const RED = 0.2126
const GREEN = 0.7152
const BLUE = 0.0722

const GAMMA = 2.4

export type RgbColorTuple = [r: number, g: number, b: number]

export const luminance = (...colortuple: RgbColorTuple) => {
  const [r, g, b] = colortuple
  const a = [r, g, b].map((v) => {
    v /= 255
    return v <= 0.03928 ? v / 12.92 : Math.pow((v + 0.055) / 1.055, GAMMA)
  })
  return a[0] * RED + a[1] * GREEN + a[2] * BLUE
}

export const contrast = (rgb1: RgbColorTuple, rgb2: RgbColorTuple) => {
  const lum1 = luminance(...rgb1)
  const lum2 = luminance(...rgb2)
  const brightest = Math.max(lum1, lum2)
  const darkest = Math.min(lum1, lum2)
  return (brightest + 0.05) / (darkest + 0.05)
}