package tests

import (
	"testing"

	"crecher.net/gones/v2/cart"
	"crecher.net/gones/v2/ppu"
)

const (
	black = 0xFF000000 // palette entry $0F
	white = 0xFFECEEEC // $30
	red   = 0xFF982220 // $16
	blue  = 0xFF4C9AEC // $21
)

// writes bytes through $2006/$2007 starting at addr, then points v back at 0
func writeVRAM(p *ppu.PPU, addr uint16, data ...uint8) {
	p.WriteRegister(0x2006, uint8(addr>>8))
	p.WriteRegister(0x2006, uint8(addr))
	for _, b := range data {
		p.WriteRegister(0x2007, b)
	}
	p.WriteRegister(0x2006, 0)
	p.WriteRegister(0x2006, 0)
}

// ticks two full frames so scroll registers have been copied from t at least once
func runFrames(p *ppu.PPU) {
	for i := 0; i < 2*341*262; i++ {
		p.Tick()
	}
}

func pixel(p *ppu.PPU, x, y int) uint32 {
	return p.Framebuffer()[y*ppu.ScreenWidth+x]
}

// tile 1: row 0 is color 1 across, row 1 is color 2 across
// palette 0: backdrop black, 1 = white, 2 = red. palette 1 color 1 = blue
func newSceneWithTile1() *ppu.PPU {
	p, _ := newTestPPU(cart.Horizontal)
	writeVRAM(p, 0x0010, 0xFF, 0x00)
	writeVRAM(p, 0x0018, 0x00, 0xFF)
	writeVRAM(p, 0x3F00, 0x0F, 0x30, 0x16)
	writeVRAM(p, 0x3F05, 0x21)
	return p
}

func TestBackgroundDrawsBackdropWhenDisabled(t *testing.T) {
	p := newSceneWithTile1()
	writeVRAM(p, 0x2000, 1)
	runFrames(p)
	if got := pixel(p, 0, 0); got != black {
		t.Errorf("pixel(0,0) = %#08x, want %#08x", got, uint32(black))
	}
}

func TestBackgroundTilePixels(t *testing.T) {
	p := newSceneWithTile1()
	writeVRAM(p, 0x2000, 1)
	p.WriteRegister(0x2001, 0x0A) // background + left 8 pixels
	runFrames(p)

	tests := []struct {
		x, y int
		want uint32
	}{
		{0, 0, white},
		{7, 0, white},
		{8, 0, black}, // next tile is tile 0, blank
		{0, 1, red},
		{7, 1, red},
		{0, 2, black}, // rows 2-7 of tile 1 are empty
	}
	for _, tt := range tests {
		if got := pixel(p, tt.x, tt.y); got != tt.want {
			t.Errorf("pixel(%d,%d) = %#08x, want %#08x", tt.x, tt.y, got, tt.want)
		}
	}
}

func TestBackgroundAttributeSelectsPalette(t *testing.T) {
	p := newSceneWithTile1()
	writeVRAM(p, 0x2000, 1, 1, 1, 1)
	writeVRAM(p, 0x23C0, 0x01) // top-left 16x16 quadrant uses palette 1
	p.WriteRegister(0x2001, 0x0A)
	runFrames(p)

	if got := pixel(p, 0, 0); got != blue {
		t.Errorf("pixel(0,0) = %#08x, want %#08x", got, uint32(blue))
	}
	if got := pixel(p, 15, 0); got != blue {
		t.Errorf("pixel(15,0) = %#08x, want %#08x", got, uint32(blue))
	}
	if got := pixel(p, 16, 0); got != white {
		t.Errorf("pixel(16,0) = %#08x, want %#08x (next quadrant, palette 0)", got, uint32(white))
	}
}

func TestBackgroundLeftClip(t *testing.T) {
	p := newSceneWithTile1()
	writeVRAM(p, 0x2000, 1, 1)
	p.WriteRegister(0x2001, 0x08) // background on, left 8 pixels hidden
	runFrames(p)

	if got := pixel(p, 0, 0); got != black {
		t.Errorf("pixel(0,0) = %#08x, want %#08x (clipped)", got, uint32(black))
	}
	if got := pixel(p, 8, 0); got != white {
		t.Errorf("pixel(8,0) = %#08x, want %#08x", got, uint32(white))
	}
}

func TestBackgroundFineXScroll(t *testing.T) {
	p, _ := newTestPPU(cart.Horizontal)
	writeVRAM(p, 0x0010, 0x01, 0x00) // only the rightmost pixel of row 0 is set
	writeVRAM(p, 0x3F00, 0x0F, 0x30)
	writeVRAM(p, 0x2000, 1)
	p.WriteRegister(0x2005, 7)
	p.WriteRegister(0x2005, 0)
	p.WriteRegister(0x2001, 0x0A)
	runFrames(p)

	if got := pixel(p, 0, 0); got != white {
		t.Errorf("pixel(0,0) = %#08x, want %#08x", got, uint32(white))
	}
	if got := pixel(p, 1, 0); got != black {
		t.Errorf("pixel(1,0) = %#08x, want %#08x", got, uint32(black))
	}
}

func TestBackgroundCoarseXScroll(t *testing.T) {
	p := newSceneWithTile1()
	writeVRAM(p, 0x2003, 1)     // tile 1 in the 4th column
	p.WriteRegister(0x2005, 24) // coarse x = 3
	p.WriteRegister(0x2005, 0)
	p.WriteRegister(0x2001, 0x0A)
	runFrames(p)

	if got := pixel(p, 0, 0); got != white {
		t.Errorf("pixel(0,0) = %#08x, want %#08x", got, uint32(white))
	}
	if got := pixel(p, 8, 0); got != black {
		t.Errorf("pixel(8,0) = %#08x, want %#08x", got, uint32(black))
	}
}

func TestBackgroundPatternTableSelect(t *testing.T) {
	p := newSceneWithTile1()
	writeVRAM(p, 0x1018, 0xFF) // tile 1 in the high pattern table, row 0 high plane only = color 2
	writeVRAM(p, 0x2000, 1)
	p.WriteRegister(0x2000, 0x10)
	p.WriteRegister(0x2001, 0x0A)
	runFrames(p)

	if got := pixel(p, 0, 0); got != red {
		t.Errorf("pixel(0,0) = %#08x, want %#08x", got, uint32(red))
	}
}