Add top DMs route and handlers

store/sqlstore/post_store.go

@@ -2963,3 +2963,55 @@ func (s *SqlPostStore) updateThreadsFromPosts(transaction *sqlxTxWrapper, posts
 	}
 	return nil
 }
+
+func (s *SqlPostStore) GetTopDMsForUserSince(userID string, since int64, offset int, limit int) (*model.TopDMList, error) {
+	channelSelector := s.getQueryBuilder().Select("Id", "TotalMsgCount").From("Channels").Join("ChannelMembers as cm on cm.ChannelId = Channels.Id").
+		Where(sq.And{
+			sq.Expr("Channels.Type = 'D'"),
+			sq.Eq{"cm.UserId": userID},
+		})
+	var aggregator string
+
+	if s.DriverName() == model.DatabaseDriverMysql {
+		aggregator = "group_concat(distinct cm.UserId) as Participants"
+	} else {
+		aggregator = "string_agg(distinct cm.UserId, ',') as Participants"
+	}
+
+	topDMsBuilder := s.getQueryBuilder().Select("count(p.id) as MessageCount", aggregator).FromSelect(channelSelector, "vch").
+		Join("ChannelMembers as cm on cm.ChannelId = vch.Id").
+		Join("Posts as p on p.ChannelId = vch.Id").
+		Where(sq.Gt{
+			"p.UpdateAt": since,
+		}).GroupBy("vch.id").
+		Limit(uint64(limit)).
+		Offset(uint64(offset))
+
+	topDMsBuilder = topDMsBuilder.OrderBy("MessageCount DESC").Limit(uint64(limit)).Offset(uint64(offset))
+
+	topDMs := make([]*model.TopDM, 0)
+	sql, args, err := topDMsBuilder.ToSql()
+	if err != nil {
+		return nil, errors.Wrap(err, "GetTopDMsForUserSince_ToSql")
+	}
+	err = s.GetReplicaX().Select(&topDMs, sql, args...)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to find top DMs for user-id: %s", userID)
+	}
+
+	// fill SecondParticipant column
+	topDMs = postProcessTopDMs(userID, topDMs)
+	return model.GetTopDMListWithPagination(topDMs, limit), nil
+}
+
+func postProcessTopDMs(userID string, topDMs []*model.TopDM) []*model.TopDM {
+	for _, topDM := range topDMs {
+		participants := strings.Split(topDM.Participants, ",")
+		if participants[0] == userID {
+			topDM.SecondParticipant = participants[1]
+		} else {
+			topDM.SecondParticipant = participants[0]
+		}
+	}
+	return topDMs
+}