<?php

namespace Nette\Caching\Storages;

use Nette;
use Nette\Caching\Cache;

/**
 * Cache file storage.
 */
class FileStorage implements Nette\Caching\Storage
{
    use Nette\SmartObject;

    /** @internal cache file structure: meta-struct size + serialized meta-struct + data */
    private const MetaHeaderLen = 6;
    private const MetaTime = 'time';
    private const MetaSerialized = 'serialized';
    private const MetaExpire = 'expire';
    private const MetaDelta = 'delta';
    private const MetaItems = 'di';
    private const MetaCallbacks = 'callbacks';

    /** additional cache structure */
    private const File = 'file';
    private const Handle = 'handle';

    /** probability that the clean() routine is started */
    public static float $gcProbability = 0.001;
    private string $dir;
    private ?Journal $journal;
    private array $locks;

    public function __construct(string $dir, ?Journal $journal = null)
    {
        if (!is_dir($dir)) {
            throw new Nette\DirectoryNotFoundException("Directory '$dir' not found.");
        }

        $this->dir = $dir;
        $this->journal = $journal;

        if (mt_rand() / mt_getrandmax() < static::$gcProbability) {
            $this->clean([]);
        }
    }

    public function read(string $key): mixed
    {
        $meta = $this->readMetaAndLock($this->getCacheFile($key), LOCK_SH);
        return $meta && $this->verify($meta)
            ? $this->readData($meta) // calls fclose()
            : null;
    }

    /**
     * Verifies dependencies.
     */
    private function verify(array $meta): bool
    {
        do {
            if (!empty($meta[self::MetaDelta])) {
                // meta[file] was added by readMetaAndLock()
                if (filemtime($meta[self::File]) + $meta[self::MetaDelta] < time()) {
                    break;
                }

                touch($meta[self::File]);

            } elseif (!empty($meta[self::MetaExpire]) && $meta[self::MetaExpire] < time()) {
                break;
            }

            if (!empty($meta[self::MetaCallbacks]) && !Cache::checkCallbacks($meta[self::MetaCallbacks])) {
                break;
            }

            if (!empty($meta[self::MetaItems])) {
                foreach ($meta[self::MetaItems] as $depFile => $time) {
                    $m = $this->readMetaAndLock($depFile, LOCK_SH);
                    if (($m[self::MetaTime] ?? null) !== $time || ($m && !$this->verify($m))) {
                        break 2;
                    }
                }
            }

            return true;
        } while (false);

        $this->delete($meta[self::File], $meta[self::Handle]); // meta[handle] & meta[file] was added by readMetaAndLock()
        return false;
    }

    public function lock(string $key): void
    {
        $cacheFile = $this->getCacheFile($key);
        if (!is_dir($dir = dirname($cacheFile))) {
            @mkdir($dir); // @ - directory may already exist
        }

        $handle = fopen($cacheFile, 'c+b');
        if (!$handle) {
            return;
        }

        $this->locks[$key] = $handle;
        flock($handle, LOCK_EX);
    }

    public function write(string $key, $data, array $dp): void
    {
        $meta = [
            self::MetaTime => microtime(),
        ];

        if (isset($dp[Cache::Expire])) {
            if (empty($dp[Cache::Sliding])) {
                $meta[self::MetaExpire] = $dp[Cache::Expire] + time(); // absolute time
            } else {
                $meta[self::MetaDelta] = (int) $dp[Cache::Expire]; // sliding time
            }
        }

        if (isset($dp[Cache::Items])) {
            foreach ($dp[Cache::Items] as $item) {
                $depFile = $this->getCacheFile($item);
                $m = $this->readMetaAndLock($depFile, LOCK_SH);
                $meta[self::MetaItems][$depFile] = $m[self::MetaTime] ?? null;
                unset($m);
            }
        }

        if (isset($dp[Cache::Callbacks])) {
            $meta[self::MetaCallbacks] = $dp[Cache::Callbacks];
        }

        if (!isset($this->locks[$key])) {
            $this->lock($key);
            if (!isset($this->locks[$key])) {
                return;
            }
        }

        $handle = $this->locks[$key];
        unset($this->locks[$key]);

        $cacheFile = $this->getCacheFile($key);

        if (isset($dp[Cache::Tags]) || isset($dp[Cache::Priority])) {
            if (!$this->journal) {
                throw new Nette\InvalidStateException('CacheJournal has not been provided.');
            }

            $this->journal->write($cacheFile, $dp);
        }

        ftruncate($handle, 0);

        if (!is_string($data)) {
            $data = serialize($data);
            $meta[self::MetaSerialized] = true;
        }

        $head = serialize($meta);
        $head = str_pad((string) strlen($head), 6, '0', STR_PAD_LEFT) . $head;
        $headLen = strlen($head);

        do {
            if (fwrite($handle, str_repeat("\x00", $headLen)) !== $headLen) {
                break;
            }

            if (fwrite($handle, $data) !== strlen($data)) {
                break;
            }

            fseek($handle, 0);
            if (fwrite($handle, $head) !== $headLen) {
                break;
            }

            flock($handle, LOCK_UN);
            fclose($handle);
            return;
        } while (false);

        $this->delete($cacheFile, $handle);
    }

    public function remove(string $key): void
    {
        unset($this->locks[$key]);
        $this->delete($this->getCacheFile($key));
    }

    public function clean(array $conditions): void
    {
        $all = !empty($conditions[Cache::All]);
        $collector = empty($conditions);
        $namespaces = $conditions[Cache::Namespaces] ?? null;

        // cleaning using file iterator
        if ($all || $collector) {
            $now = time();
            foreach (Nette\Utils\Finder::find('_*')->from($this->dir)->childFirst() as $entry) {
                $path = (string) $entry;
                if ($entry->isDir()) { // collector: remove empty dirs
                    @rmdir($path); // @ - removing dirs is not necessary
                    continue;
                }

                if ($all) {
                    $this->delete($path);

                } else { // collector
                    $meta = $this->readMetaAndLock($path, LOCK_SH);
                    if (!$meta) {
                        continue;
                    }

                    if ((!empty($meta[self::MetaDelta]) && filemtime($meta[self::File]) + $meta[self::MetaDelta] < $now)
                        || (!empty($meta[self::MetaExpire]) && $meta[self::MetaExpire] < $now)
                    ) {
                        $this->delete($path, $meta[self::Handle]);
                        continue;
                    }

                    flock($meta[self::Handle], LOCK_UN);
                    fclose($meta[self::Handle]);
                }
            }

            if ($this->journal) {
                $this->journal->clean($conditions);
            }

            return;

        } elseif ($namespaces) {
            foreach ($namespaces as $namespace) {
                $dir = $this->dir . '/_' . urlencode($namespace);
                if (!is_dir($dir)) {
                    continue;
                }

                foreach (Nette\Utils\Finder::findFiles('_*')->in($dir) as $entry) {
                    $this->delete((string) $entry);
                }

                @rmdir($dir); // may already contain new files
            }
        }

        // cleaning using journal
        if ($this->journal) {
            foreach ($this->journal->clean($conditions) as $file) {
                $this->delete($file);
            }
        }
    }

    /**
     * Reads cache data from disk.
     */
    protected function readMetaAndLock(string $file, int $lock): ?array
    {
        $handle = @fopen($file, 'r+b'); // @ - file may not exist
        if (!$handle) {
            return null;
        }

        flock($handle, $lock);

        $size = (int) stream_get_contents($handle, self::MetaHeaderLen);
        if ($size) {
            $meta = stream_get_contents($handle, $size, self::MetaHeaderLen);
            $meta = unserialize($meta);
            $meta[self::File] = $file;
            $meta[self::Handle] = $handle;
            return $meta;
        }

        flock($handle, LOCK_UN);
        fclose($handle);
        return null;
    }

    /**
     * Reads cache data from disk and closes cache file handle.
     */
    protected function readData(array $meta): mixed
    {
        $data = stream_get_contents($meta[self::Handle]);
        flock($meta[self::Handle], LOCK_UN);
        fclose($meta[self::Handle]);

        return empty($meta[self::MetaSerialized]) ? $data : unserialize($data);
    }

    /**
     * Returns file name.
     */
    protected function getCacheFile(string $key): string
    {
        $file = urlencode($key);
        if ($a = strrpos($file, '%00')) { // %00 = urlencode(Nette\Caching\Cache::NamespaceSeparator)
            $file = substr_replace($file, '/_', $a, 3);
        }

        return $this->dir . '/_' . $file;
    }

    /**
     * Deletes and closes file.
     * @param  resource  $handle
     */
    private static function delete(string $file, $handle = null): void
    {
        if (@unlink($file)) { // @ - file may not already exist
            if ($handle) {
                flock($handle, LOCK_UN);
                fclose($handle);
            }

            return;
        }

        if (!$handle) {
            $handle = @fopen($file, 'r+'); // @ - file may not exist
        }

        if (!$handle) {
            return;
        }

        flock($handle, LOCK_EX);
        ftruncate($handle, 0);
        flock($handle, LOCK_UN);
        fclose($handle);
        @unlink($file); // @ - file may not already exist
    }
}
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