import fs from 'fs';
import nodemailer from 'nodemailer';
import type SMTPTransport from 'nodemailer/lib/smtp-transport';
import path from 'path';

type MailOptions = {
  to: string;
  subject: string;
  text: string;
  html?: string;
};

async function createTransport() {
  const {
    SMTP_HOST,
    SMTP_PORT,
    SMTP_USER,
    SMTP_PASS,
    SMTP_FROM,
    SMTP_TLS,
    SMTP_SSL,
    SMTP_REJECT_UNAUTHORIZED,
    DKIM_SELECTOR,
    DKIM_DOMAIN,
    DKIM_PRIVATE_KEY_PATH,
  } = process.env;

  if (!SMTP_HOST || !SMTP_PORT || !SMTP_USER || !SMTP_PASS || !SMTP_FROM) {
    throw new Error('SMTP configuration is missing required environment variables');
  }

  const secure = SMTP_SSL === 'true';
  const requireTLS = SMTP_TLS === 'true';

  const transporterOptions: SMTPTransport.Options = {
    host: SMTP_HOST,
    port: Number(SMTP_PORT),
    secure,
    requireTLS,
    auth: { user: SMTP_USER, pass: SMTP_PASS },
  };

  if (SMTP_REJECT_UNAUTHORIZED === 'false') {
    transporterOptions.tls = { rejectUnauthorized: false };
  }

  if (DKIM_SELECTOR && DKIM_DOMAIN && DKIM_PRIVATE_KEY_PATH) {
    const keyPath = path.resolve(process.cwd(), DKIM_PRIVATE_KEY_PATH);
    if (fs.existsSync(keyPath)) {
      transporterOptions.dkim = {
        domainName: DKIM_DOMAIN,
        keySelector: DKIM_SELECTOR,
        privateKey: fs.readFileSync(keyPath, 'utf8'),
      };
    }
  }

  return nodemailer.createTransport(transporterOptions);
}

let cachedTransport: nodemailer.Transporter | null = null;

async function getTransport() {
  if (cachedTransport) return cachedTransport;
  cachedTransport = await createTransport();
  return cachedTransport;
}

export async function sendMail({ to, subject, text, html }: MailOptions) {
  const transporter = await getTransport();
  const from = process.env.SMTP_FROM!;
  return transporter.sendMail({ from, to, subject, text, html: html ?? text });
}

export async function sendVerificationEmail(to: string, link: string) {
  const subject = 'Verify your email for lomavuokraus.fi';
  const text = `Please verify your email by visiting: ${link}\n\nIf you did not request this, you can ignore this email.`;
  const html = `<p>Please verify your email by clicking <a href="${link}">this link</a>.</p><p>If you did not request this, you can ignore this email.</p>`;
  return sendMail({ to, subject, text, html });
}