MM-40148: threadsOnly query param for user threads (#19833)

* MM-40148: threadsOnly query param for user threads

Currently we always calculate counts when fetching user threads.
Those counts include total, unread replies, and unread mentions,
and are potentially expensive to calculate.

This commit adds a new query param 'threadsOnly' which won't calculate
any counts and just return threads.

Co-authored-by: koox00 <3829551+koox00@users.noreply.github.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/user_test.go

@@ -5754,6 +5754,96 @@ func TestGetThreadsForUser(t *testing.T) {
 		require.Len(t, uss3.Threads, 0)
 	})
 
+	t.Run("totalsOnly param", func(t *testing.T) {
+		client := th.Client
+		sysadminClient := th.SystemAdminClient
+
+		var rootIds []*model.Post
+		for i := 0; i < 10; i++ {
+			rpost, resp, err := client.CreatePost(&model.Post{ChannelId: th.BasicChannel.Id, Message: "testMsg"})
+			require.NoError(t, err)
+			CheckCreatedStatus(t, resp)
+			rootIds = append(rootIds, rpost)
+			if i%2 == 0 {
+				_, resp, err = client.CreatePost(&model.Post{ChannelId: th.BasicChannel.Id, Message: "testReply", RootId: rpost.Id})
+			} else {
+				_, resp, err = sysadminClient.CreatePost(&model.Post{ChannelId: th.BasicChannel.Id, Message: "testReply @" + th.BasicUser.Username, RootId: rpost.Id})
+			}
+			require.NoError(t, err)
+			CheckCreatedStatus(t, resp)
+		}
+
+		defer th.App.Srv().Store.Post().PermanentDeleteByUser(th.BasicUser.Id)
+		defer th.App.Srv().Store.Post().PermanentDeleteByUser(th.SystemAdminUser.Id)
+
+		uss, _, err := th.Client.GetUserThreads(th.BasicUser.Id, th.BasicTeam.Id, model.GetUserThreadsOpts{
+			Deleted:    false,
+			TotalsOnly: true,
+			PageSize:   30,
+		})
+		require.NoError(t, err)
+		require.Len(t, uss.Threads, 0)
+		require.Len(t, rootIds, 10)
+		require.Equal(t, int64(10), uss.Total)
+		require.Equal(t, int64(5), uss.TotalUnreadThreads)
+		require.Equal(t, int64(5), uss.TotalUnreadMentions)
+	})
+
+	t.Run("threadsOnly param", func(t *testing.T) {
+		client := th.Client
+		sysadminClient := th.SystemAdminClient
+
+		var rootIds []*model.Post
+		for i := 0; i < 10; i++ {
+			rpost, resp, err := client.CreatePost(&model.Post{ChannelId: th.BasicChannel.Id, Message: "testMsg"})
+			require.NoError(t, err)
+			CheckCreatedStatus(t, resp)
+			rootIds = append(rootIds, rpost)
+			if i%2 == 0 {
+				_, resp, err = client.CreatePost(&model.Post{ChannelId: th.BasicChannel.Id, Message: "testReply", RootId: rpost.Id})
+			} else {
+				_, resp, err = sysadminClient.CreatePost(&model.Post{ChannelId: th.BasicChannel.Id, Message: "testReply @" + th.BasicUser.Username, RootId: rpost.Id})
+			}
+
+			require.NoError(t, err)
+			CheckCreatedStatus(t, resp)
+		}
+
+		defer th.App.Srv().Store.Post().PermanentDeleteByUser(th.BasicUser.Id)
+		defer th.App.Srv().Store.Post().PermanentDeleteByUser(th.SystemAdminUser.Id)
+
+		uss, _, err := th.Client.GetUserThreads(th.BasicUser.Id, th.BasicTeam.Id, model.GetUserThreadsOpts{
+			Deleted:     false,
+			ThreadsOnly: true,
+			PageSize:    30,
+		})
+
+		require.NoError(t, err)
+		require.Len(t, rootIds, 10)
+		require.Len(t, uss.Threads, 10)
+		require.Equal(t, int64(0), uss.Total)
+		require.Equal(t, int64(0), uss.TotalUnreadThreads)
+		require.Equal(t, int64(0), uss.TotalUnreadMentions)
+		require.Equal(t, int64(1), uss.Threads[0].ReplyCount)
+
+		require.Equal(t, rootIds[9].Id, uss.Threads[0].PostId)
+		require.Equal(t, th.SystemAdminUser.Id, uss.Threads[0].Participants[0].Id)
+		require.Equal(t, th.BasicUser.Id, uss.Threads[1].Participants[0].Id)
+	})
+
+	t.Run("setting both threadsOnly, and totalsOnly params is not allowed", func(t *testing.T) {
+		defer th.App.Srv().Store.Post().PermanentDeleteByUser(th.BasicUser.Id)
+
+		_, resp, err := th.Client.GetUserThreads(th.BasicUser.Id, th.BasicTeam.Id, model.GetUserThreadsOpts{
+			ThreadsOnly: true,
+			TotalsOnly:  true,
+			PageSize:    30,
+		})
+
+		require.Error(t, err)
+		checkHTTPStatus(t, resp, http.StatusBadRequest)
+	})
+
 	t.Run("editing or reacting to reply post does not make thread unread", func(t *testing.T) {
 		client := th.Client