import net from 'node:net';
import { env } from '../config/env.js';

export interface EmailDiagnosticsResult {
  host: string;
  port: number;
  from: string;
  smtpAuth: boolean;
  startTls: boolean;
  usernameConfigured: boolean;
  passwordConfigured: boolean;
  ok: boolean;
  reachable: boolean;
  elapsedMs: number;
  checkedAt: string;
  error: string | null;
}

function mailHost(): string {
  return String(process.env.ACS_MAIL_HOST ?? env.mailHost ?? '').trim();
}

function mailPort(): number {
  const port = Number(process.env.ACS_MAIL_PORT ?? env.mailPort);
  return Number.isFinite(port) && port > 0 ? port : 25;
}

function mailFrom(): string {
  return String(process.env.ACS_MAIL_FROM ?? env.mailFrom ?? '').trim();
}

function mailUsername(): string {
  return String(process.env.ACS_MAIL_USERNAME ?? env.mailUsername ?? '').trim();
}

function mailPassword(): string {
  return String(process.env.ACS_MAIL_PASSWORD ?? env.mailPassword ?? '').trim();
}

function mailSmtpAuth(): boolean {
  return (process.env.ACS_MAIL_SMTP_AUTH ?? String(env.mailSmtpAuth)).toLowerCase() === 'true';
}

function mailStartTls(): boolean {
  return (process.env.ACS_MAIL_STARTTLS ?? String(env.mailStartTls)).toLowerCase() === 'true';
}

function mailTimeoutMs(): number {
  const timeout = Number(process.env.ACS_MAIL_TIMEOUT_MS ?? env.mailTimeoutMs);
  return Number.isFinite(timeout) && timeout > 0 ? timeout : 10000;
}

function result(partial: Partial<EmailDiagnosticsResult>): EmailDiagnosticsResult {
  return {
    host: mailHost(),
    port: mailPort(),
    from: mailFrom(),
    smtpAuth: mailSmtpAuth(),
    startTls: mailStartTls(),
    usernameConfigured: Boolean(mailUsername()),
    passwordConfigured: Boolean(mailPassword()),
    ok: false,
    reachable: false,
    elapsedMs: 0,
    checkedAt: new Date().toISOString(),
    error: null,
    ...partial,
  };
}

function connectSmtp(host: string, port: number, timeoutMs: number): Promise<void> {
  return new Promise((resolve, reject) => {
    const socket = net.createConnection({ host, port });
    let settled = false;

    const finish = (error?: Error) => {
      if (settled) return;
      settled = true;
      socket.destroy();
      if (error) reject(error);
      else resolve();
    };

    socket.setTimeout(timeoutMs);
    socket.once('connect', () => finish());
    socket.once('timeout', () => finish(new Error(`SMTP connection timed out after ${timeoutMs} ms`)));
    socket.once('error', (error) => finish(error));
  });
}

export async function diagnoseEmailConnectivity(): Promise<EmailDiagnosticsResult> {
  const host = mailHost();
  const port = mailPort();
  const startedAt = Date.now();

  if (!host) {
    return result({
      ok: false,
      reachable: false,
      checkedAt: new Date().toISOString(),
      error: 'ACS_MAIL_HOST가 설정되지 않았습니다.',
    });
  }

  try {
    await connectSmtp(host, port, mailTimeoutMs());
    return result({
      ok: true,
      reachable: true,
      elapsedMs: Date.now() - startedAt,
      checkedAt: new Date().toISOString(),
    });
  } catch (error) {
    const message = error instanceof Error ? error.message : String(error);
    return result({
      ok: false,
      reachable: false,
      elapsedMs: Date.now() - startedAt,
      checkedAt: new Date().toISOString(),
      error: message.slice(0, 500),
    });
  }
}