extract_same_part_middle Function

   pure function extract_same_part_middle(left_middle, right_middle) result(middle)
      use :: forgex_utf8_m
      implicit none
      character(*), intent(in) :: left_middle, right_middle
      character(:), allocatable :: middle
      
      integer :: i, j, max_len, len_left, len_right, len_tmp
      character(:), allocatable :: tmp_middle

      len_left = len(left_middle)
      len_right = len(right_middle)
      max_len = 0
      middle = ''

      ! Compare all substring
      do i = 1, len_left
         do j = 1, len_right
            if (left_middle(i:i) == right_middle(j:j)) then
               tmp_middle = ''
               len_tmp = 0

               ! Check whether match strings or not.
               do while (i+len_tmp <= len_left .and. j+len_tmp <= len_right)
                  if (left_middle(i:i+len_tmp) == right_middle(j:j+len_tmp)) then
                     tmp_middle = left_middle(i:i+len_tmp)
                     len_tmp = len(tmp_middle)
                  else
                     exit
                  end if
               end do

               ! Store the longest common part.
               if (len_tmp > max_len) then
                  max_len = len(tmp_middle)
                  middle = tmp_middle
               end if
            end if
         end do
      end do
   end function extract_same_part_middle