<?php
declare(strict_types=1);

require __DIR__ . '/im_web_bootstrap.php';

const WEB_MEDIA_PROXY_MAX_BYTES = 15 * 1024 * 1024;
const WEB_MEDIA_PROXY_MAX_SECONDS = 25;

function failMediaProxy(int $status, string $message): never
{
    http_response_code($status);
    header('Content-Type: text/plain; charset=utf-8');
    header('Cache-Control: no-store');
    header('X-Content-Type-Options: nosniff');
    echo $message;
    exit;
}

function mediaProxyAllowedHosts(): array
{
    $configured = webImEnv('JC_WEB_IM_MEDIA_PROXY_HOSTS');
    $hosts = array_map(
        static fn(string $host): string => strtolower(rtrim(trim($host), '.')),
        preg_split('/[,\s]+/', $configured) ?: []
    );

    return array_values(array_unique(array_filter($hosts)));
}

function validatedMediaProxyUrl(string $url): array
{
    if ($url === '' || strlen($url) > 2048 || filter_var($url, FILTER_VALIDATE_URL) === false) {
        failMediaProxy(400, '媒体地址不合法');
    }

    $parts = parse_url($url);
    $scheme = strtolower((string)($parts['scheme'] ?? ''));
    $host = strtolower(rtrim((string)($parts['host'] ?? ''), '.'));
    $port = isset($parts['port']) ? (int)$parts['port'] : 443;
    if (
        $scheme !== 'https'
        || $host === ''
        || $port !== 443
        || isset($parts['user'])
        || isset($parts['pass'])
        || !in_array($host, mediaProxyAllowedHosts(), true)
    ) {
        failMediaProxy(403, '媒体来源不允许代理');
    }

    return [$url, $host];
}

function mediaProxyCacheRoot(): string
{
    $root = rtrim(webImEnv('JC_WEB_IM_MEDIA_CACHE_ROOT', '/var/cache/jc-web-im-media'), '/');
    if ($root === '' || !is_dir($root) || !is_writable($root)) {
        failMediaProxy(503, '媒体缓存目录不可用');
    }

    return $root;
}

function mediaProxyPreferredIps(): array
{
    $configured = preg_split('/[,\s]+/', webImEnv('JC_WEB_IM_MEDIA_PROXY_IPS')) ?: [];
    $ips = [];
    foreach ($configured as $ip) {
        $ip = trim($ip);
        if (
            $ip !== ''
            && filter_var(
                $ip,
                FILTER_VALIDATE_IP,
                FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE
            ) !== false
        ) {
            $ips[$ip] = $ip;
        }
    }

    return array_values($ips);
}

function mediaProxyMime(string $path): string
{
    $finfo = finfo_open(FILEINFO_MIME_TYPE);
    $mime = $finfo !== false ? (string)(finfo_file($finfo, $path) ?: '') : '';
    if ($finfo !== false) {
        finfo_close($finfo);
    }

    return $mime;
}

function fetchMediaProxyImage(string $url, string $host, string $cacheFile): void
{
    $deadline = microtime(true) + WEB_MEDIA_PROXY_MAX_SECONDS;
    $lastError = '媒体源无响应';
    $preferredIps = mediaProxyPreferredIps();
    $targets = array_merge($preferredIps, array_fill(0, max(2, 6 - count($preferredIps)), null));

    foreach ($targets as $index => $preferredIp) {
        if (microtime(true) >= $deadline) {
            break;
        }
        $attempt = $index + 1;
        $temporaryFile = $cacheFile . '.tmp.' . getmypid() . '.' . $attempt;
        $stream = @fopen($temporaryFile, 'x+b');
        if ($stream === false) {
            $lastError = '无法创建媒体缓存文件';
            break;
        }

        $bytes = 0;
        $tooLarge = false;
        $curl = curl_init($url);
        if ($curl === false) {
            fclose($stream);
            @unlink($temporaryFile);
            $lastError = '无法初始化媒体请求';
            break;
        }

        $remainingMs = max(1000, (int)floor(($deadline - microtime(true)) * 1000));
        $curlOptions = [
            CURLOPT_RETURNTRANSFER => false,
            CURLOPT_FOLLOWLOCATION => false,
            CURLOPT_CONNECTTIMEOUT_MS => min(2500, $remainingMs),
            CURLOPT_TIMEOUT_MS => min(12000, $remainingMs),
            CURLOPT_NOSIGNAL => true,
            CURLOPT_DNS_CACHE_TIMEOUT => 0,
            CURLOPT_FRESH_CONNECT => true,
            CURLOPT_FORBID_REUSE => true,
            CURLOPT_PROTOCOLS => CURLPROTO_HTTPS,
            CURLOPT_SSL_VERIFYPEER => true,
            CURLOPT_SSL_VERIFYHOST => 2,
            CURLOPT_USERAGENT => 'JC-Web-IM-Media-Proxy/1.0',
            CURLOPT_HTTPHEADER => ['Accept: image/avif,image/webp,image/*,*/*;q=0.8'],
            CURLOPT_WRITEFUNCTION => static function ($handle, string $chunk) use ($stream, &$bytes, &$tooLarge): int {
                $length = strlen($chunk);
                if ($bytes + $length > WEB_MEDIA_PROXY_MAX_BYTES) {
                    $tooLarge = true;
                    return 0;
                }
                $written = fwrite($stream, $chunk);
                if ($written === false) {
                    return 0;
                }
                $bytes += $written;
                return $written;
            },
        ];
        if (is_string($preferredIp) && $preferredIp !== '') {
            $curlOptions[CURLOPT_RESOLVE] = [$host . ':443:' . $preferredIp];
        }
        curl_setopt_array($curl, $curlOptions);

        $result = curl_exec($curl);
        $status = (int)curl_getinfo($curl, CURLINFO_RESPONSE_CODE);
        $curlError = curl_error($curl);
        curl_close($curl);
        fflush($stream);
        fclose($stream);

        $mime = $bytes > 0 && is_file($temporaryFile) ? mediaProxyMime($temporaryFile) : '';
        if ($result !== false && $status >= 200 && $status < 300 && !$tooLarge && str_starts_with($mime, 'image/')) {
            if (!@rename($temporaryFile, $cacheFile)) {
                @unlink($temporaryFile);
                $lastError = '媒体缓存保存失败';
                break;
            }
            @chmod($cacheFile, 0644);
            return;
        }

        @unlink($temporaryFile);
        $lastError = $tooLarge
            ? '图片超过代理大小限制'
            : ($curlError !== '' ? $curlError : ($status > 0 ? '媒体源返回 HTTP ' . $status : '媒体源无响应'));
        if ($attempt < count($targets) && microtime(true) < $deadline) {
            usleep(150000);
        }
    }

    error_log(sprintf('media_proxy fetch failed host=%s error=%s', $host, $lastError));
    failMediaProxy(502, '图片源暂时不可用，请稍后重试');
}

function serveMediaProxyImage(string $cacheFile, string $etag): never
{
    if (!is_file($cacheFile)) {
        failMediaProxy(404, '媒体缓存不存在');
    }
    $mime = mediaProxyMime($cacheFile);
    if (!str_starts_with($mime, 'image/')) {
        failMediaProxy(415, '媒体内容不是图片');
    }

    header('ETag: "' . $etag . '"');
    header('Cache-Control: public, max-age=86400, immutable');
    header('Content-Type: ' . $mime);
    header('Content-Length: ' . (string)filesize($cacheFile));
    header('Content-Disposition: inline');
    header('X-Content-Type-Options: nosniff');
    if (trim((string)($_SERVER['HTTP_IF_NONE_MATCH'] ?? ''), ' W/') === '"' . $etag . '"') {
        http_response_code(304);
        exit;
    }

    readfile($cacheFile);
    exit;
}

[$url, $host] = validatedMediaProxyUrl(trim((string)($_GET['url'] ?? '')));
$cacheRoot = mediaProxyCacheRoot();
$cacheKey = hash('sha256', $url);
$cacheFile = $cacheRoot . '/' . $cacheKey . '.image';
$lockFile = $cacheRoot . '/' . $cacheKey . '.lock';

if (!is_file($cacheFile)) {
    $lock = @fopen($lockFile, 'c');
    if ($lock === false || !flock($lock, LOCK_EX)) {
        if (is_resource($lock)) {
            fclose($lock);
        }
        failMediaProxy(503, '媒体缓存暂时忙碌');
    }
    if (!is_file($cacheFile)) {
        fetchMediaProxyImage($url, $host, $cacheFile);
    }
    flock($lock, LOCK_UN);
    fclose($lock);
}

serveMediaProxyImage($cacheFile, $cacheKey);