DBConnection PHP class - Working MySQL PDO connection

<?php
namespace Lampfire\CloutLib\DB;

/**
 * Creates a PDO object based on a given configuration. Once the instance is constructed, the
 * configuration is immutable, though the internal PDO reference may change state.
 * @package Database
 * @author David Cloutman
 */
class DBConnector implements PDOWrapperInterface {
    /**
     * Database type
     * @var string
     */
    protected $dbType;

    /**
     * Database username
     * @var string
     */
    protected $username;

    /**
     * Database password
     * @var [type]
     */
    protected $password;

    /**
     * Database name
     * @var string
     */
    protected $dbName;

    /**
     * Database domain or I.P address.
     * @var string
     */
    protected $hostName;

    /**
     * The associated PDO object.
     * @var null|\PDO
     */
    protected $pdo = null;

    /**
     * An array of allowed values for $dbType.
     */
    const SUPPORTED_DB_TYPES = ['pgsql', 'mysql'];

    /**
     * Create a new DBConnector instance.
     * @param string $dbType Database type. Either 'mysql' or 'pgsql'.
     * @param string $username The database user used to authenticate into the database server.
     * @param string $password The password used to authenticate into the database server.
     * @param string $dbName   The name of the database.
     * @param string $hostname The domain name or IP address of the database server. Defaults to 'localhost'. An empty string will create a socket connection for Postgres (type='pgsql');
     * @param int $port        The port of the database server. Defaults to usual value for $dbType.
     */
    function __construct($dbType, $username, $password, $dbName, $hostname = 'localhost', $port = null) {
        $this->dbType = $dbType;
        if(!$this->isValidDBType()) {
            throw new InvalidDBTypeException();
        }

        $this->username = $username;
        $this->password = $password;
        $this->dbName = $dbName;
        $this->hostName = $hostname;
        if (null === $port) {
            $this->port = $this->setDefaultPort();
        }
    }

    /**
     * Returns the type of database specified when the constructor was called. Valid values are 'mysql' or 'pgsql'.
     * @return string
     */
    public function getDBType() {
        return $dbType;
    }

    /**
     * Returns the database username.
     * @return string
     */
    public function getUsername() {
        return $this->username;
    }

    /**
     * Returns the database password.
     * @return string
     */
    public function getPassword() {
        return $this->password;
    }

    /**
     * Returns the database name.
     * @return string
     */
    public function getDbName() {
        return $this->dbName;
    }

    /**
     * Returns the database's hostname of i.p. address depending on which was configured.
     * @return string
     */
    public function getHostName() {
        return $this->hostName;
    }

    /**
     * Returns the PDO object generated by the connector or null if one is not associated with the connector.
     * @return \PDO|null
     */
    public function getPDO() {
        return $this->pdo;
    }

    /**
     * This internal function will set the $port property to the most common default for the given database type.
     */
    protected function setDefaultPort () {
        switch ($this->dbType) {
            case 'mysql':
                $this->port = 3306;
                break;
            case 'pgsql':
                $this->port = 5432;
                break;

            default:
                throw new InvalidDBTypeException();
                break;
        }
    }

    /**
     * Tests to see if the database type string supplied in the constructor matches supported databases.
     * Supported types: mysql, pgsql
     * @return boolean True if database type is supported.
     */
    protected function isValidDBType() {
        if (false !== array_search(self::SUPPORTED_DB_TYPES)) {
            return true;
        }

        return false;
    }


    /**
     * Creates a PDO connection string for the specified type of database.
     * @return string         A connection string.
     * @throws  \Exception Throws a base exception when $dbType is unsupported.
     */
    protected function generateConnectionString() {
        $connectionString = '';
        switch ($dbType) {
            case 'mysql':
                $connectionString = "mysql:host={$this->hostName};port={$this->port};dbname={$this->dbName}";
            break;
            case 'pgsql':
                $connectionString .= 'pgsql:';
                $connectionString .= (empty($this->hostName)) ? '' : "host={$this->hostName};"; // Skip empty hostname to establish socket connection.
                $connectionString .= "port={$this->port};dbname={$this->dbName};user={$this->username};password={$this->password}";
            break;
            default:
                throw new InvalidDBTypeException();
        }

        return $connectionString;
    }

    /**
     * Create a PDO connection. Note that you must call connect() explicitly to connect to the database. connect() is NOT called by the costructor.
     * @return \PDO|null|boolean Returns a PDO object connected to the specified database on success, boolean false on failure.
     *
     */
    public function connect() {
        if(null === $this->pdo) {
            try {
                $this->pdo = new \PDO('mysql:host=' . $this->hostName . ';dbname=' . $this->dbName, $this->username, $this->password);
                return $this->pdo;
            }
            catch (\PDOException $e) {
                error_log('Error Could not connect to database. PDOException: ' . $e->getMessage());
                return false;
            }
        }
        return $this->pdo;
    }

    /**
     * Closes the PDO if no other variables reference the instance. Subsequent calls to connect() will
     * create an new PDO object and a new connection. External variables referencing the PDO object will
     * cause the connection to persist.
     * @return null
     */
    public function close() {
        $this->pdo = null;
    }

    /**
     * Automatically calls close() when the object is destroyed.
     */
    public function __destruct(){
        $this->close();
    }
}

/**
 * Flags a class as having a PDO object as part of its composition.
 * @package Database
 */
interface PDOWrapperInterface {
    /**
     * The extending contains a retrievable PDO object as part of its composition.
     * @return \PDO returns the encapsulated PDO object.
     */
    public function getPDO();
}