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use std::fmt;

use webcore::value::Reference;
use webcore::try_from::TryInto;
use webapi::event::{ConcreteEvent, IEvent};

pub struct EventListenerHandle {
    event_type: &'static str,
    reference: Reference,
    listener_reference: Reference
}

impl fmt::Debug for EventListenerHandle {
    fn fmt( &self, formatter: &mut fmt::Formatter ) -> fmt::Result {
        write!( formatter, "EventListenerHandle {{ event_type: {}, reference: {:?} }}", self.event_type, self.reference )
    }
}

impl EventListenerHandle {
    /// Removes the handler from the [IEventTarget](trait.IEventTarget.html) on
    /// which it was previously registered.
    ///
    /// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/removeEventListener)
    pub fn remove( self ) {
        js! { @(no_return)
            var self = @{self.reference};
            var event_type = @{self.event_type};
            var listener = @{self.listener_reference};
            listener.drop();
            self.removeEventListener( event_type, listener );
        }
    }
}

/// `IEventTarget` is an interface implemented by objects that
/// can receive events and may have listeners for them.
///
/// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget)
pub trait IEventTarget: AsRef< Reference > {
    /// Adds given event handler to the list the list of event listeners for
    /// the specified `EventTarget` on which it's called.
    ///
    /// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener)
    fn add_event_listener< T, F >( &self, listener: F ) -> EventListenerHandle
        where T: ConcreteEvent, F: FnMut( T ) + 'static
    {
        let reference = self.as_ref();
        let listener_reference = js! {
            var listener = @{listener};
            @{reference}.addEventListener( @{T::EVENT_TYPE}, listener );
            return listener;
        }.try_into().unwrap();

        EventListenerHandle {
            event_type: T::EVENT_TYPE,
            reference: reference.clone(),
            listener_reference: listener_reference
        }
    }

    /// Dispatches an `Event` at this `EventTarget`, invoking the affected event listeners in the
    /// appropriate order.
    /// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/dispatchEvent)
    fn dispatch_event< T: IEvent >( &self, event: &T ) -> bool {
        js! (
            return @{self.as_ref()}.dispatchEvent( @{event.as_ref()} );
        ).try_into().unwrap()
    }
}

/// A reference to a JavaScript object which implements the [IEventTarget](trait.IEventTarget.html)
/// interface.
///
/// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget)
pub struct EventTarget( Reference );

impl IEventTarget for EventTarget {}

reference_boilerplate! {
    EventTarget,
    instanceof EventTarget
}