package tg

// The type represents map of sessions using
// as key.
type SessionMap map[SessionId]*Session

// Add new empty session by it's ID.
func (sm SessionMap) Add(sid SessionId, scope SessionScope) *Session {
	ret := NewSession(sid, scope)
	sm[sid] = ret
	return ret
}

// The way to determine where the context is
// related to.
type SessionScope uint8
const (
	NoSessionScope SessionScope = iota
	PrivateSessionScope
	GroupSessionScope
	ChannelSessionScope
)

// Represents unique value to identify chats.
// In fact is simply ID of the chat.
type SessionId int64

// Convert the SessionId to Telegram API's type.
func (si SessionId) ToApi() int64 {
	return int64(si)
}

// The type represents current state of
// user interaction per each of them.
type Session struct {
	// Id of the chat of the user.
	Id SessionId
	Scope SessionScope
	// Custom value for each user.
	Data  any

	bot *Bot
	pathHistory []Path
	skippedUpdates *UpdateChan
	updates *UpdateChan
}

// Return new empty session with specified user ID.
func NewSession(id SessionId, scope SessionScope) *Session {
	return &Session{
		Id: id,
		Scope: scope,
	}
}

// Changes screen of user to the Id one.
func (s *Session) go_(pth Path, arg any) error {
	var err error
	if pth == "" {
		s.pathHistory = []Path{}
		return nil
	}
	var back bool
	if pth == "-" {
		if len(s.pathHistory) < 2 {
			return s.Go("")
		}
		pth = s.pathHistory[len(s.pathHistory)-2]
		s.pathHistory = s.pathHistory[:len(s.pathHistory)-1]
	}
	// Getting the screen and changing to
	// then executing its widget.
	if !pth.IsAbs() {
		pth = (s.Path() + "/" + pth).Clean()
	}

	if !s.PathExist(pth) {
		return ScreenNotExistErr
	}

	if !back && s.Path() != pth {
		s.pathHistory = append(s.pathHistory, pth)
	}

	// Stopping the current widget.
	screen := s.bot.behaviour.Screens[pth]
	s.skippedUpdates.Close()

	if screen.Widget != nil {
		s.skippedUpdates, err = s.runWidget(screen.Widget, arg)
		if err != nil {
			return err
		}
	} else {
		return NoWidgetForScreenErr
	}

	return nil
}

func (s *Session) runCompo(compo Component, arg any) (*UpdateChan, error) {
	if compo == nil {
		return nil, nil
	}
	s, ok := compo.(Sendable)
	if ok {
		msg, err := c.Send(s)
		if err != nil {
			return nil, err
		}
		s.SetMessage(msg)
	}
	updates := NewUpdateChan()
	go func() {
		compo.Serve(
			c.WithInput(updates).
				WithArg(arg),
		)
		// To let widgets finish themselves before
		// the channel is closed and close it by themselves.
		updates.Close()
	}()
	return updates, nil
}

// Run widget in background returning the new input channel for it.
func (c *Context) runWidget(widget Widget, arg any) (*UpdateChan, error) {
	var err error
	if widget == nil {
		return nil, EmptyWidgetErr
	}

	pth := c.Path()
	compos := widget.Render(c.WithArg(c.makeArg(args)))
	// Leave if changed path or components are empty.
	if compos == nil || pth != c.Path() {
		return nil, EmptyCompoErr
	}
	chns := make([]*UpdateChan, len(compos))
	for i, compo := range compos {
		chns[i], err = c.runCompo(compo, arg)
		if err != nil {
			for _, chn := range chns {
				chn.Close()
			}
			return nil, err
		}
	}

	ret := NewUpdateChan()
	go func() {
		ln := len(compos)
		UPDATE:
		for u := range ret.Chan() {
			if u == nil {
				break
			}
			cnt := 0
			for i, compo := range compos {
				chn := chns[i]
				if chn.Closed() {
					cnt++
					continue
				}
				if !compo.Filter(u) {
					chn.Send(u)
					continue UPDATE
				}
			}
			if cnt == ln {
				break
			}
		}
		ret.Close()
		for _, chn := range chns {
			chn.Close()
		}
	}()

	return ret, nil
}