module sorting
   ! apparently you need to put the subroutine in a module
   implicit none
contains
   subroutine sort(arr)
      !! a little insertion sort KISS
      !! also yea we have no in built sorting
      implicit none
      integer, intent(inout) :: arr(1000)
      integer :: i, j, key
      do i = 2, 1000
         key = arr(i)
         j = i - 1
         do while (j > 0 .and. arr(j) > key)
            arr(j+1) = arr(j)
            j = j - 1
         end do
         arr(j+1) = key
      end do
   end subroutine sort
end module sorting

program day_01
   use sorting
   implicit none
   integer :: io, i, dist, sim, left(1000), right(1000) ! yea we are coding to the input file and not generic
   open(newunit=io, file='./day_01_input.txt', status='old', action='read')

   do i = 1, 1000
      read(io, *) left(i), right(i) ! read both values in line
   end do

   close(10) ! close the file

   call sort(left)
   call sort(right)

   ! if we dont init these bad things happen on multiple runs
   dist = 0
   sim = 0

   do i = 1, 1000
      dist = dist + abs(left(i) - right(i))
      sim = sim + left(i) * count(right == left(i))
   end do

   print*, "distance: ", dist
   print*, "similarity: ", sim
end program day_01