import {HSL, RGB} from '../../types'

/**
 * @see https://css-tricks.com/converting-color-spaces-in-javascript/
 *
 * @internal
 */
export function rgbToHsl([r, g, b]: RGB): HSL {
  // Make r, g, and b fractions of 1
  r /= 255
  g /= 255
  b /= 255

  // Find greatest and smallest channel values
  const cmin = Math.min(r, g, b)
  const cmax = Math.max(r, g, b)
  const delta = cmax - cmin

  let h = 0
  let s = 0
  let l = 0

  // Calculate hue
  // No difference
  if (delta == 0) h = 0
  // Red is max
  else if (cmax == r) h = ((g - b) / delta) % 6
  // Green is max
  else if (cmax == g) h = (b - r) / delta + 2
  // Blue is max
  else h = (r - g) / delta + 4

  h = Math.round(h * 60)

  // Make negative hues positive behind 360°
  if (h < 0) h += 360

  // Calculate lightness
  l = (cmax + cmin) / 2

  // Calculate saturation
  s = delta == 0 ? 0 : delta / (1 - Math.abs(2 * l - 1))

  // Multiply l and s by 100
  s = +(s * 100).toFixed(0)
  l = +(l * 100).toFixed(0)

  return [h, s, l]
}