const MARKERS = [0xFFC0, 0xFFC1, 0xFFC2, 0xFFC3, 0xFFC5, 0xFFC6, 0xFFC7,
  0xFFC8, 0xFFC9, 0xFFCA, 0xFFCB, 0xFFCC, 0xFFCD, 0xFFCE, 0xFFCF];

const COLOR_SPACE_MAP = {
  1: 'DeviceGray',
  3: 'DeviceRGB',
  4: 'DeviceCMYK'
}

class JPEG {
  constructor(data, label) {
    let marker;
    this.data = data;
    this.label = label;
    if (this.data.readUInt16BE(0) !== 0xFFD8) {
      throw "SOI not found in JPEG";
    }
          
    let pos = 2;
    while (pos < this.data.length) {
      marker = this.data.readUInt16BE(pos);
      pos += 2;
      if (MARKERS.includes(marker)) { break; }
      pos += this.data.readUInt16BE(pos);
    }

    if (!MARKERS.includes(marker)) { throw "Invalid JPEG."; }
    pos += 2;

    this.bits = this.data[pos++];
    this.height = this.data.readUInt16BE(pos);
    pos += 2;

    this.width = this.data.readUInt16BE(pos);
    pos += 2;

    const channels = this.data[pos++];
    this.colorSpace = COLOR_SPACE_MAP[channels];
    
    this.obj = null;
  }
    
  embed(document) {
    if (this.obj) { return; }
  
    this.obj = document.ref({
      Type: 'XObject',
      Subtype: 'Image',
      BitsPerComponent: this.bits,
      Width: this.width,
      Height: this.height,
      ColorSpace: this.colorSpace,
      Filter: 'DCTDecode'
    });
    
    // add extra decode params for CMYK images. By swapping the
    // min and max values from the default, we invert the colors. See
    // section 4.8.4 of the spec.  
    if (this.colorSpace === 'DeviceCMYK') {
      this.obj.data['Decode'] = [1.0, 0.0, 1.0, 0.0, 1.0, 0.0, 1.0, 0.0];
    }
    
    this.obj.end(this.data);
  
    // free memory
    return this.data = null;
  }
};
    
export default JPEG;