!**********************************************************************
! Copyright 1998,1999,2000,2001,2002,2005,2007,2008,2009,2010         *
! Andreas Stohl, Petra Seibert, A. Frank, Gerhard Wotawa,             *
! Caroline Forster, Sabine Eckhardt, John Burkhart, Harald Sodemann   *
!                                                                     *
! This file is part of FLEXPART.                                      *
!                                                                     *
! FLEXPART is free software: you can redistribute it and/or modify    *
! it under the terms of the GNU General Public License as published by*
! the Free Software Foundation, either version 3 of the License, or   *
! (at your option) any later version.                                 *
!                                                                     *
! FLEXPART is distributed in the hope that it will be useful,         *
! but WITHOUT ANY WARRANTY; without even the implied warranty of      *
! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the       *
! GNU General Public License for more details.                        *
!                                                                     *
! You should have received a copy of the GNU General Public License   *
! along with FLEXPART.  If not, see <http://www.gnu.org/licenses/>.   *
!**********************************************************************

subroutine readoutgrid_nest

  !*****************************************************************************
  !                                                                            *
  !     This routine reads the user specifications for the output nest.        *
  !                                                                            *
  !     Author: A. Stohl                                                       *
  !                                                                            *
  !     4 June 1996                                                            *
  !     HSO, 1 July 2014: Add optional namelist input                          *
  !     PS, 6/2015-9/2018: read regular input with free format                 *
  !       and rename some variables                                            *
  !                                                                            *
  !*****************************************************************************
  !                                                                            *
  ! Variables:                                                                 *
  ! dxoutn,dyoutn        grid distances of output nest                         *
  ! numxgridn,numygridn,numzgrid    nest dimensions                            *
  ! outlon0n,outlat0n    lower left corner of nest                             *
  ! outheight(maxzgrid)  height levels of output grid [m]                      *
  !                                                                            *
  ! Constants:                                                                 *
  ! unitoutgrid          unit connected to file OUTGRID                        *
  !                                                                            *
  !*****************************************************************************

  use outg_mod
  use par_mod
  use com_mod

  implicit none

  integer :: stat
  real :: xr,xr1,yr,yr1
  real,parameter :: eps=1.e-4

  integer :: ios

! declare namelist
  namelist /nml_outgridn/ &
    outlon0n,outlat0n,numxgridn,numygridn,dxoutn,dyoutn

  ! helps identifying failed namelist input
  dxoutn=-1.0

  ! Open the OUTGRID file and read output grid specifications
  !**********************************************************

  open(unitoutgrid,file=path(1)(1:length(1))//'OUTGRID_NEST',form='formatted',&
    status='old',err=999)

  ! try namelist input
  read(unitoutgrid,nml_outgridn,iostat=ios)
  close(unitoutgrid)

  if (dxoutn.le.0 .or.ios.ne.0) then

    open(unitoutgrid,file=path(1)(1:length(1))//'OUTGRID_NEST',status='old',&
      err=999)
    call skplin(5,unitoutgrid)

  ! Read horizontal grid specifications
  ! ***********************************

    call skplin(3,unitoutgrid)
    read(unitoutgrid,*) outlon0n
    call skplin(3,unitoutgrid)
    read(unitoutgrid,*) outlat0n
    call skplin(3,unitoutgrid)
    read(unitoutgrid,*) numxgridn
    call skplin(3,unitoutgrid)
    read(unitoutgrid,*) numygridn
    call skplin(3,unitoutgrid)
    read(unitoutgrid,*) dxoutn
    call skplin(3,unitoutgrid)
    read(unitoutgrid,*) dyoutn

    close(unitoutgrid)
  endif

  ! write outgrid_nest file in namelist format to output directory if requested
  if (nmlout.and.lroot) then
    open(unitoutgrid,file=path(2)(1:length(2))//'OUTGRID_NEST.namelist',&
      err=1000)
    write(unitoutgrid,nml=nml_outgridn)
    close(unitoutgrid)
  endif

  allocate(orooutn(0:numxgridn-1,0:numygridn-1),stat=ios)
  if (ios.ne.0) write(*,*)'ERROR: could not allocate orooutn'
  allocate(arean(0:numxgridn-1,0:numygridn-1),stat=ios)
  if (ios.ne.0) write(*,*)'ERROR: could not allocate arean'
  allocate(volumen(0:numxgridn-1,0:numygridn-1,numzgrid),stat=ios)
  if (ios.ne.0) write(*,*)'ERROR: could not allocate volumen'

  ! Check validity of output grid (shall be within model domain)
  !*************************************************************

  xr=outlon0n+real(numxgridn)*dxoutn
  yr=outlat0n+real(numygridn)*dyoutn
  xr1=xlon0+real(nxmin1)*dx
  yr1=ylat0+real(nymin1)*dy
  if (outlon0n+eps.lt.xlon0 .or. outlat0n+eps.lt.ylat0 &
    .or. xr.gt.xr1+eps .or. yr.gt.yr1+eps) then
    write(*,*) ' #### FLEXPART MODEL ERROR! PART OF OUTPUT    ####'
    write(*,*) ' #### NEST IS OUTSIDE MODEL DOMAIN. CHANGE    ####'
    write(*,*) ' #### FILE OUTGRID IN DIRECTORY               ####'
    write(*,'(a)') trim(path(1))
    stop
  endif

  xoutshiftn=xlon0-outlon0n
  youtshiftn=ylat0-outlat0n
  return

999 write(*,*) ' #### FLEXPART MODEL ERROR! FILE "OUTGRID"    #### '
  write(*,*) ' #### CANNOT BE OPENED IN THE DIRECTORY       #### '
  write(*,'(a)') trim(path(1))
  stop

1000 write(*,*) ' #### FLEXPART MODEL ERROR! FILE "OUTGRID"    #### '
  write(*,*) ' #### CANNOT BE OPENED IN THE DIRECTORY       #### '
  write(*,'(a)') trim(path(2))
  stop

end subroutine readoutgrid_nest