/**
 * Calculate light or darker color based on the luminance arg.
 *
 * @param  {String} hex Color hex string to calculate on.
 * @param  {Number} lum Luminance.
 * @return {String}     The new color hex string.
 */
export const colorLuminance = (hex, lum) => {
  // validate hex string
  hex = String(hex).replace(/[^0-9a-f]/gi, '');
  if (hex.length < 6) {
    hex = hex[0] + hex[0] + hex[1] + hex[1] + hex[2] + hex[2];
  }
  lum = lum || 0;
  // convert to decimal and change luminosity
  let rgb = '#';
  let c;
  let i;
  for (i = 0; i < 3; i++) {
    c = parseInt(hex.substr(i * 2, 2), 16);
    c = Math.round(Math.min(Math.max(0, c + (c * lum)), 255)).toString(16);
    rgb += ('00' + c).substr(c.length);
  }

  return rgb;
}

/**
 * Calculate an appropriate contrast color.
 *
 * @param  {String} hex   Hex string of the color we're searching for the right contrast.
 * @param  {String} dark  Dark color to return. Defaults to #000000.
 * @param  {String} light Light color to return. Defaults to #ffffff.
 * @return {String}       Hex color string with the appropriate contrast color.
 */
export const contrastTextColor = (hex, dark, light) => {
  dark = dark || '#000000';
  light = light || '#ffffff';
  const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
  if (!result) {
    return dark;
  }
  const red = parseInt(result[1], 16);
  const green = parseInt(result[2], 16);
  const blue = parseInt(result[3], 16);
  let brightness;
  brightness = (red * 299) + (green * 587) + (blue * 114);
  brightness /= 255000;
  // values range from 0 to 1
  // anything greater than 0.6 should be bright enough for dark text
  if (brightness >= 0.6) {
    return dark;
  }

  return light;
}

/**
 * Convert rgb(r, g, b) to hex.
 *
 * @param  {String} rgb   Rgb string to convert.
 * @return {String}       The hex string.
 */
export const rgbToHex = rgb => {
  const matches = rgb.match(/rgb\(([0-9]+), ([0-9]+), ([0-9]+)\)/);
  if (matches.length !== 4) {
    return '';
  }

  // From https://gist.github.com/lrvick/2080648.
  const bin = matches[1] << 16 | matches[2] << 8 | matches[3];
  return (function(h) {
    return '#' + new Array(7 - h.length).join('0') + h;
  })(bin.toString(16).toLowerCase());
}