<?php

namespace ACompany\AnAppName\Dao\PdoImpl;

use PDO;
use Exception;
use PDOException;
/**
 * UPDATE: I'm leaving the author's original comments, but this has been updated to better represent a singleton PDO
 * connection. The author's original code would create a new connection on each call to getConnection.
 *
 * The other thing it did was set all of these methods and properties to 'protected', but then called 'self' - if you
 * want this class to be extendable then you should use 'static' due to PHP's 'Late static binding'.
 *
 * Also I'm using the PSR-2 style guidelines.
 *
 * While I'm NOT condoning this as a 'best practice' I thought I would at least correct the misconception that this was
 * creating a single connection.
 *
 * Usage now is:
 * $pdo = PDOConnection::instance('dsn', 'username', 'password'); // first call only.
 * $connection = $pdo->getConnection();
 *
 * Once you know the instance has been created you can just call: $pdo = PDOConnection::instance();
 *
 **** ORIGINAL COMMENTS ****
 *
 * PDOConnection is a singleton implementation.
 * getConnection() returning an instance of PDO connection.
 *
 * <code>
 * Example usage:
 *
 * $pdo = PDOConnection::instance();
 * $conn = $pdo->getConnection( 'dsn', 'username', 'password' );
 *
 * $results = $conn->query("SELECT * FROM Table");
 *
 * </code>
 *
 * @author rmurray
 */
class PDOConnection
{
    protected static $instance = null;

    /** @var PDO */
    protected $connection = null;
    /**
     * PDOConnection constructor.
     * @param $dsn
     * @param $username
     * @param $password
     * @throws PDOException
     * @throws Exception
     */
    protected function __construct($dsn, $username, $password)
    {
        try {
            $this->connection = new PDO($dsn, $username, $password);
            //Set common attributes
            $this->connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch (PDOException $e) {
            //TODO: flag to disable errors?
            throw $e;
        } catch(Exception $e) {
            //TODO: flag to disable errors?
            throw $e;
        }
    }

    /**
     * Get the current active instance if one exists, otherwise create a new instance.
     *
     * @param string|null $dsn
     * @param string|null $username
     * @param string|null $password
     * @throws PDOException
     * @throws Exception
     * @return PDOConnection
     */
    public static function instance($dsn = null, $username = null, $password = null) {
        if (!isset(static::$instance)) {
            if (!isset($dsn) || !isset($username) || !isset($password)) {
                throw new Exception('No instance exists. You must provide the dsn, username, and password.');
            }

            static::$instance = new static($dsn, $username, $password);
        }

        return static::$instance;
    }

    /**
     * Return a PDO connection
     *
     * @return PDO
     */
    public function getConnection()
    {
        return $this->connection;
    }
    /** PHP seems to need these stubbed to ensure true singleton **/
    private function __clone() {}
    private function __wakeup() {}
}