[MM-46694] A/B Test: welcome post (#20926)

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

app/app_iface.go

@@ -871,6 +871,7 @@ type AppIface interface {
 	InviteNewUsersToTeam(emailList []string, teamID, senderId string) *model.AppError
 	InviteNewUsersToTeamGracefully(memberInvite *model.MemberInvite, teamID, senderId string, reminderInterval string) ([]*model.EmailInviteWithError, *model.AppError)
 	IsCRTEnabledForUser(c request.CTX, userID string) bool
+	IsFirstAdmin(user *model.User) bool
 	IsFirstUserAccount() bool
 	IsLeader() bool
 	IsPasswordValid(password string) *model.AppError

app/channel.go

@@ -12,6 +12,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/mattermost/logr/v2"
 	"github.com/mattermost/mattermost-server/v6/app/request"
 	"github.com/mattermost/mattermost-server/v6/model"
 	"github.com/mattermost/mattermost-server/v6/plugin"
@@ -130,6 +131,35 @@ func (a *App) JoinDefaultChannels(c request.CTX, teamID string, user *model.User
 		message.Add("user_id", user.Id)
 		message.Add("team_id", channel.TeamId)
 		a.Publish(message)
+
+		// A/B Test on the welcome post
+		if a.Config().FeatureFlags.SendWelcomePost && channelName == model.DefaultChannelName {
+			nbTeams, err := a.Srv().Store().Team().AnalyticsTeamCount(&model.TeamSearch{
+				IncludeDeleted: model.NewBool(true),
+			})
+			if err != nil {
+				c.Logger().Warn("unable to get number of teams", logr.Err(err))
+				return nil
+			}
+
+			if nbTeams == 1 && a.IsFirstAdmin(user) {
+				// Post the welcome message
+				if _, err := a.CreatePost(c, &model.Post{
+					ChannelId: channel.Id,
+					Type:      model.PostTypeWelcomePost,
+					UserId:    user.Id,
+				}, channel, false, false); err != nil {
+					c.Logger().Warn("unable to post welcome message", logr.Err(err))
+					return nil
+				}
+				ts := a.Srv().GetTelemetryService()
+				if ts != nil {
+					ts.SendTelemetry("welcome-message-sent", map[string]any{
+						"category": "growth",
+					})
+				}
+			}
+		}
 	}
 
 	if nErr != nil {

app/opentracing/opentracing_layer.go

@@ -11626,6 +11626,23 @@ func (a *OpenTracingAppLayer) IsCRTEnabledForUser(c request.CTX, userID string)
 	return resultVar0
 }
 
+func (a *OpenTracingAppLayer) IsFirstAdmin(user *model.User) bool {
+	origCtx := a.ctx
+	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.IsFirstAdmin")
+
+	a.ctx = newCtx
+	a.app.Srv().Store().SetContext(newCtx)
+	defer func() {
+		a.app.Srv().Store().SetContext(origCtx)
+		a.ctx = origCtx
+	}()
+
+	defer span.Finish()
+	resultVar0 := a.app.IsFirstAdmin(user)
+
+	return resultVar0
+}
+
 func (a *OpenTracingAppLayer) IsFirstUserAccount() bool {
 	origCtx := a.ctx
 	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.IsFirstUserAccount")

app/user.go

@@ -209,6 +209,19 @@ func (a *App) IsFirstUserAccount() bool {
 	return a.ch.srv.platform.IsFirstUserAccount()
 }
 
+func (a *App) IsFirstAdmin(user *model.User) bool {
+	if !user.IsSystemAdmin() {
+		return false
+	}
+
+	adminID, err := a.Srv().Store().User().GetFirstSystemAdminID()
+	if err != nil {
+		return false
+	}
+
+	return adminID == user.Id
+}
+
 // CreateUser creates a user and sets several fields of the returned User struct to
 // their zero values.
 func (a *App) CreateUser(c request.CTX, user *model.User) (*model.User, *model.AppError) {

app/user_test.go

@@ -1801,3 +1801,54 @@ func TestCreateUserWithInitialPreferences(t *testing.T) {
 		assert.Equal(t, "false", recommendedNextStepsPref[0].Value)
 	})
 }
+
+func TestIsFirstAdmin(t *testing.T) {
+	t.Run("should return false if user is not sysadmin", func(t *testing.T) {
+		th := SetupWithStoreMock(t)
+		defer th.TearDown()
+
+		Id := model.NewId()
+		isFirstAdmin := th.App.IsFirstAdmin(&model.User{
+			Id:    Id,
+			Roles: model.SystemUserRoleId,
+		})
+		require.False(t, isFirstAdmin)
+	})
+
+	t.Run("should return false if user is sysadmin but not the first one", func(t *testing.T) {
+		th := SetupWithStoreMock(t)
+		defer th.TearDown()
+
+		Id := model.NewId()
+
+		mockUserStore := storemocks.UserStore{}
+		mockUserStore.On("GetFirstSystemAdminID").Return(model.NewId(), nil)
+
+		mockStore := th.App.Srv().Store().(*storemocks.Store)
+		mockStore.On("User").Return(&mockUserStore)
+
+		isFirstAdmin := th.App.IsFirstAdmin(&model.User{
+			Id:    Id,
+			Roles: model.SystemAdminRoleId,
+		})
+		require.False(t, isFirstAdmin)
+	})
+
+	t.Run("should return true if user is sysadmin and the first one", func(t *testing.T) {
+		th := SetupWithStoreMock(t)
+		defer th.TearDown()
+
+		Id := model.NewId()
+
+		mockStore := th.App.Srv().Store().(*storemocks.Store)
+		mockUserStore := storemocks.UserStore{}
+		mockUserStore.On("GetFirstSystemAdminID").Return(Id, nil)
+		mockStore.On("User").Return(&mockUserStore)
+
+		isFirstAdmin := th.App.IsFirstAdmin(&model.User{
+			Id:    Id,
+			Roles: model.SystemAdminRoleId,
+		})
+		require.True(t, isFirstAdmin)
+	})
+}