package telegram

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/go-telegram/bot"
	"github.com/go-telegram/bot/models"

	"nukumizu-backend/config"
	"nukumizu-backend/internal/controller"
	"nukumizu-backend/internal/netproxy"
	"nukumizu-backend/internal/node"
	"nukumizu-backend/internal/template"
	"nukumizu-backend/postLog"
)

const (
	// pollTimeout is the getUpdates long-polling window requested from the API.
	// The framework sends (pollTimeout - 1s) to getUpdates; apiTimeout, which
	// also bounds the HTTP client, is kept well above it so a poll request is
	// never cut short by the client.
	pollTimeout = 30 * time.Second

	// apiTimeout bounds individual Bot API calls (getMe, sendMessage, ...) and
	// the initial token check in Start.
	apiTimeout = 2 * time.Minute
)

// TelegramController handles Telegram Bot interactions via long polling. The
// transport and update delivery are provided by the go-telegram/bot framework;
// this type wires it into the unified controller/command pipeline.
type TelegramController struct {
	cfg    config.TelegramConfig
	client *bot.Bot     // underlying go-telegram/bot client
	self   *models.User // the bot's own user object from getMe

	mu           sync.Mutex
	usernameToID map[string]int64 // resolved @username -> numeric user ID

	pollCtx    context.Context // cancelled by Stop to end long polling
	pollCancel context.CancelFunc
}

// NewTelegramController creates a new Telegram controller. When enabled, the
// underlying bot client is built here (with the getMe handshake skipped) so
// outbound messages can be sent as soon as the controller is registered; token
// verification and polling are deferred to Start.
func NewTelegramController(cfg config.TelegramConfig) *TelegramController {
	t := &TelegramController{
		cfg:          cfg,
		usernameToID: make(map[string]int64),
	}
	t.pollCtx, t.pollCancel = context.WithCancel(context.Background())

	if cfg.Enabled && strings.TrimSpace(cfg.BotToken) != "" {
		b, err := t.newBot()
		if err != nil {
			postLog.Error("Failed to build Telegram client: " + err.Error())
			return t
		}
		t.client = b
	}
	return t
}

// Name returns the controller name.
func (t *TelegramController) Name() string {
	return "telegram"
}

// Start verifies the bot token via getMe and begins long polling.
func (t *TelegramController) Start() error {
	if !t.cfg.Enabled {
		return nil
	}
	if t.client == nil {
		if strings.TrimSpace(t.cfg.BotToken) == "" {
			postLog.Warning("Telegram controller enabled but no bot token configured")
		} else {
			postLog.Warning("Telegram controller enabled but client is nil")
		}
		return nil
	}

	ctx, cancel := context.WithTimeout(context.Background(), apiTimeout)
	self, err := t.client.GetMe(ctx)
	cancel()
	if err != nil {
		return fmt.Errorf("failed to verify Telegram bot token (getMe): %w", err)
	}
	t.self = self
	postLog.Info(fmt.Sprintf("Telegram bot authenticated: @%s (id %d)", self.Username, self.ID))

	postLog.Info("Telegram controller started (long polling)")
	go func() {
		defer func() {
			if r := recover(); r != nil {
				postLog.Error(fmt.Sprintf("Telegram poll loop panic recovered: %v", r))
			}
		}()
		// Start blocks until pollCtx is cancelled by Stop. Updates are delivered
		// to the default handler registered in newBot.
		t.client.Start(t.pollCtx)
	}()

	return nil
}

// Stop cancels the long-polling context and shuts down the controller.
func (t *TelegramController) Stop() {
	t.pollCancel()
	postLog.Info("Telegram controller stopped")
}

// IsEnabled returns whether the controller is enabled.
func (t *TelegramController) IsEnabled() bool {
	return t.cfg.Enabled
}

// IsMarkdown returns whether the channel renders Markdown, per its markdown
// setting in config.json.
func (t *TelegramController) IsMarkdown() bool {
	return t.cfg.Markdown
}

// handleUpdate processes a single Telegram update received via long polling. It
// is installed as the framework's default handler (every update with a Message
// reaches it). Updates are processed sequentially because the bot is created
// with WithNotAsyncHandlers, mirroring the original single-threaded poll loop.
func (t *TelegramController) handleUpdate(_ context.Context, _ *bot.Bot, update *models.Update) {
	// Protect the poll loop: a panic while handling one update must not take
	// down long polling.
	defer func() {
		if r := recover(); r != nil {
			postLog.Error(fmt.Sprintf("Telegram update handler panic recovered: %v", r))
		}
	}()

	if update == nil || update.Message == nil {
		return
	}
	msg := update.Message

	if config.C_globalConfig.System.DebugMode && config.C_globalConfig.Debug.ShowTelegramMsg {
		raw, _ := json.Marshal(update)
		postLog.Debug("Telegram update received: " + string(raw))
	}

	// Echo prevention: ignore messages from other bots and from this bot itself.
	if msg.From == nil || msg.From.IsBot {
		return
	}
	if t.self != nil && msg.From.ID == t.self.ID {
		return
	}

	chatType := telegramChatType(string(msg.Chat.Type))
	if chatType == "" {
		return // channel or other unsupported chat type.
	}

	// Record username -> ID so admins configured by username can be reached.
	t.recordUser(msg.From)

	// Only text messages can carry commands.
	if strings.TrimSpace(msg.Text) == "" {
		return
	}

	cmd := controller.Command{
		RawText:  msg.Text,
		ChatID:   msg.Chat.ID,
		ChatType: chatType,
		SenderID: msg.From.ID,
	}

	response := t.processCommand(cmd)
	if response == "" {
		return
	}

	message := controller.Message{
		Source:  "telegram",
		Content: response,
		ChatID:  msg.Chat.ID,
		Type:    controller.MessageTypeReply,
	}

	if err := t.sendMessage(message); err != nil {
		postLog.Warning("Failed to send Telegram reply: " + err.Error())
	}
}

// processCommand validates an incoming message as a command and hands the
// complete command to the unified processor. It returns the response text to
// reply with; an empty response means the message was discarded.
func (t *TelegramController) processCommand(cmd controller.Command) string {
	text := cmd.RawText

	// In "at" listen mode, require a mention of the bot and strip it before
	// parsing, mirroring the QQ CQ-at behavior.
	if t.cfg.ListenMethod == "at" && t.self != nil && t.self.Username != "" {
		mention := "@" + t.self.Username
		if !strings.Contains(text, mention) {
			return "" // Not mentioned, ignore.
		}
		text = strings.ReplaceAll(text, mention, "")
	}

	// Telegram appends @botname to commands sent in groups (/list@MyBot); strip
	// it so the command word parses.
	text = stripCommandBotSuffix(text)

	// First check whether the received message is a command.
	parsed, ok := controller.ParseCommand(text)
	if !ok {
		return "" // Not a command, discard.
	}

	parsed.ChatID = cmd.ChatID
	parsed.ChatType = cmd.ChatType
	parsed.SenderID = cmd.SenderID
	parsed.Source = "telegram"

	// Hand the complete command to the unified processor, which checks group
	// vs private, trusted groups, admin permissions, and executes it.
	response, err := controller.GetManager().Trigger(parsed, t.trustedGroupIDs(), t.resolvedAdminList(), t.cfg.ListenMethod)
	if config.C_globalConfig.System.DebugMode && config.C_globalConfig.Debug.ShowTriggerCmdEcho {
		postLog.Debug(fmt.Sprintf("[telegram] triggered command: \"/%s\" with args: \"%s\" from chatID: %d and senderID: %d", parsed.Command, strings.Join(parsed.Args, ", "), cmd.ChatID, cmd.SenderID))
	}
	if err != nil {
		postLog.Error("Telegram command processing failed: " + err.Error())
		return ""
	}
	return response
}

// SendMessage sends an automatic message (e.g. the bot initialization message
// and the startup server list) to all Telegram trusted groups and admins. Each
// member's opt-out options in bot_user_config.json (e.g. EventBotStarted for
// event_bot_started messages) are honored per recipient.
func (t *TelegramController) SendMessage(message controller.Message) error {
	if !t.cfg.Enabled || t.client == nil {
		return nil
	}

	// Only notify trusted groups and admins whose options allow this message type.
	if uc := config.C_botUserConfig; uc != nil {
		for groupID, opts := range uc.Telegram.TrustedGroups {
			if !controller.MemberReceives(opts, message.Type) {
				continue
			}
			t.sendGroupMessage(groupID, message.Content)
		}
		for admin, opts := range uc.Telegram.Admins {
			if !controller.MemberReceives(opts, message.Type) {
				continue
			}
			t.sendAdminMessage(admin, message.Content)
		}
	}
	return nil
}

// SendStatusChange sends a status change notification via Telegram.
func (t *TelegramController) SendStatusChange(change node.StatusChange) error {
	if !t.cfg.Enabled || t.client == nil {
		return nil
	}

	cfg := config.C_globalConfig
	params := template.BuildParamsFromStatusChange(change)
	message := template.Render(cfg.ControllerMessage.ServerStatusChanged, params, t.cfg.Markdown)

	// Only notify trusted groups and admins whose event_status_notify is true.
	if uc := config.C_botUserConfig; uc != nil {
		for groupID, opts := range uc.Telegram.TrustedGroups {
			if !opts.EventStatusNotify {
				continue
			}
			t.sendGroupMessage(groupID, message)
		}
		for admin, opts := range uc.Telegram.Admins {
			if !opts.EventStatusNotify {
				continue
			}
			t.sendAdminMessage(admin, message)
		}
	}
	return nil
}

// SendServerList sends the server list via Telegram.
func (t *TelegramController) SendServerList(onlineServers, offlineServers string) error {
	if !t.cfg.Enabled || t.client == nil {
		return nil
	}

	cfg := config.C_globalConfig
	params := template.BuildParamsFromServerList()
	message := template.Render(cfg.ControllerMessage.ServerList, params, t.cfg.Markdown)

	t.sendToGroups(message)
	return nil
}

// SendExecuteResult sends a command execution result via Telegram.
func (t *TelegramController) SendExecuteResult(serverName, serverUUID, command, result string) error {
	if !t.cfg.Enabled || t.client == nil {
		return nil
	}

	cfg := config.C_globalConfig
	params := template.BuildParamsFromExecResult(serverName, serverUUID, command, result)
	message := template.Render(cfg.ControllerMessage.ServerExecuteResult, params, t.cfg.Markdown)

	t.sendToGroups(message)
	return nil
}

// SendAlert sends an alert submitted through the incoming webhook API to all
// Telegram trusted groups and admins.
func (t *TelegramController) SendAlert(alert controller.Alert) error {
	if !t.cfg.Enabled || t.client == nil {
		return nil
	}

	return t.SendMessage(controller.Message{
		Source:  t.Name(),
		Content: alert.Render(t.cfg.Markdown),
		Type:    controller.MessageTypeAlert,
	})
}

// telegramChatType maps a Telegram chat type to the unified ChatType value used
// by the controller package. Empty means the chat type is unsupported.
func telegramChatType(chatType string) string {
	switch chatType {
	case "private":
		return "private"
	case "group", "supergroup":
		return "group"
	default:
		return ""
	}
}

// stripCommandBotSuffix removes a "@botname" suffix from the command word,
// turning "/list@MyBot" into "/list".
func stripCommandBotSuffix(text string) string {
	if !strings.HasPrefix(text, "/") {
		return text
	}

	// The command word is everything before the first space.
	spaceIdx := strings.Index(text, " ")
	if spaceIdx < 0 {
		spaceIdx = len(text)
	}

	command, _, found := strings.Cut(text[1:spaceIdx], "@")
	if !found {
		return text
	}
	return "/" + command + text[spaceIdx:]
}

// recordUser stores the numeric ID for a sender's username so admins configured
// by username (rather than numeric ID) can be resolved later.
func (t *TelegramController) recordUser(u *models.User) {
	if u == nil || u.Username == "" {
		return
	}
	t.mu.Lock()
	t.usernameToID[strings.ToLower(u.Username)] = u.ID
	t.mu.Unlock()
}

// resolveUsername resolves a Telegram username to its numeric ID, or returns
// ok == false when the user has not messaged the bot yet.
func (t *TelegramController) resolveUsername(username string) (int64, bool) {
	t.mu.Lock()
	defer t.mu.Unlock()
	id, ok := t.usernameToID[strings.ToLower(strings.TrimPrefix(username, "@"))]
	return id, ok
}

// adminIDs returns the Telegram admin entries (numeric user ID or @username)
// from bot_user_config.json.
func (t *TelegramController) adminIDs() []string {
	if c := config.C_botUserConfig; c != nil {
		return c.Telegram.Admins.IDs()
	}
	return nil
}

// trustedGroupIDs returns the Telegram trusted group IDs from bot_user_config.json.
func (t *TelegramController) trustedGroupIDs() []string {
	if c := config.C_botUserConfig; c != nil {
		return c.Telegram.TrustedGroups.IDs()
	}
	return nil
}

// resolvedAdminList maps username-based admin entries to numeric IDs so the
// unified processor's numeric IsAdmin check works. Unresolvable entries (the
// user has not messaged the bot yet) pass through unchanged and simply never
// match.
func (t *TelegramController) resolvedAdminList() []string {
	admins := t.adminIDs()
	result := make([]string, 0, len(admins))
	for _, admin := range admins {
		if id, ok := t.resolveUsername(admin); ok {
			result = append(result, strconv.FormatInt(id, 10))
		} else {
			result = append(result, admin)
		}
	}
	return result
}

// sendToGroups sends a message to all trusted groups.
func (t *TelegramController) sendToGroups(message string) {
	for _, groupID := range t.trustedGroupIDs() {
		t.sendGroupMessage(groupID, message)
	}
}

// sendGroupMessage sends a message to a single group chat.
func (t *TelegramController) sendGroupMessage(groupID string, message string) {
	chatID, err := strconv.ParseInt(groupID, 10, 64)
	if err != nil || chatID == 0 {
		postLog.Warning(fmt.Sprintf("Invalid Telegram group chat ID: %s", groupID))
		return
	}
	t.sendToChat(chatID, message)
}

// sendAdminMessage sends a message to an admin, resolving a username-based
// entry to a numeric ID. Telegram bots cannot start conversations, so an admin
// configured by username is only reachable after they have messaged the bot.
func (t *TelegramController) sendAdminMessage(admin string, message string) {
	chatID, err := strconv.ParseInt(admin, 10, 64)
	if err != nil || chatID == 0 {
		// Not a numeric ID: try to resolve a username.
		if id, ok := t.resolveUsername(admin); ok {
			t.sendToChat(id, message)
			return
		}
		postLog.Warning(fmt.Sprintf("Cannot reach Telegram admin %q: user has not messaged the bot yet (bots cannot start conversations)", admin))
		return
	}
	t.sendToChat(chatID, message)
}

// sendToChat sends a message to a chat ID, logging failures.
func (t *TelegramController) sendToChat(chatID int64, message string) {
	messaged := controller.Message{
		Source:  "telegram",
		Content: message,
		ChatID:  chatID,
		Type:    controller.MessageTypeReply,
	}
	if err := t.sendMessage(messaged); err != nil {
		postLog.Warning(fmt.Sprintf("Failed to send Telegram message to %d: %v", chatID, err))
	}
}

// newBot builds the underlying go-telegram/bot client. getMe is skipped here so
// the constructor stays non-blocking (outbound sends must work before Start
// runs); the token is actually verified in Start. Requests are routed through
// the network proxy when enabled, and poll errors are logged via postLog.
func (t *TelegramController) newBot() (*bot.Bot, error) {
	opts := []bot.Option{
		bot.WithSkipGetMe(),
		bot.WithHTTPClient(pollTimeout, netproxy.HTTPClient(t.cfg.NetworkUseProxy, apiTimeout)),
		bot.WithDefaultHandler(t.handleUpdate),
		bot.WithNotAsyncHandlers(),
		bot.WithErrorsHandler(func(err error) {
			if errors.Is(err, bot.ErrorConflict) {
				postLog.Error("Telegram getUpdates conflict (409): another poller is using the same bot token. Ensure only one instance is polling.")
			} else {
				postLog.Warning("Telegram Bot API error: " + err.Error())
			}
		}),
	}
	return bot.New(t.cfg.BotToken, opts...)
}