/**
 * @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://webvr.info/get-chrome
 *
 */

THREE.VREffect = function( renderer, onError ) {

	var vrDisplay, vrDisplays;
	var eyeTranslationL = new THREE.Vector3();
	var eyeTranslationR = new THREE.Vector3();
	var renderRectL, renderRectR;

	var frameData = null;

	if ( 'VRFrameData' in window ) {

		frameData = new window.VRFrameData();

	}

	function gotVRDisplays( displays ) {

		vrDisplays = displays;

		if ( displays.length > 0 ) {

			vrDisplay = displays[ 0 ];

		} else {

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

		}

	}

	if ( navigator.getVRDisplays ) {

		navigator.getVRDisplays().then( gotVRDisplays ).catch( function() {

			console.warn( 'THREE.VREffect: Unable to get VR Displays' );

		} );

	}

	//

	this.isPresenting = false;
	this.scale = 1;

	var scope = this;

	var rendererSize = renderer.getSize();
	var rendererUpdateStyle = false;
	var rendererPixelRatio = renderer.getPixelRatio();

	this.getVRDisplay = function() {

		return vrDisplay;

	};

	this.setVRDisplay = function( value ) {

		vrDisplay = value;

	};

	this.getVRDisplays = function() {

		console.warn( 'THREE.VREffect: getVRDisplays() is being deprecated.' );
		return vrDisplays;

	};

	this.setSize = function( width, height, updateStyle ) {

		rendererSize = { width: width, height: height };
		rendererUpdateStyle = updateStyle;

		if ( scope.isPresenting ) {

			var eyeParamsL = vrDisplay.getEyeParameters( 'left' );
			renderer.setPixelRatio( 1 );
			renderer.setSize( eyeParamsL.renderWidth * 2, eyeParamsL.renderHeight, false );

		} else {

			renderer.setPixelRatio( rendererPixelRatio );
			renderer.setSize( width, height, updateStyle );

		}

	};

	// VR presentation

	var canvas = renderer.domElement;
	var defaultLeftBounds = [ 0.0, 0.0, 0.5, 1.0 ];
	var defaultRightBounds = [ 0.5, 0.0, 0.5, 1.0 ];

	function onVRDisplayPresentChange() {

		var wasPresenting = scope.isPresenting;
		scope.isPresenting = vrDisplay !== undefined && vrDisplay.isPresenting;

		if ( scope.isPresenting ) {

			var eyeParamsL = vrDisplay.getEyeParameters( 'left' );
			var eyeWidth = eyeParamsL.renderWidth;
			var eyeHeight = eyeParamsL.renderHeight;

			if ( ! wasPresenting ) {

				rendererPixelRatio = renderer.getPixelRatio();
				rendererSize = renderer.getSize();

				renderer.setPixelRatio( 1 );
				renderer.setSize( eyeWidth * 2, eyeHeight, false );

			}

		} else if ( wasPresenting ) {

			renderer.setPixelRatio( rendererPixelRatio );
			renderer.setSize( rendererSize.width, rendererSize.height, rendererUpdateStyle );

		}

	}

	window.addEventListener( 'vrdisplaypresentchange', onVRDisplayPresentChange, false );

	this.setFullScreen = function( boolean ) {

		return new Promise( function( resolve, reject ) {

			if ( vrDisplay === undefined ) {

				reject( new Error( 'No VR hardware found.' ) );
				return;

			}

			if ( scope.isPresenting === boolean ) {

				resolve();
				return;

			}

			if ( boolean ) {

				resolve( vrDisplay.requestPresent( [ { source: canvas } ] ) );

			} else {

				resolve( vrDisplay.exitPresent() );

			}

		} );

	};

	this.requestPresent = function() {

		return this.setFullScreen( true );

	};

	this.exitPresent = function() {

		return this.setFullScreen( false );

	};

	this.requestAnimationFrame = function( f ) {

		if ( vrDisplay !== undefined ) {

			return vrDisplay.requestAnimationFrame( f );

		} else {

			return window.requestAnimationFrame( f );

		}

	};

	this.cancelAnimationFrame = function( h ) {

		if ( vrDisplay !== undefined ) {

			vrDisplay.cancelAnimationFrame( h );

		} else {

			window.cancelAnimationFrame( h );

		}

	};

	this.submitFrame = function() {

		if ( vrDisplay !== undefined && scope.isPresenting ) {

			vrDisplay.submitFrame();

		}

	};

	this.autoSubmitFrame = true;

	// render

	var cameraL = new THREE.PerspectiveCamera();
	cameraL.layers.enable( 1 );

	var cameraR = new THREE.PerspectiveCamera();
	cameraR.layers.enable( 2 );

	this.render = function( scene, camera, renderTarget, forceClear ) {

		if ( vrDisplay && scope.isPresenting ) {

			var autoUpdate = scene.autoUpdate;

			if ( autoUpdate ) {

				scene.updateMatrixWorld();
				scene.autoUpdate = false;

			}

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

			eyeTranslationL.fromArray( eyeParamsL.offset );
			eyeTranslationR.fromArray( eyeParamsR.offset );

			if ( Array.isArray( scene ) ) {

				console.warn( 'THREE.VREffect.render() no longer supports arrays. Use object.layers instead.' );
				scene = scene[ 0 ];

			}

			// When rendering we don't care what the recommended size is, only what the actual size
			// of the backbuffer is.
			var size = renderer.getSize();
			var layers = vrDisplay.getLayers();
			var leftBounds;
			var rightBounds;

			if ( layers.length ) {

				var layer = layers[ 0 ];

				leftBounds = layer.leftBounds !== null && layer.leftBounds.length === 4 ? layer.leftBounds : defaultLeftBounds;
				rightBounds = layer.rightBounds !== null && layer.rightBounds.length === 4 ? layer.rightBounds : defaultRightBounds;

			} else {

				leftBounds = defaultLeftBounds;
				rightBounds = defaultRightBounds;

			}

			renderRectL = {
				x: Math.round( size.width * leftBounds[ 0 ] ),
				y: Math.round( size.height * leftBounds[ 1 ] ),
				width: Math.round( size.width * leftBounds[ 2 ] ),
				height: Math.round( size.height * leftBounds[ 3 ] )
			};
			renderRectR = {
				x: Math.round( size.width * rightBounds[ 0 ] ),
				y: Math.round( size.height * rightBounds[ 1 ] ),
				width: Math.round( size.width * rightBounds[ 2 ] ),
				height: Math.round( size.height * rightBounds[ 3 ] )
			};

			if ( renderTarget ) {

				renderer.setRenderTarget( renderTarget );
				renderTarget.scissorTest = true;

			} else {

				renderer.setRenderTarget( null );
				renderer.setScissorTest( true );

			}

			if ( renderer.autoClear || forceClear ) renderer.clear();

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

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

			var scale = this.scale;
			cameraL.translateOnAxis( eyeTranslationL, scale );
			cameraR.translateOnAxis( eyeTranslationR, scale );

			if ( vrDisplay.getFrameData ) {

				vrDisplay.depthNear = camera.near;
				vrDisplay.depthFar = camera.far;

				vrDisplay.getFrameData( frameData );

				cameraL.projectionMatrix.elements = frameData.leftProjectionMatrix;
				cameraR.projectionMatrix.elements = frameData.rightProjectionMatrix;

			} else {

				cameraL.projectionMatrix = fovToProjection( eyeParamsL.fieldOfView, true, camera.near, camera.far );
				cameraR.projectionMatrix = fovToProjection( eyeParamsR.fieldOfView, true, camera.near, camera.far );

			}

			// render left eye
			if ( renderTarget ) {

				renderTarget.viewport.set( renderRectL.x, renderRectL.y, renderRectL.width, renderRectL.height );
				renderTarget.scissor.set( renderRectL.x, renderRectL.y, renderRectL.width, renderRectL.height );

			} else {

				renderer.setViewport( renderRectL.x, renderRectL.y, renderRectL.width, renderRectL.height );
				renderer.setScissor( renderRectL.x, renderRectL.y, renderRectL.width, renderRectL.height );

			}
			renderer.render( scene, cameraL, renderTarget, forceClear );

			// render right eye
			if ( renderTarget ) {

				renderTarget.viewport.set( renderRectR.x, renderRectR.y, renderRectR.width, renderRectR.height );
				renderTarget.scissor.set( renderRectR.x, renderRectR.y, renderRectR.width, renderRectR.height );

			} else {

				renderer.setViewport( renderRectR.x, renderRectR.y, renderRectR.width, renderRectR.height );
				renderer.setScissor( renderRectR.x, renderRectR.y, renderRectR.width, renderRectR.height );

			}
			renderer.render( scene, cameraR, renderTarget, forceClear );

			if ( renderTarget ) {

				renderTarget.viewport.set( 0, 0, size.width, size.height );
				renderTarget.scissor.set( 0, 0, size.width, size.height );
				renderTarget.scissorTest = false;
				renderer.setRenderTarget( null );

			} else {

				renderer.setViewport( 0, 0, size.width, size.height );
				renderer.setScissorTest( false );

			}

			if ( autoUpdate ) {

				scene.autoUpdate = true;

			}

			if ( scope.autoSubmitFrame ) {

				scope.submitFrame();

			}

			return;

		}

		// Regular render mode if not HMD

		renderer.render( scene, camera, renderTarget, forceClear );

	};

	this.dispose = function() {

		window.removeEventListener( 'vrdisplaypresentchange', onVRDisplayPresentChange, false );

	};

	//

	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 );

	}

};
