package main

import (
	"errors"
	"fmt"
	"html"
	"log"
	"sort"
	"strings"
	"sync"
	"time"

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

const (
	coalesceWorkerRescanEvery time.Duration = 10 * time.Second
	coalesceWorkerExpireAfter time.Duration = 20 * time.Second
)

// 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
	verbose     bool

	// Except the coalesce buffer, that requires a background worker.
	coalesceBufferMut sync.Mutex
	coalesceBuffer    map[string]time.Time
}

func coalesceKey(hubNick, message string) string {
	return hubNick + "\x00" + message
}

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

func NewNTFServer(configFile string, verbose bool) (*NTFServer, error) {
	ret := NTFServer{
		configFile:     configFile,
		hubMessages:    make(chan upstreamMessage, 0),
		conns:          make(map[string]*libnmdc.HubConnection),
		coalesceBuffer: make(map[string]time.Time),
		verbose:        verbose,
	}

	// Config

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

	ret.config = cfg

	// Coalesce background worker
	go ret.coalesceWorker()

	// 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

	if ret.verbose {
		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 {
		if existingHubNick == hubUsername {
			return nil
		}

		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)
	}

	log.Printf("Connecting to hub '%s' as user '%s'...", this.config.HubAddr, 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,
			}
		}
	}()

	hubUser := libnmdc.NewUserInfo(hubUsername)
	hubUser.ClientTag = AppName
	hubUser.ClientVersion = AppVersion

	conn := libnmdc.ConnectAsync(
		&libnmdc.HubConnectionOptions{
			Address: libnmdc.HubAddress(this.config.HubAddr),
			Self:    hubUser,
		},
		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) coalesceWorker() {
	for {
		time.Sleep(coalesceWorkerRescanEvery)

		deadLine := time.Now().Add(-coalesceWorkerExpireAfter)

		this.coalesceBufferMut.Lock()
		for k, v := range this.coalesceBuffer {
			if v.Before(deadLine) {
				delete(this.coalesceBuffer, k)
			}
		}
		this.coalesceBufferMut.Unlock()
	}
}

// Coalesce returns true if the message sticks to an existing one.
// It adds it into the coalesce buffer anyway.
func (this *NTFServer) Coalesce(hubNick, message string) bool {
	ckey := coalesceKey(hubNick, message)

	this.coalesceBufferMut.Lock()
	if _, ok := this.coalesceBuffer[ckey]; ok {
		this.coalesceBufferMut.Unlock()
		return true // stuck to existing
	} else {
		this.coalesceBuffer[ckey] = time.Now()
		this.coalesceBufferMut.Unlock()
		return false // first we've seen it
	}
}

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

	switch msg.evt.EventType {

	case libnmdc.EVENT_SYSTEM_MESSAGE_FROM_CONN, libnmdc.EVENT_CONNECTION_STATE_CHANGED:
		log.Printf("Hub(%s): * %s", msg.hubNick, msg.evt.Message)

	case libnmdc.EVENT_PRIVATE:
		err := this.DirectMessageTelegramUser(msg.telegramUserId, fmt.Sprintf("PM from user '%s': %s", msg.evt.Nick, msg.evt.Message))
		if err != nil {
			log.Printf("Delivering PM to telegram user: %s", err.Error())
		}

	case libnmdc.EVENT_PUBLIC:
		if msg.evt.Nick == this.config.HubSecNick {
			return // ignore
		}

		// Coalesce from multiple connections
		if this.Coalesce(msg.evt.Nick, msg.evt.Message) {
			return // ignore - we heard this message already recently
		}

		// Display the message
		htmlMsg := "<b>&lt;" + html.EscapeString(msg.evt.Nick) + "&gt;</b> " + html.EscapeString(msg.evt.Message)
		err := this.GroupChatSayHTML(htmlMsg)
		if err != nil {
			log.Printf("Delivering public message to group chat: %s", err.Error())
		}

	case libnmdc.EVENT_USER_JOINED, libnmdc.EVENT_USER_PART, libnmdc.EVENT_USER_UPDATED_INFO, libnmdc.EVENT_USERCOMMAND, libnmdc.EVENT_DEBUG_MESSAGE, libnmdc.EVENT_HUBNAME_CHANGED:
		// ignore

	default:
		log.Printf("Hub(%s): Unhandled(%d): %s", msg.hubNick, msg.evt.EventType, msg.evt.Message)

	}
}

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)
	}

	if this.verbose {
		fmt.Printf("%#v\n", update.Message)

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

// kickAndDrop deregisters an account and kicks them from the group chat
func (this *NTFServer) kickAndDrop(telegramUserId int64) {

	// Hubnick
	if hubNick, ok := this.config.KnownUsers[telegramUserId]; ok {

		// Close upstream connection (if any)
		if conn, ok := this.conns[hubNick]; ok {
			delete(this.conns, hubNick)

			log.Printf("Disconnecting '%s' from hub", hubNick)
			conn.Disconnect()
		}

		// Deregister from known users
		delete(this.config.KnownUsers, telegramUserId)
		err := this.config.Save(this.configFile)
		if err != nil {
			log.Printf("Couldn't save changes when deregistering user: %s", err.Error())
		}
	}

	// Kick from telegram groupchat (if logged in)
	_, err := this.bot.KickChatMember(telegram.KickChatMemberConfig{
		ChatMemberConfig: telegram.ChatMemberConfig{
			ChatID: this.config.GroupChatID,
			UserID: int(telegramUserId),
		},
		UntilDate: time.Now().Add(24 * time.Hour).Unix(),
	})
	if err != nil {
		log.Printf("Couldn't kick user from telegram group: %s", err.Error())
	}
}

// HandleTelegramUserParted processes a user leaving the groupchat, without deregistering their account
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, telegramDisplayName string, update telegram.Update) error {
	// If known, spawn the upstream connection; if unknown, kick them
	hubNick, ok := this.config.KnownUsers[telegramUserId]
	if !ok {
		log.Printf("Unexpected user '%s' (%d) joined the group chat, kicking...", telegramDisplayName, telegramUserId)
		this.kickAndDrop(telegramUserId)
	}

	// Remember which users are currently joined
	this.config.GroupChatMembers[telegramUserId] = telegramDisplayName
	err := this.config.Save(this.configFile)
	if err != nil {
		return err
	}

	// 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), joinedUser.String(), 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
		log.Printf("Telegram user '%s' (%d) leaving group chat", update.Message.LeftChatMember.String(), update.Message.LeftChatMember.ID)
		return this.HandleTelegramUserParted(int64(update.Message.LeftChatMember.ID), update)
	}

	if len(update.Message.Text) > 0 {
		// Actual chat message
		// Find the responsible user to send it to the upstream hub, using their account

		userID := int64(update.Message.From.ID)
		hubNick, ok := this.config.KnownUsers[userID]
		if !ok {
			return fmt.Errorf("Couldn't send public message for user '%d' unexpectedly missing hub nick!", userID)
		}

		conn, ok := this.conns[hubNick]
		if !ok {
			return fmt.Errorf("Couldn't send public message for user '%d' (%s) unexpectedly missing upstream connection!", userID, hubNick)
		}

		// Also add it to the coalesce buffer so that we don't replay it from someone else's NMDC connection
		this.Coalesce(hubNick, update.Message.Text)

		// Submit to NMDC
		conn.SayPublic(update.Message.Text)
	}

	// TODO probably a file/image upload???
	// TODO support "editing messages" by re-sending them with a ** suffix

	return nil
}

func (this *NTFServer) ReplyTelegramUser(userID int64, str string, replyToMessageID int) error {
	chatId, ok := this.config.DirectMessageChats[userID]
	if !ok {
		return fmt.Errorf("Can't send telegram message to user '%s': no DM chat known", userID)
	}

	msg := telegram.NewMessage(chatId, str)
	if replyToMessageID != 0 {
		msg.ReplyToMessageID = replyToMessageID
	}
	_, err := this.bot.Send(msg)
	return err
}

func (this *NTFServer) DirectMessageTelegramUser(userID int64, str string) error {
	return this.ReplyTelegramUser(userID, str, 0)
}

func (this *NTFServer) GroupChatSayHTML(str string) error {
	msg := telegram.NewMessage(this.config.GroupChatID, str)
	msg.ParseMode = telegram.ModeHTML
	_, err := this.bot.Send(msg)
	return err
}

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

	// Registration workflow

	userID := int64(update.Message.From.ID)

	// Stash the telegram user ID against this direct-message chat ID so that
	// we can always reply later on
	chatID := update.Message.Chat.ID
	if oldChatID, ok := this.config.DirectMessageChats[userID]; !ok || oldChatID != chatID {
		this.config.DirectMessageChats[userID] = chatID
		err := this.config.Save(this.configFile)
		if err != nil {
			log.Printf("Couldn't save chat ID %d for user %d", chatID, userID)
		}
	}

	respond := func(str string) error {
		return this.ReplyTelegramUser(userID, str, update.Message.MessageID)
	}

	// Find out the current status for this chat ID
	hubNick, isKnown := this.config.KnownUsers[userID]
	_, isInGroupChat := this.config.GroupChatMembers[userID]

	// Handle the incoming request

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

		conn, ok := this.conns[hubNick]
		if !ok {
			return respond("Can't send a native PM (No upstream hub connection)")
		}

		parts := strings.SplitN(msg, " ", 3)
		if len(parts) != 3 {
			return respond("Expected format /pm [recipient] [message] - try again...")
		}

		if !conn.UserExists(parts[1]) {
			return respond(fmt.Sprintf("Can't PM offline user '%s'", parts[1]))
		}

		conn.SayPrivate(parts[1], parts[2])

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

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

	} else if strings.HasPrefix(msg, "/rejoin") {
		if isKnown && !isInGroupChat {
			return respond(fmt.Sprintf("Welcome back '%s'! You can join %s at %s", hubNick, this.config.HubDescription, this.inviteLink))

		} else {
			return respond("You are either already joined (try /quit first), or not yet registered (try /join first).")
		}

	} else if strings.HasPrefix(msg, "/userlist") {
		conn, ok := this.conns[hubNick]
		if !ok {
			return respond("Can't get userlist for you (No upstream hub connection)")
		}

		usernames := make([]string, 0)
		err := conn.Users(func(umap *map[string]libnmdc.UserInfo) error {
			for k, _ := range *umap {
				usernames = append(usernames, k)
			}
			return nil
		})
		if err != nil {
			log.Printf("Error retrieving userlist: %s", err.Error())
			return respond("Can't get userlist for you (internal error)")
		}

		sort.Strings(usernames)
		return respond("Online users: " + strings.Join(usernames, " "))

	} else if strings.HasPrefix(msg, "/whois ") {
		target := msg[7:]
		conn, ok := this.conns[hubNick]
		if !ok {
			return respond("Can't get user details for you (No upstream hub connection)")
		}

		var userinfo libnmdc.UserInfo
		var exists bool
		err := conn.Users(func(umap *map[string]libnmdc.UserInfo) error {
			userinfo, exists = (*umap)[target]
			return nil
		})
		if err != nil {
			log.Printf("Error retrieving userlist: %s", err.Error())
			return respond("Can't get user details for you (internal error)")
		}

		if !exists {
			return respond(fmt.Sprintf("There is no online user '%s'.", target))
		}

		return respond(fmt.Sprintf("Description: %s\nShare size: %d\nClient: %s %s", userinfo.Description, userinfo.ShareSize, userinfo.ClientTag, userinfo.ClientVersion))

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

		this.kickAndDrop(userID)
		return respond("Disconnected. You can register again by typing /help .")

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

		helpMsg += `
		
Available commands:
/setup - Welcome message
/join [hubnick] - Register as 'hubnick' and join ` + this.config.HubDescription + `
/rejoin - Re-invite if you are already registered
/pm [recipient] [message] - Send a native PM (if connected)
/userlist - List native online users
/whois [hubnick] - Check if native user is online, and read their description
/quit - Unregister your nick and leave the group chat
`

		return respond(helpMsg)
	}

	return nil
}