/**
 * @author dmarcos / https://github.com/dmarcos
 * @author mrdoob / http://mrdoob.com
 *
 * WebVR Spec: http://mozvr.github.io/webvr-spec/webvr.html
 *
 * Firefox: http://mozvr.com/downloads/
 * Chromium: https://drive.google.com/folderview?id=0BzudLt22BqGRbW9WTHMtOWMzNjQ&usp=sharing#list
 *
 */

THREE.VREffect = function ( renderer, onError ) {

	var vrHMD;
	var eyeTranslationL, eyeFOVL;
	var eyeTranslationR, eyeFOVR;

	function gotVRDevices( devices ) {

		for ( var i = 0; i < devices.length; i ++ ) {

			if ( devices[ i ] instanceof HMDVRDevice ) {

				vrHMD = devices[ i ];

				if ( vrHMD.getEyeParameters !== undefined ) {

					var eyeParamsL = vrHMD.getEyeParameters( 'left' );
					var eyeParamsR = vrHMD.getEyeParameters( 'right' );

					eyeTranslationL = eyeParamsL.eyeTranslation;
					eyeTranslationR = eyeParamsR.eyeTranslation;
					eyeFOVL = eyeParamsL.recommendedFieldOfView;
					eyeFOVR = eyeParamsR.recommendedFieldOfView;

				} else {

					// TODO: This is an older code path and not spec compliant.
					// It should be removed at some point in the near future.
					eyeTranslationL = vrHMD.getEyeTranslation( 'left' );
					eyeTranslationR = vrHMD.getEyeTranslation( 'right' );
					eyeFOVL = vrHMD.getRecommendedEyeFieldOfView( 'left' );
					eyeFOVR = vrHMD.getRecommendedEyeFieldOfView( 'right' );

				}

				break; // We keep the first we encounter

			}

		}

		if ( vrHMD === undefined ) {

			if ( onError ) onError( 'HMD not available' );

		}

	}

	if ( navigator.getVRDevices ) {

		navigator.getVRDevices().then( gotVRDevices );

	}

	//

	this.scale = 1;

	this.setSize = function( width, height ) {

		renderer.setSize( width, height );

	};

	// fullscreen

	var isFullscreen = false;

	var canvas = renderer.domElement;
	var fullscreenchange = canvas.mozRequestFullScreen ? 'mozfullscreenchange' : 'webkitfullscreenchange';

	document.addEventListener( fullscreenchange, function ( event ) {

		isFullscreen = document.mozFullScreenElement || document.webkitFullscreenElement;

	}, false );

	this.setFullScreen = function ( boolean ) {

		if ( vrHMD === undefined ) return;
		if ( isFullscreen === boolean ) return;

		if ( canvas.mozRequestFullScreen ) {

			canvas.mozRequestFullScreen( { vrDisplay: vrHMD } );

		} else if ( canvas.webkitRequestFullscreen ) {

			canvas.webkitRequestFullscreen( { vrDisplay: vrHMD } );

		}

	};

	// render

	var cameraL = new THREE.PerspectiveCamera();
	var cameraR = new THREE.PerspectiveCamera();

	this.render = function ( scene, camera ) {

		if ( vrHMD ) {

			var sceneL, sceneR;

			if ( Array.isArray( scene ) ) {

				sceneL = scene[ 0 ];
				sceneR = scene[ 1 ];

			} else {

				sceneL = scene;
				sceneR = scene;

			}

			var size = renderer.getSize();
			size.width /= 2;

			renderer.enableScissorTest( true );
			renderer.clear();

			if ( camera.parent === null ) camera.updateMatrixWorld();

			cameraL.projectionMatrix = fovToProjection( eyeFOVL, true, camera.near, camera.far );
			cameraR.projectionMatrix = fovToProjection( eyeFOVR, true, camera.near, camera.far );

			camera.matrixWorld.decompose( cameraL.position, cameraL.quaternion, cameraL.scale );
			camera.matrixWorld.decompose( cameraR.position, cameraR.quaternion, cameraR.scale );

			cameraL.translateX( eyeTranslationL.x * this.scale );
			cameraR.translateX( eyeTranslationR.x * this.scale );

			// render left eye
			renderer.setViewport( 0, 0, size.width, size.height );
			renderer.setScissor( 0, 0, size.width, size.height );
			renderer.render( sceneL, cameraL );

			// render right eye
			renderer.setViewport( size.width, 0, size.width, size.height );
			renderer.setScissor( size.width, 0, size.width, size.height );
			renderer.render( sceneR, cameraR );

			renderer.enableScissorTest( false );

			return;

		}

		// Regular render mode if not HMD

		if ( Array.isArray( scene ) ) scene = scene[ 0 ];

		renderer.render( scene, camera );

	};

	//

	function fovToNDCScaleOffset( fov ) {

		var pxscale = 2.0 / ( fov.leftTan + fov.rightTan );
		var pxoffset = ( fov.leftTan - fov.rightTan ) * pxscale * 0.5;
		var pyscale = 2.0 / ( fov.upTan + fov.downTan );
		var pyoffset = ( fov.upTan - fov.downTan ) * pyscale * 0.5;
		return { scale: [ pxscale, pyscale ], offset: [ pxoffset, pyoffset ] };

	}

	function fovPortToProjection( fov, rightHanded, zNear, zFar ) {

		rightHanded = rightHanded === undefined ? true : rightHanded;
		zNear = zNear === undefined ? 0.01 : zNear;
		zFar = zFar === undefined ? 10000.0 : zFar;

		var handednessScale = rightHanded ? - 1.0 : 1.0;

		// start with an identity matrix
		var mobj = new THREE.Matrix4();
		var m = mobj.elements;

		// and with scale/offset info for normalized device coords
		var scaleAndOffset = fovToNDCScaleOffset( fov );

		// X result, map clip edges to [-w,+w]
		m[ 0 * 4 + 0 ] = scaleAndOffset.scale[ 0 ];
		m[ 0 * 4 + 1 ] = 0.0;
		m[ 0 * 4 + 2 ] = scaleAndOffset.offset[ 0 ] * handednessScale;
		m[ 0 * 4 + 3 ] = 0.0;

		// Y result, map clip edges to [-w,+w]
		// Y offset is negated because this proj matrix transforms from world coords with Y=up,
		// but the NDC scaling has Y=down (thanks D3D?)
		m[ 1 * 4 + 0 ] = 0.0;
		m[ 1 * 4 + 1 ] = scaleAndOffset.scale[ 1 ];
		m[ 1 * 4 + 2 ] = - scaleAndOffset.offset[ 1 ] * handednessScale;
		m[ 1 * 4 + 3 ] = 0.0;

		// Z result (up to the app)
		m[ 2 * 4 + 0 ] = 0.0;
		m[ 2 * 4 + 1 ] = 0.0;
		m[ 2 * 4 + 2 ] = zFar / ( zNear - zFar ) * - handednessScale;
		m[ 2 * 4 + 3 ] = ( zFar * zNear ) / ( zNear - zFar );

		// W result (= Z in)
		m[ 3 * 4 + 0 ] = 0.0;
		m[ 3 * 4 + 1 ] = 0.0;
		m[ 3 * 4 + 2 ] = handednessScale;
		m[ 3 * 4 + 3 ] = 0.0;

		mobj.transpose();

		return mobj;

	}

	function fovToProjection( fov, rightHanded, zNear, zFar ) {

		var DEG2RAD = Math.PI / 180.0;

		var fovPort = {
			upTan: Math.tan( fov.upDegrees * DEG2RAD ),
			downTan: Math.tan( fov.downDegrees * DEG2RAD ),
			leftTan: Math.tan( fov.leftDegrees * DEG2RAD ),
			rightTan: Math.tan( fov.rightDegrees * DEG2RAD )
		};

		return fovPortToProjection( fovPort, rightHanded, zNear, zFar );

	}

};