package chip8

import "fmt"

const graphicsBufferSize = 64 * 32

type Chip8 struct {
	address_register uint16
	beep_timer       uint16
	draw_required    bool
	delay_timer      uint16
	graphics         [graphicsBufferSize]uint8
	keys             [16]uint8
	memory           [4096]uint8
	opcode           uint16
	pc               uint16
	registers        [16]uint8 // an array - has a fixed length
	stack            []uint16  // a slice - basically a c++ vector
}

// we can't have const arrays in go
// This is a good a solution as any
func getLetters() []uint8 {
	return []uint8{
		0xF0, 0x90, 0x90, 0x90, 0xF0, // 0
		0x20, 0x60, 0x20, 0x20, 0x70, // 1
		0xF0, 0x10, 0xF0, 0x80, 0xF0, // 2
		0xF0, 0x10, 0xF0, 0x10, 0xF0, // 3
		0x90, 0x90, 0xF0, 0x10, 0x10, // 4
		0xF0, 0x80, 0xF0, 0x10, 0xF0, // 5
		0xF0, 0x80, 0xF0, 0x90, 0xF0, // 6
		0xF0, 0x10, 0x20, 0x40, 0x40, // 7
		0xF0, 0x90, 0xF0, 0x90, 0xF0, // 8
		0xF0, 0x90, 0xF0, 0x10, 0xF0, // 9
		0xF0, 0x90, 0xF0, 0x90, 0x90, // A
		0xE0, 0x90, 0xE0, 0x90, 0xE0, // B
		0xF0, 0x80, 0x80, 0x80, 0xF0, // C
		0xE0, 0x90, 0x90, 0x90, 0xE0, // D
		0xF0, 0x80, 0xF0, 0x80, 0xF0, // E
		0xF0, 0x80, 0xF0, 0x80, 0x80} // F
}

func NewCHIP8(prog []uint8) *Chip8 {
	cpu := Chip8{pc: 0x200}
	memory_slice := cpu.memory[:80]
	copy(memory_slice, getLetters())
	memory_slice = cpu.memory[200:]
	copy(memory_slice, prog)

	// Do some extra checking to ensure the right
	// Stuff is copied

	return &cpu
}

func (cpu *Chip8) GetGraphicsBuffer() [graphicsBufferSize]uint8 {
	return cpu.graphics
}

func (cpu *Chip8) clearDisplay() {
	// fuck it the gc can do the hard work for us
	cpu.graphics = [64 * 32]uint8{}
	cpu.draw_required = true
}

// what if there's nothing in the stack?
// return something sensible
func (cpu *Chip8) leaveFunction() {
	cpu.pc = cpu.stack[len(cpu.stack)-1]
	cpu.stack[len(cpu.stack)-1] = 0
	cpu.stack = cpu.stack[:len(cpu.stack)-1]
}

func (cpu *Chip8) goTo() {
	cpu.pc = cpu.opcode & 0x0FFF
}

func (cpu *Chip8) callSubroutine() {
	cpu.stack = append(cpu.stack, cpu.pc)
	cpu.pc = cpu.opcode & 0x0FFF
}

func (cpu *Chip8) skipIfRegisterEqual() {
	r := (cpu.opcode) >> 8 & 0x0F
	if cpu.registers[r] == uint8(cpu.opcode&0xFF) {
		cpu.pc += 2
	}
}

func (cpu *Chip8) skipIfRegisterNotEqual() {
	r := (cpu.opcode) >> 8 & 0x0F
	if cpu.registers[r] != uint8(cpu.opcode&0xFF) {
		cpu.pc += 2
	}
}

func (cpu *Chip8) skipIfRegistersEqual() {
	x, y := (cpu.opcode>>8)&0x0F, (cpu.opcode>>4)&0x0F
	if cpu.registers[x] == cpu.registers[y] {
		cpu.pc += 2
	}
}

func (cpu *Chip8) setRegisterTo() {
	r := (cpu.opcode >> 8) & 0x0F
	cpu.registers[r] = uint8(cpu.opcode & 0xFF)
}

func (cpu *Chip8) RegisterPlusEqualsNN() {} // QUESTION HERE - WHAT DO IF IT WOULD WRAP ROUND?

func main() {
	fmt.Printf("Hello world!\n")
	prog := []uint8{1, 2, 3, 4}
	new_cpu := NewCHIP8(prog)
	fmt.Printf("%d\n", new_cpu.opcode)
}