define(["Tone/core/Tone", "Tone/signal/Signal", "Tone/signal/Expr", 
	"Tone/signal/EqualPowerGain", "Tone/core/Gain"], function(Tone){

	"use strict";

	/**
	 * @class  Tone.Crossfade provides equal power fading between two inputs. 
	 *         More on crossfading technique [here](https://en.wikipedia.org/wiki/Fade_(audio_engineering)#Crossfading).
	 *
	 * @constructor
	 * @extends {Tone}
	 * @param {NormalRange} [initialFade=0.5]
	 * @example
	 * var crossFade = new Tone.CrossFade(0.5);
	 * //connect effect A to crossfade from
	 * //effect output 0 to crossfade input 0
	 * effectA.connect(crossFade, 0, 0);
	 * //connect effect B to crossfade from
	 * //effect output 0 to crossfade input 1
	 * effectB.connect(crossFade, 0, 1);
	 * crossFade.fade.value = 0;
	 * // ^ only effectA is output
	 * crossFade.fade.value = 1;
	 * // ^ only effectB is output
	 * crossFade.fade.value = 0.5;
	 * // ^ the two signals are mixed equally. 
	 */		
	Tone.CrossFade = function(initialFade){

		Tone.call(this);
		this.createInsOuts(2, 1);

		/**
		 *  Alias for <code>input[0]</code>. 
		 *  @type {Tone.Gain}
		 */
		this.a = this.input[0] = new Tone.Gain();

		/**
		 *  Alias for <code>input[1]</code>. 
		 *  @type {Tone.Gain}
		 */
		this.b = this.input[1] = new Tone.Gain();

		/**
		 * 	The mix between the two inputs. A fade value of 0
		 * 	will output 100% <code>input[0]</code> and 
		 * 	a value of 1 will output 100% <code>input[1]</code>. 
		 *  @type {NormalRange}
		 *  @signal
		 */
		this.fade = new Tone.Signal(this.defaultArg(initialFade, 0.5), Tone.Type.NormalRange);

		/**
		 *  equal power gain cross fade
		 *  @private
		 *  @type {Tone.EqualPowerGain}
		 */
		this._equalPowerA = new Tone.EqualPowerGain();

		/**
		 *  equal power gain cross fade
		 *  @private
		 *  @type {Tone.EqualPowerGain}
		 */
		this._equalPowerB = new Tone.EqualPowerGain();
		
		/**
		 *  invert the incoming signal
		 *  @private
		 *  @type {Tone}
		 */
		this._invert = new Tone.Expr("1 - $0");

		//connections
		this.a.connect(this.output);
		this.b.connect(this.output);
		this.fade.chain(this._equalPowerB, this.b.gain);
		this.fade.chain(this._invert, this._equalPowerA, this.a.gain);
		this._readOnly("fade");
	};

	Tone.extend(Tone.CrossFade);

	/**
	 *  clean up
	 *  @returns {Tone.CrossFade} this
	 */
	Tone.CrossFade.prototype.dispose = function(){
		Tone.prototype.dispose.call(this);
		this._writable("fade");
		this._equalPowerA.dispose();
		this._equalPowerA = null;
		this._equalPowerB.dispose();
		this._equalPowerB = null;
		this.fade.dispose();
		this.fade = null;
		this._invert.dispose();
		this._invert = null;
		this.a.dispose();
		this.a = null;
		this.b.dispose();
		this.b = null;
		return this;
	};

	return Tone.CrossFade;
});