import { exec } from "child_process";
import { writeFile, mkdir } from "fs/promises";
import { resolve } from "path";
import nodemailer, { type Transporter } from "nodemailer";
import { Resend } from "resend";
import { env } from "@/env";
import { logger } from "@/lib/logger";

let transporter: Transporter | null = null;
let resend: Resend | null = null;

function getTransport(): Transporter | null {
  if (!env.SMTP_HOST) return null;
  if (!transporter) {
    transporter = nodemailer.createTransport({
      host: env.SMTP_HOST,
      port: env.SMTP_PORT ?? 587,
      secure: env.SMTP_SECURE,
      auth: env.SMTP_USER ? { user: env.SMTP_USER, pass: env.SMTP_PASSWORD } : undefined,
    });
  }
  return transporter;
}

function getResend(): Resend | null {
  if (!env.RESEND_API_KEY) return null;
  if (!resend) resend = new Resend(env.RESEND_API_KEY);
  return resend;
}

function sendViaSendmail(to: string, subject: string, html: string, from: string): Promise<boolean> {
  return new Promise((resolve) => {
    const headers = [
      `From: ${from}`,
      `To: ${to}`,
      `Subject: ${subject}`,
      "MIME-Version: 1.0",
      'Content-Type: text/html; charset="UTF-8"',
    ].join("\r\n");

    const child = exec("sendmail -t", (error) => {
      if (error) {
        logger.error("Sendmail failed", { module: "email", error: error.message });
        resolve(false);
      } else {
        resolve(true);
      }
    });

    if (child.stdin) {
      child.stdin.write(`${headers}\r\n\r\n${html}`);
      child.stdin.end();
    }
  });
}

async function writeToFile(to: string, subject: string, html: string, from: string): Promise<boolean> {
  try {
    const logDir = resolve(process.cwd(), "storage", "logs");
    // eslint-disable-next-line security/detect-non-literal-fs-filename
    await mkdir(logDir, { recursive: true });
    const timestamp = new Date().toISOString().replace(/[:.]/g, "-");
    const filename = `email-${timestamp}.html`;
    const content = `<!-- To: ${to} | From: ${from} | Subject: ${subject} -->\n${html}`;
    // eslint-disable-next-line security/detect-non-literal-fs-filename
    await writeFile(resolve(logDir, filename), content, "utf-8");
    logger.info("Email written to file", { module: "email", filename });
    return true;
  } catch (e) {
    logger.error("Failed to write email to file", { module: "email", error: (e as Error).message });
    return false;
  }
}

/** Send an HTML email. Tries Resend → SMTP → local sendmail → file fallback. Always returns true. */
export async function sendMail(to: string, subject: string, html: string): Promise<boolean> {
  const from = env.SMTP_FROM ?? `no-reply@${env.HOTEL_NAME}`;

  const r = getResend();
  if (r) {
    try {
      await r.emails.send({ from, to, subject, html });
      return true;
    } catch (e) {
      logger.error("Resend API failed", { module: "email", error: (e as Error).message });
    }
  }

  const t = getTransport();
  if (t) {
    try {
      await t.sendMail({ from, to, subject, html });
      return true;
    } catch (e) {
      logger.error("SMTP failed", { module: "email", error: (e as Error).message });
    }
  }

  const ok = await sendViaSendmail(to, subject, html, from);
  if (ok) return true;

  await writeToFile(to, subject, html, from);
  return true;
}