package main

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/exec"
	"os/signal"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/NVIDIA/go-nvml/pkg/nvml"
	"github.com/shirou/gopsutil/v3/cpu"
	"github.com/shirou/gopsutil/v3/disk"
	"github.com/shirou/gopsutil/v3/net"
	"github.com/shirou/gopsutil/v3/process"
)

const (
	checkInterval    = 10 * time.Second
	monitoringPeriod = 3 * time.Minute
	cpuThreshold     = 20.0            // percentage
	gpuThreshold     = 20.0            // percentage
	diskThreshold    = 5 * 1024 * 1024 // 5 MB/s
	networkThreshold = 1 * 1024 * 1024 // 1 MB/s
	httpPort         = 8081
)

type ResourceUsage struct {
	Timestamp      time.Time `json:"timestamp"`
	CpuUsage       float64   `json:"cpu_usage"`
	GpuUsage       float64   `json:"gpu_usage"`
	GpuAvailable   bool      `json:"gpu_available"`
	DiskIO         float64   `json:"disk_io"`
	NetworkIO      float64   `json:"network_io"`
	SshConnections int       `json:"ssh_connections"`
	ActiveUsers    int       `json:"active_users"`
	HttpRequests   int       `json:"http_requests"`
}

type StatusResponse struct {
	Usage     ResourceUsage `json:"usage"`
	Blockers  []string      `json:"blockers"`
	Timestamp time.Time     `json:"timestamp"`
	SleepAt   time.Time     `json:"sleep_at"`
}

var (
	statusMutex    sync.RWMutex
	currentStatus  ResourceUsage
	nvmlAvailable  bool
	networkBytesIO uint64
	diskBytesIO    uint64
	nextSleepTime  time.Time
)

func main() {
	// Check if running as root
	if os.Geteuid() != 0 {
		log.Fatal("This program must be run as root")
	}

	// Initialize NVML for GPU monitoring
	ret := nvml.Init()
	if !errors.Is(ret, nvml.SUCCESS) {
		log.Printf("Warning: Could not initialize NVML: %v", ret)
		nvmlAvailable = false
	} else {
		nvmlAvailable = true
		defer nvml.Shutdown()
	}

	// Set up signal handling
	sigChan := make(chan os.Signal, 1)
	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)

	// Start HTTP server with context
	srv := startHTTPServer()

	ticker := time.NewTicker(checkInterval)
	defer ticker.Stop()

	log.Printf("Starting idle monitoring. System will suspend when:\n")
	log.Printf("- Average CPU usage across all cores < %.1f%%\n", cpuThreshold)
	if nvmlAvailable {
		log.Printf("- Average GPU usage across all GPUs < %.1f%%\n", gpuThreshold)
	} else {
		log.Printf("- GPU monitoring disabled (NVML initialization failed)")
	}
	log.Printf("- Disk I/O < %.1f MB/s\n", float64(diskThreshold)/(1024*1024))
	log.Printf("- Network I/O < %.1f MB/s\n", float64(networkThreshold)/(1024*1024))
	log.Printf("- No active SSH connections\n")
	log.Printf("- No active user sessions\n")
	log.Printf("- Over the last %v\n", monitoringPeriod)
	log.Printf("HTTP status endpoint available at http://localhost:%d/status\n", httpPort)
	log.Printf("Press Ctrl+C to exit\n")

mainLoop:
	for {
		select {
		case sig := <-sigChan:
			log.Printf("Received signal %v, shutting down...", sig)
			break mainLoop
		case <-ticker.C:
			updateCurrentUsage()
			blocked, _ := getBlockers()
			if blocked {
				delaySleep()
			}

			if time.Now().After(nextSleepTime) {
				log.Printf("System status before suspend:\n")
				log.Printf("- CPU: %.1f%%\n", currentStatus.CpuUsage)
				if nvmlAvailable {
					log.Printf("- GPU: %.1f%%\n", currentStatus.GpuUsage)
				}
				log.Printf("- SSH connections: %d\n", currentStatus.SshConnections)
				log.Printf("- Active users: %d\n", currentStatus.ActiveUsers)
				log.Printf("- Disk I/O: %.1f MB/s\n", currentStatus.DiskIO/(1024*1024))
				log.Printf("- Network I/O: %.1f MB/s\n", currentStatus.NetworkIO/(1024*1024))
				log.Println("System has been idle for the monitoring period. Suspending...")
				if err := suspendSystem(); err != nil {
					log.Printf("Failed to suspend system: %v", err)
				}
				nextSleepTime = time.Now().Add(monitoringPeriod)
				log.Printf("Resumed")
			}
		}
	}

	// Graceful shutdown of HTTP server
	shutdownCtx, shutdownCancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer shutdownCancel()

	if err := srv.Shutdown(shutdownCtx); err != nil {
		log.Printf("HTTP server shutdown error: %v", err)
	}

	log.Println("Goodbye!")
}

func startHTTPServer() *http.Server {
	srv := &http.Server{
		Addr: fmt.Sprintf(":%d", httpPort),
	}

	http.HandleFunc("/status", handleStatus)
	http.HandleFunc("/reset", handleReset)

	go func() {
		if err := srv.ListenAndServe(); !errors.Is(err, http.ErrServerClosed) {
			log.Printf("HTTP server error: %v", err)
		}
	}()

	return srv
}

func handleStatus(w http.ResponseWriter, _ *http.Request) {
	statusMutex.RLock()
	defer statusMutex.RUnlock()

	_, blockers := getBlockersNoLock()

	response := StatusResponse{
		Usage:     currentStatus,
		Blockers:  blockers,
		Timestamp: time.Now(),
		SleepAt:   nextSleepTime,
	}

	w.Header().Set("Content-Type", "application/json")
	err := json.NewEncoder(w).Encode(response)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}

func handleReset(w http.ResponseWriter, _ *http.Request) {
	statusMutex.Lock()
	defer statusMutex.Unlock()

	delaySleep()

	currentStatus.HttpRequests++
	nextSleepTime = time.Now().Add(monitoringPeriod)
	w.WriteHeader(http.StatusOK)
}

func getBlockers() (bool, []string) {
	statusMutex.Lock()
	defer statusMutex.Unlock()
	return getBlockersNoLock()
}

func getBlockersNoLock() (bool, []string) {
	blocked := true
	blockers := []string{}

	if currentStatus.CpuUsage >= cpuThreshold {
		blockers = append(blockers,
			fmt.Sprintf("CPU usage too high: %.1f%% >= %.1f%%", currentStatus.CpuUsage, cpuThreshold))
	}
	if nvmlAvailable && currentStatus.GpuUsage >= gpuThreshold {
		blockers = append(blockers,
			fmt.Sprintf("GPU usage too high: %.1f%% >= %.1f%%", currentStatus.GpuUsage, gpuThreshold))
	}
	if currentStatus.DiskIO >= float64(diskThreshold) {
		blockers = append(blockers,
			fmt.Sprintf("Disk I/O too high: %.1f MB/s >= %.1f MB/s",
				currentStatus.DiskIO/(1024*1024), float64(diskThreshold)/(1024*1024)))
	}
	if currentStatus.NetworkIO >= float64(networkThreshold) {
		blockers = append(blockers,
			fmt.Sprintf("Network I/O too high: %.1f MB/s >= %.1f MB/s",
				currentStatus.NetworkIO/(1024*1024), float64(networkThreshold)/(1024*1024)))
	}

	if currentStatus.SshConnections > 0 {
		blockers = append(blockers,
			fmt.Sprintf("Active SSH connections: %d", currentStatus.SshConnections))
	}
	if currentStatus.ActiveUsers > 0 {
		blockers = append(blockers,
			fmt.Sprintf("Active user sessions: %d", currentStatus.ActiveUsers))
	}

	if currentStatus.HttpRequests > 0 {
		blockers = append(blockers,
			fmt.Sprintf("HTTP requests received: %d", currentStatus.HttpRequests))
	}

	if len(blockers) == 0 {
		blockers = append(blockers, "No blockers - system can sleep")
		blocked = false
	}
	return blocked, blockers
}

func updateCurrentUsage() {
	statusMutex.Lock()
	defer statusMutex.Unlock()

	usage := ResourceUsage{
		Timestamp:    time.Now(),
		GpuAvailable: nvmlAvailable,
	}

	// Get CPU usage across all cores
	if cpuPercent, err := cpu.Percent(0, true); err == nil && len(cpuPercent) > 0 {
		// Calculate average CPU usage across all cores
		var totalCPU float64
		for _, percent := range cpuPercent {
			totalCPU += percent
		}
		usage.CpuUsage = totalCPU / float64(len(cpuPercent))
	}

	// Get GPU usage across all GPUs if available
	if nvmlAvailable {
		count, ret := nvml.DeviceGetCount()
		if errors.Is(ret, nvml.SUCCESS) && count > 0 {
			var totalGPU float64
			var activeGPUs int
			for i := 0; i < count; i++ {
				device, ret := nvml.DeviceGetHandleByIndex(i)
				if errors.Is(ret, nvml.SUCCESS) {
					utilization, ret := device.GetUtilizationRates()
					if errors.Is(ret, nvml.SUCCESS) {
						totalGPU += float64(utilization.Gpu)
						activeGPUs++
					}
				}
			}
			if activeGPUs > 0 {
				usage.GpuUsage = totalGPU / float64(activeGPUs)
			}
		}
	}

	// Get disk I/O
	if diskStats, err := disk.IOCounters(); err == nil {
		var totalIO uint64
		for _, stat := range diskStats {
			totalIO += stat.ReadBytes + stat.WriteBytes
		}

		previousDiskBytesIO := diskBytesIO
		diskBytesIO = totalIO
		diff := diskBytesIO - previousDiskBytesIO
		usage.DiskIO = float64(diff) / checkInterval.Seconds()
	}

	// Get network I/O
	if netStats, err := net.IOCounters(false); err == nil && len(netStats) > 0 {
		previousNetworkBytesIO := networkBytesIO
		networkBytesIO = netStats[0].BytesSent + netStats[0].BytesRecv
		diff := networkBytesIO - previousNetworkBytesIO
		usage.NetworkIO = float64(diff) / checkInterval.Seconds()
	}

	// Count SSH connections
	if sshCount, err := getSSHConnectionCount(); err == nil {
		usage.SshConnections = sshCount
	}

	// Count active user sessions
	if userCount, err := getActiveUserCount(); err == nil {
		usage.ActiveUsers = userCount
	}

	currentStatus = usage
}

func getSSHConnectionCount() (int, error) {
	processes, err := process.Processes()
	if err != nil {
		return 0, err
	}

	count := 0
	for _, p := range processes {
		name, err := p.Name()
		if err != nil {
			continue
		}
		if name == "sshd" {
			cmdline, err := p.Cmdline()
			if err != nil {
				continue
			}
			// Only count sshd processes that are handling connections
			// The main sshd process doesn't have "@" in its cmdline
			if strings.Contains(cmdline, "@") {
				count++
			}
		}
	}
	return count, nil
}

func getActiveUserCount() (int, error) {
	out, err := exec.Command("who", "-s").Output()
	if err != nil {
		return 0, err
	}

	// Count non-empty lines
	lines := strings.Split(strings.TrimSpace(string(out)), "\n")
	count := 0
	for _, line := range lines {
		if line != "" {
			count++
		}
	}
	return count, nil
}

func suspendSystem() error {
	cmd := exec.Command("systemctl", "suspend")
	return cmd.Run()
}

func delaySleep() {
	nextSleepTime = time.Now().Add(monitoringPeriod)
}