import { IRiff, IWebP } from '../interfaces'

export default function parseWebP(riff: IRiff): IWebP {
  const VP8 = riff.RIFF[0].WEBP[0]

  // A VP8 keyframe starts with the 0x9d012a header
  const frameStart = VP8.indexOf('\x9d\x01\x2a')
  const c: number[] = []

  for (let i = 0; i < 4; i++) {
    c[i] = VP8.charCodeAt(frameStart + 3 + i)
  }

  // the code below is literally copied verbatim from the bit stream spec
  let tmp = (c[1] << 8) | c[0]
  const width = tmp & 0x3FFF
  // const horizontal_scale = tmp >> 14;
  tmp = (c[3] << 8) | c[2]
  const height = tmp & 0x3FFF
  // const vertical_scale = tmp >> 14;

  return {
    width,
    height,
    data: VP8,
    riff,
  }
}