go-bananas/internal/tokenengine/color_test.go

package tokenengine

import (
	"math"
	"testing"
)

func TestParseColorFormats(t *testing.T) {
	cases := []struct {
		name  string
		input string
		want  Color
	}{
		{"hex6", "#1a2b3c", Color{RGB: RGB{R: 0x1a / 255.0, G: 0x2b / 255.0, B: 0x3c / 255.0, A: 1}, Raw: "#1a2b3c", Numeric: true}},
		{"hex3", "#abc", Color{RGB: RGB{R: 0xaa / 255.0, G: 0xbb / 255.0, B: 0xcc / 255.0, A: 1}, Raw: "#abc", Numeric: true}},
		{"hex8 alpha", "#00000080", Color{RGB: RGB{R: 0, G: 0, B: 0, A: 128 / 255.0}, Raw: "#00000080", Numeric: true}},
		{"rgb legacy comma", "rgb(255, 0, 0)", Color{RGB: RGB{R: 1, G: 0, B: 0, A: 1}, Raw: "rgb(255, 0, 0)", Numeric: true}},
		{"rgb modern space", "rgb(255 0 0)", Color{RGB: RGB{R: 1, G: 0, B: 0, A: 1}, Raw: "rgb(255 0 0)", Numeric: true}},
		{"rgba alpha", "rgba(0, 0, 0, 0.5)", Color{RGB: RGB{A: 0.5}, Raw: "rgba(0, 0, 0, 0.5)", Numeric: true}},
		{"hsl", "hsl(0, 100%, 50%)", Color{RGB: RGB{R: 1, G: 0, B: 0, A: 1}, Raw: "hsl(0, 100%, 50%)", Numeric: true}},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			got, err := ParseColor(tc.input)
			if err != nil {
				t.Fatalf("ParseColor(%q) error: %v", tc.input, err)
			}
			if !got.Numeric {
				t.Fatalf("ParseColor(%q) returned a non-numeric colour", tc.input)
			}
			assertClose(t, got.R, tc.want.R, 0.002)
			assertClose(t, got.G, tc.want.G, 0.002)
			assertClose(t, got.B, tc.want.B, 0.002)
			assertClose(t, got.A, tc.want.A, 0.002)
		})
	}
}

func TestParseColorRejectsGarbage(t *testing.T) {
	for _, bad := range []string{"", "#", "#12", "#1234567", "rgb(1,2)", "#gggggg"} {
		if _, err := ParseColor(bad); err == nil {
			t.Errorf("ParseColor(%q) should have failed", bad)
		}
	}
}

func TestParseColorPassesThroughModernSyntax(t *testing.T) {
	// These are valid CSS the engine cannot reason about numerically, but they
	// must round-trip rather than be rejected.
	for _, ok := range []string{"oklch(0.7 0.1 200)", "color(display-p3 1 0 0)", "light-dark(#fff, #000)", "currentColor", "transparent"} {
		got, err := ParseColor(ok)
		if err != nil {
			t.Errorf("ParseColor(%q) error: %v", ok, err)
		}
		if got.Numeric {
			t.Errorf("ParseColor(%q) should not be numeric", ok)
		}
		if got.Raw != ok {
			t.Errorf("ParseColor(%q).Raw = %q, want the original", ok, got.Raw)
		}
	}
}

func TestContrastRatioMatchesWCAGReferenceValues(t *testing.T) {
	// Reference values from the WCAG 2.1 relative-luminance definition.
	cases := []struct {
		a, b string
		want float64
	}{
		{"#ffffff", "#000000", 21},
		{"#ffffff", "#ffffff", 1},
		{"#000000", "#000000", 1},
		{"#777777", "#ffffff", 4.48},
		{"#767676", "#ffffff", 4.54}, // the canonical AA boundary grey
	}
	for _, tc := range cases {
		a, err := ParseColor(tc.a)
		if err != nil {
			t.Fatalf("%v", err)
		}
		b, err := ParseColor(tc.b)
		if err != nil {
			t.Fatalf("%v", err)
		}
		got := ContrastRatio(a, b)
		if math.Abs(got-tc.want) > 0.05 {
			t.Errorf("ContrastRatio(%s, %s) = %.3f, want %.3f", tc.a, tc.b, got, tc.want)
		}
	}
}

func TestBestForegroundPicksHigherContrast(t *testing.T) {
	light := Color{RGB: RGB{R: 1, G: 1, B: 1, A: 1}, Numeric: true}
	dark := Color{RGB: RGB{A: 1}, Numeric: true}

	if got := BestForeground(Color{RGB: RGB{A: 1}, Numeric: true}); got.R != light.R {
		t.Errorf("foreground for black should be white, got %s", got.Hex())
	}
	if got := BestForeground(Color{RGB: RGB{R: 1, G: 1, B: 1, A: 1}, Numeric: true}); got.R != dark.R {
		t.Errorf("foreground for white should be black, got %s", got.Hex())
	}
}

func TestHexRoundTrip(t *testing.T) {
	for _, hex := range []string{"#000000", "#ffffff", "#4f46e5", "#4f46e580"} {
		c, err := ParseColor(hex)
		if err != nil {
			t.Fatalf("%v", err)
		}
		if got := c.Hex(); got != hex {
			t.Errorf("round trip of %q produced %q", hex, got)
		}
	}
}

func TestMixProducesIntermediateColour(t *testing.T) {
	black, _ := ParseColor("#000000")
	white, _ := ParseColor("#ffffff")

	mid := black.Mix(white, 0.5)
	if got := mid.Hex(); got != "#808080" && got != "#7f7f7f" {
		t.Errorf("50%% black/white mix = %s, want roughly #808080", got)
	}
	if got := black.Mix(white, 0).Hex(); got != "#000000" {
		t.Errorf("0%% mix = %s, want #000000", got)
	}
	if got := black.Mix(white, 1).Hex(); got != "#ffffff" {
		t.Errorf("100%% mix = %s, want #ffffff", got)
	}
}

func TestLightenDarkInvertsDirectionForDarkSchemes(t *testing.T) {
	base, _ := ParseColor("#4f46e5")

	light := base.LightenDark(0.1, false)
	dark := base.LightenDark(0.1, true)

	if light.RelativeLuminance() >= base.RelativeLuminance() {
		t.Error("light scheme emphasis should reduce luminance")
	}
	if dark.RelativeLuminance() <= base.RelativeLuminance() {
		t.Error("dark scheme emphasis should increase luminance")
	}
}

func TestGenerateRampIsOrderedAndComplete(t *testing.T) {
	ramp := GenerateRamp(DefaultRampOptions())

	shades := StandardPaletteShades()
	if len(ramp) != len(shades) {
		t.Fatalf("ramp has %d steps, want %d", len(ramp), len(shades))
	}

	previous := math.Inf(1)
	for _, shade := range shades {
		leaf, ok := ramp[shade].(map[string]any)
		if !ok {
			t.Fatalf("shade %s is not a token leaf", shade)
		}
		value, ok := leaf[ValueKey].(string)
		if !ok {
			t.Fatalf("shade %s has no string value", shade)
		}
		col, err := ParseColor(value)
		if err != nil {
			t.Fatalf("shade %s value %q is not a colour: %v", shade, value, err)
		}
		luminance := col.RelativeLuminance()
		if luminance > previous {
			t.Errorf("shade %s is lighter than the preceding shade", shade)
		}
		previous = luminance
	}
}

func TestGenerateRampNormalisesOutOfRangeInput(t *testing.T) {
	opts := RampOptions{Hue: 400, Saturation: -20, Lightness: 999, HueSpread: 1000}.Normalize()

	if opts.Hue < 0 || opts.Hue >= 360 {
		t.Errorf("hue = %f, want it wrapped into 0..360", opts.Hue)
	}
	if opts.Saturation != 0 {
		t.Errorf("saturation = %f, want it clamped to 0", opts.Saturation)
	}
	if opts.Lightness != 80 {
		t.Errorf("lightness = %f, want it clamped to 80", opts.Lightness)
	}
	if opts.HueSpread != 40 {
		t.Errorf("hueSpread = %f, want it clamped to 40", opts.HueSpread)
	}
}

func TestFormatNumberIsStable(t *testing.T) {
	cases := map[float64]string{
		0:         "0",
		1:         "1",
		1.5:       "1.5",
		0.1250001: "0.125",
		-0.5:      "-0.5",
		100:       "100",
	}
	for in, want := range cases {
		if got := FormatNumber(in); got != want {
			t.Errorf("FormatNumber(%v) = %q, want %q", in, got, want)
		}
	}
}

// assertClose fails the test when want and got differ by more than tolerance.
func assertClose(t *testing.T, got, want, tolerance float64) {
	t.Helper()
	if math.Abs(got-want) > tolerance {
		t.Errorf("got %v, want %v (tolerance %v)", got, want, tolerance)
	}
}