package telegram

import (
	"bufio"
	"context"
	"encoding/base64"
	"fmt"
	"log"
	"math/rand/v2"
	"net"
	"net/url"
	"regexp"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/gotd/td/session"
	"github.com/gotd/td/telegram"
	"github.com/gotd/td/telegram/dcs"
	"github.com/gotd/td/tg"
	"github.com/gotd/td/tgerr"
	xproxy "golang.org/x/net/proxy"
)

var tmeRegexp = regexp.MustCompile(`https?://t\.me/[^\s"'<>)\]]+`)

// Client TG 客户端
type Client struct {
	account     Account
	sessionPath string
	proxyURL    string // SOCKS5/HTTP proxy URL

	mu     sync.Mutex
	tgc    *telegram.Client
	api    *tg.Client
	cancel context.CancelFunc
	ready  chan struct{} // closed when connected
	runErr error
}

// New 创建客户端（不连接，只初始化）
func New(account Account) *Client {
	return &Client{
		account:     account,
		sessionPath: account.SessionFile,
		ready:       make(chan struct{}),
	}
}

// SetProxy sets the proxy URL for this client's connections.
func (c *Client) SetProxy(proxyURL string) {
	c.mu.Lock()
	c.proxyURL = proxyURL
	c.mu.Unlock()
}

// Connect 连接并认证（从 session 文件恢复）
// session 文件不存在时返回错误（不做交互式登录，session 需要预先生成）
func (c *Client) Connect(ctx context.Context) error {
	storage := &session.FileStorage{Path: c.sessionPath}

	opts := telegram.Options{
		SessionStorage: storage,
		NoUpdates:      true,
		Device: telegram.DeviceConfig{
			DeviceModel:    c.account.Device,
			AppVersion:     c.account.AppVersion,
			SystemVersion:  c.account.SystemVersion,
			LangPack:       c.account.LangPack,
			SystemLangCode: c.account.SystemLangCode,
			LangCode:       c.account.LangCode,
		},
	}

	// Apply proxy if configured
	c.mu.Lock()
	proxyURL := c.proxyURL
	c.mu.Unlock()
	if proxyURL != "" {
		dialFunc, err := buildProxyDialer(proxyURL)
		if err != nil {
			log.Printf("[tg_client] failed to create proxy dialer: %v, connecting without proxy", err)
		} else {
			opts.Resolver = dcs.Plain(dcs.PlainOptions{Dial: dialFunc})
			log.Printf("[tg_client] connecting via proxy: %s", proxyURL)
		}
	}

	client := telegram.NewClient(c.account.AppID, c.account.AppHash, opts)

	runCtx, cancel := context.WithCancel(ctx)

	c.mu.Lock()
	c.tgc = client
	c.cancel = cancel
	c.ready = make(chan struct{})
	c.runErr = nil
	readyCh := c.ready
	c.mu.Unlock()

	errCh := make(chan error, 1)

	go func() {
		err := client.Run(runCtx, func(ctx context.Context) error {
			c.mu.Lock()
			c.api = client.API()
			close(readyCh)
			c.mu.Unlock()

			// Block until context is cancelled (Disconnect called)
			<-ctx.Done()
			return ctx.Err()
		})
		c.mu.Lock()
		c.runErr = err
		c.mu.Unlock()
		errCh <- err
	}()

	// Wait for ready or error
	select {
	case <-readyCh:
		return nil
	case err := <-errCh:
		if err != nil && err != context.Canceled {
			return err
		}
		return nil
	case <-ctx.Done():
		cancel()
		return ctx.Err()
	}
}

// Disconnect 断开连接
func (c *Client) Disconnect() {
	c.mu.Lock()
	cancel := c.cancel
	c.mu.Unlock()

	if cancel != nil {
		cancel()
	}
}

// waitReady waits for the client to be connected and returns the api client
func (c *Client) waitReady(ctx context.Context) (*tg.Client, error) {
	c.mu.Lock()
	readyCh := c.ready
	api := c.api
	c.mu.Unlock()

	if api != nil {
		return api, nil
	}

	select {
	case <-readyCh:
		c.mu.Lock()
		api = c.api
		c.mu.Unlock()
		return api, nil
	case <-ctx.Done():
		return nil, ctx.Err()
	}
}

// GetChannelInfo 获取频道/用户信息，通过用户名查找
func (c *Client) GetChannelInfo(ctx context.Context, username string) (*ChannelInfo, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, err
	}

	username = strings.TrimPrefix(username, "@")

	resolved, err := api.ContactsResolveUsername(ctx, &tg.ContactsResolveUsernameRequest{
		Username: username,
	})
	if err != nil {
		return nil, wrapFloodWait(err)
	}

	info := &ChannelInfo{Username: username}

	// Look for channel/chat in the resolved chats
	for _, ch := range resolved.Chats {
		switch v := ch.(type) {
		case *tg.Channel:
			title := v.Title
			info.Title = title
			info.IsChannel = v.GetBroadcast()
			info.IsGroup = v.GetMegagroup()
			if count, ok := v.GetParticipantsCount(); ok {
				info.MemberCount = count
			}
			// Get full channel info for About
			accessHash, hasHash := v.GetAccessHash()
			if hasHash {
				full, ferr := api.ChannelsGetFullChannel(ctx, &tg.InputChannel{
					ChannelID:  v.GetID(),
					AccessHash: accessHash,
				})
				if ferr == nil {
					if cf, ok := full.FullChat.(*tg.ChannelFull); ok {
						info.About = cf.GetAbout()
						if count, ok := cf.GetParticipantsCount(); ok && info.MemberCount == 0 {
							info.MemberCount = count
						}
					}
				}
			}
			return info, nil
		case *tg.Chat:
			info.Title = v.Title
			info.IsGroup = true
			info.MemberCount = v.ParticipantsCount
			return info, nil
		}
	}

	return info, nil
}

// GetMessages 获取频道历史消息
// offsetID: 从哪条消息开始（断点续传）
// limit: 最多取多少条
// 返回的消息按 ID 从小到大排序
func (c *Client) GetMessages(ctx context.Context, username string, offsetID, limit int) ([]Message, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, err
	}

	username = strings.TrimPrefix(username, "@")

	peer, err := c.resolveInputPeer(ctx, api, username)
	if err != nil {
		return nil, err
	}

	result, err := api.MessagesGetHistory(ctx, &tg.MessagesGetHistoryRequest{
		Peer:     peer,
		OffsetID: offsetID,
		Limit:    limit,
	})
	if err != nil {
		return nil, wrapFloodWait(err)
	}

	return extractMessages(result), nil
}

// GetPinnedMessages 获取置顶消息
func (c *Client) GetPinnedMessages(ctx context.Context, username string) ([]Message, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, err
	}

	username = strings.TrimPrefix(username, "@")

	peer, err := c.resolveInputPeer(ctx, api, username)
	if err != nil {
		return nil, err
	}

	result, err := api.MessagesSearch(ctx, &tg.MessagesSearchRequest{
		Peer:   peer,
		Filter: &tg.InputMessagesFilterPinned{},
		Limit:  100,
	})
	if err != nil {
		return nil, wrapFloodWait(err)
	}

	return extractMessages(result), nil
}

// VerifyUser 验证用户名是否存在，返回用户信息
func (c *Client) VerifyUser(ctx context.Context, username string) (*UserInfo, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, err
	}

	username = strings.TrimPrefix(username, "@")

	resolved, err := api.ContactsResolveUsername(ctx, &tg.ContactsResolveUsernameRequest{
		Username: username,
	})
	if err != nil {
		if tgerr.Is(err, "USERNAME_NOT_OCCUPIED", "USERNAME_INVALID") {
			return &UserInfo{Username: username, Exists: false}, nil
		}
		return nil, wrapFloodWait(err)
	}

	// Check if the peer is a user
	if _, ok := resolved.Peer.(*tg.PeerUser); ok {
		for _, u := range resolved.Users {
			if user, ok := u.(*tg.User); ok {
				info := &UserInfo{
					ID:        user.GetID(),
					Username:  username,
					IsBot:     user.GetBot(),
					IsPremium: user.GetPremium(),
					Exists:    true,
				}
				if fn, ok := user.GetFirstName(); ok {
					info.FirstName = fn
				}
				if ln, ok := user.GetLastName(); ok {
					info.LastName = ln
				}
				if status, ok := user.GetStatus(); ok {
					if offline, ok := status.(*tg.UserStatusOffline); ok {
						t := time.Unix(int64(offline.GetWasOnline()), 0)
						info.LastOnline = &t
					}
				}
				return info, nil
			}
		}
	}

	// Check if it's a channel or group
	for _, ch := range resolved.Chats {
		switch v := ch.(type) {
		case *tg.Channel:
			return &UserInfo{
				ID:        v.GetID(),
				Username:  username,
				IsChannel: v.GetBroadcast(),
				IsGroup:   v.GetMegagroup(),
				Exists:    true,
			}, nil
		case *tg.Chat:
			return &UserInfo{
				ID:      v.ID,
				IsGroup: true,
				Exists:  true,
			}, nil
		}
	}

	return &UserInfo{Username: username, Exists: false}, nil
}

// ResolveGroupChannel looks up a group/channel by username and returns both
// the InputChannel handle (for subsequent API calls) and the raw Channel
// struct (for metadata like title and participant count). Returns
// (nil, nil, error) for basic chats (no InputChannel).
func (c *Client) ResolveGroupChannel(ctx context.Context, username string) (*tg.InputChannel, *tg.Channel, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, nil, err
	}
	username = strings.TrimPrefix(username, "@")

	resolved, err := api.ContactsResolveUsername(ctx, &tg.ContactsResolveUsernameRequest{Username: username})
	if err != nil {
		return nil, nil, wrapFloodWait(err)
	}
	for _, ch := range resolved.Chats {
		if v, ok := ch.(*tg.Channel); ok {
			accessHash, _ := v.GetAccessHash()
			return &tg.InputChannel{ChannelID: v.GetID(), AccessHash: accessHash}, v, nil
		}
	}
	return nil, nil, fmt.Errorf("无法解析群组为超级群组: %s", username)
}

// FetchMessageSenders paginates channel/group history and returns distinct
// sender information (username + display name + user ID). For active groups
// this often yields far more usernames than participants.search (which is
// heavily restricted for non-admins) — because every message exposes its
// sender, and you can read history of any joined group.
//
// limit is the TOTAL number of messages to scan (paged 100 at a time).
// The result contains only senders that have a public @username set.
func (c *Client) FetchMessageSenders(ctx context.Context, peer tg.InputPeerClass, limit int) ([]GroupParticipant, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, err
	}
	if limit <= 0 {
		limit = 500
	}

	const pageSize = 100
	seen := make(map[int64]bool)
	var out []GroupParticipant
	offsetID := 0
	scanned := 0

	for scanned < limit {
		ps := pageSize
		if limit-scanned < ps {
			ps = limit - scanned
		}
		result, err := api.MessagesGetHistory(ctx, &tg.MessagesGetHistoryRequest{
			Peer:     peer,
			OffsetID: offsetID,
			Limit:    ps,
		})
		if err != nil {
			return out, wrapFloodWait(err)
		}

		// Build user map from response for quick lookup.
		users := make(map[int64]*tg.User)
		var msgs []tg.MessageClass
		switch v := result.(type) {
		case *tg.MessagesMessages:
			msgs = v.Messages
			for _, u := range v.Users {
				if usr, ok := u.(*tg.User); ok {
					users[usr.GetID()] = usr
				}
			}
		case *tg.MessagesMessagesSlice:
			msgs = v.Messages
			for _, u := range v.Users {
				if usr, ok := u.(*tg.User); ok {
					users[usr.GetID()] = usr
				}
			}
		case *tg.MessagesChannelMessages:
			msgs = v.Messages
			for _, u := range v.Users {
				if usr, ok := u.(*tg.User); ok {
					users[usr.GetID()] = usr
				}
			}
		default:
			return out, nil
		}

		if len(msgs) == 0 {
			break
		}

		minID := 0
		for _, raw := range msgs {
			var fromID int64
			var id int
			switch m := raw.(type) {
			case *tg.Message:
				id = m.GetID()
				if from, ok := m.GetFromID(); ok {
					if pu, ok := from.(*tg.PeerUser); ok {
						fromID = pu.UserID
					}
				}
			case *tg.MessageService:
				id = m.GetID()
				if from, ok := m.GetFromID(); ok {
					if pu, ok := from.(*tg.PeerUser); ok {
						fromID = pu.UserID
					}
				}
			}
			if id > 0 && (minID == 0 || id < minID) {
				minID = id
			}
			if fromID == 0 || seen[fromID] {
				continue
			}
			usr, ok := users[fromID]
			if !ok || usr.GetBot() {
				continue
			}
			uname, _ := usr.GetUsername()
			if uname == "" {
				continue // we only care about @-addressable accounts
			}
			seen[fromID] = true
			p := GroupParticipant{
				ID:        fromID,
				Username:  uname,
				IsPremium: usr.GetPremium(),
			}
			if fn, ok := usr.GetFirstName(); ok {
				p.FirstName = fn
			}
			if ln, ok := usr.GetLastName(); ok {
				p.LastName = ln
			}
			out = append(out, p)
		}

		scanned += len(msgs)
		if minID == 0 || minID == offsetID {
			break // no progress possible
		}
		offsetID = minID

		if err := jitterSleep(ctx, 1500*time.Millisecond, 3*time.Second); err != nil {
			return out, err
		}
	}
	return out, nil
}

// ResolveInputPeer is a public wrapper over resolveInputPeer for use outside
// the client file. Handles @username, channels, chats.
func (c *Client) ResolveInputPeer(ctx context.Context, username string) (tg.InputPeerClass, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, err
	}
	return c.resolveInputPeer(ctx, api, strings.TrimPrefix(username, "@"))
}

// GetFullChannelTotal calls channels.getFullChannel to obtain the authoritative
// participants_count (which may be much larger than what a restricted member
// can see via ChannelParticipantsSearch).
func (c *Client) GetFullChannelTotal(ctx context.Context, ch *tg.InputChannel) (int, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return 0, err
	}
	full, err := api.ChannelsGetFullChannel(ctx, ch)
	if err != nil {
		return 0, wrapFloodWait(err)
	}
	cf, ok := full.FullChat.(*tg.ChannelFull)
	if !ok {
		return 0, fmt.Errorf("unexpected FullChat type")
	}
	if n, ok := cf.GetParticipantsCount(); ok {
		return n, nil
	}
	return 0, nil
}

// FetchRecentParticipants paginates channels.getParticipants with the Recent
// filter, which returns active participants sorted by recency. This is the
// preferred Phase 1 filter for large groups — empty-string Search filter is
// often heavily restricted (returns 4-5 results) while Recent returns up to
// ~200 and is not treated as "searching".
func (c *Client) FetchRecentParticipants(ctx context.Context, channel *tg.InputChannel) ([]GroupParticipant, int, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, 0, err
	}

	const pageSize = 200
	offset := 0
	totalCount := 0
	var out []GroupParticipant

	for {
		result, err := api.ChannelsGetParticipants(ctx, &tg.ChannelsGetParticipantsRequest{
			Channel: channel,
			Filter:  &tg.ChannelParticipantsRecent{},
			Offset:  offset,
			Limit:   pageSize,
			Hash:    0,
		})
		if err != nil {
			return out, totalCount, wrapFloodWait(err)
		}
		cp, ok := result.(*tg.ChannelsChannelParticipants)
		if !ok || len(cp.Users) == 0 {
			break
		}
		if cp.Count > totalCount {
			totalCount = cp.Count
		}
		for _, u := range cp.Users {
			user, ok := u.(*tg.User)
			if !ok {
				continue
			}
			p := GroupParticipant{
				ID:        user.GetID(),
				IsBot:     user.GetBot(),
				IsPremium: user.GetPremium(),
			}
			if un, ok := user.GetUsername(); ok {
				p.Username = un
			}
			if fn, ok := user.GetFirstName(); ok {
				p.FirstName = fn
			}
			if ln, ok := user.GetLastName(); ok {
				p.LastName = ln
			}
			out = append(out, p)
		}
		offset += len(cp.Users)
		if offset >= cp.Count {
			break
		}
		if err := jitterSleep(ctx, 800*time.Millisecond, 1500*time.Millisecond); err != nil {
			return out, totalCount, err
		}
	}
	return out, totalCount, nil
}

// JoinChannel makes the current account a member of the given channel/supergroup.
// USER_ALREADY_PARTICIPANT is treated as success. FloodWait is wrapped normally.
// Side effect: this account becomes visibly a member of the group — make sure
// the caller actually wants that (private groups require it to see the member
// list, but it leaves a trace in group join/leave activity logs).
func (c *Client) JoinChannel(ctx context.Context, ch *tg.InputChannel) error {
	api, err := c.waitReady(ctx)
	if err != nil {
		return err
	}
	_, err = api.ChannelsJoinChannel(ctx, ch)
	if err != nil {
		if tgerr.Is(err, "USER_ALREADY_PARTICIPANT") {
			return nil
		}
		return wrapFloodWait(err)
	}
	return nil
}

// GetChatParticipantsByID fetches members of a basic (non-supergroup) chat.
// Basic chats have no pagination — this returns everyone in one call.
func (c *Client) GetChatParticipantsByID(ctx context.Context, chatID int64) ([]GroupParticipant, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, err
	}
	return c.getChatParticipants(ctx, api, chatID)
}

// ResolveGroupPeer is a broader resolver than ResolveGroupChannel: it also
// returns a basic-chat ID when the target is not a supergroup/channel.
// Exactly one of (inputCh, chatID) will be non-zero on success.
func (c *Client) ResolveGroupPeer(ctx context.Context, username string) (*tg.InputChannel, *tg.Channel, int64, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, nil, 0, err
	}
	username = strings.TrimPrefix(username, "@")
	resolved, err := api.ContactsResolveUsername(ctx, &tg.ContactsResolveUsernameRequest{Username: username})
	if err != nil {
		return nil, nil, 0, wrapFloodWait(err)
	}
	for _, ch := range resolved.Chats {
		if v, ok := ch.(*tg.Channel); ok {
			accessHash, _ := v.GetAccessHash()
			return &tg.InputChannel{ChannelID: v.GetID(), AccessHash: accessHash}, v, 0, nil
		}
	}
	if p, ok := resolved.Peer.(*tg.PeerChat); ok {
		return nil, nil, p.ChatID, nil
	}
	return nil, nil, 0, fmt.Errorf("无法解析群组: %s", username)
}

// FetchParticipantsByQuery runs ChannelParticipantsSearch for one query string,
// paginating through all pages. Returns the users surfaced by this query and
// the total count reported by TG. On FloodWait, returns a *FloodWaitError.
// The caller is responsible for deduping across queries.
func (c *Client) FetchParticipantsByQuery(ctx context.Context, channel *tg.InputChannel, query string) ([]GroupParticipant, int, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, 0, err
	}

	const pageSize = 200
	offset := 0
	totalCount := 0
	var out []GroupParticipant

	for {
		result, err := api.ChannelsGetParticipants(ctx, &tg.ChannelsGetParticipantsRequest{
			Channel: channel,
			Filter:  &tg.ChannelParticipantsSearch{Q: query},
			Offset:  offset,
			Limit:   pageSize,
			Hash:    0,
		})
		if err != nil {
			return out, totalCount, wrapFloodWait(err)
		}
		cp, ok := result.(*tg.ChannelsChannelParticipants)
		if !ok || len(cp.Users) == 0 {
			break
		}
		if cp.Count > totalCount {
			totalCount = cp.Count
		}
		for _, u := range cp.Users {
			user, ok := u.(*tg.User)
			if !ok {
				continue
			}
			p := GroupParticipant{
				ID:        user.GetID(),
				IsBot:     user.GetBot(),
				IsPremium: user.GetPremium(),
			}
			if un, ok := user.GetUsername(); ok {
				p.Username = un
			}
			if fn, ok := user.GetFirstName(); ok {
				p.FirstName = fn
			}
			if ln, ok := user.GetLastName(); ok {
				p.LastName = ln
			}
			out = append(out, p)
		}
		offset += len(cp.Users)
		if offset >= cp.Count {
			break
		}
		if err := jitterSleep(ctx, 800*time.Millisecond, 1500*time.Millisecond); err != nil {
			return out, totalCount, err
		}
	}
	return out, totalCount, nil
}

// GetGroupParticipants 获取群组/超级群组的成员列表（分页拉取全部）
func (c *Client) GetGroupParticipants(ctx context.Context, username string) ([]GroupParticipant, error) {
	api, err := c.waitReady(ctx)
	if err != nil {
		return nil, err
	}

	username = strings.TrimPrefix(username, "@")

	// Resolve the channel/group
	resolved, err := api.ContactsResolveUsername(ctx, &tg.ContactsResolveUsernameRequest{
		Username: username,
	})
	if err != nil {
		return nil, wrapFloodWait(err)
	}

	// Find the channel in resolved chats
	var inputChannel *tg.InputChannel
	for _, ch := range resolved.Chats {
		switch v := ch.(type) {
		case *tg.Channel:
			accessHash, _ := v.GetAccessHash()
			inputChannel = &tg.InputChannel{
				ChannelID:  v.GetID(),
				AccessHash: accessHash,
			}
		}
	}

	if inputChannel == nil {
		// Try as basic chat - get participants via MessagesGetFullChat
		if p, ok := resolved.Peer.(*tg.PeerChat); ok {
			return c.getChatParticipants(ctx, api, p.ChatID)
		}
		return nil, fmt.Errorf("无法解析群组: %s", username)
	}

	// Strategy: use ChannelParticipantsSearch with empty query (returns more than Recent),
	// then iterate alphabet queries to discover members beyond the 200 limit per query.
	seen := make(map[int64]bool)
	var allParticipants []GroupParticipant

	// Helper to extract users from a page
	extractUsers := func(cp *tg.ChannelsChannelParticipants) int {
		added := 0
		for _, u := range cp.Users {
			user, ok := u.(*tg.User)
			if !ok || seen[user.GetID()] {
				continue
			}
			seen[user.GetID()] = true
			p := GroupParticipant{
				ID:        user.GetID(),
				IsBot:     user.GetBot(),
				IsPremium: user.GetPremium(),
			}
			if un, ok := user.GetUsername(); ok {
				p.Username = un
			}
			if fn, ok := user.GetFirstName(); ok {
				p.FirstName = fn
			}
			if ln, ok := user.GetLastName(); ok {
				p.LastName = ln
			}
			allParticipants = append(allParticipants, p)
			added++
		}
		return added
	}

	// Phase 1: Search with empty query (gets up to ~200)
	totalCount := 0
	if err := c.fetchParticipantPages(ctx, api, inputChannel, "", seen, extractUsers, &totalCount); err != nil {
		if len(allParticipants) > 0 {
			return allParticipants, err
		}
		return nil, err
	}

	// Phase 2: If group has more members than we found, search by character sets to discover more.
	// We pace queries with jitter (2–4s) to avoid looking like a bot scanner and triggering FloodWait.
	// If FloodWait does hit, stop early and return what we already have — the calling task can
	// re-attempt later after the account cools down.
	if totalCount > len(allParticipants) && totalCount <= 10000 {
		queries := participantSearchQueries()
		for _, q := range queries {
			if ctx.Err() != nil {
				break
			}
			if len(allParticipants) >= totalCount {
				break // already collected everyone visible
			}
			beforeCount := len(allParticipants)
			err := c.fetchParticipantPages(ctx, api, inputChannel, q, seen, extractUsers, nil)
			if err != nil {
				if fwe, ok := err.(*FloodWaitError); ok {
					log.Printf("[tg_client] flood wait %ds during search q=%q for %s; returning %d/%d",
						fwe.Seconds, q, username, len(allParticipants), totalCount)
				} else {
					log.Printf("[tg_client] search q=%q for %s: %v (returning partial)", q, username, err)
				}
				break
			}
			if len(allParticipants) == beforeCount {
				continue // no new results; skip sleep and try next query
			}
			if err := jitterSleep(ctx, 2*time.Second, 4*time.Second); err != nil {
				return allParticipants, err
			}
		}
	}

	log.Printf("[tg_client] fetched %d/%d participants for %s", len(allParticipants), totalCount, username)
	return allParticipants, nil
}

// jitterSleep sleeps a random duration in [min, max) while respecting ctx.
// Returns ctx.Err() if cancelled. Used to spread out TG API calls and avoid
// looking like a deterministic scanner.
func jitterSleep(ctx context.Context, min, max time.Duration) error {
	d := min + time.Duration(rand.Int64N(int64(max-min)))
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-time.After(d):
		return nil
	}
}

// participantSearchQueries returns search queries covering Latin, Cyrillic, Japanese,
// Korean, and CJK scripts. TG's ChannelParticipantsSearch does substring matching on
// first_name + last_name + username, so more starter-character coverage = more users
// surfaced on groups beyond the 200-per-query cap. Total ~150 queries.
func participantSearchQueries() []string {
	queries := make([]string, 0, 170)
	// Latin a-z
	for c := 'a'; c <= 'z'; c++ {
		queries = append(queries, string(c))
	}
	// Digits 0-9
	for c := '0'; c <= '9'; c++ {
		queries = append(queries, string(c))
	}
	// Cyrillic а-я
	for c := 'а'; c <= 'я'; c++ {
		queries = append(queries, string(c))
	}
	// Japanese Hiragana — common name-starter syllables
	queries = append(queries,
		"あ", "い", "う", "え", "お",
		"か", "さ", "た", "な", "ま",
	)
	// Korean Hangul — common initial syllables
	queries = append(queries,
		"가", "나", "다", "라", "마", "바", "사", "아", "자", "차",
		"카", "타", "파", "하",
	)
	// CJK: top Chinese surnames (百家姓 high frequency)
	surnames := []string{
		"王", "李", "张", "刘", "陈", "杨", "黄", "赵", "周", "吴",
		"徐", "孙", "马", "朱", "胡", "林", "何", "高", "郭", "罗",
		"谢", "宋", "唐", "许", "邓", "梁", "韩", "曹", "彭", "余",
		"潘", "袁", "蒋", "蔡", "卢", "田", "董", "叶", "程", "姜",
	}
	queries = append(queries, surnames...)
	// CJK: common given-name characters (高频二字名)
	given := []string{
		"伟", "芳", "娜", "秀", "敏", "静", "丽", "强", "磊", "军",
		"洋", "勇", "艳", "杰", "涛", "明", "超", "霞", "平", "刚",
	}
	queries = append(queries, given...)
	// CJK: common modifiers and city prefixes (covers nicknames/titles)
	misc := []string{
		"大", "小", "新", "老", "中", "天", "金", "一", "龙", "虎",
		"京", "沪", "深", "广", "杭", "苏",
	}
	queries = append(queries, misc...)
	return queries
}

// fetchParticipantPages paginates through ChannelParticipantsSearch results.
func (c *Client) fetchParticipantPages(
	ctx context.Context,
	api *tg.Client,
	channel *tg.InputChannel,
	query string,
	seen map[int64]bool,
	extractUsers func(*tg.ChannelsChannelParticipants) int,
	outTotalCount *int,
) error {
	const pageSize = 200
	offset := 0

	for {
		result, err := api.ChannelsGetParticipants(ctx, &tg.ChannelsGetParticipantsRequest{
			Channel: channel,
			Filter:  &tg.ChannelParticipantsSearch{Q: query},
			Offset:  offset,
			Limit:   pageSize,
			Hash:    0,
		})
		if err != nil {
			return wrapFloodWait(err)
		}

		cp, ok := result.(*tg.ChannelsChannelParticipants)
		if !ok || len(cp.Users) == 0 {
			break
		}

		if outTotalCount != nil && cp.Count > *outTotalCount {
			*outTotalCount = cp.Count
		}

		added := extractUsers(cp)
		offset += len(cp.Users)

		// If no new users were added in this page, stop
		if added == 0 || offset >= cp.Count {
			break
		}

		// Page interval: jittered to avoid a detectable request cadence.
		if err := jitterSleep(ctx, 800*time.Millisecond, 1500*time.Millisecond); err != nil {
			return err
		}
	}
	return nil
}

// getChatParticipants 获取普通群组的成员
func (c *Client) getChatParticipants(ctx context.Context, api *tg.Client, chatID int64) ([]GroupParticipant, error) {
	full, err := api.MessagesGetFullChat(ctx, chatID)
	if err != nil {
		return nil, wrapFloodWait(err)
	}

	var participants []GroupParticipant
	for _, u := range full.Users {
		user, ok := u.(*tg.User)
		if !ok {
			continue
		}
		p := GroupParticipant{
			ID:        user.GetID(),
			IsBot:     user.GetBot(),
			IsPremium: user.GetPremium(),
		}
		if un, ok := user.GetUsername(); ok {
			p.Username = un
		}
		if fn, ok := user.GetFirstName(); ok {
			p.FirstName = fn
		}
		if ln, ok := user.GetLastName(); ok {
			p.LastName = ln
		}
		participants = append(participants, p)
	}

	return participants, nil
}

// buildProxyDialer creates a DialFunc that routes connections through the given proxy URL.
// Supports socks5://, http://, https:// proxy protocols.
func buildProxyDialer(rawURL string) (dcs.DialFunc, error) {
	u, err := url.Parse(rawURL)
	if err != nil {
		return nil, fmt.Errorf("parse proxy URL: %w", err)
	}

	switch u.Scheme {
	case "socks5", "socks5h":
		var auth *xproxy.Auth
		if u.User != nil {
			auth = &xproxy.Auth{User: u.User.Username()}
			if p, ok := u.User.Password(); ok {
				auth.Password = p
			}
		}
		dialer, err := xproxy.SOCKS5("tcp", u.Host, auth, xproxy.Direct)
		if err != nil {
			return nil, fmt.Errorf("create SOCKS5 dialer: %w", err)
		}
		ctxDialer, ok := dialer.(xproxy.ContextDialer)
		if !ok {
			return nil, fmt.Errorf("SOCKS5 dialer does not support DialContext")
		}
		return ctxDialer.DialContext, nil

	case "http", "https":
		// For HTTP proxies, use CONNECT tunneling
		return func(ctx context.Context, network, addr string) (net.Conn, error) {
			proxyConn, err := (&net.Dialer{Timeout: 15 * time.Second}).DialContext(ctx, "tcp", u.Host)
			if err != nil {
				return nil, fmt.Errorf("connect to proxy: %w", err)
			}

			// Set deadline for the CONNECT handshake
			if deadline, ok := ctx.Deadline(); ok {
				proxyConn.SetDeadline(deadline)
			} else {
				proxyConn.SetDeadline(time.Now().Add(15 * time.Second))
			}

			// Send CONNECT request
			connectReq := fmt.Sprintf("CONNECT %s HTTP/1.1\r\nHost: %s\r\n", addr, addr)
			if u.User != nil {
				pass, _ := u.User.Password()
				connectReq += fmt.Sprintf("Proxy-Authorization: Basic %s\r\n",
					encodeBasicAuth(u.User.Username(), pass))
			}
			connectReq += "\r\n"

			if _, err := proxyConn.Write([]byte(connectReq)); err != nil {
				proxyConn.Close()
				return nil, fmt.Errorf("write CONNECT: %w", err)
			}

			// Read HTTP response using bufio for proper line parsing
			br := bufio.NewReader(proxyConn)
			statusLine, err := br.ReadString('\n')
			if err != nil {
				proxyConn.Close()
				return nil, fmt.Errorf("read CONNECT status: %w", err)
			}

			// Parse status code from "HTTP/1.x NNN reason"
			parts := strings.SplitN(strings.TrimSpace(statusLine), " ", 3)
			if len(parts) < 2 || parts[1] != "200" {
				proxyConn.Close()
				return nil, fmt.Errorf("CONNECT failed: %s", strings.TrimSpace(statusLine))
			}

			// Consume remaining headers until empty line
			for {
				line, err := br.ReadString('\n')
				if err != nil {
					proxyConn.Close()
					return nil, fmt.Errorf("read CONNECT headers: %w", err)
				}
				if strings.TrimSpace(line) == "" {
					break
				}
			}

			// Clear deadline — gotd manages its own timeouts
			proxyConn.SetDeadline(time.Time{})

			return proxyConn, nil
		}, nil

	default:
		return nil, fmt.Errorf("unsupported proxy scheme: %s", u.Scheme)
	}
}

// encodeBasicAuth returns base64-encoded "user:password" for proxy auth.
func encodeBasicAuth(user, password string) string {
	return base64.StdEncoding.EncodeToString([]byte(user + ":" + password))
}

// resolveInputPeer resolves a username to an InputPeer
func (c *Client) resolveInputPeer(ctx context.Context, api *tg.Client, username string) (tg.InputPeerClass, error) {
	resolved, err := api.ContactsResolveUsername(ctx, &tg.ContactsResolveUsernameRequest{
		Username: username,
	})
	if err != nil {
		return nil, wrapFloodWait(err)
	}

	switch p := resolved.Peer.(type) {
	case *tg.PeerChannel:
		for _, ch := range resolved.Chats {
			if channel, ok := ch.(*tg.Channel); ok && channel.GetID() == p.ChannelID {
				accessHash, _ := channel.GetAccessHash()
				return &tg.InputPeerChannel{
					ChannelID:  p.ChannelID,
					AccessHash: accessHash,
				}, nil
			}
		}
		return &tg.InputPeerChannel{ChannelID: p.ChannelID}, nil
	case *tg.PeerUser:
		for _, u := range resolved.Users {
			if user, ok := u.(*tg.User); ok && user.GetID() == p.UserID {
				accessHash, _ := user.GetAccessHash()
				return &tg.InputPeerUser{
					UserID:     p.UserID,
					AccessHash: accessHash,
				}, nil
			}
		}
		return &tg.InputPeerUser{UserID: p.UserID}, nil
	case *tg.PeerChat:
		return &tg.InputPeerChat{ChatID: p.ChatID}, nil
	}

	return &tg.InputPeerEmpty{}, nil
}

// extractMessages extracts messages from a MessagesMessagesClass
func extractMessages(result tg.MessagesMessagesClass) []Message {
	var rawMsgs []tg.MessageClass
	switch v := result.(type) {
	case *tg.MessagesMessages:
		rawMsgs = v.Messages
	case *tg.MessagesMessagesSlice:
		rawMsgs = v.Messages
	case *tg.MessagesChannelMessages:
		rawMsgs = v.Messages
	case *tg.MessagesMessagesNotModified:
		return nil
	}

	var msgs []Message
	for _, raw := range rawMsgs {
		switch m := raw.(type) {
		case *tg.Message:
			msg := Message{
				ID:        m.GetID(),
				Text:      m.GetMessage(),
				IsService: false,
			}

			// Extract forward source channel username
			if fwd, ok := m.GetFwdFrom(); ok {
				if fromID, ok := fwd.GetFromID(); ok {
					if peerCh, ok := fromID.(*tg.PeerChannel); ok {
						_ = peerCh // We'd need channel map to resolve username; skip for now
					}
				}
			}

			// Extract t.me links from text
			msg.Links = tmeRegexp.FindAllString(msg.Text, -1)

			msgs = append(msgs, msg)
		case *tg.MessageService:
			msgs = append(msgs, Message{
				ID:        m.GetID(),
				IsService: true,
			})
		}
	}

	// Sort by ID ascending
	sort.Slice(msgs, func(i, j int) bool {
		return msgs[i].ID < msgs[j].ID
	})

	return msgs
}

// isFloodWait 检查错误是否是 FloodWait，提取等待时间
func isFloodWait(err error) (bool, int) {
	if d, ok := tgerr.AsFloodWait(err); ok {
		return true, int(d.Seconds())
	}
	return false, 0
}

// wrapFloodWait wraps a FloodWait error into FloodWaitError
func wrapFloodWait(err error) error {
	if ok, secs := isFloodWait(err); ok {
		return &FloodWaitError{Seconds: secs}
	}
	return err
}