class DatabaseStorageExpirable

class DatabaseStorageExpirable extends DatabaseStorage implements KeyValueStoreExpirableInterface {
    
    /**
     * Overrides Drupal\Core\KeyValueStore\StorageBase::__construct().
     *
     * @param string $collection
     *   The name of the collection holding key and value pairs.
     * @param \Drupal\Component\Serialization\SerializationInterface $serializer
     *   The serialization class to use.
     * @param \Drupal\Core\Database\Connection $connection
     *   The database connection to use.
     * @param string $table
     *   The name of the SQL table to use, defaults to key_value_expire.
     */
    public function __construct($collection, SerializationInterface $serializer, Connection $connection, $table = 'key_value_expire') {
        parent::__construct($collection, $serializer, $connection, $table);
    }
    
    /**
     * {@inheritdoc}
     */
    public function has($key) {
        try {
            return (bool) $this->connection
                ->query('SELECT 1 FROM {' . $this->connection
                ->escapeTable($this->table) . '} WHERE [collection] = :collection AND [name] = :key AND [expire] > :now', [
                ':collection' => $this->collection,
                ':key' => $key,
                ':now' => REQUEST_TIME,
            ])
                ->fetchField();
        } catch (\Exception $e) {
            $this->catchException($e);
            return FALSE;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMultiple(array $keys) {
        try {
            $values = $this->connection
                ->query('SELECT [name], [value] FROM {' . $this->connection
                ->escapeTable($this->table) . '} WHERE [expire] > :now AND [name] IN ( :keys[] ) AND [collection] = :collection', [
                ':now' => REQUEST_TIME,
                ':keys[]' => $keys,
                ':collection' => $this->collection,
            ])
                ->fetchAllKeyed();
            return array_map([
                $this->serializer,
                'decode',
            ], $values);
        } catch (\Exception $e) {
            // @todo: Perhaps if the database is never going to be available,
            // key/value requests should return FALSE in order to allow exception
            // handling to occur but for now, keep it an array, always.
            // https://www.drupal.org/node/2787737
            $this->catchException($e);
        }
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getAll() {
        try {
            $values = $this->connection
                ->query('SELECT [name], [value] FROM {' . $this->connection
                ->escapeTable($this->table) . '} WHERE [collection] = :collection AND [expire] > :now', [
                ':collection' => $this->collection,
                ':now' => REQUEST_TIME,
            ])
                ->fetchAllKeyed();
            return array_map([
                $this->serializer,
                'decode',
            ], $values);
        } catch (\Exception $e) {
            $this->catchException($e);
        }
        return [];
    }
    
    /**
     * Saves a value for a given key with a time to live.
     *
     * This will be called by setWithExpire() within a try block.
     *
     * @param string $key
     *   The key of the data to store.
     * @param mixed $value
     *   The data to store.
     * @param int $expire
     *   The time to live for items, in seconds.
     */
    protected function doSetWithExpire($key, $value, $expire) {
        $this->connection
            ->merge($this->table)
            ->keys([
            'name' => $key,
            'collection' => $this->collection,
        ])
            ->fields([
            'value' => $this->serializer
                ->encode($value),
            'expire' => REQUEST_TIME + $expire,
        ])
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function setWithExpire($key, $value, $expire) {
        try {
            $this->doSetWithExpire($key, $value, $expire);
        } catch (\Exception $e) {
            // If there was an exception, then try to create the table.
            if ($this->ensureTableExists()) {
                $this->doSetWithExpire($key, $value, $expire);
            }
            else {
                throw $e;
            }
        }
    }
    
    /**
     * Sets a value for a given key with a time to live if it does not yet exist.
     *
     * This will be called by setWithExpireIfNotExists() within a try block.
     *
     * @param string $key
     *   The key of the data to store.
     * @param mixed $value
     *   The data to store.
     * @param int $expire
     *   The time to live for items, in seconds.
     *
     * @return bool
     *   TRUE if the data was set, or FALSE if it already existed.
     */
    protected function doSetWithExpireIfNotExists($key, $value, $expire) {
        if (!$this->has($key)) {
            $this->setWithExpire($key, $value, $expire);
            return TRUE;
        }
        return FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setWithExpireIfNotExists($key, $value, $expire) {
        try {
            return $this->doSetWithExpireIfNotExists($key, $value, $expire);
        } catch (\Exception $e) {
            // If there was an exception, try to create the table.
            if ($this->ensureTableExists()) {
                return $this->doSetWithExpireIfNotExists($key, $value, $expire);
            }
            else {
                throw $e;
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function setMultipleWithExpire(array $data, $expire) {
        foreach ($data as $key => $value) {
            $this->setWithExpire($key, $value, $expire);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteMultiple(array $keys) {
        parent::deleteMultiple($keys);
    }
    
    /**
     * Defines the schema for the key_value_expire table.
     */
    public static function schemaDefinition() {
        return [
            'description' => 'Generic key/value storage table with an expiration.',
            'fields' => [
                'collection' => [
                    'description' => 'A named collection of key and value pairs.',
                    'type' => 'varchar_ascii',
                    'length' => 128,
                    'not null' => TRUE,
                    'default' => '',
                ],
                'name' => [
                    // KEY is an SQL reserved word, so use 'name' as the key's field name.
'description' => 'The key of the key/value pair.',
                    'type' => 'varchar_ascii',
                    'length' => 128,
                    'not null' => TRUE,
                    'default' => '',
                ],
                'value' => [
                    'description' => 'The value of the key/value pair.',
                    'type' => 'blob',
                    'not null' => TRUE,
                    'size' => 'big',
                ],
                'expire' => [
                    'description' => 'The time since Unix epoch in seconds when this item expires. Defaults to the maximum possible time.',
                    'type' => 'int',
                    'not null' => TRUE,
                    'default' => 2147483647,
                ],
            ],
            'primary key' => [
                'collection',
                'name',
            ],
            'indexes' => [
                'expire' => [
                    'expire',
                ],
            ],
        ];
    }

}