// Package bot wraps the Telegram Bot API client (github.com/go-telegram/bot): it
// runs the long-poll update loop — replying to /start (with an optional deep-link
// payload) and any other message with a Mini App launch button — and sends the
// notification and admin messages the connector requests. The bot token lives only
// in this process.
package bot

import (
	"context"
	"net/url"
	"strconv"
	"strings"

	tgbot "github.com/go-telegram/bot"
	"github.com/go-telegram/bot/models"
	"go.uber.org/zap"
	"golang.org/x/time/rate"
)

// Config configures the bot wrapper.
type Config struct {
	// Token is the Bot API token.
	Token string
	// APIBaseURL overrides the Bot API host ("" uses https://api.telegram.org).
	APIBaseURL string
	// TestEnv routes requests to the Bot API test environment.
	TestEnv bool
	// MiniAppURL is the base URL of the Mini App launch button.
	MiniAppURL string
	// SendRatePerSecond caps outbound sends (Notify and SendText) to respect the
	// Telegram Bot API flood limits; 0 disables the limiter. The burst equals the
	// per-second rate.
	SendRatePerSecond int
	// ChatID is the moderated discussion chat the bot gates write access in; 0
	// disables chat gating (and the chat_member long-poll subscription). Gating needs
	// the bot to be an administrator there with the restrict-members right.
	ChatID int64
}

// EligibilityResolver answers whether the Telegram user identified by externalID
// (the decimal user id) may write in the moderated chat: registered and neither
// admin-suspended nor chat-muted. The bot calls it when a user joins the chat. It is
// late-bound (SetEligibilityResolver) because it is backed by the bot-link client,
// which is built after the bot.
type EligibilityResolver func(ctx context.Context, externalID string) (eligible bool, err error)

// Bot wraps a Telegram Bot API client and the Mini App launch URL.
type Bot struct {
	api        *tgbot.Bot
	miniAppURL string
	log        *zap.Logger
	// limiter throttles outbound sends to stay under the Bot API flood limits; nil
	// disables throttling.
	limiter *rate.Limiter
	// chatID is the moderated discussion chat (0 disables gating).
	chatID int64
	// eligibility resolves a joining user's chat write eligibility; nil leaves a
	// joiner muted (fail-closed) until it is wired.
	eligibility EligibilityResolver
}

// New builds the bot wrapper, registering the /start handler and a default handler
// that both reply with a Mini App launch button. It does not start polling; call
// Run for that.
func New(cfg Config, log *zap.Logger) (*Bot, error) {
	if log == nil {
		log = zap.NewNop()
	}
	t := &Bot{miniAppURL: cfg.MiniAppURL, log: log, chatID: cfg.ChatID}
	if cfg.SendRatePerSecond > 0 {
		t.limiter = rate.NewLimiter(rate.Limit(cfg.SendRatePerSecond), cfg.SendRatePerSecond)
	}

	opts := []tgbot.Option{
		tgbot.WithDefaultHandler(t.handleUpdate),
		tgbot.WithMessageTextHandler("/start", tgbot.MatchTypePrefix, t.handleStart),
	}
	if cfg.ChatID != 0 {
		// chat_member updates are off by default; subscribe explicitly (alongside
		// messages) so the bot sees joins in the moderated chat. The bot must also be an
		// administrator there for Telegram to deliver them.
		opts = append(opts, tgbot.WithAllowedUpdates(tgbot.AllowedUpdates{
			models.AllowedUpdateMessage,
			models.AllowedUpdateMyChatMember,
			models.AllowedUpdateChatMember,
		}))
	}
	if cfg.TestEnv {
		// Route to the Bot API test environment (.../bot<token>/test/METHOD).
		opts = append(opts, tgbot.UseTestEnvironment())
	}
	if cfg.APIBaseURL != "" {
		opts = append(opts, tgbot.WithServerURL(cfg.APIBaseURL))
	}
	api, err := tgbot.New(cfg.Token, opts...)
	if err != nil {
		return nil, err
	}
	t.api = api
	return t, nil
}

// Run sets the bot commands and the Mini App menu button, then blocks on the
// long-poll update loop until ctx is cancelled.
func (t *Bot) Run(ctx context.Context) {
	if _, err := t.api.SetMyCommands(ctx, &tgbot.SetMyCommandsParams{
		Commands: []models.BotCommand{{Command: "start", Description: "Open Scrabble"}},
	}); err != nil {
		t.log.Warn("set commands failed", zap.Error(err))
	}
	if _, err := t.api.SetChatMenuButton(ctx, &tgbot.SetChatMenuButtonParams{
		MenuButton: models.MenuButtonWebApp{
			Type:   models.MenuButtonTypeWebApp,
			Text:   "Play",
			WebApp: models.WebAppInfo{URL: t.miniAppURL},
		},
	}); err != nil {
		t.log.Warn("set menu button failed", zap.Error(err))
	}
	t.api.Start(ctx)
}

// Notify sends a notification message with a Mini App launch button that opens the
// app at startParam (empty opens the lobby).
func (t *Bot) Notify(ctx context.Context, chatID int64, text, buttonText, startParam string) error {
	if err := t.throttle(ctx); err != nil {
		return err
	}
	_, err := t.api.SendMessage(ctx, &tgbot.SendMessageParams{
		ChatID:      chatID,
		Text:        text,
		ReplyMarkup: t.launchMarkup(buttonText, startParam),
	})
	return err
}

// SendText sends a plain text message with no markup (admin use).
func (t *Bot) SendText(ctx context.Context, chatID int64, text string) error {
	if err := t.throttle(ctx); err != nil {
		return err
	}
	_, err := t.api.SendMessage(ctx, &tgbot.SendMessageParams{ChatID: chatID, Text: text})
	return err
}

// throttle blocks until the rate limiter admits one send, or ctx is cancelled. It
// is a no-op when no limiter is configured.
func (t *Bot) throttle(ctx context.Context) error {
	if t.limiter == nil {
		return nil
	}
	return t.limiter.Wait(ctx)
}

// handleStart replies to /start (with an optional deep-link payload) and to any
// other message with a Mini App launch button.
func (t *Bot) handleStart(ctx context.Context, api *tgbot.Bot, update *models.Update) {
	if update.Message == nil {
		return
	}
	startParam := startPayload(update.Message.Text)
	if _, err := api.SendMessage(ctx, &tgbot.SendMessageParams{
		ChatID:      update.Message.Chat.ID,
		Text:        "Tap to open Scrabble.",
		ReplyMarkup: t.launchMarkup("Open Scrabble", startParam),
	}); err != nil {
		t.log.Warn("reply to start failed", zap.Error(err))
	}
}

// launchMarkup builds the single-button inline keyboard that opens the Mini App at
// startParam.
func (t *Bot) launchMarkup(buttonText, startParam string) *models.InlineKeyboardMarkup {
	return &models.InlineKeyboardMarkup{
		InlineKeyboard: [][]models.InlineKeyboardButton{{
			{Text: buttonText, WebApp: &models.WebAppInfo{URL: t.launchURL(startParam)}},
		}},
	}
}

// launchURL appends the deep-link start parameter to the Mini App URL as a startapp
// query parameter; an empty parameter returns the base URL unchanged.
func (t *Bot) launchURL(startParam string) string {
	if startParam == "" {
		return t.miniAppURL
	}
	u, err := url.Parse(t.miniAppURL)
	if err != nil {
		return t.miniAppURL
	}
	q := u.Query()
	q.Set("startapp", startParam)
	u.RawQuery = q.Encode()
	return u.String()
}

// startPayload extracts the deep-link payload from a "/start <payload>" command;
// any other text yields an empty payload (open the lobby).
func startPayload(text string) string {
	const cmd = "/start"
	if !strings.HasPrefix(text, cmd) {
		return ""
	}
	return strings.TrimSpace(strings.TrimPrefix(text, cmd))
}

// handleUpdate is the default-handler dispatcher: a chat-member change in the
// moderated chat drives the write-access gate; anything else is treated as a message
// and gets the Mini App launch reply.
func (t *Bot) handleUpdate(ctx context.Context, api *tgbot.Bot, update *models.Update) {
	if update.ChatMember != nil {
		t.handleChatMember(ctx, update.ChatMember)
		return
	}
	t.handleStart(ctx, api, update)
}

// SetEligibilityResolver wires the chat-eligibility resolver after construction (the
// bot-link client backing it is built after the bot).
func (t *Bot) SetEligibilityResolver(resolve EligibilityResolver) {
	t.eligibility = resolve
}

// handleChatMember grants write access to a user who joins the moderated chat when
// they are registered and not blocked. A non-eligible joiner is left muted (the chat
// defaults to no-send), and a resolve failure fails closed (also left muted). Other
// status changes (leaves, restrictions, admin edits) are ignored.
func (t *Bot) handleChatMember(ctx context.Context, cm *models.ChatMemberUpdated) {
	if t.chatID == 0 || cm.Chat.ID != t.chatID {
		return
	}
	// Only a transition into plain membership is a join to evaluate.
	if cm.NewChatMember.Type != models.ChatMemberTypeMember || cm.OldChatMember.Type == models.ChatMemberTypeMember {
		return
	}
	user := chatMemberUser(cm.NewChatMember)
	if user == nil || user.IsBot {
		return
	}
	if t.eligibility == nil {
		return // resolver not wired: leave muted (fail closed)
	}
	eligible, err := t.eligibility(ctx, strconv.FormatInt(user.ID, 10))
	if err != nil {
		t.log.Warn("chat join eligibility failed", zap.Int64("user_id", user.ID), zap.Error(err))
		return
	}
	if !eligible {
		return // not registered or blocked: leave muted
	}
	if err := t.setChatWrite(ctx, user.ID, true); err != nil {
		t.log.Warn("grant chat write failed", zap.Int64("user_id", user.ID), zap.Error(err))
	}
}

// ApplyChatGate applies a chat-gate command (an admin block/unblock or chat_muted
// change relayed by the gateway): it sets the user's write access, but only when they
// are currently in the chat. Bots cannot list members, so it probes the single user
// with getChatMember and is a no-op when they are absent (left/kicked) or an
// administrator (who cannot be restricted). It reports whether a restriction was
// applied.
func (t *Bot) ApplyChatGate(ctx context.Context, userID int64, allow bool) (bool, error) {
	if t.chatID == 0 {
		return false, nil
	}
	member, err := t.api.GetChatMember(ctx, &tgbot.GetChatMemberParams{ChatID: t.chatID, UserID: userID})
	if err != nil {
		return false, err
	}
	switch member.Type {
	case models.ChatMemberTypeMember, models.ChatMemberTypeRestricted:
		if err := t.setChatWrite(ctx, userID, allow); err != nil {
			return false, err
		}
		return true, nil
	default:
		return false, nil // absent, or an admin/owner who cannot be restricted
	}
}

// setChatWrite restricts the user in the moderated chat to either the full send
// permission set (allow) or none (mute); the non-send permissions stay at their
// default-deny either way.
func (t *Bot) setChatWrite(ctx context.Context, userID int64, allow bool) error {
	perms := models.ChatPermissions{}
	if allow {
		perms = chatWritePerms()
	}
	_, err := t.api.RestrictChatMember(ctx, &tgbot.RestrictChatMemberParams{
		ChatID:      t.chatID,
		UserID:      userID,
		Permissions: &perms,
	})
	return err
}

// chatWritePerms grants a member the ability to send every kind of message; the
// non-send permissions stay denied.
func chatWritePerms() models.ChatPermissions {
	return models.ChatPermissions{
		CanSendMessages:       true,
		CanSendAudios:         true,
		CanSendDocuments:      true,
		CanSendPhotos:         true,
		CanSendVideos:         true,
		CanSendVideoNotes:     true,
		CanSendVoiceNotes:     true,
		CanSendPolls:          true,
		CanSendOtherMessages:  true,
		CanAddWebPagePreviews: true,
	}
}

// chatMemberUser returns the user a ChatMember refers to across the union variants,
// or nil for an unrecognised type.
func chatMemberUser(m models.ChatMember) *models.User {
	switch m.Type {
	case models.ChatMemberTypeOwner:
		return m.Owner.User
	case models.ChatMemberTypeAdministrator:
		return &m.Administrator.User
	case models.ChatMemberTypeMember:
		return m.Member.User
	case models.ChatMemberTypeRestricted:
		return m.Restricted.User
	case models.ChatMemberTypeLeft:
		return m.Left.User
	case models.ChatMemberTypeBanned:
		return m.Banned.User
	}
	return nil
}