package nes

import (
	"crecher.net/gones/v2/cart"
	"crecher.net/gones/v2/cpu"
	"crecher.net/gones/v2/ppu"
)

type Console struct {
	CPU  *cpu.CPU
	PPU  *ppu.PPU
	Cart *cart.Cartridge
	RAM  [0x800]uint8
	// APU, controllers once they exist
	cycles uint64
}

func New(c *cart.Cartridge) *Console {
	n := &Console{Cart: c}
	n.PPU = ppu.New(c.Mapper, c.Mirroring)
	n.CPU = cpu.NewCPU(n)
	n.CPU.Reset()
	return n
}

// Step runs one CPU instruction and the PPU dots (3 per CPU cycle) that
// elapse alongside it, firing NMI on a PPUCTRL/vblank edge. PPU state seen
// by bus accesses mid-instruction still lags behind by up to one
// instruction's worth of dots, since the CPU isn't cycle-stepped yet (see
// README: "CPU stall hook and proper IRQ/NMI line (polled between
// instructions)") - timing-sensitive register logic (the $2002 race window,
// NMI edge detection) is implemented to the real dot granularity and is
// exercised directly in the ppu package's tests, but end-to-end precision
// against real games/test ROMs needs that CPU work to land too.
func (n *Console) Step() int {
	cycles := n.CPU.Step()
	n.cycles += uint64(cycles)
	for i := 0; i < cycles*3; i++ {
		n.PPU.Tick()
		if n.PPU.PollNMI() {
			n.CPU.NMI()
		}
	}
	return cycles
}

func (n *Console) StepFrame() {
	// 29780 is roughly one frame:
	// ~ 1789773 cycles per sec
	// ~ 60.1 fps
	// 1789773 / 60.1 = 29779.916...
	const cyclesPerFrame = 29780
	for done := 0; done < cyclesPerFrame; {
		done += n.Step()
	}
}