package generator

import (
	"encoding/binary"
	"image"
	"image/color"
	"math"
	"path/filepath"
	"testing"
)

const logoW, logoH = 8, 4

func TestWGPUDVDLogo(t *testing.T) {
	const width, height = 1920, 1080

	// Synthetic 8x4 logo: white left half, near-75% red right half, one
	// transparent pixel at (2,1) to exercise the alpha fallback.
	img := image.NewRGBA(image.Rect(0, 0, logoW, logoH))
	for yy := 0; yy < logoH; yy++ {
		for xx := 0; xx < logoW; xx++ {
			if xx < 4 {
				img.Set(xx, yy, color.RGBA{255, 255, 255, 255})
			} else {
				img.Set(xx, yy, color.RGBA{191, 0, 0, 255})
			}
		}
	}
	img.Set(2, 1, color.RGBA{0, 0, 0, 0})
	plane, err := BuildLogoPlane(img)
	if err != nil {
		t.Fatalf("plane: %v", err)
	}

	g, err := NewWGPUGenerator(width, height,
		filepath.Join("..", "..", "kernels", "v210_dvd_logo.wgsl"), WithLogo(plane))
	if err != nil {
		t.Fatalf("init: %v", err)
	}
	defer g.Close()

	buf := make([]byte, width*height*8/3)
	sample := func(x, y int) (yc, cb, cr uint32) {
		p := y*width + x
		off := (p / 6) * 16
		w0 := binary.LittleEndian.Uint32(buf[off:])
		w1 := binary.LittleEndian.Uint32(buf[off+4:])
		w2 := binary.LittleEndian.Uint32(buf[off+8:])
		w3 := binary.LittleEndian.Uint32(buf[off+12:])
		switch p % 6 {
		case 0:
			return (w0 >> 10) & 0x3FF, w0 & 0x3FF, (w0 >> 20) & 0x3FF
		case 1:
			return w1 & 0x3FF, w0 & 0x3FF, (w0 >> 20) & 0x3FF
		case 2:
			return (w1 >> 20) & 0x3FF, (w1 >> 10) & 0x3FF, w2 & 0x3FF
		case 3:
			return (w2 >> 10) & 0x3FF, (w1 >> 10) & 0x3FF, w2 & 0x3FF
		case 4:
			return w3 & 0x3FF, (w2 >> 20) & 0x3FF, (w3 >> 10) & 0x3FF
		default:
			return (w3 >> 20) & 0x3FF, (w2 >> 20) & 0x3FF, (w3 >> 10) & 0x3FF
		}
	}

	// Float32 mirrors of the shader position math and bilinear tap blend
	// (kernels/v210_dvd_logo.wgsl), so expectations track the shader exactly.
	tri01 := func(x float32) float32 {
		f := x - float32(math.Floor(float64(x)))
		if f > 0.5 {
			return 2 - 2*f
		}
		return 2 * f
	}
	type logoPos struct {
		bx, by int
		fx, fy float32
	}
	logoOrigin := func(frame uint32) logoPos {
		tick := float32(frame) / 25.0
		lx := tri01(tick*0.061) * (float32(width) - logoW)
		ly := tri01(tick*0.088) * (float32(height) - logoH)
		return logoPos{int(lx), int(ly), lx - float32(int(lx)), ly - float32(int(ly))}
	}
	tap := func(dx, dy int) [3]float32 {
		if dx < 0 || dy < 0 || dx >= logoW || dy >= logoH {
			return [3]float32{}
		}
		s := plane[1+dy*logoW+dx]
		if s>>30 == 0 {
			return [3]float32{}
		}
		return [3]float32{float32(s&0x3FF) - 64, float32((s>>10)&0x3FF) - 512, float32((s>>20)&0x3FF) - 512}
	}
	mix3 := func(a, b [3]float32, k float32) [3]float32 {
		return [3]float32{a[0] + k*(b[0]-a[0]), a[1] + k*(b[1]-a[1]), a[2] + k*(b[2]-a[2])}
	}
	expect := func(p logoPos, px, py int) (yc, cb, cr uint32) {
		m, n := px-p.bx, py-p.by
		top := mix3(tap(m, n-1), tap(m-1, n-1), p.fx)
		bot := mix3(tap(m, n), tap(m-1, n), p.fx)
		d := mix3(bot, top, p.fy)
		return uint32(64 + d[0] + 0.5), uint32(512 + d[1] + 0.5), uint32(512 + d[2] + 0.5)
	}
	// tol allows +-1 code for blended pixels (FMA contraction on GPU may
	// differ from Go's separately-rounded float32 ops by 1 ulp).
	check := func(p logoPos, px, py int, tol int, desc string) {
		t.Helper()
		yc, cb, cr := sample(px, py)
		wy, wcb, wcr := expect(p, px, py)
		dy, dcb, dcr := int(yc)-int(wy), int(cb)-int(wcb), int(cr)-int(wcr)
		if abs(dy) > tol || abs(dcb) > tol || abs(dcr) > tol {
			t.Fatalf("%s: (%d,%d) got %d/%d/%d, want %d/%d/%d (diff %d/%d/%d, tol %d)",
				desc, px, py, yc, cb, cr, wy, wcb, wcr, dy, dcb, dcr, tol)
		}
	}

	// tick 0: fx=fy=0 -> pure nearest lookup, exact values known upfront
	if err := g.GenerateFrame(buf, 0); err != nil {
		t.Fatalf("tick 0: %v", err)
	}
	p0 := logoOrigin(0)
	if p0.bx != 0 || p0.by != 0 || p0.fx != 0 || p0.fy != 0 {
		t.Fatalf("tick 0 origin %+v, want (0,0,0,0)", p0)
	}
	check(p0, 1, 1, 0, "tick 0 white pixel")
	if y, cb, cr := sample(1, 1); y != 940 || cb != 512 || cr != 512 {
		t.Fatalf("tick 0 white pixel: got %d/%d/%d, want 940/512/512", y, cb, cr)
	}
	check(p0, 2, 1, 0, "tick 0 transparent pixel")
	if y, _, _ := sample(2, 1); y != 64 {
		t.Fatalf("tick 0 transparent pixel: Y=%d, want background 64", y)
	}
	check(p0, 5, 2, 0, "tick 0 red pixel")
	if y, cb, cr := sample(5, 2); y != 203 || cb != 435 || cr != 848 {
		t.Fatalf("tick 0 red pixel: got %d/%d/%d, want 203/435/848", y, cb, cr)
	}
	check(p0, 10, 1, 0, "tick 0 right of logo")
	check(p0, 1, 5, 0, "tick 0 below logo")

	// tick 100: origin (933,757), fx~0.056 fy~0.504 -> bilinear blending.
	// (934,758) lands on solid white (all 4 taps white) and must reproduce
	// the texel exactly; (935,759) straddles the transparent pixel (2,1)
	// and must match the mirrored blend within +-1.
	if err := g.GenerateFrame(buf, 100); err != nil {
		t.Fatalf("tick 100: %v", err)
	}
	p100 := logoOrigin(100)
	if p100.bx != 933 || p100.by != 757 {
		t.Fatalf("tick 100 origin (%d,%d), want (933,757)", p100.bx, p100.by)
	}
	check(p100, 934, 758, 0, "tick 100 solid pixel exact")
	if y, _, _ := sample(934, 758); y != 940 {
		t.Fatalf("tick 100 solid pixel: Y=%d, want exact texel 940", y)
	}
	check(p100, 935, 759, 1, "tick 100 blended over transparent pixel")
	check(p100, 960, 540, 0, "tick 100 frame center")
	if y, _, _ := sample(960, 540); y != 64 {
		t.Fatalf("tick 100 frame center: Y=%d, want background 64", y)
	}
	check(p100, 2, 1, 0, "tick 100 old logo position")
}

func abs(v int) int {
	if v < 0 {
		return -v
	}
	return v
}