# 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/>.

require "ldap"
require "uuid"
require "uuid/json"
require "random/secure"

module Backend
  module Api
    module Schema
      @[GraphQL::Object]
      class Mutation < GraphQL::BaseMutation
        @[GraphQL::Field]
        # Logs in as *username* with credential *password*
        def login(username : String, password : String) : LoginPayload?
          raise Errors::Authentication.new if username.empty? || password.empty?

          user = Db::User.query.find { var(:username) == username }
          raise Errors::Authentication.new unless user && Ldap.authenticate?(Ldap::DN.uid(username), password)

          token = Db::Token.create!(
            id: UUID.random(Random::Secure),
            iat: Time.utc,
            exp: Time.utc + Backend.config.api.jwt_expiration.minutes,
            active: true,
            user_id: user.id
          )

          LoginPayload.new(
            user: User.new(user),
            token: Auth::Token.new(
              iat: token.iat.to_unix,
              exp: token.exp.to_unix,
              jti: token.id.not_nil!,
              context: Auth::Context.new(user.id.not_nil!)
            ).encode
          )
        end

        @[GraphQL::Field]
        # Logs out of account by revoking token
        def logout(context : Context) : Scalars::UUID?
          context.authenticated!

          jti = context.jti.not_nil!

          token = Db::Token.find!(jti)
          token.active = false
          token.save!

          Scalars::UUID.new(jti)
        end

        @[GraphQL::Field]
        def revoke_token(context : Context, token : Scalars::UUID) : Scalars::UUID
          context.authenticated!

          Db::Token.query.find!(token.value).delete

          Scalars::UUID.new(token.value)
        end

        @[GraphQL::Field]
        # Creates user
        def create_user(context : Context, input : UserCreateInput, check_ldap : Bool = true) : User?
          context.admin!

          raise Errors::LdapUserDoesNotExist.new if check_ldap && begin
                                                      !Ldap::User.from_username(input.username)
                                                    rescue LDAP::Client::AuthError
                                                      true
                                                    end
          user = Db::User.create!(username: input.username, role: input.role.to_db, admin: input.admin)
          Worker::Jobs::CacheLdapUserJob.new(user.id.not_nil!.to_i).enqueue

          User.new(user)
        end

        @[GraphQL::Field]
        # Deletes user by ID
        def delete_user(context : Context, id : Int32) : Int32?
          context.admin!

          user = Db::User.find!(id)
          user.delete

          id
        end

        @[GraphQL::Field]
        # Starts assignment job of mentors to students
        def start_assignment(context : Context) : Bool?
          context.admin!

          Worker::Jobs::AssignStudentsJob.new.enqueue

          true
        end

        # @[GraphQL::Field]
        # # Creates teacher
        # def create_teacher(context : Context, input : TeacherCreateInput) : Teacher
        #   context.admin!

        #   teacher = Db::Teacher.create!(user_id: input.user_id, max_students: input.max_students)
        #   Teacher.new(teacher)
        # end

        @[GraphQL::Field]
        def register_teacher(context : Context, input : TeacherInput) : Teacher?
          context.teacher!(false)
          raise Errors::InvalidPermissions.new if context.user.not_nil!.teacher

          teacher = Db::Teacher.create!(user_id: context.user.not_nil!.id, max_students: input.max_students)
          Teacher.new(teacher)
        end

        # @[GraphQL::Field]
        # # Deletes teacher by ID
        # def delete_teacher(context : Context, id : Int32) : Int32
        #   context.admin!

        #   teacher = Db::Teacher.find!(id)
        #   teacher.delete

        #   id
        # end

        # @[GraphQL::Field]
        # # Self register as teacher
        # def register_teacher(context : Context, input : TeacherInput) : Teacher
        #   context.teacher! external_check: false

        #   Teacher.new(
        #     Db::Teacher.create!(user_id: context.user.not_nil!.id, max_students: input.max_students)
        #   )
        # end

        # @[GraphQL::Field]
        # # Creates student
        # def create_student(context : Context, input : StudentCreateInput) : Student
        #   context.admin!

        #   user = Db::User.find!(input.user_id)
        #   raise "User not a student" unless user.role.to_api.student?

        #   student = Db::Student.create!(user_id: user.id)
        #   Student.new(student)
        # end

        # @[GraphQL::Field]
        # # Deletes student by ID
        # def delete_student(context : Context, id : Int32) : Int32
        #   context.admin!

        #   student = Db::Student.find!(id)
        #   student.delete

        #   id
        # end

        # @[GraphQL::Field]
        # # Self register as student
        # def register_student(context : Context) : Student
        #   context.student! external_check: false

        #   Student.new(
        #     Db::Student.create!(user_id: context.user.not_nil!.id)
        #   )
        # end

        @[GraphQL::Field]
        # Creates vote for authenticated user's student
        def create_vote(context : Context, input : VoteCreateInput) : Vote?
          context.student!

          raise Errors::DuplicateTeachers.new if input.teacher_ids.uniq.size != input.teacher_ids.size
          raise Errors::NotEnoughTeachers.new if input.teacher_ids.size < Backend.config.minimum_teacher_selection_count
          teacher_role_count = Db::User.query.where(role: Db::UserRole::Teacher).count
          raise Errors::TeachersNotRegistered.new if teacher_role_count != Db::Teacher.query.count || teacher_role_count.zero?

          input.teacher_ids.each do |id|
            teacher = Db::Teacher.find(id)

            if teacher.nil?
              raise Errors::TeachersNotFound.new
              # elsif teacher.user.skif != context.user.not_nil!.skif
              #   if teacher.user.skif
              #     raise "Teacher is SKIF, student is not"
              #   else
              #     raise "Teacher is not SKIF, student is"
              #   end
            end
          end

          student = context.external.not_nil!.as(Db::Student)
          vote = Db::Vote.create!(student_id: student.id)
          Db::TeacherVote.import(input.teacher_ids.map_with_index { |id, i| Db::TeacherVote.new({vote_id: vote.id, teacher_id: id, priority: i}) })

          Vote.new(vote)
        end
      end
    end
  end
end