Add waiting room to create programming groups (#1919)

Co-authored-by: Sebastian Serth <Sebastian.Serth@hpi.de>

app/channels/pg_matching_channel.rb

@@ -8,6 +8,8 @@ class PgMatchingChannel < ApplicationCable::Channel
 
   def unsubscribed
     # Any cleanup needed when channel is unsubscribed
+    @current_waiting_user.status_disconnected! if @current_waiting_user&.reload&.status_waiting?
+
     stop_all_streams
   end
 
@@ -15,8 +17,29 @@ class PgMatchingChannel < ApplicationCable::Channel
     "pg_matching_channel_exercise_#{@exercise.id}"
   end
 
+  def waiting_for_match
+    @current_waiting_user = PairProgrammingWaitingUser.find_or_initialize_by(user: current_user, exercise: @exercise)
+    @current_waiting_user.status_waiting!
+
+    match_waiting_users
+  end
+
   private
 
+  def match_waiting_users
+    # Check if there is another waiting user for this exercise
+    waiting_user = PairProgrammingWaitingUser.where(exercise: @exercise, status: :waiting).where.not(user: current_user).order(created_at: :asc).first
+    return if waiting_user.blank?
+
+    # If there is another waiting user, create a programming group with both users
+    match = [waiting_user, @current_waiting_user]
+    # Create the programming group. Note that an unhandled exception will be raised if the programming group
+    # is not valid (i.e., if one of the users already joined a programming group for this exercise).
+    pg = ProgrammingGroup.create!(exercise: @exercise, users: match.map(&:user))
+    match.each {|wu| wu.update(status: :created_pg, programming_group: pg) }
+    ActionCable.server.broadcast(specific_channel, {action: 'joined_pg', users: pg.users.map(&:to_page_context)})
+  end
+
   def set_and_authorize_exercise
     @exercise = Exercise.find(params[:exercise_id])
     reject unless ExercisePolicy.new(current_user, @exercise).implement?