package system

import (
	"syscall"
	"unsafe"
)

var (
	modkernel32 = syscall.NewLazyDLL("kernel32.dll")

	procGlobalMemoryStatusEx = modkernel32.NewProc("GlobalMemoryStatusEx")
)

// https://msdn.microsoft.com/en-us/library/windows/desktop/aa366589(v=vs.85).aspx
// https://msdn.microsoft.com/en-us/library/windows/desktop/aa366770(v=vs.85).aspx
type memorystatusex struct {
	dwLength                uint32
	dwMemoryLoad            uint32
	ullTotalPhys            uint64
	ullAvailPhys            uint64
	ullTotalPageFile        uint64
	ullAvailPageFile        uint64
	ullTotalVirtual         uint64
	ullAvailVirtual         uint64
	ullAvailExtendedVirtual uint64
}

// ReadMemInfo retrieves memory statistics of the host system and returns a
//  MemInfo type.
func ReadMemInfo() (*MemInfo, error) {
	msi := &memorystatusex{
		dwLength: 64,
	}
	r1, _, _ := procGlobalMemoryStatusEx.Call(uintptr(unsafe.Pointer(msi)))
	if r1 == 0 {
		return &MemInfo{}, nil
	}
	return &MemInfo{
		MemTotal:  int64(msi.ullTotalPhys),
		MemFree:   int64(msi.ullAvailPhys),
		SwapTotal: int64(msi.ullTotalPageFile),
		SwapFree:  int64(msi.ullAvailPageFile),
	}, nil
}