'use strict';
var Cesium = require('cesium');
var path = require('path');
var Promise = require('bluebird');
var loadTexture = require('./loadTexture');
var outsideDirectory = require('./outsideDirectory');
var readLines = require('./readLines');
var Texture = require('./Texture');

var CesiumMath = Cesium.Math;
var combine = Cesium.combine;
var defaultValue = Cesium.defaultValue;
var defined = Cesium.defined;

module.exports = loadMtl;

/**
 * Parse a .mtl file and load textures referenced within. Returns an array of glTF materials with Texture
 * objects stored in the texture slots.
 * <p>
 * Packed PBR textures (like metallicRoughnessOcclusion and specularGlossiness) require all input textures to be decoded before hand.
 * If a texture is of an unsupported format like .gif or .tga it can't be packed and a metallicRoughness texture will not be created.
 * Similarly if a texture cannot be found it will be ignored and a default value will be used instead.
 * </p>
 *
 * @param {String} mtlPath Path to the .mtl file.
 * @param {Object} options The options object passed along from lib/obj2gltf.js
 * @returns {Promise} A promise resolving to an array of glTF materials with Texture objects stored in the texture slots.
 *
 * @private
 */
function loadMtl(mtlPath, options) {
    var material;
    var values;
    var value;

    var mtlDirectory = path.dirname(mtlPath);
    var materials = [];
    var texturePromiseMap = {}; // Maps texture paths to load promises so that no texture is loaded twice
    var texturePromises = [];

    var overridingTextures = options.overridingTextures;
    var overridingSpecularTexture = defaultValue(overridingTextures.metallicRoughnessOcclusionTexture, overridingTextures.specularGlossinessTexture);
    var overridingSpecularShininessTexture = defaultValue(overridingTextures.metallicRoughnessOcclusionTexture, overridingTextures.specularGlossinessTexture);
    var overridingAmbientTexture = defaultValue(overridingTextures.metallicRoughnessOcclusionTexture, overridingTextures.occlusionTexture);
    var overridingNormalTexture = overridingTextures.normalTexture;
    var overridingDiffuseTexture = overridingTextures.baseColorTexture;
    var overridingEmissiveTexture = overridingTextures.emissiveTexture;
    var overridingAlphaTexture = overridingTextures.alphaTexture;

    // Textures that are packed into PBR textures need to be decoded first
    var decodeOptions = {
        decode : true
    };

    var diffuseTextureOptions = {
        checkTransparency : options.checkTransparency
    };

    var ambientTextureOptions = defined(overridingAmbientTexture) ? undefined : (options.packOcclusion ? decodeOptions : undefined);
    var specularTextureOptions = defined(overridingSpecularTexture) ? undefined : decodeOptions;
    var specularShinessTextureOptions = defined(overridingSpecularShininessTexture) ? undefined : decodeOptions;
    var emissiveTextureOptions;
    var normalTextureOptions;
    var alphaTextureOptions = {
        decode : true
    };

    function createMaterial(name) {
        material = new Material();
        material.name = name;
        material.specularShininess = options.metallicRoughness ? 1.0 : 0.0;
        material.specularTexture = overridingSpecularTexture;
        material.specularShininessTexture = overridingSpecularShininessTexture;
        material.diffuseTexture = overridingDiffuseTexture;
        material.ambientTexture = overridingAmbientTexture;
        material.normalTexture = overridingNormalTexture;
        material.emissiveTexture = overridingEmissiveTexture;
        material.alphaTexture = overridingAlphaTexture;
        materials.push(material);
    }

    function normalizeTexturePath(texturePath, mtlDirectory) {
        // Removes texture options from texture name
        // Assumes no spaces in texture name
        var re = /-(bm|t|s|o|blendu|blendv|boost|mm|texres|clamp|imfchan|type)/;
        if (re.test(texturePath)) {
            texturePath = texturePath.split(/\s+/).pop();
        }
        texturePath = texturePath.replace(/\\/g, '/');
        return path.normalize(path.join(mtlDirectory, texturePath));
    }

    function parseLine(line) {
        line = line.trim();
        if (/^newmtl /i.test(line)) {
            var name = line.substring(7).trim();
            createMaterial(name);
        } else if (/^Ka /i.test(line)) {
            values = line.substring(3).trim().split(' ');
            material.ambientColor = [
                parseFloat(values[0]),
                parseFloat(values[1]),
                parseFloat(values[2]),
                1.0
            ];
        } else if (/^Ke /i.test(line)) {
            values = line.substring(3).trim().split(' ');
            material.emissiveColor = [
                parseFloat(values[0]),
                parseFloat(values[1]),
                parseFloat(values[2]),
                1.0
            ];
        } else if (/^Kd /i.test(line)) {
            values = line.substring(3).trim().split(' ');
            material.diffuseColor = [
                parseFloat(values[0]),
                parseFloat(values[1]),
                parseFloat(values[2]),
                1.0
            ];
        } else if (/^Ks /i.test(line)) {
            values = line.substring(3).trim().split(' ');
            material.specularColor = [
                parseFloat(values[0]),
                parseFloat(values[1]),
                parseFloat(values[2]),
                1.0
            ];
        } else if (/^Ns /i.test(line)) {
            value = line.substring(3).trim();
            material.specularShininess = parseFloat(value);
        } else if (/^d /i.test(line)) {
            value = line.substring(2).trim();
            material.alpha = correctAlpha(parseFloat(value));
        } else if (/^Tr /i.test(line)) {
            value = line.substring(3).trim();
            material.alpha = correctAlpha(1.0 - parseFloat(value));
        } else if (/^map_Ka /i.test(line)) {
            if (!defined(overridingAmbientTexture)) {
                material.ambientTexture = normalizeTexturePath(line.substring(7).trim(), mtlDirectory);
            }
        } else if (/^map_Ke /i.test(line)) {
            if (!defined(overridingEmissiveTexture)) {
                material.emissiveTexture = normalizeTexturePath(line.substring(7).trim(), mtlDirectory);
            }
        } else if (/^map_Kd /i.test(line)) {
            if (!defined(overridingDiffuseTexture)) {
                material.diffuseTexture = normalizeTexturePath(line.substring(7).trim(), mtlDirectory);
            }
        } else if (/^map_Ks /i.test(line)) {
            if (!defined(overridingSpecularTexture)) {
                material.specularTexture = normalizeTexturePath(line.substring(7).trim(), mtlDirectory);
            }
        } else if (/^map_Ns /i.test(line)) {
            if (!defined(overridingSpecularShininessTexture)) {
                material.specularShininessTexture = normalizeTexturePath(line.substring(7).trim(), mtlDirectory);
            }
        } else if (/^map_Bump /i.test(line)) {
            if (!defined(overridingNormalTexture)) {
                material.normalTexture = normalizeTexturePath(line.substring(9).trim(), mtlDirectory);
            }
        } else if (/^map_d /i.test(line)) {
            if (!defined(overridingAlphaTexture)) {
                material.alphaTexture = normalizeTexturePath(line.substring(6).trim(), mtlDirectory);
            }
        }
    }

    function loadMaterialTextures(material) {
        // If an alpha texture is present the diffuse texture needs to be decoded so they can be packed together
        var diffuseAlphaTextureOptions = defined(material.alphaTexture) ? alphaTextureOptions : diffuseTextureOptions;

        if (material.diffuseTexture === material.ambientTexture) {
            // OBJ models are often exported with the same texture in the diffuse and ambient slots but this is typically not desirable, particularly
            // when saving with PBR materials where the ambient texture is treated as the occlusion texture.
            material.ambientTexture = undefined;
        }

        loadMaterialTexture(material, 'diffuseTexture', diffuseAlphaTextureOptions, mtlDirectory, texturePromiseMap, texturePromises, options);
        loadMaterialTexture(material, 'ambientTexture', ambientTextureOptions, mtlDirectory, texturePromiseMap, texturePromises, options);
        loadMaterialTexture(material, 'emissiveTexture', emissiveTextureOptions, mtlDirectory, texturePromiseMap, texturePromises, options);
        loadMaterialTexture(material, 'specularTexture', specularTextureOptions, mtlDirectory, texturePromiseMap, texturePromises, options);
        loadMaterialTexture(material, 'specularShininessTexture', specularShinessTextureOptions, mtlDirectory, texturePromiseMap, texturePromises, options);
        loadMaterialTexture(material, 'normalTexture', normalTextureOptions, mtlDirectory, texturePromiseMap, texturePromises, options);
        loadMaterialTexture(material, 'alphaTexture', alphaTextureOptions, mtlDirectory, texturePromiseMap, texturePromises, options);
    }

    return readLines(mtlPath, parseLine)
        .then(function() {
            var length = materials.length;
            for (var i = 0; i < length; ++i) {
                loadMaterialTextures(materials[i]);
            }
            return Promise.all(texturePromises);
        })
        .then(function() {
            return convertMaterials(materials, options);
        });
}

function correctAlpha(alpha) {
    // An alpha of 0.0 usually implies a problem in the export, change to 1.0 instead
    return alpha === 0.0 ? 1.0 : alpha;
}

function Material() {
    this.name = undefined;
    this.ambientColor = [0.0, 0.0, 0.0, 1.0];    // Ka
    this.emissiveColor = [0.0, 0.0, 0.0, 1.0];   // Ke
    this.diffuseColor = [0.5, 0.5, 0.5, 1.0];    // Kd
    this.specularColor = [0.0, 0.0, 0.0, 1.0];   // Ks
    this.specularShininess = 0.0;                // Ns
    this.alpha = 1.0;                            // d / Tr
    this.ambientTexture = undefined;             // map_Ka
    this.emissiveTexture = undefined;            // map_Ke
    this.diffuseTexture = undefined;             // map_Kd
    this.specularTexture = undefined;            // map_Ks
    this.specularShininessTexture = undefined;   // map_Ns
    this.normalTexture = undefined;              // map_Bump
    this.alphaTexture = undefined;               // map_d
}

loadMtl.getDefaultMaterial = function(options) {
    return convertMaterial(new Material(), options);
};

// Exposed for testing
loadMtl._createMaterial = function(materialOptions, options) {
    return convertMaterial(combine(materialOptions, new Material()), options);
};

function loadMaterialTexture(material, name, textureOptions, mtlDirectory, texturePromiseMap, texturePromises, options) {
    var texturePath = material[name];
    if (!defined(texturePath)) {
        return;
    }

    var texturePromise = texturePromiseMap[texturePath];
    if (!defined(texturePromise)) {
        var shallowPath = path.join(mtlDirectory, path.basename(texturePath));
        if (options.secure && outsideDirectory(texturePath, mtlDirectory)) {
            // Try looking for the texture in the same directory as the obj
            options.logger('Texture file is outside of the mtl directory and the secure flag is true. Attempting to read the texture file from within the obj directory instead.');
            texturePromise = loadTexture(shallowPath, textureOptions)
                .catch(function(error) {
                    options.logger(error.message);
                    options.logger('Could not read texture file at ' + shallowPath + '. This texture will be ignored');
                });
        } else {
            texturePromise = loadTexture(texturePath, textureOptions)
                .catch(function(error) {
                    // Try looking for the texture in the same directory as the obj
                    options.logger(error.message);
                    options.logger('Could not read texture file at ' + texturePath + '. Attempting to read the texture file from within the obj directory instead.');
                    return loadTexture(shallowPath, textureOptions);
                })
                .catch(function(error) {
                    options.logger(error.message);
                    options.logger('Could not read texture file at ' + shallowPath + '. This texture will be ignored.');
                });
        }
        texturePromiseMap[texturePath] = texturePromise;
    }

    texturePromises.push(texturePromise
        .then(function(texture) {
            material[name] = texture;
        }));
}

function convertMaterial(material, options) {
    if (options.specularGlossiness) {
        return createSpecularGlossinessMaterial(material, options);
    } else if (options.metallicRoughness) {
        return createMetallicRoughnessMaterial(material, options);
    }
    // No material type specified, convert the material to metallic roughness
    convertTraditionalToMetallicRoughness(material);
    return createMetallicRoughnessMaterial(material, options);
}

function convertMaterials(materials, options) {
    return materials.map(function(material) {
        return convertMaterial(material, options);
    });
}

function resizeChannel(sourcePixels, sourceWidth, sourceHeight, targetPixels, targetWidth, targetHeight) {
    // Nearest neighbor sampling
    var widthRatio = sourceWidth / targetWidth;
    var heightRatio = sourceHeight / targetHeight;

    for (var y = 0; y < targetHeight; ++y) {
        for (var x = 0; x < targetWidth; ++x) {
            var targetIndex = y * targetWidth + x;
            var sourceY = Math.round(y * heightRatio);
            var sourceX = Math.round(x * widthRatio);
            var sourceIndex = sourceY * sourceWidth + sourceX;
            var sourceValue = sourcePixels.readUInt8(sourceIndex);
            targetPixels.writeUInt8(sourceValue, targetIndex);
        }
    }
    return targetPixels;
}

var scratchResizeChannel;

function getTextureChannel(texture, index, targetWidth, targetHeight, targetChannel) {
    var pixels = texture.pixels; // RGBA
    var sourceWidth = texture.width;
    var sourceHeight = texture.height;
    var sourcePixelsLength = sourceWidth * sourceHeight;
    var targetPixelsLength = targetWidth * targetHeight;

    // Allocate the scratchResizeChannel on demand if the texture needs to be resized
    var sourceChannel = targetChannel;
    if (sourcePixelsLength > targetPixelsLength) {
        if (!defined(scratchResizeChannel) || (sourcePixelsLength > scratchResizeChannel.length)) {
            scratchResizeChannel = Buffer.alloc(sourcePixelsLength);
        }
        sourceChannel = scratchResizeChannel;
    }

    for (var i = 0; i < sourcePixelsLength; ++i) {
        var value = pixels.readUInt8(i * 4 + index);
        sourceChannel.writeUInt8(value, i);
    }

    if (sourcePixelsLength > targetPixelsLength) {
        resizeChannel(sourceChannel, sourceWidth, sourceHeight, targetChannel, targetWidth, targetHeight);
    }

    return targetChannel;
}

function writeChannel(pixels, channel, index) {
    var pixelsLength = pixels.length / 4;
    for (var i = 0; i < pixelsLength; ++i) {
        var value = channel.readUInt8(i);
        pixels.writeUInt8(value, i * 4 + index);
    }
}

function getMinimumDimensions(textures, options) {
    var i;
    var texture;
    var width = Number.POSITIVE_INFINITY;
    var height = Number.POSITIVE_INFINITY;

    var length = textures.length;
    for (i = 0; i < length; ++i) {
        texture = textures[i];
        width = Math.min(texture.width, width);
        height = Math.min(texture.height, height);
    }

    for (i = 0; i < length; ++i) {
        texture = textures[i];
        if (texture.width !== width || texture.height !== height) {
            options.logger('Texture ' + texture.path + ' will be scaled from ' + texture.width + 'x' + texture.height + ' to ' + width + 'x' + height + '.');
        }
    }

    return [width, height];
}

function isChannelSingleColor(buffer) {
    var first = buffer.readUInt8(0);
    var length = buffer.length;
    for (var i = 1; i < length; ++i) {
        if (buffer[i] !== first) {
            return false;
        }
    }
    return true;
}

function createDiffuseAlphaTexture(diffuseTexture, alphaTexture, options) {
    var packDiffuse = defined(diffuseTexture);
    var packAlpha = defined(alphaTexture);

    if (!packDiffuse) {
        return undefined;
    }

    if (!packAlpha) {
        return diffuseTexture;
    }

    if (!defined(diffuseTexture.pixels) || !defined(alphaTexture.pixels)) {
        options.logger('Could not get decoded texture data for ' + diffuseTexture.path + ' or ' + alphaTexture.path + '. The material will be created without an alpha texture.');
        return diffuseTexture;
    }

    var packedTextures = [diffuseTexture, alphaTexture];
    var dimensions = getMinimumDimensions(packedTextures, options);
    var width = dimensions[0];
    var height = dimensions[1];
    var pixelsLength = width * height;
    var pixels = Buffer.alloc(pixelsLength * 4, 0xFF); // Initialize with 4 channels
    var scratchChannel = Buffer.alloc(pixelsLength);

    // Write into the R, G, B channels
    var redChannel = getTextureChannel(diffuseTexture, 0, width, height, scratchChannel);
    writeChannel(pixels, redChannel, 0);
    var greenChannel = getTextureChannel(diffuseTexture, 1, width, height, scratchChannel);
    writeChannel(pixels, greenChannel, 1);
    var blueChannel = getTextureChannel(diffuseTexture, 2, width, height, scratchChannel);
    writeChannel(pixels, blueChannel, 2);

    // First try reading the alpha component from the alpha channel, but if it is a single color read from the red channel instead.
    var alphaChannel = getTextureChannel(alphaTexture, 3, width, height, scratchChannel);
    if (isChannelSingleColor(alphaChannel)) {
        alphaChannel = getTextureChannel(alphaTexture, 0, width, height, scratchChannel);
    }
    writeChannel(pixels, alphaChannel, 3);

    var texture = new Texture();
    texture.name = diffuseTexture.name;
    texture.extension = '.png';
    texture.pixels = pixels;
    texture.width = width;
    texture.height = height;
    texture.transparent = true;

    return texture;
}

function createMetallicRoughnessTexture(metallicTexture, roughnessTexture, occlusionTexture, options) {
    if (defined(options.overridingTextures.metallicRoughnessOcclusionTexture)) {
        return metallicTexture;
    }

    var packMetallic = defined(metallicTexture);
    var packRoughness = defined(roughnessTexture);
    var packOcclusion = defined(occlusionTexture) && options.packOcclusion;

    if (!packMetallic && !packRoughness) {
        return undefined;
    }

    if (packMetallic && !defined(metallicTexture.pixels)) {
        options.logger('Could not get decoded texture data for ' + metallicTexture.path + '. The material will be created without a metallicRoughness texture.');
        return undefined;
    }

    if (packRoughness && !defined(roughnessTexture.pixels)) {
        options.logger('Could not get decoded texture data for ' + roughnessTexture.path + '. The material will be created without a metallicRoughness texture.');
        return undefined;
    }

    if (packOcclusion && !defined(occlusionTexture.pixels)) {
        options.logger('Could not get decoded texture data for ' + occlusionTexture.path + '. The occlusion texture will not be packed in the metallicRoughness texture.');
        return undefined;
    }

    var packedTextures = [metallicTexture, roughnessTexture, occlusionTexture].filter(function(texture) {
        return defined(texture) && defined(texture.pixels);
    });

    var dimensions = getMinimumDimensions(packedTextures, options);
    var width = dimensions[0];
    var height = dimensions[1];
    var pixelsLength = width * height;
    var pixels = Buffer.alloc(pixelsLength * 4, 0xFF); // Initialize with 4 channels, unused channels will be white
    var scratchChannel = Buffer.alloc(pixelsLength);

    if (packMetallic) {
        // Write into the B channel
        var metallicChannel = getTextureChannel(metallicTexture, 0, width, height, scratchChannel);
        writeChannel(pixels, metallicChannel, 2);
    }

    if (packRoughness) {
        // Write into the G channel
        var roughnessChannel = getTextureChannel(roughnessTexture, 0, width, height, scratchChannel);
        writeChannel(pixels, roughnessChannel, 1);
    }

    if (packOcclusion) {
        // Write into the R channel
        var occlusionChannel = getTextureChannel(occlusionTexture, 0, width, height, scratchChannel);
        writeChannel(pixels, occlusionChannel, 0);
    }

    var length = packedTextures.length;
    var names = new Array(length);
    for (var i = 0; i < length; ++i) {
        names[i] = packedTextures[i].name;
    }
    var name = names.join('_');

    var texture = new Texture();
    texture.name = name;
    texture.extension = '.png';
    texture.pixels = pixels;
    texture.width = width;
    texture.height = height;

    return texture;
}

function createSpecularGlossinessTexture(specularTexture, glossinessTexture, options) {
    if (defined(options.overridingTextures.specularGlossinessTexture)) {
        return specularTexture;
    }

    var packSpecular = defined(specularTexture);
    var packGlossiness = defined(glossinessTexture);

    if (!packSpecular && !packGlossiness) {
        return undefined;
    }

    if (packSpecular && !defined(specularTexture.pixels)) {
        options.logger('Could not get decoded texture data for ' + specularTexture.path + '. The material will be created without a specularGlossiness texture.');
        return undefined;
    }

    if (packGlossiness && !defined(glossinessTexture.pixels)) {
        options.logger('Could not get decoded texture data for ' + glossinessTexture.path + '. The material will be created without a specularGlossiness texture.');
        return undefined;
    }

    var packedTextures = [specularTexture, glossinessTexture].filter(function(texture) {
        return defined(texture) && defined(texture.pixels);
    });

    var dimensions = getMinimumDimensions(packedTextures, options);
    var width = dimensions[0];
    var height = dimensions[1];
    var pixelsLength = width * height;
    var pixels = Buffer.alloc(pixelsLength * 4, 0xFF); // Initialize with 4 channels, unused channels will be white
    var scratchChannel = Buffer.alloc(pixelsLength);

    if (packSpecular) {
        // Write into the R, G, B channels
        var redChannel = getTextureChannel(specularTexture, 0, width, height, scratchChannel);
        writeChannel(pixels, redChannel, 0);
        var greenChannel = getTextureChannel(specularTexture, 1, width, height, scratchChannel);
        writeChannel(pixels, greenChannel, 1);
        var blueChannel = getTextureChannel(specularTexture, 2, width, height, scratchChannel);
        writeChannel(pixels, blueChannel, 2);
    }

    if (packGlossiness) {
        // Write into the A channel
        var glossinessChannel = getTextureChannel(glossinessTexture, 0, width, height, scratchChannel);
        writeChannel(pixels, glossinessChannel, 3);
    }

    var length = packedTextures.length;
    var names = new Array(length);
    for (var i = 0; i < length; ++i) {
        names[i] = packedTextures[i].name;
    }
    var name = names.join('_');

    var texture = new Texture();
    texture.name = name;
    texture.extension = '.png';
    texture.pixels = pixels;
    texture.width = width;
    texture.height = height;

    return texture;
}

function createSpecularGlossinessMaterial(material, options) {
    var emissiveTexture = material.emissiveTexture;
    var normalTexture = material.normalTexture;
    var occlusionTexture = material.ambientTexture;
    var diffuseTexture = material.diffuseTexture;
    var alphaTexture = material.alphaTexture;
    var specularTexture = material.specularTexture;
    var glossinessTexture = material.specularShininessTexture;
    var specularGlossinessTexture = createSpecularGlossinessTexture(specularTexture, glossinessTexture, options);
    var diffuseAlphaTexture = createDiffuseAlphaTexture(diffuseTexture, alphaTexture, options);

    var emissiveFactor = material.emissiveColor.slice(0, 3);
    var diffuseFactor = material.diffuseColor;
    var specularFactor = material.specularColor.slice(0, 3);
    var glossinessFactor = material.specularShininess;

    if (defined(emissiveTexture)) {
        emissiveFactor = [1.0, 1.0, 1.0];
    }

    if (defined(diffuseTexture)) {
        diffuseFactor = [1.0, 1.0, 1.0, 1.0];
    }

    if (defined(specularTexture)) {
        specularFactor = [1.0, 1.0, 1.0];
    }

    if (defined(glossinessTexture)) {
        glossinessFactor = 1.0;
    }

    var transparent = false;
    if (defined(alphaTexture)) {
        transparent = true;
    } else {
        var alpha = material.alpha;
        diffuseFactor[3] = alpha;
        transparent = alpha < 1.0;
    }

    if (defined(diffuseTexture)) {
        transparent = transparent || diffuseTexture.transparent;
    }

    var doubleSided = transparent;
    var alphaMode = transparent ? 'BLEND' : 'OPAQUE';

    return {
        name : material.name,
        extensions : {
            KHR_materials_pbrSpecularGlossiness: {
                diffuseTexture : diffuseAlphaTexture,
                specularGlossinessTexture : specularGlossinessTexture,
                diffuseFactor : diffuseFactor,
                specularFactor : specularFactor,
                glossinessFactor : glossinessFactor
            }
        },
        emissiveTexture : emissiveTexture,
        normalTexture : normalTexture,
        occlusionTexture : occlusionTexture,
        emissiveFactor : emissiveFactor,
        alphaMode : alphaMode,
        doubleSided : doubleSided
    };
}

function createMetallicRoughnessMaterial(material, options) {
    var emissiveTexture = material.emissiveTexture;
    var normalTexture = material.normalTexture;
    var occlusionTexture = material.ambientTexture;
    var baseColorTexture = material.diffuseTexture;
    var alphaTexture = material.alphaTexture;
    var metallicTexture = material.specularTexture;
    var roughnessTexture = material.specularShininessTexture;
    var metallicRoughnessTexture = createMetallicRoughnessTexture(metallicTexture, roughnessTexture, occlusionTexture, options);
    var diffuseAlphaTexture = createDiffuseAlphaTexture(baseColorTexture, alphaTexture, options);

    if (options.packOcclusion) {
        occlusionTexture = metallicRoughnessTexture;
    }

    var emissiveFactor = material.emissiveColor.slice(0, 3);
    var baseColorFactor = material.diffuseColor;
    var metallicFactor = material.specularColor[0];
    var roughnessFactor = material.specularShininess;

    if (defined(emissiveTexture)) {
        emissiveFactor = [1.0, 1.0, 1.0];
    }

    if (defined(baseColorTexture)) {
        baseColorFactor = [1.0, 1.0, 1.0, 1.0];
    }

    if (defined(metallicTexture)) {
        metallicFactor = 1.0;
    }

    if (defined(roughnessTexture)) {
        roughnessFactor = 1.0;
    }

    var transparent = false;
    if (defined(alphaTexture)) {
        transparent = true;
    } else {
        var alpha = material.alpha;
        baseColorFactor[3] = alpha;
        transparent = alpha < 1.0;
    }

    if (defined(baseColorTexture)) {
        transparent = transparent || baseColorTexture.transparent;
    }

    var doubleSided = transparent;
    var alphaMode = transparent ? 'BLEND' : 'OPAQUE';

    return {
        name : material.name,
        pbrMetallicRoughness : {
            baseColorTexture : diffuseAlphaTexture,
            metallicRoughnessTexture : metallicRoughnessTexture,
            baseColorFactor : baseColorFactor,
            metallicFactor : metallicFactor,
            roughnessFactor : roughnessFactor
        },
        emissiveTexture : emissiveTexture,
        normalTexture : normalTexture,
        occlusionTexture : occlusionTexture,
        emissiveFactor : emissiveFactor,
        alphaMode : alphaMode,
        doubleSided : doubleSided
    };
}

function luminance(color) {
    return color[0] * 0.2125 + color[1] * 0.7154 + color[2] * 0.0721;
}

function convertTraditionalToMetallicRoughness(material) {
    // Translate the blinn-phong model to the pbr metallic-roughness model
    // Roughness factor is a combination of specular intensity and shininess
    // Metallic factor is 0.0
    // Textures are not converted for now
    var specularIntensity = luminance(material.specularColor);

    // Transform from 0-1000 range to 0-1 range. Then invert.
    var roughnessFactor = material.specularShininess;
    roughnessFactor = roughnessFactor / 1000.0;
    roughnessFactor = 1.0 - roughnessFactor;
    roughnessFactor = CesiumMath.clamp(roughnessFactor, 0.0, 1.0);

    // Low specular intensity values should produce a rough material even if shininess is high.
    if (specularIntensity < 0.1) {
        roughnessFactor *= (1.0 - specularIntensity);
    }

    var metallicFactor = 0.0;

    material.specularColor = [metallicFactor, metallicFactor, metallicFactor, 1.0];
    material.specularShininess = roughnessFactor;
}