import { decodeBlurHash } from "fast-blurhash"

export function blurhashToBase64(hash: string, width = 8, height = 8) {
  const rgba = decodeBlurHash(hash, width, height)
  const base64Image = rgbaToDataUri(rgba, width, height)
  return base64Image
}

function rgbaToDataUri(
  /** The pixels in the input image, row-by-row. Must have w*h*4 elements. */
  rgba: ArrayLike<number>,
  /** The width of the input image. Must be ≤100px. */
  w: number,
  /** The height of the input image. Must be ≤100px. */
  h: number,
) {
  const row = w * 4 + 1
  const idat = 6 + h * (5 + row)
  const bytes = [
    137,
    80,
    78,
    71,
    13,
    10,
    26,
    10,
    0,
    0,
    0,
    13,
    73,
    72,
    68,
    82,
    0,
    0,
    w >> 8,
    w & 255,
    0,
    0,
    h >> 8,
    h & 255,
    8,
    6,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    idat >>> 24,
    (idat >> 16) & 255,
    (idat >> 8) & 255,
    idat & 255,
    73,
    68,
    65,
    84,
    120,
    1,
  ]
  const table = [
    0, 498536548, 997073096, 651767980, 1994146192, 1802195444, 1303535960,
    1342533948, -306674912, -267414716, -690576408, -882789492, -1687895376,
    -2032938284, -1609899400, -1111625188,
  ]
  let a = 1
  let b = 0

  for (let y = 0, i = 0, end = row - 1; y < h; y++, end += row - 1) {
    bytes.push(
      y + 1 < h ? 0 : 1,
      row & 255,
      row >> 8,
      ~row & 255,
      (row >> 8) ^ 255,
      0,
    )
    for (b = (b + a) % 65521; i < end; i++) {
      const u = rgba[i] & 255
      bytes.push(u)
      a = (a + u) % 65521
      b = (b + a) % 65521
    }
  }

  bytes.push(
    b >> 8,
    b & 255,
    a >> 8,
    a & 255,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    73,
    69,
    78,
    68,
    174,
    66,
    96,
    130,
  )

  // eslint-disable-next-line prefer-const
  for (let [start, end] of [
    [12, 29],
    [37, 41 + idat],
  ]) {
    let c = ~0
    for (let i = start; i < end; i++) {
      c ^= bytes[i]
      c = (c >>> 4) ^ table[c & 15]
      c = (c >>> 4) ^ table[c & 15]
    }

    c = ~c
    bytes[end++] = c >>> 24
    bytes[end++] = (c >> 16) & 255
    bytes[end++] = (c >> 8) & 255
    bytes[end++] = c & 255
  }

  const base64 = globalThis.btoa(String.fromCharCode(...bytes))

  return `data:image/png;base64,${base64}`
}