1 files changed, 84 insertions, 0 deletions
diff --git a/app/channels/awareness_channel.rb b/app/channels/awareness_channel.rb
new file mode 100644
index 00000000000..554e057ca83
--- /dev/null
+++ b/app/channels/awareness_channel.rb
@@ -0,0 +1,84 @@
+# frozen_string_literal: true
+
+class AwarenessChannel < ApplicationCable::Channel # rubocop:disable Gitlab/NamespacedClass
+  REFRESH_INTERVAL = ENV.fetch("GITLAB_AWARENESS_REFRESH_INTERVAL_SEC", 60)
+  private_constant :REFRESH_INTERVAL
+
+  # Produces a refresh interval value, based of the
+  # GITLAB_AWARENESS_REFRESH_INTERVAL_SEC environment variable or the given
+  # default. Makes sure, that the interval after a jitter is applied, is never
+  # less than half the predefined interval.
+  def self.refresh_interval(range: -10..10)
+    min = REFRESH_INTERVAL / 2.to_f
+    [min.to_i, REFRESH_INTERVAL.to_i + rand(range)].max.seconds
+  end
+  private_class_method :refresh_interval
+
+  # keep clients updated about session membership
+  periodically every: self.refresh_interval do
+    transmit payload
+  end
+
+  def subscribed
+    reject unless valid_subscription?
+    return if subscription_rejected?
+
+    stream_for session, coder: ActiveSupport::JSON
+
+    session.join(current_user)
+    AwarenessChannel.broadcast_to(session, payload)
+  end
+
+  def unsubscribed
+    return if subscription_rejected?
+
+    session.leave(current_user)
+    AwarenessChannel.broadcast_to(session, payload)
+  end
+
+  # Allows a client to let the server know they are still around. This is not
+  # like a heartbeat mechanism. This can be triggered by any action that results
+  # in a meaningful "presence" update. Like scrolling the screen (debounce),
+  # window becoming active, user starting to type in a text field, etc.
+  def touch
+    session.touch!(current_user)
+
+    transmit payload
+  end
+
+  private
+
+  def valid_subscription?
+    current_user.present? && path.present?
+  end
+
+  def payload
+    { collaborators: collaborators }
+  end
+
+  def collaborators
+    session.online_users_with_last_activity.map do |user, last_activity|
+      collaborator(user, last_activity)
+    end
+  end
+
+  def collaborator(user, last_activity)
+    {
+      id: user.id,
+      name: user.name,
+      avatar_url: user.avatar_url(size: 36),
+      last_activity: last_activity,
+      last_activity_humanized: ActionController::Base.helpers.distance_of_time_in_words(
+        Time.zone.now, last_activity
+      )
+    }
+  end
+
+  def session
+    @session ||= AwarenessSession.for(path)
+  end
+
+  def path
+    params[:path]
+  end
+end