include Rails.application.routes.url_helpers namespace :detect_exercise_anomalies do # uncomment for debug logging: # logger = Logger.new(STDOUT) # logger.level = Logger::DEBUG # Rails.logger = logger # These factors determine if an exercise is an anomaly, given the average working time (avg): # (avg * MIN_TIME_FACTOR) <= working_time <= (avg * MAX_TIME_FACTOR) MIN_TIME_FACTOR = 0.1 MAX_TIME_FACTOR = 2 # Determines how many users are picked from the best/average/worst performers of each anomaly for feedback NUMBER_OF_USERS_PER_CLASS = 10 # Determines margin below which user working times will be considered data errors (e.g. copy/paste solutions) MIN_USER_WORKING_TIME = 0.0 # Cache exercise working times, because queries are expensive and values do not change between collections WORKING_TIME_CACHE = {} AVERAGE_WORKING_TIME_CACHE = {} task :with_at_least, [:number_of_exercises, :number_of_solutions] => :environment do |task, args| include TimeHelper number_of_exercises = args[:number_of_exercises] number_of_solutions = args[:number_of_solutions] puts "Searching for exercise collections with at least #{number_of_exercises} exercises and #{number_of_solutions} users." # Get all exercise collections that have at least the specified amount of exercises and at least the specified # number of submissions AND are flagged for anomaly detection collections = get_collections(number_of_exercises, number_of_solutions) puts "Found #{collections.length}." collections.each do |collection| puts "\t- #{collection}" anomalies = find_anomalies(collection) if anomalies.length > 0 and not collection.user.nil? notify_collection_author(collection, anomalies) notify_users(collection, anomalies) reset_anomaly_detection_flag(collection) end end puts 'Done.' end def get_collections(number_of_exercises, number_of_solutions) ExerciseCollection .where(:use_anomaly_detection => true) .joins("join exercise_collections_exercises ece on exercise_collections.id = ece.exercise_collection_id join (select e.id from exercises e join submissions s on s.exercise_id = e.id group by e.id having count(s.user_id) > #{ExerciseCollection.sanitize(number_of_solutions)} ) as exercises_with_submissions on exercises_with_submissions.id = ece.exercise_id") .group('exercise_collections.id') .having('count(exercises_with_submissions.id) > ?', number_of_exercises) end def collect_working_times(collection) working_times = {} collection.exercises.each do |exercise| puts "\t\t> #{exercise.title}" working_times[exercise.id] = get_average_working_time(exercise) end working_times end def find_anomalies(collection) working_times = collect_working_times(collection).reject {|_, value| value.nil?} if working_times.values.size > 0 average = working_times.values.reduce(:+) / working_times.values.size return working_times.select do |_, working_time| working_time > average * MAX_TIME_FACTOR or working_time < average * MIN_TIME_FACTOR end end {} end def get_average_working_time(exercise) unless AVERAGE_WORKING_TIME_CACHE.key?(exercise.id) seconds = time_to_f exercise.average_working_time AVERAGE_WORKING_TIME_CACHE[exercise.id] = seconds end AVERAGE_WORKING_TIME_CACHE[exercise.id] end def get_user_working_times(exercise) unless WORKING_TIME_CACHE.key?(exercise.id) exercise.retrieve_working_time_statistics WORKING_TIME_CACHE[exercise.id] = exercise.working_time_statistics end WORKING_TIME_CACHE[exercise.id] end def notify_collection_author(collection, anomalies) puts "\t\tSending E-Mail to author (#{collection.user.displayname} <#{collection.user.email}>)..." UserMailer.exercise_anomaly_detected(collection, anomalies).deliver_now end def notify_users(collection, anomalies) by_id_and_type = proc { |u| {user_id: u[:user_id], user_type: u[:user_type]} } puts "\t\tSending E-Mails to best and worst performing users of each anomaly..." anomalies.each do |exercise_id, average_working_time| puts "\t\tAnomaly in exercise #{exercise_id} (avg: #{average_working_time} seconds):" exercise = Exercise.find(exercise_id) users_to_notify = [] users = {} [:performers_by_time, :performers_by_score].each do |method| # merge users found by multiple methods returning a hash {best: [], worst: []} users = users.merge(send(method, exercise, NUMBER_OF_USERS_PER_CLASS)) {|key, this, other| this + other} end # write reasons for feedback emails to db users.keys.each do |key| segment = users[key].uniq &by_id_and_type users_to_notify += segment segment.each do |user| reason = "{\"segment\": \"#{key.to_s}\", \"feature\": \"#{user[:reason]}\", value: \"#{user[:value]}\"}" AnomalyNotification.create(user_id: user[:user_id], user_type: user[:user_type], exercise: exercise, exercise_collection: collection, reason: reason) end end users_to_notify.uniq! &by_id_and_type users_to_notify.each do |u| user = u[:user_type] == InternalUser.name ? InternalUser.find(u[:user_id]) : ExternalUser.find(u[:user_id]) host = CodeOcean::Application.config.action_mailer.default_url_options[:host] feedback_link = url_for(action: :new, controller: :user_exercise_feedbacks, exercise_id: exercise.id, host: host) UserMailer.exercise_anomaly_needs_feedback(user, exercise, feedback_link).deliver end puts "\t\tAsked #{users_to_notify.size} users for feedback." end end def performers_by_score(exercise, n) submissions = exercise.last_submission_per_user.where('score is not null').order(score: :desc) map_block = proc {|item| {user_id: item.user_id, user_type: item.user_type, value: item.score, reason: 'score'}} best_performers = submissions.first(n).to_a.map &map_block worst_performers = submissions.last(n).to_a.map &map_block return {:best => best_performers, :worst => worst_performers} end def performers_by_time(exercise, n) working_times = get_user_working_times(exercise).values.map do |item| {user_id: item['user_id'], user_type: item['user_type'], score: item['score'].to_f, value: time_to_f(item['working_time']), reason: 'time'} end avg_score = exercise.average_score working_times.reject! {|item| item[:value].nil? or item[:value] <= MIN_USER_WORKING_TIME or item[:score] < avg_score} working_times.sort_by! {|item| item[:value]} return {:best => working_times.first(n), :worst => working_times.last(n)} end def reset_anomaly_detection_flag(collection) puts "\t\tResetting flag..." collection.use_anomaly_detection = false collection.save! end end