Remove Mattermost team with GitLab group

When destroying a group, now an API call is made to the Mattermost
server to request the deletion of the project. Actual team deletion on
the Mattermost side happens async, so the runtime shouldn't increase by
more than a second.

6 files changed, 42 insertions, 0 deletions

diff --git a/app/models/chat_team.rb b/app/models/chat_team.rb
index c52b6f15913..25ecf2d5937 100644
--- a/app/models/chat_team.rb
+++ b/app/models/chat_team.rb
@@ -3,4 +3,13 @@ class ChatTeam < ActiveRecord::Base
   validates :namespace, uniqueness: true
 
   belongs_to :namespace
+
+  def remove_mattermost_team(current_user)
+    Mattermost::Team.new(current_user).destroy(team_id: team_id)
+  rescue Mattermost::ClientError => e
+    # Either the group is not found, or the user doesn't have the proper
+    # access on the mattermost instance. In the first case, we're done either way
+    # in the latter case, we can't recover by retrying, so we just log what happened
+    Rails.logger.error("Mattermost team deletion failed: #{e}")
+  end
 end
diff --git a/app/services/groups/destroy_service.rb b/app/services/groups/destroy_service.rb
index 80c51cb5a72..f565612a89d 100644
--- a/app/services/groups/destroy_service.rb
+++ b/app/services/groups/destroy_service.rb
@@ -21,6 +21,8 @@ module Groups
         DestroyService.new(group, current_user).execute
       end
 
+      group.chat_team&.remove_mattermost_team(current_user)
+
       group.really_destroy!
     end
   end
diff --git a/changelogs/unreleased/zj-delete-mm-team.yml b/changelogs/unreleased/zj-delete-mm-team.yml
new file mode 100644
index 00000000000..f0c782c4566
--- /dev/null
+++ b/changelogs/unreleased/zj-delete-mm-team.yml
@@ -0,0 +1,4 @@
+---
+title: Remove Mattermost team when deleting a group
+merge_request: 11362
+author:
diff --git a/lib/mattermost/client.rb b/lib/mattermost/client.rb
index 3d60618006c..d80cd7d2a4e 100644
--- a/lib/mattermost/client.rb
+++ b/lib/mattermost/client.rb
@@ -24,6 +24,10 @@ module Mattermost
       json_response session.post(path, options)
     end
 
+    def delete(session, path, options)
+      json_response session.delete(path, options)
+    end
+
     def session_get(path, options = {})
       with_session do |session|
         get(session, path, options)
@@ -36,6 +40,12 @@ module Mattermost
       end
     end
 
+    def session_delete(path, options = {})
+      with_session do |session|
+        delete(session, path, options)
+      end
+    end
+
     def json_response(response)
       json_response = JSON.parse(response.body)
 
diff --git a/lib/mattermost/team.rb b/lib/mattermost/team.rb
index 2cdbbdece16..b2511f3af1d 100644
--- a/lib/mattermost/team.rb
+++ b/lib/mattermost/team.rb
@@ -14,5 +14,12 @@ module Mattermost
         type: type
       }.to_json)
     end
+
+    # The deletion is done async, so the response is fast.
+    # On the mattermost side, this triggers an soft deletion first, after which
+    # the actuall data is removed
+    def destroy(team_id:)
+      session_delete("/api/v4/teams/#{team_id}?permanent=true")
+    end
   end
 end
diff --git a/spec/services/groups/destroy_service_spec.rb b/spec/services/groups/destroy_service_spec.rb
index d59b37bee36..449fb33e0dc 100644
--- a/spec/services/groups/destroy_service_spec.rb
+++ b/spec/services/groups/destroy_service_spec.rb
@@ -35,6 +35,16 @@ describe Groups::DestroyService, services: true do
       it { expect(NotificationSetting.unscoped.all).not_to include(notification_setting) }
     end
 
+    context 'mattermost team' do
+      let!(:chat_team) { create(:chat_team, namespace: group) }
+
+      it 'destroys the team too' do
+        expect_any_instance_of(Mattermost::Team).to receive(:destroy)
+
+        destroy_group(group, user, async)
+      end
+    end
+
     context 'file system' do
       context 'Sidekiq inline' do
         before do