MM42267: Add member count in the browse channel modal (#23800)

* add base for calling the endpoint

* add endpoint and handler

* update store and layers

* call the endpoint

* align types

* update app layers

* generate mocks

* complete handler

* finish store query

* add todos

* add ui for member count

* add selector

* add a todo

* add cache layer

* optimize calls in FE

* handle invalidation of the cache

* fix go style

* fix test

* use existing channel layer count

* fix import error

* delete unnecessary code

* write tests for channel cache layer

* fix testname

* fix mocks

* fix cache layer test

* fix a test

* really fix the test

* write more tests for server

* address PR comments

* remove comment

* rename more_channels to browse_channels

* fix style

* update snapshot

* add translations

* Revert "add translations"

This reverts commit 56476a5dabe357703ef02be9a38b3e88f5c8b1e7.

* add only related translations

* address PR review points

* add test

* fix test

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/app_iface.go

@@ -625,6 +625,7 @@ type AppIface interface {
 	GetChannelsForTeamForUser(c request.CTX, teamID string, userID string, opts *model.ChannelSearchOpts) (model.ChannelList, *model.AppError)
 	GetChannelsForTeamForUserWithCursor(c request.CTX, teamID string, userID string, opts *model.ChannelSearchOpts, afterChannelID string) (model.ChannelList, *model.AppError)
 	GetChannelsForUser(c request.CTX, userID string, includeDeleted bool, lastDeleteAt, pageSize int, fromChannelID string) (model.ChannelList, *model.AppError)
+	GetChannelsMemberCount(c request.CTX, channelIDs []string) (map[string]int64, *model.AppError)
 	GetChannelsUserNotIn(c request.CTX, teamID string, userID string, offset int, limit int) (model.ChannelList, *model.AppError)
 	GetCloudSession(token string) (*model.Session, *model.AppError)
 	GetClusterId() string

server/channels/app/channel.go

@@ -1834,6 +1834,20 @@ func (a *App) GetChannels(c request.CTX, channelIDs []string) ([]*model.Channel,
 	return channels, nil
 }
 
+func (a *App) GetChannelsMemberCount(c request.CTX, channelIDs []string) (map[string]int64, *model.AppError) {
+	channelsCount, err := a.Srv().Store().Channel().GetChannelsMemberCount(channelIDs)
+	if err != nil {
+		var nfErr *store.ErrNotFound
+		switch {
+		case errors.As(err, &nfErr):
+			return nil, model.NewAppError("GetChannelsMemberCount", "app.channel.get_channels_member_count.existing.app_error", nil, "", http.StatusNotFound).Wrap(err)
+		default:
+			return nil, model.NewAppError("GetChannelsMemberCount", "app.channel.get_channels_member_count.find.app_error", nil, "", http.StatusInternalServerError).Wrap(err)
+		}
+	}
+	return channelsCount, nil
+}
+
 func (a *App) GetChannelByName(c request.CTX, channelName, teamID string, includeDeleted bool) (*model.Channel, *model.AppError) {
 	var channel *model.Channel
 	var err error

server/channels/app/channel_test.go

@@ -2195,6 +2195,24 @@ func TestGetMemberCountsByGroup(t *testing.T) {
 	require.ElementsMatch(t, cmc, resp)
 }
 
+func TestGetChannelsMemberCount(t *testing.T) {
+	th := SetupWithStoreMock(t)
+	defer th.TearDown()
+
+	mockStore := th.App.Srv().Store().(*mocks.Store)
+	mockChannelStore := mocks.ChannelStore{}
+	channelsMemberCount := map[string]int64{
+		"channel1": int64(10),
+		"channel2": int64(20),
+	}
+	mockChannelStore.On("GetChannelsMemberCount", []string{"channel1", "channel2"}).Return(channelsMemberCount, nil)
+	mockStore.On("Channel").Return(&mockChannelStore)
+	mockStore.On("GetDBSchemaVersion").Return(1, nil)
+	resp, err := th.App.GetChannelsMemberCount(th.Context, []string{"channel1", "channel2"})
+	require.Nil(t, err)
+	require.Equal(t, channelsMemberCount, resp)
+}
+
 func TestViewChannelCollapsedThreadsTurnedOff(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()

server/channels/app/opentracing/opentracing_layer.go

@@ -5612,6 +5612,28 @@ func (a *OpenTracingAppLayer) GetChannelsForUser(c request.CTX, userID string, i
 	return resultVar0, resultVar1
 }
 
+func (a *OpenTracingAppLayer) GetChannelsMemberCount(c request.CTX, channelIDs []string) (map[string]int64, *model.AppError) {
+	origCtx := a.ctx
+	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.GetChannelsMemberCount")
+
+	a.ctx = newCtx
+	a.app.Srv().Store().SetContext(newCtx)
+	defer func() {
+		a.app.Srv().Store().SetContext(origCtx)
+		a.ctx = origCtx
+	}()
+
+	defer span.Finish()
+	resultVar0, resultVar1 := a.app.GetChannelsMemberCount(c, channelIDs)
+
+	if resultVar1 != nil {
+		span.LogFields(spanlog.Error(resultVar1))
+		ext.Error.Set(span, true)
+	}
+
+	return resultVar0, resultVar1
+}
+
 func (a *OpenTracingAppLayer) GetChannelsUserNotIn(c request.CTX, teamID string, userID string, offset int, limit int) (model.ChannelList, *model.AppError) {
 	origCtx := a.ctx
 	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.GetChannelsUserNotIn")