package systemd

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

	"github.com/warkanum/unitdore/config"
)

const systemUnitDir = "/etc/systemd/system"

// UnitPath returns the filesystem path where the .service file should be written.
func UnitPath(u config.Unit, prefix, suffix string) (string, error) {
	svcName := ServiceName(u, prefix, suffix)
	if u.User == "" {
		return filepath.Join(systemUnitDir, svcName), nil
	}
	// Rootless: write to the user's systemd config dir
	home, err := userHomeDir(u.User)
	if err != nil {
		return "", err
	}
	return filepath.Join(home, ".config", "systemd", "user", svcName), nil
}

// Install writes the .service file for a unit and reloads systemd.
func Install(u config.Unit, prefix, suffix string) error {
	content, err := Generate(u, prefix, suffix)
	if err != nil {
		return err
	}

	path, err := UnitPath(u, prefix, suffix)
	if err != nil {
		return err
	}

	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
		return fmt.Errorf("creating unit dir: %w", err)
	}

	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
		return fmt.Errorf("writing unit file: %w", err)
	}

	return daemonReload(u.User)
}

// Uninstall removes the .service file for a unit and reloads systemd.
func Uninstall(u config.Unit, prefix, suffix string) error {
	path, err := UnitPath(u, prefix, suffix)
	if err != nil {
		return err
	}

	if err := os.Remove(path); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("removing unit file: %w", err)
	}

	return daemonReload(u.User)
}

// Enable enables and starts a unit.
func Enable(u config.Unit, prefix, suffix string) error {
	return systemctl(u.User, "enable", "--now", ServiceName(u, prefix, suffix))
}

// Disable disables and stops a unit.
func Disable(u config.Unit, prefix, suffix string) error {
	return systemctl(u.User, "disable", "--now", ServiceName(u, prefix, suffix))
}

// Start starts a unit without enabling it.
func Start(u config.Unit, prefix, suffix string) error {
	return systemctl(u.User, "start", ServiceName(u, prefix, suffix))
}

// Stop stops a unit without disabling it.
func Stop(u config.Unit, prefix, suffix string) error {
	return systemctl(u.User, "stop", ServiceName(u, prefix, suffix))
}

// Status returns the ActiveState of a unit ("active", "inactive", "failed", "unknown").
func Status(u config.Unit, prefix, suffix string) string {
	args := []string{"show", "-p", "ActiveState", "--value", ServiceName(u, prefix, suffix)}
	var out []byte
	var err error

	if u.User == "" {
		out, err = exec.Command("systemctl", args...).Output()
	} else {
		out, err = runAsUser(u.User, "systemctl", append([]string{"--user"}, args...)...)
	}
	if err != nil {
		return "unknown"
	}
	return strings.TrimSpace(string(out))
}

// IsInstalled returns true if the unit file exists on disk.
func IsInstalled(u config.Unit, prefix, suffix string) bool {
	path, err := UnitPath(u, prefix, suffix)
	if err != nil {
		return false
	}
	_, err = os.Stat(path)
	return err == nil
}

// --- helpers ---

func daemonReload(user string) error {
	if user == "" {
		return systemctl("", "daemon-reload")
	}
	return systemctl(user, "daemon-reload")
}

func systemctl(user string, args ...string) error {
	if user == "" {
		cmd := exec.Command("systemctl", args...)
		cmd.Stdout = os.Stdout
		cmd.Stderr = os.Stderr
		return cmd.Run()
	}
	return runAsUserCmd(user, "systemctl", append([]string{"--user"}, args...)...)
}

func runAsUser(user string, bin string, args ...string) ([]byte, error) {
	full := append([]string{"-u", user, "--", bin}, args...)
	return exec.Command("runuser", full...).Output()
}

func runAsUserCmd(user string, bin string, args ...string) error {
	full := append([]string{"-u", user, "--", bin}, args...)
	cmd := exec.Command("runuser", full...)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	return cmd.Run()
}

func userHomeDir(user string) (string, error) {
	out, err := exec.Command("getent", "passwd", user).Output()
	if err != nil {
		return "", fmt.Errorf("looking up user %s: %w", user, err)
	}
	// passwd format: name:pass:uid:gid:gecos:home:shell
	parts := strings.Split(strings.TrimSpace(string(out)), ":")
	if len(parts) < 6 {
		return "", fmt.Errorf("unexpected passwd entry for %s", user)
	}
	return parts[5], nil
}