//go:build windows

package clipboard

import (
	"bytes"
	"image"
	"image/color"
	"image/png"
	"testing"
)

func TestDIBRoundTrip(t *testing.T) {
	// Build a small 4x3 RGBA image with distinct corner colors.
	img := image.NewRGBA(image.Rect(0, 0, 4, 3))
	img.Set(0, 0, color.RGBA{255, 0, 0, 255})   // red
	img.Set(3, 0, color.RGBA{0, 255, 0, 255})   // green
	img.Set(0, 2, color.RGBA{0, 0, 255, 255})   // blue
	img.Set(3, 2, color.RGBA{255, 255, 0, 128}) // semi-transparent yellow

	var buf bytes.Buffer
	if err := png.Encode(&buf, img); err != nil {
		t.Fatalf("png.Encode: %v", err)
	}
	pngData := buf.Bytes()

	dib, err := pngToDIB(pngData)
	if err != nil {
		t.Fatalf("pngToDIB: %v", err)
	}
	got, err := dibToPNG(dib)
	if err != nil {
		t.Fatalf("dibToPNG: %v", err)
	}

	decoded, err := png.Decode(bytes.NewReader(got))
	if err != nil {
		t.Fatalf("decode round-trip: %v", err)
	}
	if decoded.Bounds() != img.Bounds() {
		t.Errorf("bounds = %v, want %v", decoded.Bounds(), img.Bounds())
	}

	// Spot-check the corner colors survived the round-trip.
	for _, tc := range []struct {
		x, y int
		want color.RGBA
	}{
		{0, 0, color.RGBA{255, 0, 0, 255}},
		{3, 0, color.RGBA{0, 255, 0, 255}},
		{0, 2, color.RGBA{0, 0, 255, 255}},
	} {
		r, g, b, a := decoded.At(tc.x, tc.y).RGBA()
		got := color.RGBA{uint8(r >> 8), uint8(g >> 8), uint8(b >> 8), uint8(a >> 8)}
		if got != tc.want {
			t.Errorf("pixel (%d,%d) = %v, want %v", tc.x, tc.y, got, tc.want)
		}
	}
}

func TestDIBRejectsUnsupportedCompression(t *testing.T) {
	dib := make([]byte, 44)
	dib[14] = 32 // biBitCount
	// biCompression = BI_RLE8 (1) at offset 16
	dib[16] = 1
	dib[4] = 1 // width 1
	dib[8] = 1 // height 1

	if _, err := dibToPNG(dib); err == nil {
		t.Error("expected error for unsupported compression, got nil")
	}
}

func BenchmarkDIBRoundTrip(b *testing.B) {
	img := image.NewRGBA(image.Rect(0, 0, 256, 256))
	var buf bytes.Buffer
	_ = png.Encode(&buf, img)
	pngData := buf.Bytes()

	dib, err := pngToDIB(pngData)
	if err != nil {
		b.Fatalf("pngToDIB: %v", err)
	}

	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		if _, err := dibToPNG(dib); err != nil {
			b.Fatalf("dibToPNG: %v", err)
		}
	}
}