<?php
/**
 * 图片代理与缓存系统
 * 
 * 提供安全的图片代理和缓存服务，支持多种图片格式，具有完善的错误处理和日志记录功能
 */
class ImageProxy {
    // 支持的图片类型
    private const SUPPORTED_TYPES = [
        'gif' => 'image/gif',
        'jpeg' => 'image/jpeg',
        'jpg' => 'image/jpeg',
        'jpe' => 'image/jpeg',
        'png' => 'image/png',
        'webp' => 'image/webp',
        'bmp' => 'image/bmp',
        'svg' => 'image/svg+xml'
    ];

    // 默认配置
    private const DEFAULT_CONFIG = [
        'cache_dir' => 'cache',
        'timeout' => 30,
        'connect_timeout' => 15,
        'max_redirects' => 5,
        'user_agent' => 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36'
    ];

    private $config;
    private $logger;

    /**
     * 构造函数
     * 
     * @param array $config 配置参数
     */
    public function __construct(array $config = []) {
        $this->config = array_merge(self::DEFAULT_CONFIG, $config);
        $this->initCacheDir();
        $this->initLogger();
    }

    /**
     * 初始化缓存目录
     */
    private function initCacheDir() {
        if (!file_exists($this->config['cache_dir'])) {
            mkdir($this->config['cache_dir'], 0755, true);
        }
    }

    /**
     * 初始化日志记录器
     */
    private function initLogger() {
        $logDir = $this->config['cache_dir'] . '/logs';
        if (!file_exists($logDir)) {
            mkdir($logDir, 0755, true);
        }
        $this->logger = new Logger($logDir);
    }

    /**
     * 处理图片请求
     * 
     * @param string $url 图片URL
     * @return void
     */
    public function processRequest(string $url) {
        try {
            if (!$this->validateUrl($url)) {
                throw new Exception('Invalid URL format');
            }

            $cachePath = $this->getCachePath($url);
            
            // 检查缓存
            if ($this->isCached($cachePath)) {
                $this->serveFromCache($cachePath);
                return;
            }

            // 获取远程图片
            $imageData = $this->fetchRemoteImage($url);
            
            // 验证图片数据
            if (!$this->validateImageData($imageData)) {
                throw new Exception('Invalid image data');
            }

            // 保存到缓存
            $this->saveToCache($cachePath, $imageData);
            
            // 输出图片
            $this->outputImage($imageData, $this->getImageType($url));
        } catch (Exception $e) {
            $this->logger->error('Image processing error: ' . $e->getMessage());
            $this->outputError();
        }
    }

    /**
     * 验证URL格式
     * 
     * @param string $url URL地址
     * @return bool
     */
    private function validateUrl(string $url): bool {
        return filter_var($url, FILTER_VALIDATE_URL) !== false && 
               preg_match('/^https?:\/\//i', $url);
    }

    /**
     * 获取缓存路径
     * 
     * @param string $url 图片URL
     * @return string
     */
    private function getCachePath(string $url): string {
        $parsedUrl = parse_url($url);
        $domain = $parsedUrl['host'];
        $path = $parsedUrl['path'];
        
        $cacheSubDir = $this->config['cache_dir'] . '/' . $domain;
        if (!file_exists($cacheSubDir)) {
            mkdir($cacheSubDir, 0755, true);
        }
        
        return $cacheSubDir . '/' . md5($url) . '.' . pathinfo($path, PATHINFO_EXTENSION);
    }

    /**
     * 检查图片是否已缓存
     * 
     * @param string $cachePath 缓存路径
     * @return bool
     */
    private function isCached(string $cachePath): bool {
        return file_exists($cachePath) && 
               (time() - filemtime($cachePath)) < 86400; // 缓存24小时
    }

    /**
     * 从缓存输出图片
     * 
     * @param string $cachePath 缓存路径
     */
    private function serveFromCache(string $cachePath) {
        $type = $this->getImageType($cachePath);
        header("Content-type: " . $type);
        readfile($cachePath);
    }

    /**
     * 获取远程图片
     * 
     * @param string $url 图片URL
     * @return string
     */
    private function fetchRemoteImage(string $url): string {
        $ch = curl_init($url);
        curl_setopt_array($ch, [
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_FOLLOWLOCATION => true,
            CURLOPT_MAXREDIRS => $this->config['max_redirects'],
            CURLOPT_CONNECTTIMEOUT => $this->config['connect_timeout'],
            CURLOPT_TIMEOUT => $this->config['timeout'],
            CURLOPT_SSL_VERIFYPEER => true,
            CURLOPT_SSL_VERIFYHOST => 2,
            CURLOPT_USERAGENT => $this->config['user_agent'],
            CURLOPT_REFERER => parse_url($url, PHP_URL_SCHEME) . '://' . parse_url($url, PHP_URL_HOST) . '/',
            CURLOPT_HTTPHEADER => ['Accept: image/*']
        ]);

        $data = curl_exec($ch);
        $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        curl_close($ch);

        if ($httpCode !== 200 || empty($data)) {
            throw new Exception('Failed to fetch image: HTTP ' . $httpCode);
        }

        return $data;
    }

    /**
     * 验证图片数据
     * 
     * @param string $data 图片数据
     * @return bool
     */
    private function validateImageData(string $data): bool {
        if (empty($data)) {
            return false;
        }

        // 检查文件头
        $headers = [
            'image/jpeg' => "\xFF\xD8\xFF",
            'image/png' => "\x89PNG\r\n\x1a\n",
            'image/gif' => "GIF",
            'image/webp' => "RIFF....WEBP",
            'image/bmp' => "BM",
            'image/svg+xml' => '<?xml'
        ];

        foreach ($headers as $type => $header) {
            if (strpos($data, $header) === 0) {
                return true;
            }
        }

        return false;
    }

    /**
     * 保存到缓存
     * 
     * @param string $cachePath 缓存路径
     * @param string $data 图片数据
     */
    private function saveToCache(string $cachePath, string $data) {
        file_put_contents($cachePath, $data);
    }

    /**
     * 输出图片
     * 
     * @param string $data 图片数据
     * @param string $type 图片类型
     */
    private function outputImage(string $data, string $type) {
        header("Content-type: " . $type);
        header("Cache-Control: public, max-age=86400");
        echo $data;
    }

    /**
     * 获取图片类型
     * 
     * @param string $url 图片URL
     * @return string
     */
    private function getImageType(string $url): string {
        $ext = strtolower(pathinfo($url, PATHINFO_EXTENSION));
        return self::SUPPORTED_TYPES[$ext] ?? 'image/jpeg';
    }

    /**
     * 输出错误信息
     */
    private function outputError() {
        header("HTTP/1.1 500 Internal Server Error");
        header("Content-type: image/jpeg");
        // 输出一个1x1的透明图片
        echo base64_decode('R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7');
    }
}

/**
 * 简单的日志记录类
 */
class Logger {
    private $logDir;

    public function __construct(string $logDir) {
        $this->logDir = $logDir;
    }

    public function error(string $message) {
        $this->log('ERROR', $message);
    }

    public function info(string $message) {
        $this->log('INFO', $message);
    }

    private function log(string $level, string $message) {
        $date = date('Y-m-d');
        $time = date('Y-m-d H:i:s');
        $logFile = $this->logDir . "/{$date}.log";
        
        $logMessage = "[{$time}] [{$level}] {$message}\n";
        file_put_contents($logFile, $logMessage, FILE_APPEND);
    }
}