package main

import (
	"fmt"
	"log"
	"os"
	"os/signal"
	"time"

	"github.com/postfinance/single"
	"github.com/shirou/gopsutil/process"
	"golang.org/x/sys/windows"
)

const (
	memThreshold   = 512 * 1024 * 1024
	selfPriority   = windows.IDLE_PRIORITY_CLASS
	targetPriority = windows.HIGH_PRIORITY_CLASS
)

func setPriority(pid int32, class uint32) error {
	h, err := windows.OpenProcess(windows.PROCESS_SET_INFORMATION, false, uint32(pid))
	if err != nil {
		return fmt.Errorf("open process %d: %w", pid, err)
	}
	defer windows.CloseHandle(h)
	return windows.SetPriorityClass(h, class)
}

func main() {
	lock, err := single.New("autoPriority")
	if err != nil {
		log.Fatalf("create lock: %v", err)
	}
	if err := lock.Lock(); err != nil {
		windows.MessageBox(0,
			windows.StringToUTF16Ptr("The program is already running.\nYou can close it via the Task Manager."),
			windows.StringToUTF16Ptr("autoPriority"),
			windows.MB_OK|windows.MB_ICONWARNING,
		)
		os.Exit(1)
	}
	defer lock.Unlock()

	if err := setPriority(int32(os.Getpid()), selfPriority); err != nil {
		log.Printf("set self priority: %v", err)
	}

	sig := make(chan os.Signal, 1)
	signal.Notify(sig, os.Interrupt)

	tk := time.NewTicker(time.Minute)
	defer tk.Stop()

	for {
		select {
		case <-sig:
			log.Println("exit")
			return
		case <-tk.C:
			procs, err := process.Processes()
			if err != nil {
				log.Printf("list processes: %v", err)
				continue
			}
			for _, p := range procs {
				m, err := p.MemoryInfo()
				if err != nil {
					continue
				}
				if m.RSS >= memThreshold {
					if err := setPriority(p.Pid, targetPriority); err != nil {
						log.Printf("PID %d: %v", p.Pid, err)
					}
				}
			}
		}
	}
}