//go:build linux

package service

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

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

var currentUID = os.Geteuid

// linuxManager 通过 systemd 管理 agent 服务。
type linuxManager struct{}

// newManager 返回基于 Linux systemd 的服务管理器。
func newManager() Manager {
	return linuxManager{}
}

// Install 写入 systemd unit、重载 systemd 并 enable 配置的服务。
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 生成 Install 使用的 Linux systemd unit 内容。
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 禁用服务、删除 unit 文件并重载 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 请求 systemd 启动配置的服务。
func (linuxManager) Start(cfg config.Config) error {
	return exec.Command("systemctl", "start", cfg.Service.Name).Run()
}

// Stop 请求 systemd 停止配置的服务。
func (linuxManager) Stop(cfg config.Config) error {
	return exec.Command("systemctl", "stop", cfg.Service.Name).Run()
}