package tg

import (
	"context"

	"go.uber.org/multierr"
)

type Handler = func(context.Context, Entities, UpdateClass) error

type UpdateDispatcher struct {
	handlers map[uint32]Handler
	fallback Handler
}

func NewUpdateDispatcher() UpdateDispatcher {
	return UpdateDispatcher{
		handlers: map[uint32]Handler{},
		fallback: func(ctx context.Context, entities Entities, class UpdateClass) error { return nil },
	}
}

type Entities struct {
	Short    bool
	Users    map[int64]*User
	Chats    map[int64]*Chat
	Channels map[int64]*Channel
}

func (u *Entities) short() {
	u.Short = true
	u.Users = make(map[int64]*User, 0)
	u.Chats = make(map[int64]*Chat, 0)
	u.Channels = make(map[int64]*Channel, 0)
}

// Handle implements UpdateDispatcher.
func (u UpdateDispatcher) Handle(ctx context.Context, updates UpdatesClass) error {
	var (
		e    Entities
		upds []UpdateClass
	)
	switch u := updates.(type) {
	case *Updates:
		upds = u.Updates
		e.Users = u.MapUsers().NotEmptyToMap()
		chats := u.MapChats()
		e.Chats = chats.ChatToMap()
		e.Channels = chats.ChannelToMap()
	case *UpdatesCombined:
		upds = u.Updates
		e.Users = u.MapUsers().NotEmptyToMap()
		chats := u.MapChats()
		e.Chats = chats.ChatToMap()
		e.Channels = chats.ChannelToMap()
	case *UpdateShort:
		upds = []UpdateClass{u.Update}
		e.short()
	default:
		// *UpdateShortMessage
		// *UpdateShortChatMessage
		// *UpdateShortSentMessage
		// *UpdatesTooLong
		return nil
	}

	var err error
	for _, update := range upds {
		multierr.AppendInto(&err, u.dispatch(ctx, e, update))
	}
	return err
}

func (u UpdateDispatcher) dispatch(ctx context.Context, e Entities, update UpdateClass) error {
	if update == nil {
		return nil
	}
	if err := u.fallback(ctx, e, update); err != nil {
		return err
	}
	typeID := update.TypeID()
	handler, ok := u.handlers[typeID]
	if ok {
		return handler(ctx, e, update)
	}
	return nil
}