MODULE off_oper
   !!----------------------------------------------------------------------
   !!                    ***  MODULE off_oper ***
   !! ** Purpose : Run NEMO observation operator in offline mode
   !!----------------------------------------------------------------------
   !! NEMO modules
   USE diaobs
   USE nemogcm
   USE lib_mpp
   USE in_out_manager
   USE obs_fbm, ONLY: ln_cl4
   !! Offline obs_oper modules
   USE off_data
   USE off_read
   CONTAINS
      SUBROUTINE off_oper_init
         !!----------------------------------------------------------------------
         !!                    ***  SUBROUTINE off_oper_init ***
         !!
         !! ** Purpose : To initialise the model as if it were running online.
         !!
         !!----------------------------------------------------------------------
         IMPLICIT NONE
         !! Initialise NEMO
         CALL nemo_init
         !! Initialise Offline obs_oper data
         CALL off_data_init( ln_cl4 )
      END SUBROUTINE off_oper_init

      SUBROUTINE off_obs_oper
         !!----------------------------------------------------------------------
         !!                    ***  SUBROUTINE off_obs_oper ***
         !!
         !! ** Purpose : To use NEMO components to interpolate model fields
         !!              to observation space.
         !!
         !!----------------------------------------------------------------------
         IMPLICIT NONE
         !! Initialise offline obs_oper
         CALL off_oper_init
         !! Loop over various model counterparts
         DO jimatch = 1, cl4_match_len
            IF (jimatch .GT. 1) THEN
               !! Initialise obs_oper
               CALL dia_obs_init
            END IF
            !! Interpolate to observation space
            CALL off_oper_interp
            !! Pipe to output files
            CALL dia_obs_wri
            !! Reset the obs_oper
            CALL dia_obs_dealloc
         END DO
         !! Safely stop MPI
         CALL off_oper_stop
      END SUBROUTINE off_obs_oper

      SUBROUTINE off_oper_interp
         !!----------------------------------------------------------------------
         !!                    ***  SUBROUTINE off_oper_interp ***
         !!
         !! ** Purpose : To interpolate the model as if it were running online.
         !!
         !! ** Method : 1. Populate model counterparts
         !!             2. Call dia_obs at appropriate time steps
         !!----------------------------------------------------------------------
         IMPLICIT NONE
         INTEGER :: istp ! time step index
         !! Loop over entire run
         istp = nit000
         nstop = 0
         DO WHILE ( istp <= nitend .AND. nstop == 0 )
            IF (jifile <= n_files + 1) THEN
               IF ( MOD(istp, nn_off_freq) == nit000 ) THEN
                  !! Read next model counterpart
                  CALL off_rea_dri(jifile)
                  jifile = jifile + 1
               ENDIF
               !! Interpolate single time step
               CALL dia_obs(istp)
            ENDIF
            !! Increment model step
            istp = istp + 1
         END DO
      END SUBROUTINE off_oper_interp

      SUBROUTINE off_oper_stop
         !!----------------------------------------------------------------------
         !!                    ***  SUBROUTINE off_oper_stop ***
         !!
         !! ** Purpose : To finalise the model as if it were running online.
         !!
         !!----------------------------------------------------------------------
         IMPLICIT NONE
         IF(lk_mpp) CALL mppstop  ! end mpp communications
      END SUBROUTINE off_oper_stop

END MODULE off_oper