Add MattermostController

app/controllers/projects/mattermost_controller.rb

+class Projects::MattermostController < Projects::ApplicationController
+  layout 'project_settings'
+  before_action :authorize_admin_project!
+  before_action :service
+  before_action :teams, only: [:new]
+
+  def new
+  end
+
+  def configure
+    @service.configure(host, current_user, params)
+
+    redirect_to(
+      new_namespace_project_service_path(@project.namespace, @project, @service.to_param),
+      notice: 'This service is now configured.'
+    )
+  rescue Mattermost::NoSessionError
+    redirect_to(
+      edit_namespace_project_service_path(@project.namespace, @project, @service.to_param),
+      alert: 'No session could be set up, is Mattermost configured with Single Sign on?'
+    )
+  end
+
+  private
+
+  def configure_params
+    params.require(:configure_params).permit(:trigger, :team_id)
+  end
+
+  def service
+    @service ||= @project.services.find_by(type: 'MattermostSlashCommandsService')
+  end
+
+  def teams
+    # Mocking for frontend development
+    @teams = [{"id"=>"qz8gdr1fopncueb8n9on8ohk3h", "create_at"=>1479992105904, "update_at"=>1479992105904, "delete_at"=>0, "display_name"=>"chatops", "name"=>"chatops", "email"=>"admin@example.com", "type"=>"O", "company_name"=>"", "allowed_domains"=>"", "invite_id"=>"gthxi47gj7rxtcx6zama63zd1w", "allow_open_invite"=>false}]
+
+    #  @teams =
+    #       begin
+    #         Mattermost::Mattermost.new(Gitlab.config.mattermost.host, current_user).with_session do
+    #          Mattermost::Team.all
+    #        end
+    #      rescue Mattermost::NoSessionError
+    #        @teams = []
+    #      end
+  end
+end

app/views/projects/mattermost/new.html.haml

+= "hello world"
+= form_for(:create, method: :post, url: configure_namespace_project_mattermost_path(@project.namespace, @project, @service.to_param)) do |f|
+  = "Team ID"
+  = f.text_field(:team_id)
+  = f.submit 'Configure', class: 'btn btn-save'
+

app/views/projects/services/mattermost_slash_commands/_help.html.haml

 - pretty_path_with_namespace = "#{@project ? @project.namespace.name : 'namespace'} / #{@project ? @project.name : 'name'}"
 - run_actions_text = "Perform common operations on this project: #{pretty_path_with_namespace}"
 
-- unless GitLab.config.mattermost.enabled
-  .well
+.well
   This service allows GitLab users to perform common operations on this
   project by entering slash commands in Mattermost.
   %br
@@ -99,3 +98,6 @@
       3. After adding the slash command, paste the
       %strong token
       into the field below
+
+- if Gitlab.config.mattermost.enabled
+  = link_to "Auto config", new_namespace_project_mattermost_path(@project.namespace, @project)

config/routes/project.rb

@@ -65,6 +65,12 @@ constraints(ProjectUrlConstrainer.new) do
         end
       end
 
+      resources :mattermost, only: [:new] do
+        member do
+          post :configure
+        end
+      end
+
       resources :deploy_keys, constraints: { id: /\d+/ }, only: [:index, :new, :create] do
         member do
           put :enable