! SPDX-FileCopyrightText: FLEXPART 1998-2019, see flexpart_license.txt
! SPDX-License-Identifier: GPL-3.0-or-later

subroutine gethourlyOH(itime)
  !                     i     
  !*****************************************************************************
  !                                                                            *
  !                                                                            *
  !    Author: R.L. Thompson                                                   *
  !                                                                            *
  !    Nov 2014                                                                *
  !                                                                            *
  !                                                                            *
  !*****************************************************************************
  ! Variables:                                                                 *
  !                                                                            *
  !*****************************************************************************

  use oh_mod
  use par_mod
  use com_mod

  implicit none
  
  integer :: itime
  integer :: ix,jy,kz,m1,m2
  integer :: ijx,jjy
  integer :: jjjjmmdd,hhmmss
  real :: sza,jrate,photo_O1D,zenithangle
  real(kind=dp) :: jul1,jul2

!  print*, 'itime: ',itime
!  print*, 'memOHtime(1):',memOHtime(1)
!  print*, 'memOHtime(2):',memOHtime(2)


  ! Check hourly OH field is available for the current time step
  !**************************************************************

  if ((ldirect*memOHtime(1).le.ldirect*itime).and. &
       (ldirect*memOHtime(2).gt.ldirect*itime)) then

  ! The right OH fields are already in memory -> don't do anything
  !****************************************************************

    continue

  else if ((ldirect*memOHtime(2).le.ldirect*itime).and. &
       (memOHtime(2).ne.0.)) then

    ! Current time is after 2nd OH field
    !************************************

    memOHtime(1)=memOHtime(2)
    memOHtime(2)=memOHtime(1)+ldirect*3600.
    OH_hourly(:,:,:,1)=OH_hourly(:,:,:,2)

    ! Compute new hourly value of OH
    !**********************************************************

    jul2=bdate+memOHtime(2)/86400._dp  ! date for next hour
    call caldate(jul2,jjjjmmdd,hhmmss)
    m2=(jjjjmmdd-(jjjjmmdd/10000)*10000)/100

!    print*, 'jul2:',jul2
!    print*, 'm2:',m2

    do kz=1,nzOH
      do jy=1,nyOH
        do ix=1,nxOH
          ijx=minloc(abs(lonjr-lonOH(ix)),dim=1,mask=abs(lonjr-lonOH(ix)).eq.minval(abs(lonjr-lonOH(ix))))
          jjy=minloc(abs(latjr-latOH(jy)),dim=1,mask=abs(latjr-latOH(jy)).eq.minval(abs(latjr-latOH(jy))))
          ! calculate solar zenith angle in degrees (sza) 
          sza=zenithangle(latOH(jy),lonOH(ix),jul2)
          ! calculate J(O1D) (jrate)
          jrate=photo_O1D(sza)
          ! apply hourly correction to OH
          if(jrate_average(ijx,jjy,m2).gt.0.) then
            OH_hourly(ix,jy,kz,2)=OH_field(ix,jy,kz,m2)*jrate/jrate_average(ijx,jjy,m2)
          else
            OH_hourly(ix,jy,kz,2)=0.
          endif
          !! for testing !!
          ! if(jy.eq.36.and.ix.eq.36.and.kz.eq.1) then
          !   write(999,fmt='(F6.3)') jrate/jrate_average(ijx,jjy,m2)
          ! endif
          ! if(jy.eq.11.and.ix.eq.36.and.kz.eq.1) then
          !   write(998,fmt='(F6.3)') jrate/jrate_average(ijx,jjy,m2)
          ! endif
        end do
      end do
    end do

  else

    ! No OH fields in memory -> compute both hourly OH fields
    !**********************************************************

    jul1=bdate  ! begin date of simulation (julian)
    call caldate(jul1,jjjjmmdd,hhmmss)
    m1=(jjjjmmdd-(jjjjmmdd/10000)*10000)/100
    memOHtime(1)=0.

    jul2=bdate+ldirect*real(1./24.,kind=dp)  ! date for next hour
    call caldate(jul2,jjjjmmdd,hhmmss)
    m2=(jjjjmmdd-(jjjjmmdd/10000)*10000)/100
    memOHtime(2)=ldirect*3600.

!    print*, 'jul1:',jul1
!    print*, 'jul2:',jul2
!    print*, 'm1,m2:',m1,m2

    do kz=1,nzOH
      do jy=1,nyOH
        do ix=1,nxOH
          ijx=minloc(abs(lonjr-lonOH(ix)),dim=1,mask=abs(lonjr-lonOH(ix)).eq.minval(abs(lonjr-lonOH(ix))))
          jjy=minloc(abs(latjr-latOH(jy)),dim=1,mask=abs(latjr-latOH(jy)).eq.minval(abs(latjr-latOH(jy))))
          ! calculate solar zenith angle in degrees (sza), beginning 
          sza=zenithangle(latOH(jy),lonOH(ix),jul1)
          ! calculate J(O1D) (jrate), beginning
          jrate=photo_O1D(sza)
          ! apply hourly correction to OH
          if(jrate_average(ijx,jjy,m1).gt.0.) then
            OH_hourly(ix,jy,kz,1)=OH_field(ix,jy,kz,m1)*jrate/jrate_average(ijx,jjy,m1)
          else
            OH_hourly(ix,jy,kz,1)=0.
          endif
          ! calculate solar zenith angle in degrees (sza), after 1-hour 
          sza=zenithangle(latOH(jy),lonOH(ix),jul2)
          ! calculate J(O1D) (jrate), after 1-hour
          jrate=photo_O1D(sza)
          ! apply hourly correction to OH
          if(jrate_average(ijx,jjy,m2).gt.0.) then
            OH_hourly(ix,jy,kz,2)=OH_field(ix,jy,kz,m2)*jrate/jrate_average(ijx,jjy,m2)
          else
            OH_hourly(ix,jy,kz,2)=0.
          endif
        end do
      end do
    end do

  endif

end subroutine gethourlyOH