import Tone from "../core/Tone";
import "../signal/Signal";
import "../signal/Subtract";
import "../signal/EqualPowerGain";
import "../core/Gain";
import "../core/AudioNode";

/**
 * @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.AudioNode}
 * @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.AudioNode.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(Tone.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._one = this.context.getConstant(1);

	/**
	 *  invert the incoming signal
	 *  @private
	 *  @type {Tone.Subtract}
	 */
	this._invert = new Tone.Subtract();

	//connections
	this.a.connect(this.output);
	this.b.connect(this.output);
	this.fade.chain(this._equalPowerB, this.b.gain);
	Tone.connect(this._one, this._invert, 0, 0);
	this.fade.connect(this._invert, 0, 1);
	this._invert.chain(this._equalPowerA, this.a.gain);
	this._readOnly("fade");
};

Tone.extend(Tone.CrossFade, Tone.AudioNode);

/**
 *  clean up
 *  @returns {Tone.CrossFade} this
 */
Tone.CrossFade.prototype.dispose = function(){
	Tone.AudioNode.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._one = null;
	this.a.dispose();
	this.a = null;
	this.b.dispose();
	this.b = null;
	return this;
};

export default Tone.CrossFade;