files/gmailService.ts

// packages/server/src/services/gmailService.ts
//
// Gmail API integration for fetching Interac e-Transfer emails
// Install: npm install googleapis

import { google, gmail_v1 } from 'googleapis';
import type { ScanDateRange } from '../../shared/types/scan';
import database from '../db/database';

// ═══════════════════════════════════════════
// OAUTH CLIENT SETUP
// ═══════════════════════════════════════════

const GOOGLE_CLIENT_ID = process.env.GOOGLE_CLIENT_ID!;
const GOOGLE_CLIENT_SECRET = process.env.GOOGLE_CLIENT_SECRET!;
const GOOGLE_REDIRECT_URI = process.env.GOOGLE_REDIRECT_URI || 'http://localhost:3001/api/auth/google/callback';

export function createOAuthClient() {
  return new google.auth.OAuth2(
    GOOGLE_CLIENT_ID,
    GOOGLE_CLIENT_SECRET,
    GOOGLE_REDIRECT_URI
  );
}

/** Generate the Google OAuth consent URL */
export function getAuthUrl(): string {
  const oauth2Client = createOAuthClient();
  return oauth2Client.generateAuthUrl({
    access_type: 'offline',       // Get refresh_token
    prompt: 'consent',            // Force consent to always get refresh_token
    scope: [
      'https://www.googleapis.com/auth/gmail.readonly',
      'https://www.googleapis.com/auth/userinfo.email',
      'https://www.googleapis.com/auth/userinfo.profile',
    ],
  });
}

/** Exchange authorization code for tokens */
export async function exchangeCode(code: string) {
  const oauth2Client = createOAuthClient();
  const { tokens } = await oauth2Client.getToken(code);
  oauth2Client.setCredentials(tokens);

  // Get user profile info
  const oauth2 = google.oauth2({ version: 'v2', auth: oauth2Client });
  const { data: profile } = await oauth2.userinfo.get();

  return {
    tokens,
    profile: {
      google_id: profile.id!,
      email: profile.email!,
      name: profile.name || profile.email!,
      avatar_url: profile.picture || null,
    },
  };
}

/** Get an authenticated Gmail client for a specific user */
export function getGmailClient(userId: string): gmail_v1.Gmail {
  const user = database.getUserById(userId);
  if (!user) throw new Error(`User ${userId} not found`);
  if (!user.access_token) throw new Error('User has no Gmail tokens — please re-authenticate');

  const oauth2Client = createOAuthClient();
  oauth2Client.setCredentials({
    access_token: user.access_token,
    refresh_token: user.refresh_token,
    expiry_date: user.token_expires ? new Date(user.token_expires).getTime() : undefined,
  });

  // Auto-refresh handler: save new tokens when Google refreshes them
  oauth2Client.on('tokens', (tokens) => {
    console.log('[Gmail] Token refreshed for user', userId);
    database.updateUserTokens({
      id: userId,
      access_token: tokens.access_token || user.access_token,
      refresh_token: tokens.refresh_token || user.refresh_token,
      token_expires: tokens.expiry_date ? new Date(tokens.expiry_date).toISOString() : user.token_expires,
    });
  });

  return google.gmail({ version: 'v1', auth: oauth2Client });
}

// ═══════════════════════════════════════════
// GMAIL QUERY BUILDER
// ═══════════════════════════════════════════

/**
 * Build a Gmail search query for Interac emails within a date range.
 * Gmail's after:/before: use YYYY/MM/DD format and are date-only (not datetime).
 * after: is inclusive (includes emails from that date onward).
 * before: is exclusive → add 1 day to include the end date.
 */
export function buildGmailQuery(dateRange: ScanDateRange): string {
  const start = new Date(dateRange.startDate);
  const end = new Date(dateRange.endDate);

  // after: is already inclusive — use start date as-is
  const afterDate = new Date(start);

  // Make before: inclusive of end date by adding 1 day
  const beforeDate = new Date(end);
  beforeDate.setDate(beforeDate.getDate() + 1);

  const fmt = (d: Date) => `${d.getFullYear()}/${d.getMonth() + 1}/${d.getDate()}`;

  return `from:notify@payments.interac.ca after:${fmt(afterDate)} before:${fmt(beforeDate)}`;
}

// ═══════════════════════════════════════════
// EMAIL FETCHING
// ═══════════════════════════════════════════

/**
 * Fetch all matching message IDs from Gmail using pagination.
 * Returns an array of Gmail message ID strings.
 */
export async function fetchAllMessageIds(
  gmail: gmail_v1.Gmail,
  query: string
): Promise<string[]> {
  const messageIds: string[] = [];
  let pageToken: string | undefined;

  console.log(`[Gmail] Searching: "${query}"`);

  do {
    const response = await gmail.users.messages.list({
      userId: 'me',
      q: query,
      maxResults: 500,
      pageToken,
    });

    const messages = response.data.messages || [];
    messageIds.push(...messages.map((m) => m.id!));
    pageToken = response.data.nextPageToken || undefined;

    console.log(`[Gmail] Found ${messages.length} messages (total: ${messageIds.length})`);
  } while (pageToken);

  console.log(`[Gmail] Total messages found: ${messageIds.length}`);
  return messageIds;
}

/**
 * Fetch the full body of a single email by message ID.
 * Returns the decoded text/plain or text/html body.
 */
export async function fetchEmailBody(
  gmail: gmail_v1.Gmail,
  messageId: string
): Promise<{ body: string; subject: string; internalDate: string }> {
  const response = await gmail.users.messages.get({
    userId: 'me',
    id: messageId,
    format: 'full',
  });

  const message = response.data;
  const headers = message.payload?.headers || [];

  const subject = headers.find((h) => h.name?.toLowerCase() === 'subject')?.value || '';
  const internalDate = message.internalDate || '';

  // Extract body: try text/plain first, then text/html, then multipart
  let body = '';

  if (message.payload?.body?.data) {
    // Simple single-part message
    body = decodeBase64Url(message.payload.body.data);
  } else if (message.payload?.parts) {
    // Multipart message — look for text/plain or text/html
    body = extractBodyFromParts(message.payload.parts);
  }

  return { body, subject, internalDate };
}

/** Recursively extract text body from multipart MIME parts */
function extractBodyFromParts(parts: gmail_v1.Schema$MessagePart[]): string {
  // Prefer text/plain for cleaner AI parsing
  for (const part of parts) {
    if (part.mimeType === 'text/plain' && part.body?.data) {
      return decodeBase64Url(part.body.data);
    }
  }

  // Fall back to text/html
  for (const part of parts) {
    if (part.mimeType === 'text/html' && part.body?.data) {
      return decodeBase64Url(part.body.data);
    }
  }

  // Recurse into nested multipart
  for (const part of parts) {
    if (part.parts) {
      const result = extractBodyFromParts(part.parts);
      if (result) return result;
    }
  }

  return '';
}

/** Decode Gmail's base64url-encoded body */
function decodeBase64Url(data: string): string {
  const base64 = data.replace(/-/g, '+').replace(/_/g, '/');
  return Buffer.from(base64, 'base64').toString('utf-8');
}

export const gmailService = {
  createOAuthClient,
  getAuthUrl,
  exchangeCode,
  getGmailClient,
  buildGmailQuery,
  fetchAllMessageIds,
  fetchEmailBody,
};

export default gmailService;