class Database

abstract class Database {
    
    /**
     * Flag to indicate a query call should simply return NULL.
     *
     * This is used for queries that have no reasonable return value anyway, such
     * as INSERT statements to a table without a serial primary key.
     */
    const RETURN_NULL = 0;
    
    /**
     * Flag to indicate a query call should return the prepared statement.
     */
    const RETURN_STATEMENT = 1;
    
    /**
     * Flag to indicate a query call should return the number of affected rows.
     */
    const RETURN_AFFECTED = 2;
    
    /**
     * Flag to indicate a query call should return the "last insert id".
     */
    const RETURN_INSERT_ID = 3;
    
    /**
     * An nested array of all active connections. It is keyed by database name
     * and target.
     *
     * @var array
     */
    protected static $connections = [];
    
    /**
     * A processed copy of the database connection information from settings.php.
     *
     * @var array
     */
    protected static $databaseInfo = [];
    
    /**
     * A list of key/target credentials to simply ignore.
     *
     * @var array
     */
    protected static $ignoreTargets = [];
    
    /**
     * The key of the currently active database connection.
     *
     * @var string
     */
    protected static $activeKey = 'default';
    
    /**
     * An array of active query log objects.
     *
     * Every connection has one and only one logger object for all targets and
     * logging keys.
     *
     * array(
     *   '$db_key' => DatabaseLog object.
     * );
     *
     * @var array
     */
    protected static $logs = [];
    
    /**
     * Starts logging a given logging key on the specified connection.
     *
     * @param string $logging_key
     *   The logging key to log.
     * @param string $key
     *   The database connection key for which we want to log.
     *
     * @return \Drupal\Core\Database\Log
     *   The query log object. Note that the log object does support richer
     *   methods than the few exposed through the Database class, so in some
     *   cases it may be desirable to access it directly.
     *
     * @see \Drupal\Core\Database\Log
     */
    public static final function startLog($logging_key, $key = 'default') {
        if (empty(self::$logs[$key])) {
            self::$logs[$key] = new Log($key);
            // Every target already active for this connection key needs to have the
            // logging object associated with it.
            if (!empty(self::$connections[$key])) {
                foreach (self::$connections[$key] as $connection) {
                    $connection->setLogger(self::$logs[$key]);
                }
            }
        }
        self::$logs[$key]->start($logging_key);
        return self::$logs[$key];
    }
    
    /**
     * Retrieves the queries logged on for given logging key.
     *
     * This method also ends logging for the specified key. To get the query log
     * to date without ending the logger request the logging object by starting
     * it again (which does nothing to an open log key) and call methods on it as
     * desired.
     *
     * @param string $logging_key
     *   The logging key to log.
     * @param string $key
     *   The database connection key for which we want to log.
     *
     * @return array
     *   The query log for the specified logging key and connection.
     *
     * @see \Drupal\Core\Database\Log
     */
    public static final function getLog($logging_key, $key = 'default') {
        if (empty(self::$logs[$key])) {
            return [];
        }
        $queries = self::$logs[$key]->get($logging_key);
        self::$logs[$key]->end($logging_key);
        return $queries;
    }
    
    /**
     * Gets the connection object for the specified database key and target.
     *
     * @param string $target
     *   The database target name.
     * @param string $key
     *   The database connection key. Defaults to NULL which means the active key.
     *
     * @return \Drupal\Core\Database\Connection
     *   The corresponding connection object.
     */
    public static final function getConnection($target = 'default', $key = NULL) {
        if (!isset($key)) {
            // By default, we want the active connection, set in setActiveConnection.
            $key = self::$activeKey;
        }
        // If the requested target does not exist, or if it is ignored, we fall back
        // to the default target. The target is typically either "default" or
        // "replica", indicating to use a replica SQL server if one is available. If
        // it's not available, then the default/primary server is the correct server
        // to use.
        if (!empty(self::$ignoreTargets[$key][$target]) || !isset(self::$databaseInfo[$key][$target])) {
            $target = 'default';
        }
        if (!isset(self::$connections[$key][$target])) {
            // If necessary, a new connection is opened.
            self::$connections[$key][$target] = self::openConnection($key, $target);
        }
        return self::$connections[$key][$target];
    }
    
    /**
     * Determines if there is an active connection.
     *
     * Note that this method will return FALSE if no connection has been
     * established yet, even if one could be.
     *
     * @return bool
     *   TRUE if there is at least one database connection established, FALSE
     *   otherwise.
     */
    public static final function isActiveConnection() {
        return !empty(self::$activeKey) && !empty(self::$connections) && !empty(self::$connections[self::$activeKey]);
    }
    
    /**
     * Sets the active connection to the specified key.
     *
     * @return string|null
     *   The previous database connection key.
     */
    public static final function setActiveConnection($key = 'default') {
        if (!empty(self::$databaseInfo[$key])) {
            $old_key = self::$activeKey;
            self::$activeKey = $key;
            return $old_key;
        }
    }
    
    /**
     * Process the configuration file for database information.
     *
     * @param array $info
     *   The database connection information, as defined in settings.php. The
     *   structure of this array depends on the database driver it is connecting
     *   to.
     */
    public static final function parseConnectionInfo(array $info) {
        // If there is no "driver" property, then we assume it's an array of
        // possible connections for this target. Pick one at random. That allows
        // us to have, for example, multiple replica servers.
        if (empty($info['driver'])) {
            $info = $info[mt_rand(0, count($info) - 1)];
        }
        // Parse the prefix information.
        if (!isset($info['prefix'])) {
            // Default to an empty prefix.
            $info['prefix'] = [
                'default' => '',
            ];
        }
        elseif (!is_array($info['prefix'])) {
            // Transform the flat form into an array form.
            $info['prefix'] = [
                'default' => $info['prefix'],
            ];
        }
        return $info;
    }
    
    /**
     * Adds database connection information for a given key/target.
     *
     * This method allows to add new connections at runtime.
     *
     * Under normal circumstances the preferred way to specify database
     * credentials is via settings.php. However, this method allows them to be
     * added at arbitrary times, such as during unit tests, when connecting to
     * admin-defined third party databases, etc.
     *
     * If the given key/target pair already exists, this method will be ignored.
     *
     * @param string $key
     *   The database key.
     * @param string $target
     *   The database target name.
     * @param array $info
     *   The database connection information, as defined in settings.php. The
     *   structure of this array depends on the database driver it is connecting
     *   to.
     */
    public static final function addConnectionInfo($key, $target, array $info) {
        if (empty(self::$databaseInfo[$key][$target])) {
            self::$databaseInfo[$key][$target] = self::parseConnectionInfo($info);
        }
    }
    
    /**
     * Gets information on the specified database connection.
     *
     * @param string $key
     *   (optional) The connection key for which to return information.
     *
     * @return array|null
     */
    public static final function getConnectionInfo($key = 'default') {
        if (!empty(self::$databaseInfo[$key])) {
            return self::$databaseInfo[$key];
        }
    }
    
    /**
     * Gets connection information for all available databases.
     *
     * @return array
     */
    public static final function getAllConnectionInfo() {
        return self::$databaseInfo;
    }
    
    /**
     * Sets connection information for multiple databases.
     *
     * @param array $databases
     *   A multi-dimensional array specifying database connection parameters, as
     *   defined in settings.php.
     */
    public static final function setMultipleConnectionInfo(array $databases) {
        foreach ($databases as $key => $targets) {
            foreach ($targets as $target => $info) {
                self::addConnectionInfo($key, $target, $info);
            }
        }
    }
    
    /**
     * Rename a connection and its corresponding connection information.
     *
     * @param string $old_key
     *   The old connection key.
     * @param string $new_key
     *   The new connection key.
     *
     * @return bool
     *   TRUE in case of success, FALSE otherwise.
     */
    public static final function renameConnection($old_key, $new_key) {
        if (!empty(self::$databaseInfo[$old_key]) && empty(self::$databaseInfo[$new_key])) {
            // Migrate the database connection information.
            self::$databaseInfo[$new_key] = self::$databaseInfo[$old_key];
            unset(self::$databaseInfo[$old_key]);
            // Migrate over the DatabaseConnection object if it exists.
            if (isset(self::$connections[$old_key])) {
                self::$connections[$new_key] = self::$connections[$old_key];
                unset(self::$connections[$old_key]);
            }
            return TRUE;
        }
        else {
            return FALSE;
        }
    }
    
    /**
     * Remove a connection and its corresponding connection information.
     *
     * @param string $key
     *   The connection key.
     *
     * @return bool
     *   TRUE in case of success, FALSE otherwise.
     */
    public static final function removeConnection($key) {
        if (isset(self::$databaseInfo[$key])) {
            self::closeConnection(NULL, $key);
            unset(self::$databaseInfo[$key]);
            return TRUE;
        }
        else {
            return FALSE;
        }
    }
    
    /**
     * Opens a connection to the server specified by the given key and target.
     *
     * @param string $key
     *   The database connection key, as specified in settings.php. The default is
     *   "default".
     * @param string $target
     *   The database target to open.
     *
     * @throws \Drupal\Core\Database\ConnectionNotDefinedException
     * @throws \Drupal\Core\Database\DriverNotSpecifiedException
     */
    protected static final function openConnection($key, $target) {
        // If the requested database does not exist then it is an unrecoverable
        // error.
        if (!isset(self::$databaseInfo[$key])) {
            throw new ConnectionNotDefinedException('The specified database connection is not defined: ' . $key);
        }
        if (!($driver = self::$databaseInfo[$key][$target]['driver'])) {
            throw new DriverNotSpecifiedException('Driver not specified for this database connection: ' . $key);
        }
        $namespace = static::getDatabaseDriverNamespace(self::$databaseInfo[$key][$target]);
        $driver_class = $namespace . '\\Connection';
        $pdo_connection = $driver_class::open(self::$databaseInfo[$key][$target]);
        $new_connection = new $driver_class($pdo_connection, self::$databaseInfo[$key][$target]);
        $new_connection->setTarget($target);
        $new_connection->setKey($key);
        // If we have any active logging objects for this connection key, we need
        // to associate them with the connection we just opened.
        if (!empty(self::$logs[$key])) {
            $new_connection->setLogger(self::$logs[$key]);
        }
        return $new_connection;
    }
    
    /**
     * Closes a connection to the server specified by the given key and target.
     *
     * @param string $target
     *   The database target name.  Defaults to NULL meaning that all target
     *   connections will be closed.
     * @param string $key
     *   The database connection key. Defaults to NULL which means the active key.
     */
    public static function closeConnection($target = NULL, $key = NULL) {
        // Gets the active connection by default.
        if (!isset($key)) {
            $key = self::$activeKey;
        }
        // To close a connection, it needs to be set to NULL and removed from the
        // static variable. In all cases, closeConnection() might be called for a
        // connection that was not opened yet, in which case the key is not defined
        // yet and we just ensure that the connection key is undefined.
        if (isset($target)) {
            if (isset(self::$connections[$key][$target])) {
                self::$connections[$key][$target]->destroy();
                self::$connections[$key][$target] = NULL;
            }
            unset(self::$connections[$key][$target]);
        }
        else {
            if (isset(self::$connections[$key])) {
                foreach (self::$connections[$key] as $target => $connection) {
                    self::$connections[$key][$target]->destroy();
                    self::$connections[$key][$target] = NULL;
                }
            }
            unset(self::$connections[$key]);
        }
    }
    
    /**
     * Instructs the system to temporarily ignore a given key/target.
     *
     * At times we need to temporarily disable replica queries. To do so, call this
     * method with the database key and the target to disable. That database key
     * will then always fall back to 'default' for that key, even if it's defined.
     *
     * @param string $key
     *   The database connection key.
     * @param string $target
     *   The target of the specified key to ignore.
     */
    public static function ignoreTarget($key, $target) {
        self::$ignoreTargets[$key][$target] = TRUE;
    }
    
    /**
     * Converts a URL to a database connection info array.
     *
     * @param string $url
     *   The URL.
     * @param string $root
     *   The root directory of the Drupal installation.
     *
     * @return array
     *   The database connection info.
     *
     * @throws \InvalidArgumentException
     *   Exception thrown when the provided URL does not meet the minimum
     *   requirements.
     * @throws \RuntimeException
     *   Exception thrown when a module provided database driver does not exist.
     */
    public static function convertDbUrlToConnectionInfo($url, $root) {
        // Check that the URL is well formed, starting with 'scheme://', where
        // 'scheme' is a database driver name.
        if (preg_match('/^(.*):\\/\\//', $url, $matches) !== 1) {
            throw new \InvalidArgumentException("Missing scheme in URL '{$url}'");
        }
        $driver = $matches[1];
        // Determine if the database driver is provided by a module.
        $module = NULL;
        $connection_class = NULL;
        $url_components = parse_url($url);
        if (isset($url_components['query'])) {
            parse_str($url_components['query'], $query);
            if (isset($query['module']) && $query['module']) {
                $module = $query['module'];
                // Set up an additional autoloader. We don't use the main autoloader as
                // this method can be called before Drupal is installed and is never
                // called during regular runtime.
                $namespace = "Drupal\\{$module}\\Driver\\Database\\{$driver}";
                $psr4_base_directory = Database::findDriverAutoloadDirectory($namespace, $root, TRUE);
                $additional_class_loader = new ClassLoader();
                $additional_class_loader->addPsr4($namespace . '\\', $psr4_base_directory);
                $additional_class_loader->register(TRUE);
                $connection_class = $custom_connection_class = $namespace . '\\Connection';
            }
        }
        if (!$module) {
            // Determine the connection class to use. Discover if the URL has a valid
            // driver scheme. Try with Drupal 8 style custom drivers first, since
            // those can override/extend the core ones.
            $connection_class = $custom_connection_class = "Drupal\\Driver\\Database\\{$driver}\\Connection";
            if (!class_exists($connection_class)) {
                // If the URL is not relative to a custom driver, try with core ones.
                $connection_class = "Drupal\\Core\\Database\\Driver\\{$driver}\\Connection";
            }
        }
        if (!class_exists($connection_class)) {
            throw new \InvalidArgumentException("Can not convert '{$url}' to a database connection, class '{$custom_connection_class}' does not exist");
        }
        $options = $connection_class::createConnectionOptionsFromUrl($url, $root);
        // If the driver is provided by a module add the necessary information to
        // autoload the code.
        // @see \Drupal\Core\Site\Settings::initialize()
        if (isset($psr4_base_directory)) {
            $options['autoload'] = $psr4_base_directory;
        }
        return $options;
    }
    
    /**
     * Finds the directory to add to the autoloader for the driver's namespace.
     *
     * For Drupal sites that manage their codebase with Composer, the package
     * that provides the database driver should add the driver's namespace to
     * Composer's autoloader. However, to support sites that add Drupal modules
     * without Composer, and because the database connection must be established
     * before Drupal adds the module's entire namespace to the autoloader, the
     * database connection info array can include an "autoload" key containing
     * the autoload directory for the driver's namespace. For requests that
     * connect to the database via a connection info array, the value of the
     * "autoload" key is automatically added to the autoloader.
     *
     * This method can be called to find the default value of that key when the
     * database connection info array isn't available. This includes:
     * - Console commands and test runners that connect to a database specified
     *   by a database URL rather than a connection info array.
     * - During installation, prior to the connection info array being written to
     *   settings.php.
     *
     * This method returns the directory that must be added to the autoloader for
     * the given namespace.
     * - If the namespace is a sub-namespace of a Drupal module, then this method
     *   returns the autoload directory for that namespace, allowing Drupal
     *   modules containing database drivers to be added to a Drupal website
     *   without Composer.
     * - If the namespace is a sub-namespace of Drupal\Core or Drupal\Driver,
     *   then this method returns FALSE, because Drupal core's autoloader already
     *   includes these namespaces, so no additional autoload directory is
     *   required for any code within them.
     * - If the namespace is anything else, then this method returns FALSE,
     *   because neither drupal_get_database_types() nor
     *   static::convertDbUrlToConnectionInfo() support that anyway. One can
     *   manually edit the connection info array in settings.php to reference
     *   any arbitrary namespace, but requests using that would use the
     *   corresponding 'autoload' key in that connection info rather than calling
     *   this method.
     *
     * @param string $namespace
     *   The database driver's namespace.
     * @param string $root
     *   The root directory of the Drupal installation.
     *
     * @return string|false
     *   The PSR-4 directory to add to the autoloader for the namespace if the
     *   namespace is a sub-namespace of a Drupal module. FALSE otherwise, as
     *   explained above.
     *
     * @throws \RuntimeException
     *   Exception thrown when a module provided database driver does not exist.
     */
    public static function findDriverAutoloadDirectory($namespace, $root) {
        // As explained by this method's documentation, return FALSE if the
        // namespace is not a sub-namespace of a Drupal module.
        if (!static::isWithinModuleNamespace($namespace)) {
            return FALSE;
        }
        // Extract the module information from the namespace.
        list(, $module, $module_relative_namespace) = explode('\\', $namespace, 3);
        // The namespace is within a Drupal module. Find the directory where the
        // module is located.
        $extension_discovery = new ExtensionDiscovery($root, FALSE, []);
        $modules = $extension_discovery->scan('module');
        if (!isset($modules[$module])) {
            throw new \RuntimeException(sprintf("Cannot find the module '%s' for the database driver namespace '%s'", $module, $namespace));
        }
        $module_directory = $modules[$module]->getPath();
        // All code within the Drupal\MODULE namespace is expected to follow a
        // PSR-4 layout within the module's "src" directory.
        $driver_directory = $module_directory . '/src/' . str_replace('\\', '/', $module_relative_namespace) . '/';
        if (!is_dir($root . '/' . $driver_directory)) {
            throw new \RuntimeException(sprintf("Cannot find the database driver namespace '%s' in module '%s'", $namespace, $module));
        }
        return $driver_directory;
    }
    
    /**
     * Gets database connection info as a URL.
     *
     * @param string $key
     *   (Optional) The database connection key.
     *
     * @return string
     *   The connection info as a URL.
     *
     * @throws \RuntimeException
     *   When the database connection is not defined.
     */
    public static function getConnectionInfoAsUrl($key = 'default') {
        $db_info = static::getConnectionInfo($key);
        if (empty($db_info) || empty($db_info['default'])) {
            throw new \RuntimeException("Database connection {$key} not defined or missing the 'default' settings");
        }
        $namespace = static::getDatabaseDriverNamespace($db_info['default']);
        // If the driver namespace is within a Drupal module, add the module name
        // to the connection options to make it easy for the connection class's
        // createUrlFromConnectionOptions() method to add it to the URL.
        if (static::isWithinModuleNamespace($namespace)) {
            $db_info['default']['module'] = explode('\\', $namespace)[1];
        }
        $connection_class = $namespace . '\\Connection';
        return $connection_class::createUrlFromConnectionOptions($db_info['default']);
    }
    
    /**
     * Gets the PHP namespace of a database driver from the connection info.
     *
     * @param array $connection_info
     *   The database connection information, as defined in settings.php. The
     *   structure of this array depends on the database driver it is connecting
     *   to.
     *
     * @return string
     *   The PHP namespace of the driver's database.
     */
    protected static function getDatabaseDriverNamespace(array $connection_info) {
        if (isset($connection_info['namespace'])) {
            return $connection_info['namespace'];
        }
        // Fallback for Drupal 7 settings.php.
        return 'Drupal\\Core\\Database\\Driver\\' . $connection_info['driver'];
    }
    
    /**
     * Checks whether a namespace is within the namespace of a Drupal module.
     *
     * This can be used to determine if a database driver's namespace is provided
     * by a Drupal module.
     *
     * @param string $namespace
     *   The namespace (for example, of a database driver) to check.
     *
     * @return bool
     *   TRUE if the passed in namespace is a sub-namespace of a Drupal module's
     *   namespace.
     *
     * @todo https://www.drupal.org/project/drupal/issues/3125476 Remove if we
     *   add this to the extension API or if
     *   \Drupal\Core\Database\Database::getConnectionInfoAsUrl() is removed.
     */
    private static function isWithinModuleNamespace(string $namespace) {
        list($first, $second) = explode('\\', $namespace, 3);
        // The namespace for Drupal modules is Drupal\MODULE_NAME, and the module
        // name must be all lowercase. Second-level namespaces containing uppercase
        // letters (e.g., "Core", "Component", "Driver") are not modules.
        // @see \Drupal\Core\DrupalKernel::getModuleNamespacesPsr4()
        // @see https://www.drupal.org/docs/8/creating-custom-modules/naming-and-placing-your-drupal-8-module#s-name-your-module
        return $first === 'Drupal' && strtolower($second) === $second;
    }

}