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/api4/channel_test.go

@@ -4469,6 +4469,74 @@ func TestGetChannelMemberCountsByGroup(t *testing.T) {
 	})
 }
 
+func TestGetChannelsMemberCount(t *testing.T) {
+	// Setup
+	th := Setup(t).InitBasic()
+	defer th.TearDown()
+
+	client := th.Client
+
+	channel1 := th.CreatePublicChannel()
+	channel2 := th.CreatePublicChannel()
+
+	user1 := th.CreateUser()
+	user2 := th.CreateUser()
+	user3 := th.CreateUser()
+
+	th.LinkUserToTeam(user1, th.BasicTeam)
+	th.LinkUserToTeam(user2, th.BasicTeam)
+	th.LinkUserToTeam(user3, th.BasicTeam)
+
+	th.AddUserToChannel(user1, channel1)
+	th.AddUserToChannel(user2, channel1)
+	th.AddUserToChannel(user3, channel1)
+	th.AddUserToChannel(user2, channel2)
+
+	t.Run("Should return correct member count", func(t *testing.T) {
+		// Create a request with channel IDs
+		channelIDs := []string{channel1.Id, channel2.Id}
+		channelsMemberCount, _, err := client.GetChannelsMemberCount(context.Background(), channelIDs)
+		require.NoError(t, err)
+
+		// Verify the member counts
+		require.Contains(t, channelsMemberCount, channel1.Id)
+		require.Contains(t, channelsMemberCount, channel2.Id)
+		require.Equal(t, int64(4), channelsMemberCount[channel1.Id])
+		require.Equal(t, int64(2), channelsMemberCount[channel2.Id])
+	})
+
+	t.Run("Should return empty object when empty array is passed", func(t *testing.T) {
+		channelsMemberCount, _, err := client.GetChannelsMemberCount(context.Background(), []string{})
+		require.NoError(t, err)
+		require.Equal(t, 0, len(channelsMemberCount))
+	})
+
+	t.Run("Should fail due to permissions", func(t *testing.T) {
+		_, resp, err := client.GetChannelsMemberCount(context.Background(), []string{"junk"})
+		require.Error(t, err)
+		CheckForbiddenStatus(t, resp)
+		CheckErrorID(t, err, "api.context.permissions.app_error")
+	})
+
+	t.Run("Should fail due to expired session when logged out", func(t *testing.T) {
+		client.Logout(context.Background())
+		channelIDs := []string{channel1.Id, channel2.Id}
+		_, resp, err := client.GetChannelsMemberCount(context.Background(), channelIDs)
+		require.Error(t, err)
+		CheckUnauthorizedStatus(t, resp)
+		CheckErrorID(t, err, "api.context.session_expired.app_error")
+	})
+
+	t.Run("Should fail due to expired session when logged out", func(t *testing.T) {
+		th.LoginBasic2()
+		channelIDs := []string{channel1.Id, channel2.Id}
+		_, resp, err := client.GetChannelsMemberCount(context.Background(), channelIDs)
+		require.Error(t, err)
+		CheckForbiddenStatus(t, resp)
+		CheckErrorID(t, err, "api.context.permissions.app_error")
+	})
+}
+
 func TestMoveChannel(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()