var BABYLON = BABYLON || {};

(function () {
    BABYLON.Tools = BABYLON.Tools || {};

    // Based on https://github.com/toji/webgl-texture-utils/blob/master/texture-util/dds.js

    // All values and structures referenced from:
    // http://msdn.microsoft.com/en-us/library/bb943991.aspx/
    var DDS_MAGIC = 0x20534444;

    var DDSD_CAPS = 0x1,
        DDSD_HEIGHT = 0x2,
        DDSD_WIDTH = 0x4,
        DDSD_PITCH = 0x8,
        DDSD_PIXELFORMAT = 0x1000,
        DDSD_MIPMAPCOUNT = 0x20000,
        DDSD_LINEARSIZE = 0x80000,
        DDSD_DEPTH = 0x800000;

    var DDSCAPS_COMPLEX = 0x8,
        DDSCAPS_MIPMAP = 0x400000,
        DDSCAPS_TEXTURE = 0x1000;

    var DDSCAPS2_CUBEMAP = 0x200,
        DDSCAPS2_CUBEMAP_POSITIVEX = 0x400,
        DDSCAPS2_CUBEMAP_NEGATIVEX = 0x800,
        DDSCAPS2_CUBEMAP_POSITIVEY = 0x1000,
        DDSCAPS2_CUBEMAP_NEGATIVEY = 0x2000,
        DDSCAPS2_CUBEMAP_POSITIVEZ = 0x4000,
        DDSCAPS2_CUBEMAP_NEGATIVEZ = 0x8000,
        DDSCAPS2_VOLUME = 0x200000;

    var DDPF_ALPHAPIXELS = 0x1,
        DDPF_ALPHA = 0x2,
        DDPF_FOURCC = 0x4,
        DDPF_RGB = 0x40,
        DDPF_YUV = 0x200,
        DDPF_LUMINANCE = 0x20000;

    function fourCCToInt32(value) {
        return value.charCodeAt(0) +
            (value.charCodeAt(1) << 8) +
            (value.charCodeAt(2) << 16) +
            (value.charCodeAt(3) << 24);
    }

    function int32ToFourCC(value) {
        return String.fromCharCode(
            value & 0xff,
            (value >> 8) & 0xff,
            (value >> 16) & 0xff,
            (value >> 24) & 0xff
        );
    }

    var FOURCC_DXT1 = fourCCToInt32("DXT1");
    var FOURCC_DXT3 = fourCCToInt32("DXT3");
    var FOURCC_DXT5 = fourCCToInt32("DXT5");

    var headerLengthInt = 31; // The header length in 32 bit ints

    // Offsets into the header array
    var off_magic = 0;

    var off_size = 1;
    var off_flags = 2;
    var off_height = 3;
    var off_width = 4;

    var off_mipmapCount = 7;

    var off_pfFlags = 20;
    var off_pfFourCC = 21;

    function dxtToRgb565(src, src16Offset, width, height) {
        var c = new Uint16Array(4);
        var dst = new Uint16Array(width * height);
        var nWords = (width * height) / 4;
        var m = 0;
        var dstI = 0;
        var i = 0;
        var r0 = 0, g0 = 0, b0 = 0, r1 = 0, g1 = 0, b1 = 0;

        var blockWidth = width / 4;
        var blockHeight = height / 4;
        for (var blockY = 0; blockY < blockHeight; blockY++) {
            for (var blockX = 0; blockX < blockWidth; blockX++) {
                i = src16Offset + 4 * (blockY * blockWidth + blockX);
                c[0] = src[i];
                c[1] = src[i + 1];
                r0 = c[0] & 0x1f;
                g0 = c[0] & 0x7e0;
                b0 = c[0] & 0xf800;
                r1 = c[1] & 0x1f;
                g1 = c[1] & 0x7e0;
                b1 = c[1] & 0xf800;
                // Interpolate between c0 and c1 to get c2 and c3.
                // Note that we approximate 1/3 as 3/8 and 2/3 as 5/8 for
                // speed.  This also appears to be what the hardware DXT
                // decoder in many GPUs does :)
                c[2] = ((5 * r0 + 3 * r1) >> 3)
                    | (((5 * g0 + 3 * g1) >> 3) & 0x7e0)
                    | (((5 * b0 + 3 * b1) >> 3) & 0xf800);
                c[3] = ((5 * r1 + 3 * r0) >> 3)
                    | (((5 * g1 + 3 * g0) >> 3) & 0x7e0)
                    | (((5 * b1 + 3 * b0) >> 3) & 0xf800);
                m = src[i + 2];
                dstI = (blockY * 4) * width + blockX * 4;
                dst[dstI] = c[m & 0x3];
                dst[dstI + 1] = c[(m >> 2) & 0x3];
                dst[dstI + 2] = c[(m >> 4) & 0x3];
                dst[dstI + 3] = c[(m >> 6) & 0x3];
                dstI += width;
                dst[dstI] = c[(m >> 8) & 0x3];
                dst[dstI + 1] = c[(m >> 10) & 0x3];
                dst[dstI + 2] = c[(m >> 12) & 0x3];
                dst[dstI + 3] = c[(m >> 14)];
                m = src[i + 3];
                dstI += width;
                dst[dstI] = c[m & 0x3];
                dst[dstI + 1] = c[(m >> 2) & 0x3];
                dst[dstI + 2] = c[(m >> 4) & 0x3];
                dst[dstI + 3] = c[(m >> 6) & 0x3];
                dstI += width;
                dst[dstI] = c[(m >> 8) & 0x3];
                dst[dstI + 1] = c[(m >> 10) & 0x3];
                dst[dstI + 2] = c[(m >> 12) & 0x3];
                dst[dstI + 3] = c[(m >> 14)];
            }
        }
        return dst;
    }

    function uploadDDSLevels(gl, ext, arrayBuffer) {
        var header = new Int32Array(arrayBuffer, 0, headerLengthInt),
            fourCC, blockBytes, internalFormat,
            width, height, dataLength, dataOffset,
            rgb565Data, byteArray, mipmapCount, i;


        if (header[off_magic] != DDS_MAGIC) {
            console.error("Invalid magic number in DDS header");
            return 0;
        }

        if (!header[off_pfFlags] & DDPF_FOURCC) {
            console.error("Unsupported format, must contain a FourCC code");
            return 0;
        }


        fourCC = header[off_pfFourCC];
        switch (fourCC) {
            case FOURCC_DXT1:
                blockBytes = 8;
                internalFormat = ext ? ext.COMPRESSED_RGB_S3TC_DXT1_EXT : null;
                break;


            case FOURCC_DXT3:
                blockBytes = 16;
                internalFormat = ext ? ext.COMPRESSED_RGBA_S3TC_DXT3_EXT : null;
                break;


            case FOURCC_DXT5:
                blockBytes = 16;
                internalFormat = ext ? ext.COMPRESSED_RGBA_S3TC_DXT5_EXT : null;
                break;


            default:
                console.error("Unsupported FourCC code:", int32ToFourCC(fourCC));
                return null;
        }


        mipmapCount = 1;
        if (header[off_flags] & DDSD_MIPMAPCOUNT && loadMipmaps !== false) {
            mipmapCount = Math.max(1, header[off_mipmapCount]);
        }


        width = header[off_width];
        height = header[off_height];
        dataOffset = header[off_size] + 4;


        if (ext) {
            for (i = 0; i < mipmapCount; ++i) {
                dataLength = Math.max(4, width) / 4 * Math.max(4, height) / 4 * blockBytes;
                byteArray = new Uint8Array(arrayBuffer, dataOffset, dataLength);
                gl.compressedTexImage2D(gl.TEXTURE_2D, i, internalFormat, width, height, 0, byteArray);
                dataOffset += dataLength;
                width *= 0.5;
                height *= 0.5;
            }
        } else {
            if (fourCC == FOURCC_DXT1) {
                dataLength = Math.max(4, width) / 4 * Math.max(4, height) / 4 * blockBytes;
                byteArray = new Uint16Array(arrayBuffer);
                rgb565Data = dxtToRgb565(byteArray, dataOffset / 2, width, height);
                gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGB, width, height, 0, gl.RGB, gl.UNSIGNED_SHORT_5_6_5, rgb565Data);
                if (loadMipmaps) {
                    gl.generateMipmap(gl.TEXTURE_2D);
                }
            } else {
                console.error("No manual decoder for", int32ToFourCC(fourCC), "and no native support");
                return 0;
            }
        }

        return mipmapCount;
    }

    BABYLON.Tools.LoadDDSTexture = function(gl, ext, data) {
        return uploadDDSLevels(gl, ext, data);
    };
})();