<?php
/**
 * Product storage/collection/list or what you want.
 *
 * @author Manuel Pichler <mapi@manuel-pichler.de>
 */
class mpProductCatalog
{
    /**
     * GoF singleton instance.
     *
     * @type mpProductCatalog
     * @var mpProductCatalog $instance
     */
    private static $instance = null;

    /**
     * GoF singleton method
     *
     * @return mpProductCatalog
     */
    public static function getInstance()
    {
        if ( self::$instance === null )
        {
            self::$instance = new mpProductCatalog();
        }
        return self::$instance;
    }

    /**
     * List of existing products.
     *
     * @type array<mpProduct>
     * @var array $products
     */
    private $products = array();

    /**
     * Private ctor
     */
    private function __construct()
    {
        $this->products = (array) @unserialize( @file_get_contents( dirname( __FILE__ ) . "/../data/catalog.dat" ) );
    }

    /**
     * Catalog destructor.
     */
    public function __destruct()
    {
        file_put_contents( dirname( __FILE__ ) . "/../data/catalog.dat", serialize( $this->products ) );
    }

    /**
     * Creates a new transaction for the product.
     *
     * @param mpProduct $product
     * @return mpProductTransaction
     */
    public function createTransaction( mpProduct $product )
    {
        return new mpProductTransaction( $product );
    }

    /**
     * Adds the given product to the catalog.
     *
     * @param mpProduct $product
     * @throws mpProductExistsException
     */
    public function addProduct( mpProduct $product )
    {
        if ( isset( $this->products[$product->name] ) )
        {
            throw new mpProductExistsException( $product->name );
        }
        $this->products[$product->name] = $product;
    }
}

/**
 * Product transaction class.
 *
 * @author Manuel Pichler <mapi@manuel-pichler.de>
 */
class mpProductTransaction
{

    /**
     * List of open transactions.
     *
     * @type array<mpProductTransaction>
     * @var array $openTransactions
     */
    private static $openTransactions = array();

    /**
     * The context product.
     *
     * @type mpProduct
     * @var mpProduct $product
     */
    private $product = null;

    /**
     * The transaction ctor.
     *
     * @param mpProduct $product
     */
    public function __construct( mpProduct $product )
    {
        $this->product = $product;
    }

    /**
     * Starts a new product transaction.
     *
     * @throws mpProductInTransactionException
     */
    public function begin() {
        self::openTransaction( $this );
    }

    /**
     * Commits the product transaction.
     *
     * @throws mpProductTransactionNotOpenException
     */
    public function commit() {
        self::closeTransaction( $this );
    }

    /**
     * Rolls the product transaction back.
     *
     * @throws mpProductTransactionNotOpenException
     */
    public function rollback() {
        self::closeTransaction( $this );
    }

    /**
     * Opens the given transaction.
     *
     * @param mpProductTransaction $transaction
     * @throws mpProductInTransactionException
     */
    private static function openTransaction( mpProductTransaction $transaction )
    {
        if ( isset( self::$openTransactions[$transaction->product->name] ) )
        {
            throw new mpProductInTransactionException( $transaction->product->name );
        }
        self::$openTransactions[$transaction->product->name] = true;
    }

    /**
     * Closes the given transaction.
     *
     * @param mpProductTransaction $transaction
     * @throws mpProductTransactionNotOpenException
     */
    private static function closeTransaction( $transaction )
    {
        if ( !isset( self::$openTransactions[$transaction->product->name] ) )
        {
            throw new mpProductTransactionNotOpenException( $transaction->product->name );
        }
        unset( self::$openTransactions[$transaction->product->name] );
    }
}

/**
 * Simple product model.
 *
 * @author Manuel Pichler <mapi@manuel-pichler.de>
 */
class mpProduct
{
    /**
     * The product name.
     *
     * @type string
     * @var string $name
     */
    public $name = null;

    /**
     * Product ctor.
     */
    public function __construct( $name = null )
    {
        $this->name = $name;
    }
}

/**
 * Exception
 *
 * @author Manuel Pichler <mapi@manuel-pichler.de>
 */
class mpProductExistsException extends RuntimeException
{
    /**
     * Exception ctor.
     *
     * @param string $name
     */
    public function __construct( $name )
    {
        parent::__construct( "A product '{$name}' already exists." );
    }
}

/**
 * Exception
 *
 * @author Manuel Pichler <mapi@manuel-pichler.de>
 */
class mpProductInTransactionException extends RuntimeException
{
    /**
     * Exception ctor.
     *
     * @param string $name
     */
    public function __construct( $name )
    {
        parent::__construct( "An open transaction for product '{$name}' already exists." );
    }
}

/**
 * Exception
 *
 * @author Manuel Pichler <mapi@manuel-pichler.de>
 */
class mpProductTransactionNotOpenException extends RuntimeException
{
    /**
     * Exception ctor.
     *
     * @param string $name
     */
    public function __construct( $name )
    {
        parent::__construct( "No open transaction for product '{$name}'." );
    }
}