import type { Transporter } from 'nodemailer';
import { createTransport } from 'nodemailer';

import { ResendTransport } from '@documenso/nodemailer-resend';

import { MailChannelsTransport } from './transports/mailchannels';

/**
 * Creates a Nodemailer transport object for sending emails.
 *
 * This function uses various environment variables to configure the appropriate
 * email transport mechanism. It supports multiple types of email transports,
 * including MailChannels, Resend, and different SMTP configurations.
 *
 * @returns {Transporter} A configured Nodemailer transporter instance.
 *
 * Supported Transports:
 * - **mailchannels**: Uses MailChannelsTransport, requiring:
 *   - `NEXT_PRIVATE_MAILCHANNELS_API_KEY`: API key for MailChannels
 *   - `NEXT_PRIVATE_MAILCHANNELS_ENDPOINT`: Endpoint for MailChannels (optional)
 * - **resend**: Uses ResendTransport, requiring:
 *   - `NEXT_PRIVATE_RESEND_API_KEY`: API key for Resend
 * - **smtp-api**: Uses a custom SMTP API configuration, requiring:
 *   - `NEXT_PRIVATE_SMTP_HOST`: The SMTP server host
 *   - `NEXT_PRIVATE_SMTP_APIKEY`: The API key for SMTP authentication
 *   - `NEXT_PRIVATE_SMTP_APIKEY_USER`: The username for SMTP authentication (default: 'apikey')
 * - **smtp-auth** (default): Uses a standard SMTP configuration, requiring:
 *   - `NEXT_PRIVATE_SMTP_HOST`: The SMTP server host (default: 'localhost:2500')
 *   - `NEXT_PRIVATE_SMTP_PORT`: The port to connect to (default: 587)
 *   - `NEXT_PRIVATE_SMTP_SECURE`: Whether to use SSL/TLS (default: false)
 *   - `NEXT_PRIVATE_SMTP_UNSAFE_IGNORE_TLS`: Whether to ignore TLS (default: false)
 *   - `NEXT_PRIVATE_SMTP_USERNAME`: The username for SMTP authentication
 *   - `NEXT_PRIVATE_SMTP_PASSWORD`: The password for SMTP authentication
 *   - `NEXT_PRIVATE_SMTP_SERVICE`: The SMTP service provider (e.g., "gmail"). This option is used
 *     when integrating with well-known services (like Gmail), enabling simplified configuration.
 *
 * Example Usage:
 * ```env
 * NEXT_PRIVATE_SMTP_TRANSPORT='smtp-auth';
 * NEXT_PRIVATE_SMTP_HOST='smtp.example.com';
 * NEXT_PRIVATE_SMTP_PORT=587;
 * NEXT_PRIVATE_SMTP_SERVICE='gmail';
 * NEXT_PRIVATE_SMTP_SECURE='true';
 * NEXT_PRIVATE_SMTP_USERNAME='your-email@gmail.com';
 * NEXT_PRIVATE_SMTP_PASSWORD='your-password';
 * ```
 *
 * Notes:
 * - Ensure that the required environment variables for each transport type are set.
 * - If `NEXT_PRIVATE_SMTP_TRANSPORT` is not specified, the default is `smtp-auth`.
 * - `NEXT_PRIVATE_SMTP_SERVICE` is optional and used specifically for well-known services like Gmail.
 */
const getTransport = (): Transporter => {
  const transport = process.env.NEXT_PRIVATE_SMTP_TRANSPORT ?? 'smtp-auth';

  if (transport === 'mailchannels') {
    return createTransport(
      MailChannelsTransport.makeTransport({
        apiKey: process.env.NEXT_PRIVATE_MAILCHANNELS_API_KEY,
        endpoint: process.env.NEXT_PRIVATE_MAILCHANNELS_ENDPOINT,
      }),
    );
  }

  if (transport === 'resend') {
    return createTransport(
      ResendTransport.makeTransport({
        apiKey: process.env.NEXT_PRIVATE_RESEND_API_KEY || '',
      }),
    );
  }

  if (transport === 'smtp-api') {
    if (!process.env.NEXT_PRIVATE_SMTP_HOST || !process.env.NEXT_PRIVATE_SMTP_APIKEY) {
      throw new Error(
        'SMTP API transport requires NEXT_PRIVATE_SMTP_HOST and NEXT_PRIVATE_SMTP_APIKEY',
      );
    }

    return createTransport({
      host: process.env.NEXT_PRIVATE_SMTP_HOST,
      port: Number(process.env.NEXT_PRIVATE_SMTP_PORT) || 587,
      secure: process.env.NEXT_PRIVATE_SMTP_SECURE === 'true',
      auth: {
        user: process.env.NEXT_PRIVATE_SMTP_APIKEY_USER ?? 'apikey',
        pass: process.env.NEXT_PRIVATE_SMTP_APIKEY ?? '',
      },
    });
  }

  return createTransport({
    host: process.env.NEXT_PRIVATE_SMTP_HOST ?? 'localhost:2500',
    port: Number(process.env.NEXT_PRIVATE_SMTP_PORT) || 587,
    secure: process.env.NEXT_PRIVATE_SMTP_SECURE === 'true',
    ignoreTLS: process.env.NEXT_PRIVATE_SMTP_UNSAFE_IGNORE_TLS === 'true',
    auth: process.env.NEXT_PRIVATE_SMTP_USERNAME
      ? {
          user: process.env.NEXT_PRIVATE_SMTP_USERNAME,
          pass: process.env.NEXT_PRIVATE_SMTP_PASSWORD ?? '',
        }
      : undefined,
    ...(process.env.NEXT_PRIVATE_SMTP_SERVICE
      ? { service: process.env.NEXT_PRIVATE_SMTP_SERVICE }
      : {}),
  });
};

export const mailer = getTransport();