/**
 * @author Don McCurdy / https://www.donmccurdy.com
 * @author Austin Eng / https://github.com/austinEng
 * @author Shrek Shao / https://github.com/shrekshao
 */

/**
 * An example three.js loader for Basis compressed textures.
 */
THREE.BasisTextureLoader = class BasisTextureLoader {

  constructor () {

    this.etcSupported = false;
    this.dxtSupported = false;
    this.pvrtcSupported = false;

    this.format = null;

  }

  detectSupport ( renderer ) {

    const context = renderer.context;

    this.etcSupported = context.getExtension('WEBGL_compressed_texture_etc1');
    this.dxtSupported = context.getExtension('WEBGL_compressed_texture_s3tc');
    this.pvrtcSupported = context.getExtension('WEBGL_compressed_texture_pvrtc')
      || context.getExtension('WEBKIT_WEBGL_compressed_texture_pvrtc');

    if ( ! this.etcSupported && ! this.dxtSupported && ! this.pvrtcSupported ) {

      throw new Error( 'THREE.BasisTextureLoader: No suitable compressed texture format found.' );

    }

    this.format = this.etcSupported
      ? BASIS_FORMAT.cTFETC1
      : ( this.dxtSupported
        ? BASIS_FORMAT.cTFBC1
        : BASIS_FORMAT.cTFPVRTC1_4_OPAQUE_ONLY );

     return this;

  }

  load ( url, onLoad, onProgress, onError ) {

    fetch( url )
      .then( ( res ) => res.arrayBuffer() )
      .then( (arrayBuffer) => this._createTexture( arrayBuffer ) )
      .then( onLoad )
      .catch( onError );

  }

  _createTexture ( arrayBuffer ) {

    const BASIS_FORMAT = THREE.BasisTextureLoader.BASIS_FORMAT;
    const DXT_FORMAT_MAP = THREE.BasisTextureLoader.DXT_FORMAT_MAP;

    const basisFile = new BasisFile( new Uint8Array( arrayBuffer ) );

    const width = basisFile.getImageWidth( 0, 0 );
    const height = basisFile.getImageHeight( 0, 0 );
    const images = basisFile.getNumImages();
    const levels = basisFile.getNumLevels( 0 );

    function cleanup () {

      basisFile.close();
      basisFile.delete();

    }

    if ( ! width || ! height || ! images || ! levels ) {

      cleanup();
      throw new Error( 'THREE.BasisTextureLoader:  Invalid .basis file' );

    }

    if ( ! basisFile.startTranscoding() ) {

      cleanup();
      throw new Error( 'THREE.BasisTextureLoader: .startTranscoding failed' );

    }

    const dst = new Uint8Array( basisFile.getImageTranscodedSizeInBytes( 0, 0, this.format ) );

    const startTime = performance.now();

    const status = basisFile.transcodeImage(
      dst,
      0,
      0,
      this.format,
      this.etcSupported ? 0 : ( this.dxtSupported ? 1 : 0 ),
      0
    );

    console.log( `THREE.BasisTextureLoader: Transcode time: ${performance.now() - startTime}ms`, dst );

    cleanup();

    if ( ! status ) {

      throw new Error( 'THREE.BasisTextureLoader: .transcodeImage failed.' );

    }

    const mipmaps = [ { data: dst, width, height } ];

    let texture;

    if ( this.etcSupported ) {

      texture = new THREE.CompressedTexture( mipmaps, width, height, THREE.RGB_ETC1_Format );

    } else if ( this.dxtSupported ) {

      texture = new THREE.CompressedTexture( mipmaps, width, height, DXT_FORMAT_MAP[ this.format ], THREE.UnsignedByteType );

    } else if ( this.pvrtcSupported ) {

      texture = new THREE.CompressedTexture( mipmaps, width, height, THREE.RGB_PVRTC_4BPPV1_Format );

    } else {

      throw new Error( 'THREE.BasisTextureLoader: No supported format available.' );

    }

    texture.minFilter = THREE.LinearMipMapLinearFilter;
    texture.magFilter = THREE.LinearFilter;
    texture.encoding = THREE.sRGBEncoding;
    texture.generateMipmaps = false;
    texture.flipY = false;
    texture.needsUpdate = true;

    return texture;

  }
}

const BASIS_FORMAT = {
  cTFETC1: 0,
  cTFBC1: 1,
  cTFBC4: 2,
  cTFPVRTC1_4_OPAQUE_ONLY: 3,
  cTFBC7_M6_OPAQUE_ONLY: 4,
  cTFETC2: 5,
  cTFBC3: 6,
  cTFBC5: 7,
};

// DXT formats, from:
// http://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_s3tc/
const DXT_FORMAT_MAP = {};
const COMPRESSED_RGB_S3TC_DXT1_EXT  = 0x83F0;
const COMPRESSED_RGBA_S3TC_DXT1_EXT = 0x83F1;
const COMPRESSED_RGBA_S3TC_DXT3_EXT = 0x83F2;
const COMPRESSED_RGBA_S3TC_DXT5_EXT = 0x83F3;
DXT_FORMAT_MAP[ BASIS_FORMAT.cTFBC1 ] = COMPRESSED_RGB_S3TC_DXT1_EXT;
DXT_FORMAT_MAP[ BASIS_FORMAT.cTFBC3 ] = COMPRESSED_RGBA_S3TC_DXT5_EXT;

THREE.BasisTextureLoader.BASIS_FORMAT = BASIS_FORMAT;
THREE.BasisTextureLoader.DXT_FORMAT_MAP = DXT_FORMAT_MAP;