package service

import (
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strconv"
	"strings"
	"syscall"
	"time"

	"github.com/mhsanaei/3x-ui/v2/config"
	"github.com/mhsanaei/3x-ui/v2/logger"
)

// PanelService provides business logic for panel management operations.
// It handles panel restart, updates, and system-level panel controls.
type PanelService struct{}

// PanelUpdateInfo contains the current and latest available panel versions.
type PanelUpdateInfo struct {
	CurrentVersion  string `json:"currentVersion"`
	LatestVersion   string `json:"latestVersion"`
	UpdateAvailable bool   `json:"updateAvailable"`
}

func (s *PanelService) RestartPanel(delay time.Duration) error {
	p, err := os.FindProcess(syscall.Getpid())
	if err != nil {
		return err
	}
	go func() {
		time.Sleep(delay)
		err := p.Signal(syscall.SIGHUP)
		if err != nil {
			logger.Error("failed to send SIGHUP signal:", err)
		}
	}()
	return nil
}

// GetUpdateInfo checks GitHub for the latest 3x-ui release.
func (s *PanelService) GetUpdateInfo() (*PanelUpdateInfo, error) {
	latest, err := fetchLatestPanelVersion()
	if err != nil {
		return nil, err
	}
	current := config.GetVersion()
	return &PanelUpdateInfo{
		CurrentVersion:  current,
		LatestVersion:   latest,
		UpdateAvailable: isNewerVersion(latest, current),
	}, nil
}

// StartUpdate starts the official updater outside of the current web request.
func (s *PanelService) StartUpdate() error {
	if runtime.GOOS != "linux" {
		return fmt.Errorf("panel web update is supported only on Linux installations")
	}

	bash, err := exec.LookPath("bash")
	if err != nil {
		return fmt.Errorf("bash is required to run the panel updater: %w", err)
	}
	curl, err := exec.LookPath("curl")
	if err != nil {
		return fmt.Errorf("curl is required to download the panel updater: %w", err)
	}

	mainFolder, serviceFolder := resolveUpdateFolders()
	updateScript := fmt.Sprintf("set -o pipefail; %s -fLs https://raw.githubusercontent.com/MHSanaei/3x-ui/main/update.sh | %s", shellQuote(curl), shellQuote(bash))

	if systemdRun, err := exec.LookPath("systemd-run"); err == nil {
		unitName := fmt.Sprintf("x-ui-web-update-%d", time.Now().Unix())
		cmd := exec.Command(systemdRun,
			"--unit", unitName,
			"--setenv", "XUI_MAIN_FOLDER="+mainFolder,
			"--setenv", "XUI_SERVICE="+serviceFolder,
			bash, "-lc", updateScript,
		)
		out, err := cmd.CombinedOutput()
		if err != nil {
			output := strings.TrimSpace(string(out))
			if !strings.Contains(output, "System has not been booted with systemd") &&
				!strings.Contains(output, "Failed to connect to bus") {
				return fmt.Errorf("failed to start panel update job: %w: %s", err, output)
			}
			logger.Warning("systemd-run is unavailable, falling back to detached update process:", output)
		} else {
			logger.Infof("started panel update job via systemd-run unit %s", unitName)
			return nil
		}
	}

	cmd := exec.Command(bash, "-lc", updateScript)
	cmd.Env = append(os.Environ(),
		"XUI_MAIN_FOLDER="+mainFolder,
		"XUI_SERVICE="+serviceFolder,
	)
	setDetachedProcess(cmd)
	if err := cmd.Start(); err != nil {
		return fmt.Errorf("failed to start panel update job: %w", err)
	}
	if err := cmd.Process.Release(); err != nil {
		logger.Warning("failed to release panel update process:", err)
	}
	logger.Infof("started panel update job with pid %d", cmd.Process.Pid)
	return nil
}

func fetchLatestPanelVersion() (string, error) {
	client := &http.Client{Timeout: 10 * time.Second}
	resp, err := client.Get("https://api.github.com/repos/MHSanaei/3x-ui/releases/latest")
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("GitHub API returned status %d: %s", resp.StatusCode, resp.Status)
	}

	var release Release
	if err := json.NewDecoder(resp.Body).Decode(&release); err != nil {
		return "", err
	}
	if release.TagName == "" {
		return "", fmt.Errorf("latest panel release tag is empty")
	}
	return release.TagName, nil
}

func resolveUpdateFolders() (string, string) {
	mainFolder := os.Getenv("XUI_MAIN_FOLDER")
	if mainFolder == "" {
		if exePath, err := os.Executable(); err == nil {
			mainFolder = filepath.Dir(exePath)
		}
	}
	if mainFolder == "" {
		mainFolder = "/usr/local/x-ui"
	}

	serviceFolder := os.Getenv("XUI_SERVICE")
	if serviceFolder == "" {
		serviceFolder = "/etc/systemd/system"
	}
	return mainFolder, serviceFolder
}

func isNewerVersion(latest string, current string) bool {
	cmp, ok := compareVersionStrings(latest, current)
	if !ok {
		return normalizeVersionTag(latest) != normalizeVersionTag(current)
	}
	return cmp > 0
}

func compareVersionStrings(a string, b string) (int, bool) {
	aParts, okA := parseVersionParts(a)
	bParts, okB := parseVersionParts(b)
	if !okA || !okB {
		return 0, false
	}
	for i := 0; i < len(aParts); i++ {
		if aParts[i] > bParts[i] {
			return 1, true
		}
		if aParts[i] < bParts[i] {
			return -1, true
		}
	}
	return 0, true
}

func parseVersionParts(version string) ([3]int, bool) {
	var result [3]int
	parts := strings.Split(normalizeVersionTag(version), ".")
	if len(parts) != 3 {
		return result, false
	}
	for i, part := range parts {
		n, err := strconv.Atoi(part)
		if err != nil {
			return result, false
		}
		result[i] = n
	}
	return result, true
}

func normalizeVersionTag(version string) string {
	return strings.TrimPrefix(strings.TrimSpace(version), "v")
}

func shellQuote(value string) string {
	return "'" + strings.ReplaceAll(value, "'", "'\\''") + "'"
}