//go:build windows

package api

import (
	"syscall"
	"unsafe"
)

var (
	kernel32              = syscall.NewLazyDLL("kernel32.dll")
	globalMemoryStatusEx  = kernel32.NewProc("GlobalMemoryStatusEx")
	getSystemTimes        = kernel32.NewProc("GetSystemTimes")
)

// MEMORYSTATUSEX structure
type memoryStatusEx struct {
	dwLength                uint32
	dwMemoryLoad            uint32
	ullTotalPhys            uint64
	ullAvailPhys            uint64
	ullTotalPageFile        uint64
	ullAvailPageFile        uint64
	ullTotalVirtual         uint64
	ullAvailVirtual         uint64
	ullAvailExtendedVirtual uint64
}

func getMemoryInfo() (total, used uint64) {
	var ms memoryStatusEx
	ms.dwLength = uint32(unsafe.Sizeof(ms))

	ret, _, _ := globalMemoryStatusEx.Call(uintptr(unsafe.Pointer(&ms)))
	if ret == 0 {
		return 0, 0
	}

	return ms.ullTotalPhys, ms.ullTotalPhys - ms.ullAvailPhys
}

type filetime struct {
	dwLowDateTime  uint32
	dwHighDateTime uint32
}

func (ft filetime) ticks() uint64 {
	return uint64(ft.dwHighDateTime)<<32 | uint64(ft.dwLowDateTime)
}

var prevIdleWin, prevTotalWin uint64

func getCPUUsage() float64 {
	var idleTime, kernelTime, userTime filetime

	ret, _, _ := getSystemTimes.Call(
		uintptr(unsafe.Pointer(&idleTime)),
		uintptr(unsafe.Pointer(&kernelTime)),
		uintptr(unsafe.Pointer(&userTime)),
	)
	if ret == 0 {
		return 0
	}

	idle := idleTime.ticks()
	total := kernelTime.ticks() + userTime.ticks() // kernel includes idle

	deltaTotal := total - prevTotalWin
	deltaIdle := idle - prevIdleWin
	prevIdleWin = idle
	prevTotalWin = total

	if deltaTotal == 0 {
		return 0
	}

	return float64(deltaTotal-deltaIdle) / float64(deltaTotal) * 100
}