/**
 * @author arya-s / https://github.com/arya-s
 *
 * This is a helper for visualising a given light's shadow map.
 * It works for shadow casting lights: DirectionalLight and SpotLight.
 * It renders out the shadow map and displays it on a HUD.
 *
 * Example usage:
 *	1) Import ShadowMapViewer into your app.
 *
 *	2) Create a shadow casting light and name it optionally:
 *		var light = new DirectionalLight( 0xffffff, 1 );
 *		light.castShadow = true;
 *		light.name = 'Sun';
 *
 *	3) Create a shadow map viewer for that light and set its size and position optionally:
 *		var shadowMapViewer = new ShadowMapViewer( light );
 *		shadowMapViewer.size.set( 128, 128 );	//width, height  default: 256, 256
 *		shadowMapViewer.position.set( 10, 10 );	//x, y in pixel	 default: 0, 0 (top left corner)
 *
 *	4) Render the shadow map viewer in your render loop:
 *		shadowMapViewer.render( renderer );
 *
 *	5) Optionally: Update the shadow map viewer on window resize:
 *		shadowMapViewer.updateForWindowResize();
 *
 *	6) If you set the position or size members directly, you need to call shadowMapViewer.update();
 */

THREE.ShadowMapViewer = function ( light ) {

	//- Internals
	var scope = this;
	var doRenderLabel = ( light.name !== undefined && light.name !== '' );
	var userAutoClearSetting;

	//Holds the initial position and dimension of the HUD
	var frame = {
		x: 10,
		y: 10,
		width: 256,
		height: 256
	};

	var camera = new THREE.OrthographicCamera( window.innerWidth / - 2, window.innerWidth / 2, window.innerHeight / 2, window.innerHeight / - 2, 1, 10 );
	camera.position.set( 0, 0, 2 );
	var scene = new THREE.Scene();

	//HUD for shadow map
	var shader = THREE.UnpackDepthRGBAShader;

	var uniforms = THREE.UniformsUtils.clone( shader.uniforms );
	var material = new THREE.ShaderMaterial( {
		uniforms: uniforms,
		vertexShader: shader.vertexShader,
		fragmentShader: shader.fragmentShader
	} );
	var plane = new THREE.PlaneBufferGeometry( frame.width, frame.height );
	var mesh = new THREE.Mesh( plane, material );

	scene.add( mesh );


	//Label for light's name
	var labelCanvas, labelMesh;

	if ( doRenderLabel ) {

		labelCanvas = document.createElement( 'canvas' );

		var context = labelCanvas.getContext( '2d' );
		context.font = 'Bold 20px Arial';

		var labelWidth = context.measureText( light.name ).width;
		labelCanvas.width = labelWidth;
		labelCanvas.height = 25;	//25 to account for g, p, etc.

		context.font = 'Bold 20px Arial';
		context.fillStyle = 'rgba( 255, 0, 0, 1 )';
		context.fillText( light.name, 0, 20 );

		var labelTexture = new THREE.Texture( labelCanvas );
		labelTexture.magFilter = THREE.LinearFilter;
		labelTexture.minFilter = THREE.LinearFilter;
		labelTexture.needsUpdate = true;

		var labelMaterial = new THREE.MeshBasicMaterial( { map: labelTexture, side: THREE.DoubleSide } );
		labelMaterial.transparent = true;

		var labelPlane = new THREE.PlaneBufferGeometry( labelCanvas.width, labelCanvas.height );
		labelMesh = new THREE.Mesh( labelPlane, labelMaterial );

		scene.add( labelMesh );

	}


	function resetPosition() {

		scope.position.set( scope.position.x, scope.position.y );

	}

	//- API
	// Set to false to disable displaying this shadow map
	this.enabled = true;

	// Set the size of the displayed shadow map on the HUD
	this.size = {
		width: frame.width,
		height: frame.height,
		set: function ( width, height ) {

			this.width = width;
			this.height = height;

			mesh.scale.set( this.width / frame.width, this.height / frame.height, 1 );

			//Reset the position as it is off when we scale stuff
			resetPosition();

		}
	};

	// Set the position of the displayed shadow map on the HUD
	this.position = {
		x: frame.x,
		y: frame.y,
		set: function ( x, y ) {

			this.x = x;
			this.y = y;

			var width = scope.size.width;
			var height = scope.size.height;

			mesh.position.set( - window.innerWidth / 2 + width / 2 + this.x, window.innerHeight / 2 - height / 2 - this.y, 0 );

			if ( doRenderLabel ) labelMesh.position.set( mesh.position.x, mesh.position.y - scope.size.height / 2 + labelCanvas.height / 2, 0 );

		}
	};

	this.render = function ( renderer ) {

		if ( this.enabled ) {

			//Because a light's .shadowMap is only initialised after the first render pass
			//we have to make sure the correct map is sent into the shader, otherwise we
			//always end up with the scene's first added shadow casting light's shadowMap
			//in the shader
			//See: https://github.com/mrdoob/three.js/issues/5932
			uniforms.tDiffuse.value = light.shadow.map.texture;

			userAutoClearSetting = renderer.autoClear;
			renderer.autoClear = false; // To allow render overlay
			renderer.clearDepth();
			renderer.render( scene, camera );
			renderer.autoClear = userAutoClearSetting;	//Restore user's setting

		}

	};

	this.updateForWindowResize = function () {

		if ( this.enabled ) {

			 camera.left = window.innerWidth / - 2;
			 camera.right = window.innerWidth / 2;
			 camera.top = window.innerHeight / 2;
			 camera.bottom = window.innerHeight / - 2;
			 camera.updateProjectionMatrix();

			 this.update();

		}

	};

	this.update = function () {

		this.position.set( this.position.x, this.position.y );
		this.size.set( this.size.width, this.size.height );

	};

	//Force an update to set position/size
	this.update();

};

THREE.ShadowMapViewer.prototype.constructor = THREE.ShadowMapViewer;
