package tests

import (
	"testing"

	"crecher.net/gones/v2/nes"
)

func fillPage(n *nes.Console, page uint8) {
	for i := 0; i < 256; i++ {
		n.Write(uint16(page)<<8|uint16(i), uint8(i))
	}
}

func TestOAMDMACopiesPage(t *testing.T) {
	n := newTestConsole(t)
	fillPage(n, 0x02)
	n.Write(0x4014, 0x02)

	for i := 0; i < 256; i++ {
		if n.PPU.OAM[i] != uint8(i) {
			t.Fatalf("OAM[%d] = %d, want %d", i, n.PPU.OAM[i], i)
		}
	}
}

func TestOAMDMAStartsAtOAMAddr(t *testing.T) {
	n := newTestConsole(t)
	fillPage(n, 0x03)
	n.Write(0x2003, 0x10)
	n.Write(0x4014, 0x03)

	// source byte 0 lands at OAM[0x10], and the copy wraps around
	for _, i := range []int{0, 1, 0xF0, 0xFF} {
		if got := n.PPU.OAM[(0x10+i)&0xFF]; got != uint8(i) {
			t.Errorf("OAM[0x%02X] = %d, want %d", (0x10+i)&0xFF, got, i)
		}
	}
}

// runs `lda ; sta $4014` from RAM and returns the cycles the sta step took
func dmaStepCycles(t *testing.T, lda []uint8) int {
	t.Helper()
	n := newTestConsole(t)
	prog := append(lda, 0x8D, 0x14, 0x40) // sta $4014
	for i, b := range prog {
		n.Write(0x0200+uint16(i), b)
	}
	n.Write(0x0000, 0x02) // for the zero page lda
	n.CPU.PC = 0x0200
	n.Step()
	return n.Step()
}

func TestOAMDMAStallCycles(t *testing.T) {
	// reset leaves the cpu at 7 cycles
	// lda #imm (2): sta ends on cycle 13, odd -> 4 + 514
	if got := dmaStepCycles(t, []uint8{0xA9, 0x02}); got != 518 {
		t.Errorf("odd start: sta step = %d cycles, want 518", got)
	}
	// lda zp (3): sta ends on cycle 14, even -> 4 + 513
	if got := dmaStepCycles(t, []uint8{0xA5, 0x00}); got != 517 {
		t.Errorf("even start: sta step = %d cycles, want 517", got)
	}
}

func TestOAMDMAAdvancesCPUCycles(t *testing.T) {
	n := newTestConsole(t)
	for i, b := range []uint8{0xA9, 0x02, 0x8D, 0x14, 0x40} {
		n.Write(0x0200+uint16(i), b)
	}
	n.CPU.PC = 0x0200
	n.Step()
	n.Step()
	if n.CPU.Cycles != 7+2+4+514 {
		t.Errorf("CPU.Cycles = %d, want %d", n.CPU.Cycles, 7+2+4+514)
	}
}