class Database {
        const RETURN_QUERY = 0;
        const RETURN_ROW_COUNT = 1;
        const RETURN_LAST_INSERTED = 2;
        const RETURN_ALL_ROWS = 3;


        protected $available_connections = [];
        public $connections = [];

        public function __construct( array $db_connections ) {
            $this->available_connections = $db_connections;
            return $this;
        }

        /**
         * Checks $connections for the specified index. If the index is not found, attempts to create a PDO instance using the provided settings and store it in $connections.
         *
         * @param string $connection_type The index of the desired connection config array passed to the constructor.
         * @param bool $return (optional) If true, return the PDO object. If false, return bool true. Defaults to false.
         * @return bool|PDO Returns bool false on failure. Success return type determined by $return param.
         */
        private function openLink( string $connection_type, $return=false ) {
            if ( !isset( $this->connections[ $connection_type ] ) ) {
                if ( !isset( $this->available_connections[ $connection_type ] ) || !ArrayHelper::multiIsset( $this->available_connections[ $connection_type ], [ 'host', 'database', 'charset', 'user', 'pass' ] ) ) return false;
                try {
                    $this->connections[ $connection_type ] = new PDO(
                        'mysql:host='.$this->available_connections[ $connection_type ][ 'host' ].';dbname='.$this->available_connections[ $connection_type ][ 'database' ].';charset='.$this->available_connections[ $connection_type ][ 'charset' ],
                        ''.$this->available_connections[ $connection_type ][ 'user' ].'',
                        ''.$this->available_connections[ $connection_type ][ 'pass' ].''
                    );
                }
                catch ( Exception $e ) {
                    return false;
                }
            }
            return $return ? $this->connections[ $connection_type ] : true;
        }

        public function closeLink( $connection_type ) {
            if ( isset( $this->connections[ $connection_type ] ) ) {
                $this->connections[ $connection_type ] = NULL;
            }
        }

        public function query( string $connection_type, string $query_text, array $prepared = [], $return=self::RETURN_QUERY ) {
            if ( $this->openLink( $connection_type ) === false ) return false;
            $query = $this->connections[ $connection_type ]->prepare( $query_text );
            if ( $query->execute( $prepared ) !== false ) {
                if ( $return === self::RETURN_QUERY ) return $query;
                elseif ( $return === self::RETURN_ROW_COUNT ) return $query->rowCount();
                elseif ( $return === self::RETURN_ALL_ROWS ) return $query->fetchAll( PDO::FETCH_ASSOC );
                elseif ( $return === self::RETURN_LAST_INSERTED ) return $this->connections[ $connection_type ]->lastInsertId();
            }
            return false;
        }
    }