/**
 * Uniforms of a program.
 * Those form a tree structure with a special top-level container for the root,
 * which you get by calling 'new WebGLUniforms( gl, program )'.
 *
 *
 * Properties of inner nodes including the top-level container:
 *
 * .seq - array of nested uniforms
 * .map - nested uniforms by name
 *
 *
 * Methods of all nodes except the top-level container:
 *
 * .setValue( gl, value, [textures] )
 *
 * 		uploads a uniform value(s)
 *  	the 'textures' parameter is needed for sampler uniforms
 *
 *
 * Static methods of the top-level container (textures factorizations):
 *
 * .upload( gl, seq, values, textures )
 *
 * 		sets uniforms in 'seq' to 'values[id].value'
 *
 * .seqWithValue( seq, values ) : filteredSeq
 *
 * 		filters 'seq' entries with corresponding entry in values
 *
 *
 * Methods of the top-level container (textures factorizations):
 *
 * .setValue( gl, name, value, textures )
 *
 * 		sets uniform with  name 'name' to 'value'
 *
 * .setOptional( gl, obj, prop )
 *
 * 		like .set for an optional property of the object
 *
 */

import { CubeTexture } from '../../textures/CubeTexture.js';
import { Texture } from '../../textures/Texture.js';
import { DataArrayTexture } from '../../textures/DataArrayTexture.js';
import { Data3DTexture } from '../../textures/Data3DTexture.js';
import { DepthTexture } from '../../textures/DepthTexture.js';
import { LessEqualCompare, GreaterEqualCompare } from '../../constants.js';

const emptyTexture = /*@__PURE__*/ new Texture();

const emptyShadowTexture = /*@__PURE__*/ new DepthTexture( 1, 1 );

const emptyArrayTexture = /*@__PURE__*/ new DataArrayTexture();
const empty3dTexture = /*@__PURE__*/ new Data3DTexture();
const emptyCubeTexture = /*@__PURE__*/ new CubeTexture();

// --- Utilities ---

// Array Caches (provide typed arrays for temporary by size)

const arrayCacheF32 = [];
const arrayCacheI32 = [];

// Float32Array caches used for uploading Matrix uniforms

const mat4array = new Float32Array( 16 );
const mat3array = new Float32Array( 9 );
const mat2array = new Float32Array( 4 );

// Flattening for arrays of vectors and matrices

function flatten( array, nBlocks, blockSize ) {

	const firstElem = array[ 0 ];

	if ( firstElem <= 0 || firstElem > 0 ) return array;
	// unoptimized: ! isNaN( firstElem )
	// see http://jacksondunstan.com/articles/983

	const n = nBlocks * blockSize;
	let r = arrayCacheF32[ n ];

	if ( r === undefined ) {

		r = new Float32Array( n );
		arrayCacheF32[ n ] = r;

	}

	if ( nBlocks !== 0 ) {

		firstElem.toArray( r, 0 );

		for ( let i = 1, offset = 0; i !== nBlocks; ++ i ) {

			offset += blockSize;
			array[ i ].toArray( r, offset );

		}

	}

	return r;

}

function arraysEqual( a, b ) {

	if ( a.length !== b.length ) return false;

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

		if ( a[ i ] !== b[ i ] ) return false;

	}

	return true;

}

function copyArray( a, b ) {

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

		a[ i ] = b[ i ];

	}

}

// Texture unit allocation

function allocTexUnits( textures, n ) {

	let r = arrayCacheI32[ n ];

	if ( r === undefined ) {

		r = new Int32Array( n );
		arrayCacheI32[ n ] = r;

	}

	for ( let i = 0; i !== n; ++ i ) {

		r[ i ] = textures.allocateTextureUnit();

	}

	return r;

}

// --- Setters ---

// Note: Defining these methods externally, because they come in a bunch
// and this way their names minify.

// Single scalar

function setValueV1f( gl, v ) {

	const cache = this.cache;

	if ( cache[ 0 ] === v ) return;

	gl.uniform1f( this.addr, v );

	cache[ 0 ] = v;

}

// Single float vector (from flat array or THREE.VectorN)

function setValueV2f( gl, v ) {

	const cache = this.cache;

	if ( v.x !== undefined ) {

		if ( cache[ 0 ] !== v.x || cache[ 1 ] !== v.y ) {

			gl.uniform2f( this.addr, v.x, v.y );

			cache[ 0 ] = v.x;
			cache[ 1 ] = v.y;

		}

	} else {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniform2fv( this.addr, v );

		copyArray( cache, v );

	}

}

function setValueV3f( gl, v ) {

	const cache = this.cache;

	if ( v.x !== undefined ) {

		if ( cache[ 0 ] !== v.x || cache[ 1 ] !== v.y || cache[ 2 ] !== v.z ) {

			gl.uniform3f( this.addr, v.x, v.y, v.z );

			cache[ 0 ] = v.x;
			cache[ 1 ] = v.y;
			cache[ 2 ] = v.z;

		}

	} else if ( v.r !== undefined ) {

		if ( cache[ 0 ] !== v.r || cache[ 1 ] !== v.g || cache[ 2 ] !== v.b ) {

			gl.uniform3f( this.addr, v.r, v.g, v.b );

			cache[ 0 ] = v.r;
			cache[ 1 ] = v.g;
			cache[ 2 ] = v.b;

		}

	} else {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniform3fv( this.addr, v );

		copyArray( cache, v );

	}

}

function setValueV4f( gl, v ) {

	const cache = this.cache;

	if ( v.x !== undefined ) {

		if ( cache[ 0 ] !== v.x || cache[ 1 ] !== v.y || cache[ 2 ] !== v.z || cache[ 3 ] !== v.w ) {

			gl.uniform4f( this.addr, v.x, v.y, v.z, v.w );

			cache[ 0 ] = v.x;
			cache[ 1 ] = v.y;
			cache[ 2 ] = v.z;
			cache[ 3 ] = v.w;

		}

	} else {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniform4fv( this.addr, v );

		copyArray( cache, v );

	}

}

// Single matrix (from flat array or THREE.MatrixN)

function setValueM2( gl, v ) {

	const cache = this.cache;
	const elements = v.elements;

	if ( elements === undefined ) {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniformMatrix2fv( this.addr, false, v );

		copyArray( cache, v );

	} else {

		if ( arraysEqual( cache, elements ) ) return;

		mat2array.set( elements );

		gl.uniformMatrix2fv( this.addr, false, mat2array );

		copyArray( cache, elements );

	}

}

function setValueM3( gl, v ) {

	const cache = this.cache;
	const elements = v.elements;

	if ( elements === undefined ) {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniformMatrix3fv( this.addr, false, v );

		copyArray( cache, v );

	} else {

		if ( arraysEqual( cache, elements ) ) return;

		mat3array.set( elements );

		gl.uniformMatrix3fv( this.addr, false, mat3array );

		copyArray( cache, elements );

	}

}

function setValueM4( gl, v ) {

	const cache = this.cache;
	const elements = v.elements;

	if ( elements === undefined ) {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniformMatrix4fv( this.addr, false, v );

		copyArray( cache, v );

	} else {

		if ( arraysEqual( cache, elements ) ) return;

		mat4array.set( elements );

		gl.uniformMatrix4fv( this.addr, false, mat4array );

		copyArray( cache, elements );

	}

}

// Single integer / boolean

function setValueV1i( gl, v ) {

	const cache = this.cache;

	if ( cache[ 0 ] === v ) return;

	gl.uniform1i( this.addr, v );

	cache[ 0 ] = v;

}

// Single integer / boolean vector (from flat array or THREE.VectorN)

function setValueV2i( gl, v ) {

	const cache = this.cache;

	if ( v.x !== undefined ) {

		if ( cache[ 0 ] !== v.x || cache[ 1 ] !== v.y ) {

			gl.uniform2i( this.addr, v.x, v.y );

			cache[ 0 ] = v.x;
			cache[ 1 ] = v.y;

		}

	} else {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniform2iv( this.addr, v );

		copyArray( cache, v );

	}

}

function setValueV3i( gl, v ) {

	const cache = this.cache;

	if ( v.x !== undefined ) {

		if ( cache[ 0 ] !== v.x || cache[ 1 ] !== v.y || cache[ 2 ] !== v.z ) {

			gl.uniform3i( this.addr, v.x, v.y, v.z );

			cache[ 0 ] = v.x;
			cache[ 1 ] = v.y;
			cache[ 2 ] = v.z;

		}

	} else {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniform3iv( this.addr, v );

		copyArray( cache, v );

	}

}

function setValueV4i( gl, v ) {

	const cache = this.cache;

	if ( v.x !== undefined ) {

		if ( cache[ 0 ] !== v.x || cache[ 1 ] !== v.y || cache[ 2 ] !== v.z || cache[ 3 ] !== v.w ) {

			gl.uniform4i( this.addr, v.x, v.y, v.z, v.w );

			cache[ 0 ] = v.x;
			cache[ 1 ] = v.y;
			cache[ 2 ] = v.z;
			cache[ 3 ] = v.w;

		}

	} else {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniform4iv( this.addr, v );

		copyArray( cache, v );

	}

}

// Single unsigned integer

function setValueV1ui( gl, v ) {

	const cache = this.cache;

	if ( cache[ 0 ] === v ) return;

	gl.uniform1ui( this.addr, v );

	cache[ 0 ] = v;

}

// Single unsigned integer vector (from flat array or THREE.VectorN)

function setValueV2ui( gl, v ) {

	const cache = this.cache;

	if ( v.x !== undefined ) {

		if ( cache[ 0 ] !== v.x || cache[ 1 ] !== v.y ) {

			gl.uniform2ui( this.addr, v.x, v.y );

			cache[ 0 ] = v.x;
			cache[ 1 ] = v.y;

		}

	} else {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniform2uiv( this.addr, v );

		copyArray( cache, v );

	}

}

function setValueV3ui( gl, v ) {

	const cache = this.cache;

	if ( v.x !== undefined ) {

		if ( cache[ 0 ] !== v.x || cache[ 1 ] !== v.y || cache[ 2 ] !== v.z ) {

			gl.uniform3ui( this.addr, v.x, v.y, v.z );

			cache[ 0 ] = v.x;
			cache[ 1 ] = v.y;
			cache[ 2 ] = v.z;

		}

	} else {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniform3uiv( this.addr, v );

		copyArray( cache, v );

	}

}

function setValueV4ui( gl, v ) {

	const cache = this.cache;

	if ( v.x !== undefined ) {

		if ( cache[ 0 ] !== v.x || cache[ 1 ] !== v.y || cache[ 2 ] !== v.z || cache[ 3 ] !== v.w ) {

			gl.uniform4ui( this.addr, v.x, v.y, v.z, v.w );

			cache[ 0 ] = v.x;
			cache[ 1 ] = v.y;
			cache[ 2 ] = v.z;
			cache[ 3 ] = v.w;

		}

	} else {

		if ( arraysEqual( cache, v ) ) return;

		gl.uniform4uiv( this.addr, v );

		copyArray( cache, v );

	}

}


// Single texture (2D / Cube)

function setValueT1( gl, v, textures ) {

	const cache = this.cache;
	const unit = textures.allocateTextureUnit();

	if ( cache[ 0 ] !== unit ) {

		gl.uniform1i( this.addr, unit );
		cache[ 0 ] = unit;

	}

	let emptyTexture2D;

	if ( this.type === gl.SAMPLER_2D_SHADOW ) {

		emptyShadowTexture.compareFunction = textures.isReversedDepthBuffer() ? GreaterEqualCompare : LessEqualCompare;
		emptyTexture2D = emptyShadowTexture;

	} else {

		emptyTexture2D = emptyTexture;

	}

	textures.setTexture2D( v || emptyTexture2D, unit );

}

function setValueT3D1( gl, v, textures ) {

	const cache = this.cache;
	const unit = textures.allocateTextureUnit();

	if ( cache[ 0 ] !== unit ) {

		gl.uniform1i( this.addr, unit );
		cache[ 0 ] = unit;

	}

	textures.setTexture3D( v || empty3dTexture, unit );

}

function setValueT6( gl, v, textures ) {

	const cache = this.cache;
	const unit = textures.allocateTextureUnit();

	if ( cache[ 0 ] !== unit ) {

		gl.uniform1i( this.addr, unit );
		cache[ 0 ] = unit;

	}

	textures.setTextureCube( v || emptyCubeTexture, unit );

}

function setValueT2DArray1( gl, v, textures ) {

	const cache = this.cache;
	const unit = textures.allocateTextureUnit();

	if ( cache[ 0 ] !== unit ) {

		gl.uniform1i( this.addr, unit );
		cache[ 0 ] = unit;

	}

	textures.setTexture2DArray( v || emptyArrayTexture, unit );

}

// Helper to pick the right setter for the singular case

function getSingularSetter( type ) {

	switch ( type ) {

		case 0x1406: return setValueV1f; // FLOAT
		case 0x8b50: return setValueV2f; // _VEC2
		case 0x8b51: return setValueV3f; // _VEC3
		case 0x8b52: return setValueV4f; // _VEC4

		case 0x8b5a: return setValueM2; // _MAT2
		case 0x8b5b: return setValueM3; // _MAT3
		case 0x8b5c: return setValueM4; // _MAT4

		case 0x1404: case 0x8b56: return setValueV1i; // INT, BOOL
		case 0x8b53: case 0x8b57: return setValueV2i; // _VEC2
		case 0x8b54: case 0x8b58: return setValueV3i; // _VEC3
		case 0x8b55: case 0x8b59: return setValueV4i; // _VEC4

		case 0x1405: return setValueV1ui; // UINT
		case 0x8dc6: return setValueV2ui; // _VEC2
		case 0x8dc7: return setValueV3ui; // _VEC3
		case 0x8dc8: return setValueV4ui; // _VEC4

		case 0x8b5e: // SAMPLER_2D
		case 0x8d66: // SAMPLER_EXTERNAL_OES
		case 0x8dca: // INT_SAMPLER_2D
		case 0x8dd2: // UNSIGNED_INT_SAMPLER_2D
		case 0x8b62: // SAMPLER_2D_SHADOW
			return setValueT1;

		case 0x8b5f: // SAMPLER_3D
		case 0x8dcb: // INT_SAMPLER_3D
		case 0x8dd3: // UNSIGNED_INT_SAMPLER_3D
			return setValueT3D1;

		case 0x8b60: // SAMPLER_CUBE
		case 0x8dcc: // INT_SAMPLER_CUBE
		case 0x8dd4: // UNSIGNED_INT_SAMPLER_CUBE
		case 0x8dc5: // SAMPLER_CUBE_SHADOW
			return setValueT6;

		case 0x8dc1: // SAMPLER_2D_ARRAY
		case 0x8dcf: // INT_SAMPLER_2D_ARRAY
		case 0x8dd7: // UNSIGNED_INT_SAMPLER_2D_ARRAY
		case 0x8dc4: // SAMPLER_2D_ARRAY_SHADOW
			return setValueT2DArray1;

	}

}


// Array of scalars

function setValueV1fArray( gl, v ) {

	gl.uniform1fv( this.addr, v );

}

// Array of vectors (from flat array or array of THREE.VectorN)

function setValueV2fArray( gl, v ) {

	const data = flatten( v, this.size, 2 );

	gl.uniform2fv( this.addr, data );

}

function setValueV3fArray( gl, v ) {

	const data = flatten( v, this.size, 3 );

	gl.uniform3fv( this.addr, data );

}

function setValueV4fArray( gl, v ) {

	const data = flatten( v, this.size, 4 );

	gl.uniform4fv( this.addr, data );

}

// Array of matrices (from flat array or array of THREE.MatrixN)

function setValueM2Array( gl, v ) {

	const data = flatten( v, this.size, 4 );

	gl.uniformMatrix2fv( this.addr, false, data );

}

function setValueM3Array( gl, v ) {

	const data = flatten( v, this.size, 9 );

	gl.uniformMatrix3fv( this.addr, false, data );

}

function setValueM4Array( gl, v ) {

	const data = flatten( v, this.size, 16 );

	gl.uniformMatrix4fv( this.addr, false, data );

}

// Array of integer / boolean

function setValueV1iArray( gl, v ) {

	gl.uniform1iv( this.addr, v );

}

// Array of integer / boolean vectors (from flat array)

function setValueV2iArray( gl, v ) {

	gl.uniform2iv( this.addr, v );

}

function setValueV3iArray( gl, v ) {

	gl.uniform3iv( this.addr, v );

}

function setValueV4iArray( gl, v ) {

	gl.uniform4iv( this.addr, v );

}

// Array of unsigned integer

function setValueV1uiArray( gl, v ) {

	gl.uniform1uiv( this.addr, v );

}

// Array of unsigned integer vectors (from flat array)

function setValueV2uiArray( gl, v ) {

	gl.uniform2uiv( this.addr, v );

}

function setValueV3uiArray( gl, v ) {

	gl.uniform3uiv( this.addr, v );

}

function setValueV4uiArray( gl, v ) {

	gl.uniform4uiv( this.addr, v );

}


// Array of textures (2D / 3D / Cube / 2DArray)

function setValueT1Array( gl, v, textures ) {

	const cache = this.cache;

	const n = v.length;

	const units = allocTexUnits( textures, n );

	if ( ! arraysEqual( cache, units ) ) {

		gl.uniform1iv( this.addr, units );

		copyArray( cache, units );

	}

	let emptyTexture2D;

	if ( this.type === gl.SAMPLER_2D_SHADOW ) {

		emptyTexture2D = emptyShadowTexture;

	} else {

		emptyTexture2D = emptyTexture;

	}

	for ( let i = 0; i !== n; ++ i ) {

		textures.setTexture2D( v[ i ] || emptyTexture2D, units[ i ] );

	}

}

function setValueT3DArray( gl, v, textures ) {

	const cache = this.cache;

	const n = v.length;

	const units = allocTexUnits( textures, n );

	if ( ! arraysEqual( cache, units ) ) {

		gl.uniform1iv( this.addr, units );

		copyArray( cache, units );

	}

	for ( let i = 0; i !== n; ++ i ) {

		textures.setTexture3D( v[ i ] || empty3dTexture, units[ i ] );

	}

}

function setValueT6Array( gl, v, textures ) {

	const cache = this.cache;

	const n = v.length;

	const units = allocTexUnits( textures, n );

	if ( ! arraysEqual( cache, units ) ) {

		gl.uniform1iv( this.addr, units );

		copyArray( cache, units );

	}

	for ( let i = 0; i !== n; ++ i ) {

		textures.setTextureCube( v[ i ] || emptyCubeTexture, units[ i ] );

	}

}

function setValueT2DArrayArray( gl, v, textures ) {

	const cache = this.cache;

	const n = v.length;

	const units = allocTexUnits( textures, n );

	if ( ! arraysEqual( cache, units ) ) {

		gl.uniform1iv( this.addr, units );

		copyArray( cache, units );

	}

	for ( let i = 0; i !== n; ++ i ) {

		textures.setTexture2DArray( v[ i ] || emptyArrayTexture, units[ i ] );

	}

}


// Helper to pick the right setter for a pure (bottom-level) array

function getPureArraySetter( type ) {

	switch ( type ) {

		case 0x1406: return setValueV1fArray; // FLOAT
		case 0x8b50: return setValueV2fArray; // _VEC2
		case 0x8b51: return setValueV3fArray; // _VEC3
		case 0x8b52: return setValueV4fArray; // _VEC4

		case 0x8b5a: return setValueM2Array; // _MAT2
		case 0x8b5b: return setValueM3Array; // _MAT3
		case 0x8b5c: return setValueM4Array; // _MAT4

		case 0x1404: case 0x8b56: return setValueV1iArray; // INT, BOOL
		case 0x8b53: case 0x8b57: return setValueV2iArray; // _VEC2
		case 0x8b54: case 0x8b58: return setValueV3iArray; // _VEC3
		case 0x8b55: case 0x8b59: return setValueV4iArray; // _VEC4

		case 0x1405: return setValueV1uiArray; // UINT
		case 0x8dc6: return setValueV2uiArray; // _VEC2
		case 0x8dc7: return setValueV3uiArray; // _VEC3
		case 0x8dc8: return setValueV4uiArray; // _VEC4

		case 0x8b5e: // SAMPLER_2D
		case 0x8d66: // SAMPLER_EXTERNAL_OES
		case 0x8dca: // INT_SAMPLER_2D
		case 0x8dd2: // UNSIGNED_INT_SAMPLER_2D
		case 0x8b62: // SAMPLER_2D_SHADOW
			return setValueT1Array;

		case 0x8b5f: // SAMPLER_3D
		case 0x8dcb: // INT_SAMPLER_3D
		case 0x8dd3: // UNSIGNED_INT_SAMPLER_3D
			return setValueT3DArray;

		case 0x8b60: // SAMPLER_CUBE
		case 0x8dcc: // INT_SAMPLER_CUBE
		case 0x8dd4: // UNSIGNED_INT_SAMPLER_CUBE
		case 0x8dc5: // SAMPLER_CUBE_SHADOW
			return setValueT6Array;

		case 0x8dc1: // SAMPLER_2D_ARRAY
		case 0x8dcf: // INT_SAMPLER_2D_ARRAY
		case 0x8dd7: // UNSIGNED_INT_SAMPLER_2D_ARRAY
		case 0x8dc4: // SAMPLER_2D_ARRAY_SHADOW
			return setValueT2DArrayArray;

	}

}

// --- Uniform Classes ---

class SingleUniform {

	constructor( id, activeInfo, addr ) {

		this.id = id;
		this.addr = addr;
		this.cache = [];
		this.type = activeInfo.type;
		this.setValue = getSingularSetter( activeInfo.type );

		// this.path = activeInfo.name; // DEBUG

	}

}

class PureArrayUniform {

	constructor( id, activeInfo, addr ) {

		this.id = id;
		this.addr = addr;
		this.cache = [];
		this.type = activeInfo.type;
		this.size = activeInfo.size;
		this.setValue = getPureArraySetter( activeInfo.type );

		// this.path = activeInfo.name; // DEBUG

	}

}

class StructuredUniform {

	constructor( id ) {

		this.id = id;

		this.seq = [];
		this.map = {};

	}

	setValue( gl, value, textures ) {

		const seq = this.seq;

		for ( let i = 0, n = seq.length; i !== n; ++ i ) {

			const u = seq[ i ];
			u.setValue( gl, value[ u.id ], textures );

		}

	}

}

// --- Top-level ---

// Parser - builds up the property tree from the path strings

const RePathPart = /(\w+)(\])?(\[|\.)?/g;

// extracts
// 	- the identifier (member name or array index)
//  - followed by an optional right bracket (found when array index)
//  - followed by an optional left bracket or dot (type of subscript)
//
// Note: These portions can be read in a non-overlapping fashion and
// allow straightforward parsing of the hierarchy that WebGL encodes
// in the uniform names.

function addUniform( container, uniformObject ) {

	container.seq.push( uniformObject );
	container.map[ uniformObject.id ] = uniformObject;

}

function parseUniform( activeInfo, addr, container ) {

	const path = activeInfo.name,
		pathLength = path.length;

	// reset RegExp object, because of the early exit of a previous run
	RePathPart.lastIndex = 0;

	while ( true ) {

		const match = RePathPart.exec( path ),
			matchEnd = RePathPart.lastIndex;

		let id = match[ 1 ];
		const idIsIndex = match[ 2 ] === ']',
			subscript = match[ 3 ];

		if ( idIsIndex ) id = id | 0; // convert to integer

		if ( subscript === undefined || subscript === '[' && matchEnd + 2 === pathLength ) {

			// bare name or "pure" bottom-level array "[0]" suffix

			addUniform( container, subscript === undefined ?
				new SingleUniform( id, activeInfo, addr ) :
				new PureArrayUniform( id, activeInfo, addr ) );

			break;

		} else {

			// step into inner node / create it in case it doesn't exist

			const map = container.map;
			let next = map[ id ];

			if ( next === undefined ) {

				next = new StructuredUniform( id );
				addUniform( container, next );

			}

			container = next;

		}

	}

}

// Root Container

class WebGLUniforms {

	constructor( gl, program ) {

		this.seq = [];
		this.map = {};

		const n = gl.getProgramParameter( program, gl.ACTIVE_UNIFORMS );

		for ( let i = 0; i < n; ++ i ) {

			const info = gl.getActiveUniform( program, i ),
				addr = gl.getUniformLocation( program, info.name );

			parseUniform( info, addr, this );

		}

		// Sort uniforms to prioritize shadow samplers first (for optimal texture unit allocation)

		const shadowSamplers = [];
		const otherUniforms = [];

		for ( const u of this.seq ) {

			if ( u.type === gl.SAMPLER_2D_SHADOW || u.type === gl.SAMPLER_CUBE_SHADOW || u.type === gl.SAMPLER_2D_ARRAY_SHADOW ) {

				shadowSamplers.push( u );

			} else {

				otherUniforms.push( u );

			}

		}

		if ( shadowSamplers.length > 0 ) {

			this.seq = shadowSamplers.concat( otherUniforms );

		}

	}

	setValue( gl, name, value, textures ) {

		const u = this.map[ name ];

		if ( u !== undefined ) u.setValue( gl, value, textures );

	}

	setOptional( gl, object, name ) {

		const v = object[ name ];

		if ( v !== undefined ) this.setValue( gl, name, v );

	}

	static upload( gl, seq, values, textures ) {

		for ( let i = 0, n = seq.length; i !== n; ++ i ) {

			const u = seq[ i ],
				v = values[ u.id ];

			if ( v.needsUpdate !== false ) {

				// note: always updating when .needsUpdate is undefined
				u.setValue( gl, v.value, textures );

			}

		}

	}

	static seqWithValue( seq, values ) {

		const r = [];

		for ( let i = 0, n = seq.length; i !== n; ++ i ) {

			const u = seq[ i ];
			if ( u.id in values ) r.push( u );

		}

		return r;

	}

}

export { WebGLUniforms };
