read_input Subroutine

  subroutine read_input(this, unit, verbose)
    !! Read an input layer from a file
    use athena__tools_infile, only: assign_val, assign_vec, get_val
    use coreutils, only: to_lower, to_upper, icount
    implicit none

    ! Arguments
    class(input_layer_type), intent(inout) :: this
    !! Instance of the input layer
    integer, intent(in) :: unit
    !! Unit number
    integer, optional, intent(in) :: verbose
    !! Verbosity level

    ! Local variables
    integer :: verbose_ = 0
    !! Verbosity level
    integer :: stat
    !! File status
    integer :: itmp1= 0
    !! Temporary integer

    ! Local variables
    integer :: input_rank = 0
    !! Rank of the input data
    integer, dimension(:), allocatable :: input_shape
    !! Shape of the input data
    logical :: use_graph_input = .false.
    !! Use graph input
    character(256) :: buffer, tag, err_msg
    !! Buffer for reading lines, tag for identifying lines, error message


    ! Initialise optional arguments
    !---------------------------------------------------------------------------
    if(present(verbose)) verbose_ = verbose


    ! Loop over tags in layer card
    !---------------------------------------------------------------------------
    tag_loop: do

       ! Check for end of file
       !------------------------------------------------------------------------
       read(unit,'(A)',iostat=stat) buffer
       if(stat.ne.0)then
          write(err_msg,'("file encountered error (EoF?) before END ",A)') &
               to_upper(this%name)
          call stop_program(err_msg)
          return
       end if
       if(trim(adjustl(buffer)).eq."") cycle tag_loop

       ! Check for end of layer card
       !------------------------------------------------------------------------
       if(trim(adjustl(buffer)).eq."END INPUT")then
          backspace(unit)
          exit tag_loop
       end if

       tag=trim(adjustl(buffer))
       if(scan(buffer,"=").ne.0) tag=trim(tag(:scan(tag,"=")-1))

       ! Read parameters from save file
       !------------------------------------------------------------------------
       select case(trim(tag))
       case("INPUT_RANK")
          call assign_val(buffer, input_rank, itmp1)
       case("INPUT_SHAPE")
          itmp1 = icount(get_val(buffer))
          allocate(input_shape(itmp1))
          call assign_vec(buffer, input_shape, itmp1)
       case("USE_GRAPH_INPUT")
          call assign_val(buffer, use_graph_input, itmp1)
       case default
          ! Don't look for "e" due to scientific notation of numbers
          ! ... i.e. exponent (E+00)
          if(scan(to_lower(trim(adjustl(buffer))),&
               'abcdfghijklmnopqrstuvwxyz').eq.0)then
             cycle tag_loop
          elseif(tag(:3).eq.'END')then
             cycle tag_loop
          end if
          write(err_msg,'("Unrecognised line in input file: ",A)') &
               trim(adjustl(buffer))
          call stop_program(err_msg)
          return
       end select
    end do tag_loop
    if(.not.allocated(input_shape))then
       write(err_msg,'("No input shape found in ",A)') to_upper(this%name)
       call stop_program(err_msg)
       return
    end if


    ! Set hyperparameters and initialise layer
    !---------------------------------------------------------------------------
    call this%set_hyperparams( &
         input_rank = input_rank, &
         use_graph_input = use_graph_input, &
         verbose = verbose_ &
    )
    call this%init(input_shape = input_shape)


    ! Check for end of layer card
    !---------------------------------------------------------------------------
    read(unit,'(A)') buffer
    if(trim(adjustl(buffer)).ne."END INPUT")then
       write(0,*) trim(adjustl(buffer))
       write(err_msg,'("END ",A," not where expected")') to_upper(this%name)
       call stop_program(err_msg)
       return
    end if

  end subroutine read_input