class MemoryBackend

class MemoryBackend implements CacheBackendInterface, CacheTagsInvalidatorInterface {
    
    /**
     * Array to store cache objects.
     */
    protected $cache = [];
    
    /**
     * {@inheritdoc}
     */
    public function get($cid, $allow_invalid = FALSE) {
        if (isset($this->cache[$cid])) {
            return $this->prepareItem($this->cache[$cid], $allow_invalid);
        }
        else {
            return FALSE;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMultiple(&$cids, $allow_invalid = FALSE) {
        $ret = [];
        $items = array_intersect_key($this->cache, array_flip($cids));
        foreach ($items as $item) {
            $item = $this->prepareItem($item, $allow_invalid);
            if ($item) {
                $ret[$item->cid] = $item;
            }
        }
        $cids = array_diff($cids, array_keys($ret));
        return $ret;
    }
    
    /**
     * Prepares a cached item.
     *
     * Checks that items are either permanent or did not expire, and returns data
     * as appropriate.
     *
     * @param object $cache
     *   An item loaded from self::get() or self::getMultiple().
     * @param bool $allow_invalid
     *   (optional) If TRUE, cache items may be returned even if they have expired
     *   or been invalidated.
     *
     * @return mixed
     *   The item with data as appropriate or FALSE if there is no
     *   valid item to load.
     */
    protected function prepareItem($cache, $allow_invalid) {
        if (!isset($cache->data)) {
            return FALSE;
        }
        // The object passed into this function is the one stored in $this->cache.
        // We must clone it as part of the preparation step so that the actual
        // cache object is not affected by the unserialize() call or other
        // manipulations of the returned object.
        $prepared = clone $cache;
        $prepared->data = unserialize($prepared->data);
        // Check expire time.
        $prepared->valid = $prepared->expire == Cache::PERMANENT || $prepared->expire >= $this->getRequestTime();
        if (!$allow_invalid && !$prepared->valid) {
            return FALSE;
        }
        return $prepared;
    }
    
    /**
     * {@inheritdoc}
     */
    public function set($cid, $data, $expire = Cache::PERMANENT, array $tags = []) {
        assert(Inspector::assertAllStrings($tags), 'Cache Tags must be strings.');
        $tags = array_unique($tags);
        // Sort the cache tags so that they are stored consistently in the database.
        sort($tags);
        $this->cache[$cid] = (object) [
            'cid' => $cid,
            'data' => serialize($data),
            'created' => $this->getRequestTime(),
            'expire' => $expire,
            'tags' => $tags,
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function setMultiple(array $items = []) {
        foreach ($items as $cid => $item) {
            $this->set($cid, $item['data'], $item['expire'] ?? CacheBackendInterface::CACHE_PERMANENT, $item['tags'] ?? []);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function delete($cid) {
        unset($this->cache[$cid]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteMultiple(array $cids) {
        $this->cache = array_diff_key($this->cache, array_flip($cids));
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteAll() {
        $this->cache = [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function invalidate($cid) {
        if (isset($this->cache[$cid])) {
            $this->cache[$cid]->expire = $this->getRequestTime() - 1;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function invalidateMultiple(array $cids) {
        $items = array_intersect_key($this->cache, array_flip($cids));
        foreach ($items as $cid => $item) {
            $this->cache[$cid]->expire = $this->getRequestTime() - 1;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function invalidateTags(array $tags) {
        foreach ($this->cache as $cid => $item) {
            if (array_intersect($tags, $item->tags)) {
                $this->cache[$cid]->expire = $this->getRequestTime() - 1;
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function invalidateAll() {
        foreach ($this->cache as $cid => $item) {
            $this->cache[$cid]->expire = $this->getRequestTime() - 1;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function garbageCollection() {
    }
    
    /**
     * {@inheritdoc}
     */
    public function removeBin() {
        $this->cache = [];
    }
    
    /**
     * Wrapper method for REQUEST_TIME constant.
     *
     * @return int
     */
    protected function getRequestTime() {
        return defined('REQUEST_TIME') ? REQUEST_TIME : (int) $_SERVER['REQUEST_TIME'];
    }
    
    /**
     * Prevents data stored in memory backends from being serialized.
     */
    public function __sleep() {
        return [];
    }
    
    /**
     * Reset statically cached variables.
     *
     * This is only used by tests.
     */
    public function reset() {
        $this->cache = [];
    }

}