<?php
/**
 * Component class file.
 *
 * @link http://www.yiiframework.com/
 * @copyright Copyright &copy; 2008-2012 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

namespace yii\base;

/**
 * Component is the base class for all component classes in Yii.
 *
 * Component provides the *event* and *behavior* features, in addition to
 * the *property* feature which is implemented in its parent class [[Object]].
 *
 * Event is a way to "inject" custom code into existing code at certain places.
 * For example, a button object can trigger a "click" event when the user clicks
 * on the button. We can write custom code and attach it to this event so that
 * when the event is triggered, our custom code will be executed.
 *
 * An event is identified by a name (unique within the class it is defined).
 * Event names are *case-sensitive*.
 *
 * An event can be attached with one or multiple PHP callbacks, called *event handlers*.
 * One can call [[trigger()]] to raise an event. When an event is raised, the attached
 * event handlers will be invoked automatically in the order they are attached to the event.
 *
 * To attach an event handler to an event, call [[on()]]. For example,
 *
 * ~~~
 * $button->on('click', function($event) {
 *     echo "I'm clicked!";
 * });
 * ~~~
 *
 * In the above, we attach an anonymous function to the "click" event of the button.
 * Valid event handlers include:
 *
 * - anonymous function: `function($event) { ... }`
 * - object method: `array($object, 'handleOnClick')`
 * - static method: `array('Page', 'handleOnClick')`
 * - global function: `'handleOnClick'`
 *
 * The signature of an event handler should be like the following:
 * ~~~
 * function foo($event)
 * ~~~
 *
 * where `$event` is an [[Event]] object which includes parameters associated with the event.
 *
 * One can call [[getEventHandlers()]] to retrieve all event handlers that are attached
 * to a specified event. Because this method returns a [[Vector]] object, we can manipulate
 * this object to attach/detach event handlers, or adjust their relative orders.
 *
 * ~~~
 * $handlers = $button->getEventHandlers('click');
 * $handlers->insertAt(0, $callback); // attach a handler as the first one
 * $handlers[] = $callback;           // attach a handler as the last one
 * unset($handlers[0]);               // detach the first handler
 * ~~~
 *
 *
 * A behavior is an instance of [[Behavior]] or its child class. A component can be attached
 * with one or multiple behaviors. When a behavior is attached to a component, its public
 * properties and methods can be accessed via the component directly, as if the component owns
 * those properties and methods.
 *
 * To attach a behavior to a component, declare it in [[behaviors()]], or explicitly call [[attachBehavior]].
 * Behaviors declared in [[behaviors()]] are automatically attached to the corresponding component.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
 */
class Component extends \yii\base\Object
{
	/**
	 * @var Vector[] the attached event handlers (event name => handlers)
	 */
	private $_e;
	/**
	 * @var Behavior[] the attached behaviors (behavior name => behavior)
	 */
	private $_b;

	/**
	 * Returns the value of a component property.
	 * This method will check in the following order and act accordingly:
	 *
	 *  - a property defined by a getter: return the getter result
	 *  - a behavior: return the behavior object
	 *  - a property of a behavior: return the behavior property value
	 *
	 * Do not call this method directly as it is a PHP magic method that
	 * will be implicitly called when executing `$value = $component->property;`.
	 * @param string $name the property name
	 * @return mixed the property value, event handlers attached to the event,
	 * the named behavior, or the value of a behavior's property
	 * @throws Exception if the property is not defined
	 * @see __set
	 */
	public function __get($name)
	{
		$getter = 'get' . $name;
		if (method_exists($this, $getter)) { // read property, e.g. getName()
			return $this->$getter();
		} else { // behavior property
			$this->ensureBehaviors();
			foreach ($this->_b as $behavior) {
				if ($behavior->canGetProperty($name)) {
					return $behavior->$name;
				}
			}
		}
		throw new Exception('Getting unknown property: ' . get_class($this) . '.' . $name);
	}

	/**
	 * Sets the value of a component property.
	 * This method will check in the following order and act accordingly:
	 *
	 *  - a property defined by a setter: set the property value
	 *  - an event: attach the handler to the event
	 *  - a property of a behavior: set the behavior property value
	 *
	 * Do not call this method directly as it is a PHP magic method that
	 * will be implicitly called when executing `$component->property = $value;`.
	 * @param string $name the property name or the event name
	 * @param mixed $value the property value
	 * @throws Exception if the property is not defined or read-only.
	 * @see __get
	 */
	public function __set($name, $value)
	{
		$setter = 'set' . $name;
		if (method_exists($this, $setter)) { // write property
			$this->$setter($value);
			return;
		} elseif (strncmp($name, 'on ', 3) === 0) { // on event
			$name = substr($name, 3);
			$this->getEventHandlers($name)->add($value);
			return;
		} else { // behavior property
			$this->ensureBehaviors();
			foreach ($this->_b as $behavior) {
				if ($behavior->canSetProperty($name)) {
					$behavior->$name = $value;
					return;
				}
			}
		}
		if (method_exists($this, 'get' . $name)) {
			throw new Exception('Setting read-only property: ' . get_class($this) . '.' . $name);
		} else {
			throw new Exception('Setting unknown property: ' . get_class($this) . '.' . $name);
		}
	}

	/**
	 * Checks if a property value is null.
	 * This method will check in the following order and act accordingly:
	 *
	 *  - a property defined by a setter: return whether the property value is null
	 *  - a property of a behavior: return whether the property value is null
	 *
	 * Do not call this method directly as it is a PHP magic method that
	 * will be implicitly called when executing `isset($component->property)`.
	 * @param string $name the property name or the event name
	 * @return boolean whether the named property is null
	 */
	public function __isset($name)
	{
		$getter = 'get' . $name;
		if (method_exists($this, $getter)) { // property is not null
			return $this->$getter() !== null;
		} else { // behavior property
			$this->ensureBehaviors();
			foreach ($this->_b as $behavior) {
				if ($behavior->canGetProperty($name)) {
					return $behavior->$name !== null;
				}
			}
		}
		return false;
	}

	/**
	 * Sets a component property to be null.
	 * This method will check in the following order and act accordingly:
	 *
	 *  - a property defined by a setter: set the property value to be null
	 *  - a property of a behavior: set the property value to be null
	 *
	 * Do not call this method directly as it is a PHP magic method that
	 * will be implicitly called when executing `unset($component->property)`.
	 * @param string $name the property name
	 * @throws Exception if the property is read only.
	 */
	public function __unset($name)
	{
		$setter = 'set' . $name;
		if (method_exists($this, $setter)) { // write property
			$this->$setter(null);
			return;
		} else { // behavior property
			$this->ensureBehaviors();
			foreach ($this->_b as $behavior) {
				if ($behavior->canSetProperty($name)) {
					$behavior->$name = null;
					return;
				}
			}
		}
		if (method_exists($this, 'get' . $name)) {
			throw new Exception('Unsetting read-only property: ' . get_class($this) . '.' . $name);
		}
	}

	/**
	 * Calls the named method which is not a class method.
	 * If the name refers to a component property whose value is
	 * an anonymous function, the method will execute the function.
	 * Otherwise, it will check if any attached behavior has
	 * the named method and will execute it if available.
	 *
	 * Do not call this method directly as it is a PHP magic method that
	 * will be implicitly called when an unknown method is being invoked.
	 * @param string $name the method name
	 * @param array $params method parameters
	 * @return mixed the method return value
	 */
	public function __call($name, $params)
	{
		if ($this->canGetProperty($name, false)) {
			$func = $this->$name;
			if ($func instanceof \Closure) {
				return call_user_func_array($func, $params);
			}
		}

		$this->ensureBehaviors();
		foreach ($this->_b as $object) {
			if (method_exists($object, $name)) {
				return call_user_func_array(array($object, $name), $params);
			}
		}

		throw new Exception('Calling unknown method: ' . get_class($this) . "::$name()");
	}

	/**
	 * Returns a list of behaviors that this component should behave as.
	 *
	 * Child classes may override this method to specify the behaviors they want to behave as.
	 *
	 * The return value of this method should be an array of behavior objects or configurations
	 * indexed by behavior names. A behavior configuration can be either a string specifying
	 * the behavior class or an array of the following structure:
	 *
	 * ~~~
	 * 'behaviorName' => array(
	 *	 'class' => 'BehaviorClass',
	 *	 'property1' => 'value1',
	 *	 'property2' => 'value2',
	 * )
	 * ~~~
	 *
	 * Note that a behavior class must extend from [[Behavior]].
	 *
	 * Behaviors declared in this method will be attached to the component automatically (on demand).
	 *
	 * @return array the behavior configurations.
	 */
	public function behaviors()
	{
		return array();
	}

	/**
	 * Returns a value indicating whether there is any handler attached to the named event.
	 * @param string $name the event name
	 * @return boolean whether there is any handler attached to the event.
	 */
	public function hasEventHandlers($name)
	{
		$this->ensureBehaviors();
		return isset($this->_e[$name]) && $this->_e[$name]->getCount();
	}

	/**
	 * Returns the list of attached event handlers for an event.
	 * You may manipulate the returned [[Vector]] object by adding or removing handlers.
	 * For example,
	 *
	 * ~~~
	 * $component->getEventHandlers($eventName)->insertAt(0, $eventHandler);
	 * ~~~
	 *
	 * @param string $name the event name
	 * @return Vector list of attached event handlers for the event
	 * @throws Exception if the event is not defined
	 */
	public function getEventHandlers($name)
	{
		if (!isset($this->_e[$name])) {
			$this->_e[$name] = new Vector;
		}
		$this->ensureBehaviors();
		return $this->_e[$name];
	}

	/**
	 * Attaches an event handler to an event.
	 *
	 * This is equivalent to the following code:
	 *
	 * ~~~
	 * $component->getEventHandlers($eventName)->add($eventHandler);
	 * ~~~
	 *
	 * An event handler must be a valid PHP callback. The followings are
	 * some examples:
	 *
	 * ~~~
	 * function($event) { ... }		    // anonymous function
	 * array($object, 'handleClick')	// $object->handleClick()
	 * array('Page', 'handleClick')	    // Page::handleClick()
	 * 'handleClick'					// global function handleClick()
	 * ~~~
	 *
	 * An event handler must be defined with the following signature,
	 *
	 * ~~~
	 * function handlerName($event) {}
	 * ~~~
	 *
	 * where `$event` is an [[Event]] object which includes parameters associated with the event.
	 *
	 * @param string $name the event name
	 * @param callback $handler the event handler
	 * @see off
	 */
	public function on($name, $handler)
	{
		$this->getEventHandlers($name)->add($handler);
	}

	/**
	 * Detaches an existing event handler.
	 * This method is the opposite of [[on]].
	 * @param string $name event name
	 * @param callback $handler the event handler to be removed
	 * @return boolean if a handler is found and detached
	 * @see on
	 */
	public function off($name, $handler)
	{
		return $this->getEventHandlers($name)->remove($handler) !== false;
	}

	/**
	 * Triggers an event.
	 * This method represents the happening of an event. It invokes
	 * all attached handlers for the event.
	 * @param string $name the event name
	 * @param Event $event the event parameter
	 * @throws Exception if the event is undefined or an event handler is invalid.
	 */
	public function trigger($name, $event)
	{
		$this->ensureBehaviors();
		if (isset($this->_e[$name])) {
			if ($event instanceof Event) {
				$event->name = $name;
				$event->handled = false;
			}
			foreach ($this->_e[$name] as $handler) {
				call_user_func($handler, $event);
				// stop further handling if the event is handled
				if ($event instanceof Event && $event->handled) {
					return;
				}
			}
		}
	}

	/**
	 * Returns the named behavior object.
	 * The name 'asa' stands for 'as a'.
	 * @param string $behavior the behavior name
	 * @return Behavior the behavior object, or null if the behavior does not exist
	 */
	public function asa($behavior)
	{
		$this->ensureBehaviors();
		return isset($this->_b[$behavior]) ? $this->_b[$behavior] : null;
	}

	/**
	 * Attaches a behavior to this component.
	 * This method will create the behavior object based on the given
	 * configuration. After that, the behavior object will be attached to
	 * this component by calling the [[Behavior::attach]] method.
	 * @param string $name the behavior's name. It should uniquely identify this behavior.
	 * @param string|array|Behavior $behavior the behavior configuration. This can be one of the following:
	 *
	 *  - a [[Behavior]] object
	 *  - a string specifying the behavior class
	 *  - an object configuration array that will be passed to [[\Yii::createObject()]] to create the behavior object.
	 *
	 * @return Behavior the behavior object
	 * @see detachBehavior
	 */
	public function attachBehavior($name, $behavior)
	{
		$this->ensureBehaviors();
		return $this->attachBehaviorInternal($name, $behavior);
	}

	/**
	 * Attaches a list of behaviors to the component.
	 * Each behavior is indexed by its name and should be a [[Behavior]] object,
	 * a string specifying the behavior class, or an
	 * configuration array for creating the behavior.
	 * @param array $behaviors list of behaviors to be attached to the component
	 * @see attachBehavior
	 */
	public function attachBehaviors($behaviors)
	{
		$this->ensureBehaviors();
		foreach ($behaviors as $name => $behavior) {
			$this->attachBehaviorInternal($name, $behavior);
		}
	}

	/**
	 * Detaches a behavior from the component.
	 * The behavior's [[Behavior::detach]] method will be invoked.
	 * @param string $name the behavior's name.
	 * @return Behavior the detached behavior. Null if the behavior does not exist.
	 */
	public function detachBehavior($name)
	{
		if (isset($this->_b[$name])) {
			$behavior = $this->_b[$name];
			unset($this->_b[$name]);
			$behavior->detach($this);
			return $behavior;
		} else {
			return null;
		}
	}

	/**
	 * Detaches all behaviors from the component.
	 */
	public function detachBehaviors()
	{
		if ($this->_b !== null) {
			$behaviors = $this->_b;
			$this->_b = null;
			foreach ($behaviors as $name => $behavior) {
				$this->detachBehavior($name);
			}
		}
	}

	/**
	 * Makes sure that the behaviors declared in [[behaviors()]] are attached to this component.
	 */
	public function ensureBehaviors()
	{
		if ($this->_b === null) {
			$this->_b = array();
			foreach ($this->behaviors() as $name => $behavior) {
				$this->attachBehaviorInternal($name, $behavior);
			}
		}
	}

	/**
	 * Attaches a behavior to this component.
	 * @param string $name the name of the behavior.
	 * @param string|array|Behavior $behavior the behavior to be attached
	 * @return Behavior the attached behavior.
	 */
	private function attachBehaviorInternal($name, $behavior)
	{
		if (!($behavior instanceof Behavior)) {
			$behavior = \Yii::createObject($behavior);
		}
		$behavior->attach($this);
		return $this->_b[$name] = $behavior;
	}
}