/*
Blurhash toolkit.

base83 decoder/encoder is copied from
https://github.com/woltapp/blurhash/blob/master/TypeScript/src/base83.ts,
which is MIT Licensed: https://github.com/woltapp/blurhash?tab=MIT-1-ov-file#readme
*/
const digitCharacters = [
  "0",
  "1",
  "2",
  "3",
  "4",
  "5",
  "6",
  "7",
  "8",
  "9",
  "A",
  "B",
  "C",
  "D",
  "E",
  "F",
  "G",
  "H",
  "I",
  "J",
  "K",
  "L",
  "M",
  "N",
  "O",
  "P",
  "Q",
  "R",
  "S",
  "T",
  "U",
  "V",
  "W",
  "X",
  "Y",
  "Z",
  "a",
  "b",
  "c",
  "d",
  "e",
  "f",
  "g",
  "h",
  "i",
  "j",
  "k",
  "l",
  "m",
  "n",
  "o",
  "p",
  "q",
  "r",
  "s",
  "t",
  "u",
  "v",
  "w",
  "x",
  "y",
  "z",
  "#",
  "$",
  "%",
  "*",
  "+",
  ",",
  "-",
  ".",
  ":",
  ";",
  "=",
  "?",
  "@",
  "[",
  "]",
  "^",
  "_",
  "{",
  "|",
  "}",
  "~",
];

function decode83(str: string) {
  let value = 0;
  for (let i = 0; i < str.length; i++) {
    const c = str[i];
    const digit = digitCharacters.indexOf(c);
    value = value * 83 + digit;
  }
  return value;
}

function encode83(n: number, length: number): string {
  var result = "";
  for (let i = 1; i <= length; i++) {
    let digit = (Math.floor(n) / Math.pow(83, length - i)) % 83;
    result += digitCharacters[Math.floor(digit)];
  }
  return result;
}

/* toColorHex() is modified from
https://www.xaymar.com/articles/2020/12/08/fastest-uint8array-to-hex-string-conversion-in-javascript/,
licensed BSD-3. */

// Pre-Init
const LUT_HEX_4b = [
  "0",
  "1",
  "2",
  "3",
  "4",
  "5",
  "6",
  "7",
  "8",
  "9",
  "A",
  "B",
  "C",
  "D",
  "E",
  "F",
];
const LUT_HEX_8b = new Array(0x100);
for (let n = 0; n < 0x100; n++) {
  LUT_HEX_8b[n] = `${LUT_HEX_4b[(n >>> 4) & 0xf]}${LUT_HEX_4b[n & 0xf]}`;
}
// End Pre-Init
function toColorHex(buffer: Uint8ClampedArray): `#${string}` {
  let out = "#";
  for (let idx = 0, edx = buffer.length; idx < edx; idx++) {
    out += LUT_HEX_8b[buffer[idx]];
  }
  return out as `#${string}`;
}

export function averageColor(blurhash: string) {
  const v = decode83(blurhash.substring(2, 6)); // 24-bit RGB

  return [v >> 16, (v >> 8) & 255, v & 255] as const;
}

export function averageColorHex(blurhash: string) : `#${string}` {
  const [r, g, b] = averageColor(blurhash);

  const buf = new Uint8ClampedArray(3);
  buf[0] = r;
  buf[1] = g;
  buf[2] = b;

  return toColorHex(buf);
}