Refactor common JoinThread helper struct (#21511)

* Refactor common JoinThread helper struct

* avoid exporting ToThreadResponse

store/sqlstore/thread_store.go

@@ -18,6 +18,42 @@ import (
 	"github.com/mattermost/mattermost-server/v6/utils"
 )
 
+// JoinedThread allows querying the Threads + Posts table in a single query, before looking up
+// users and unpacking into a model.ThreadResponse.
+type JoinedThread struct {
+	PostId         string
+	ReplyCount     int64
+	LastReplyAt    int64
+	LastViewedAt   int64
+	UnreadReplies  int64
+	UnreadMentions int64
+	Participants   model.StringArray
+	ThreadDeleteAt int64
+	TeamId         string
+	model.Post
+}
+
+func (thread *JoinedThread) toThreadResponse(users map[string]*model.User) *model.ThreadResponse {
+	threadParticipants := make([]*model.User, 0, len(thread.Participants))
+	for _, participantUserId := range thread.Participants {
+		if participant, ok := users[participantUserId]; ok {
+			threadParticipants = append(threadParticipants, participant)
+		}
+	}
+
+	return &model.ThreadResponse{
+		PostId:         thread.PostId,
+		ReplyCount:     thread.ReplyCount,
+		LastReplyAt:    thread.LastReplyAt,
+		LastViewedAt:   thread.LastViewedAt,
+		UnreadReplies:  thread.UnreadReplies,
+		UnreadMentions: thread.UnreadMentions,
+		Participants:   threadParticipants,
+		Post:           thread.Post.ToNilIfInvalid(),
+		DeleteAt:       thread.ThreadDeleteAt,
+	}
+}
+
 type SqlThreadStore struct {
 	*SqlStore
 
@@ -183,19 +219,6 @@ func (s *SqlThreadStore) GetThreadsForUser(userId, teamId string, opts model.Get
 		pageSize = opts.PageSize
 	}
 
-	var threads []*struct {
-		PostId         string
-		ReplyCount     int64
-		LastReplyAt    int64
-		LastViewedAt   int64
-		UnreadReplies  int64
-		UnreadMentions int64
-		Participants   model.StringArray
-		ThreadDeleteAt int64
-		TeamId         string
-		model.Post
-	}
-
 	unreadRepliesQuery := sq.
 		Select("COUNT(Posts.Id)").
 		From("Posts").
@@ -258,6 +281,7 @@ func (s *SqlThreadStore) GetThreadsForUser(userId, teamId string, opts model.Get
 		OrderBy("Threads.LastReplyAt " + order).
 		Limit(pageSize)
 
+	var threads []*JoinedThread
 	err := s.GetReplicaX().SelectBuilder(&threads, query)
 	if err != nil {
 		return nil, errors.Wrapf(err, "failed to fetch threads for user id=%s", userId)
@@ -290,27 +314,7 @@ func (s *SqlThreadStore) GetThreadsForUser(userId, teamId string, opts model.Get
 
 	result := make([]*model.ThreadResponse, 0, len(threads))
 	for _, thread := range threads {
-		// Find only this thread's participants
-		threadParticipants := make([]*model.User, 0, len(thread.Participants))
-		for _, participantUserId := range thread.Participants {
-			participant, ok := allParticipants[participantUserId]
-			if !ok {
-				return nil, errors.Errorf("cannot find participant with user id=%s for thread id=%s", participantUserId, thread.PostId)
-			}
-			threadParticipants = append(threadParticipants, participant)
-		}
-
-		result = append(result, &model.ThreadResponse{
-			PostId:         thread.PostId,
-			ReplyCount:     thread.ReplyCount,
-			LastReplyAt:    thread.LastReplyAt,
-			LastViewedAt:   thread.LastViewedAt,
-			UnreadReplies:  thread.UnreadReplies,
-			UnreadMentions: thread.UnreadMentions,
-			Participants:   threadParticipants,
-			Post:           thread.Post.ToNilIfInvalid(),
-			DeleteAt:       thread.ThreadDeleteAt,
-		})
+		result = append(result, thread.toThreadResponse(allParticipants))
 	}
 
 	return result, nil
@@ -437,20 +441,6 @@ func (s *SqlThreadStore) GetThreadForUser(teamId string, threadMembership *model
 		return nil, nil // in case the thread is not followed anymore - return nil error to be interpreted as 404
 	}
 
-	type JoinedThread struct {
-		PostId         string
-		Following      bool
-		ReplyCount     int64
-		LastReplyAt    int64
-		LastViewedAt   int64
-		UnreadReplies  int64
-		UnreadMentions int64
-		Participants   model.StringArray
-		ThreadDeleteAt int64
-		TeamId         string
-		model.Post
-	}
-
 	unreadRepliesQuery := sq.
 		Select("COUNT(Posts.Id)").
 		From("Posts").
@@ -501,33 +491,12 @@ func (s *SqlThreadStore) GetThreadForUser(teamId string, threadMembership *model
 		}
 	}
 
-	participants := []*model.User{}
-	for _, participantId := range thread.Participants {
-		var participant *model.User
-		for _, u := range users {
-			if u.Id == participantId {
-				participant = u
-				break
-			}
-		}
-		if participant != nil {
-			participants = append(participants, participant)
-		}
+	usersMap := make(map[string]*model.User)
+	for _, user := range users {
+		usersMap[user.Id] = user
 	}
 
-	result := &model.ThreadResponse{
-		PostId:         thread.PostId,
-		ReplyCount:     thread.ReplyCount,
-		LastReplyAt:    thread.LastReplyAt,
-		LastViewedAt:   thread.LastViewedAt,
-		UnreadReplies:  thread.UnreadReplies,
-		UnreadMentions: thread.UnreadMentions,
-		Participants:   participants,
-		Post:           thread.Post.ToNilIfInvalid(),
-		DeleteAt:       thread.ThreadDeleteAt,
-	}
-
-	return result, nil
+	return thread.toThreadResponse(usersMap), nil
 }
 
 // MarkAllAsReadByChannels marks thread membership for the given users in the given channels
@@ -1012,7 +981,7 @@ func (s *SqlThreadStore) GetTopThreadsForUserSince(teamID string, userID string,
 	var args []any
 
 	// gets all threads within the team which user follows.
-	query := `select 
+	query := `select
 		threads_list.PostId,
 		threads_list.ReplyCount,
 		threads_list.ChannelId,