class DatabaseStorage

class DatabaseStorage implements StorageInterface {
    use DependencySerializationTrait;
    
    /**
     * The database connection.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $connection;
    
    /**
     * The database table name.
     *
     * @var string
     */
    protected $table;
    
    /**
     * Additional database connection options to use in queries.
     *
     * @var array
     */
    protected $options = [];
    
    /**
     * The storage collection.
     *
     * @var string
     */
    protected $collection = StorageInterface::DEFAULT_COLLECTION;
    
    /**
     * Constructs a new DatabaseStorage.
     *
     * @param \Drupal\Core\Database\Connection $connection
     *   A Database connection to use for reading and writing configuration data.
     * @param string $table
     *   A database table name to store configuration data in.
     * @param array $options
     *   (optional) Any additional database connection options to use in queries.
     * @param string $collection
     *   (optional) The collection to store configuration in. Defaults to the
     *   default collection.
     */
    public function __construct(Connection $connection, $table, array $options = [], $collection = StorageInterface::DEFAULT_COLLECTION) {
        $this->connection = $connection;
        $this->table = $table;
        $this->options = $options;
        $this->collection = $collection;
    }
    
    /**
     * {@inheritdoc}
     */
    public function exists($name) {
        try {
            return (bool) $this->connection
                ->queryRange('SELECT 1 FROM {' . $this->connection
                ->escapeTable($this->table) . '} WHERE collection = :collection AND name = :name', 0, 1, [
                ':collection' => $this->collection,
                ':name' => $name,
            ], $this->options)
                ->fetchField();
        } catch (\Exception $e) {
            // If we attempt a read without actually having the database or the table
            // available, just return FALSE so the caller can handle it.
            return FALSE;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function read($name) {
        $data = FALSE;
        try {
            $raw = $this->connection
                ->query('SELECT data FROM {' . $this->connection
                ->escapeTable($this->table) . '} WHERE collection = :collection AND name = :name', [
                ':collection' => $this->collection,
                ':name' => $name,
            ], $this->options)
                ->fetchField();
            if ($raw !== FALSE) {
                $data = $this->decode($raw);
            }
        } catch (\Exception $e) {
            // If we attempt a read without actually having the database or the table
            // available, just return FALSE so the caller can handle it.
        }
        return $data;
    }
    
    /**
     * {@inheritdoc}
     */
    public function readMultiple(array $names) {
        $list = [];
        try {
            $list = $this->connection
                ->query('SELECT name, data FROM {' . $this->connection
                ->escapeTable($this->table) . '} WHERE collection = :collection AND name IN ( :names[] )', [
                ':collection' => $this->collection,
                ':names[]' => $names,
            ], $this->options)
                ->fetchAllKeyed();
            foreach ($list as &$data) {
                $data = $this->decode($data);
            }
        } catch (\Exception $e) {
            // If we attempt a read without actually having the database or the table
            // available, just return an empty array so the caller can handle it.
        }
        return $list;
    }
    
    /**
     * {@inheritdoc}
     */
    public function write($name, array $data) {
        $data = $this->encode($data);
        try {
            return $this->doWrite($name, $data);
        } catch (\Exception $e) {
            // If there was an exception, try to create the table.
            if ($this->ensureTableExists()) {
                return $this->doWrite($name, $data);
            }
            // Some other failure that we can not recover from.
            throw $e;
        }
    }
    
    /**
     * Helper method so we can re-try a write.
     *
     * @param string $name
     *   The config name.
     * @param string $data
     *   The config data, already dumped to a string.
     *
     * @return bool
     */
    protected function doWrite($name, $data) {
        $options = [
            'return' => Database::RETURN_AFFECTED,
        ] + $this->options;
        return (bool) $this->connection
            ->merge($this->table, $options)
            ->keys([
            'collection',
            'name',
        ], [
            $this->collection,
            $name,
        ])
            ->fields([
            'data' => $data,
        ])
            ->execute();
    }
    
    /**
     * Check if the config table exists and create it if not.
     *
     * @return bool
     *   TRUE if the table was created, FALSE otherwise.
     *
     * @throws \Drupal\Core\Config\StorageException
     *   If a database error occurs.
     */
    protected function ensureTableExists() {
        try {
            if (!$this->connection
                ->schema()
                ->tableExists($this->table)) {
                $this->connection
                    ->schema()
                    ->createTable($this->table, static::schemaDefinition());
                return TRUE;
            }
        } catch (DatabaseException $e) {
            return TRUE;
        } catch (\Exception $e) {
            throw new StorageException($e->getMessage(), NULL, $e);
        }
        return FALSE;
    }
    
    /**
     * Defines the schema for the configuration table.
     *
     * @internal
     */
    protected static function schemaDefinition() {
        $schema = [
            'description' => 'The base table for configuration data.',
            'fields' => [
                'collection' => [
                    'description' => 'Primary Key: Config object collection.',
                    'type' => 'varchar_ascii',
                    'length' => 255,
                    'not null' => TRUE,
                    'default' => '',
                ],
                'name' => [
                    'description' => 'Primary Key: Config object name.',
                    'type' => 'varchar_ascii',
                    'length' => 255,
                    'not null' => TRUE,
                    'default' => '',
                ],
                'data' => [
                    'description' => 'A serialized configuration object data.',
                    'type' => 'blob',
                    'not null' => FALSE,
                    'size' => 'big',
                ],
            ],
            'primary key' => [
                'collection',
                'name',
            ],
        ];
        return $schema;
    }
    
    /**
     * Implements Drupal\Core\Config\StorageInterface::delete().
     *
     * @throws PDOException
     *
     * @todo Ignore replica targets for data manipulation operations.
     */
    public function delete($name) {
        $options = [
            'return' => Database::RETURN_AFFECTED,
        ] + $this->options;
        return (bool) $this->connection
            ->delete($this->table, $options)
            ->condition('collection', $this->collection)
            ->condition('name', $name)
            ->execute();
    }
    
    /**
     * Implements Drupal\Core\Config\StorageInterface::rename().
     *
     * @throws PDOException
     */
    public function rename($name, $new_name) {
        $options = [
            'return' => Database::RETURN_AFFECTED,
        ] + $this->options;
        return (bool) $this->connection
            ->update($this->table, $options)
            ->fields([
            'name' => $new_name,
        ])
            ->condition('name', $name)
            ->condition('collection', $this->collection)
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function encode($data) {
        return serialize($data);
    }
    
    /**
     * Implements Drupal\Core\Config\StorageInterface::decode().
     *
     * @throws ErrorException
     *   The unserialize() call will trigger E_NOTICE if the string cannot
     *   be unserialized.
     */
    public function decode($raw) {
        $data = @unserialize($raw);
        return is_array($data) ? $data : FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function listAll($prefix = '') {
        try {
            $query = $this->connection
                ->select($this->table);
            $query->fields($this->table, [
                'name',
            ]);
            $query->condition('collection', $this->collection, '=');
            $query->condition('name', $prefix . '%', 'LIKE');
            $query->orderBy('collection')
                ->orderBy('name');
            return $query->execute()
                ->fetchCol();
        } catch (\Exception $e) {
            return [];
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteAll($prefix = '') {
        try {
            $options = [
                'return' => Database::RETURN_AFFECTED,
            ] + $this->options;
            return (bool) $this->connection
                ->delete($this->table, $options)
                ->condition('name', $prefix . '%', 'LIKE')
                ->condition('collection', $this->collection)
                ->execute();
        } catch (\Exception $e) {
            return FALSE;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function createCollection($collection) {
        return new static($this->connection, $this->table, $this->options, $collection);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCollectionName() {
        return $this->collection;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getAllCollectionNames() {
        try {
            return $this->connection
                ->query('SELECT DISTINCT collection FROM {' . $this->connection
                ->escapeTable($this->table) . '} WHERE collection <> :collection ORDER by collection', [
                ':collection' => StorageInterface::DEFAULT_COLLECTION,
            ])
                ->fetchCol();
        } catch (\Exception $e) {
            return [];
        }
    }

}