! Copyright 2005-2007 ECMWF
! 
! Licensed under the GNU Lesser General Public License which
! incorporates the terms and conditions of version 3 of the GNU
! General Public License.
! See LICENSE and gpl-3.0.txt for details.
!
!
!  Description: how to create a new GRIB message from a sample.
!               
!
program sample
  use grib_api
  implicit none  
  integer  :: err
  integer  :: outfile, infile, datafile
  integer  :: igribsample,igribclone,igribdata, size
  integer  :: date, startStep, endStep, table2Version, indicatorOfParameter
  integer  :: decimalPrecision
  real     :: missingValue
  character(len=10) stepType
  double precision, dimension(:), allocatable   :: v1,v2,v 

  date = 20080104
  startStep = 0
  endStep = 12
  stepType = 'accum'
  table2Version = 2
  indicatorOfParameter = 61
  decimalPrecision = 2

  !     a new grib message is loaded from an existing sample
  !     samples are searched in a default sample path (use grib_info
  !     to see where it is. The default sample path can be changed by
  !     setting the environment variable GRIB_SAMPLES_PATH
  call grib_new_from_samples(igribsample, "regular_latlon_surface.grib1")

  call grib_open_file(outfile, 'out.grib1','w')
  call grib_open_file(datafile,'../../data/tp_ecmwf.grib','r')

  call grib_new_from_file(datafile,igribdata,err)

  call grib_get_size(igribdata,'values',size)
  allocate(v(size))
  allocate(v1(size))
  allocate(v2(size))

  call grib_get(igribdata,'values',v)

  v=v*1000.0 ! different units for the output grib
  v1=v

  do while (err/=GRIB_END_OF_FILE) 
 
    call grib_clone(igribsample,igribclone) ! clone sample before modifying it

    call grib_set(igribclone,'dataDate',date)
    call grib_set(igribclone,'table2Version',table2Version)
    call grib_set(igribclone,'indicatorOfParameter',indicatorOfParameter)

    call grib_set(igribclone,'stepType',stepType)
    call grib_set(igribclone,'startStep',startStep)
    call grib_set(igribclone,'endStep',endStep)

    call grib_set(igribclone,'decimalPrecision',decimalPrecision)

    call grib_set(igribclone,'values',v)

    call grib_write(igribclone,outfile)
    
    call grib_new_from_file(datafile,igribdata,err)

    if (err==0) then
      call grib_get(igribdata,'values',v2)

      v2=v2*1000.0 ! different units for the output grib

      v=v2-v1 ! accumulation from startStep to endStep

      v1=v2 ! save previous step field

      startStep=startStep+12
      endStep=endStep+12

    endif

  enddo

  deallocate(v)
  deallocate(v1)
  deallocate(v2)

  call grib_close_file(outfile)

end program sample