//go:build windows

package mem

import (
	"syscall"
	"unsafe"
)

func reserve(total_address_space uintptr) ([]byte, error) {
	addr, _, err := _VirtualAlloc.Call(0, total_address_space, _MEM_RESERVE, _PAGE_NOACCESS)
	if addr == 0 {
		return nil, err
	}

	return unsafe.Slice((*byte)(unsafe.Pointer(addr)), total_address_space), nil
}

func release(reserved []byte) error {
	res, _, err := _VirtualFree.Call(uintptr(unsafe.Pointer(&reserved[0])), 0, _MEM_RELEASE)
	if res == 0 {
		return err
	}

	return nil
}

func commit(reserved []byte, access Access) error {
	ret, _, err := _VirtualAlloc.Call(
		uintptr(unsafe.Pointer(&reserved[0])),
		uintptr(len(reserved)),
		_MEM_COMMIT,
		uintptr(access_to_prot(access)),
	)
	if ret == 0 {
		return err
	}

	return nil
}

func decommit(committed []byte) error {
	ret, _, err := _VirtualFree.Call(
		uintptr(unsafe.Pointer(&committed[0])),
		uintptr(len(committed)),
		_MEM_DECOMMIT,
	)
	if ret == 0 {
		return err
	}

	return nil
}

var (
	kernel32      = syscall.NewLazyDLL("kernel32.dll")
	_VirtualAlloc = kernel32.NewProc("VirtualAlloc")
	_VirtualFree  = kernel32.NewProc("VirtualFree")
)

const (
	_MEM_COMMIT   = 0x1000
	_MEM_RESERVE  = 0x2000
	_MEM_DECOMMIT = 0x4000
	_MEM_RELEASE  = 0x8000

	_PAGE_NOACCESS  = 0x01
	_PAGE_READONLY  = 0x02
	_PAGE_READWRITE = 0x04

	_PAGE_EXECUTE_READ      = 0x20
	_PAGE_EXECUTE_READWRITE = 0x40
)

func access_to_prot(access Access) uint32 {
	switch access {
	case AccessRead | AccessWrite | AccessExecute:
		return _PAGE_EXECUTE_READWRITE
	case AccessRead | AccessExecute:
		return _PAGE_EXECUTE_READ
	case AccessRead | AccessWrite:
		return _PAGE_READWRITE
	case AccessRead:
		return _PAGE_READONLY
	default:
		return _PAGE_NOACCESS
	}
}