flow like the river

VISUALIZACION/node_modules/polished/lib/internalHelpers/_rgbToHsl.js.flow

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+// @flow
+
+import type {
+  HslColor, HslaColor, RgbColor, RgbaColor,
+} from '../types/color'
+
+function rgbToHsl(color: RgbColor | RgbaColor): HslColor | HslaColor {
+  // make sure rgb are contained in a set of [0, 255]
+  const red = color.red / 255
+  const green = color.green / 255
+  const blue = color.blue / 255
+
+  const max = Math.max(red, green, blue)
+  const min = Math.min(red, green, blue)
+  const lightness = (max + min) / 2
+
+  if (max === min) {
+    // achromatic
+    if (color.alpha !== undefined) {
+      return {
+        hue: 0,
+        saturation: 0,
+        lightness,
+        alpha: color.alpha,
+      }
+    } else {
+      return { hue: 0, saturation: 0, lightness }
+    }
+  }
+
+  let hue
+  const delta = max - min
+  const saturation = lightness > 0.5 ? delta / (2 - max - min) : delta / (max + min)
+  switch (max) {
+    case red:
+      hue = (green - blue) / delta + (green < blue ? 6 : 0)
+      break
+    case green:
+      hue = (blue - red) / delta + 2
+      break
+    default:
+      // blue case
+      hue = (red - green) / delta + 4
+      break
+  }
+
+  hue *= 60
+  if (color.alpha !== undefined) {
+    return {
+      hue,
+      saturation,
+      lightness,
+      alpha: color.alpha,
+    }
+  }
+  return { hue, saturation, lightness }
+}
+
+export default rgbToHsl