//go:build linux

package service

import (
	"fmt"
	"os"
	"os/exec"
	"strings"

	"mfd-monitor-agent/internal/config"
)

var currentUID = os.Geteuid

// linuxManager manages a systemd service for the agent.
type linuxManager struct{}

// newManager returns the Linux systemd-backed service manager.
func newManager() Manager {
	return linuxManager{}
}

// Install writes a systemd unit, reloads systemd, and enables the configured service.
func (linuxManager) Install(executable string, cfg config.Config, opts InstallOptions) error {
	if currentUID() != 0 {
		return fmt.Errorf("install requires root")
	}
	unit := renderSystemdUnit(executable, opts.ConfigPath, cfg)
	path := "/etc/systemd/system/" + cfg.Service.Name + ".service"
	if err := os.WriteFile(path, []byte(unit), 0644); err != nil {
		return fmt.Errorf("write systemd unit: %w", err)
	}
	if err := exec.Command("systemctl", "daemon-reload").Run(); err != nil {
		return fmt.Errorf("systemctl daemon-reload: %w", err)
	}
	if err := exec.Command("systemctl", "enable", cfg.Service.Name).Run(); err != nil {
		return fmt.Errorf("systemctl enable: %w", err)
	}
	return nil
}

// renderSystemdUnit builds the Linux systemd unit used by Install.
func renderSystemdUnit(executable string, configPath string, cfg config.Config) string {
	args := []string{executable, "run"}
	if configPath != "" {
		args = append(args, "-config", configPath)
	}
	return fmt.Sprintf(`[Unit]
Description=%s
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
ExecStart=%s
Restart=always
RestartSec=5s

[Install]
WantedBy=multi-user.target
`, cfg.Service.Description, strings.Join(args, " "))
}

// Uninstall disables the service, removes its unit file, and reloads systemd.
func (linuxManager) Uninstall(cfg config.Config) error {
	_ = exec.Command("systemctl", "disable", "--now", cfg.Service.Name).Run()
	if err := os.Remove("/etc/systemd/system/" + cfg.Service.Name + ".service"); err != nil && !os.IsNotExist(err) {
		return err
	}
	return exec.Command("systemctl", "daemon-reload").Run()
}

// Start asks systemd to start the configured service.
func (linuxManager) Start(cfg config.Config) error {
	return exec.Command("systemctl", "start", cfg.Service.Name).Run()
}

// Stop asks systemd to stop the configured service.
func (linuxManager) Stop(cfg config.Config) error {
	return exec.Command("systemctl", "stop", cfg.Service.Name).Run()
}