fix: sync moderation flag convergence

internal/store/postgres/channel_settings.go

@@ -6,7 +6,11 @@ import (
 	"errors"
 	"fmt"
 	"strings"
+
+	"github.com/jackc/pgx/v5"
+
 	"telesrv/internal/domain"
+	"telesrv/internal/store/postgres/sqlcgen"
 )
 
 func (s *ChannelStore) EditChannelTitle(ctx context.Context, req domain.EditChannelTitleRequest) (domain.EditChannelTitleResult, error) {
@@ -292,16 +296,80 @@ func (s *ChannelStore) SetChannelScamFake(ctx context.Context, channelID int64,
 	if scam && fake {
 		return domain.Channel{}, domain.ErrPeerModerationFlagsInvalid
 	}
-	channel, err := s.channelByID(ctx, s.db, channelID)
+	beginner, ok := s.db.(txBeginner)
+	if !ok {
+		return domain.Channel{}, fmt.Errorf("set channel scam/fake: db does not support transactions")
+	}
+	tx, err := beginner.Begin(ctx)
+	if err != nil {
+		return domain.Channel{}, fmt.Errorf("begin set channel scam/fake: %w", err)
+	}
+	committed := false
+	defer func() {
+		if !committed {
+			_ = tx.Rollback(ctx)
+		}
+	}()
+	var currentScam, currentFake bool
+	if err := tx.QueryRow(ctx, `
+SELECT scam, fake
+FROM channels
+WHERE id = $1 AND NOT deleted
+FOR UPDATE`, channelID).Scan(&currentScam, &currentFake); err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return domain.Channel{}, domain.ErrChannelInvalid
+		}
+		return domain.Channel{}, fmt.Errorf("lock channel scam/fake: %w", err)
+	}
+	channel, err := s.channelByID(ctx, tx, channelID)
 	if err != nil {
 		return domain.Channel{}, err
 	}
 	if channel.Scam == scam && channel.Fake == fake {
+		if err := tx.Commit(ctx); err != nil {
+			return domain.Channel{}, fmt.Errorf("commit unchanged channel scam/fake: %w", err)
+		}
+		committed = true
 		return channel, nil
 	}
-	if _, err := s.db.Exec(ctx, `UPDATE channels SET scam = $2, fake = $3, updated_at = now() WHERE id = $1 AND NOT deleted`, channelID, scam, fake); err != nil {
+	if currentScam != channel.Scam || currentFake != channel.Fake {
+		return domain.Channel{}, fmt.Errorf("channel scam/fake snapshot changed while locked")
+	}
+	if _, err := tx.Exec(ctx, `UPDATE channels SET scam = $2, fake = $3, updated_at = now() WHERE id = $1 AND NOT deleted`, channelID, scam, fake); err != nil {
 		return domain.Channel{}, fmt.Errorf("set channel scam/fake: %w", err)
 	}
+	audience, err := channelModerationFlagAudience(ctx, tx, channelID, maxModerationFlagAudience)
+	if err != nil {
+		return domain.Channel{}, err
+	}
+	qtx := sqlcgen.New(tx)
+	date := nowUnix()
+	for _, viewerUserID := range audience {
+		pts, err := reserveUserPts(ctx, tx, viewerUserID, 1)
+		if err != nil {
+			return domain.Channel{}, fmt.Errorf("reserve channel moderation flag pts for viewer %d: %w", viewerUserID, err)
+		}
+		event := domain.UpdateEvent{
+			UserID: viewerUserID,
+			Type:   domain.UpdateEventChannelState,
+			Pts:    pts, PtsCount: 1, Date: date,
+			Peer: domain.Peer{Type: domain.PeerTypeChannel, ID: channelID},
+		}
+		if err := appendUserUpdateEvent(ctx, tx, qtx, viewerUserID, event); err != nil {
+			return domain.Channel{}, fmt.Errorf("append channel moderation flag event for viewer %d: %w", viewerUserID, err)
+		}
+		if err := enqueueDispatch(ctx, qtx, sqlcgen.EnqueueDispatchParams{
+			TargetUserID: viewerUserID,
+			Pts:          int32(pts),
+			EventType:    string(event.Type),
+		}); err != nil {
+			return domain.Channel{}, fmt.Errorf("enqueue channel moderation flag dispatch for viewer %d: %w", viewerUserID, err)
+		}
+	}
+	if err := tx.Commit(ctx); err != nil {
+		return domain.Channel{}, fmt.Errorf("commit channel scam/fake: %w", err)
+	}
+	committed = true
 	if s.rowCache != nil {
 		s.rowCache.delete(channelID)
 	}
@@ -310,6 +378,37 @@ func (s *ChannelStore) SetChannelScamFake(ctx context.Context, channelID int64,
 	return channel, nil
 }
 
+func channelModerationFlagAudience(ctx context.Context, db sqlcgen.DBTX, channelID int64, limit int) ([]int64, error) {
+	if channelID <= 0 || limit <= 0 {
+		return nil, nil
+	}
+	rows, err := db.Query(ctx, `
+SELECT cm.user_id
+FROM channel_members cm
+JOIN users u ON u.id = cm.user_id AND u.deleted_at IS NULL
+WHERE cm.channel_id = $1 AND cm.status = 'active'
+ORDER BY cm.user_id
+LIMIT $2`, channelID, limit)
+	if err != nil {
+		return nil, fmt.Errorf("list channel moderation flag audience: %w", err)
+	}
+	defer rows.Close()
+	out := make([]int64, 0)
+	for rows.Next() {
+		var userID int64
+		if err := rows.Scan(&userID); err != nil {
+			return nil, fmt.Errorf("scan channel moderation flag audience: %w", err)
+		}
+		if userID != 0 {
+			out = append(out, userID)
+		}
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("iterate channel moderation flag audience: %w", err)
+	}
+	return out, nil
+}
+
 // SetChannelAdminSettings applies an admin-direct moderation-settings patch
 // (no membership/permission checks). nil fields are left unchanged.
 func (s *ChannelStore) SetChannelAdminSettings(ctx context.Context, channelID int64, patch domain.ChannelAdminSettings) (domain.Channel, error) {