add the generic handler and the request classes

ChainOfResponsibilities/Handler.php

@@ -0,0 +1,58 @@
+<?php
+
+/*
+ * DesignPatternPHP
+ */
+
+namespace DesignPatterns\ChainOfResponsibilities;
+
+/**
+ * Handler is a generic handler in the chain of responsibilities
+ */
+abstract class Handler implements KeyValueStorage
+{
+
+    protected $successor = null;
+
+    /**
+     * Append a responsibility to the end of chain
+     * 
+     * A prepend method could be done with the same spirit
+     * 
+     * You could also send the successor in the contructor but in PHP it is a
+     * bad idea because you have to remove the type-hint of the parameter because
+     * the last handler has a null successor.
+     * 
+     * And if you override the contructor, your Handler can no longer have a
+     * successor. One solution is to provide a NullObject (see pattern) 
+     */
+    final public function append(Handler $handler)
+    {
+        if (is_null($this->successor)) {
+            $this->successor = $handler;
+        } else {
+            $this->successor->append($handler);
+        }
+    }
+
+    /**
+     * Handle the request. 
+     * 
+     * This approach by using a template method pattern ensures you that 
+     * each subclass will not forget to call the successor. Beside, the returned
+     * boolean value indicates you if the request have been processed or not.
+     */
+    final public function handle(Request $req)
+    {
+        $processed = $this->processing($req);
+        if (!$processed) {
+            if (!is_null($this->successor)) {
+                $processed = $this->successor->handle($req);
+            }
+        }
+
+        return $processed;
+    }
+
+    abstract protected function processing(Request $req);
+}