.find((p: any) => p.mimeType === 'text/plain');
        if (textPart && textPart.body?.data) {
          body = Buffer.from(textPart.body.data, 'base64').toString();
        }
      } else if (message.payload?.body?.data) {
        body = Buffer.from(message.payload.body.data, 'base64').toString();
      }

      logger.info(`[GmailService] Processing message ${messageId} from ${from}: ${subject}`);

      // 3. Save to database
      const incomingEmail = await IncomingEmail.create({
        messageId,
        threadId: message.threadId!,
        from,
        to,
        subject,
        body,
        receivedAt: new Date(parseInt(message.internalDate!)),
        processed: false
      } as any);

      // 4. Parse Action
      const { action, requestNumber, comments } = parseEmailAction(subject, body);
      
      if (action === 'NONE' || !requestNumber) {
        logger.info(`[GmailService] No action or request number found in message ${messageId}`);
        await incomingEmail.update({ processed: true, actionTaken: 'NONE' });
        // Mark as read anyway?
        await this.markAsRead(messageId);
        return;
      }

      // 5. Apply Workflow Logic
      await this.applyWorkflowAction(incomingEmail, { action, requestNumber, comments });

      // 6. Mark message as read/processed in Gmail
      await this.markAsRead(messageId);
    } catch (error) {
      logger.error(`[GmailService] Error processing message ${messageId}:`, error);
    }
  }

  private async applyWorkflowAction(incomingEmail: any, parsedAction: any) {
    const { action, requestNumber, comments } = parsedAction;
    
    try {
      // 1. Find Request
      const request = await WorkflowRequest.findOne({ where: { requestNumber } });
      if (!request) {
        throw new Error(`Request ${requestNumber} not found`);
      }

      // 2. Resolve User by Email
      // Extract email from "Name <email@domain.com>"
      const emailMatch = incomingEmail.from.match(/<(.+?)>/) || [null, incomingEmail.from];
      const approverEmail = emailMatch[1].trim();

      const user = await User.findOne({ where: { email: approverEmail } });
      if (!user) {
        throw new Error(`User with email ${approverEmail} not found`);
      }

      // 3. Find current pending level for this user and request
      const currentLevel = await ApprovalLevel.findOne({
        where: {
          requestId: request.requestId,
          approverId: user.userId,
          status: 'IN_PROGRESS' // Or PENDING if it was just assigned
        }
      });

      if (!currentLevel) {
        // Broaden search to PENDING if not yet IN_PROGRESS (some implementations delay IN_PROGRESS)
        const pendingLevel = await ApprovalLevel.findOne({
          where: {
            requestId: request.requestId,
            approverId: user.userId,
            status: 'PENDING'
          }
        });
        
        if (!pendingLevel) {
          throw new Error(`No pending/in-progress approval step found for user ${approverEmail} on request ${requestNumber}`);
        }
        
        // Use pending level
        await this.executeApproval(request, pendingLevel, action, user, comments, incomingEmail);
      } else {
        await this.executeApproval(request, currentLevel, action, user, comments, incomingEmail);
      }

    } catch (error: any) {
      logger.error(`[GmailService] Workflow action failed for ${requestNumber}:`, error);
      await incomingEmail.update({ 
        processed: true, 
        error: error.message,
        actionTaken: action
      });
    }
  }

  private async executeApproval(request: any, level: any, action: string, user: any, comments: string, incomingEmail: any) {
    const approvalAction: ApprovalAction = {
      action: action as any,
      comments: comments || `${action} via email`,
      rejectionReason: action === 'REJECT' ? (comments || 'Rejected via email') : undefined
    };

    logger.info(`[GmailService] Executing ${action} for ${request.requestNumber} level ${level.levelNumber} by ${user.email}`);

    await approvalService.approveLevel(
      level.levelId,
      approvalAction,
      user.userId,
      { ipAddress: 'GMAIL_WEBHOOK', userAgent: 'Gmail/PubSub' }
    );

    await incomingEmail.update({
      processed: true,
      actionTaken: action,
      parsedComments: comments,
      requestId: request.requestId
    });

    logger.info(`[GmailService] ✅ Workflow ${request.requestNumber} updated successfully via email.`);
  }

  private async markAsRead(messageId: string) {
    try {
      await this.gmail.users.messages.batchModify({
        userId: 'me',
        requestBody: {
          ids: [messageId],
          removeLabelIds: ['UNREAD']
        }
      });
    } catch (error) {
      logger.error(`[GmailService] Failed to mark message ${messageId} as read:`, error);
    }
  }
}

export const gmailService = new GmailService();