Only Update Slack User Group via Slack API when Membership changes

adapters/slack/usergroup/usergroup.go

@@ -171,6 +171,8 @@ func (u *UserGroup) Add(ctx context.Context, emails []string) error {
 	// The updatedUserGroup is existing users + new users.
 	updatedUserGroup := make([]string, 0, len(u.cache)+len(emails))
 
+	isUserGroupUpdated := false
+
 	// Prefill the updatedUserGroup with everyone currently in the group.
 	for _, id := range u.cache {
 		updatedUserGroup = append(updatedUserGroup, id)
@@ -183,25 +185,35 @@ func (u *UserGroup) Add(ctx context.Context, emails []string) error {
 			return fmt.Errorf("slack.usergroup.add.getuserbyemail(%s) -> %w", email, err)
 		}
 
-		// Add the new email user IDs to the list.
-		updatedUserGroup = append(updatedUserGroup, user.ID)
+		_, ok := u.cache[email]
+		if !ok {
+			// Add the new email user IDs to the list.
+			updatedUserGroup = append(updatedUserGroup, user.ID)
+
+			// Add the new email user ID to the cache
+			u.cache[email] = user.ID
 
-		// Add the new email user ID to the cache
-		u.cache[email] = user.ID
+			// Set flag so we know to update Slack API
+			isUserGroupUpdated = true
+		}
 
 		// Calls to GetUserByEmail are heavily rate limited, so sleep to avoid this.
 		time.Sleep(2 * time.Second) //nolint:gomnd
 	}
 
-	// Add the members to the Slack UserGroup.
-	joinedSlackIds := strings.Join(updatedUserGroup, ",")
+	if isUserGroupUpdated {
+		// Add the members to the Slack UserGroup.
+		joinedSlackIds := strings.Join(updatedUserGroup, ",")
 
-	_, err := u.client.UpdateUserGroupMembersContext(ctx, u.userGroupID, joinedSlackIds)
-	if err != nil {
-		return fmt.Errorf("slack.usergroup.add.updateusergroupmembers(%s) -> %w", u.userGroupID, err)
-	}
+		_, err := u.client.UpdateUserGroupMembersContext(ctx, u.userGroupID, joinedSlackIds)
+		if err != nil {
+			return fmt.Errorf("slack.usergroup.add.updateusergroupmembers(%s) -> %w", u.userGroupID, err)
+		}
 
-	u.Logger.Println("Finished adding accounts successfully")
+		u.Logger.Println("Finished adding accounts successfully")
+	} else {
+		u.Logger.Println("No change to UserGroup")
+	}
 
 	return nil
 }

adapters/slack/usergroup/usergroup_internal_test.go

@@ -142,6 +142,29 @@ func TestUserGroup_Add(t *testing.T) {
 		assert.Contains(t, adapter.cache, "fizz@email")
 		assert.Contains(t, adapter.cache, "buzz@email")
 	})
+
+	t.Run("Doesn't call API if no changes", func(t *testing.T) {
+		t.Parallel()
+
+		slackClient := newMockISlackUserGroup(t)
+
+		adapter := &UserGroup{
+			client:      slackClient,
+			userGroupID: "test",
+			Logger:      log.New(os.Stdout, "", log.LstdFlags),
+		}
+
+		slackClient.EXPECT().GetUserByEmailContext(ctx, "foo@email").Return(&slack.User{ID: "foo"}, nil)
+		slackClient.EXPECT().GetUserByEmailContext(ctx, "bar@email").Return(&slack.User{ID: "bar"}, nil)
+
+		adapter.cache = map[string]string{"foo@email": "foo", "bar@email": "bar"}
+		err := adapter.Add(ctx, []string{"foo@email", "bar@email"})
+
+		require.NoError(t, err)
+		assert.Contains(t, adapter.cache, "foo@email")
+		assert.Contains(t, adapter.cache, "bar@email")
+		slackClient.AssertNotCalled(t, "UpdateUserGroupMembersContext")
+	})
 }
 
 func TestUserGroup_Remove(t *testing.T) {