mentorenwahl/backend/src/backend/worker/jobs/assignment_job.cr

# Mentorenwahl: A fullstack application for assigning mentors to students based on their whishes.
# Copyright (C) 2022  Dominic Grimm
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

module Backend
  module Worker
    module Jobs
      # Assigns students to teachers when all students voted
      class AssignStudentsJob < Mosquito::QueuedJob
        # run_every 1.minute

        def rescheduleable? : Bool
          false
        end

        alias TeacherVote = {student: Int32, priority: Int32}
        alias Assignment = {teacher: Int32, priority: Int32}

        # :ditto:
        def perform : Nil
          teacher_count = Db::Teacher.query.count
          student_count = Db::Student.query.count
          vote_count = Db::Vote.query.count

          if teacher_count == 0
            log "No teachers found, skipping assignment"
            fail
          elsif student_count == 0
            log "No students found, skipping assignment"
            fail
          elsif student_count != Db::User.query.where(role: Db::UserRole::Student).count
            log "Not all students registered, skipping assignment"
            fail
          elsif vote_count < student_count
            log "Not all students voted, skipping assignment"
            fail
          elsif Db::Assignment.query.count > 0
            log "Assignment has already run, skipping another assignment"
            fail
          end

          teachers = Db::Teacher.query
            .where do
              raw("EXISTS (SELECT 1 FROM teacher_votes WHERE teacher_id = teachers.id)") &
                (max_students > 0)
            end
            .with_teacher_votes
            .to_a
          vote_index = Hash.zip(teachers.map(&.id), [0] * teachers.size)
          teacher_votes : Hash(Int32, Array(TeacherVote)) = Hash.zip(
            teachers.map(&.id),
            teachers.map do |t|
              t.teacher_votes.map do |tv|
                vote_index[t.id] += 1

                {
                  student:  tv.vote.student.id,
                  priority: tv.priority,
                }
              end
            end
          )
          teachers.sort_by! { |t| vote_index[t.id] }

          students = Db::Student.query
            .with_vote(&.with_teacher_votes(&.order_by(priority: :asc)))
            .to_a
          student_ids = students.map(&.id)
          votes = Hash.zip(
            student_ids,
            students.map do |s|
              s.vote.not_nil!.teacher_votes
                .to_a
                .select { |tv| teacher_votes.has_key?(tv.teacher.id) }
                .map do |tv|
                  {
                    teacher:              tv.teacher.id,
                    teacher_max_students: tv.teacher.max_students,
                  }
                end
            end
          )

          best_assignment = {
            assignment: {} of Int32 => Assignment,
            score:      Float32::INFINITY,
          }

          Backend.config.assignment_possibility_count.times.each do
            assignment = {} of Int32 => Assignment
            assignment_count = Hash.zip(teachers.map(&.id), [0] * teachers.size)
            # teachers.each do |t|
            #   queue = Deque.new(teacher_votes[t.id].shuffle)

            #   count = 1
            #   while count < t.max_students
            #     break unless x = queue.shift?
            #     tv = x.not_nil!

            #     if assignment[tv[:student]]?.nil? || assignment[tv[:student]][:priority] <= tv[:priority]
            #       assignment[tv[:student]] = {teacher: t.id, priority: tv[:priority]}
            #       count += 1
            #     end
            #   end
            # end
            votes.to_a.shuffle.each do |s, tvs|
              tvs.each_with_index do |tv, i|
                if assignment[s]?.nil?
                  assignment_count[tv[:teacher]] += 1
                  assignment[s] = {teacher: tv[:teacher], priority: i}
                elsif assignment_count[tv[:teacher]] < tv[:teacher_max_students]
                  assignment_count[assignment[s][:teacher]] -= 1
                  assignment_count[tv[:teacher]] += 1
                  assignment[s] = {teacher: tv[:teacher], priority: i}
                end
              end
            end

            pp! assignment, assignment_count

            score = 0_f32
            # positivity = 0
            # assignment.each do |s, a|
            #   ratio = (vote_sizes[s] - a[:priority]) / vote_sizes[s]
            #   score += 2 ** ratio
            #   positivity += ratio > 0.5 ? 1 : -1
            # end
            assignment.each do |s, a|
              size = votes[s].size
              p! a[:priority], (votes[s].size - a[:priority]) / size
              # score += 1 if ((votes[s].size - a[:priority]) / size) >= 0.5
              score += a[:priority]
            end

            # full_score = score ** positivity
            if score < best_assignment[:score]
              best_assignment = {
                assignment: assignment,
                score:      score,
              }
            end
          end

          pp! best_assignment

          str = String.build do |str|
            str << "===========================\n"
            best_assignment[:assignment].each do |s, a|
              str << "#{Db::Student.query.find!(s).user.username} : #{Db::Teacher.query.find!(a[:teacher]).user.username} (#{a[:priority]} / #{votes[s].size})\n"
            end
            str << "===========================\n"
          end
          print str
        end
      end
    end
  end
end