<?php
// 纯 PHP socket 实现的 SMTP 发信类，无需 Composer / PHPMailer。
// 支持 SSL（465）与 STARTTLS（587）以及无加密，使用 AUTH LOGIN 鉴权。
if (!defined('IN_APP')) {
    http_response_code(403);
    exit('Forbidden');
}

class SmtpMailer
{
    public $log = [];
    public $lastError = '';

    private $host;
    private $port;
    private $enc;   // '' | 'ssl' | 'tls'
    private $user;
    private $pass;

    public function __construct($host, $port, $enc, $user, $pass)
    {
        $this->host = (string) $host;
        $this->port = (int) $port;
        $this->enc  = (string) $enc;
        $this->user = (string) $user;
        $this->pass = (string) $pass;
    }

    /**
     * 发送邮件。
     * @param string $to        收件人，多个用逗号分隔
     * @param string $subject   主题
     * @param string $bodyHtml  正文（HTML）
     * @param string $fromEmail 发件人邮箱
     * @param string $fromName  发件人名称
     * @return bool
     */
    public function send($to, $subject, $bodyHtml, $fromEmail, $fromName)
    {
        if ($this->host === '') {
            $this->lastError = 'SMTP 主机未配置';
            return false;
        }
        $port = $this->port ?: ($this->enc === 'ssl' ? 465 : 587);
        $timeout = 20;
        $scheme = $this->enc === 'ssl' ? 'ssl' : 'tcp';
        $opts = [];
        if ($this->enc === 'ssl' || $this->enc === 'tls') {
            $opts['ssl'] = [
                'verify_peer'       => false,
                'verify_peer_name'   => false,
                'allow_self_signed'  => true,
            ];
        }
        $ctx = $opts ? stream_context_create($opts) : null;

        $errno = 0;
        $errstr = '';
        $sock = @stream_socket_client(
            $scheme . '://' . $this->host . ':' . $port,
            $errno, $errstr, $timeout, STREAM_CLIENT_CONNECT, $ctx
        );
        if (!$sock) {
            $this->lastError = "无法连接 SMTP 服务器（{$this->host}:{$port}）：$errstr ($errno)";
            return false;
        }
        stream_set_timeout($sock, $timeout);

        // 读取服务商标语 220
        if ($this->talk($sock, null, [220]) === false) {
            fclose($sock);
            return false;
        }

        $hostHeader = isset($_SERVER['HTTP_HOST']) ? $_SERVER['HTTP_HOST'] : 'localhost';

        // EHLO
        if ($this->talk($sock, 'EHLO ' . $hostHeader, [250]) === false) {
            fclose($sock);
            return false;
        }

        // STARTTLS 协商
        if ($this->enc === 'tls') {
            if ($this->talk($sock, 'STARTTLS', [220]) === false) {
                fclose($sock);
                return false;
            }
            if (!@stream_socket_enable_crypto($sock, true, STREAM_CRYPTO_METHOD_TLS_CLIENT)) {
                $this->lastError = 'STARTTLS 加密协商失败';
                fclose($sock);
                return false;
            }
            if ($this->talk($sock, 'EHLO ' . $hostHeader, [250]) === false) {
                fclose($sock);
                return false;
            }
        }

        // AUTH LOGIN
        if ($this->talk($sock, 'AUTH LOGIN', [334]) === false) {
            fclose($sock);
            return false;
        }
        if ($this->talk($sock, base64_encode($this->user), [334]) === false) {
            fclose($sock);
            return false;
        }
        if ($this->talk($sock, base64_encode($this->pass), [235]) === false) {
            fclose($sock);
            return false;
        }

        // 信封
        if ($this->talk($sock, 'MAIL FROM:<' . $fromEmail . '>', [250]) === false) {
            fclose($sock);
            return false;
        }
        $recipients = array_filter(array_map('trim', explode(',', $to)));
        foreach ($recipients as $rcpt) {
            $this->talk($sock, 'RCPT TO:<' . $rcpt . '>', [250, 251]);
        }

        // 信体
        if ($this->talk($sock, 'DATA', [354]) === false) {
            fclose($sock);
            return false;
        }
        $data = $this->buildData($to, $subject, $bodyHtml, $fromEmail, $fromName);
        fwrite($sock, $data);
        if ($this->talk($sock, '.', [250]) === false) {
            fclose($sock);
            return false;
        }
        $this->talk($sock, 'QUIT', [221]);
        fclose($sock);
        return true;
    }

    private function buildData($to, $subject, $body, $fromEmail, $fromName)
    {
        $eol = "\r\n";
        $headers = [];
        $headers[] = 'From: ' . $this->encodeHeader($fromName) . ' <' . $fromEmail . '>';
        $headers[] = 'To: ' . $to;
        $headers[] = 'Subject: ' . $this->encodeHeader($subject);
        $headers[] = 'Date: ' . date('r');
        $headers[] = 'MIME-Version: 1.0';
        $headers[] = 'Content-Type: text/html; charset=UTF-8';
        $headers[] = 'Content-Transfer-Encoding: base64';
        $msg = implode($eol, $headers) . $eol . $eol;
        $msg .= chunk_split(base64_encode($body), 76, $eol);
        return $msg;
    }

    private function encodeHeader($s)
    {
        if (preg_match('/[^\x00-\x7F]/', (string) $s)) {
            return '=?UTF-8?B?' . base64_encode($s) . '?=';
        }
        return $s;
    }

    /**
     * 与服务器交互：发送命令并读取响应。
     * @param resource $sock
     * @param string|null $cmd    为 null 时仅读取（用于读取初始标语）
     * @param array $expectCodes   期望的状态码数组
     * @return string|false
     */
    private function talk($sock, $cmd, $expectCodes)
    {
        if ($cmd !== null) {
            fwrite($sock, $cmd . "\r\n");
            $this->log[] = 'C: ' . $cmd;
        }
        $resp = '';
        while (true) {
            $line = @fgets($sock, 515);
            if ($line === false) {
                break;
            }
            $resp .= $line;
            // 末位第 4 个字符为空格表示响应结束（多行响应以 "- " 续接）
            if (isset($line[3]) && $line[3] === ' ') {
                break;
            }
        }
        $this->log[] = 'S: ' . trim($resp);
        $code = (int) substr($resp, 0, 3);
        if (!in_array($code, (array) $expectCodes, true)) {
            $this->lastError = '服务器返回错误：' . trim($resp);
            return false;
        }
        return $resp;
    }
}