package colorcrop

import (
	"image/color"
	"math"
)

// comparator is a function that returns a difference between two colors in
// range 0.0..1.0 (0.0 - same colors, 1.0 - totally different colors).
type comparator func(color.Color, color.Color) float64

// CmpEuclidean returns Euclidean difference of two colors.
//
// https://en.wikipedia.org/wiki/Color_difference#Euclidean
func CmpEuclidean(color1 color.Color, color2 color.Color) float64 {
	const maxDiff = 113509.94967402637 // Difference between black and white colors

	r1, g1, b1, _ := color1.RGBA()
	r2, g2, b2, _ := color2.RGBA()

	return math.Sqrt(distance(float64(r2), float64(r1))+
		distance(float64(g2), float64(g1))+
		distance(float64(b2), float64(b1))) / maxDiff
}

// CmpRGBComponents returns RGB components difference of two colors.
func CmpRGBComponents(color1 color.Color, color2 color.Color) float64 {
	const maxDiff = 765.0 // Difference between black and white colors

	r1, g1, b1, _ := color1.RGBA()
	r2, g2, b2, _ := color2.RGBA()

	r1, g1, b1 = r1>>8, g1>>8, b1>>8
	r2, g2, b2 = r2>>8, g2>>8, b2>>8

	return float64((max(r1, r2)-min(r1, r2))+
		(max(g1, g2)-min(g1, g2))+
		(max(b1, b2)-min(b1, b2))) / maxDiff
}

// CmpCIE76 returns difference of two colors defined in CIE76 standart.
//
// https://en.wikipedia.org/wiki/Color_difference#CIE76
func CmpCIE76(color1 color.Color, color2 color.Color) float64 {
	const maxDiff = 149.95514755 // Difference between blue and white colors

	cl1, ca1, cb1 := colorToLAB(color1)
	cl2, ca2, cb2 := colorToLAB(color2)

	return math.Sqrt(distance(cl2, cl1)+distance(ca2, ca1)+distance(cb2, cb1)) / maxDiff
}

func distance(x, y float64) float64 {
	return (x - y) * (x - y)
}

// min is minimum of two uint32
func min(a, b uint32) uint32 {
	if a < b {
		return a
	}
	return b
}

// max is maximum of two uint32
func max(a, b uint32) uint32 {
	if a > b {
		return a
	}
	return b
}