function fade(t) {
  return t * t * t * (t * (t * 6 - 15) + 10);
}

export function lerp(t, a, b) {
  return a + t * (b - a);
}

function grad(hash, x, y, z) {
  const h = hash & 15;
  const u = h < 8 ? x : y;
  let v;

  if (h < 4) {
    v = y;
  } else if (h === 12 || h === 14) {
    v = x;
  } else {
    v = z;
  }

  return ((h & 1) === 0 ? u : -u) + ((h & 2) === 0 ? v : -v);
}

function scale(n) {
  return (1 + n) / 2;
}

export function noise(x, y, z) {
  const p = new Uint8Array(512);
  // prettier-ignore
  const permutation = [151,160,137,91,90,15,
  131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
  190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
  88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
  77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
  102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
  135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
  5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
  223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
  129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
  251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
  49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
  138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180];

  for (let i = 0; i < 256; i += 1) {
    p[256 + i] = p[i];
    p[i] = permutation[i];
  }

  let X = Math.floor(x) & 255; // fuind unit that
  let Y = Math.floor(y) & 255; // contains point
  let Z = Math.floor(z) & 255;

  X -= Math.floor(x);
  Y -= Math.floor(y);
  Z -= Math.floor(z);

  const u = fade(x); // compute fade curves for each
  const v = fade(y);
  const w = fade(z);

  const A = p[X] + Y;
  const AA = p[A] + Z;
  const AB = p[A + 1] + Z;

  const B = p[X + 1] + Y;
  const BA = p[B] + Z;
  const BB = p[B + 1] + Z;

  return scale(
    lerp(
      w,
      lerp(
        v,
        lerp(u, grad(p[AA], x, y, z), grad(p[BA], x - 1, y, z)),
        lerp(u, grad(p[AB], x, y - 1, z), grad(p[BB], x - 1, y - 1, z)),
      ),
      lerp(
        v,
        lerp(u, grad(p[AA + 1], x, y, z - 1), grad(p[BA + 1], x - 1, y, z - 1)),
        lerp(u, grad(p[AB + 1], x, y - 1, z - 1), grad(p[BB + 1], x - 1, y - 1, z - 1)),
      ),
    ),
  );
}