package telegram

import (
	"context"
	"fmt"
	"log/slog"
	"strconv"
	"strings"
	"sync"

	"gitea.computernetthings.ru/yash/crypto_alert_bot/internal/entities"
	"gitea.computernetthings.ru/yash/crypto_alert_bot/internal/provider"
	tgbotapi "github.com/go-telegram-bot-api/telegram-bot-api/v5"
	"github.com/shopspring/decimal"
)

const (
	alertsPageSize = 5
	instrPageSize  = 4
)

// Usecase defines the business logic operations required by the bot.
type Usecase interface {
	RegisterNewUser(ctx context.Context, user *entities.User) error
	UserByID(ctx context.Context, userID entities.UserID) (*entities.User, error)
	UserByTgID(ctx context.Context, telegramID entities.TelegramID) (*entities.User, error)
	InstrumentList(ctx context.Context, userID entities.UserID, offset, limit int) ([]entities.Instrument, error)
	AddUserInstrument(ctx context.Context, userID entities.UserID, base, quote string) (*entities.Instrument, error)
	RemoveUserInstrument(ctx context.Context, userID entities.UserID, instrumentID entities.InstrumentID) error
	CreateAlert(ctx context.Context, alert *entities.Alert) (entities.AlertID, error)
	Alert(ctx context.Context, alertID entities.AlertID) (*entities.Alert, error)
	Alerts(ctx context.Context, userID entities.UserID, offset, limit int) ([]entities.Alert, error)
	RemoveAlert(ctx context.Context, alertID entities.AlertID) error
	UpdateAlertPrice(ctx context.Context, alertID entities.AlertID, price decimal.Decimal) error
}

// Alerter keeps the in-memory alert cache in sync with created/removed alerts.
type Alerter interface {
	AddAlert(alert *entities.Alert)
	RemoveAlert(id entities.AlertID)
}

// PriceProvider fetches the current market price for an instrument and validates pairs.
type PriceProvider interface {
	Price(ctx context.Context, instrument entities.Instrument) (*entities.Price, error)
	InstrumentExists(ctx context.Context, base, quote string) (bool, error)
}

// Reply keyboard button labels.
const (
	btnAddAlert    = "Add Alert"
	btnMyAlerts    = "My Alerts"
	btnInstruments = "Instruments"
	btnAddPair     = "Add Pair"
)

type flowStep string

const (
	stepAddAlertPrice     flowStep = "add_alert_price"
	stepAddAlertAwaitType flowStep = "add_alert_await_type" // price entered, waiting for type callback
	stepEditAlertPrice    flowStep = "edit_alert_price"
	stepAddPair           flowStep = "add_pair"
)

type userState struct {
	step         flowStep
	instrument   entities.Instrument // set during add_alert flow
	currentPrice *entities.Price     // fetched when instrument is selected
	targetPrice  decimal.Decimal     // set after price is entered, before type selection
	alertID      entities.AlertID    // set during edit flow
}

// alertTimeframe pairs a KlineInterval with its display label.
type alertTimeframe struct {
	interval provider.KlineInterval
	label    string
}

// offeredTimeframes are the timeframes shown to the user when creating a candle-close alert.
var offeredTimeframes = []alertTimeframe{
	{provider.Kline1m, "1m"},
	{provider.Kline5m, "5m"},
	{provider.Kline15m, "15m"},
	{provider.Kline1H, "1H"},
	{provider.Kline4H, "4H"},
	{provider.Kline1D, "1D"},
	{provider.Kline1W, "1W"},
}

// Bot is the Telegram bot handling all user interactions.
type Bot struct {
	api      *tgbotapi.BotAPI
	log      *slog.Logger
	usecase  Usecase
	alerter  Alerter
	provider PriceProvider
	states   map[entities.TelegramID]*userState
	mu       sync.Mutex
}

// New creates and initialises a new Bot. Call SetAlerter before Run to enable cache sync.
func New(token string, log *slog.Logger, uc Usecase, pp PriceProvider) (*Bot, error) {
	api, err := tgbotapi.NewBotAPI(token)
	if err != nil {
		return nil, fmt.Errorf("failed to create bot: %w", err)
	}

	return &Bot{
		api:      api,
		log:      log,
		usecase:  uc,
		provider: pp,
		states:   make(map[entities.TelegramID]*userState),
	}, nil
}

// SetAlerter injects the alerter after construction, resolving the circular dependency.
func (b *Bot) SetAlerter(al Alerter) {
	b.alerter = al
}

// Run starts the update loop and blocks until ctx is cancelled.
func (b *Bot) Run(ctx context.Context) {
	u := tgbotapi.NewUpdate(0)
	u.Timeout = 60

	updates := b.api.GetUpdatesChan(u)
	b.log.Info("bot started", "username", b.api.Self.UserName)

	for {
		select {
		case <-ctx.Done():
			b.api.StopReceivingUpdates()
			return
		case update, ok := <-updates:
			if !ok {
				return
			}
			go b.handleUpdate(ctx, update)
		}
	}
}

// NotifyAlert implements alerter.Notifier. Called by the alerter service when a price threshold is hit.
func (b *Bot) NotifyAlert(ctx context.Context, userID entities.UserID, alert *entities.Alert, currentPrice decimal.Decimal) error {
	user, err := b.usecase.UserByID(ctx, userID)
	if err != nil {
		return fmt.Errorf("failed to get user: %w", err)
	}

	text := fmt.Sprintf(
		"Alert triggered!\n\n%s/%s %s %s%s\nClose price: %s",
		alert.Instrument.BaseCurrency,
		alert.Instrument.QuoteCurrency,
		formatCondition(alert.Condition),
		alert.Price.String(),
		formatTimeframeSuffix(alert),
		currentPrice.String(),
	)
	msg := tgbotapi.NewMessage(int64(user.TelegramID), text)
	kb := menuKeyboard()
	kb.ResizeKeyboard = true
	msg.ReplyMarkup = kb
	_, err = b.api.Send(msg)
	return err
}

// formatCondition returns a human-readable alert condition label.
func formatCondition(c entities.AlertCondition) string {
	switch c {
	case entities.AlertConditionAbove:
		return "above"
	case entities.AlertConditionBelow:
		return "below"
	case entities.AlertConditionCloseAbove:
		return "close above"
	case entities.AlertConditionCloseBelow:
		return "close below"
	default:
		return string(c)
	}
}

// formatTimeframeSuffix returns " (4H)" for candle-close alerts, empty string otherwise.
func formatTimeframeSuffix(alert *entities.Alert) string {
	if alert.Timeframe == "" {
		return ""
	}
	return fmt.Sprintf(" (%s)", alert.Timeframe)
}

// --- Routing ---

func (b *Bot) handleUpdate(ctx context.Context, update tgbotapi.Update) {
	switch {
	case update.Message != nil:
		b.handleMessage(ctx, update.Message)
	case update.CallbackQuery != nil:
		b.handleCallback(ctx, update.CallbackQuery)
	}
}

func (b *Bot) handleMessage(ctx context.Context, msg *tgbotapi.Message) {
	tgID := entities.TelegramID(msg.From.ID)
	chatID := msg.Chat.ID

	if msg.IsCommand() {
		b.handleCommand(ctx, tgID, chatID, msg.Command())
		return
	}

	// Map persistent reply-keyboard buttons to actions.
	switch msg.Text {
	case btnAddAlert:
		b.cmdAddAlert(ctx, tgID, chatID)
		return
	case btnMyAlerts:
		b.cmdMyAlerts(ctx, tgID, chatID)
		return
	case btnInstruments:
		b.cmdInstruments(ctx, tgID, chatID)
		return
	case btnAddPair:
		b.cmdAddPair(ctx, tgID, chatID)
		return
	}

	// Route plain-text input to the active multi-step flow.
	state := b.getState(tgID)
	switch state.step {
	case stepAddAlertPrice:
		b.handleAddAlertPrice(ctx, tgID, chatID, msg.Text, state)
	case stepAddAlertAwaitType:
		b.send(chatID, "Please select the alert type using the buttons above.")
	case stepEditAlertPrice:
		b.handleEditAlertPrice(ctx, tgID, chatID, msg.Text, state)
	case stepAddPair:
		b.handleAddPairInput(ctx, tgID, chatID, msg.Text)
	default:
		b.sendMenu(chatID, "Use the menu below or /add_alert to set a price alert.")
	}
}

func (b *Bot) handleCommand(ctx context.Context, tgID entities.TelegramID, chatID int64, cmd string) {
	switch cmd {
	case "start":
		b.cmdStart(ctx, tgID, chatID)
	case "instruments":
		b.cmdInstruments(ctx, tgID, chatID)
	case "add_alert":
		b.cmdAddAlert(ctx, tgID, chatID)
	case "my_alerts":
		b.cmdMyAlerts(ctx, tgID, chatID)
	case "add_pair":
		b.cmdAddPair(ctx, tgID, chatID)
	case "cancel":
		b.cmdCancel(tgID, chatID)
	default:
		b.sendMenu(chatID, "Unknown command.\n\nAvailable commands:\n/start — register\n/instruments — list trading pairs\n/add_alert — create a price alert\n/my_alerts — view your alerts\n/add_pair — add a custom trading pair\n/cancel — cancel current operation")
	}
}

func (b *Bot) handleCallback(ctx context.Context, cb *tgbotapi.CallbackQuery) {
	tgID := entities.TelegramID(cb.From.ID)
	chatID := cb.Message.Chat.ID
	messageID := cb.Message.MessageID

	// Acknowledge the callback immediately so the button stops spinning.
	b.api.Request(tgbotapi.NewCallback(cb.ID, "")) //nolint:errcheck

	data := cb.Data
	switch {
	case strings.HasPrefix(data, "instrument:"):
		instrID := entities.InstrumentID(strings.TrimPrefix(data, "instrument:"))
		b.handleInstrumentSelected(ctx, tgID, chatID, instrID)

	case strings.HasPrefix(data, "add_alert_instr_page:"):
		page, _ := strconv.Atoi(strings.TrimPrefix(data, "add_alert_instr_page:"))
		b.handleAddAlertInstrPage(ctx, tgID, chatID, messageID, page)

	case strings.HasPrefix(data, "instr_page:"):
		page, _ := strconv.Atoi(strings.TrimPrefix(data, "instr_page:"))
		b.handleInstrumentsPage(ctx, tgID, chatID, messageID, page)

	case strings.HasPrefix(data, "instr_select:"):
		// format: instr_select:<instrID>:<page>
		rest := strings.TrimPrefix(data, "instr_select:")
		idx := strings.LastIndex(rest, ":")
		instrID := entities.InstrumentID(rest[:idx])
		page, _ := strconv.Atoi(rest[idx+1:])
		b.handleInstrumentSelect(ctx, tgID, chatID, messageID, instrID, page)

	case strings.HasPrefix(data, "instr_remove:"):
		// format: instr_remove:<instrID>:<page>
		rest := strings.TrimPrefix(data, "instr_remove:")
		idx := strings.LastIndex(rest, ":")
		instrID := entities.InstrumentID(rest[:idx])
		page, _ := strconv.Atoi(rest[idx+1:])
		b.handleInstrumentRemoveConfirm(chatID, messageID, instrID, page)

	case strings.HasPrefix(data, "confirm_remove_instr:"):
		// format: confirm_remove_instr:<instrID>:<page>
		rest := strings.TrimPrefix(data, "confirm_remove_instr:")
		idx := strings.LastIndex(rest, ":")
		instrID := entities.InstrumentID(rest[:idx])
		page, _ := strconv.Atoi(rest[idx+1:])
		b.handleInstrumentRemoveDo(ctx, tgID, chatID, messageID, instrID, page)

	case strings.HasPrefix(data, "cancel_remove_instr:"):
		// format: cancel_remove_instr:<instrID>:<page>
		rest := strings.TrimPrefix(data, "cancel_remove_instr:")
		idx := strings.LastIndex(rest, ":")
		instrID := entities.InstrumentID(rest[:idx])
		page, _ := strconv.Atoi(rest[idx+1:])
		b.handleInstrumentSelect(ctx, tgID, chatID, messageID, instrID, page)

	case strings.HasPrefix(data, "alerts_page:"), strings.HasPrefix(data, "alerts_back:"):
		rest := data[strings.Index(data, ":")+1:]
		page, _ := strconv.Atoi(rest)
		b.handleAlertsPage(ctx, tgID, chatID, messageID, page)

	case strings.HasPrefix(data, "alert_select:"):
		// format: alert_select:<alertID>:<page>
		rest := strings.TrimPrefix(data, "alert_select:")
		idx := strings.LastIndex(rest, ":")
		alertID := entities.AlertID(rest[:idx])
		page, _ := strconv.Atoi(rest[idx+1:])
		b.handleAlertSelect(ctx, chatID, messageID, alertID, page)

	case strings.HasPrefix(data, "edit_alert:"):
		alertID := entities.AlertID(strings.TrimPrefix(data, "edit_alert:"))
		b.handleEditAlertStart(tgID, chatID, alertID)

	case strings.HasPrefix(data, "remove_alert:"):
		// format: remove_alert:<alertID>:<page>
		rest := strings.TrimPrefix(data, "remove_alert:")
		idx := strings.LastIndex(rest, ":")
		alertID := entities.AlertID(rest[:idx])
		page, _ := strconv.Atoi(rest[idx+1:])
		b.handleRemoveAlertConfirm(chatID, messageID, alertID, page)

	case strings.HasPrefix(data, "confirm_remove:"):
		// format: confirm_remove:<alertID>:<page>
		rest := strings.TrimPrefix(data, "confirm_remove:")
		idx := strings.LastIndex(rest, ":")
		alertID := entities.AlertID(rest[:idx])
		page, _ := strconv.Atoi(rest[idx+1:])
		b.handleRemoveAlertDo(ctx, tgID, chatID, messageID, alertID, page)

	case strings.HasPrefix(data, "cancel_remove:"):
		// format: cancel_remove:<alertID>:<page>
		rest := strings.TrimPrefix(data, "cancel_remove:")
		idx := strings.LastIndex(rest, ":")
		alertID := entities.AlertID(rest[:idx])
		page, _ := strconv.Atoi(rest[idx+1:])
		b.handleAlertSelect(ctx, chatID, messageID, alertID, page)

	case data == "alert_type:crossing":
		b.handleAlertTypeCrossing(ctx, tgID, chatID)

	case data == "alert_type:close":
		b.handleAlertTypeClose(tgID, chatID)

	case strings.HasPrefix(data, "alert_timeframe:"):
		tf := provider.KlineInterval(strings.TrimPrefix(data, "alert_timeframe:"))
		b.handleAlertTimeframe(ctx, tgID, chatID, tf)
	}
}

// --- Command handlers ---

func (b *Bot) cmdStart(ctx context.Context, tgID entities.TelegramID, chatID int64) {
	// If already registered, just greet them.
	if _, err := b.usecase.UserByTgID(ctx, tgID); err == nil {
		b.sendMenu(chatID, "Welcome back! Use the menu below to manage your alerts.")
		return
	}

	user := &entities.User{TelegramID: tgID}
	if err := b.usecase.RegisterNewUser(ctx, user); err != nil {
		b.log.Error("failed to register user", "tg_id", tgID, "err", err)
		b.sendMenu(chatID, "Registration failed. Please try again.")
		return
	}
	b.sendMenu(chatID, "Welcome! You are now registered.\n\nUse the menu below to get started.")
}

func (b *Bot) cmdInstruments(ctx context.Context, tgID entities.TelegramID, chatID int64) {
	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	instruments, err := b.usecase.InstrumentList(ctx, user.ID, 0, 200)
	if err != nil {
		b.log.Error("failed to list instruments", "err", err)
		b.sendMenu(chatID, "Failed to load instruments.")
		return
	}
	if len(instruments) == 0 {
		b.sendMenu(chatID, "No instruments available.")
		return
	}

	text, kb := buildInstrumentsPage(instruments, 0)
	msg := tgbotapi.NewMessage(chatID, text)
	msg.ReplyMarkup = kb
	b.sendMsg(msg)
}

func (b *Bot) cmdAddAlert(ctx context.Context, tgID entities.TelegramID, chatID int64) {
	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	instruments, err := b.usecase.InstrumentList(ctx, user.ID, 0, 200)
	if err != nil {
		b.log.Error("failed to list instruments", "err", err)
		b.sendMenu(chatID, "Failed to load instruments.")
		return
	}
	if len(instruments) == 0 {
		b.sendMenu(chatID, "No instruments available. Use \"Add Pair\" to add one.")
		return
	}

	text, kb := buildAddAlertInstrPage(instruments, 0)
	msg := tgbotapi.NewMessage(chatID, text)
	msg.ReplyMarkup = kb
	b.sendMsg(msg)
}

func (b *Bot) cmdMyAlerts(ctx context.Context, tgID entities.TelegramID, chatID int64) {
	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	alerts, err := b.usecase.Alerts(ctx, user.ID, 0, 100)
	if err != nil {
		b.log.Error("failed to get alerts", "err", err)
		b.sendMenu(chatID, "Failed to load alerts.")
		return
	}
	if len(alerts) == 0 {
		b.sendMenu(chatID, "You have no active alerts. Use \"Add Alert\" to create one.")
		return
	}

	text, kb := buildAlertsPage(alerts, 0)
	msg := tgbotapi.NewMessage(chatID, text)
	msg.ReplyMarkup = kb
	b.sendMsg(msg)
}

func (b *Bot) cmdAddPair(ctx context.Context, tgID entities.TelegramID, chatID int64) {
	if _, err := b.requireUser(ctx, tgID, chatID); err != nil {
		return
	}
	b.setState(tgID, &userState{step: stepAddPair})
	b.send(chatID, "Enter the trading pair in BASE/QUOTE format (e.g. DOGE/USDT):")
}

func (b *Bot) cmdCancel(tgID entities.TelegramID, chatID int64) {
	b.setState(tgID, &userState{})
	b.sendMenu(chatID, "Operation cancelled.")
}

// --- Instruments pagination ---

// buildInstrumentsPage constructs a paginated instruments list.
// Numbered buttons let users open a detail view; ◀ ▶ navigate pages.
func buildInstrumentsPage(instruments []entities.Instrument, page int) (string, tgbotapi.InlineKeyboardMarkup) {
	total := len(instruments)
	totalPages := (total + instrPageSize - 1) / instrPageSize

	start := page * instrPageSize
	end := start + instrPageSize
	if end > total {
		end = total
	}
	pageItems := instruments[start:end]

	var sb strings.Builder
	fmt.Fprintf(&sb, "Trading pairs (page %d/%d):\n\n", page+1, totalPages)
	for i, instr := range pageItems {
		marker := ""
		if !instr.IsGlobal {
			marker = " ✦" // marks user-added pairs
		}
		fmt.Fprintf(&sb, "%d. %s/%s%s\n", start+i+1, instr.BaseCurrency, instr.QuoteCurrency, marker)
	}

	var rows [][]tgbotapi.InlineKeyboardButton

	// One button per instrument on this page.
	var itemRow []tgbotapi.InlineKeyboardButton
	for i, instr := range pageItems {
		itemRow = append(itemRow, tgbotapi.NewInlineKeyboardButtonData(
			strconv.Itoa(start+i+1),
			fmt.Sprintf("instr_select:%s:%d", instr.ID, page),
		))
	}
	if len(itemRow) > 0 {
		rows = append(rows, itemRow)
	}

	var navRow []tgbotapi.InlineKeyboardButton
	if page > 0 {
		navRow = append(navRow, tgbotapi.NewInlineKeyboardButtonData("◀", fmt.Sprintf("instr_page:%d", page-1)))
	}
	if end < total {
		navRow = append(navRow, tgbotapi.NewInlineKeyboardButtonData("▶", fmt.Sprintf("instr_page:%d", page+1)))
	}
	if len(navRow) > 0 {
		rows = append(rows, navRow)
	}

	return sb.String(), tgbotapi.NewInlineKeyboardMarkup(rows...)
}

// handleInstrumentsPage re-fetches instruments and edits the message to show the requested page.
func (b *Bot) handleInstrumentsPage(ctx context.Context, tgID entities.TelegramID, chatID int64, messageID int, page int) {
	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	instruments, err := b.usecase.InstrumentList(ctx, user.ID, 0, 200)
	if err != nil {
		b.log.Error("failed to list instruments", "err", err)
		return
	}

	totalPages := (len(instruments) + instrPageSize - 1) / instrPageSize
	if page >= totalPages {
		page = totalPages - 1
	}

	text, kb := buildInstrumentsPage(instruments, page)
	edit := tgbotapi.NewEditMessageTextAndMarkup(chatID, messageID, text, kb)
	if _, err := b.api.Send(edit); err != nil {
		b.log.Error("failed to edit message", "err", err)
	}
}

// handleInstrumentSelect shows instrument detail with a Remove button (for user-added pairs).
func (b *Bot) handleInstrumentSelect(ctx context.Context, tgID entities.TelegramID, chatID int64, messageID int, instrID entities.InstrumentID, page int) {
	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	instruments, err := b.usecase.InstrumentList(ctx, user.ID, 0, 200)
	if err != nil {
		b.log.Error("failed to list instruments", "err", err)
		return
	}

	var selected entities.Instrument
	for _, instr := range instruments {
		if instr.ID == instrID {
			selected = instr
			break
		}
	}
	if selected.ID == "" {
		b.editMsgText(chatID, messageID, "Instrument not found.")
		return
	}

	text := fmt.Sprintf("%s/%s", selected.BaseCurrency, selected.QuoteCurrency)
	if !selected.IsGlobal {
		text += "\n(user-added pair)"
	}

	var btns []tgbotapi.InlineKeyboardButton
	if !selected.IsGlobal {
		btns = append(btns, tgbotapi.NewInlineKeyboardButtonData(
			"Remove", fmt.Sprintf("instr_remove:%s:%d", instrID, page),
		))
	}
	btns = append(btns, tgbotapi.NewInlineKeyboardButtonData(
		"◀ Back", fmt.Sprintf("instr_page:%d", page),
	))

	edit := tgbotapi.NewEditMessageTextAndMarkup(chatID, messageID, text,
		tgbotapi.NewInlineKeyboardMarkup(btns))
	if _, err := b.api.Send(edit); err != nil {
		b.log.Error("failed to edit message", "err", err)
	}
}

// handleInstrumentRemoveConfirm asks the user to confirm removal.
func (b *Bot) handleInstrumentRemoveConfirm(chatID int64, messageID int, instrID entities.InstrumentID, page int) {
	kb := tgbotapi.NewInlineKeyboardMarkup(tgbotapi.NewInlineKeyboardRow(
		tgbotapi.NewInlineKeyboardButtonData("Yes, remove", fmt.Sprintf("confirm_remove_instr:%s:%d", instrID, page)),
		tgbotapi.NewInlineKeyboardButtonData("Cancel", fmt.Sprintf("cancel_remove_instr:%s:%d", instrID, page)),
	))
	edit := tgbotapi.NewEditMessageTextAndMarkup(chatID, messageID, "Remove this pair from your list?", kb)
	if _, err := b.api.Send(edit); err != nil {
		b.log.Error("failed to edit message", "err", err)
	}
}

// handleInstrumentRemoveDo removes the instrument from the user's list and refreshes the page.
func (b *Bot) handleInstrumentRemoveDo(ctx context.Context, tgID entities.TelegramID, chatID int64, messageID int, instrID entities.InstrumentID, page int) {
	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	if err := b.usecase.RemoveUserInstrument(ctx, user.ID, instrID); err != nil {
		b.log.Error("failed to remove user instrument", "instrument_id", instrID, "err", err)
		b.editMsgText(chatID, messageID, "Failed to remove pair.")
		return
	}

	b.handleInstrumentsPage(ctx, tgID, chatID, messageID, page)
}

// buildAddAlertInstrPage builds the instrument selection keyboard for the add-alert flow.
func buildAddAlertInstrPage(instruments []entities.Instrument, page int) (string, tgbotapi.InlineKeyboardMarkup) {
	total := len(instruments)
	totalPages := (total + instrPageSize - 1) / instrPageSize

	start := page * instrPageSize
	end := start + instrPageSize
	if end > total {
		end = total
	}
	pageItems := instruments[start:end]

	text := fmt.Sprintf("Select a trading pair (page %d/%d):", page+1, totalPages)

	var rows [][]tgbotapi.InlineKeyboardButton
	for _, instr := range pageItems {
		btn := tgbotapi.NewInlineKeyboardButtonData(
			fmt.Sprintf("%s/%s", instr.BaseCurrency, instr.QuoteCurrency),
			fmt.Sprintf("instrument:%s", instr.ID),
		)
		rows = append(rows, tgbotapi.NewInlineKeyboardRow(btn))
	}

	var navRow []tgbotapi.InlineKeyboardButton
	if page > 0 {
		navRow = append(navRow, tgbotapi.NewInlineKeyboardButtonData("◀", fmt.Sprintf("add_alert_instr_page:%d", page-1)))
	}
	if end < total {
		navRow = append(navRow, tgbotapi.NewInlineKeyboardButtonData("▶", fmt.Sprintf("add_alert_instr_page:%d", page+1)))
	}
	if len(navRow) > 0 {
		rows = append(rows, navRow)
	}

	return text, tgbotapi.NewInlineKeyboardMarkup(rows...)
}

// handleAddAlertInstrPage edits the instrument selection message to show a different page.
func (b *Bot) handleAddAlertInstrPage(ctx context.Context, tgID entities.TelegramID, chatID int64, messageID int, page int) {
	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	instruments, err := b.usecase.InstrumentList(ctx, user.ID, 0, 200)
	if err != nil {
		b.log.Error("failed to list instruments", "err", err)
		return
	}

	totalPages := (len(instruments) + instrPageSize - 1) / instrPageSize
	if page >= totalPages {
		page = totalPages - 1
	}

	text, kb := buildAddAlertInstrPage(instruments, page)
	edit := tgbotapi.NewEditMessageTextAndMarkup(chatID, messageID, text, kb)
	if _, err := b.api.Send(edit); err != nil {
		b.log.Error("failed to edit message", "err", err)
	}
}

// --- Alerts pagination ---

// buildAlertsPage constructs the message text and inline keyboard for a paginated alerts list.
func buildAlertsPage(alerts []entities.Alert, page int) (string, tgbotapi.InlineKeyboardMarkup) {
	total := len(alerts)
	totalPages := (total + alertsPageSize - 1) / alertsPageSize

	start := page * alertsPageSize
	end := start + alertsPageSize
	if end > total {
		end = total
	}
	pageAlerts := alerts[start:end]

	var sb strings.Builder
	fmt.Fprintf(&sb, "Your active alerts (page %d/%d):\n\n", page+1, totalPages)
	for i, alert := range pageAlerts {
		fmt.Fprintf(&sb, "%d. %s/%s %s %s%s\n",
			start+i+1,
			alert.Instrument.BaseCurrency,
			alert.Instrument.QuoteCurrency,
			formatCondition(alert.Condition),
			alert.Price.String(),
			formatTimeframeSuffix(&alert),
		)
	}

	var rows [][]tgbotapi.InlineKeyboardButton

	// One button per alert on this page.
	var alertRow []tgbotapi.InlineKeyboardButton
	for i, alert := range pageAlerts {
		alertRow = append(alertRow, tgbotapi.NewInlineKeyboardButtonData(
			strconv.Itoa(start+i+1),
			fmt.Sprintf("alert_select:%s:%d", alert.ID, page),
		))
	}
	if len(alertRow) > 0 {
		rows = append(rows, alertRow)
	}

	// Prev / Next navigation.
	var navRow []tgbotapi.InlineKeyboardButton
	if page > 0 {
		navRow = append(navRow, tgbotapi.NewInlineKeyboardButtonData("◀", fmt.Sprintf("alerts_page:%d", page-1)))
	}
	if end < total {
		navRow = append(navRow, tgbotapi.NewInlineKeyboardButtonData("▶", fmt.Sprintf("alerts_page:%d", page+1)))
	}
	if len(navRow) > 0 {
		rows = append(rows, navRow)
	}

	return sb.String(), tgbotapi.NewInlineKeyboardMarkup(rows...)
}

// handleAlertsPage re-fetches alerts and edits the existing message to show the requested page.
func (b *Bot) handleAlertsPage(ctx context.Context, tgID entities.TelegramID, chatID int64, messageID int, page int) {
	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	alerts, err := b.usecase.Alerts(ctx, user.ID, 0, 100)
	if err != nil {
		b.log.Error("failed to get alerts", "err", err)
		return
	}
	if len(alerts) == 0 {
		b.editMsgText(chatID, messageID, "You have no active alerts.")
		return
	}

	// Clamp page to valid range (e.g. after last alert on a page is removed).
	totalPages := (len(alerts) + alertsPageSize - 1) / alertsPageSize
	if page >= totalPages {
		page = totalPages - 1
	}

	text, kb := buildAlertsPage(alerts, page)
	edit := tgbotapi.NewEditMessageTextAndMarkup(chatID, messageID, text, kb)
	if _, err := b.api.Send(edit); err != nil {
		b.log.Error("failed to edit message", "err", err)
	}
}

// handleAlertSelect edits the message to show the chosen alert with Edit / Remove / Back buttons.
func (b *Bot) handleAlertSelect(ctx context.Context, chatID int64, messageID int, alertID entities.AlertID, page int) {
	alert, err := b.usecase.Alert(ctx, alertID)
	if err != nil {
		b.log.Error("failed to get alert", "alert_id", alertID, "err", err)
		return
	}

	text := fmt.Sprintf("%s/%s\nCondition: %s %s%s",
		alert.Instrument.BaseCurrency,
		alert.Instrument.QuoteCurrency,
		formatCondition(alert.Condition),
		alert.Price.String(),
		formatTimeframeSuffix(alert),
	)

	kb := tgbotapi.NewInlineKeyboardMarkup(tgbotapi.NewInlineKeyboardRow(
		tgbotapi.NewInlineKeyboardButtonData("Edit price", fmt.Sprintf("edit_alert:%s", alertID)),
		tgbotapi.NewInlineKeyboardButtonData("Remove", fmt.Sprintf("remove_alert:%s:%d", alertID, page)),
		tgbotapi.NewInlineKeyboardButtonData("◀ Back", fmt.Sprintf("alerts_back:%d", page)),
	))

	edit := tgbotapi.NewEditMessageTextAndMarkup(chatID, messageID, text, kb)
	if _, err := b.api.Send(edit); err != nil {
		b.log.Error("failed to edit message", "err", err)
	}
}

// --- Multi-step flow handlers ---

// handleInstrumentSelected fetches the current price, stores it in state, and prompts for a target price.
func (b *Bot) handleInstrumentSelected(ctx context.Context, tgID entities.TelegramID, chatID int64, instrID entities.InstrumentID) {
	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	instruments, err := b.usecase.InstrumentList(ctx, user.ID, 0, 200)
	if err != nil {
		b.log.Error("failed to list instruments", "err", err)
		b.sendMenu(chatID, "Failed to load instruments.")
		return
	}

	var selected entities.Instrument
	for _, instr := range instruments {
		if instr.ID == instrID {
			selected = instr
			break
		}
	}
	if selected.ID == "" {
		b.sendMenu(chatID, "Unknown instrument. Please try again.")
		return
	}

	state := &userState{
		step:       stepAddAlertPrice,
		instrument: selected,
	}

	price, err := b.provider.Price(ctx, selected)
	if err != nil {
		b.log.Error("failed to fetch current price", "instrument", selected.ID, "err", err)
		b.setState(tgID, state)
		b.send(chatID, fmt.Sprintf("Selected: %s/%s\n\nCould not fetch current price. Enter your target price:", selected.BaseCurrency, selected.QuoteCurrency))
		return
	}

	state.currentPrice = price
	b.setState(tgID, state)
	b.send(chatID, fmt.Sprintf(
		"Selected: %s/%s\n\nCurrent price:\n  Ask: %s\n  Bid: %s\n\nEnter your target price:",
		selected.BaseCurrency, selected.QuoteCurrency,
		price.Ask.String(), price.Bid.String(),
	))
}

// handleAddAlertPrice parses the target price, stores it in state, then asks for the alert type.
func (b *Bot) handleAddAlertPrice(ctx context.Context, tgID entities.TelegramID, chatID int64, text string, state *userState) {
	target, err := decimal.NewFromString(strings.TrimSpace(text))
	if err != nil || !target.IsPositive() {
		b.send(chatID, "Invalid price. Please enter a positive number (e.g. 50000.5):")
		return
	}

	// Re-fetch price if missing (e.g. failed earlier).
	if state.currentPrice == nil {
		state.currentPrice, err = b.provider.Price(ctx, state.instrument)
		if err != nil {
			b.log.Error("failed to fetch current price", "instrument", state.instrument.ID, "err", err)
			b.send(chatID, "Could not fetch current price. Please try again:")
			return
		}
	}

	state.targetPrice = target
	state.step = stepAddAlertAwaitType
	b.setState(tgID, state)

	kb := tgbotapi.NewInlineKeyboardMarkup(
		tgbotapi.NewInlineKeyboardRow(
			tgbotapi.NewInlineKeyboardButtonData("Price crossing", "alert_type:crossing"),
			tgbotapi.NewInlineKeyboardButtonData("Candle close", "alert_type:close"),
		),
	)
	msg := tgbotapi.NewMessage(chatID, fmt.Sprintf("Target price: %s\n\nSelect alert type:", target.String()))
	msg.ReplyMarkup = kb
	b.sendMsg(msg)
}

// handleAlertTypeCrossing creates a standard crossing alert (High/Low vs target).
func (b *Bot) handleAlertTypeCrossing(ctx context.Context, tgID entities.TelegramID, chatID int64) {
	state := b.getState(tgID)
	if state.step != stepAddAlertAwaitType {
		return
	}

	condition := b.detectCondition(state)

	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	alert := &entities.Alert{
		UserID:     user.ID,
		Price:      state.targetPrice,
		Condition:  condition,
		Instrument: state.instrument,
	}

	id, err := b.usecase.CreateAlert(ctx, alert)
	if err != nil {
		b.log.Error("failed to create alert", "err", err)
		b.sendMenu(chatID, "Failed to create alert. Please try again.")
		b.setState(tgID, &userState{})
		return
	}

	alert.ID = id
	b.alerter.AddAlert(alert)
	b.setState(tgID, &userState{})
	b.sendMenu(chatID, fmt.Sprintf(
		"Alert created!\n\n%s/%s %s %s\n\nYou will be notified when the price crosses your target.",
		state.instrument.BaseCurrency, state.instrument.QuoteCurrency,
		formatCondition(condition), state.targetPrice.String(),
	))
}

// handleAlertTypeClose shows a timeframe selection keyboard for candle-close alerts.
func (b *Bot) handleAlertTypeClose(tgID entities.TelegramID, chatID int64) {
	state := b.getState(tgID)
	if state.step != stepAddAlertAwaitType {
		return
	}

	// Build one row of timeframe buttons.
	var row []tgbotapi.InlineKeyboardButton
	for _, tf := range offeredTimeframes {
		row = append(row, tgbotapi.NewInlineKeyboardButtonData(
			tf.label,
			fmt.Sprintf("alert_timeframe:%s", tf.interval),
		))
	}

	msg := tgbotapi.NewMessage(chatID, "Select the candle timeframe:")
	msg.ReplyMarkup = tgbotapi.NewInlineKeyboardMarkup(row)
	b.sendMsg(msg)
}

// handleAlertTimeframe creates a candle-close alert for the selected timeframe.
func (b *Bot) handleAlertTimeframe(ctx context.Context, tgID entities.TelegramID, chatID int64, tf provider.KlineInterval) {
	state := b.getState(tgID)
	if state.step != stepAddAlertAwaitType {
		return
	}

	condition := b.detectCloseCondition(state)

	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	alert := &entities.Alert{
		UserID:     user.ID,
		Price:      state.targetPrice,
		Condition:  condition,
		Instrument: state.instrument,
		Timeframe:  string(tf),
	}

	id, err := b.usecase.CreateAlert(ctx, alert)
	if err != nil {
		b.log.Error("failed to create alert", "err", err)
		b.sendMenu(chatID, "Failed to create alert. Please try again.")
		b.setState(tgID, &userState{})
		return
	}

	alert.ID = id
	b.alerter.AddAlert(alert)
	b.setState(tgID, &userState{})
	b.sendMenu(chatID, fmt.Sprintf(
		"Alert created!\n\n%s/%s %s %s (%s)\n\nYou will be notified when a %s candle closes %s the target.",
		state.instrument.BaseCurrency, state.instrument.QuoteCurrency,
		formatCondition(condition), state.targetPrice.String(), string(tf),
		string(tf),
		closeDirectionWord(condition),
	))
}

// handleAddPairInput processes the user-entered trading pair symbol.
func (b *Bot) handleAddPairInput(ctx context.Context, tgID entities.TelegramID, chatID int64, text string) {
	user, err := b.requireUser(ctx, tgID, chatID)
	if err != nil {
		return
	}

	parts := strings.SplitN(strings.TrimSpace(text), "/", 2)
	if len(parts) != 2 || strings.TrimSpace(parts[0]) == "" || strings.TrimSpace(parts[1]) == "" {
		b.send(chatID, "Invalid format. Please enter the pair as BASE/QUOTE (e.g. DOGE/USDT):")
		return
	}

	base := strings.ToUpper(strings.TrimSpace(parts[0]))
	quote := strings.ToUpper(strings.TrimSpace(parts[1]))

	exists, err := b.provider.InstrumentExists(ctx, base, quote)
	if err != nil {
		b.log.Error("failed to check instrument existence", "base", base, "quote", quote, "err", err)
		b.sendMenu(chatID, "Could not verify the trading pair. Please try again later.")
		b.setState(tgID, &userState{})
		return
	}
	if !exists {
		b.send(chatID, fmt.Sprintf("Pair %s/%s is not available on Bybit. Please enter a valid pair:", base, quote))
		return
	}

	instr, err := b.usecase.AddUserInstrument(ctx, user.ID, base, quote)
	if err != nil {
		b.log.Error("failed to add user instrument", "err", err)
		b.sendMenu(chatID, "Failed to add the pair. Please try again.")
		b.setState(tgID, &userState{})
		return
	}

	b.setState(tgID, &userState{})
	b.sendMenu(chatID, fmt.Sprintf("Pair %s/%s has been added to your list!", instr.BaseCurrency, instr.QuoteCurrency))
}

// detectCondition returns above/below based on target vs current ask.
func (b *Bot) detectCondition(state *userState) entities.AlertCondition {
	if state.currentPrice != nil && state.targetPrice.GreaterThanOrEqual(state.currentPrice.Ask) {
		return entities.AlertConditionAbove
	}
	return entities.AlertConditionBelow
}

// detectCloseCondition returns close_above/close_below based on target vs current ask.
func (b *Bot) detectCloseCondition(state *userState) entities.AlertCondition {
	if state.currentPrice != nil && state.targetPrice.GreaterThanOrEqual(state.currentPrice.Ask) {
		return entities.AlertConditionCloseAbove
	}
	return entities.AlertConditionCloseBelow
}

func closeDirectionWord(c entities.AlertCondition) string {
	if c == entities.AlertConditionCloseAbove {
		return "above"
	}
	return "below"
}

// handleEditAlertStart begins the edit flow for a specific alert.
func (b *Bot) handleEditAlertStart(tgID entities.TelegramID, chatID int64, alertID entities.AlertID) {
	b.setState(tgID, &userState{
		step:    stepEditAlertPrice,
		alertID: alertID,
	})
	b.send(chatID, "Enter the new target price:")
}

// handleEditAlertPrice applies the new price entered by the user.
func (b *Bot) handleEditAlertPrice(ctx context.Context, tgID entities.TelegramID, chatID int64, text string, state *userState) {
	price, err := decimal.NewFromString(strings.TrimSpace(text))
	if err != nil || !price.IsPositive() {
		b.send(chatID, "Invalid price. Please enter a positive number:")
		return
	}

	if err := b.usecase.UpdateAlertPrice(ctx, state.alertID, price); err != nil {
		b.log.Error("failed to update alert price", "alert_id", state.alertID, "err", err)
		b.sendMenu(chatID, "Failed to update alert.")
		b.setState(tgID, &userState{})
		return
	}

	// Refresh the alerter cache: remove stale entry and re-add with updated price.
	b.alerter.RemoveAlert(state.alertID)
	if updated, err := b.usecase.Alert(ctx, state.alertID); err == nil {
		b.alerter.AddAlert(updated)
	}

	b.setState(tgID, &userState{})
	b.sendMenu(chatID, fmt.Sprintf("Alert price updated to %s.", price.String()))
}

// handleRemoveAlertConfirm edits the message to show a confirmation prompt.
func (b *Bot) handleRemoveAlertConfirm(chatID int64, messageID int, alertID entities.AlertID, page int) {
	kb := tgbotapi.NewInlineKeyboardMarkup(tgbotapi.NewInlineKeyboardRow(
		tgbotapi.NewInlineKeyboardButtonData("Yes, remove", fmt.Sprintf("confirm_remove:%s:%d", alertID, page)),
		tgbotapi.NewInlineKeyboardButtonData("Cancel", fmt.Sprintf("cancel_remove:%s:%d", alertID, page)),
	))
	edit := tgbotapi.NewEditMessageTextAndMarkup(chatID, messageID, "Are you sure you want to remove this alert?", kb)
	if _, err := b.api.Send(edit); err != nil {
		b.log.Error("failed to edit message", "err", err)
	}
}

// handleRemoveAlertDo deletes the alert and refreshes the list in the same message.
func (b *Bot) handleRemoveAlertDo(ctx context.Context, tgID entities.TelegramID, chatID int64, messageID int, alertID entities.AlertID, page int) {
	if err := b.usecase.RemoveAlert(ctx, alertID); err != nil {
		b.log.Error("failed to remove alert", "alert_id", alertID, "err", err)
		b.editMsgText(chatID, messageID, "Failed to remove alert.")
		return
	}
	b.alerter.RemoveAlert(alertID)
	b.handleAlertsPage(ctx, tgID, chatID, messageID, page)
}

// --- Helpers ---

func (b *Bot) requireUser(ctx context.Context, tgID entities.TelegramID, chatID int64) (*entities.User, error) {
	user, err := b.usecase.UserByTgID(ctx, tgID)
	if err != nil {
		b.sendMenu(chatID, "You are not registered. Please send /start first.")
		return nil, err
	}
	return user, nil
}

func (b *Bot) getState(tgID entities.TelegramID) *userState {
	b.mu.Lock()
	defer b.mu.Unlock()
	if s, ok := b.states[tgID]; ok {
		return s
	}
	s := &userState{}
	b.states[tgID] = s
	return s
}

func (b *Bot) setState(tgID entities.TelegramID, state *userState) {
	b.mu.Lock()
	defer b.mu.Unlock()
	b.states[tgID] = state
}

// menuKeyboard returns the persistent reply keyboard shown at the bottom of the chat.
func menuKeyboard() tgbotapi.ReplyKeyboardMarkup {
	return tgbotapi.NewReplyKeyboard(
		tgbotapi.NewKeyboardButtonRow(
			tgbotapi.NewKeyboardButton(btnAddAlert),
			tgbotapi.NewKeyboardButton(btnMyAlerts),
		),
		tgbotapi.NewKeyboardButtonRow(
			tgbotapi.NewKeyboardButton(btnInstruments),
			tgbotapi.NewKeyboardButton(btnAddPair),
		),
	)
}

// sendMenu sends a text message and (re-)attaches the persistent menu keyboard.
func (b *Bot) sendMenu(chatID int64, text string) {
	msg := tgbotapi.NewMessage(chatID, text)
	kb := menuKeyboard()
	kb.ResizeKeyboard = true
	msg.ReplyMarkup = kb
	if _, err := b.api.Send(msg); err != nil {
		b.log.Error("failed to send message", "chat_id", chatID, "err", err)
	}
}

// send sends a plain text message without altering the keyboard.
func (b *Bot) send(chatID int64, text string) {
	if _, err := b.api.Send(tgbotapi.NewMessage(chatID, text)); err != nil {
		b.log.Error("failed to send message", "chat_id", chatID, "err", err)
	}
}

// sendMsg sends a pre-built MessageConfig.
func (b *Bot) sendMsg(msg tgbotapi.MessageConfig) {
	if _, err := b.api.Send(msg); err != nil {
		b.log.Error("failed to send message", "chat_id", msg.ChatID, "err", err)
	}
}

// editMsgText edits only the text of an existing message (removes inline keyboard).
func (b *Bot) editMsgText(chatID int64, messageID int, text string) {
	edit := tgbotapi.NewEditMessageText(chatID, messageID, text)
	if _, err := b.api.Send(edit); err != nil {
		b.log.Error("failed to edit message", "err", err)
	}
}