package agent

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"time"

	"github.com/x-grk/longpolling-remote-access/internal/proto"
)

// doUpdate downloads the latest agent binary for this platform, atomically
// replaces the running executable, and schedules a service restart. It never
// uninstalls — only updates.
func (a *Agent) doUpdate() proto.TaskResult {
	exe, err := os.Executable()
	if err != nil {
		return proto.TaskResult{Error: "не удалось определить путь бинарника: " + err.Error()}
	}
	exe, _ = filepath.EvalSymlinks(exe)

	url := fmt.Sprintf("%s/download/agent-%s-%s", a.cfg.Host, runtime.GOOS, runtime.GOARCH)
	req, _ := http.NewRequestWithContext(context.Background(), http.MethodGet, url, nil)
	resp, err := a.http.Do(req)
	if err != nil {
		return proto.TaskResult{Error: "скачивание: " + err.Error()}
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return proto.TaskResult{Error: "скачивание: сервер вернул " + resp.Status}
	}

	tmp := exe + ".new"
	f, err := os.OpenFile(tmp, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o755)
	if err != nil {
		return proto.TaskResult{Error: "создание файла: " + err.Error()}
	}
	if _, err := io.Copy(f, resp.Body); err != nil {
		f.Close()
		os.Remove(tmp)
		return proto.TaskResult{Error: "запись: " + err.Error()}
	}
	f.Close()

	// Atomic replace: renaming over a running executable is allowed on Linux;
	// the live process keeps the old inode until it restarts.
	if err := os.Rename(tmp, exe); err != nil {
		os.Remove(tmp)
		return proto.TaskResult{Error: "замена бинарника: " + err.Error()}
	}

	// Restart shortly, after the result has been reported.
	go func() {
		time.Sleep(1500 * time.Millisecond)
		restartSelf()
	}()

	data, _ := json.Marshal(map[string]string{"status": "обновлено, перезапуск"})
	return proto.TaskResult{OK: true, Data: data}
}

// restartSelf restarts the agent so the new binary takes effect.
func restartSelf() {
	if path, err := exec.LookPath("systemctl"); err == nil {
		_ = exec.Command(path, "restart", "lpagent").Start()
		return
	}
	// No systemd (e.g. launchd/manual run): exit so the supervisor restarts us.
	os.Exit(0)
}