package x64

import "git.akyoto.dev/cli/q/src/cpu"

// memoryAccessDynamic encodes a memory access using the value of a register as an offset.
func memoryAccessDynamic(code []byte, opCode8 byte, opCode32 byte, destination cpu.Register, offset cpu.Register, numBytes byte, source cpu.Register) []byte {
	var (
		w      = byte(0)
		r      = byte(0)
		x      = byte(0)
		b      = byte(0)
		opCode = opCode32
		mod    = AddressMemory
	)

	if numBytes == 1 {
		opCode = opCode8
	}

	if offset == RSP {
		tmp := offset
		offset = destination
		destination = tmp
	}

	if numBytes == 8 {
		w = 1
	}

	if source > 0b111 {
		r = 1
		source &= 0b111
	}

	if offset > 0b111 {
		x = 1
		offset &= 0b111
	}

	if destination > 0b111 {
		b = 1
		destination &= 0b111
	}

	if destination == RBP || destination == R13 {
		mod = AddressMemoryOffset8
	}

	if numBytes == 2 {
		code = append(code, 0x66)
	}

	code = append(code, REX(w, r, x, b))
	code = append(code, opCode)
	code = append(code, ModRM(mod, byte(source), 0b100))
	code = append(code, SIB(Scale1, byte(offset), byte(destination)))

	if mod == AddressMemoryOffset8 {
		code = append(code, 0x00)
	}

	return code
}