/**
 * Adds up the chunk delays to find out how long a APNG is
 * @param {data} apngFile the APNG data
 */
const calculateApngLength = (apngFile) => {
  const d = new Uint8Array(apngFile);
  // https://wiki.mozilla.org/APNG_Specification#.60fcTL.60:_The_Frame_Control_Chunk
  let duration = 0;
  for (let i = 0; i < d.length; i++) {
    // Find fcTL header (66 63 54 4C)
    if (
      d[i] === 0x66 &&
      d[i + 1] === 0x63 &&
      d[i + 2] === 0x54 &&
      d[i + 3] === 0x4c
    ) {
      // numerator and denominator
      const delayNum = Number(d[i + 23]);
      const delayDen = Number(d[i + 25]);
      let delay;
      // minimum is 100ms
      if (delayDen === 0) {
        delay = delayNum / 100;
      } else {
        delay = delayNum / delayDen;
      }
      duration += delay;
    }
  }
  return duration * 10;
};
export default calculateApngLength;