// @flow
import getLuminance from './getLuminance'

/**
 * Returns the contrast ratio between two colors based on
 * [W3's recommended equation for calculating contrast](http://www.w3.org/TR/WCAG20/#contrast-ratiodef).
 *
 * @example
 * const contrastRatio = getContrast('#444', '#fff');
 */
export default function getContrast(color1: string, color2: string): number {
  const luminance1 = getLuminance(color1)
  const luminance2 = getLuminance(color2)
  return parseFloat(
    (luminance1 > luminance2
      ? (luminance1 + 0.05) / (luminance2 + 0.05)
      : (luminance2 + 0.05) / (luminance1 + 0.05)
    ).toFixed(2),
  )
}