package budget

import (
	"errors"
	"strings"

	"github.com/godbus/dbus/v5"
)

const api = "org.freedesktop.systemd1"
const noUnit = api + ".NoSuchUnit"
const noPID = "org.freedesktop.DBus.Error.UnixProcessIdUnknown"

type unit struct {
	Name        string
	Description string
	Load        string
	Active      string
	Sub         string
	Following   string
	Path        dbus.ObjectPath
	Job         uint32
	JobType     string
	JobPath     dbus.ObjectPath
}

type unitState struct {
	Active string
	Group  string
}

type unitCtl interface {
	Units() ([]unit, error)
	Group(string) (string, error)
	Set(string, []property) error
	Start(string, []property) error
	State(string) (unitState, error)
	Stop(string) error
}

type manager struct {
	conn *dbus.Conn
	obj  dbus.BusObject
}

type auxiliary struct {
	Name       string
	Properties []property
}

func connect() (*manager, error) {
	conn, err := dbus.ConnectSessionBus()
	if err != nil {
		return nil, err
	}
	return &manager{conn: conn, obj: conn.Object(api, "/org/freedesktop/systemd1")}, nil
}

func busError(err error, name string) bool {
	var e dbus.Error
	return errors.As(err, &e) && e.Name == name
}

func (m *manager) Units() ([]unit, error) {
	var units []unit
	err := m.obj.Call(api+".Manager.ListUnits", 0).Store(&units)
	return units, err
}

func (m *manager) object(name string) (dbus.BusObject, error) {
	var path dbus.ObjectPath
	if err := m.obj.Call(api+".Manager.GetUnit", 0, name).Store(&path); err != nil {
		return nil, err
	}
	return m.conn.Object(api, path), nil
}

func (m *manager) Group(name string) (string, error) {
	obj, err := m.object(name)
	if err != nil {
		return "", err
	}
	kind := name[strings.LastIndex(name, ".")+1:]
	kind = strings.ToUpper(kind[:1]) + kind[1:]
	var group string
	err = obj.StoreProperty(api+"."+kind+".ControlGroup", &group)
	return group, err
}

func (m *manager) Set(name string, values []property) error {
	return m.obj.Call(api+".Manager.SetUnitProperties", 0, name, true, values).Err
}

func (m *manager) Start(name string, values []property) error {
	return m.obj.Call(api+".Manager.StartTransientUnit", 0, name, "fail", values, []auxiliary{}).Err
}

func (m *manager) State(name string) (unitState, error) {
	obj, err := m.object(name)
	if err != nil {
		return unitState{}, err
	}
	var state unitState
	if err = obj.StoreProperty(api+".Unit.ActiveState", &state.Active); err != nil {
		return unitState{}, err
	}
	err = obj.StoreProperty(api+".Scope.ControlGroup", &state.Group)
	return state, err
}

func (m *manager) Stop(name string) error {
	return m.obj.Call(api+".Manager.StopUnit", 0, name, "replace").Err
}