<?php
declare(strict_types=1);

/**
 * Shared release scanning for the download page and the latest-build endpoint.
 *
 * Expected file names under bin/<kind>/ (anything else is ignored):
 *
 *   bin/gui/zagan-bet-gui-<version>-<platform>-<arch>[.exe]
 *   bin/client/zagan-bet-client-<version>-<platform>-<arch>[.exe]
 *   bin/server/zagan-bet-server-<version>-<platform>-<arch>[.exe]
 *
 * <version> is MAJOR.MINOR.PATCH, <platform> is linux|windows|macos and
 * <arch> is x86_64|i686|aarch64.
 *
 * SHA-256 values are cached in a JSON file keyed on size and mtime, so a file
 * is only re-read when it changes. The cache lives in the system temp
 * directory by default (the web root is often not writable by the PHP user);
 * set ZAGAN_HASH_CACHE to put it somewhere else.
 */

const KINDS = [
    'gui' => [
        'title' => 'Desktop app',
        'hint' => 'Windows 10 or newer, or a Linux desktop. No terminal needed.',
    ],
    'client' => [
        'title' => 'Client',
        'hint' => 'Needs a terminal of at least 80×24 cells.',
    ],
    'server' => [
        'title' => 'Server',
        'hint' => 'Generates its own TLS identity on first run.',
    ],
];

const PLATFORMS = [
    'linux' => 'Linux',
    'windows' => 'Windows',
    'macos' => 'macOS',
];

const ARCHES = [
    'x86_64' => '64-bit',
    'i686' => '32-bit',
    'aarch64' => 'ARM64',
];

// Newest version first, then 64-bit builds before 32-bit.
const PLATFORM_ORDER = ['linux' => 0, 'windows' => 1, 'macos' => 2];
const ARCH_ORDER = ['x86_64' => 0, 'aarch64' => 1, 'i686' => 2];

/**
 * Hash to use for a published file, reusing the cached value when the file has
 * not changed since it was hashed.
 *
 * A cached hash is valid only when the size and mtime still match and the hash
 * was taken at or after the file's mtime, so a restored or touched file is
 * re-read.
 *
 * @param array{files:array<string,array{size:int,mtime:int,sha256:string,hashed_at:int}>} $cache
 */
function cached_hash(
    string $key,
    string $path,
    int $size,
    int $mtime,
    array &$cache,
    bool &$dirty
): ?string {
    $entry = $cache['files'][$key] ?? null;
    if (
        is_array($entry)
        && ($entry['size'] ?? null) === $size
        && ($entry['mtime'] ?? null) === $mtime
        && (int) ($entry['hashed_at'] ?? 0) >= $mtime
        && isset($entry['sha256'])
        && is_string($entry['sha256'])
        && preg_match('/\A[0-9a-f]{64}\z/', $entry['sha256']) === 1
    ) {
        return $entry['sha256'];
    }

    $hash = hash_file('sha256', $path);
    if ($hash === false) {
        return null;
    }

    $cache['files'][$key] = [
        'size' => $size,
        'mtime' => $mtime,
        'sha256' => $hash,
        'hashed_at' => time(),
    ];
    $dirty = true;

    return $hash;
}

/** @return array{files:array<string,array{size:int,mtime:int,sha256:string,hashed_at:int}>} */
function load_hash_cache(string $path): array
{
    $raw = @file_get_contents($path);
    if ($raw === false || $raw === '') {
        return ['files' => []];
    }
    $decoded = json_decode($raw, true);
    if (!is_array($decoded) || !isset($decoded['files']) || !is_array($decoded['files'])) {
        return ['files' => []];
    }

    return ['files' => $decoded['files']];
}

/**
 * Best effort: a read-only web root, a full disk or a racing writer must never
 * break the page, so failures are ignored and the next request recomputes.
 *
 * @param array{files:array<string,array{size:int,mtime:int,sha256:string,hashed_at:int}>} $cache
 */
function save_hash_cache(string $path, array $cache): void
{
    $json = json_encode($cache, JSON_UNESCAPED_SLASHES);
    if ($json === false) {
        return;
    }
    $directory = dirname($path);
    $temporary = @tempnam($directory, '.zagan-hashes-');
    if ($temporary === false) {
        return;
    }
    if (@file_put_contents($temporary, $json, LOCK_EX) === false || !@rename($temporary, $path)) {
        @unlink($temporary);
    }
}

/**
 * @return array{kind:string,version:string,platform:string,arch:string,file:string,size:int,mtime:int,sha256:string}|null
 */
function read_release(
    string $kind,
    string $directory,
    string $entry,
    array &$cache,
    bool &$dirty
): ?array {
    $pattern = '/^zagan-bet-' . preg_quote($kind, '/')
        . '-v?(\d+\.\d+\.\d+)-([a-z]+)-([a-z0-9_]+)(\.exe)?$/i';
    if (preg_match($pattern, $entry, $matches) !== 1) {
        return null;
    }

    $realDirectory = realpath($directory);
    $real = realpath($directory . '/' . $entry);
    if ($realDirectory === false || $real === false) {
        return null;
    }
    // Never serve anything that resolves outside the published directory.
    if (!str_starts_with($real, $realDirectory . DIRECTORY_SEPARATOR)) {
        return null;
    }
    if (!is_file($real)) {
        return null;
    }

    $size = filesize($real);
    $mtime = filemtime($real);
    if ($size === false || $mtime === false) {
        return null;
    }

    $hash = cached_hash($kind . '/' . $entry, $real, $size, $mtime, $cache, $dirty);
    if ($hash === null) {
        return null;
    }

    return [
        'kind' => $kind,
        'version' => $matches[1],
        'platform' => strtolower($matches[2]),
        'arch' => strtolower($matches[3]),
        'file' => $entry,
        'size' => $size,
        'mtime' => $mtime,
        'sha256' => $hash,
    ];
}

/**
 * Scan every kind and return its releases, newest version first.
 *
 * @return array{releases:array<string,array<int,array{kind:string,version:string,platform:string,arch:string,file:string,size:int,mtime:int,sha256:string}>>,newest_mtime:int}
 */
function scan_releases(): array
{
    $cachePath = getenv('ZAGAN_HASH_CACHE');
    if (!is_string($cachePath) || $cachePath === '') {
        $cachePath = rtrim(sys_get_temp_dir(), DIRECTORY_SEPARATOR)
            . DIRECTORY_SEPARATOR . 'zagan-bet-hashes-'
            . substr(hash('sha256', __DIR__), 0, 16) . '.json';
    }
    $cache = load_hash_cache($cachePath);
    $dirty = false;
    $seen = [];

    $releases = [];
    $newestMtime = 0;

    foreach (KINDS as $kind => $meta) {
        $found = [];
        $directory = __DIR__ . '/bin/' . $kind;

        if (is_dir($directory)) {
            $entries = scandir($directory);
            if ($entries !== false) {
                foreach ($entries as $entry) {
                    if ($entry === '.' || $entry === '..') {
                        continue;
                    }
                    $release = read_release($kind, $directory, $entry, $cache, $dirty);
                    if ($release === null) {
                        continue;
                    }
                    $seen[$kind . '/' . $entry] = true;
                    $found[] = $release;
                    $newestMtime = max($newestMtime, $release['mtime']);
                }
            }
        }

        usort($found, static function (array $a, array $b): int {
            $byVersion = version_compare($b['version'], $a['version']);
            if ($byVersion !== 0) {
                return $byVersion;
            }
            $byPlatform = (PLATFORM_ORDER[$a['platform']] ?? 9) <=> (PLATFORM_ORDER[$b['platform']] ?? 9);
            if ($byPlatform !== 0) {
                return $byPlatform;
            }
            $byArch = (ARCH_ORDER[$a['arch']] ?? 9) <=> (ARCH_ORDER[$b['arch']] ?? 9);
            if ($byArch !== 0) {
                return $byArch;
            }
            return strcmp($a['file'], $b['file']);
        });

        $releases[$kind] = $found;
    }

    // Drop cache entries for files that are no longer published.
    foreach (array_keys($cache['files']) as $key) {
        if (!isset($seen[$key])) {
            unset($cache['files'][$key]);
            $dirty = true;
        }
    }
    if ($dirty) {
        save_hash_cache($cachePath, $cache);
    }

    return ['releases' => $releases, 'newest_mtime' => $newestMtime];
}