const HEX_COLOR_PATTERN = /^#?([0-9a-fA-F]{6})$/;

export const hexToRgb = (input) => {
  if (!input) return null;
  const match = HEX_COLOR_PATTERN.exec(input.trim());
  if (!match) return null;
  const value = parseInt(match[1], 16);
  return {
    r: (value >> 16) & 0xff,
    g: (value >> 8) & 0xff,
    b: value & 0xff,
    hex: `#${match[1].toLowerCase()}`,
  };
};

const relativeLuminance = ({ r, g, b }) => {
  const transform = (channel) => {
    const normalized = channel / 255;
    return normalized <= 0.03928
      ? normalized / 12.92
      : ((normalized + 0.055) / 1.055) ** 2.4;
  };

  const [red, green, blue] = [transform(r), transform(g), transform(b)];
  return 0.2126 * red + 0.7152 * green + 0.0722 * blue;
};

export const getTagColorStyle = (hex) => {
  const rgb = hexToRgb(hex);
  if (!rgb) return null;
  const luminance = relativeLuminance(rgb);
  const textColor = luminance > 0.6 ? '#1f1f1f' : '#ffffff';
  return {
    backgroundColor: rgb.hex,
    borderColor: rgb.hex,
    color: textColor,
  };
};

export { HEX_COLOR_PATTERN };