<?php
/**
 * Copyright since 2007 PrestaShop SA and Contributors
 * PrestaShop is an International Registered Trademark & Property of PrestaShop SA
 *
 * NOTICE OF LICENSE
 *
 * This source file is subject to the Open Software License (OSL 3.0)
 * that is bundled with this package in the file LICENSE.md.
 * It is also available through the world-wide-web at this URL:
 * https://opensource.org/licenses/OSL-3.0
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@prestashop.com so we can send you a copy immediately.
 *
 * DISCLAIMER
 *
 * Do not edit or add to this file if you wish to upgrade PrestaShop to newer
 * versions in the future. If you wish to customize PrestaShop for your
 * needs please refer to https://devdocs.prestashop.com/ for more information.
 *
 * @author    PrestaShop SA and Contributors <contact@prestashop.com>
 * @copyright Since 2007 PrestaShop SA and Contributors
 * @license   https://opensource.org/licenses/OSL-3.0 Open Software License (OSL 3.0)
 */
abstract class CacheCore
{
    /**
     * Name of keys index.
     */
    public const KEYS_NAME = '__keys__';

    /**
     * Name of SQL cache index.
     */
    public const SQL_TABLES_NAME = 'tablesCached';

    /**
     * Store the number of time a query is fetched from the cache.
     *
     * @var array
     */
    protected $queryCounter = [];

    /**
     * @var Cache|null
     */
    protected static $instance;

    /**
     * Max number of queries cached in memcached, for each SQL table.
     *
     * @var int
     */
    protected $maxCachedObjectsByTable = 10000;

    /**
     * If a cache set this variable to true, we need to adjust the size of the table cache object.
     *
     * @var bool
     */
    protected $adjustTableCacheSize = false;

    /**
     * @var array List all keys of cached data and their associated ttl
     */
    protected $keys = [];

    /**
     * @var array Store list of tables and their associated keys for SQL cache
     */
    protected $sql_tables_cached = [];

    /**
     * @var array List of blacklisted tables for SQL cache, these tables won't be indexed
     */
    protected $blacklist = [
        'cart',
        'cart_cart_rule',
        'cart_product',
        'connections',
        'connections_source',
        'connections_page',
        'customer',
        'customer_group',
        'customized_data',
        'guest',
        'pagenotfound',
        'page_viewed',
        'employee',
        'log',
    ];

    /**
     * @var array Store local cache
     */
    protected static $local = [];

    /**
     * Cache a data.
     *
     * @param string $key
     * @param mixed $value
     * @param int $ttl
     *
     * @return bool
     */
    abstract protected function _set($key, $value, $ttl = 0);

    /**
     * Retrieve a cached data by key.
     *
     * @param string $key
     *
     * @return mixed
     */
    abstract protected function _get($key);

    /**
     * Check if a data is cached by key.
     *
     * @param string $key
     *
     * @return bool
     */
    abstract protected function _exists($key);

    /**
     * Delete a data from the cache by key.
     *
     * @param string $key
     *
     * @return bool
     */
    abstract protected function _delete($key);

    /**
     * Delete multiple keys from the cache.
     *
     * @param array $keyArray
     */
    protected function _deleteMulti(array $keyArray)
    {
        foreach ($keyArray as $key) {
            $this->delete($key);
        }
    }

    /**
     * Write keys index.
     */
    abstract protected function _writeKeys();

    /**
     * Clean all cached data.
     *
     * @return bool
     */
    abstract public function flush();

    /**
     * @return int
     */
    public function getMaxCachedObjectsByTable()
    {
        return $this->maxCachedObjectsByTable;
    }

    /**
     * @param int $maxCachedObjectsByTable
     */
    public function setMaxCachedObjectsByTable($maxCachedObjectsByTable)
    {
        $this->maxCachedObjectsByTable = $maxCachedObjectsByTable;
    }

    /**
     * @return Cache
     */
    public static function getInstance()
    {
        if (!self::$instance) {
            $caching_system = _PS_CACHING_SYSTEM_;
            if (class_exists($caching_system)) {
                /** @var Cache $cache */
                $cache = new $caching_system();
                self::$instance = $cache;
            }
        }

        return self::$instance;
    }

    /**
     * Unit testing purpose only.
     *
     * @param Cache $test_instance
     */
    public static function setInstanceForTesting($test_instance)
    {
        self::$instance = $test_instance;
    }

    /**
     * If a cache set this variable to true, we need to adjust the size of the table cache object
     * Useful when the cache is reported to be full (e.g. memcached::RES_E2BIG error message).
     *
     * @param bool $value
     */
    protected function setAdjustTableCacheSize($value)
    {
        $this->adjustTableCacheSize = (bool) $value;
    }

    /**
     * Unit testing purpose only.
     */
    public static function deleteTestingInstance()
    {
        self::$instance = null;
    }

    /**
     * Store a data in cache.
     *
     * @param string $key
     * @param mixed $value
     * @param int $ttl
     *
     * @return bool
     */
    public function set($key, $value, $ttl = 0)
    {
        if ($this->_set($key, $value, $ttl)) {
            if ($ttl < 0) {
                $ttl = 0;
            }

            $this->keys[$key] = ($ttl == 0) ? 0 : time() + $ttl;
            $this->_writeKeys();

            return true;
        }

        return false;
    }

    /**
     * Retrieve a data from cache.
     *
     * @param string $key
     *
     * @return mixed
     */
    public function get($key)
    {
        if (!isset($this->keys[$key])) {
            return false;
        }

        return $this->_get($key);
    }

    /**
     * Check if a data is cached.
     *
     * @param string $key
     *
     * @return bool
     */
    public function exists($key)
    {
        if (!isset($this->keys[$key])) {
            return false;
        }

        return $this->_exists($key);
    }

    /**
     * Delete several keys at once from the cache.
     *
     * @param array $keyArray
     */
    public function deleteMulti(array $keyArray)
    {
        $this->_deleteMulti($keyArray);
    }

    /**
     * Delete one or several data from cache (* joker can be used)
     *  E.g.: delete('*'); delete('my_prefix_*'); delete('my_key_name');.
     *
     * @param string $key
     *
     * @return bool
     */
    public function delete($key)
    {
        // Get list of keys to delete
        $keys = [];
        if ($key == '*') {
            $keys = $this->keys;
        } elseif (strpos($key, '*') === false) {
            $keys = [$key];
        } else {
            $pattern = str_replace('\\*', '.*', preg_quote($key));
            foreach ($this->keys as $k => $ttl) {
                if (preg_match('#^' . $pattern . '$#', $k)) {
                    $keys[] = $k;
                }
            }
        }

        // Delete keys
        foreach ($keys as $key) {
            if (!isset($this->keys[$key])) {
                continue;
            }

            if ($this->_delete($key)) {
                unset($this->keys[$key]);
            }
        }

        $this->_writeKeys();

        return true;
    }

    /**
     * Increment the query counter for the given query.
     *
     * @param string $query
     */
    public function incrementQueryCounter($query)
    {
        if (isset($this->queryCounter[$query])) {
            ++$this->queryCounter[$query];
        } else {
            $this->queryCounter[$query] = 1;
        }
    }

    /**
     * Store a query in cache.
     *
     * @param string $query
     * @param array $result
     */
    public function setQuery($query, $result)
    {
        if ($this->isBlacklist($query)) {
            return;
        }

        if (empty($result)) {
            $result = [];
        }

        // use the query counter to update the cache statistics
        $this->updateQueryCacheStatistics();

        $key = $this->updateTableToQueryMap($query);

        // Store query results in cache
        // no need to check the key existence before the set : if the query is already
        // in the cache, setQuery is not invoked
        $this->set($key, $result);
    }

    /**
     * Return the hash associated with a query, used to store data into the cache.
     *
     * @param string $query
     *
     * @return string
     */
    public function getQueryHash($query)
    {
        return Tools::hashIV($query);
    }

    /**
     * Return the hash associated with a table name, used to store the "table to query hash" map.
     *
     * @param string $table
     *
     * @return string
     */
    public function getTableMapCacheKey($table)
    {
        return Tools::hashIV(self::SQL_TABLES_NAME . '_' . $table);
    }

    /**
     * This function extract all the tables involded in a query, and in the each table map the query hash.
     *
     * @param string $query
     *
     * @return string
     */
    private function updateTableToQueryMap($query)
    {
        $key = $this->getQueryHash($query);

        // Get all table from the query and save them in cache
        if ($tables = $this->getTables($query)) {
            foreach ($tables as $table) {
                $this->addQueryKeyToTableMap($key, $table, $tables);
            }
        }

        return $key;
    }

    /**
     * Add the given query hash to the table to query key map.
     *
     * @param string $key query hash
     * @param string $table table name
     * @param array $otherTables the tables associated with the query
     */
    private function addQueryKeyToTableMap($key, $table, $otherTables)
    {
        // the name of the cache entry which cache the table map
        $cacheKey = $this->getTableMapCacheKey($table);

        $this->initializeTableCache($table);

        if (!isset($this->sql_tables_cached[$table][$key])) {
            if (count($this->sql_tables_cached[$table]) >= $this->maxCachedObjectsByTable) {
                $this->adjustTableCacheSize($table);
            }

            unset($otherTables[array_search($table, $otherTables)]);
            $this->sql_tables_cached[$table][$key] = [
                'count' => 1,
                'otherTables' => $otherTables,
            ];
            $this->set($cacheKey, $this->sql_tables_cached[$table]);
            // if the set fails because the object is too big, the adjustTableCacheSize flag is set
            if ($this->adjustTableCacheSize) {
                $this->adjustTableCacheSize($table, $key);
                $this->set($cacheKey, $this->sql_tables_cached[$table]);
            }
        }
    }

    /**
     * Use the query counter to update the query cache statistics
     * So far its only called during a set operation to avoid overloading / slowing down the cache server.
     */
    protected function updateQueryCacheStatistics()
    {
        $changedTables = [];

        foreach ($this->queryCounter as $query => $count) {
            $key = $this->getQueryHash($query);

            if ($tables = $this->getTables($query)) {
                foreach ($tables as $table) {
                    $this->initializeTableCache($table);

                    if (isset($this->sql_tables_cached[$table][$key])) {
                        $this->sql_tables_cached[$table][$key]['count'] += $count;
                        $changedTables[$table] = true;
                    }
                }
            }
        }

        foreach (array_keys($changedTables) as $table) {
            $this->set($this->getTableMapCacheKey($table), $this->sql_tables_cached[$table]);
        }

        $this->queryCounter = [];
    }

    /**
     * Remove the first less used query results from the cache.
     *
     * @param string $table
     * @param string|null $keyToKeep the key we want to keep inside the table cache
     */
    protected function adjustTableCacheSize($table, $keyToKeep = null)
    {
        $invalidKeys = [];
        if (isset($this->sql_tables_cached[$table])) {
            if ($keyToKeep && isset($this->sql_tables_cached[$table][$keyToKeep])) {
                $toKeep = $this->sql_tables_cached[$table][$keyToKeep];
                // remove the key we plan to keep before adjusting the table cache size
                unset($this->sql_tables_cached[$table][$keyToKeep]);
            }

            // sort the array with the query with the lowest count first
            uasort($this->sql_tables_cached[$table], function ($a, $b) {
                if ($a['count'] == $b['count']) {
                    return 0;
                }

                return ($a['count'] < $b['count']) ? -1 : 1;
            });
            // reduce the size of the cache : delete the first entries (those with the lowest count)
            $tableBuffer = array_slice(
                $this->sql_tables_cached[$table],
                0,
                (int) ceil($this->maxCachedObjectsByTable / 3),
                true
            );
            foreach (array_keys($tableBuffer) as $fs_key) {
                $invalidKeys[] = $fs_key;
                $invalidKeys[] = $fs_key . '_nrows';
                unset($this->sql_tables_cached[$table][$fs_key]);
            }
            $this->_deleteMulti($invalidKeys);

            if ($keyToKeep) {
                $this->sql_tables_cached[$table][$keyToKeep] = $toKeep ?? null;
            }
        }
        $this->adjustTableCacheSize = false;
    }

    /**
     * Get the tables used in a SQL query.
     *
     * @param string $string
     *
     * @return array|bool
     */
    public function getTables($string)
    {
        if (preg_match_all('/(?:from|join|update|into)\s+`?(' . _DB_PREFIX_ .
            '[0-9a-z_-]+)(?:`?\s{0,},\s{0,}`?(' . _DB_PREFIX_ .
            '[0-9a-z_-]+)`?)?(?:`|\s+|\Z)(?!\s*,)/Umsi', $string, $res)) {
            foreach ($res[2] as $table) {
                if ($table != '') {
                    $res[1][] = $table;
                }
            }

            return array_unique($res[1]);
        } else {
            return false;
        }
    }

    /**
     * Delete a query from cache.
     *
     * @param string $query
     */
    public function deleteQuery($query)
    {
        if ($this->isBlacklist($query)) {
            return;
        }

        $invalidKeys = [];
        $tableKeysToUpdate = [];
        if ($tables = $this->getTables($query)) {
            foreach ($tables as $table) {
                $cacheKey = $this->initializeTableCache($table);

                if (!empty($this->sql_tables_cached[$table])) {
                    foreach ($this->sql_tables_cached[$table] as $fs_key => $tableMapInfos) {
                        $invalidKeys[] = $fs_key;
                        $invalidKeys[] = $fs_key . '_nrows';

                        foreach ($tableMapInfos['otherTables'] as $otherTable) {
                            if ($this->removeEntryInTableMapCache($fs_key, $otherTable)) {
                                $tableKeysToUpdate[$otherTable] = 1;
                            }
                        }
                    }
                    unset($this->sql_tables_cached[$table]);
                    $this->deleteMulti($invalidKeys);
                    $this->delete($cacheKey);
                }
            }
            $this->flushUpdatedTableKeyEntries($tableKeysToUpdate);
        }
    }

    /**
     * Flush into the cache the updated entries from the sql_tables_caches.
     *
     * @param array $tableKeysToUpdate
     */
    private function flushUpdatedTableKeyEntries($tableKeysToUpdate)
    {
        foreach (array_keys($tableKeysToUpdate) as $tableKeyToUpdate) {
            $cacheKey = $this->getTableMapCacheKey($tableKeyToUpdate);
            if (empty($this->sql_tables_cached[$tableKeyToUpdate])) {
                $this->delete($cacheKey);
            } else {
                $this->set($cacheKey, $this->sql_tables_cached[$tableKeyToUpdate]);
            }
        }
    }

    /**
     * Initialize the table cache entry associated with $table.
     *
     * @param string $table
     *
     * @return string
     */
    private function initializeTableCache($table)
    {
        $cacheKey = $this->getTableMapCacheKey($table);

        if (!array_key_exists($table, $this->sql_tables_cached)) {
            $this->sql_tables_cached[$table] = $this->get($cacheKey);
            if (!is_array($this->sql_tables_cached[$table])) {
                $this->sql_tables_cached[$table] = [];
            }
        }

        return $cacheKey;
    }

    /**
     * Remove $key from the tableMap.
     *
     * @param string $key
     * @param string $table
     *
     * @return bool True is the key exists in the table
     */
    private function removeEntryInTableMapCache($key, $table)
    {
        if (isset($this->sql_tables_cached[$table][$key])) {
            unset($this->sql_tables_cached[$table][$key]);

            return true;
        }

        return false;
    }

    /**
     * Check if a query contain blacklisted tables.
     *
     * @param string $query
     *
     * @return bool
     */
    protected function isBlacklist($query)
    {
        foreach ($this->blacklist as $find) {
            if (false !== strpos($query, _DB_PREFIX_ . $find)) {
                return true;
            }
        }

        return false;
    }

    /**
     * @param string $key
     * @param mixed $value
     */
    public static function store($key, $value)
    {
        // PHP is not efficient at storing array
        // Better delete the whole cache if there are
        // more than 1000 elements in the array
        if (count(Cache::$local) > 1000) {
            Cache::$local = [];
        }
        Cache::$local[$key] = $value;
    }

    public static function clear()
    {
        Cache::$local = [];
    }

    /**
     * @param string $key
     *
     * @return mixed|null The cache item if found, null otherwise
     */
    public static function retrieve($key)
    {
        return isset(Cache::$local[$key]) ? Cache::$local[$key] : null;
    }

    /**
     * @return array
     */
    public static function retrieveAll()
    {
        return Cache::$local;
    }

    /**
     * @param string $key
     *
     * @return bool
     */
    public static function isStored($key)
    {
        return isset(Cache::$local[$key]);
    }

    /**
     * @param string $key
     */
    public static function clean($key)
    {
        if (strpos($key, '*') !== false) {
            $regexp = str_replace('\\*', '.*', preg_quote($key, '#'));
            foreach (array_keys(Cache::$local) as $key) {
                if (preg_match('#^' . $regexp . '$#', $key)) {
                    unset(Cache::$local[$key]);
                }
            }
        } else {
            unset(Cache::$local[$key]);
        }
    }
}