package helper

import (
	"cmp"
	"image/color"
	"math"
	"testing"
)

func TestTestDistance(t *testing.T) {
	mt := mockTester{t: t}

	midpoint := func(c0, c1 color.RGBA) color.RGBA {
		return color.RGBA{
			uint8((uint16(c0.R) + uint16(c1.R)) / 2),
			uint8((uint16(c0.G) + uint16(c1.G)) / 2),
			uint8((uint16(c0.B) + uint16(c1.B)) / 2),
			uint8((uint16(c0.A) + uint16(c1.A)) / 2),
		}
	}

	mt.run("non-zero distance for identical colours", func(t *mockTest) {
		TestDistance(t, true, midpoint, func(c0, c1 color.RGBA) float64 {
			return 1
		}, color.RGBAModel)
	})

	mt.run("NaN distance", func(t *mockTest) {
		TestDistance(t, true, midpoint, func(c0, c1 color.RGBA) float64 {
			if c0 == c1 {
				return 0
			}

			return math.NaN()
		}, color.RGBAModel)
	})

	mt.run("negative distance", func(t *mockTest) {
		TestDistance(t, true, midpoint, func(c0, c1 color.RGBA) float64 {
			if c0 == c1 {
				return 0
			}

			return -1
		}, color.RGBAModel)
	})

	mt.run("asymmetric distance", func(t *mockTest) {
		TestDistance(t, true, midpoint, func(c0, c1 color.RGBA) float64 {
			if c0 == c1 {
				return 0
			}

			if cmp.Or(int(c0.R)-int(c1.R), int(c0.G)-int(c1.G), int(c0.B)-int(c1.B), int(c0.A)-int(c1.A)) > 0 {
				return 1
			}

			return 2
		}, color.RGBAModel)
	})

	mt.run("triangle inequality", func(t *mockTest) {
		TestDistance(t, true, midpoint, func(c0, c1 color.RGBA) float64 {
			dR := int(c0.R) - int(c1.R)
			dG := int(c0.G) - int(c1.G)
			dB := int(c0.B) - int(c1.B)
			dA := int(c0.A) - int(c1.A)

			d2 := float64(dR*dR + dG*dG + dB*dB + dA*dA)

			return d2
		}, color.RGBAModel)
	})

	mt.run("euclidean distance", func(t *mockTest) {
		TestDistance(t, true, midpoint, func(c0, c1 color.RGBA) float64 {
			dR := int(c0.R) - int(c1.R)
			dG := int(c0.G) - int(c1.G)
			dB := int(c0.B) - int(c1.B)
			dA := int(c0.A) - int(c1.A)

			d2 := float64(dR*dR + dG*dG + dB*dB + dA*dA)

			return math.Sqrt(d2)
		}, color.RGBAModel)
	})

	mt.expectError(
		"non-zero distance for identical colours",
		`Distance(color.RGBA{R:0x0, G:0x0, B:0x0, A:0x0}, color.RGBA{R:0x0, G:0x0, B:0x0, A:0x0}) = 1.000000, want 0`,
	)

	mt.expectError(
		"NaN distance",
		`Distance(color.RGBA{R:0x0, G:0x0, B:0x0, A:0x0}, color.RGBA{R:0x0, G:0x0, B:0x0, A:0x55}) = NaN, want finite`,
	)

	mt.expectError(
		"negative distance",
		`Distance(color.RGBA{R:0x0, G:0x0, B:0x0, A:0x0}, color.RGBA{R:0x0, G:0x0, B:0x0, A:0x55}) = -1.000000, want > 0`,
	)

	mt.expectError(
		"asymmetric distance",
		`Distance(color.RGBA{R:0x0, G:0x0, B:0x0, A:0x55}, color.RGBA{R:0x0, G:0x0, B:0x0, A:0x0}) != Distance(color.RGBA{R:0x0, G:0x0, B:0x0, A:0x0}, color.RGBA{R:0x0, G:0x0, B:0x0, A:0x55}), want 2.000000 == 1.000000`,
	)

	mt.expectError(
		"triangle inequality",
		`Distance(color.RGBA{R:0x0, G:0x0, B:0x0, A:0x0}, color.RGBA{R:0x0, G:0x0, B:0x0, A:0x2a})+Distance(color.RGBA{R:0x0, G:0x0, B:0x0, A:0x2a}, color.RGBA{R:0x0, G:0x0, B:0x0, A:0x55}) < Distance(color.RGBA{R:0x0, G:0x0, B:0x0, A:0x0}, color.RGBA{R:0x0, G:0x0, B:0x0, A:0x55}), want 3613.000000 >= 7225.000000`,
	)

	mt.expectSuccess("euclidean distance")

	mt.expectAllHandled()
}