/**
 * @author Mugen87 / https://github.com/Mugen87
 *
 */

THREE.Refractor = function ( geometry, options ) {

	THREE.Mesh.call( this, geometry );

	this.type = 'Refractor';

	var scope = this;

	options = options || {};

	var color = ( options.color !== undefined ) ? new THREE.Color( options.color ) : new THREE.Color( 0x7F7F7F );
	var textureWidth = options.textureWidth || 512;
	var textureHeight = options.textureHeight || 512;
	var clipBias = options.clipBias || 0;
	var shader = options.shader || THREE.Refractor.RefractorShader;

	//

	var virtualCamera = new THREE.PerspectiveCamera();
	virtualCamera.matrixAutoUpdate = false;
	virtualCamera.userData.refractor = true;

	//

	var refractorPlane = new THREE.Plane();
	var textureMatrix = new THREE.Matrix4();

	// render target

	var parameters = {
		minFilter: THREE.LinearFilter,
		magFilter: THREE.LinearFilter,
		format: THREE.RGBFormat,
		stencilBuffer: false
	};

	var renderTarget = new THREE.WebGLRenderTarget( textureWidth, textureHeight, parameters );

	if ( ! THREE.Math.isPowerOfTwo( textureWidth ) || ! THREE.Math.isPowerOfTwo( textureHeight ) ) {

		renderTarget.texture.generateMipmaps = false;

	}

	// material

	this.material = new THREE.ShaderMaterial( {
		uniforms: THREE.UniformsUtils.clone( shader.uniforms ),
		vertexShader: shader.vertexShader,
		fragmentShader: shader.fragmentShader,
		transparent: true // ensures, refractors are drawn from farthest to closest
	} );

	this.material.uniforms[ "color" ].value = color;
	this.material.uniforms[ "tDiffuse" ].value = renderTarget.texture;
	this.material.uniforms[ "textureMatrix" ].value = textureMatrix;

	// functions

	var visible = ( function () {

		var refractorWorldPosition = new THREE.Vector3();
		var cameraWorldPosition = new THREE.Vector3();
		var rotationMatrix = new THREE.Matrix4();

		var view = new THREE.Vector3();
		var normal = new THREE.Vector3();

		return function visible( camera ) {

			refractorWorldPosition.setFromMatrixPosition( scope.matrixWorld );
			cameraWorldPosition.setFromMatrixPosition( camera.matrixWorld );

			view.subVectors( refractorWorldPosition, cameraWorldPosition );

			rotationMatrix.extractRotation( scope.matrixWorld );

			normal.set( 0, 0, 1 );
			normal.applyMatrix4( rotationMatrix );

			return view.dot( normal ) < 0;

		};

	} )();

	var updateRefractorPlane = ( function () {

		var normal = new THREE.Vector3();
		var position = new THREE.Vector3();
		var quaternion = new THREE.Quaternion();
		var scale = new THREE.Vector3();

		return function updateRefractorPlane() {

			scope.matrixWorld.decompose( position, quaternion, scale );
			normal.set( 0, 0, 1 ).applyQuaternion( quaternion ).normalize();

			// flip the normal because we want to cull everything above the plane

			normal.negate();

			refractorPlane.setFromNormalAndCoplanarPoint( normal, position );

		};

	} )();

	var updateVirtualCamera = ( function () {

		var clipPlane = new THREE.Plane();
		var clipVector = new THREE.Vector4();
		var q = new THREE.Vector4();

		return function updateVirtualCamera( camera ) {

			virtualCamera.matrixWorld.copy( camera.matrixWorld );
			virtualCamera.matrixWorldInverse.getInverse( virtualCamera.matrixWorld );
			virtualCamera.projectionMatrix.copy( camera.projectionMatrix );
			virtualCamera.far = camera.far; // used in WebGLBackground

			// The following code creates an oblique view frustum for clipping.
			// see: Lengyel, Eric. “Oblique View Frustum Depth Projection and Clipping”.
			// Journal of Game Development, Vol. 1, No. 2 (2005), Charles River Media, pp. 5–16

			clipPlane.copy( refractorPlane );
			clipPlane.applyMatrix4( virtualCamera.matrixWorldInverse );

			clipVector.set( clipPlane.normal.x, clipPlane.normal.y, clipPlane.normal.z, clipPlane.constant );

			// calculate the clip-space corner point opposite the clipping plane and
			// transform it into camera space by multiplying it by the inverse of the projection matrix

			var projectionMatrix = virtualCamera.projectionMatrix;

			q.x = ( Math.sign( clipVector.x ) + projectionMatrix.elements[ 8 ] ) / projectionMatrix.elements[ 0 ];
			q.y = ( Math.sign( clipVector.y ) + projectionMatrix.elements[ 9 ] ) / projectionMatrix.elements[ 5 ];
			q.z = - 1.0;
			q.w = ( 1.0 + projectionMatrix.elements[ 10 ] ) / projectionMatrix.elements[ 14 ];

			// calculate the scaled plane vector

			clipVector.multiplyScalar( 2.0 / clipVector.dot( q ) );

			// replacing the third row of the projection matrix

			projectionMatrix.elements[ 2 ] = clipVector.x;
			projectionMatrix.elements[ 6 ] = clipVector.y;
			projectionMatrix.elements[ 10 ] = clipVector.z + 1.0 - clipBias;
			projectionMatrix.elements[ 14 ] = clipVector.w;

		};

	} )();

	// This will update the texture matrix that is used for projective texture mapping in the shader.
	// see: http://developer.download.nvidia.com/assets/gamedev/docs/projective_texture_mapping.pdf

	function updateTextureMatrix( camera ) {

		// this matrix does range mapping to [ 0, 1 ]

		textureMatrix.set(
			0.5, 0.0, 0.0, 0.5,
			0.0, 0.5, 0.0, 0.5,
			0.0, 0.0, 0.5, 0.5,
			0.0, 0.0, 0.0, 1.0
		);

		// we use "Object Linear Texgen", so we need to multiply the texture matrix T
		// (matrix above) with the projection and view matrix of the virtual camera
		// and the model matrix of the refractor

		textureMatrix.multiply( camera.projectionMatrix );
		textureMatrix.multiply( camera.matrixWorldInverse );
		textureMatrix.multiply( scope.matrixWorld );

	}

	//

	function render( renderer, scene, camera ) {

		scope.visible = false;

		var currentRenderTarget = renderer.getRenderTarget();
		var currentVrEnabled = renderer.vr.enabled;
		var currentShadowAutoUpdate = renderer.shadowMap.autoUpdate;

		renderer.vr.enabled = false; // avoid camera modification
		renderer.shadowMap.autoUpdate = false; // avoid re-computing shadows

		renderer.setRenderTarget( renderTarget );
		renderer.clear();
		renderer.render( scene, virtualCamera );

		renderer.vr.enabled = currentVrEnabled;
		renderer.shadowMap.autoUpdate = currentShadowAutoUpdate;
		renderer.setRenderTarget( currentRenderTarget );

		// restore viewport

		if ( camera.isArrayCamera ) {

			renderer.state.viewport( camera.viewport );

		}

		scope.visible = true;

	}

	//

	this.onBeforeRender = function ( renderer, scene, camera ) {

		// ensure refractors are rendered only once per frame

		if ( camera.userData.refractor === true ) return;

		// avoid rendering when the refractor is viewed from behind

		if ( ! visible( camera ) === true ) return;

		// update

		updateRefractorPlane();

		updateTextureMatrix( camera );

		updateVirtualCamera( camera );

		render( renderer, scene, camera );

	};

	this.getRenderTarget = function () {

		return renderTarget;

	};

};

THREE.Refractor.prototype = Object.create( THREE.Mesh.prototype );
THREE.Refractor.prototype.constructor = THREE.Refractor;

THREE.Refractor.RefractorShader = {

	uniforms: {

		'color': {
			value: null
		},

		'tDiffuse': {
			value: null
		},

		'textureMatrix': {
			value: null
		}

	},

	vertexShader: [

		'uniform mat4 textureMatrix;',

		'varying vec4 vUv;',

		'void main() {',

		'	vUv = textureMatrix * vec4( position, 1.0 );',

		'	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );',

		'}'

	].join( '\n' ),

	fragmentShader: [

		'uniform vec3 color;',
		'uniform sampler2D tDiffuse;',

		'varying vec4 vUv;',

		'float blendOverlay( float base, float blend ) {',

		'	return( base < 0.5 ? ( 2.0 * base * blend ) : ( 1.0 - 2.0 * ( 1.0 - base ) * ( 1.0 - blend ) ) );',

		'}',

		'vec3 blendOverlay( vec3 base, vec3 blend ) {',

		'	return vec3( blendOverlay( base.r, blend.r ), blendOverlay( base.g, blend.g ), blendOverlay( base.b, blend.b ) );',

		'}',

		'void main() {',

		'	vec4 base = texture2DProj( tDiffuse, vUv );',

		'	gl_FragColor = vec4( blendOverlay( base.rgb, color ), 1.0 );',

		'}'

	].join( '\n' )
};
