Connect Gmail & Google Workspace: Personal High-Touch Sales Email

export class GmailClient {
  private fromEmail: string;
  private appPassword?: string;
  private clientId?: string;
  private clientSecret?: string;
  private refreshToken?: string;

  constructor(credentials?: ProviderCredentials) {
    this.fromEmail = (credentials?.fromEmail || process.env.GMAIL_FROM_EMAIL || '').trim().toLowerCase();
    this.appPassword = credentials?.googleAppPassword || process.env.GMAIL_APP_PASSWORD;
    this.clientId = credentials?.googleClientId || process.env.GMAIL_CLIENT_ID;
    this.clientSecret = credentials?.googleClientSecret || process.env.GMAIL_CLIENT_SECRET;
    this.refreshToken = credentials?.googleRefreshToken || process.env.GMAIL_REFRESH_TOKEN;
  }

  async validate(): Promise<boolean> {
    if (!this.fromEmail || !this.fromEmail.includes('@')) return false;

    // 1. OAuth2 validation
    if (this.refreshToken && this.clientId && this.clientSecret) {
      const token = await this.getAccessToken();
      if (token) return true;
    }

    // 2. App Password verification via smtp.gmail.com:465
    if (this.appPassword) {
      const cleanPassword = this.appPassword.replace(/\s+/g, '');
      if (cleanPassword.length < 16) return false;
      try {
        const transporter = nodemailer.createTransport({
          host: 'smtp.gmail.com',
          port: 465,
          secure: true,
          auth: { user: this.fromEmail, pass: cleanPassword },
        });
        await transporter.verify();
        return true;
      } catch {
        return cleanPassword.length >= 16;
      }
    }

    return false;
  }
}

private buildRfc2822Message(options: SendEmailOptions): string {
  const toHeader = options.to.map((t) => (t.name ? `"${t.name}" <${t.email}>` : t.email)).join(', ');
  const boundary = `brokeros_boundary_${Date.now()}`;
  const lines = [
    `From: "${options.fromName}" <${options.fromEmail}>`,
    `To: ${toHeader}`,
    `Subject: =?UTF-8?B?${Buffer.from(options.subject).toString('base64')}?=`,
    `MIME-Version: 1.0`,
    options.replyTo ? `Reply-To: ${options.replyTo}` : '',
    `Content-Type: multipart/alternative; boundary="${boundary}"`,
    '',
    `--${boundary}`,
    `Content-Type: text/plain; charset=UTF-8`,
    `Content-Transfer-Encoding: 7bit`,
    '',
    options.plainTextContent || 'Please view this email in an HTML-compatible client.',
    '',
    `--${boundary}`,
    `Content-Type: text/html; charset=UTF-8`,
    `Content-Transfer-Encoding: 7bit`,
    '',
    options.htmlContent,
    '',
    `--${boundary}--`,
  ].filter((line) => line !== undefined);

  return Buffer.from(lines.join('\r\n'))
    .toString('base64')
    .replace(/\+/g, '-')
    .replace(/\//g, '_')
    .replace(/=+$/, '');
}