hashColor.js

'use strict';

const crypto = require('crypto');
const toId = require('toid');

let colorCache = {};

function hashColor(name) {
  name = toId(name);
  if (name === 'panpawn') colorCache[name] = 'crowt';
  if (colorCache[name]) return colorCache[name];
  let hash = crypto.createHash('md5').update(name).digest('hex');
  let H = parseInt(hash.substr(4, 4), 16) % 360; // 0 to 360
  let S = parseInt(hash.substr(0, 4), 16) % 50 + 40; // 40 to 89
  let L = Math.floor(parseInt(hash.substr(8, 4), 16) % 20 + 30); // 30 to 49
  let C = (100 - Math.abs(2 * L - 100)) * S / 100 / 100;
  let X = C * (1 - Math.abs((H / 60) % 2 - 1));
  let m = L / 100 - C / 2;

  let R1, G1, B1;
  switch (Math.floor(H / 60)) {
    case 1: R1 = X; G1 = C; B1 = 0; break;
    case 2: R1 = 0; G1 = C; B1 = X; break;
    case 3: R1 = 0; G1 = X; B1 = C; break;
    case 4: R1 = X; G1 = 0; B1 = C; break;
    case 5: R1 = C; G1 = 0; B1 = X; break;
    case 0: default: R1 = C; G1 = X; B1 = 0; break;
  }
  let lum = (R1 + m) * 0.2126 + (G1 + m) * 0.7152 + (B1 + m) * 0.0722; // 0.05 (dark blue) to 0.93 (yellow)
  let HLmod = (lum - 0.5) * -100; // -43 (yellow) to 45 (dark blue)
  if (HLmod > 12) HLmod -= 12;
  else if (HLmod < -10) HLmod = (HLmod + 10) * 2 / 3;
  else HLmod = 0;

  L += HLmod;
  let Smod = 10 - Math.abs(50 - L);
  if (HLmod > 15) Smod += (HLmod - 15) / 2;
  S -= Smod;

  let rgb = hslToRgb(H, S, L);
  colorCache[name] = '#' + rgbToHex(rgb.r, rgb.g, rgb.b);
  return colorCache[name];
}

function hslToRgb(h, s, l) {
  let r, g, b, m, c, x;
  if (!isFinite(h)) h = 0;
  if (!isFinite(s)) s = 0;
  if (!isFinite(l)) l = 0;
  h /= 60;
  if (h < 0) h = 6 - (-h % 6);
  h %= 6;
  s = Math.max(0, Math.min(1, s / 100));
  l = Math.max(0, Math.min(1, l / 100));
  c = (1 - Math.abs((2 * l) - 1)) * s;
  x = c * (1 - Math.abs((h % 2) - 1));
  if (h < 1) {
    r = c;
    g = x;
    b = 0;
  } else if (h < 2) {
    r = x;
    g = c;
    b = 0;
  } else if (h < 3) {
    r = 0;
    g = c;
    b = x;
  } else if (h < 4) {
    r = 0;
    g = x;
    b = c;
  } else if (h < 5) {
    r = x;
    g = 0;
    b = c;
  } else {
    r = c;
    g = 0;
    b = x;
  }
  m = l - c / 2;
  r = Math.round((r + m) * 255);
  g = Math.round((g + m) * 255);
  b = Math.round((b + m) * 255);
  return {
    r: r,
    g: g,
    b: b
  };
}

function rgbToHex(R, G, B) {
  return toHex(R) + toHex(G) + toHex(B);
}

function toHex(N) {
  if (N == null) return '00';
  N = parseInt(N);
  if (N == 0 || isNaN(N)) return '00';
  N = Math.max(0, N);
  N = Math.min(N, 255);
  N = Math.round(N);
  return '0123456789ABCDEF'.charAt((N - N % 16) / 16) + '0123456789ABCDEF'.charAt(N % 16);
}

module.exports = hashColor;