[MM-23264] Get channel member counts by group (#14068)

* MM-23264 Add api endpoint for get groups with members in channel

Add store tests

Add tests for api func

Gofmt

Apply changes from code review

* MM-23264 Make store layers

* MM-23264 Check read permission on channel member counts

* Trigger CI

store/sqlstore/channel_store.go

@@ -1779,6 +1779,38 @@ func (s SqlChannelStore) GetMemberCount(channelId string, allowFromCache bool) (
 	return count, nil
 }
 
+// GetMemberCountsByGroup returns a slice of ChannelMemberCountByGroup for a given channel
+// which contains the number of channel members for each group and optionally the number of unique timezones present for each group in the channel
+func (s SqlChannelStore) GetMemberCountsByGroup(channelID string, includeTimezones bool) ([]*model.ChannelMemberCountByGroup, *model.AppError) {
+	selectStr := "GroupMembers.GroupId, COUNT(ChannelMembers.UserId) AS ChannelMemberCount"
+
+	if includeTimezones {
+		selectStr = "GroupMembers.GroupId, COUNT(ChannelMembers.UserId) AS ChannelMemberCount, COUNT( DISTINCT Users.Timezone ) AS ChannelMemberTimezonesCount"
+	}
+
+	query := s.getQueryBuilder().
+		Select(selectStr).
+		From("ChannelMembers").
+		Join("GroupMembers ON GroupMembers.UserId = ChannelMembers.UserId")
+
+	if includeTimezones {
+		query = query.Join("Users ON Users.Id = GroupMembers.UserId")
+	}
+
+	query = query.Where(sq.Eq{"ChannelMembers.ChannelId": channelID}).GroupBy("GroupMembers.GroupId")
+
+	queryString, args, err := query.ToSql()
+	if err != nil {
+		return nil, model.NewAppError("SqlChannelStore.GetMemberCountsByGroup", "store.sql.build_query.app_error", nil, err.Error(), http.StatusInternalServerError)
+	}
+	var data []*model.ChannelMemberCountByGroup
+	if _, err = s.GetReplica().Select(&data, queryString, args...); err != nil {
+		return nil, model.NewAppError("SqlChannelStore.GetMemberCountsByGroup", "store.sql_channel.get_member_count.app_error", nil, "channel_id="+channelID+", "+err.Error(), http.StatusInternalServerError)
+	}
+
+	return data, nil
+}
+
 func (s SqlChannelStore) InvalidatePinnedPostCount(channelId string) {
 }