! -----------------------------------------------------------------------------
! BSD 3-Clause License
!
! Copyright (c) 2021, Science and Technology Facilities Council.
! All rights reserved.
!
! Redistribution and use in source and binary forms, with or without
! modification, are permitted provided that the following conditions are met:
!
! * Redistributions of source code must retain the above copyright notice, this
!   list of conditions and the following disclaimer.
!
! * Redistributions in binary form must reproduce the above copyright notice,
!   this list of conditions and the following disclaimer in the documentation
!   and/or other materials provided with the distribution.
!
! * Neither the name of the copyright holder nor the names of its
!   contributors may be used to endorse or promote products derived from
!   this software without specific prior written permission.
!
! THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
! AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
! IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
! DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
! FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
! DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
! SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
! CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
! OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
! OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
! -----------------------------------------------------------------------------
! Author: J. Henrichs, Bureau of Meteorology

!> This module contains a simple 'update' kernel that
!! creates some NAN values in the output field by
!! calling some division by 0. If the compiler should
!! catch floating point exceptions, the code for checking
!! for NANs will not be executed.

module update_field_mod
  use kind_params_mod
  use kernel_mod
  use argument_mod
  use grid_mod, only: GO_OFFSET_SW
  implicit none

  type, extends(kernel_type) :: update_field
     type(go_arg), dimension(2) :: meta_args =                 &
          (/ go_arg(GO_READWRITE, GO_CT,       GO_POINTWISE),  & ! field
             go_arg(GO_READ,      GO_CT,       GO_POINTWISE)   & ! field
           /)
     !> This kernel writes only to internal points of the
     !! simulation domain.
     integer :: ITERATES_OVER = GO_ALL_PTS

     !> Although the staggering of variables used in an Arakawa
     !! C grid is well defined, the way in which they are indexed is
     !! an implementation choice. This can be thought of as choosing
     !! which grid-point types have the same (i,j) index as a T
     !! point. This kernel assumes that the U,V and F points that
     !! share the same index as a given T point are those immediately
     !! to the South and West of it.
     integer :: index_offset = GO_OFFSET_SW

  contains
    procedure, nopass :: code => update_field_code
  end type update_field

contains

  subroutine update_field_code(i, j, a_f, b_f)
    integer, intent(in) :: i, j
    real(go_wp), dimension(:,:), intent(inout) :: a_f
    real(go_wp), dimension(:,:), intent(in) :: b_f

    ! Trigger a NAN result on the diagonal:
    a_f(i,j) = b_f(i,j) / (i-j)

  end subroutine update_field_code

end module update_field_mod
