module sort

use Environment
use List_IO

   implicit none



contains
    pure recursive subroutine Sort_List(Custom_List, N)
           type(List), pointer, intent(inout) :: Custom_List
           integer, intent(in)  :: N


           call Drop_down(Custom_List, 1, N-1)

           if( N >= 3) call Sort_List(Custom_List,N-1)

   end subroutine Sort_List

   pure recursive subroutine Drop_down(Custom_List,j,N)
          type(List),pointer :: Custom_List
          integer, intent(in) :: j,N


          if (Swap(Custom_List)) call Swap_from_cur(Custom_List)
          if (j < N) call Drop_down(Custom_List%next,j+1,N)
   end subroutine Drop_down

   pure logical function Swap(current_elem)
          type(List), intent(in) :: current_elem

          Swap = .false.
          if (current_elem%Surname >  current_elem%next%Surname) then
            Swap = .true.
          else if (current_elem%Surname == current_elem%next%Surname &
                   .and. current_elem%Initials >  current_elem%next%Initials) then
            Swap = .true.
         end if
   end function Swap

   pure subroutine Swap_from_cur(current_elem)
           type(List), pointer :: current_elem

           type(List), pointer :: tmp_elem

           tmp_elem => current_elem%next
           current_elem%next => current_elem%next%next
           tmp_elem%next => current_elem
           current_elem => tmp_elem
   end subroutine Swap_from_cur
 end module sort