DCI_Context.php

<?php

interface Context {
    public function execute($params);
}

DCI_Data.php

<?php

class Data
{
    private $roles = array();

    private $method_map = array();

    public function extend($class)
    {
        $role = new $class($this);
        $this->roles[$class] = $role;

        foreach(get_class_methods($class) as $method)
        {
            $this->method_map[$method] = $role;
        }
    }

    public function unextend($class)
    {
        $role = $this->roles[$class];
        unset($this->roles[$class]);

        $this->method_map = array_filter(
            $this->method_map,
            function($stored_role) use($role){
                return $stored_role !== $role;
            });
    }

    public function __call($method, $args)
    {
        if(! array_key_exists($method, $this->method_map)) {
            throw new Exception("Method $method doesn't exist on this object");
        }

        return call_user_func_array(
            array($this->method_map[$method], $method), $args
        );
    }
}

DCI_Role.php

<?php

class Role
{
    private $data;

    public function __construct($data)
    {
        $this->data = $data;
    }

    public function __get($property)
    {
        return $this->data->$property;
    }

    public function __set($property, $value)
    {
        $this->data->$property = $value;
    }
}

gistfile1.php

<?php

require('DCI_Data.php');
require('DCI_Role.php');
require('DCI_Context.php');

class Account extends Data {
    public $balance = 0;
}

class MoneySource extends Role
{
    public function withdraw($amount)
    {
        if ($amount <= $this->balance)
        {
            $this->balance -= $amount;
            return $amount;
        }
        else
        {
            throw new Exception("Insufficient Funds\n". "Tried to withdraw $amount. {$this->balance} available.");
        }
    }
}

class MoneyDestination extends Role
{
    public function deposit($amount)
    {
        $this->balance += $amount;
    }
}

class Transfer implements Context
{
    private $_source;
    private $_destination;
    private $_amount;

    public function __construct(Account $source, Account $destination, $amount = 0)
    {
        $this->_source = $source;
        $this->_source->extend('MoneySource');
        $this->_destination = $destination;
        $this->_destination->extend('MoneyDestination');
        $this->_amount = $amount;
    }

    public function execute($params = array())
    {
		$withdrawn = $this->_source->withdraw($this->_amount);
		if ($withdrawn)
        {
            $this->_destination->deposit($this->_amount);
        }
    }

}

$source_account = new Account();
$source_account->balance = 20;

$destination_account = new Account();
$destination_account->balance = 0;

$context = new Transfer($source_account, $destination_account, 15);
$context->execute();

var_dump($source_account->balance, $destination_account->balance);