text: import {
  	AnimationMixer,
  	Object3D,
  	Quaternion,
  	Vector3
  } from '../../../build/three.module.js';
  import { CCDIKSolver } from '../animation/CCDIKSolver.js';
  import { MMDPhysics } from '../animation/MMDPhysics.js';
  
  /**
   * MMDAnimationHelper handles animation of MMD assets loaded by MMDLoader
   * with MMD special features as IK, Grant, and Physics.
   *
   * Dependencies
   *  - ammo.js https://github.com/kripken/ammo.js
   *  - MMDPhysics
   *  - CCDIKSolver
   *
   * TODO
   *  - more precise grant skinning support.
   */
  class MMDAnimationHelper {
  
  	/**
  	 * @param {Object} params - (optional)
  	 * @param {boolean} params.sync - Whether animation durations of added objects are synched. Default is true.
  	 * @param {Number} params.afterglow - Default is 0.0.
  	 * @param {boolean} params.resetPhysicsOnLoop - Default is true.
  	 */
  	constructor( params = {} ) {
  
  		this.meshes = [];
  
  		this.camera = null;
  		this.cameraTarget = new Object3D();
  		this.cameraTarget.name = 'target';
  
  		this.audio = null;
  		this.audioManager = null;
  
  		this.objects = new WeakMap();
  
  		this.configuration = {
  			sync: params.sync !== undefined ? params.sync : true,
  			afterglow: params.afterglow !== undefined ? params.afterglow : 0.0,
  			resetPhysicsOnLoop: params.resetPhysicsOnLoop !== undefined ? params.resetPhysicsOnLoop : true,
  			pmxAnimation: params.pmxAnimation !== undefined ? params.pmxAnimation : false
  		};
  
  		this.enabled = {
  			animation: true,
  			ik: true,
  			grant: true,
  			physics: true,
  			cameraAnimation: true
  		};
  
  		this.onBeforePhysics = function ( /* mesh */ ) {};
  
  		// experimental
  		this.sharedPhysics = false;
  		this.masterPhysics = null;
  
  	}
  
  	/**
  	 * Adds an Three.js Object to helper and setups animation.
  	 * The anmation durations of added objects are synched
  	 * if this.configuration.sync is true.
  	 *
  	 * @param {THREE.SkinnedMesh|THREE.Camera|THREE.Audio} object
  	 * @param {Object} params - (optional)
  	 * @param {THREE.AnimationClip|Array<THREE.AnimationClip>} params.animation - Only for THREE.SkinnedMesh and THREE.Camera. Default is undefined.
  	 * @param {boolean} params.physics - Only for THREE.SkinnedMesh. Default is true.
  	 * @param {Integer} params.warmup - Only for THREE.SkinnedMesh and physics is true. Default is 60.
  	 * @param {Number} params.unitStep - Only for THREE.SkinnedMesh and physics is true. Default is 1 / 65.
  	 * @param {Integer} params.maxStepNum - Only for THREE.SkinnedMesh and physics is true. Default is 3.
  	 * @param {Vector3} params.gravity - Only for THREE.SkinnedMesh and physics is true. Default ( 0, - 9.8 * 10, 0 ).
  	 * @param {Number} params.delayTime - Only for THREE.Audio. Default is 0.0.
  	 * @return {MMDAnimationHelper}
  	 */
  	add( object, params = {} ) {
  
  		if ( object.isSkinnedMesh ) {
  
  			this._addMesh( object, params );
  
  		} else if ( object.isCamera ) {
  
  			this._setupCamera( object, params );
  
  		} else if ( object.type === 'Audio' ) {
  
  			this._setupAudio( object, params );
  
  		} else {
  
  			throw new Error( 'THREE.MMDAnimationHelper.add: '
  				+ 'accepts only '
  				+ 'THREE.SkinnedMesh or '
  				+ 'THREE.Camera or '
  				+ 'THREE.Audio instance.' );
  
  		}
  
  		if ( this.configuration.sync ) this._syncDuration();
  
  		return this;
  
  	}
  
  	/**
  	 * Removes an Three.js Object from helper.
  	 *
  	 * @param {THREE.SkinnedMesh|THREE.Camera|THREE.Audio} object
  	 * @return {MMDAnimationHelper}
  	 */
  	remove( object ) {
  
  		if ( object.isSkinnedMesh ) {
  
  			this._removeMesh( object );
  
  		} else if ( object.isCamera ) {
  
  			this._clearCamera( object );
  
  		} else if ( object.type === 'Audio' ) {
  
  			this._clearAudio( object );
  
  		} else {
  
  			throw new Error( 'THREE.MMDAnimationHelper.remove: '
  				+ 'accepts only '
  				+ 'THREE.SkinnedMesh or '
  				+ 'THREE.Camera or '
  				+ 'THREE.Audio instance.' );
  
  		}
  
  		if ( this.configuration.sync ) this._syncDuration();
  
  		return this;
  
  	}
  
  	/**
  	 * Updates the animation.
  	 *
  	 * @param {Number} delta
  	 * @return {MMDAnimationHelper}
  	 */
  	update( delta ) {
  
  		if ( this.audioManager !== null ) this.audioManager.control( delta );
  
  		for ( let i = 0; i < this.meshes.length; i ++ ) {
  
  			this._animateMesh( this.meshes[ i ], delta );
  
  		}
  
  		if ( this.sharedPhysics ) this._updateSharedPhysics( delta );
  
  		if ( this.camera !== null ) this._animateCamera( this.camera, delta );
  
  		return this;
  
  	}
  
  	/**
  	 * Changes the pose of SkinnedMesh as VPD specifies.
  	 *
  	 * @param {THREE.SkinnedMesh} mesh
  	 * @param {Object} vpd - VPD content parsed MMDParser
  	 * @param {Object} params - (optional)
  	 * @param {boolean} params.resetPose - Default is true.
  	 * @param {boolean} params.ik - Default is true.
  	 * @param {boolean} params.grant - Default is true.
  	 * @return {MMDAnimationHelper}
  	 */
  	pose( mesh, vpd, params = {} ) {
  
  		if ( params.resetPose !== false ) mesh.pose();
  
  		const bones = mesh.skeleton.bones;
  		const boneParams = vpd.bones;
  
  		const boneNameDictionary = {};
  
  		for ( let i = 0, il = bones.length; i < il; i ++ ) {
  
  			boneNameDictionary[ bones[ i ].name ] = i;
  
  		}
  
  		const vector = new Vector3();
  		const quaternion = new Quaternion();
  
  		for ( let i = 0, il = boneParams.length; i < il; i ++ ) {
  
  			const boneParam = boneParams[ i ];
  			const boneIndex = boneNameDictionary[ boneParam.name ];
  
  			if ( boneIndex === undefined ) continue;
  
  			const bone = bones[ boneIndex ];
  			bone.position.add( vector.fromArray( boneParam.translation ) );
  			bone.quaternion.multiply( quaternion.fromArray( boneParam.quaternion ) );
  
  		}
  
  		mesh.updateMatrixWorld( true );
  
  		// PMX animation system special path
  		if ( this.configuration.pmxAnimation &&
  			mesh.geometry.userData.MMD && mesh.geometry.userData.MMD.format === 'pmx' ) {
  
  			const sortedBonesData = this._sortBoneDataArray( mesh.geometry.userData.MMD.bones.slice() );
  			const ikSolver = params.ik !== false ? this._createCCDIKSolver( mesh ) : null;
  			const grantSolver = params.grant !== false ? this.createGrantSolver( mesh ) : null;
  			this._animatePMXMesh( mesh, sortedBonesData, ikSolver, grantSolver );
  
  		} else {
  
  			if ( params.ik !== false ) {
  
  				this._createCCDIKSolver( mesh ).update();
  
  			}
  
  			if ( params.grant !== false ) {
  
  				this.createGrantSolver( mesh ).update();
  
  			}
  
  		}
  
  		return this;
  
  	}
  
  	/**
  	 * Enabes/Disables an animation feature.
  	 *
  	 * @param {string} key
  	 * @param {boolean} enabled
  	 * @return {MMDAnimationHelper}
  	 */
  	enable( key, enabled ) {
  
  		if ( this.enabled[ key ] === undefined ) {
  
  			throw new Error( 'THREE.MMDAnimationHelper.enable: '
  				+ 'unknown key ' + key );
  
  		}
  
  		this.enabled[ key ] = enabled;
  
  		if ( key === 'physics' ) {
  
  			for ( let i = 0, il = this.meshes.length; i < il; i ++ ) {
  
  				this._optimizeIK( this.meshes[ i ], enabled );
  
  			}
  
  		}
  
  		return this;
  
  	}
  
  	/**
  	 * Creates an GrantSolver instance.
  	 *
  	 * @param {THREE.SkinnedMesh} mesh
  	 * @return {GrantSolver}
  	 */
  	createGrantSolver( mesh ) {
  
  		return new GrantSolver( mesh, mesh.geometry.userData.MMD.grants );
  
  	}
  
  	// private methods
  
  	_addMesh( mesh, params ) {
  
  		if ( this.meshes.indexOf( mesh ) >= 0 ) {
  
  			throw new Error( 'THREE.MMDAnimationHelper._addMesh: '
  				+ 'SkinnedMesh \'' + mesh.name + '\' has already been added.' );
  
  		}
  
  		this.meshes.push( mesh );
  		this.objects.set( mesh, { looped: false } );
  
  		this._setupMeshAnimation( mesh, params.animation );
  
  		if ( params.physics !== false ) {
  
  			this._setupMeshPhysics( mesh, params );
  
  		}
  
  		return this;
  
  	}
  
  	_setupCamera( camera, params ) {
  
  		if ( this.camera === camera ) {
  
  			throw new Error( 'THREE.MMDAnimationHelper._setupCamera: '
  				+ 'Camera \'' + camera.name + '\' has already been set.' );
  
  		}
  
  		if ( this.camera ) this.clearCamera( this.camera );
  
  		this.camera = camera;
  
  		camera.add( this.cameraTarget );
  
  		this.objects.set( camera, {} );
  
  		if ( params.animation !== undefined ) {
  
  			this._setupCameraAnimation( camera, params.animation );
  
  		}
  
  		return this;
  
  	}
  
  	_setupAudio( audio, params ) {
  
  		if ( this.audio === audio ) {
  
  			throw new Error( 'THREE.MMDAnimationHelper._setupAudio: '
  				+ 'Audio \'' + audio.name + '\' has already been set.' );
  
  		}
  
  		if ( this.audio ) this.clearAudio( this.audio );
  
  		this.audio = audio;
  		this.audioManager = new AudioManager( audio, params );
  
  		this.objects.set( this.audioManager, {
  			duration: this.audioManager.duration
  		} );
  
  		return this;
  
  	}
  
  	_removeMesh( mesh ) {
  
  		let found = false;
  		let writeIndex = 0;
  
  		for ( let i = 0, il = this.meshes.length; i < il; i ++ ) {
  
  			if ( this.meshes[ i ] === mesh ) {
  
  				this.objects.delete( mesh );
  				found = true;
  
  				continue;
  
  			}
  
  			this.meshes[ writeIndex ++ ] = this.meshes[ i ];
  
  		}
  
  		if ( ! found ) {
  
  			throw new Error( 'THREE.MMDAnimationHelper._removeMesh: '
  				+ 'SkinnedMesh \'' + mesh.name + '\' has not been added yet.' );
  
  		}
  
  		this.meshes.length = writeIndex;
  
  		return this;
  
  	}
  
  	_clearCamera( camera ) {
  
  		if ( camera !== this.camera ) {
  
  			throw new Error( 'THREE.MMDAnimationHelper._clearCamera: '
  				+ 'Camera \'' + camera.name + '\' has not been set yet.' );
  
  		}
  
  		this.camera.remove( this.cameraTarget );
  
  		this.objects.delete( this.camera );
  		this.camera = null;
  
  		return this;
  
  	}
  
  	_clearAudio( audio ) {
  
  		if ( audio !== this.audio ) {
  
  			throw new Error( 'THREE.MMDAnimationHelper._clearAudio: '
  				+ 'Audio \'' + audio.name + '\' has not been set yet.' );
  
  		}
  
  		this.objects.delete( this.audioManager );
  
  		this.audio = null;
  		this.audioManager = null;
  
  		return this;
  
  	}
  
  	_setupMeshAnimation( mesh, animation ) {
  
  		const objects = this.objects.get( mesh );
  
  		if ( animation !== undefined ) {
  
  			const animations = Array.isArray( animation )
  				? animation : [ animation ];
  
  			objects.mixer = new AnimationMixer( mesh );
  
  			for ( let i = 0, il = animations.length; i < il; i ++ ) {
  
  				objects.mixer.clipAction( animations[ i ] ).play();
  
  			}
  
  			// TODO: find a workaround not to access ._clip looking like a private property
  			objects.mixer.addEventListener( 'loop', function ( event ) {
  
  				const tracks = event.action._clip.tracks;
  
  				if ( tracks.length > 0 && tracks[ 0 ].name.slice( 0, 6 ) !== '.bones' ) return;
  
  				objects.looped = true;
  
  			} );
  
  		}
  
  		objects.ikSolver = this._createCCDIKSolver( mesh );
  		objects.grantSolver = this.createGrantSolver( mesh );
  
  		return this;
  
  	}
  
  	_setupCameraAnimation( camera, animation ) {
  
  		const animations = Array.isArray( animation )
  			? animation : [ animation ];
  
  		const objects = this.objects.get( camera );
  
  		objects.mixer = new AnimationMixer( camera );
  
  		for ( let i = 0, il = animations.length; i < il; i ++ ) {
  
  			objects.mixer.clipAction( animations[ i ] ).play();
  
  		}
  
  	}
  
  	_setupMeshPhysics( mesh, params ) {
  
  		const objects = this.objects.get( mesh );
  
  		// shared physics is experimental
  
  		if ( params.world === undefined && this.sharedPhysics ) {
  
  			const masterPhysics = this._getMasterPhysics();
  
  			if ( masterPhysics !== null ) world = masterPhysics.world; // eslint-disable-line no-undef
  
  		}
  
  		objects.physics = this._createMMDPhysics( mesh, params );
  
  		if ( objects.mixer && params.animationWarmup !== false ) {
  
  			this._animateMesh( mesh, 0 );
  			objects.physics.reset();
  
  		}
  
  		objects.physics.warmup( params.warmup !== undefined ? params.warmup : 60 );
  
  		this._optimizeIK( mesh, true );
  
  	}
  
  	_animateMesh( mesh, delta ) {
  
  		const objects = this.objects.get( mesh );
  
  		const mixer = objects.mixer;
  		const ikSolver = objects.ikSolver;
  		const grantSolver = objects.grantSolver;
  		const physics = objects.physics;
  		const looped = objects.looped;
  
  		if ( mixer && this.enabled.animation ) {
  
  			// alternate solution to save/restore bones but less performant?
  			//mesh.pose();
  			//this._updatePropertyMixersBuffer( mesh );
  
  			this._restoreBones( mesh );
  
  			mixer.update( delta );
  
  			this._saveBones( mesh );
  
  			// PMX animation system special path
  			if ( this.configuration.pmxAnimation &&
  				mesh.geometry.userData.MMD && mesh.geometry.userData.MMD.format === 'pmx' ) {
  
  				if ( ! objects.sortedBonesData ) objects.sortedBonesData = this._sortBoneDataArray( mesh.geometry.userData.MMD.bones.slice() );
  
  				this._animatePMXMesh(
  					mesh,
  					objects.sortedBonesData,
  					ikSolver && this.enabled.ik ? ikSolver : null,
  					grantSolver && this.enabled.grant ? grantSolver : null
  				);
  
  			} else {
  
  				if ( ikSolver && this.enabled.ik ) {
  
  					mesh.updateMatrixWorld( true );
  					ikSolver.update();
  
  				}
  
  				if ( grantSolver && this.enabled.grant ) {
  
  					grantSolver.update();
  
  				}
  
  			}
  
  		}
  
  		if ( looped === true && this.enabled.physics ) {
  
  			if ( physics && this.configuration.resetPhysicsOnLoop ) physics.reset();
  
  			objects.looped = false;
  
  		}
  
  		if ( physics && this.enabled.physics && ! this.sharedPhysics ) {
  
  			this.onBeforePhysics( mesh );
  			physics.update( delta );
  
  		}
  
  	}
  
  	// Sort bones in order by 1. transformationClass and 2. bone index.
  	// In PMX animation system, bone transformations should be processed
  	// in this order.
  	_sortBoneDataArray( boneDataArray ) {
  
  		return boneDataArray.sort( function ( a, b ) {
  
  			if ( a.transformationClass !== b.transformationClass ) {
  
  				return a.transformationClass - b.transformationClass;
  
  			} else {
  
  				return a.index - b.index;
  
  			}
  
  		} );
  
  	}
  
  	// PMX Animation system is a bit too complex and doesn't great match to
  	// Three.js Animation system. This method attempts to simulate it as much as
  	// possible but doesn't perfectly simulate.
  	// This method is more costly than the regular one so
  	// you are recommended to set constructor parameter "pmxAnimation: true"
  	// only if your PMX model animation doesn't work well.
  	// If you need better method you would be required to write your own.
  	_animatePMXMesh( mesh, sortedBonesData, ikSolver, grantSolver ) {
  
  		_quaternionIndex = 0;
  		_grantResultMap.clear();
  
  		for ( let i = 0, il = sortedBonesData.length; i < il; i ++ ) {
  
  			updateOne( mesh, sortedBonesData[ i ].index, ikSolver, grantSolver );
  
  		}
  
  		mesh.updateMatrixWorld( true );
  		return this;
  
  	}
  
  	_animateCamera( camera, delta ) {
  
  		const mixer = this.objects.get( camera ).mixer;
  
  		if ( mixer && this.enabled.cameraAnimation ) {
  
  			mixer.update( delta );
  
  			camera.updateProjectionMatrix();
  
  			camera.up.set( 0, 1, 0 );
  			camera.up.applyQuaternion( camera.quaternion );
  			camera.lookAt( this.cameraTarget.position );
  
  		}
  
  	}
  
  	_optimizeIK( mesh, physicsEnabled ) {
  
  		const iks = mesh.geometry.userData.MMD.iks;
  		const bones = mesh.geometry.userData.MMD.bones;
  
  		for ( let i = 0, il = iks.length; i < il; i ++ ) {
  
  			const ik = iks[ i ];
  			const links = ik.links;
  
  			for ( let j = 0, jl = links.length; j < jl; j ++ ) {
  
  				const link = links[ j ];
  
  				if ( physicsEnabled === true ) {
  
  					// disable IK of the bone the corresponding rigidBody type of which is 1 or 2
  					// because its rotation will be overriden by physics
  					link.enabled = bones[ link.index ].rigidBodyType > 0 ? false : true;
  
  				} else {
  
  					link.enabled = true;
  
  				}
  
  			}
  
  		}
  
  	}
  
  	_createCCDIKSolver( mesh ) {
  
  		if ( CCDIKSolver === undefined ) {
  
  			throw new Error( 'THREE.MMDAnimationHelper: Import CCDIKSolver.' );
  
  		}
  
  		return new CCDIKSolver( mesh, mesh.geometry.userData.MMD.iks );
  
  	}
  
  	_createMMDPhysics( mesh, params ) {
  
  		if ( MMDPhysics === undefined ) {
  
  			throw new Error( 'THREE.MMDPhysics: Import MMDPhysics.' );
  
  		}
  
  		return new MMDPhysics(
  			mesh,
  			mesh.geometry.userData.MMD.rigidBodies,
  			mesh.geometry.userData.MMD.constraints,
  			params );
  
  	}
  
  	/*
  	 * Detects the longest duration and then sets it to them to sync.
  	 * TODO: Not to access private properties ( ._actions and ._clip )
  	 */
  	_syncDuration() {
  
  		let max = 0.0;
  
  		const objects = this.objects;
  		const meshes = this.meshes;
  		const camera = this.camera;
  		const audioManager = this.audioManager;
  
  		// get the longest duration
  
  		for ( let i = 0, il = meshes.length; i < il; i ++ ) {
  
  			const mixer = this.objects.get( meshes[ i ] ).mixer;
  
  			if ( mixer === undefined ) continue;
  
  			for ( let j = 0; j < mixer._actions.length; j ++ ) {
  
  				const clip = mixer._actions[ j ]._clip;
  
  				if ( ! objects.has( clip ) ) {
  
  					objects.set( clip, {
  						duration: clip.duration
  					} );
  
  				}
  
  				max = Math.max( max, objects.get( clip ).duration );
  
  			}
  
  		}
  
  		if ( camera !== null ) {
  
  			const mixer = this.objects.get( camera ).mixer;
  
  			if ( mixer !== undefined ) {
  
  				for ( let i = 0, il = mixer._actions.length; i < il; i ++ ) {
  
  					const clip = mixer._actions[ i ]._clip;
  
  					if ( ! objects.has( clip ) ) {
  
  						objects.set( clip, {
  							duration: clip.duration
  						} );
  
  					}
  
  					max = Math.max( max, objects.get( clip ).duration );
  
  				}
  
  			}
  
  		}
  
  		if ( audioManager !== null ) {
  
  			max = Math.max( max, objects.get( audioManager ).duration );
  
  		}
  
  		max += this.configuration.afterglow;
  
  		// update the duration
  
  		for ( let i = 0, il = this.meshes.length; i < il; i ++ ) {
  
  			const mixer = this.objects.get( this.meshes[ i ] ).mixer;
  
  			if ( mixer === undefined ) continue;
  
  			for ( let j = 0, jl = mixer._actions.length; j < jl; j ++ ) {
  
  				mixer._actions[ j ]._clip.duration = max;
  
  			}
  
  		}
  
  		if ( camera !== null ) {
  
  			const mixer = this.objects.get( camera ).mixer;
  
  			if ( mixer !== undefined ) {
  
  				for ( let i = 0, il = mixer._actions.length; i < il; i ++ ) {
  
  					mixer._actions[ i ]._clip.duration = max;
  
  				}
  
  			}
  
  		}
  
  		if ( audioManager !== null ) {
  
  			audioManager.duration = max;
  
  		}
  
  	}
  
  	// workaround
  
  	_updatePropertyMixersBuffer( mesh ) {
  
  		const mixer = this.objects.get( mesh ).mixer;
  
  		const propertyMixers = mixer._bindings;
  		const accuIndex = mixer._accuIndex;
  
  		for ( let i = 0, il = propertyMixers.length; i < il; i ++ ) {
  
  			const propertyMixer = propertyMixers[ i ];
  			const buffer = propertyMixer.buffer;
  			const stride = propertyMixer.valueSize;
  			const offset = ( accuIndex + 1 ) * stride;
  
  			propertyMixer.binding.getValue( buffer, offset );
  
  		}
  
  	}
  
  	/*
  	 * Avoiding these two issues by restore/save bones before/after mixer animation.
  	 *
  	 * 1. PropertyMixer used by AnimationMixer holds cache value in .buffer.
  	 *    Calculating IK, Grant, and Physics after mixer animation can break
  	 *    the cache coherency.
  	 *
  	 * 2. Applying Grant two or more times without reset the posing breaks model.
  	 */
  	_saveBones( mesh ) {
  
  		const objects = this.objects.get( mesh );
  
  		const bones = mesh.skeleton.bones;
  
  		let backupBones = objects.backupBones;
  
  		if ( backupBones === undefined ) {
  
  			backupBones = new Float32Array( bones.length * 7 );
  			objects.backupBones = backupBones;
  
  		}
  
  		for ( let i = 0, il = bones.length; i < il; i ++ ) {
  
  			const bone = bones[ i ];
  			bone.position.toArray( backupBones, i * 7 );
  			bone.quaternion.toArray( backupBones, i * 7 + 3 );
  
  		}
  
  	}
  
  	_restoreBones( mesh ) {
  
  		const objects = this.objects.get( mesh );
  
  		const backupBones = objects.backupBones;
  
  		if ( backupBones === undefined ) return;
  
  		const bones = mesh.skeleton.bones;
  
  		for ( let i = 0, il = bones.length; i < il; i ++ ) {
  
  			const bone = bones[ i ];
  			bone.position.fromArray( backupBones, i * 7 );
  			bone.quaternion.fromArray( backupBones, i * 7 + 3 );
  
  		}
  
  	}
  
  	// experimental
  
  	_getMasterPhysics() {
  
  		if ( this.masterPhysics !== null ) return this.masterPhysics;
  
  		for ( let i = 0, il = this.meshes.length; i < il; i ++ ) {
  
  			const physics = this.meshes[ i ].physics;
  
  			if ( physics !== undefined && physics !== null ) {
  
  				this.masterPhysics = physics;
  				return this.masterPhysics;
  
  			}
  
  		}
  
  		return null;
  
  	}
  
  	_updateSharedPhysics( delta ) {
  
  		if ( this.meshes.length === 0 || ! this.enabled.physics || ! this.sharedPhysics ) return;
  
  		const physics = this._getMasterPhysics();
  
  		if ( physics === null ) return;
  
  		for ( let i = 0, il = this.meshes.length; i < il; i ++ ) {
  
  			const p = this.meshes[ i ].physics;
  
  			if ( p !== null && p !== undefined ) {
  
  				p.updateRigidBodies();
  
  			}
  
  		}
  
  		physics.stepSimulation( delta );
  
  		for ( let i = 0, il = this.meshes.length; i < il; i ++ ) {
  
  			const p = this.meshes[ i ].physics;
  
  			if ( p !== null && p !== undefined ) {
  
  				p.updateBones();
  
  			}
  
  		}
  
  	}
  
  }
  
  // Keep working quaternions for less GC
  const _quaternions = [];
  let _quaternionIndex = 0;
  
  function getQuaternion() {
  
  	if ( _quaternionIndex >= _quaternions.length ) {
  
  		_quaternions.push( new Quaternion() );
  
  	}
  
  	return _quaternions[ _quaternionIndex ++ ];
  
  }
  
  // Save rotation whose grant and IK are already applied
  // used by grant children
  const _grantResultMap = new Map();
  
  function updateOne( mesh, boneIndex, ikSolver, grantSolver ) {
  
  	const bones = mesh.skeleton.bones;
  	const bonesData = mesh.geometry.userData.MMD.bones;
  	const boneData = bonesData[ boneIndex ];
  	const bone = bones[ boneIndex ];
  
  	// Return if already updated by being referred as a grant parent.
  	if ( _grantResultMap.has( boneIndex ) ) return;
  
  	const quaternion = getQuaternion();
  
  	// Initialize grant result here to prevent infinite loop.
  	// If it's referred before updating with actual result later
  	// result without applyting IK or grant is gotten
  	// but better than composing of infinite loop.
  	_grantResultMap.set( boneIndex, quaternion.copy( bone.quaternion ) );
  
  	// @TODO: Support global grant and grant position
  	if ( grantSolver && boneData.grant &&
  		! boneData.grant.isLocal && boneData.grant.affectRotation ) {
  
  		const parentIndex = boneData.grant.parentIndex;
  		const ratio = boneData.grant.ratio;
  
  		if ( ! _grantResultMap.has( parentIndex ) ) {
  
  			updateOne( mesh, parentIndex, ikSolver, grantSolver );
  
  		}
  
  		grantSolver.addGrantRotation( bone, _grantResultMap.get( parentIndex ), ratio );
  
  	}
  
  	if ( ikSolver && boneData.ik ) {
  
  		// @TODO: Updating world matrices every time solving an IK bone is
  		// costly. Optimize if possible.
  		mesh.updateMatrixWorld( true );
  		ikSolver.updateOne( boneData.ik );
  
  		// No confident, but it seems the grant results with ik links should be updated?
  		const links = boneData.ik.links;
  
  		for ( let i = 0, il = links.length; i < il; i ++ ) {
  
  			const link = links[ i ];
  
  			if ( link.enabled === false ) continue;
  
  			const linkIndex = link.index;
  
  			if ( _grantResultMap.has( linkIndex ) ) {
  
  				_grantResultMap.set( linkIndex, _grantResultMap.get( linkIndex ).copy( bones[ linkIndex ].quaternion ) );
  
  			}
  
  		}
  
  	}
  
  	// Update with the actual result here
  	quaternion.copy( bone.quaternion );
  
  }
  
  //
  
  class AudioManager {
  
  	/**
  	 * @param {THREE.Audio} audio
  	 * @param {Object} params - (optional)
  	 * @param {Nuumber} params.delayTime
  	 */
  	constructor( audio, params = {} ) {
  
  		this.audio = audio;
  
  		this.elapsedTime = 0.0;
  		this.currentTime = 0.0;
  		this.delayTime = params.delayTime !== undefined
  			? params.delayTime : 0.0;
  
  		this.audioDuration = this.audio.buffer.duration;
  		this.duration = this.audioDuration + this.delayTime;
  
  	}
  
  	/**
  	 * @param {Number} delta
  	 * @return {AudioManager}
  	 */
  	control( delta ) {
  
  		this.elapsed += delta;
  		this.currentTime += delta;
  
  		if ( this._shouldStopAudio() ) this.audio.stop();
  		if ( this._shouldStartAudio() ) this.audio.play();
  
  		return this;
  
  	}
  
  	// private methods
  
  	_shouldStartAudio() {
  
  		if ( this.audio.isPlaying ) return false;
  
  		while ( this.currentTime >= this.duration ) {
  
  			this.currentTime -= this.duration;
  
  		}
  
  		if ( this.currentTime < this.delayTime ) return false;
  
  		// 'duration' can be bigger than 'audioDuration + delayTime' because of sync configuration
  		if ( ( this.currentTime - this.delayTime ) > this.audioDuration ) return false;
  
  		return true;
  
  	}
  
  	_shouldStopAudio() {
  
  		return this.audio.isPlaying &&
  			this.currentTime >= this.duration;
  
  	}
  
  }
  
  const _q = new Quaternion();
  
  /**
   * Solver for Grant (Fuyo in Japanese. I just google translated because
   * Fuyo may be MMD specific term and may not be common word in 3D CG terms.)
   * Grant propagates a bone's transform to other bones transforms even if
   * they are not children.
   * @param {THREE.SkinnedMesh} mesh
   * @param {Array<Object>} grants
   */
  class GrantSolver {
  
  	constructor( mesh, grants = [] ) {
  
  		this.mesh = mesh;
  		this.grants = grants;
  
  	}
  
  	/**
  	 * Solve all the grant bones
  	 * @return {GrantSolver}
  	 */
  	update() {
  
  		const grants = this.grants;
  
  		for ( let i = 0, il = grants.length; i < il; i ++ ) {
  
  			this.updateOne( grants[ i ] );
  
  		}
  
  		return this;
  
  	}
  
  	/**
  	 * Solve a grant bone
  	 * @param {Object} grant - grant parameter
  	 * @return {GrantSolver}
  	 */
  	updateOne( grant ) {
  
  		const bones = this.mesh.skeleton.bones;
  		const bone = bones[ grant.index ];
  		const parentBone = bones[ grant.parentIndex ];
  
  		if ( grant.isLocal ) {
  
  			// TODO: implement
  			if ( grant.affectPosition ) {
  
  			}
  
  			// TODO: implement
  			if ( grant.affectRotation ) {
  
  			}
  
  		} else {
  
  			// TODO: implement
  			if ( grant.affectPosition ) {
  
  			}
  
  			if ( grant.affectRotation ) {
  
  				this.addGrantRotation( bone, parentBone.quaternion, grant.ratio );
  
  			}
  
  		}
  
  		return this;
  
  	}
  
  	addGrantRotation( bone, q, ratio ) {
  
  		_q.set( 0, 0, 0, 1 );
  		_q.slerp( q, ratio );
  		bone.quaternion.multiply( _q );
  
  		return this;
  
  	}
  
  }
  
  export { MMDAnimationHelper };
  