/**
 * @author Mugen87 / https://github.com/Mugen87
 * @author spite / https://github.com/spite
 *
 * You can use this geometry to create a decal mesh, that serves different kinds of purposes.
 * e.g. adding unique details to models, performing dynamic visual environmental changes or covering seams.
 *
 * Constructor parameter:
 *
 * mesh — Any mesh object
 * position — Position of the decal projector
 * orientation — Orientation of the decal projector
 * size — Size of the decal projector
 *
 * reference: http://blog.wolfire.com/2009/06/how-to-project-decals/
 *
 */

( function () {

	function DecalGeometry( mesh, position, orientation, size ) {

		THREE.BufferGeometry.call( this );

		// buffers

		var vertices = [];
		var normals = [];
		var uvs = [];

		// helpers

		var plane = new THREE.Vector3();

		// this matrix represents the transformation of the decal projector

		var projectorMatrix = new THREE.Matrix4();
		projectorMatrix.makeRotationFromEuler( orientation );
		projectorMatrix.setPosition( position );

		var projectorMatrixInverse = new THREE.Matrix4().getInverse( projectorMatrix );

		// generate buffers

		generate();

		// build geometry

		this.addAttribute( 'position', new THREE.Float32BufferAttribute( vertices, 3 ) );
		this.addAttribute( 'normal', new THREE.Float32BufferAttribute( normals, 3 ) );
		this.addAttribute( 'uv', new THREE.Float32BufferAttribute( uvs, 2 ) );

		function generate() {

			var i;
			var geometry = new THREE.BufferGeometry();
			var decalVertices = [];

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

			// handle different geometry types

			if ( mesh.geometry.isGeometry ) {

				geometry.fromGeometry( mesh.geometry );

			} else {

				geometry.copy( mesh.geometry );

			}

			var positionAttribute = geometry.attributes.position;
			var normalAttribute = geometry.attributes.normal;

			// first, create an array of 'DecalVertex' objects
			// three consecutive 'DecalVertex' objects represent a single face
			//
			// this data structure will be later used to perform the clipping

			if ( geometry.index !== null ) {

				// indexed BufferGeometry

				var index = geometry.index;

				for ( i = 0; i < index.count; i ++ ) {

					vertex.fromBufferAttribute( positionAttribute, index.getX( i ) );
					normal.fromBufferAttribute( normalAttribute, index.getX( i ) );

					pushDecalVertex( decalVertices, vertex, normal );

				}

			} else {

				// non-indexed BufferGeometry

				for ( i = 0; i < positionAttribute.count; i ++ ) {

					vertex.fromBufferAttribute( positionAttribute, i );
					normal.fromBufferAttribute( normalAttribute, i );

					pushDecalVertex( decalVertices, vertex, normal );

				}

			}

			// second, clip the geometry so that it doesn't extend out from the projector

			decalVertices = clipGeometry( decalVertices, plane.set( 1, 0, 0 ) );
			decalVertices = clipGeometry( decalVertices, plane.set( - 1, 0, 0 ) );
			decalVertices = clipGeometry( decalVertices, plane.set( 0, 1, 0 ) );
			decalVertices = clipGeometry( decalVertices, plane.set( 0, - 1, 0 ) );
			decalVertices = clipGeometry( decalVertices, plane.set( 0, 0, 1 ) );
			decalVertices = clipGeometry( decalVertices, plane.set( 0, 0, - 1 ) );

			// third, generate final vertices, normals and uvs

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

				var decalVertex = decalVertices[ i ];

				// create texture coordinates (we are still in projector space)

				uvs.push(
					0.5 + ( decalVertex.position.x / size.x ),
					0.5 + ( decalVertex.position.y / size.y )
				);

				// transform the vertex back to world space

				decalVertex.position.applyMatrix4( projectorMatrix );

				// now create vertex and normal buffer data

				vertices.push( decalVertex.position.x, decalVertex.position.y, decalVertex.position.z );
				normals.push( decalVertex.normal.x, decalVertex.normal.y, decalVertex.normal.z );

			}

		}

		function pushDecalVertex( decalVertices, vertex, normal ) {

			// transform the vertex to world space, then to projector space

			vertex.applyMatrix4( mesh.matrixWorld );
			vertex.applyMatrix4( projectorMatrixInverse );

			decalVertices.push( new DecalVertex( vertex.clone(), normal.clone() ) );

		}

		function clipGeometry( inVertices, plane ) {

			var outVertices = [];

			var s = 0.5 * Math.abs( size.dot( plane ) );

			// a single iteration clips one face,
			// which consists of three consecutive 'DecalVertex' objects

			for ( var i = 0; i < inVertices.length; i += 3 ) {

				var v1Out, v2Out, v3Out, total = 0;
				var nV1, nV2, nV3, nV4;

				var d1 = inVertices[ i + 0 ].position.dot( plane ) - s;
				var d2 = inVertices[ i + 1 ].position.dot( plane ) - s;
				var d3 = inVertices[ i + 2 ].position.dot( plane ) - s;

				v1Out = d1 > 0;
				v2Out = d2 > 0;
				v3Out = d3 > 0;

				// calculate, how many vertices of the face lie outside of the clipping plane

				total = ( v1Out ? 1 : 0 ) + ( v2Out ? 1 : 0 ) + ( v3Out ? 1 : 0 );

				switch ( total ) {

					case 0: {

						// the entire face lies inside of the plane, no clipping needed

						outVertices.push( inVertices[ i ] );
						outVertices.push( inVertices[ i + 1 ] );
						outVertices.push( inVertices[ i + 2 ] );
						break;

					}

					case 1: {

						// one vertex lies outside of the plane, perform clipping

						if ( v1Out ) {

							nV1 = inVertices[ i + 1 ];
							nV2 = inVertices[ i + 2 ];
							nV3 = clip( inVertices[ i ], nV1, plane, s );
							nV4 = clip( inVertices[ i ], nV2, plane, s );

						}

						if ( v2Out ) {

							nV1 = inVertices[ i ];
							nV2 = inVertices[ i + 2 ];
							nV3 = clip( inVertices[ i + 1 ], nV1, plane, s );
							nV4 = clip( inVertices[ i + 1 ], nV2, plane, s );

							outVertices.push( nV3 );
							outVertices.push( nV2.clone() );
							outVertices.push( nV1.clone() );

							outVertices.push( nV2.clone() );
							outVertices.push( nV3.clone() );
							outVertices.push( nV4 );
							break;

						}

						if ( v3Out ) {

							nV1 = inVertices[ i ];
							nV2 = inVertices[ i + 1 ];
							nV3 = clip( inVertices[ i + 2 ], nV1, plane, s );
							nV4 = clip( inVertices[ i + 2 ], nV2, plane, s );

						}

						outVertices.push( nV1.clone() );
						outVertices.push( nV2.clone() );
						outVertices.push( nV3 );

						outVertices.push( nV4 );
						outVertices.push( nV3.clone() );
						outVertices.push( nV2.clone() );

						break;

					}

					case 2: {

						// two vertices lies outside of the plane, perform clipping

						if ( ! v1Out ) {

							nV1 = inVertices[ i ].clone();
							nV2 = clip( nV1, inVertices[ i + 1 ], plane, s );
							nV3 = clip( nV1, inVertices[ i + 2 ], plane, s );
							outVertices.push( nV1 );
							outVertices.push( nV2 );
							outVertices.push( nV3 );

						}

						if ( ! v2Out ) {

							nV1 = inVertices[ i + 1 ].clone();
							nV2 = clip( nV1, inVertices[ i + 2 ], plane, s );
							nV3 = clip( nV1, inVertices[ i ], plane, s );
							outVertices.push( nV1 );
							outVertices.push( nV2 );
							outVertices.push( nV3 );

						}

						if ( ! v3Out ) {

							nV1 = inVertices[ i + 2 ].clone();
							nV2 = clip( nV1, inVertices[ i ], plane, s );
							nV3 = clip( nV1, inVertices[ i + 1 ], plane, s );
							outVertices.push( nV1 );
							outVertices.push( nV2 );
							outVertices.push( nV3 );

						}

						break;

					}

					case 3: {

						// the entire face lies outside of the plane, so let's discard the corresponding vertices

						break;

					}

				}

			}

			return outVertices;

		}

		function clip( v0, v1, p, s ) {

			var d0 = v0.position.dot( p ) - s;
			var d1 = v1.position.dot( p ) - s;

			var s0 = d0 / ( d0 - d1 );

			var v = new DecalVertex(
				new THREE.Vector3(
					v0.position.x + s0 * ( v1.position.x - v0.position.x ),
					v0.position.y + s0 * ( v1.position.y - v0.position.y ),
					v0.position.z + s0 * ( v1.position.z - v0.position.z )
				),
				new THREE.Vector3(
					v0.normal.x + s0 * ( v1.normal.x - v0.normal.x ),
					v0.normal.y + s0 * ( v1.normal.y - v0.normal.y ),
					v0.normal.z + s0 * ( v1.normal.z - v0.normal.z )
				)
			);

			// need to clip more values (texture coordinates)? do it this way:
			// intersectpoint.value = a.value + s * ( b.value - a.value );

			return v;

		}

	}

	DecalGeometry.prototype = Object.create( THREE.BufferGeometry.prototype );
	DecalGeometry.prototype.constructor = DecalGeometry;

	// helper

	function DecalVertex( position, normal ) {

		this.position = position;
		this.normal = normal;

	}

	DecalVertex.prototype.clone = function () {

		return new DecalVertex( this.position.clone(), this.normal.clone() );

	};

	// export

	THREE.DecalGeometry = DecalGeometry;

} )();
