1 files changed, 60 insertions, 0 deletions
diff --git a/app/models/concerns/update_project_statistics.rb b/app/models/concerns/update_project_statistics.rb
new file mode 100644
index 00000000000..bffc711c886
--- /dev/null
+++ b/app/models/concerns/update_project_statistics.rb
@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+# This module is providing helpers for updating `ProjectStatistics` with `after_save` and `before_destroy` hooks.
+#
+# It deals with `ProjectStatistics.increment_statistic` making sure not to update statistics on a cascade delete from the
+# project, and keeping track of value deltas on each save. It updates the DB only when a change is needed.
+#
+# How to use
+# - Invoke `update_project_statistics stat: :a_project_statistics_column, attribute: :an_attr_to_track` in a model class body.
+#
+# Expectation
+# - `attribute` must be an ActiveRecord attribute
+# - The model must implement `project` and `project_id`. i.e. direct Project relationship or delegation
+module UpdateProjectStatistics
+  extend ActiveSupport::Concern
+
+  class_methods do
+    attr_reader :statistic_name, :statistic_attribute
+
+    # Configure the model to update +stat+ on ProjectStatistics when +attribute+ changes
+    #
+    # +stat+:: a column of ProjectStatistics to update
+    # +attribute+:: an attribute of the current model, default to +:size+
+    def update_project_statistics(stat:, attribute: :size)
+      @statistic_name = stat
+      @statistic_attribute = attribute
+
+      after_save(:update_project_statistics_after_save, if: :update_project_statistics_attribute_changed?)
+      after_destroy(:update_project_statistics_after_destroy, unless: :project_destroyed?)
+    end
+    private :update_project_statistics
+  end
+
+  included do
+    private
+
+    def project_destroyed?
+      project.pending_delete?
+    end
+
+    def update_project_statistics_attribute_changed?
+      attribute_changed?(self.class.statistic_attribute)
+    end
+
+    def update_project_statistics_after_save
+      attr = self.class.statistic_attribute
+      delta = read_attribute(attr).to_i - attribute_was(attr).to_i
+
+      update_project_statistics(delta)
+    end
+
+    def update_project_statistics_after_destroy
+      update_project_statistics(-read_attribute(self.class.statistic_attribute).to_i)
+    end
+
+    def update_project_statistics(delta)
+      ProjectStatistics.increment_statistic(project_id, self.class.statistic_name, delta)
+    end
+  end
+end