Allow registering callback functions for the debug console

plugins/system/debug/debug.php

@@ -82,6 +82,14 @@ class PlgSystemDebug extends JPlugin
 	 */
 	protected $app;
 
+	/**
+	 * Container for callback functions to be triggered when rendering the console.
+	 *
+	 * @var    callable[]
+	 * @since  __DEPLOY_VERSION__
+	 */
+	private static $displayCallbacks = array();
+
 	/**
 	 * Constructor.
 	 *
@@ -306,11 +314,56 @@ public function onAfterRespond()
 			}
 		}
 
+		foreach (self::$displayCallbacks as $name => $callable)
+		{
+			$html[] = $this->displayCallback($name, $callable);
+		}
+
 		$html[] = '</div>';
 
 		echo str_replace('</body>', implode('', $html) . '</body>', $contents);
 	}
 
+	/**
+	 * Add a display callback to be rendered with the debug console.
+	 *
+	 * @param   string    $name      The name of the callable, this is used to generate the section title.
+	 * @param   callable  $callable  The callback function to be added.
+	 *
+	 * @return  boolean
+	 *
+	 * @since   __DEPLOY_VERSION__
+	 * @throws  InvalidArgumentException
+	 */
+	public static function addDisplayCallback($name, $callable)
+	{
+		// TODO - When PHP 5.4 is the minimum the parameter should be typehinted "callable" and this check removed
+		if (!is_callable($callable))
+		{
+			throw new InvalidArgumentException('A valid callback function must be given.');
+		}
+
+		self::$displayCallbacks[$name] = $callable;
+
+		return true;
+	}
+
+	/**
+	 * Remove a registered display callback
+	 *
+	 * @param   string  $name  The name of the callable.
+	 *
+	 * @return  boolean
+	 *
+	 * @since   __DEPLOY_VERSION__
+	 */
+	public static function removeDisplayCallback($name)
+	{
+		unset(self::$displayCallbacks[$name]);
+
+		return true;
+	}
+
 	/**
 	 * Method to check if the current user is allowed to see the debug information or not.
 	 *
@@ -393,6 +446,38 @@ protected function display($item, array $errors = array())
 		return implode('', $html);
 	}
 
+	/**
+	 * Display method for callback functions.
+	 *
+	 * @param   string    $name      The name of the callable.
+	 * @param   callable  $callable  The callable function.
+	 *
+	 * @return  string
+	 *
+	 * @since   __DEPLOY_VERSION__
+	 */
+	protected function displayCallback($name, $callable)
+	{
+		$title = JText::_('PLG_DEBUG_' . strtoupper($name));
+
+		$html = array();
+
+		$js = "toggleContainer('dbg_container_" . $name . "');";
+
+		$class = 'dbg-header';
+
+		$html[] = '<div class="' . $class . '" onclick="' . $js . '"><a href="javascript:void(0);"><h3>' . $title . '</h3></a></div>';
+
+		// @todo set with js.. ?
+		$style = ' style="display: none;"';
+
+		$html[] = '<div ' . $style . ' class="dbg-container" id="dbg_container_' . $name . '">';
+		$html[] = call_user_func($callable);
+		$html[] = '</div>';
+
+		return implode('', $html);
+	}
+
 	/**
 	 * Display session information.
 	 *