Reverse function of WCAG 2.0 that returns ideal Luminance of colour at current index (to be used with Array.map)

idealLuminanceAtIndex.ts

// Contrast ratio formula:
// (L1 + 0.05) / (L2 + 0.05), where
// L1 is the relative luminance of the lighter of the foreground or background colors, and
// L2 is the relative luminance of the darker of the foreground or background colors.
function idealLuminanceAtIndex(index: number, colorsCount: number) {
  const exponent = (1 - (index * 1 / (colorsCount - 1)))

  return (Math.pow(colorsCount, exponent) * 0.05 - 0.05) / (colorsCount - 1) * 20
}