diff --git a/lib/open_project/costs/engine.rb b/lib/open_project/costs/engine.rb
index 39eb9fe051..184645966a 100644
--- a/lib/open_project/costs/engine.rb
+++ b/lib/open_project/costs/engine.rb
@@ -2,191 +2,116 @@ module OpenProject::Costs
   class Engine < ::Rails::Engine
     engine_name :openproject_costs
 
-    def self.settings
-      { :default => { 'costs_currency' => 'EUR',
-                      'costs_currency_format' => '%n %u' },
-        :partial => 'settings/openproject_costs' }
-    end
+    include OpenProject::Plugins::ActsAsOpEngine
 
-    initializer "costs.register_hooks" do
-      require_dependency 'open_project/costs/hooks'
-      require_dependency 'open_project/costs/hooks/activity_hook'
-      require_dependency 'open_project/costs/hooks/work_package_hook'
-      require_dependency 'open_project/costs/hooks/project_hook'
-      require_dependency 'open_project/costs/hooks/work_package_action_menu'
-      require_dependency 'open_project/costs/hooks/work_packages_show_attributes'
-    end
+    register 'openproject-costs',
+             :author_url => 'http://finn.de',
+             :requires_openproject => '>= 3.0.0pre42',
+             :settings =>  { 'default' => { 'costs_currency' => 'EUR','costs_currency_format' => '%n %u' },
+             :partial => 'settings/openproject_costs' } do
 
-    config.autoload_paths += Dir["#{config.root}/lib/"]
+      project_module :costs_module do
+        permission :view_own_hourly_rate, {}
+        permission :view_hourly_rates, {}
 
-    initializer 'costs.precompile_assets' do
-      Rails.application.config.assets.precompile += %w(costs.css costs.js)
-    end
+        permission :edit_own_hourly_rate, {:hourly_rates => [:set_rate, :edit, :update]},
+                                          :require => :member
+        permission :edit_hourly_rates, {:hourly_rates => [:set_rate, :edit, :update]},
+                                       :require => :member
+        permission :view_cost_rates, {} # cost item values
 
-    # adds our factories to factory girl's load path
-    initializer "costs.register_factories", :after => "factory_girl.set_factory_paths" do |app|
-      FactoryGirl.definition_file_paths << File.expand_path(self.root.to_s + '/spec/factories') if defined?(FactoryGirl)
-    end
+        permission :log_own_costs, { :costlog => [:new, :create] },
+                                   :require => :loggedin
+        permission :log_costs, {:costlog => [:new, :create]},
+                               :require => :member
 
-    initializer 'costs.register_test_paths' do |app|
-      app.config.plugins_to_test_paths << self.root
-    end
+        permission :edit_own_cost_entries, {:costlog => [:edit, :update, :destroy]},
+                                           :require => :loggedin
+        permission :edit_cost_entries, {:costlog => [:edit, :update, :destroy]},
+                                       :require => :member
 
-    initializer 'costs.register_observers' do |app|
-      # Observers
-      ActiveRecord::Base.observers.push :rate_observer, :default_hourly_rate_observer, :costs_work_package_observer
-    end
+        permission :block_tickets, {}, :require => :member
+        permission :view_cost_objects, {:cost_objects => [:index, :show]}
 
-    config.before_configuration do |app|
-      # This is required for the routes to be loaded first
-      # as the routes should be prepended so they take precedence over the core.
-      app.config.paths['config/routes'].unshift File.join(File.dirname(__FILE__), "..", "..", "..", "config", "routes.rb")
-    end
+        permission :view_cost_entries, { :cost_objects => [:index, :show], :costlog => [:index] }
+        permission :view_own_cost_entries, { :cost_objects => [:index, :show], :costlog => [:index] }
 
-    initializer "costs.remove_duplicate_routes", :after => "add_routing_paths" do |app|
-      # removes duplicate entry from app.routes_reloader
-      # As we prepend the plugin's routes to the load_path up front and rails
-      # adds all engines' config/routes.rb later, we have double loaded the routes
-      # This is not harmful as such but leads to duplicate routes which decreases performance
-      app.routes_reloader.paths.uniq!
-    end
+        permission :edit_cost_objects, {:cost_objects => [:index, :show, :edit, :update, :destroy, :new, :create, :copy]}
+      end
 
-    initializer "costs.patch_i18n" do
-      # This is done here instead of doing it along with the rest of the patches as
-      # i18n is not unloaded between requests. Hence, placing it inside the config.to_prepare
-      # block would patch i18n once for every request.
-      require_dependency 'open_project/costs/patches/i18n_patch'
-    end
+      # register additional permissions for the time log
+      project_module :time_tracking do
+        permission :view_own_time_entries, {:timelog => [:index, :report]}
+      end
 
-    initializer 'costs.append_migrations' do |app|
-      unless app.root.to_s.match root.to_s
-        config.paths["db/migrate"].expanded.each do |expanded_path|
-          app.config.paths["db/migrate"] << expanded_path
-        end
+      # Menu extensions
+      menu :top_menu,
+           :cost_types,
+           {:controller => '/cost_types', :action => 'index'},
+           :caption => :cost_types_title,
+           :if => Proc.new { User.current.admin? }
+
+      menu :project_menu,
+           :cost_objects,
+           {:controller => '/cost_objects', :action => 'index'},
+           :param => :project_id,
+           :before => :settings,
+           :caption => :cost_objects_title,
+           :html => {:class => 'icon2 icon-budget'}
+
+      menu :project_menu,
+           :new_budget,
+           {:controller => '/cost_objects', :action => 'new' },
+           :param => :project_id,
+           :caption => :label_cost_object_new,
+           :parent => :cost_objects,
+           :html => {:class => 'icon2 icon-add'}
+
+      menu :project_menu,
+           :show_all,
+           {:controller => '/cost_objects', :action => 'index' },
+           :param => :project_id,
+           :caption => :label_view_all_cost_objects,
+           :parent => :cost_objects,
+           :html => {:class => 'icon2 icon-list-view1'}
+
+      Redmine::Activity.map do |activity|
+        activity.register :cost_objects, class_name: 'Activity::CostObjectActivityProvider', default: false
       end
     end
 
-    config.to_prepare do
-
-      # TODO: avoid this dirty hack necessary to prevent settings method getting lost after reloading
-      Setting.create_setting("plugin_openproject_costs", {'default' => Engine.settings[:default], 'serialized' => true})
-      Setting.create_setting_accessors("plugin_openproject_costs")
-
-      require 'open_project/costs/patches'
+    patches [:WorkPackage, :Project, :Query, :User, :TimeEntry, :Version, :PermittedParams, :ApplicationController,
+      :ProjectsController, :ApplicationHelper, :UsersHelper]
 
-      # Model Patches
-      require_dependency 'open_project/costs/patches/work_package_patch'
-      require_dependency 'open_project/costs/patches/project_patch'
-      require_dependency 'open_project/costs/patches/query_patch'
-      require_dependency 'open_project/costs/patches/user_patch'
-      require_dependency 'open_project/costs/patches/time_entry_patch'
-      require_dependency 'open_project/costs/patches/version_patch'
-      require_dependency 'open_project/costs/patches/permitted_params_patch'
+    assets %w(costs.css costs.js)
 
-      # Controller Patches
-      require_dependency 'open_project/costs/patches/application_controller_patch'
-      require_dependency 'open_project/costs/patches/projects_controller_patch'
+    initializer "costs.register_hooks" do
+      require 'open_project/costs/hooks'
+      require 'open_project/costs/hooks/activity_hook'
+      require 'open_project/costs/hooks/work_package_hook'
+      require 'open_project/costs/hooks/project_hook'
+      require 'open_project/costs/hooks/work_package_action_menu'
+      require 'open_project/costs/hooks/work_packages_show_attributes'
+    end
 
-      # Helper Patches
-      require_dependency 'open_project/costs/patches/application_helper_patch'
-      require_dependency 'open_project/costs/patches/users_helper_patch'
+    initializer 'costs.register_observers' do |app|
+      # Observers
+      ActiveRecord::Base.observers.push :rate_observer, :default_hourly_rate_observer, :costs_work_package_observer
+    end
 
-      require_dependency 'open_project/costs/patches/work_package_observer'
+    initializer 'costs.patch_number_helper' do |app|
+      # we have to do the patching in the initializer to make sure we only do this once in development
+      # since the NumberHelper is not unloaded
+      ActionView::Helpers::NumberHelper.send(:include, OpenProject::Costs::Patches::NumberHelperPatch)
+    end
 
+    config.to_prepare do
       # loading the class so that acts_as_journalized gets registered
       VariableCostObject
 
       # TODO: this recreates the original behaviour
       # however, it might not be desirable to allow assigning of cost_object regardless of the permissions
       PermittedParams.permit(:new_work_package, :cost_object_id)
-
-      unless Redmine::Plugin.registered_plugins.include?(:openproject_costs)
-        Redmine::Plugin.register :openproject_costs do
-
-          name 'OpenProject Costs'
-          author 'Finn GmbH'
-          author_url 'http://finn.de/'
-          url 'https://www.openproject.org/projects/costs-plugin'
-          description 'The costs plugin provides basic cost management functionality for OpenProject.'
-
-          version OpenProject::Costs::VERSION
-
-          settings Engine.settings
-
-          requires_openproject ">= 3.0.0pre42"
-
-          # register our custom permissions
-          project_module :costs_module do
-            permission :view_own_hourly_rate, {}
-            permission :view_hourly_rates, {}
-
-            permission :edit_own_hourly_rate, {:hourly_rates => [:set_rate, :edit, :update]},
-                                              :require => :member
-            permission :edit_hourly_rates, {:hourly_rates => [:set_rate, :edit, :update]},
-                                           :require => :member
-            permission :view_cost_rates, {} # cost item values
-
-            permission :log_own_costs, { :costlog => [:new, :create] },
-                                       :require => :loggedin
-            permission :log_costs, {:costlog => [:new, :create]},
-                                   :require => :member
-
-            permission :edit_own_cost_entries, {:costlog => [:edit, :update, :destroy]},
-                                               :require => :loggedin
-            permission :edit_cost_entries, {:costlog => [:edit, :update, :destroy]},
-                                           :require => :member
-
-            permission :block_tickets, {}, :require => :member
-            permission :view_cost_objects, {:cost_objects => [:index, :show]}
-
-            permission :view_cost_entries, { :cost_objects => [:index, :show], :costlog => [:index] }
-            permission :view_own_cost_entries, { :cost_objects => [:index, :show], :costlog => [:index] }
-
-            permission :edit_cost_objects, {:cost_objects => [:index, :show, :edit, :update, :destroy, :new, :create, :copy]}
-          end
-
-          # register additional permissions for the time log
-          project_module :time_tracking do
-            permission :view_own_time_entries, {:timelog => [:index, :report]}
-          end
-
-
-          # Menu extensions
-          menu :top_menu,
-               :cost_types,
-               {:controller => '/cost_types', :action => 'index'},
-               :caption => :cost_types_title,
-               :if => Proc.new { User.current.admin? }
-
-          menu :project_menu,
-               :cost_objects,
-               {:controller => '/cost_objects', :action => 'index'},
-               :param => :project_id,
-               :before => :settings,
-               :caption => :cost_objects_title,
-               :html => {:class => 'icon2 icon-budget'}
-
-          menu :project_menu,
-               :new_budget,
-               {:controller => '/cost_objects', :action => 'new' },
-               :param => :project_id,
-               :caption => :label_cost_object_new,
-               :parent => :cost_objects,
-               :html => {:class => 'icon2 icon-add'}
-
-          menu :project_menu,
-               :show_all,
-               {:controller => '/cost_objects', :action => 'index' },
-               :param => :project_id,
-               :caption => :label_view_all_cost_objects,
-               :parent => :cost_objects,
-               :html => {:class => 'icon2 icon-list-view1'}
-
-          Redmine::Activity.map do |activity|
-            activity.register :cost_objects, class_name: 'Activity::CostObjectActivityProvider', default: false
-          end
-        end
-      end
     end
   end
 end