package openfl.events;

/**
	The IEventDispatcher interface defines methods for adding or removing event listeners,
	checks whether specific types of event listeners are registered, and dispatches events.

	Event targets are an important part of the Flash® Player and Adobe AIR event model. The
	event target serves as the focal point for how events flow through the display list
	hierarchy. When an event such as a mouse click or a keypress occurs, an event object is
	dispatched into the event flow from the root of the display list. The event object
	makes a round-trip journey to the event target, which is conceptually divided into
	three phases: the capture phase includes the journey from the root to the last node
	before the event target's node; the target phase includes only the event target node;
	and the bubbling phase includes any subsequent nodes encountered on the return trip to
	the root of the display list.

	In general, the easiest way for a user-defined class to gain event dispatching
	capabilities is to extend EventDispatcher. If this is impossible (that is, if the class
	is already extending another class), you can instead implement the IEventDispatcher
	interface, create an EventDispatcher member, and write simple hooks to route calls
	into the aggregated EventDispatcher.
**/
@:jsRequire("openfl/events/IEventDispatcher", "default")
#if flash
@:native("flash.events.IEventDispatcher")
#end
extern interface IEventDispatcher
{
	/**
		Registers an event listener object with an EventDispatcher object so that the
		listener receives notification of an event. You can register event listeners on all
		nodes in the display list for a specific type of event, phase, and priority.

		After you successfully register an event listener, you cannot change its priority
		through additional calls to `addEventListener()`. To change a listener's priority,
		you must first call `removeEventListener()`. Then you can register the listener
		again with the new priority level.

		After the listener is registered, subsequent calls to `addEventListener()` with a
		different value for either `type` or `useCapture` result in the creation of a
		separate listener registration. For example, if you first register a listener with
		`useCapture` set to true, it listens only during the capture phase. If you call
		`addEventListener()` again using the same listener object, but with `useCapture`
		set to `false`, you have two separate listeners: one that listens during the
		capture phase, and another that listens during the target and bubbling phases.

		You cannot register an event listener for only the target phase or the bubbling
		phase. Those phases are coupled during registration because bubbling applies only
		to the ancestors of the target node.

		When you no longer need an event listener, remove it by calling
		`EventDispatcher.removeEventListener()`; otherwise, memory problems might result.
		Objects with registered event listeners are not automatically removed from memory
		because the garbage collector does not remove objects that still have references.

		Copying an EventDispatcher instance does not copy the event listeners attached to
		it. (If your newly created node needs an event listener, you must attach the
		listener after creating the node.) However, if you move an EventDispatcher
		instance, the event listeners attached to it move along with it.

		If the event listener is being registered on a node while an event is also being
		processed on this node, the event listener is not triggered during the current
		phase but may be triggered during a later phase in the event flow, such as the
		bubbling phase.

		If an event listener is removed from a node while an event is being processed on
		the node, it is still triggered by the current actions. After it is removed, the
		event listener is never invoked again (unless it is registered again for future
		processing).

		@param	type	The type of event.
		@param	listener	The listener function that processes the event. This function
		must accept an event object as its only parameter and must return nothing, as
		this example shows:
		```haxe
		function(evt:Event):Void
		```
		The function can have any name.
		@param	useCapture	Determines whether the listener works in the capture phase or
		the target and bubbling phases. If `useCapture` is set to `true`, the listener
		processes the event only during the capture phase and not in the target or
		bubbling phase. If `useCapture` is `false`, the listener processes the event only
		during the target or bubbling phase. To listen for the event in all three phases,
		call `addEventListener()` twice, once with `useCapture` set to `true`, then again
		with `useCapture` set to `false`.
		@param	priority	The priority level of the event listener. Priorities are
		designated by a 32-bit integer. The higher the number, the higher the priority.
		All listeners with priority `n` are processed before listeners of priority `n-1`.
		If two or more listeners share the same priority, they are processed in the order
		in which they were added. The default priority is 0.
		@param	useWeakReference	Determines whether the reference to the listener is
		strong or weak. A strong reference (the default) prevents your listener from being
		garbage-collected. A weak reference does not.
		Class-level member functions are not subject to garbage collection, so you can set
		`useWeakReference` to `true` for class-level member functions without subjecting
		them to garbage collection. If you set `useWeakReference` to `true` for a listener
		that is a nested inner function, the function will be garbage-collected and no
		longer be persistent. If you create references to the inner function (save it in
		another variable) then it is not garbage-collected and stays persistent.
	**/
	public function addEventListener(type:String, listener:Dynamic->Void, useCapture:Bool = false, priority:Int = 0, useWeakReference:Bool = false):Void;
	
	/**
		Dispatches an event into the event flow. The event target is the EventDispatcher
		object upon which `dispatchEvent()` is called.

		@param	event	The event object dispatched into the event flow.
		@returns	A value of true unless `preventDefault()` is called on the event, in
		which case it returns `false`.
	**/
	public function dispatchEvent(event:Event):Bool;

	/**
		Checks whether the EventDispatcher object has any listeners registered for a
		specific type of event. This allows you to determine where an EventDispatcher
		object has altered handling of an event type in the event flow hierarchy. To
		determine whether a specific event type will actually trigger an event listener,
		use `IEventDispatcher.willTrigger()`.

		The difference between `hasEventListener()` and `willTrigger()` is that
		`hasEventListener()` examines only the object to which it belongs, whereas
		`willTrigger()` examines the entire event flow for the event specified by the `type`
		parameter.

		@param	type	The type of event.
		@returns	A value of `true` if a listener of the specified type is registered;
		`false` otherwise.
	**/
	public function hasEventListener(type:String):Bool;

	/**
		Removes a listener from the EventDispatcher object. If there is no matching
		listener registered with the EventDispatcher object, a call to this method has no
		effect.

		@param	type	The type of event.
		@param	listener	The listener object to remove.
		@param	useCapture	Specifies whether the listener was registered for the capture
		phase or the target and bubbling phases. If the listener was registered for both
		the capture phase and the target and bubbling phases, two calls to
		`removeEventListener()` are required to remove both: one call with `useCapture` set
		to `true`, and another call with `useCapture` set to `false`.
	**/
	public function removeEventListener(type:String, listener:Dynamic->Void, useCapture:Bool = false):Void;
	
	/**
		Checks whether an event listener is registered with this EventDispatcher object or
		any of its ancestors for the specified event type. This method returns `true` if an
		event listener is triggered during any phase of the event flow when an event of
		the specified type is dispatched to this EventDispatcher object or any of its
		descendants.

		The difference between `hasEventListener()` and `willTrigger()` is that
		`hasEventListener()` examines only the object to which it belongs, whereas
		`willTrigger()` examines the entire event flow for the event specified by the
		`type` parameter.

		@param	type	The type of event.
		@returns	A value of `true` if a listener of the specified type will be
		triggered; `false` otherwise.
	**/
	public function willTrigger(type:String):Bool;
}