made ZapHandler library

lib/ZAPController.class.php

@@ -35,6 +35,9 @@ class ZAPController {
 	 * @return string content
 	 */
 	public function fetch() {
+		if (!($this->action instanceof ZAPHandler)) {
+			die('Handler does not implement ZAPHandler interface');
+		}
 		return $this->action->getContent();
 	}
 }

lib/ZAPDisplay.class.php

@@ -2,7 +2,7 @@
 /**
  * Class is responsible for starting up ZAP machine
  */
-class ZAPDisplay {
+class ZAPDisplay implements ZAPHandler {
 	/**
 	 * Template file
 	 */

lib/ZAPHandler.interface.php

@@ -0,0 +1,12 @@
+<?php
+/**
+ * Interface for ZAP mode handlers.
+ * All ZAP handler classes must implement this interface.
+ */
+interface ZAPHandler {
+	/**
+	 * Renders and returns the content for this mode.
+	 * @return string
+	 */
+	public function getContent();
+}

lib/ZAPHome.class.php

@@ -2,7 +2,7 @@
 /**
  * Index class
  */
-class ZAPHome {
+class ZAPHome implements ZAPHandler {
 	/**
 	 * Template file prefix
 	 */

lib/ZAPZap.class.php

@@ -2,7 +2,7 @@
 /**
  * ZAP factory
  */
-class ZAPZap {
+class ZAPZap implements ZAPHandler {
 	private $tpl = '';
 	private $folder;
 	private $height;