88 - Added undo example for command pattern

Behavioral/Command/AddMessageDateCommand.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace DesignPatterns\Behavioral\Command;
+
+/**
+ * This concrete command tweaks receiver to add current date to messages
+ * invoker just knows that it can call "execute".
+ */
+class AddMessageDateCommand implements CommandInterface, UndoableCommandInterface
+{
+    /**
+     * @var Receiver
+     */
+    protected $output;
+
+    /**
+     * Each concrete command is built with different receivers.
+     * There can be one, many or completely no receivers, but there can be other commands in the parameters.
+     *
+     * @param Receiver $console
+     */
+    public function __construct(Receiver $console)
+    {
+        $this->output = $console;
+    }
+
+    /**
+     * Execute and make receiver to enable displaying messages date.
+     */
+    public function execute()
+    {
+        // sometimes, there is no receiver and this is the command which
+        // does all the work
+        $this->output->enableDate();
+    }
+
+    /**
+     * Undo the command and make receiver to disable displaying messages date.
+     */
+    public function undo()
+    {
+        // sometimes, there is no receiver and this is the command which
+        // does all the work
+        $this->output->disableDate();
+    }
+}