package main

import (
	"errors"
	"fmt"
	"log"
	"strings"
	"time"

	"code.ivysaur.me/libnmdc"
	telegram "github.com/go-telegram-bot-api/telegram-bot-api"
)

// NTFServer methods all run on the same thread, so no mutexes are needed for field access
type NTFServer struct {
	bot         *telegram.BotAPI
	hubMessages chan upstreamMessage
	chatName    string
	inviteLink  string
	configFile  string
	config      NTFConfig
	conns       map[string]*libnmdc.HubConnection // hubnick -> hubconn
}

type upstreamMessage struct {
	telegramUserId int64
	hubNick        string
	evt            libnmdc.HubEvent
}

func NewNTFServer(configFile string) (*NTFServer, error) {
	ret := NTFServer{
		configFile:  configFile,
		hubMessages: make(chan upstreamMessage, 0),
	}

	// Config

	cfg, err := LoadConfig(configFile)
	if err != nil {
		return nil, err
	}

	ret.config = cfg

	// Bot connection

	if len(cfg.BotAPIKey) == 0 {
		return nil, errors.New("No bot API key supplied (register with BotFather first)")
	}

	bot, err := telegram.NewBotAPI(cfg.BotAPIKey)
	if err != nil {
		return nil, fmt.Errorf("Connecting to Telegram: %s", err.Error())
	}

	ret.bot = bot

	bot.Debug = true

	log.Printf("Connected to telegram as '%s'", bot.Self.UserName)

	// Groupchat properties

	if ret.IsSetupMode() {
		log.Println("Group chat ID unknown, running in setup mode only - find the groupchat ID then re-run")

	} else {
		chatInfo, err := bot.GetChat(telegram.ChatConfig{ChatID: ret.config.GroupChatID})
		if err != nil {
			return nil, fmt.Errorf("Couldn't get supergroup properties: %s", err.Error())
		}

		inviteLink, err := bot.GetInviteLink(telegram.ChatConfig{ChatID: ret.config.GroupChatID})
		if err != nil {
			return nil, fmt.Errorf("Couldn't get supergroup invite link: %s", err.Error())
		}

		log.Printf("Group chat: %s", chatInfo.Title)
		log.Printf("Invite link: %s", inviteLink)

		ret.chatName = chatInfo.Title
		ret.inviteLink = inviteLink

	}

	// Spawn upstream connections for all pre-existing known users
	for telegramUserId, telegramDisplayName := range ret.config.GroupChatMembers {
		hubNick, ok := ret.config.KnownUsers[telegramUserId]
		if !ok {
			log.Fatalf("Chat member '%d' (%s) is missing a hub mapping!!!", telegramUserId, telegramDisplayName) // fatal - inconsistent DB
		}

		err := ret.LaunchUpstreamWorker(telegramUserId, hubNick)
		if err != nil {
			return nil, fmt.Errorf("Reconnecting upstream for '%s': %s", hubNick, err.Error()) // fatal
		}
	}

	return &ret, nil
}

// registerUser lodges a user mapping in the configuration file.
// This allows them to join the group chat (unbanning them if necessary).
// An actual NMDC connection will occur once the user joins for the first time.
func (this *NTFServer) registerUser(telegramUserId int64, hubUsername string) error {
	if existingHubNick, ok := this.config.KnownUsers[telegramUserId]; ok {
		return fmt.Errorf("Telegram account is already registered with hub nick '%s'", existingHubNick)
	}

	for _, v := range this.config.KnownUsers {
		if v == hubUsername {
			return fmt.Errorf("Requested hub nick '%s' is already used by another member", hubUsername)
		}
	}

	this.config.KnownUsers[telegramUserId] = hubUsername
	err := this.config.Save(this.configFile)
	if err != nil {
		return err
	}

	// Unban from groupchat, if necessary
	// Ignore errors because the user might not have been banned
	_, err = this.bot.UnbanChatMember(telegram.ChatMemberConfig{
		ChatID: this.config.GroupChatID,
		UserID: int(telegramUserId),
	})
	if err != nil {
		log.Printf("Couldn't unban user '%s' from groupchat because: %s (assuming OK, continuing)", hubUsername, err.Error())
	}

	return nil
}

// LaunchUpstreamWorker opens an NMDC connection.
func (this *NTFServer) LaunchUpstreamWorker(telegramUserId int64, hubUsername string) error {

	if _, exists := this.conns[hubUsername]; exists {
		return fmt.Errorf("Duplicate hub connection for user '%s', abandoning", hubUsername)
	}

	// We want to use the async NMDC connection, but at the same time, provide
	// extra information in the channel. Wrap the upstream NMDC channel with one
	// of our own
	upstreamChan := make(chan libnmdc.HubEvent, 0)
	go func() {
		for msg := range upstreamChan {
			this.hubMessages <- upstreamMessage{
				telegramUserId: telegramUserId,
				hubNick:        hubUsername,
				evt:            msg,
			}
		}
	}()

	conn := libnmdc.ConnectAsync(
		&libnmdc.HubConnectionOptions{
			Address: libnmdc.HubAddress(this.config.HubAddr),
			Self: &libnmdc.UserInfo{
				Nick:          hubUsername,
				ClientTag:     AppName,
				ClientVersion: AppVersion,
			},
		},
		upstreamChan,
	)

	// Stash conn so that we can refer to it / close it later
	this.conns[hubUsername] = conn

	return nil
}

func (this *NTFServer) IsSetupMode() bool {
	return this.config.GroupChatID == 0
}

func (this *NTFServer) Run() error {
	updateProps := telegram.NewUpdate(0)
	updateProps.Timeout = 60 // seconds

	updateChan, err := this.bot.GetUpdatesChan(updateProps)
	if err != nil {
		return err
	}

	for {
		select {
		case update, ok := <-updateChan:
			if !ok {
				log.Fatalf("Telegram update channel closed unexpectedly")
			}
			this.HandleMessage(update)

		case hubMsg, ok := <-this.hubMessages:
			if !ok {
				log.Fatalf("Upstream update channel closed unexpectedly")
			}
			this.HandleHubMessage(hubMsg)
		}
	}

	return nil // UNREACHABLE
}

func (this *NTFServer) HandleHubMessage(msg upstreamMessage) {
	log.Printf("Hub: %#v", msg)
}

func (this *NTFServer) HandleMessage(update telegram.Update) {
	if update.Message == nil {
		return
	}

	if this.IsSetupMode() {
		log.Printf("Message from '%s': '%s', chat ID '%d'\n", update.Message.From.UserName, update.Message.Text, update.Message.Chat.ID)

	} else if update.Message.Chat.ID == this.config.GroupChatID {
		err := this.HandleGroupMessage(update)
		if err != nil {
			log.Printf("Handling group message: %s", err.Error())
		}

	} else if update.Message.Chat.IsPrivate() {
		err := this.HandleDirectMessage(update)
		if err != nil {
			log.Printf("Handling private message: %s", err.Error())
		}

	} else {
		log.Printf("Message from unknown chat %d (not our supergroup, not a PM, ...)", update.Message.Chat.ID)
	}

	fmt.Printf("%#v\n", update.Message)

	log.Printf("[%s] %s", update.Message.From.UserName, update.Message.Text)
}

func (this *NTFServer) HandleTelegramUserParted(telegramUserId int64, update telegram.Update) error {
	delete(this.config.GroupChatMembers, telegramUserId)
	return this.config.Save(this.configFile)
}

func (this *NTFServer) HandleTelegramUserJoined(telegramUserId int64, update telegram.Update) error {
	// If known, spawn the upstream connection; if unknown, kick them
	hubNick, ok := this.config.KnownUsers[telegramUserId]
	if !ok {
		_, err := this.bot.KickChatMember(telegram.KickChatMemberConfig{
			ChatMemberConfig: telegram.ChatMemberConfig{
				ChatID: update.Message.Chat.ID,
				UserID: int(telegramUserId),
			},
			UntilDate: time.Now().Add(24 * time.Hour).Unix(),
		})
		if err != nil {
			log.Printf("Couldn't kick unexpected chat member from group: %s", err.Error())
		}

		return nil
	}

	// Spawn the upstream connection for this user
	return this.LaunchUpstreamWorker(telegramUserId, hubNick)
}

func (this *NTFServer) HandleGroupMessage(update telegram.Update) error {

	// Joins: ????
	if update.Message.NewChatMembers != nil && len(*update.Message.NewChatMembers) > 0 {
		// Users joining
		// Ensure that they have a valid user mapping
		// Create upstream NMDC connection for them
		for _, joinedUser := range *update.Message.NewChatMembers {
			err := this.HandleTelegramUserJoined(int64(joinedUser.ID), update)
			if err != nil {
				log.Printf("Handling user join: %s", err.Error())
			}
		}
		return nil
	}

	if update.Message.LeftChatMember != nil {
		// User parted
		// Close upstream NMDC connection for them
		return this.HandleTelegramUserParted(int64(update.Message.LeftChatMember.ID), update)
	}

	// Actual chat message
	// Find the responsible user and send it to the upstream hub using their account
	// TODO

	return nil
}

func (this *NTFServer) HandleDirectMessage(update telegram.Update) error {

	// Registration workflow

	// Find out the current status for this chat ID
	userID := int64(update.Message.From.ID)
	hubNick, isKnown := this.config.KnownUsers[userID]

	respond := func(str string) error {
		msg := telegram.NewMessage(update.Message.Chat.ID, str)
		msg.ReplyToMessageID = update.Message.MessageID
		_, err := this.bot.Send(msg)
		return err
	}

	// Handle the incoming request

	msg := update.Message.Text
	if strings.HasPrefix(msg, "/pm ") {
		if !isKnown {
			return respond("Can't send a native PM until you've joined.")
		}

		// TODO
		return respond("Not yet implemented.")

	} else if strings.HasPrefix(msg, "/join ") {
		if isKnown {
			return respond("You've already joined as '" + hubNick + "'.")
		}

		requestedHubNick := msg[6:]
		err := this.registerUser(userID, requestedHubNick)
		if err != nil {
			log.Printf("Failed to join user: %s", err.Error())
			return respond(fmt.Sprintf("Couldn't allow join because: %s", err.Error()))
		}

		return respond(fmt.Sprintf("Hi '%s'! You can join %s at %s", requestedHubNick, this.config.HubDescription, this.inviteLink))

	} else if strings.HasPrefix(msg, "/quit") {

		// TODO
		return respond("Not yet implemented.")

	} else { // e.g. /setup or /help
		// Help
		helpMsg := `I am a bot that connects Telegram with ` + this.config.HubDescription + ".\n"
		if isKnown {
			helpMsg += "You are currently connected as: '" + hubNick + "'\n"
		} else {
			helpMsg += "You aren't connected yet.\n"
		}

		helpMsg += `
		
Available commands:
/setup - Welcome message
/join [hubnick] - Join ` + this.config.HubDescription + ` as user 'hubnick'
/pm [recipient] [message] - Send a native PM (if connected)
/quit - Leave the group chat
`

		return respond(helpMsg)
	}

	return nil
}