1 files changed, 44 insertions, 0 deletions
diff --git a/app/models/concerns/subscribable.rb b/app/models/concerns/subscribable.rb
new file mode 100644
index 00000000000..d5a881b2445
--- /dev/null
+++ b/app/models/concerns/subscribable.rb
@@ -0,0 +1,44 @@
+# == Subscribable concern
+#
+# Users can subscribe to these models.
+#
+# Used by Issue, MergeRequest, Label
+#
+
+module Subscribable
+  extend ActiveSupport::Concern
+
+  included do
+    has_many :subscriptions, dependent: :destroy, as: :subscribable
+  end
+
+  def subscribed?(user)
+    if subscription = subscriptions.find_by_user_id(user.id)
+      subscription.subscribed
+    else
+      subscribed_without_subscriptions?(user)
+    end
+  end
+
+  # Override this method to define custom logic to consider a subscribable as
+  # subscribed without an explicit subscription record.
+  def subscribed_without_subscriptions?(user)
+    false
+  end
+
+  def subscribers
+    subscriptions.where(subscribed: true).map(&:user)
+  end
+
+  def toggle_subscription(user)
+    subscriptions.
+      find_or_initialize_by(user_id: user.id).
+      update(subscribed: !subscribed?(user))
+  end
+
+  def unsubscribe(user)
+    subscriptions.
+      find_or_initialize_by(user_id: user.id).
+      update(subscribed: false)
+  end
+end