import { BufferAttribute } from '../core/BufferAttribute.js';
import { BufferGeometry } from '../core/BufferGeometry.js';
import { DataTexture } from '../textures/DataTexture.js';
import { FloatType, RedIntegerFormat, UnsignedIntType, RGBAFormat } from '../constants.js';
import { Matrix4 } from '../math/Matrix4.js';
import { Mesh } from './Mesh.js';
import { ColorManagement } from '../math/ColorManagement.js';
import { Box3 } from '../math/Box3.js';
import { Sphere } from '../math/Sphere.js';
import { Frustum } from '../math/Frustum.js';
import { Vector3 } from '../math/Vector3.js';
import { Color } from '../math/Color.js';
import { FrustumArray } from '../math/FrustumArray.js';

function ascIdSort( a, b ) {

	return a - b;

}

function sortOpaque( a, b ) {

	return a.z - b.z;

}

function sortTransparent( a, b ) {

	return b.z - a.z;

}

class MultiDrawRenderList {

	constructor() {

		this.index = 0;
		this.pool = [];
		this.list = [];

	}

	push( start, count, z, index ) {

		const pool = this.pool;
		const list = this.list;
		if ( this.index >= pool.length ) {

			pool.push( {

				start: - 1,
				count: - 1,
				z: - 1,
				index: - 1,

			} );

		}

		const item = pool[ this.index ];
		list.push( item );
		this.index ++;

		item.start = start;
		item.count = count;
		item.z = z;
		item.index = index;

	}

	reset() {

		this.list.length = 0;
		this.index = 0;

	}

}

const _matrix = /*@__PURE__*/ new Matrix4();
const _whiteColor = /*@__PURE__*/ new Color( 1, 1, 1 );
const _frustum = /*@__PURE__*/ new Frustum();
const _frustumArray = /*@__PURE__*/ new FrustumArray();
const _box = /*@__PURE__*/ new Box3();
const _sphere = /*@__PURE__*/ new Sphere();
const _vector = /*@__PURE__*/ new Vector3();
const _forward = /*@__PURE__*/ new Vector3();
const _temp = /*@__PURE__*/ new Vector3();
const _renderList = /*@__PURE__*/ new MultiDrawRenderList();
const _mesh = /*@__PURE__*/ new Mesh();
const _batchIntersects = [];

// copies data from attribute "src" into "target" starting at "targetOffset"
function copyAttributeData( src, target, targetOffset = 0 ) {

	const itemSize = target.itemSize;
	if ( src.isInterleavedBufferAttribute || src.array.constructor !== target.array.constructor ) {

		// use the component getters and setters if the array data cannot
		// be copied directly
		const vertexCount = src.count;
		for ( let i = 0; i < vertexCount; i ++ ) {

			for ( let c = 0; c < itemSize; c ++ ) {

				target.setComponent( i + targetOffset, c, src.getComponent( i, c ) );

			}

		}

	} else {

		// faster copy approach using typed array set function
		target.array.set( src.array, targetOffset * itemSize );

	}

	target.needsUpdate = true;

}

// safely copies array contents to a potentially smaller array
function copyArrayContents( src, target ) {

	if ( src.constructor !== target.constructor ) {

		// if arrays are of a different type (eg due to index size increasing) then data must be per-element copied
		const len = Math.min( src.length, target.length );
		for ( let i = 0; i < len; i ++ ) {

			target[ i ] = src[ i ];

		}

	} else {

		// if the arrays use the same data layout we can use a fast block copy
		const len = Math.min( src.length, target.length );
		target.set( new src.constructor( src.buffer, 0, len ) );

	}

}

/**
 * A special version of a mesh with multi draw batch rendering support. Use
 * this class if you have to render a large number of objects with the same
 * material but with different geometries or world transformations. The usage of
 * `BatchedMesh` will help you to reduce the number of draw calls and thus improve the overall
 * rendering performance in your application.
 *
 * ```js
 * const box = new THREE.BoxGeometry( 1, 1, 1 );
 * const sphere = new THREE.SphereGeometry( 1, 12, 12 );
 * const material = new THREE.MeshBasicMaterial( { color: 0x00ff00 } );
 *
 * // initialize and add geometries into the batched mesh
 * const batchedMesh = new BatchedMesh( 10, 5000, 10000, material );
 * const boxGeometryId = batchedMesh.addGeometry( box );
 * const sphereGeometryId = batchedMesh.addGeometry( sphere );
 *
 * // create instances of those geometries
 * const boxInstancedId1 = batchedMesh.addInstance( boxGeometryId );
 * const boxInstancedId2 = batchedMesh.addInstance( boxGeometryId );
 *
 * const sphereInstancedId1 = batchedMesh.addInstance( sphereGeometryId );
 * const sphereInstancedId2 = batchedMesh.addInstance( sphereGeometryId );
 *
 * // position the geometries
 * batchedMesh.setMatrixAt( boxInstancedId1, boxMatrix1 );
 * batchedMesh.setMatrixAt( boxInstancedId2, boxMatrix2 );
 *
 * batchedMesh.setMatrixAt( sphereInstancedId1, sphereMatrix1 );
 * batchedMesh.setMatrixAt( sphereInstancedId2, sphereMatrix2 );
 *
 * scene.add( batchedMesh );
 * ```
 *
 * @augments Mesh
 */
class BatchedMesh extends Mesh {

	/**
	 * Constructs a new batched mesh.
	 *
	 * @param {number} maxInstanceCount - The maximum number of individual instances planned to be added and rendered.
	 * @param {number} maxVertexCount - The maximum number of vertices to be used by all unique geometries.
	 * @param {number} [maxIndexCount=maxVertexCount*2] - The maximum number of indices to be used by all unique geometries
	 * @param {Material|Array<Material>} [material] - The mesh material.
	 */
	constructor( maxInstanceCount, maxVertexCount, maxIndexCount = maxVertexCount * 2, material ) {

		super( new BufferGeometry(), material );

		/**
		 * This flag can be used for type testing.
		 *
		 * @type {boolean}
		 * @readonly
		 * @default true
		 */
		this.isBatchedMesh = true;

		/**
		 * When set ot `true`, the individual objects of a batch are frustum culled.
		 *
		 * @type {boolean}
		 * @default true
		 */
		this.perObjectFrustumCulled = true;

		/**
		 * When set to `true`, the individual objects of a batch are sorted to improve overdraw-related artifacts.
		 * If the material is marked as "transparent" objects are rendered back to front and if not then they are
		 * rendered front to back.
		 *
		 * @type {boolean}
		 * @default true
		 */
		this.sortObjects = true;

		/**
		 * The bounding box of the batched mesh. Can be computed via {@link BatchedMesh#computeBoundingBox}.
		 *
		 * @type {?Box3}
		 * @default null
		 */
		this.boundingBox = null;

		/**
		 * The bounding sphere of the batched mesh. Can be computed via {@link BatchedMesh#computeBoundingSphere}.
		 *
		 * @type {?Sphere}
		 * @default null
		 */
		this.boundingSphere = null;

		/**
		 * Takes a sort a function that is run before render. The function takes a list of instances to
		 * sort and a camera. The objects in the list include a "z" field to perform a depth-ordered
		 * sort with.
		 *
		 * @type {?Function}
		 * @default null
		 */
		this.customSort = null;

		// stores visible, active, and geometry id per instance and reserved buffer ranges for geometries
		this._instanceInfo = [];
		this._geometryInfo = [];

		// instance, geometry ids that have been set as inactive, and are available to be overwritten
		this._availableInstanceIds = [];
		this._availableGeometryIds = [];

		// used to track where the next point is that geometry should be inserted
		this._nextIndexStart = 0;
		this._nextVertexStart = 0;
		this._geometryCount = 0;

		// flags
		this._visibilityChanged = true;
		this._geometryInitialized = false;

		// cached user options
		this._maxInstanceCount = maxInstanceCount;
		this._maxVertexCount = maxVertexCount;
		this._maxIndexCount = maxIndexCount;

		// buffers for multi draw
		this._multiDrawCounts = new Int32Array( maxInstanceCount );
		this._multiDrawStarts = new Int32Array( maxInstanceCount );
		this._multiDrawCount = 0;
		this._multiDrawInstances = null;

		// Local matrix per geometry by using data texture
		this._matricesTexture = null;
		this._indirectTexture = null;
		this._colorsTexture = null;

		this._initMatricesTexture();
		this._initIndirectTexture();

	}

	/**
	 * The maximum number of individual instances that can be stored in the batch.
	 *
	 * @type {number}
	 * @readonly
	 */
	get maxInstanceCount() {

		return this._maxInstanceCount;

	}

	/**
	 * The instance count.
	 *
	 * @type {number}
	 * @readonly
	 */
	get instanceCount() {

		return this._instanceInfo.length - this._availableInstanceIds.length;

	}

	/**
	 * The number of unused vertices.
	 *
	 * @type {number}
	 * @readonly
	 */
	get unusedVertexCount() {

		return this._maxVertexCount - this._nextVertexStart;

	}

	/**
	 * The number of unused indices.
	 *
	 * @type {number}
	 * @readonly
	 */
	get unusedIndexCount() {

		return this._maxIndexCount - this._nextIndexStart;

	}

	_initMatricesTexture() {

		// layout (1 matrix = 4 pixels)
		//      RGBA RGBA RGBA RGBA (=> column1, column2, column3, column4)
		//  with  8x8  pixel texture max   16 matrices * 4 pixels =  (8 * 8)
		//       16x16 pixel texture max   64 matrices * 4 pixels = (16 * 16)
		//       32x32 pixel texture max  256 matrices * 4 pixels = (32 * 32)
		//       64x64 pixel texture max 1024 matrices * 4 pixels = (64 * 64)

		let size = Math.sqrt( this._maxInstanceCount * 4 ); // 4 pixels needed for 1 matrix
		size = Math.ceil( size / 4 ) * 4;
		size = Math.max( size, 4 );

		const matricesArray = new Float32Array( size * size * 4 ); // 4 floats per RGBA pixel
		const matricesTexture = new DataTexture( matricesArray, size, size, RGBAFormat, FloatType );

		this._matricesTexture = matricesTexture;

	}

	_initIndirectTexture() {

		let size = Math.sqrt( this._maxInstanceCount );
		size = Math.ceil( size );

		const indirectArray = new Uint32Array( size * size );
		const indirectTexture = new DataTexture( indirectArray, size, size, RedIntegerFormat, UnsignedIntType );

		this._indirectTexture = indirectTexture;

	}

	_initColorsTexture() {

		let size = Math.sqrt( this._maxInstanceCount );
		size = Math.ceil( size );

		// 4 floats per RGBA pixel initialized to white
		const colorsArray = new Float32Array( size * size * 4 ).fill( 1 );
		const colorsTexture = new DataTexture( colorsArray, size, size, RGBAFormat, FloatType );
		colorsTexture.colorSpace = ColorManagement.workingColorSpace;

		this._colorsTexture = colorsTexture;

	}

	_initializeGeometry( reference ) {

		const geometry = this.geometry;
		const maxVertexCount = this._maxVertexCount;
		const maxIndexCount = this._maxIndexCount;
		if ( this._geometryInitialized === false ) {

			for ( const attributeName in reference.attributes ) {

				const srcAttribute = reference.getAttribute( attributeName );
				const { array, itemSize, normalized } = srcAttribute;

				const dstArray = new array.constructor( maxVertexCount * itemSize );
				const dstAttribute = new BufferAttribute( dstArray, itemSize, normalized );

				geometry.setAttribute( attributeName, dstAttribute );

			}

			if ( reference.getIndex() !== null ) {

				// Reserve last u16 index for primitive restart.
				const indexArray = maxVertexCount > 65535
					? new Uint32Array( maxIndexCount )
					: new Uint16Array( maxIndexCount );

				geometry.setIndex( new BufferAttribute( indexArray, 1 ) );

			}

			this._geometryInitialized = true;

		}

	}

	// Make sure the geometry is compatible with the existing combined geometry attributes
	_validateGeometry( geometry ) {

		// check to ensure the geometries are using consistent attributes and indices
		const batchGeometry = this.geometry;
		if ( Boolean( geometry.getIndex() ) !== Boolean( batchGeometry.getIndex() ) ) {

			throw new Error( 'THREE.BatchedMesh: All geometries must consistently have "index".' );

		}

		for ( const attributeName in batchGeometry.attributes ) {

			if ( ! geometry.hasAttribute( attributeName ) ) {

				throw new Error( `THREE.BatchedMesh: Added geometry missing "${ attributeName }". All geometries must have consistent attributes.` );

			}

			const srcAttribute = geometry.getAttribute( attributeName );
			const dstAttribute = batchGeometry.getAttribute( attributeName );
			if ( srcAttribute.itemSize !== dstAttribute.itemSize || srcAttribute.normalized !== dstAttribute.normalized ) {

				throw new Error( 'THREE.BatchedMesh: All attributes must have a consistent itemSize and normalized value.' );

			}

		}

	}

	/**
	 * Validates the instance defined by the given ID.
	 *
	 * @param {number} instanceId - The instance to validate.
	 */
	validateInstanceId( instanceId ) {

		const instanceInfo = this._instanceInfo;
		if ( instanceId < 0 || instanceId >= instanceInfo.length || instanceInfo[ instanceId ].active === false ) {

			throw new Error( `THREE.BatchedMesh: Invalid instanceId ${instanceId}. Instance is either out of range or has been deleted.` );

		}

	}

	/**
	 * Validates the geometry defined by the given ID.
	 *
	 * @param {number} geometryId - The geometry to validate.
	 */
	validateGeometryId( geometryId ) {

		const geometryInfoList = this._geometryInfo;
		if ( geometryId < 0 || geometryId >= geometryInfoList.length || geometryInfoList[ geometryId ].active === false ) {

			throw new Error( `THREE.BatchedMesh: Invalid geometryId ${geometryId}. Geometry is either out of range or has been deleted.` );

		}

	}

	/**
	 * Takes a sort a function that is run before render. The function takes a list of instances to
	 * sort and a camera. The objects in the list include a "z" field to perform a depth-ordered sort with.
	 *
	 * @param {Function} func - The custom sort function.
	 * @return {BatchedMesh} A reference to this batched mesh.
	 */
	setCustomSort( func ) {

		this.customSort = func;
		return this;

	}

	/**
	 * Computes the bounding box, updating {@link BatchedMesh#boundingBox}.
	 * Bounding boxes aren't computed by default. They need to be explicitly computed,
	 * otherwise they are `null`.
	 */
	computeBoundingBox() {

		if ( this.boundingBox === null ) {

			this.boundingBox = new Box3();

		}

		const boundingBox = this.boundingBox;
		const instanceInfo = this._instanceInfo;

		boundingBox.makeEmpty();
		for ( let i = 0, l = instanceInfo.length; i < l; i ++ ) {

			if ( instanceInfo[ i ].active === false ) continue;

			const geometryId = instanceInfo[ i ].geometryIndex;
			this.getMatrixAt( i, _matrix );
			this.getBoundingBoxAt( geometryId, _box ).applyMatrix4( _matrix );
			boundingBox.union( _box );

		}

	}

	/**
	 * Computes the bounding sphere, updating {@link BatchedMesh#boundingSphere}.
	 * Bounding spheres aren't computed by default. They need to be explicitly computed,
	 * otherwise they are `null`.
	 */
	computeBoundingSphere() {

		if ( this.boundingSphere === null ) {

			this.boundingSphere = new Sphere();

		}

		const boundingSphere = this.boundingSphere;
		const instanceInfo = this._instanceInfo;

		boundingSphere.makeEmpty();
		for ( let i = 0, l = instanceInfo.length; i < l; i ++ ) {

			if ( instanceInfo[ i ].active === false ) continue;

			const geometryId = instanceInfo[ i ].geometryIndex;
			this.getMatrixAt( i, _matrix );
			this.getBoundingSphereAt( geometryId, _sphere ).applyMatrix4( _matrix );
			boundingSphere.union( _sphere );

		}

	}

	/**
	 * Adds a new instance to the batch using the geometry of the given ID and returns
	 * a new id referring to the new instance to be used by other functions.
	 *
	 * @param {number} geometryId - The ID of a previously added geometry via {@link BatchedMesh#addGeometry}.
	 * @return {number} The instance ID.
	 */
	addInstance( geometryId ) {

		const atCapacity = this._instanceInfo.length >= this.maxInstanceCount;

		// ensure we're not over geometry
		if ( atCapacity && this._availableInstanceIds.length === 0 ) {

			throw new Error( 'THREE.BatchedMesh: Maximum item count reached.' );

		}

		const instanceInfo = {
			visible: true,
			active: true,
			geometryIndex: geometryId,
		};

		let drawId = null;

		// Prioritize using previously freed instance ids
		if ( this._availableInstanceIds.length > 0 ) {

			this._availableInstanceIds.sort( ascIdSort );

			drawId = this._availableInstanceIds.shift();
			this._instanceInfo[ drawId ] = instanceInfo;

		} else {

			drawId = this._instanceInfo.length;
			this._instanceInfo.push( instanceInfo );

		}

		const matricesTexture = this._matricesTexture;
		_matrix.identity().toArray( matricesTexture.image.data, drawId * 16 );
		matricesTexture.needsUpdate = true;

		const colorsTexture = this._colorsTexture;
		if ( colorsTexture ) {

			_whiteColor.toArray( colorsTexture.image.data, drawId * 4 );
			colorsTexture.needsUpdate = true;

		}

		this._visibilityChanged = true;
		return drawId;

	}

	/**
	 * Adds the given geometry to the batch and returns the associated
	 * geometry id referring to it to be used in other functions.
	 *
	 * @param {BufferGeometry} geometry - The geometry to add.
	 * @param {number} [reservedVertexCount=-1] - Optional parameter specifying the amount of
	 * vertex buffer space to reserve for the added geometry. This is necessary if it is planned
	 * to set a new geometry at this index at a later time that is larger than the original geometry.
	 * Defaults to the length of the given geometry vertex buffer.
	 * @param {number} [reservedIndexCount=-1] - Optional parameter specifying the amount of index
	 * buffer space to reserve for the added geometry. This is necessary if it is planned to set a
	 * new geometry at this index at a later time that is larger than the original geometry. Defaults to
	 * the length of the given geometry index buffer.
	 * @return {number} The geometry ID.
	 */
	addGeometry( geometry, reservedVertexCount = - 1, reservedIndexCount = - 1 ) {

		this._initializeGeometry( geometry );

		this._validateGeometry( geometry );

		const geometryInfo = {
			// geometry information
			vertexStart: - 1,
			vertexCount: - 1,
			reservedVertexCount: - 1,

			indexStart: - 1,
			indexCount: - 1,
			reservedIndexCount: - 1,

			// draw range information
			start: - 1,
			count: - 1,

			// state
			boundingBox: null,
			boundingSphere: null,
			active: true,
		};

		const geometryInfoList = this._geometryInfo;
		geometryInfo.vertexStart = this._nextVertexStart;
		geometryInfo.reservedVertexCount = reservedVertexCount === - 1 ? geometry.getAttribute( 'position' ).count : reservedVertexCount;

		const index = geometry.getIndex();
		const hasIndex = index !== null;
		if ( hasIndex ) {

			geometryInfo.indexStart = this._nextIndexStart;
			geometryInfo.reservedIndexCount = reservedIndexCount === - 1 ? index.count : reservedIndexCount;

		}

		if (
			geometryInfo.indexStart !== - 1 &&
			geometryInfo.indexStart + geometryInfo.reservedIndexCount > this._maxIndexCount ||
			geometryInfo.vertexStart + geometryInfo.reservedVertexCount > this._maxVertexCount
		) {

			throw new Error( 'THREE.BatchedMesh: Reserved space request exceeds the maximum buffer size.' );

		}

		// update id
		let geometryId;
		if ( this._availableGeometryIds.length > 0 ) {

			this._availableGeometryIds.sort( ascIdSort );

			geometryId = this._availableGeometryIds.shift();
			geometryInfoList[ geometryId ] = geometryInfo;


		} else {

			geometryId = this._geometryCount;
			this._geometryCount ++;
			geometryInfoList.push( geometryInfo );

		}

		// update the geometry
		this.setGeometryAt( geometryId, geometry );

		// increment the next geometry position
		this._nextIndexStart = geometryInfo.indexStart + geometryInfo.reservedIndexCount;
		this._nextVertexStart = geometryInfo.vertexStart + geometryInfo.reservedVertexCount;

		return geometryId;

	}

	/**
	 * Replaces the geometry at the given ID with the provided geometry. Throws an error if there
	 * is not enough space reserved for geometry. Calling this will change all instances that are
	 * rendering that geometry.
	 *
	 * @param {number} geometryId - The ID of the geometry that should be replaced with the given geometry.
	 * @param {BufferGeometry} geometry - The new geometry.
	 * @return {number} The geometry ID.
	 */
	setGeometryAt( geometryId, geometry ) {

		if ( geometryId >= this._geometryCount ) {

			throw new Error( 'THREE.BatchedMesh: Maximum geometry count reached.' );

		}

		this._validateGeometry( geometry );

		const batchGeometry = this.geometry;
		const hasIndex = batchGeometry.getIndex() !== null;
		const dstIndex = batchGeometry.getIndex();
		const srcIndex = geometry.getIndex();
		const geometryInfo = this._geometryInfo[ geometryId ];
		if (
			hasIndex &&
			srcIndex.count > geometryInfo.reservedIndexCount ||
			geometry.attributes.position.count > geometryInfo.reservedVertexCount
		) {

			throw new Error( 'THREE.BatchedMesh: Reserved space not large enough for provided geometry.' );

		}

		// copy geometry buffer data over
		const vertexStart = geometryInfo.vertexStart;
		const reservedVertexCount = geometryInfo.reservedVertexCount;
		geometryInfo.vertexCount = geometry.getAttribute( 'position' ).count;

		for ( const attributeName in batchGeometry.attributes ) {

			// copy attribute data
			const srcAttribute = geometry.getAttribute( attributeName );
			const dstAttribute = batchGeometry.getAttribute( attributeName );
			copyAttributeData( srcAttribute, dstAttribute, vertexStart );

			// fill the rest in with zeroes
			const itemSize = srcAttribute.itemSize;
			for ( let i = srcAttribute.count, l = reservedVertexCount; i < l; i ++ ) {

				const index = vertexStart + i;
				for ( let c = 0; c < itemSize; c ++ ) {

					dstAttribute.setComponent( index, c, 0 );

				}

			}

			dstAttribute.needsUpdate = true;
			dstAttribute.addUpdateRange( vertexStart * itemSize, reservedVertexCount * itemSize );

		}

		// copy index
		if ( hasIndex ) {

			const indexStart = geometryInfo.indexStart;
			const reservedIndexCount = geometryInfo.reservedIndexCount;
			geometryInfo.indexCount = geometry.getIndex().count;

			// copy index data over
			for ( let i = 0; i < srcIndex.count; i ++ ) {

				dstIndex.setX( indexStart + i, vertexStart + srcIndex.getX( i ) );

			}

			// fill the rest in with zeroes
			for ( let i = srcIndex.count, l = reservedIndexCount; i < l; i ++ ) {

				dstIndex.setX( indexStart + i, vertexStart );

			}

			dstIndex.needsUpdate = true;
			dstIndex.addUpdateRange( indexStart, geometryInfo.reservedIndexCount );

		}

		// update the draw range
		geometryInfo.start = hasIndex ? geometryInfo.indexStart : geometryInfo.vertexStart;
		geometryInfo.count = hasIndex ? geometryInfo.indexCount : geometryInfo.vertexCount;

		// store the bounding boxes
		geometryInfo.boundingBox = null;
		if ( geometry.boundingBox !== null ) {

			geometryInfo.boundingBox = geometry.boundingBox.clone();

		}

		geometryInfo.boundingSphere = null;
		if ( geometry.boundingSphere !== null ) {

			geometryInfo.boundingSphere = geometry.boundingSphere.clone();

		}

		this._visibilityChanged = true;
		return geometryId;

	}

	/**
	 * Deletes the geometry defined by the given ID from this batch. Any instances referencing
	 * this geometry will also be removed as a side effect.
	 *
	 * @param {number} geometryId - The ID of the geometry to remove from the batch.
	 * @return {BatchedMesh} A reference to this batched mesh.
	 */
	deleteGeometry( geometryId ) {

		const geometryInfoList = this._geometryInfo;
		if ( geometryId >= geometryInfoList.length || geometryInfoList[ geometryId ].active === false ) {

			return this;

		}

		// delete any instances associated with this geometry
		const instanceInfo = this._instanceInfo;
		for ( let i = 0, l = instanceInfo.length; i < l; i ++ ) {

			if ( instanceInfo[ i ].active && instanceInfo[ i ].geometryIndex === geometryId ) {

				this.deleteInstance( i );

			}

		}

		geometryInfoList[ geometryId ].active = false;
		this._availableGeometryIds.push( geometryId );
		this._visibilityChanged = true;

		return this;

	}

	/**
	 * Deletes an existing instance from the batch using the given ID.
	 *
	 * @param {number} instanceId - The ID of the instance to remove from the batch.
	 * @return {BatchedMesh} A reference to this batched mesh.
	 */
	deleteInstance( instanceId ) {

		this.validateInstanceId( instanceId );

		this._instanceInfo[ instanceId ].active = false;
		this._availableInstanceIds.push( instanceId );
		this._visibilityChanged = true;

		return this;

	}

	/**
	 * Repacks the sub geometries in BatchedMesh to remove any unused space remaining from
	 * previously deleted geometry, freeing up space to add new geometry.
	 *
	 * @return {BatchedMesh} A reference to this batched mesh.
	 */
	optimize() {

		// track the next indices to copy data to
		let nextVertexStart = 0;
		let nextIndexStart = 0;

		// Iterate over all geometry ranges in order sorted from earliest in the geometry buffer to latest
		// in the geometry buffer. Because draw range objects can be reused there is no guarantee of their order.
		const geometryInfoList = this._geometryInfo;
		const indices = geometryInfoList
			.map( ( e, i ) => i )
			.sort( ( a, b ) => {

				return geometryInfoList[ a ].vertexStart - geometryInfoList[ b ].vertexStart;

			} );

		const geometry = this.geometry;
		for ( let i = 0, l = geometryInfoList.length; i < l; i ++ ) {

			// if a geometry range is inactive then don't copy anything
			const index = indices[ i ];
			const geometryInfo = geometryInfoList[ index ];
			if ( geometryInfo.active === false ) {

				continue;

			}

			// if a geometry contains an index buffer then shift it, as well
			if ( geometry.index !== null ) {

				if ( geometryInfo.indexStart !== nextIndexStart ) {

					const { indexStart, vertexStart, reservedIndexCount } = geometryInfo;
					const index = geometry.index;
					const array = index.array;

					// shift the index pointers based on how the vertex data will shift
					// adjusting the index must happen first so the original vertex start value is available
					const elementDelta = nextVertexStart - vertexStart;
					for ( let j = indexStart; j < indexStart + reservedIndexCount; j ++ ) {

						array[ j ] = array[ j ] + elementDelta;

					}

					index.array.copyWithin( nextIndexStart, indexStart, indexStart + reservedIndexCount );
					index.addUpdateRange( nextIndexStart, reservedIndexCount );
					index.needsUpdate = true;

					geometryInfo.indexStart = nextIndexStart;

				}

				nextIndexStart += geometryInfo.reservedIndexCount;

			}

			// if a geometry needs to be moved then copy attribute data to overwrite unused space
			if ( geometryInfo.vertexStart !== nextVertexStart ) {

				const { vertexStart, reservedVertexCount } = geometryInfo;
				const attributes = geometry.attributes;
				for ( const key in attributes ) {

					const attribute = attributes[ key ];
					const { array, itemSize } = attribute;
					array.copyWithin( nextVertexStart * itemSize, vertexStart * itemSize, ( vertexStart + reservedVertexCount ) * itemSize );
					attribute.addUpdateRange( nextVertexStart * itemSize, reservedVertexCount * itemSize );
					attribute.needsUpdate = true;

				}

				geometryInfo.vertexStart = nextVertexStart;

			}

			nextVertexStart += geometryInfo.reservedVertexCount;
			geometryInfo.start = geometry.index ? geometryInfo.indexStart : geometryInfo.vertexStart;

		}

		this._nextIndexStart = nextIndexStart;
		this._nextVertexStart = nextVertexStart;
		this._visibilityChanged = true;

		return this;

	}

	/**
	 * Returns the bounding box for the given geometry.
	 *
	 * @param {number} geometryId - The ID of the geometry to return the bounding box for.
	 * @param {Box3} target - The target object that is used to store the method's result.
	 * @return {?Box3} The geometry's bounding box. Returns `null` if no geometry has been found for the given ID.
	 */
	getBoundingBoxAt( geometryId, target ) {

		if ( geometryId >= this._geometryCount ) {

			return null;

		}

		// compute bounding box
		const geometry = this.geometry;
		const geometryInfo = this._geometryInfo[ geometryId ];
		if ( geometryInfo.boundingBox === null ) {

			const box = new Box3();
			const index = geometry.index;
			const position = geometry.attributes.position;
			for ( let i = geometryInfo.start, l = geometryInfo.start + geometryInfo.count; i < l; i ++ ) {

				let iv = i;
				if ( index ) {

					iv = index.getX( iv );

				}

				box.expandByPoint( _vector.fromBufferAttribute( position, iv ) );

			}

			geometryInfo.boundingBox = box;

		}

		target.copy( geometryInfo.boundingBox );
		return target;

	}

	/**
	 * Returns the bounding sphere for the given geometry.
	 *
	 * @param {number} geometryId - The ID of the geometry to return the bounding sphere for.
	 * @param {Sphere} target - The target object that is used to store the method's result.
	 * @return {?Sphere} The geometry's bounding sphere. Returns `null` if no geometry has been found for the given ID.
	 */
	getBoundingSphereAt( geometryId, target ) {

		if ( geometryId >= this._geometryCount ) {

			return null;

		}

		// compute bounding sphere
		const geometry = this.geometry;
		const geometryInfo = this._geometryInfo[ geometryId ];
		if ( geometryInfo.boundingSphere === null ) {

			const sphere = new Sphere();
			this.getBoundingBoxAt( geometryId, _box );
			_box.getCenter( sphere.center );

			const index = geometry.index;
			const position = geometry.attributes.position;

			let maxRadiusSq = 0;
			for ( let i = geometryInfo.start, l = geometryInfo.start + geometryInfo.count; i < l; i ++ ) {

				let iv = i;
				if ( index ) {

					iv = index.getX( iv );

				}

				_vector.fromBufferAttribute( position, iv );
				maxRadiusSq = Math.max( maxRadiusSq, sphere.center.distanceToSquared( _vector ) );

			}

			sphere.radius = Math.sqrt( maxRadiusSq );
			geometryInfo.boundingSphere = sphere;

		}

		target.copy( geometryInfo.boundingSphere );
		return target;

	}

	/**
	 * Sets the given local transformation matrix to the defined instance.
	 * Negatively scaled matrices are not supported.
	 *
	 * @param {number} instanceId - The ID of an instance to set the matrix of.
	 * @param {Matrix4} matrix - A 4x4 matrix representing the local transformation of a single instance.
	 * @return {BatchedMesh} A reference to this batched mesh.
	 */
	setMatrixAt( instanceId, matrix ) {

		this.validateInstanceId( instanceId );

		const matricesTexture = this._matricesTexture;
		const matricesArray = this._matricesTexture.image.data;
		matrix.toArray( matricesArray, instanceId * 16 );
		matricesTexture.needsUpdate = true;

		return this;

	}

	/**
	 * Returns the local transformation matrix of the defined instance.
	 *
	 * @param {number} instanceId - The ID of an instance to get the matrix of.
	 * @param {Matrix4} matrix - The target object that is used to store the method's result.
	 * @return {Matrix4} The instance's local transformation matrix.
	 */
	getMatrixAt( instanceId, matrix ) {

		this.validateInstanceId( instanceId );
		return matrix.fromArray( this._matricesTexture.image.data, instanceId * 16 );

	}

	/**
	 * Sets the given color to the defined instance.
	 *
	 * @param {number} instanceId - The ID of an instance to set the color of.
	 * @param {Color|Vector4} color - The color to set the instance to. Use a `Vector4` to also define alpha.
	 * @return {BatchedMesh} A reference to this batched mesh.
	 */
	setColorAt( instanceId, color ) {

		this.validateInstanceId( instanceId );

		if ( this._colorsTexture === null ) {

			this._initColorsTexture();

		}

		color.toArray( this._colorsTexture.image.data, instanceId * 4 );
		this._colorsTexture.needsUpdate = true;

		return this;

	}

	/**
	 * Returns the color of the defined instance.
	 *
	 * @param {number} instanceId - The ID of an instance to get the color of.
	 * @param {Color|Vector4} color - The target object that is used to store the method's result.
	 * @return {Color|Vector4} The instance's color.  Use a `Vector4` to also retrieve alpha.
	 */
	getColorAt( instanceId, color ) {

		this.validateInstanceId( instanceId );
		return color.fromArray( this._colorsTexture.image.data, instanceId * 4 );

	}

	/**
	 * Sets the visibility of the instance.
	 *
	 * @param {number} instanceId - The id of the instance to set the visibility of.
	 * @param {boolean} visible - Whether the instance is visible or not.
	 * @return {BatchedMesh} A reference to this batched mesh.
	 */
	setVisibleAt( instanceId, visible ) {

		this.validateInstanceId( instanceId );

		if ( this._instanceInfo[ instanceId ].visible === visible ) {

			return this;

		}

		this._instanceInfo[ instanceId ].visible = visible;
		this._visibilityChanged = true;

		return this;

	}

	/**
	 * Returns the visibility state of the defined instance.
	 *
	 * @param {number} instanceId - The ID of an instance to get the visibility state of.
	 * @return {boolean} Whether the instance is visible or not.
	 */
	getVisibleAt( instanceId ) {

		this.validateInstanceId( instanceId );

		return this._instanceInfo[ instanceId ].visible;

	}

	/**
	 * Sets the geometry ID of the instance at the given index.
	 *
	 * @param {number} instanceId - The ID of the instance to set the geometry ID of.
	 * @param {number} geometryId - The geometry ID to be use by the instance.
	 * @return {BatchedMesh} A reference to this batched mesh.
	 */
	setGeometryIdAt( instanceId, geometryId ) {

		this.validateInstanceId( instanceId );
		this.validateGeometryId( geometryId );

		this._instanceInfo[ instanceId ].geometryIndex = geometryId;

		return this;

	}

	/**
	 * Returns the geometry ID of the defined instance.
	 *
	 * @param {number} instanceId - The ID of an instance to get the geometry ID of.
	 * @return {number} The instance's geometry ID.
	 */
	getGeometryIdAt( instanceId ) {

		this.validateInstanceId( instanceId );

		return this._instanceInfo[ instanceId ].geometryIndex;

	}

	/**
	 * Get the range representing the subset of triangles related to the attached geometry,
	 * indicating the starting offset and count, or `null` if invalid.
	 *
	 * @param {number} geometryId - The id of the geometry to get the range of.
	 * @param {Object} [target] - The target object that is used to store the method's result.
	 * @return {{
	 * 	vertexStart:number,vertexCount:number,reservedVertexCount:number,
	 * 	indexStart:number,indexCount:number,reservedIndexCount:number,
	 * 	start:number,count:number
	 * }} The result object with range data.
	 */
	getGeometryRangeAt( geometryId, target = {} ) {

		this.validateGeometryId( geometryId );

		const geometryInfo = this._geometryInfo[ geometryId ];
		target.vertexStart = geometryInfo.vertexStart;
		target.vertexCount = geometryInfo.vertexCount;
		target.reservedVertexCount = geometryInfo.reservedVertexCount;

		target.indexStart = geometryInfo.indexStart;
		target.indexCount = geometryInfo.indexCount;
		target.reservedIndexCount = geometryInfo.reservedIndexCount;

		target.start = geometryInfo.start;
		target.count = geometryInfo.count;

		return target;

	}

	/**
	 * Resizes the necessary buffers to support the provided number of instances.
	 * If the provided arguments shrink the number of instances but there are not enough
	 * unused Ids at the end of the list then an error is thrown.
	 *
	 * @param {number} maxInstanceCount - The max number of individual instances that can be added and rendered by the batch.
	*/
	setInstanceCount( maxInstanceCount ) {

		// shrink the available instances as much as possible
		const availableInstanceIds = this._availableInstanceIds;
		const instanceInfo = this._instanceInfo;
		availableInstanceIds.sort( ascIdSort );
		while ( availableInstanceIds[ availableInstanceIds.length - 1 ] === instanceInfo.length - 1 ) {

			instanceInfo.pop();
			availableInstanceIds.pop();

		}

		// throw an error if it can't be shrunk to the desired size
		if ( maxInstanceCount < instanceInfo.length ) {

			throw new Error( `BatchedMesh: Instance ids outside the range ${ maxInstanceCount } are being used. Cannot shrink instance count.` );

		}

		// copy the multi draw counts
		const multiDrawCounts = new Int32Array( maxInstanceCount );
		const multiDrawStarts = new Int32Array( maxInstanceCount );
		copyArrayContents( this._multiDrawCounts, multiDrawCounts );
		copyArrayContents( this._multiDrawStarts, multiDrawStarts );

		this._multiDrawCounts = multiDrawCounts;
		this._multiDrawStarts = multiDrawStarts;
		this._maxInstanceCount = maxInstanceCount;

		// update texture data for instance sampling
		const indirectTexture = this._indirectTexture;
		const matricesTexture = this._matricesTexture;
		const colorsTexture = this._colorsTexture;

		indirectTexture.dispose();
		this._initIndirectTexture();
		copyArrayContents( indirectTexture.image.data, this._indirectTexture.image.data );

		matricesTexture.dispose();
		this._initMatricesTexture();
		copyArrayContents( matricesTexture.image.data, this._matricesTexture.image.data );

		if ( colorsTexture ) {

			colorsTexture.dispose();
			this._initColorsTexture();
			copyArrayContents( colorsTexture.image.data, this._colorsTexture.image.data );

		}

	}

	/**
	 * Resizes the available space in the batch's vertex and index buffer attributes to the provided sizes.
	 * If the provided arguments shrink the geometry buffers but there is not enough unused space at the
	 * end of the geometry attributes then an error is thrown.
	 *
	 * @param {number} maxVertexCount - The maximum number of vertices to be used by all unique geometries to resize to.
	 * @param {number} maxIndexCount - The maximum number of indices to be used by all unique geometries to resize to.
	*/
	setGeometrySize( maxVertexCount, maxIndexCount ) {

		// Check if we can shrink to the requested vertex attribute size
		const validRanges = [ ...this._geometryInfo ].filter( info => info.active );
		const requiredVertexLength = Math.max( ...validRanges.map( range => range.vertexStart + range.reservedVertexCount ) );
		if ( requiredVertexLength > maxVertexCount ) {

			throw new Error( `BatchedMesh: Geometry vertex values are being used outside the range ${ maxIndexCount }. Cannot shrink further.` );

		}

		// Check if we can shrink to the requested index attribute size
		if ( this.geometry.index ) {

			const requiredIndexLength = Math.max( ...validRanges.map( range => range.indexStart + range.reservedIndexCount ) );
			if ( requiredIndexLength > maxIndexCount ) {

				throw new Error( `BatchedMesh: Geometry index values are being used outside the range ${ maxIndexCount }. Cannot shrink further.` );

			}

		}

		//

		// dispose of the previous geometry
		const oldGeometry = this.geometry;
		oldGeometry.dispose();

		// recreate the geometry needed based on the previous variant
		this._maxVertexCount = maxVertexCount;
		this._maxIndexCount = maxIndexCount;

		if ( this._geometryInitialized ) {

			this._geometryInitialized = false;
			this.geometry = new BufferGeometry();
			this._initializeGeometry( oldGeometry );

		}

		// copy data from the previous geometry
		const geometry = this.geometry;
		if ( oldGeometry.index ) {

			copyArrayContents( oldGeometry.index.array, geometry.index.array );

		}

		for ( const key in oldGeometry.attributes ) {

			copyArrayContents( oldGeometry.attributes[ key ].array, geometry.attributes[ key ].array );

		}

	}

	raycast( raycaster, intersects ) {

		const instanceInfo = this._instanceInfo;
		const geometryInfoList = this._geometryInfo;
		const matrixWorld = this.matrixWorld;
		const batchGeometry = this.geometry;

		// iterate over each geometry
		_mesh.material = this.material;
		_mesh.geometry.index = batchGeometry.index;
		_mesh.geometry.attributes = batchGeometry.attributes;
		if ( _mesh.geometry.boundingBox === null ) {

			_mesh.geometry.boundingBox = new Box3();

		}

		if ( _mesh.geometry.boundingSphere === null ) {

			_mesh.geometry.boundingSphere = new Sphere();

		}

		for ( let i = 0, l = instanceInfo.length; i < l; i ++ ) {

			if ( ! instanceInfo[ i ].visible || ! instanceInfo[ i ].active ) {

				continue;

			}

			const geometryId = instanceInfo[ i ].geometryIndex;
			const geometryInfo = geometryInfoList[ geometryId ];
			_mesh.geometry.setDrawRange( geometryInfo.start, geometryInfo.count );

			// get the intersects
			this.getMatrixAt( i, _mesh.matrixWorld ).premultiply( matrixWorld );
			this.getBoundingBoxAt( geometryId, _mesh.geometry.boundingBox );
			this.getBoundingSphereAt( geometryId, _mesh.geometry.boundingSphere );
			_mesh.raycast( raycaster, _batchIntersects );

			// add batch id to the intersects
			for ( let j = 0, l = _batchIntersects.length; j < l; j ++ ) {

				const intersect = _batchIntersects[ j ];
				intersect.object = this;
				intersect.batchId = i;
				intersects.push( intersect );

			}

			_batchIntersects.length = 0;

		}

		_mesh.material = null;
		_mesh.geometry.index = null;
		_mesh.geometry.attributes = {};
		_mesh.geometry.setDrawRange( 0, Infinity );

	}

	copy( source ) {

		super.copy( source );

		this.geometry = source.geometry.clone();
		this.perObjectFrustumCulled = source.perObjectFrustumCulled;
		this.sortObjects = source.sortObjects;
		this.boundingBox = source.boundingBox !== null ? source.boundingBox.clone() : null;
		this.boundingSphere = source.boundingSphere !== null ? source.boundingSphere.clone() : null;

		this._geometryInfo = source._geometryInfo.map( info => ( {
			...info,

			boundingBox: info.boundingBox !== null ? info.boundingBox.clone() : null,
			boundingSphere: info.boundingSphere !== null ? info.boundingSphere.clone() : null,
		} ) );
		this._instanceInfo = source._instanceInfo.map( info => ( { ...info } ) );

		this._availableInstanceIds = source._availableInstanceIds.slice();
		this._availableGeometryIds = source._availableGeometryIds.slice();

		this._nextIndexStart = source._nextIndexStart;
		this._nextVertexStart = source._nextVertexStart;
		this._geometryCount = source._geometryCount;

		this._maxInstanceCount = source._maxInstanceCount;
		this._maxVertexCount = source._maxVertexCount;
		this._maxIndexCount = source._maxIndexCount;

		this._geometryInitialized = source._geometryInitialized;
		this._multiDrawCounts = source._multiDrawCounts.slice();
		this._multiDrawStarts = source._multiDrawStarts.slice();

		this._indirectTexture = source._indirectTexture.clone();
		this._indirectTexture.image.data = this._indirectTexture.image.data.slice();

		this._matricesTexture = source._matricesTexture.clone();
		this._matricesTexture.image.data = this._matricesTexture.image.data.slice();

		if ( this._colorsTexture !== null ) {

			this._colorsTexture = source._colorsTexture.clone();
			this._colorsTexture.image.data = this._colorsTexture.image.data.slice();

		}

		return this;

	}

	/**
	 * Frees the GPU-related resources allocated by this instance. Call this
	 * method whenever this instance is no longer used in your app.
	 */
	dispose() {

		// Assuming the geometry is not shared with other meshes
		this.geometry.dispose();

		this._matricesTexture.dispose();
		this._matricesTexture = null;

		this._indirectTexture.dispose();
		this._indirectTexture = null;

		if ( this._colorsTexture !== null ) {

			this._colorsTexture.dispose();
			this._colorsTexture = null;

		}

	}

	onBeforeRender( renderer, scene, camera, geometry, material/*, _group*/ ) {

		// if visibility has not changed and frustum culling and object sorting is not required
		// then skip iterating over all items
		if ( ! this._visibilityChanged && ! this.perObjectFrustumCulled && ! this.sortObjects ) {

			return;

		}

		// the indexed version of the multi draw function requires specifying the start
		// offset in bytes.
		const index = geometry.getIndex();
		let bytesPerElement = index === null ? 1 : index.array.BYTES_PER_ELEMENT;


		// the "wireframe" attribute implicitly creates a line attribute in the renderer, which is double
		// the vertices to draw (3 lines per triangle) so we multiply the draw counts / starts and make
		// assumptions about the index buffer byte size.
		let multiDrawMultiplier = 1;
		if ( material.wireframe ) {

			multiDrawMultiplier = 2;
			bytesPerElement = geometry.attributes.position.count > 65535 ? 4 : 2;

		}

		const instanceInfo = this._instanceInfo;
		const multiDrawStarts = this._multiDrawStarts;
		const multiDrawCounts = this._multiDrawCounts;
		const geometryInfoList = this._geometryInfo;
		const perObjectFrustumCulled = this.perObjectFrustumCulled;
		const indirectTexture = this._indirectTexture;
		const indirectArray = indirectTexture.image.data;

		const frustum = camera.isArrayCamera ? _frustumArray : _frustum;
		// prepare the frustum in the local frame
		if ( perObjectFrustumCulled && ! camera.isArrayCamera ) {

			_matrix
				.multiplyMatrices( camera.projectionMatrix, camera.matrixWorldInverse )
				.multiply( this.matrixWorld );

			_frustum.setFromProjectionMatrix(
				_matrix,
				camera.coordinateSystem,
				camera.reversedDepth
			);

		}

		let multiDrawCount = 0;
		if ( this.sortObjects ) {

			// get the camera position in the local frame
			_matrix.copy( this.matrixWorld ).invert();
			_vector.setFromMatrixPosition( camera.matrixWorld ).applyMatrix4( _matrix );
			_forward.set( 0, 0, - 1 ).transformDirection( camera.matrixWorld ).transformDirection( _matrix );

			for ( let i = 0, l = instanceInfo.length; i < l; i ++ ) {

				if ( instanceInfo[ i ].visible && instanceInfo[ i ].active ) {

					const geometryId = instanceInfo[ i ].geometryIndex;

					// get the bounds in world space
					this.getMatrixAt( i, _matrix );
					this.getBoundingSphereAt( geometryId, _sphere ).applyMatrix4( _matrix );

					// determine whether the batched geometry is within the frustum
					let culled = false;
					if ( perObjectFrustumCulled ) {

						culled = ! frustum.intersectsSphere( _sphere, camera );

					}

					if ( ! culled ) {

						// get the distance from camera used for sorting
						const geometryInfo = geometryInfoList[ geometryId ];
						const z = _temp.subVectors( _sphere.center, _vector ).dot( _forward );
						_renderList.push( geometryInfo.start, geometryInfo.count, z, i );

					}

				}

			}

			// Sort the draw ranges and prep for rendering
			const list = _renderList.list;
			const customSort = this.customSort;
			if ( customSort === null ) {

				list.sort( material.transparent ? sortTransparent : sortOpaque );

			} else {

				customSort.call( this, list, camera );

			}

			for ( let i = 0, l = list.length; i < l; i ++ ) {

				const item = list[ i ];
				multiDrawStarts[ multiDrawCount ] = item.start * bytesPerElement * multiDrawMultiplier;
				multiDrawCounts[ multiDrawCount ] = item.count * multiDrawMultiplier;
				indirectArray[ multiDrawCount ] = item.index;
				multiDrawCount ++;

			}

			_renderList.reset();

		} else {

			for ( let i = 0, l = instanceInfo.length; i < l; i ++ ) {

				if ( instanceInfo[ i ].visible && instanceInfo[ i ].active ) {

					const geometryId = instanceInfo[ i ].geometryIndex;

					// determine whether the batched geometry is within the frustum
					let culled = false;
					if ( perObjectFrustumCulled ) {

						// get the bounds in world space
						this.getMatrixAt( i, _matrix );
						this.getBoundingSphereAt( geometryId, _sphere ).applyMatrix4( _matrix );
						culled = ! frustum.intersectsSphere( _sphere, camera );

					}

					if ( ! culled ) {

						const geometryInfo = geometryInfoList[ geometryId ];
						multiDrawStarts[ multiDrawCount ] = geometryInfo.start * bytesPerElement * multiDrawMultiplier;
						multiDrawCounts[ multiDrawCount ] = geometryInfo.count * multiDrawMultiplier;
						indirectArray[ multiDrawCount ] = i;
						multiDrawCount ++;

					}

				}

			}

		}

		indirectTexture.needsUpdate = true;
		this._multiDrawCount = multiDrawCount;
		this._visibilityChanged = false;

	}

	onBeforeShadow( renderer, object, camera, shadowCamera, geometry, depthMaterial/* , group */ ) {

		this.onBeforeRender( renderer, null, shadowCamera, geometry, depthMaterial );

	}

}

export { BatchedMesh };
