package webcam

import "testing"

func TestDecodeBMP_roundtripRGB(t *testing.T) {
	// 2x2 24-bit BI_RGB bottom-up BMP
	row := []byte{
		0, 0, 255, // BGR red
		0, 255, 0, // green
		0, 0, // pad to 4-byte boundary: 6 bytes -> pad 2
	}
	row2 := []byte{
		255, 0, 0, // blue
		255, 255, 255, // white
		0, 0,
	}
	pixelData := append(append([]byte{}, row2...), row...) // bottom row first
	header := make([]byte, 54)
	header[0], header[1] = 'B', 'M'
	binaryPutUint32 := func(b []byte, v uint32) {
		b[0] = byte(v)
		b[1] = byte(v >> 8)
		b[2] = byte(v >> 16)
		b[3] = byte(v >> 24)
	}
	binaryPutUint16 := func(b []byte, v uint16) {
		b[0] = byte(v)
		b[1] = byte(v >> 8)
	}
	fileSize := uint32(54 + len(pixelData))
	binaryPutUint32(header[2:], fileSize)
	binaryPutUint32(header[10:], 54)
	binaryPutUint32(header[14:], 40) // DIB header size
	binaryPutUint32(header[18:], 2)  // width
	binaryPutUint32(header[22:], 2)  // height (bottom-up)
	binaryPutUint16(header[26:], 1)  // planes
	binaryPutUint16(header[28:], 24) // bpp

	img, err := decodeBMP(append(header, pixelData...))
	if err != nil {
		t.Fatal(err)
	}
	if img.Bounds().Dx() != 2 || img.Bounds().Dy() != 2 {
		t.Fatalf("size = %v", img.Bounds())
	}
	r, g, b, _ := img.At(0, 0).RGBA()
	if r>>8 != 255 || g>>8 != 0 || b>>8 != 0 {
		t.Fatalf("pixel 0,0 = %d,%d,%d want red", r>>8, g>>8, b>>8)
	}
}