[MM-43917] Cloud Freemium limits API: messages/posts (#20152)

* WIP - Add api and app funcs

* Add test cases

* Add utils testcases

* Exclude deleted posts

* Add doc for func

* Move api from cloud to usage

* Allow api access to authenticated users

* Change int to int64

* Fix lint issue

* Simplify err check

Co-authored-by: Ashish Bhate <ashish.bhate@mattermost.com>

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Ashish Bhate <ashish.bhate@mattermost.com>

app/usage_test.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package app
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
+
+	"github.com/mattermost/mattermost-server/v6/store/storetest/mocks"
+)
+
+func TestGetPostsUsage(t *testing.T) {
+	t.Run("returns error when AnalyticsPostCount fails", func(t *testing.T) {
+		th := SetupWithStoreMock(t)
+		defer th.TearDown()
+
+		errMsg := "Test posts count error"
+
+		mockStore := th.App.Srv().Store.(*mocks.Store)
+		mockPostStore := mocks.PostStore{}
+		mockPostStore.On("AnalyticsPostCount", mock.Anything).Return(int64(0), errors.New(errMsg))
+		mockStore.On("Post").Return(&mockPostStore)
+
+		usage, appErr := th.App.GetPostsUsage()
+		assert.Zero(t, usage)
+		assert.ErrorContains(t, appErr, errMsg)
+	})
+
+	t.Run("returns rounded off count when AnalyticsPostCount returns valid count", func(t *testing.T) {
+		th := SetupWithStoreMock(t)
+		defer th.TearDown()
+
+		var mockCount int64 = 4321
+		var expected int64 = 4000
+
+		mockStore := th.App.Srv().Store.(*mocks.Store)
+		mockPostStore := mocks.PostStore{}
+		mockPostStore.On("AnalyticsPostCount", mock.Anything).Return(mockCount, nil)
+		mockStore.On("Post").Return(&mockPostStore)
+
+		count, appErr := th.App.GetPostsUsage()
+		assert.Nil(t, appErr)
+		assert.Equal(t, expected, count)
+	})
+}