// Package initsys selects the init system backend that installs and controls
// unitdore services.
package initsys

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

	"github.com/warkanum/unitdore/config"
	"github.com/warkanum/unitdore/openrc"
	"github.com/warkanum/unitdore/runit"
	"github.com/warkanum/unitdore/systemd"
)

// Backend names.
const (
	Systemd = "systemd"
	OpenRC  = "openrc"
	Runit   = "runit"
)

// Init is implemented by every init system backend. u.User selects the scope;
// backends that cannot do per-user managers run user units as system services.
type Init interface {
	Name() string
	ServiceName(u config.Unit, prefix, suffix string) string
	UnitPath(u config.Unit, prefix, suffix string) (string, error)
	Generate(u config.Unit, prefix, suffix string) (string, error)
	Install(u config.Unit, prefix, suffix string) error
	Uninstall(u config.Unit, prefix, suffix string) error
	Enable(u config.Unit, prefix, suffix string) error
	Disable(u config.Unit, prefix, suffix string) error
	Start(u config.Unit, prefix, suffix string) error
	Stop(u config.Unit, prefix, suffix string) error
	// Status returns active | inactive | failed | activating | deactivating | unknown.
	Status(u config.Unit, prefix, suffix string) string
	IsInstalled(u config.Unit, prefix, suffix string) bool
	// SupportsLinger reports whether user units need systemd-style linger.
	SupportsLinger() bool
}

// New returns the backend named in cfg.Init, or the detected one.
func New(cfg *config.Config) (Init, error) {
	name := cfg.Init
	if name == "" {
		name = Detect("/")
	}
	switch name {
	case Systemd:
		return systemd.Backend{}, nil
	case OpenRC:
		return openrc.Backend{}, nil
	case Runit:
		return runit.Backend{ServiceDir: cfg.ServiceDir}, nil
	default:
		return nil, fmt.Errorf("unknown init %q (want systemd, openrc or runit)", name)
	}
}

// Detect guesses the running init system below root. Falls back to systemd.
func Detect(root string) string {
	has := func(p string) bool {
		_, err := os.Stat(filepath.Join(root, p))
		return err == nil
	}
	switch {
	case has("run/systemd/system"):
		return Systemd
	case has("run/openrc"), has("sbin/openrc-run"):
		return OpenRC
	case has("run/runit"), has("etc/runit"):
		return Runit
	default:
		return Systemd
	}
}