package machine

//  System struct, init, constants, fontset

System :: struct {
	// 4kb ram
	memory: [4096]u8,
	// 16 general purpose 8bit registers 0 -> F
	v: [16]u8,
	// Call stack, up to 16, 2 byte addresses.
	stack: [16]u16,
	// Stack pointer
	sp: u8,
	// index register
	i: u16,
	// PC program counter
	pc: u16,
	// 64x32-pixel monochrome display
	display: [32][64]u8,
	// Keypad
	keypad: [16]bool,
	// -1 = no key pressed, 0-15 = key index
	current_key: i16,
	// Timers
	delay_timer: u8,
	sound_timer: u8,
}

FONT_SET := [80]u8 {
	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
}

init :: proc() -> System {
	// log.info("Booting chip 8 cpu")

	// Structs are zero initialized so timers, sp etc are good.
	s := System { pc = 0x200 }

	// load fonts into the memory
	for v, i in FONT_SET {
		s.memory[i] = v
	}

	return s
}

run_machine :: proc(s: ^System, cycles: int) {
	// CPU cycles
	for _ in 0..<cycles {
		handle_input(s)
		cycle(s)
	}
}

reset_machine :: proc(s: ^System) {
	s.memory = {}
	s.v = {}
	s.stack = {}
	s.sp = 0
	s.i = 0
	s.pc = 0x200
	s.display = {}
	s.keypad = {}
	s.current_key = -1
	s.delay_timer = 0
	s.sound_timer = 0

	for v, i in FONT_SET {
		s.memory[i] = v
	}
}