package telegram

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"strconv"

	"github.com/redis/go-redis/v9"
)

// CloneGroupMembersFromMessages scrapes senders of recent messages in a
// group/channel. This is the preferred strategy for active groups where the
// member-list API is restricted: every message exposes its sender, and any
// joined account can read history. In a 1k+ member active group this
// routinely yields 100-300 usernames in one pass vs 5-20 from the members
// API for a non-admin account.
//
// State lives in the same Redis keys as CloneGroupMembers (spider:tg:clone:
// <username>:{seen,participants,total,status}). Running both strategies on
// the same group merges results naturally — dedup by user ID is shared.
//
// maxMessages caps how many recent messages to scan (default 2000).
func CloneGroupMembersFromMessages(ctx context.Context, mgr *AccountManager, rdb *redis.Client, username string, maxMessages int) (*CloneResult, error) {
	if mgr == nil {
		return nil, errors.New("account manager is nil")
	}
	if rdb == nil {
		return nil, errors.New("redis client is nil")
	}
	if maxMessages <= 0 {
		maxMessages = 2000
	}

	res := &CloneResult{Username: username, Status: "running"}

	// Restore existing seen set so this pass is additive to member-API runs.
	seen := make(map[int64]bool)
	if ids, err := rdb.SMembers(ctx, cloneKey(username, "seen")).Result(); err == nil {
		for _, s := range ids {
			if id, err := strconv.ParseInt(s, 10, 64); err == nil {
				seen[id] = true
			}
		}
	}
	if pts, err := rdb.LRange(ctx, cloneKey(username, "participants"), 0, -1).Result(); err == nil {
		for _, s := range pts {
			var p GroupParticipant
			if err := json.Unmarshal([]byte(s), &p); err == nil {
				res.Participants = append(res.Participants, p)
			}
		}
	}
	if t, err := rdb.Get(ctx, cloneKey(username, "total")).Int(); err == nil {
		res.Total = t
	}

	acc, err := mgr.Acquire(ctx)
	if err != nil {
		if errors.Is(err, ErrAllCooling) {
			res.Partial = true
			res.Status = "paused"
			return res, nil
		}
		return res, err
	}

	cooldownSecs := 0
	defer func() {
		if cooldownSecs > 0 {
			mgr.HandleFloodWait(acc, cooldownSecs)
		} else {
			mgr.Release(acc, 0)
		}
	}()

	if err := acc.Client.Connect(ctx); err != nil {
		return res, fmt.Errorf("connect %s: %w", acc.Account.Phone, err)
	}
	defer acc.Client.Disconnect()

	// Best-effort auto-join so we have history-read permission.
	if inputCh, ch, _, err := acc.Client.ResolveGroupPeer(ctx, username); err == nil && inputCh != nil {
		_ = acc.Client.JoinChannel(ctx, inputCh)
		if res.GroupTitle == "" && ch != nil {
			res.GroupTitle = ch.Title
		}
		// Refresh authoritative total opportunistically.
		if t, err := acc.Client.GetFullChannelTotal(ctx, inputCh); err == nil && t > 0 && t > res.Total {
			res.Total = t
			_ = rdb.Set(ctx, cloneKey(username, "total"), t, cloneTTL).Err()
		}
	}

	peer, err := acc.Client.ResolveInputPeer(ctx, username)
	if err != nil {
		if fwe, ok := err.(*FloodWaitError); ok {
			cooldownSecs = fwe.Seconds
			return res, nil
		}
		return res, fmt.Errorf("resolve peer: %w", err)
	}

	senders, err := acc.Client.FetchMessageSenders(ctx, peer, maxMessages)
	if err != nil {
		if fwe, ok := err.(*FloodWaitError); ok {
			cooldownSecs = fwe.Seconds
		} else {
			log.Printf("[clone_msg] %s fetch history error: %v", username, err)
		}
		// fall through — persist whatever we got before the error.
	}

	added := 0
	pipe := rdb.TxPipeline()
	for _, p := range senders {
		if seen[p.ID] {
			continue
		}
		seen[p.ID] = true
		res.Participants = append(res.Participants, p)
		pipe.SAdd(ctx, cloneKey(username, "seen"), strconv.FormatInt(p.ID, 10))
		if b, jerr := json.Marshal(p); jerr == nil {
			pipe.RPush(ctx, cloneKey(username, "participants"), string(b))
		}
		added++
	}
	if added > 0 {
		pipe.Expire(ctx, cloneKey(username, "seen"), cloneTTL)
		pipe.Expire(ctx, cloneKey(username, "participants"), cloneTTL)
		_, _ = pipe.Exec(ctx)
	}

	log.Printf("[clone_msg] %s: scanned up to %d messages, +%d new senders with @username (pool now %d)",
		username, maxMessages, added, len(res.Participants))

	if cooldownSecs > 0 {
		res.Partial = true
		res.Status = "paused"
	} else {
		res.Status = "done"
	}
	_ = rdb.Set(ctx, cloneKey(username, "status"), res.Status, cloneTTL).Err()
	return res, nil
}