<?php declare(strict_types=1);
/**
 * hcl-catalog-serve.php
 *
 * Serves the pre-generated catalog.json to HC Launcher clients.
 *
 * Responsibilities:
 *   - Anonymous access metrics (IP, launcher version, timestamp → access log)
 *   - Simple file-based rate limiting (60 req/hour per anonymized IP)
 *   - HTTP conditional GET (If-Modified-Since / 304 Not Modified)
 *   - Appropriate cache headers (Cache-Control: public, max-age=900)
 *
 * Configuration:
 *   Set the CONFIG_PATH constant below, or define the HC_LAUNCHER_CONFIG
 *   environment variable to point to your hcl-config.php outside the web root.
 *
 * Deploy note:
 *   In production, point a web server rewrite rule at this file, e.g.
 *     /hcl/catalog.json  →  hcl-catalog-serve.php
 */

// ---------------------------------------------------------------------------
// Configuration
// ---------------------------------------------------------------------------

// Allow the config path to be overridden by an environment variable so that
// hcl-config.php can live outside the web root without touching this file.
$configPath = getenv('HC_LAUNCHER_CONFIG') ?: (__DIR__ . '/../../safePHP/hcl-config.php');

if (!is_file($configPath)) {
    http_response_code(500);
    header('Content-Type: text/plain');
    exit("Server configuration error.\n");
}

/** @var array<string,mixed> $cfg */
$cfg = require $configPath;

$outputDir = rtrim((string)($cfg['output_dir'] ?? __DIR__), '/\\');
$cacheDir  = rtrim((string)($cfg['cache_dir']  ?? $outputDir . '/cache'), '/\\');

$catalogPath  = $outputDir . '/catalog.json';
$accessLog    = $outputDir . '/hcl-catalog-access.log';
$rateLimitDir = $cacheDir;  // rate-limit files live alongside other cache files

if (!is_dir($rateLimitDir)) {
    mkdir($rateLimitDir, 0755, true);
}

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

/**
 * Return the client IP address, with the last octet zeroed for IPv4 privacy
 * (IPv6 last 80 bits zeroed).  Never returns an empty string.
 *
 * @return string  e.g. "203.0.113.0" or "2001:db8::"
 */
function anonymizeIp(): string
{
    $ip = $_SERVER['REMOTE_ADDR'] ?? '0.0.0.0';

    if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4)) {
        // Zero the last octet.
        $parts    = explode('.', $ip);
        $parts[3] = '0';
        return implode('.', $parts);
    }

    if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6)) {
        // Expand, zero last 80 bits (last 5 groups of 4 hex digits).
        $expanded = expandIPv6($ip);
        if ($expanded !== null) {
            $groups = explode(':', $expanded);
            for ($i = 3; $i < 8; $i++) {
                $groups[$i] = '0000';
            }
            return implode(':', $groups);
        }
    }

    return $ip;
}

/**
 * Expand a compressed IPv6 address to its full 8-group form.
 *
 * @param  string $ip
 * @return string|null  null if not a valid IPv6 address.
 */
function expandIPv6(string $ip): ?string
{
    $bin = inet_pton($ip);
    if ($bin === false) {
        return null;
    }
    $hex    = bin2hex($bin);
    $groups = str_split($hex, 4);
    return implode(':', $groups);
}

/**
 * Derive a filesystem-safe token from an anonymized IP (SHA-256, first 16 hex).
 *
 * @param  string $anonIp
 * @return string
 */
function ipHash(string $anonIp): string
{
    return substr(hash('sha256', $anonIp), 0, 16);
}

/**
 * Determine the launcher version string from request headers.
 *
 * HC Launcher sends either:
 *   X-HCL-Version: 2025.024
 * or embeds the version in the User-Agent:
 *   HCLauncher/2025.024 ...
 *
 * Falls back to the raw User-Agent if neither pattern matches.
 *
 * @return string
 */
function launcherVersion(): string
{
    $xVersion = $_SERVER['HTTP_X_HCL_VERSION'] ?? '';
    if ($xVersion !== '') {
        return $xVersion;
    }

    $ua = $_SERVER['HTTP_USER_AGENT'] ?? '';
    if (preg_match('/HCLauncher\/(\S+)/i', $ua, $m)) {
        return $m[1];
    }

    return '';
}

// ---------------------------------------------------------------------------
// Metrics: access log
// ---------------------------------------------------------------------------

$anonIp    = anonymizeIp();
$version   = launcherVersion();
$userAgent = $_SERVER['HTTP_USER_AGENT'] ?? '';
$timestamp = gmdate('Y-m-d\TH:i:s\Z');

// Sanitize fields before writing to the log (strip tabs and newlines).
$logVersion   = str_replace(["\t", "\n", "\r"], ' ', $version);
$logUserAgent = str_replace(["\t", "\n", "\r"], ' ', $userAgent);

$logLine = "{$timestamp}\t{$anonIp}\t{$logVersion}\t{$logUserAgent}\n";
file_put_contents($accessLog, $logLine, FILE_APPEND | LOCK_EX);

// ---------------------------------------------------------------------------
// Rate limiting (60 requests per hour, file-based)
// ---------------------------------------------------------------------------

$ipHashStr    = ipHash($anonIp);
$rateLimitFile = "{$rateLimitDir}/rate_{$ipHashStr}.txt";
$rateWindow   = 3600; // seconds
$rateLimit    = 60;   // max requests per window
$now          = time();

/** @var int[] $requestTimes */
$requestTimes = [];

if (is_file($rateLimitFile)) {
    $raw = file_get_contents($rateLimitFile);
    if ($raw !== false) {
        $requestTimes = array_map('intval', array_filter(explode("\n", trim($raw))));
    }
}

// Discard timestamps outside the current window.
$requestTimes = array_values(array_filter($requestTimes, fn(int $t) => ($now - $t) < $rateWindow));

if (count($requestTimes) >= $rateLimit) {
    $oldestInWindow = min($requestTimes);
    $retryAfter     = $rateWindow - ($now - $oldestInWindow);
    http_response_code(429);
    header('Content-Type: text/plain');
    header("Retry-After: {$retryAfter}");
    exit("Too Many Requests. Please retry after {$retryAfter} seconds.\n");
}

// Record this request.
$requestTimes[] = $now;
file_put_contents($rateLimitFile, implode("\n", $requestTimes) . "\n", LOCK_EX);

// ---------------------------------------------------------------------------
// Verify catalog exists
// ---------------------------------------------------------------------------

if (!is_file($catalogPath)) {
    http_response_code(503);
    header('Content-Type: text/plain');
    header('Retry-After: 900');
    exit("Catalog not yet generated. Please try again shortly.\n");
}

$mtime = filemtime($catalogPath);
if ($mtime === false) {
    http_response_code(500);
    header('Content-Type: text/plain');
    exit("Could not stat catalog file.\n");
}

// ---------------------------------------------------------------------------
// Conditional GET (If-Modified-Since → 304)
// ---------------------------------------------------------------------------

$lastModifiedStr = gmdate('D, d M Y H:i:s', $mtime) . ' GMT';

if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
    $ifModifiedSince = strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']);
    if ($ifModifiedSince !== false && $mtime <= $ifModifiedSince) {
        http_response_code(304);
        header("Last-Modified: {$lastModifiedStr}");
        exit;
    }
}

// ---------------------------------------------------------------------------
// Serve catalog.json
// ---------------------------------------------------------------------------

$body = file_get_contents($catalogPath);
if ($body === false) {
    http_response_code(500);
    header('Content-Type: text/plain');
    exit("Could not read catalog file.\n");
}

header('Content-Type: application/json');
header("Last-Modified: {$lastModifiedStr}");
header('Cache-Control: public, max-age=900');   // clients may cache for 15 min
header('Content-Length: ' . strlen($body));

echo $body;