<?php
/**
 * SMTP服务器核心类
 */
require_once __DIR__ . '/../utils/Config.php';
require_once __DIR__ . '/../utils/Logger.php';
require_once __DIR__ . '/SmtpHandler.php';

class SmtpServer {
    private $host;
    private $port;
    private $maxConnections;
    private $socket;
    private $connections = [];
    private $logger;
    private $config;
    
    /**
     * 构造函数
     * @param string $host 监听地址
     * @param int $port 监听端口
     * @param int $maxConnections 最大连接数
     */
    public function __construct($host = '0.0.0.0', $port = 25, $maxConnections = 100) {
        $this->config = Config::getInstance();
        $this->host = $host;
        $this->port = $port;
        $this->maxConnections = $maxConnections;
        
        // 初始化日志记录器
        $logPath = $this->config->get('log.path', '../logs/');
        $logLevel = $this->config->get('log.level', 'info');
        $this->logger = new Logger($logPath, $logLevel);
    }
    
    /**
     * 启动SMTP服务器
     * @return bool 是否启动成功
     */
    public function start() {
        // 创建socket
        $this->socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
        if ($this->socket === false) {
            $this->logger->error("Failed to create socket: " . socket_strerror(socket_last_error()));
            return false;
        }
        
        // 设置socket选项
        socket_set_option($this->socket, SOL_SOCKET, SO_REUSEADDR, 1);
        
        // 绑定地址和端口
        if (!socket_bind($this->socket, $this->host, $this->port)) {
            $this->logger->error("Failed to bind socket: " . socket_strerror(socket_last_error($this->socket)));
            socket_close($this->socket);
            return false;
        }
        
        // 开始监听，提高监听队列长度
        $backlog = $this->config->get('smtp.backlog', 50);
        if (!socket_listen($this->socket, $backlog)) {
            $this->logger->error("Failed to listen on socket: " . socket_strerror(socket_last_error($this->socket)));
            socket_close($this->socket);
            return false;
        }
        
        $this->logger->info("SMTP server started on {host}:{port}", ['host' => $this->host, 'port' => $this->port]);
        
        // 主循环，处理连接
        while (true) {
            // 处理客户端连接和请求
            $this->handleConnections();
        }
        
        return true;
    }
    
    /**
     * 停止SMTP服务器
     */
    public function stop() {
        // 关闭所有客户端连接
        foreach ($this->connections as $connection) {
            socket_close($connection['socket']);
        }
        
        // 关闭服务器socket
        if ($this->socket) {
            socket_close($this->socket);
        }
        
        $this->logger->info("SMTP server stopped");
    }
    
    /**
     * 处理客户端请求
     */
    private function handleConnections() {
        // 检查是否有客户端数据可读
        $readSockets = array_column($this->connections, 'socket');
        $readSockets[] = $this->socket;
        $writeSockets = null;
        $exceptSockets = null;
        
        $activity = socket_select($readSockets, $writeSockets, $exceptSockets, 1);
        if ($activity === false) {
            $this->logger->error("Socket select error: " . socket_strerror(socket_last_error()));
            return;
        }
        
        // 处理可读的socket
        foreach ($readSockets as $socket) {
            // 如果是服务器socket，接受新连接
            if ($socket === $this->socket) {
                $this->acceptNewConnection();
            } else {
                // 处理客户端请求
                $this->handleClientRequest($socket);
            }
        }
        
        // 清理超时连接
        $this->cleanupTimeoutConnections();
    }
    
    /**
     * 接受新连接
     */
    private function acceptNewConnection() {
        // 检查连接数是否超过最大值
        if (count($this->connections) >= $this->maxConnections) {
            $this->logger->warning("Maximum connections reached: {max}", ['max' => $this->maxConnections]);
            return;
        }
        
        // 接受新连接
        $clientSocket = socket_accept($this->socket);
        if ($clientSocket === false) {
            $this->logger->error("Failed to accept connection: " . socket_strerror(socket_last_error($this->socket)));
            return;
        }
        
        // 获取客户端信息
        socket_getpeername($clientSocket, $clientIp, $clientPort);
        $this->logger->info("New connection from {ip}:{port}", ['ip' => $clientIp, 'port' => $clientPort]);
        
        // 添加到连接列表
        $connectionId = uniqid();
        $socketKey = (int)$clientSocket;
        $this->connections[$connectionId] = [
            'socket' => $clientSocket,
            'ip' => $clientIp,
            'port' => $clientPort,
            'handler' => new SmtpHandler($clientSocket, $clientIp, $this->logger),
            'lastActivity' => time()
        ];
        
        // 维护socket到connectionId的映射
        static $socketToConnection = [];
        $socketToConnection[$socketKey] = $connectionId;
        
        // 发送欢迎消息
        $welcomeMsg = "220 {domain} ESMTP Service Ready\r\n";
        socket_write($clientSocket, $welcomeMsg, strlen($welcomeMsg));
    }
    
    /**
     * 处理客户端请求
     * @param resource $socket 客户端socket
     */
    private function handleClientRequest($socket) {
        // 优化：使用socket资源作为键直接查找
        // 在acceptNewConnection中维护socket到connectionId的映射
        $socketKey = (int)$socket;
        static $socketToConnection = [];
        
        // 初始化映射表（如果为空）
        if (empty($socketToConnection) && !empty($this->connections)) {
            foreach ($this->connections as $id => $connection) {
                $socketToConnection[(int)$connection['socket']] = $id;
            }
        }
        
        // 查找对应的连接
        if (!isset($socketToConnection[$socketKey])) {
            // 重建映射表并再次查找
            $socketToConnection = [];
            foreach ($this->connections as $id => $connection) {
                $socketToConnection[(int)$connection['socket']] = $id;
            }
            
            if (!isset($socketToConnection[$socketKey])) {
                return;
            }
        }
        
        $connectionId = $socketToConnection[$socketKey];
        
        // 读取客户端数据
        $data = socket_read($socket, 1024);
        if ($data === false) {
            $this->logger->error("Failed to read from socket: " . socket_strerror(socket_last_error($socket)));
            $this->closeConnection($connectionId);
            return;
        }
        
        // 如果客户端关闭连接
        if (empty($data)) {
            $this->logger->info("Connection closed by client: {ip}:{port}", [
                'ip' => $this->connections[$connectionId]['ip'],
                'port' => $this->connections[$connectionId]['port']
            ]);
            $this->closeConnection($connectionId);
            return;
        }
        
        // 更新最后活动时间
        $this->connections[$connectionId]['lastActivity'] = time();
        
        // 处理数据
        $this->connections[$connectionId]['handler']->handle($data);
    }
    
    /**
     * 关闭客户端连接
     * @param string $connectionId 连接ID
     */
    private function closeConnection($connectionId) {
        if (isset($this->connections[$connectionId])) {
            $socket = $this->connections[$connectionId]['socket'];
            $socketKey = (int)$socket;
            
            // 从映射表中移除
            static $socketToConnection = [];
            if (isset($socketToConnection[$socketKey])) {
                unset($socketToConnection[$socketKey]);
            }
            
            socket_close($socket);
            unset($this->connections[$connectionId]);
        }
    }
    
    /**
     * 清理超时连接
     */
    private function cleanupTimeoutConnections() {
        $timeout = 300; // 5分钟超时
        $now = time();
        
        foreach ($this->connections as $id => $connection) {
            if ($now - $connection['lastActivity'] > $timeout) {
                $this->logger->info("Connection timed out: {ip}:{port}", [
                    'ip' => $connection['ip'],
                    'port' => $connection['port']
                ]);
                $this->closeConnection($id);
            }
        }
    }
}