MODULE daymod
   !!======================================================================
   !!                       ***  MODULE  daymod  ***
   !! Ocean        :  calendar
   !!=====================================================================
   !! History :  OPA  ! 1994-09  (M. Pontaud M. Imbard)  Original code
   !!                 ! 1997-03  (O. Marti)
   !!                 ! 1997-05  (G. Madec)
   !!                 ! 1997-08  (M. Imbard)
   !!   NEMO     1.0  ! 2003-09  (G. Madec)  F90 + nyear, nmonth, nday
   !!                 ! 2004-01  (A.M. Treguier) new calculation based on adatrj
   !!                 ! 2006-08  (G. Madec)  surface module major update
   !!----------------------------------------------------------------------

   !!----------------------------------------------------------------------
   !!   day        : calendar
   !!
   !!           -------------------------------
   !!           ----------- WARNING -----------
   !!
   !!   we suppose that the time step is deviding the number of second of in a day
   !!             ---> MOD( rday, rdttra(1) ) == 0
   !!
   !!           ----------- WARNING -----------
   !!           -------------------------------
   !!
   !!----------------------------------------------------------------------
   USE dom_oce         ! ocean space and time domain
   USE phycst          ! physical constants
   USE in_out_manager  ! I/O manager
   USE iom             !
   USE ioipsl, ONLY :   ymds2ju   ! for calendar
   USE prtctl          ! Print control
   USE trc_oce, ONLY : lk_offline ! offline flag
   USE timing          ! Timing
   USE restart         ! restart

   IMPLICIT NONE
   PRIVATE

   PUBLIC   day        ! called by step.F90
   PUBLIC   day_init   ! called by istate.F90
   PUBLIC   day_mth    ! Needed by TAM

   INTEGER, PUBLIC ::   nsecd, nsecd05, ndt, ndt05 ! (PUBLIC for TAM)

   !!----------------------------------------------------------------------
   !! NEMO/OPA 3.3 , NEMO Consortium (2010)
   !! $Id: daymod.F90 5564 2015-07-08 12:10:46Z clem $
   !! Software governed by the CeCILL licence     (NEMOGCM/NEMO_CeCILL.txt)
   !!----------------------------------------------------------------------
CONTAINS

   SUBROUTINE day_init
      !!----------------------------------------------------------------------
      !!                   ***  ROUTINE day_init  ***
      !!
      !! ** Purpose :   Initialization of the calendar values to their values 1 time step before nit000
      !!                because day will be called at the beginning of step
      !!
      !! ** Action  : - nyear        : current year
      !!              - nmonth       : current month of the year nyear
      !!              - nday         : current day of the month nmonth
      !!              - nday_year    : current day of the year nyear
      !!              - nsec_year    : current time step counted in second since 00h jan 1st of the current year
      !!              - nsec_month   : current time step counted in second since 00h 1st day of the current month
      !!              - nsec_day     : current time step counted in second since 00h of the current day
      !!              - nsec1jan000  : second since Jan. 1st 00h of nit000 year and Jan. 1st 00h of the current year
      !!              - nmonth_len, nyear_len, nmonth_half, nmonth_end through day_mth
      !!----------------------------------------------------------------------
      INTEGER  ::   inbday, idweek
      REAL(wp) ::   zjul
      !!----------------------------------------------------------------------
      !
      ! max number of seconds between each restart
      IF( REAL( nitend - nit000 + 1 ) * rdt > REAL( HUGE( nsec1jan000 ) ) ) THEN
         CALL ctl_stop( 'The number of seconds between each restart exceeds the integer 4 max value: 2^31-1. ',   &
            &           'You must do a restart at higher frequency (or remove this stop and recompile the code in I8)' )
      ENDIF
      ! all calendar staff is based on the fact that MOD( rday, rdttra(1) ) == 0
      IF( MOD( rday     , rdttra(1) ) /= 0. )   CALL ctl_stop( 'the time step must devide the number of second of in a day' )
      IF( MOD( rday     , 2.        ) /= 0. )   CALL ctl_stop( 'the number of second of in a day must be an even number'    )
      IF( MOD( rdttra(1), 2.        ) /= 0. )   CALL ctl_stop( 'the time step (in second) must be an even number'           )
      nsecd   = NINT(rday           )
      nsecd05 = NINT(0.5 * rday     )
      ndt     = NINT(      rdttra(1))
      ndt05   = NINT(0.5 * rdttra(1))

      IF( .NOT. lk_offline ) CALL day_rst( nit000, 'READ' )

      ! set the calandar from ndastp (read in restart file and namelist)

      nyear   =   ndastp / 10000
      nmonth  = ( ndastp - (nyear * 10000) ) / 100
      nday    =   ndastp - (nyear * 10000) - ( nmonth * 100 )

      CALL ymds2ju( nyear, nmonth, nday, 0.0, fjulday )  ! we assume that we start run at 00:00
      IF( ABS(fjulday - REAL(NINT(fjulday),wp)) < 0.1 / rday )   fjulday = REAL(NINT(fjulday),wp)   ! avoid truncation error
      fjulday = fjulday + 1.                             ! move back to the day at nit000 (and not at nit000 - 1)

      nsec1jan000 = 0
      CALL day_mth

      IF ( nday == 0 ) THEN     !   for ex if ndastp = ndate0 - 1
         nmonth = nmonth - 1
         nday = nmonth_len(nmonth)
      ENDIF
      IF ( nmonth == 0 ) THEN   ! go at the end of previous year
         nmonth = 12
         nyear = nyear - 1
         nsec1jan000 = nsec1jan000 - nsecd * nyear_len(0)
         IF( nleapy == 1 )   CALL day_mth
      ENDIF

      ! day since january 1st
      nday_year = nday + SUM( nmonth_len(1:nmonth - 1) )

      !compute number of days between last monday and today
      CALL ymds2ju( 1900, 01, 01, 0.0, zjul )  ! compute julian day value of 01.01.1900 (our reference that was a Monday)
      inbday = NINT(fjulday - zjul)            ! compute nb day between  01.01.1900 and current day
      idweek = MOD(inbday, 7)                  ! compute nb day between last monday and current day

      ! number of seconds since the beginning of current year/month/week/day at the middle of the time-step
      nsec_year  = nday_year * nsecd - ndt05   ! 1 time step before the middle of the first time step
      nsec_month = nday      * nsecd - ndt05   ! because day will be called at the beginning of step
      nsec_week  = idweek    * nsecd - ndt05
      nsec_day   =             nsecd - ndt05

      ! control print
      IF(lwp) WRITE(numout,'(a,i6,a,i2,a,i2,a,i8,a,i8)')' =======>> 1/2 time step before the start of the run DATE Y/M/D = ',   &
           &                   nyear, '/', nmonth, '/', nday, '  nsec_day:', nsec_day, '  nsec_week:', nsec_week

      ! Up to now, calendar parameters are related to the end of previous run (nit000-1)
      ! call day to set the calendar parameters at the begining of the current simulaton. needed by iom_init
      CALL day( nit000 )
      !
   END SUBROUTINE day_init


   SUBROUTINE day_mth
      !!----------------------------------------------------------------------
      !!                   ***  ROUTINE day_init  ***
      !!
      !! ** Purpose :   calendar values related to the months
      !!
      !! ** Action  : - nmonth_len    : length in days of the months of the current year
      !!              - nyear_len     : length in days of the previous/current year
      !!              - nmonth_half   : second since the beginning of the year and the halft of the months
      !!              - nmonth_end    : second since the beginning of the year and the end of the months
      !!----------------------------------------------------------------------
      INTEGER  ::   jm               ! dummy loop indice
      !!----------------------------------------------------------------------

      ! length of the month of the current year (from nleapy, read in namelist)
      IF ( nleapy < 2 ) THEN
         nmonth_len(:) = (/ 31, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31, 31 /)
         nyear_len(:) = 365
         IF ( nleapy == 1 ) THEN   ! we are using calandar with leap years
            IF ( MOD(nyear-1, 4) == 0 .AND. ( MOD(nyear-1, 400) == 0 .OR. MOD(nyear-1, 100) /= 0 ) ) THEN
               nyear_len(0)  = 366
            ENDIF
            IF ( MOD(nyear  , 4) == 0 .AND. ( MOD(nyear  , 400) == 0 .OR. MOD(nyear  , 100) /= 0 ) ) THEN
               nmonth_len(2) = 29
               nyear_len(1)  = 366
            ENDIF
            IF ( MOD(nyear+1, 4) == 0 .AND. ( MOD(nyear+1, 400) == 0 .OR. MOD(nyear+1, 100) /= 0 ) ) THEN
               nyear_len(2)  = 366
            ENDIF
         ENDIF
      ELSE
         nmonth_len(:) = nleapy   ! all months with nleapy days per year
         nyear_len(:) = 12 * nleapy
      ENDIF

      ! half month in second since the begining of the year:
      ! time since Jan 1st   0     1     2    ...    11    12    13
      !          ---------*--|--*--|--*--| ... |--*--|--*--|--*--|--------------------------------------
      !                 <---> <---> <--->  ...  <---> <---> <--->
      ! month number      0     1     2    ...    11    12    13
      !
      ! nmonth_half(jm) = rday * REAL( 0.5 * nmonth_len(jm) + SUM(nmonth_len(1:jm-1)) )
      nmonth_half(0) = - nsecd05 * nmonth_len(0)
      DO jm = 1, 13
         nmonth_half(jm) = nmonth_half(jm-1) + nsecd05 * ( nmonth_len(jm-1) + nmonth_len(jm) )
      END DO

      nmonth_end(0) = 0
      DO jm = 1, 13
         nmonth_end(jm) = nmonth_end(jm-1) + nsecd * nmonth_len(jm)
      END DO
      !
   END SUBROUTINE


   SUBROUTINE day( kt )
      !!----------------------------------------------------------------------
      !!                      ***  ROUTINE day  ***
      !!
      !! ** Purpose :   Compute the date with a day iteration IF necessary.
      !!
      !! ** Method  : - ???
      !!
      !! ** Action  : - nyear     : current year
      !!              - nmonth    : current month of the year nyear
      !!              - nday      : current day of the month nmonth
      !!              - nday_year : current day of the year nyear
      !!              - ndastp    : = nyear*10000 + nmonth*100 + nday
      !!              - adatrj    : date in days since the beginning of the run
      !!              - nsec_year : current time of the year (in second since 00h, jan 1st)
      !!----------------------------------------------------------------------
      INTEGER, INTENT(in) ::   kt        ! ocean time-step indices
      !
      CHARACTER (len=25) ::   charout
      REAL(wp)           ::   zprec      ! fraction of day corresponding to 0.1 second
      !!----------------------------------------------------------------------
      !
      IF( nn_timing == 1 )  CALL timing_start('day')
      !
      zprec = 0.1 / rday
      !                                                 ! New time-step
      nsec_year  = nsec_year  + ndt
      nsec_month = nsec_month + ndt
      nsec_week  = nsec_week  + ndt
      nsec_day   = nsec_day   + ndt
      adatrj  = adatrj  + rdttra(1) / rday
      fjulday = fjulday + rdttra(1) / rday
      IF( ABS(fjulday - REAL(NINT(fjulday),wp)) < zprec )   fjulday = REAL(NINT(fjulday),wp)   ! avoid truncation error
      IF( ABS(adatrj  - REAL(NINT(adatrj ),wp)) < zprec )   adatrj  = REAL(NINT(adatrj ),wp)   ! avoid truncation error

      IF( nsec_day > nsecd ) THEN                       ! New day
         !
         nday      = nday + 1
         nday_year = nday_year + 1
         nsec_day  = ndt05
         !
         IF( nday == nmonth_len(nmonth) + 1 ) THEN      ! New month
            nday   = 1
            nmonth = nmonth + 1
            nsec_month = ndt05
            IF( nmonth == 13 ) THEN                     ! New year
               nyear     = nyear + 1
               nmonth    = 1
               nday_year = 1
               nsec_year = ndt05
               nsec1jan000 = nsec1jan000 + nsecd * nyear_len(1)
               IF( nleapy == 1 )   CALL day_mth
            ENDIF
         ENDIF
         !
         ndastp = nyear * 10000 + nmonth * 100 + nday   ! New date
         !
         !compute first day of the year in julian days
         CALL ymds2ju( nyear, 01, 01, 0.0, fjulstartyear )
         !
         IF(lwp) WRITE(numout,'(a,i8,a,i4.4,a,i2.2,a,i2.2,a,i3.3)') '======>> time-step =', kt,   &
              &   '      New day, DATE Y/M/D = ', nyear, '/', nmonth, '/', nday, '      nday_year = ', nday_year
         IF(lwp) WRITE(numout,'(a,i8,a,i7,a,i5)') '         nsec_year = ', nsec_year,   &
              &   '   nsec_month = ', nsec_month, '   nsec_day = ', nsec_day, '   nsec_week = ', nsec_week
      ENDIF

      IF( nsec_week > 7*nsecd )   nsec_week = ndt05     ! New week

      IF(ln_ctl) THEN
         WRITE(charout,FMT="('kt =', I4,'  d/m/y =',I2,I2,I4)") kt, nday, nmonth, nyear
         CALL prt_ctl_info(charout)
      ENDIF

      IF( .NOT. lk_offline ) CALL rst_opn( kt )               ! Open the restart file if needed and control lrst_oce
      IF( lrst_oce         ) CALL day_rst( kt, 'WRITE' )      ! write day restart information
      !
      IF( nn_timing == 1 )  CALL timing_stop('day')
      !
   END SUBROUTINE day


   SUBROUTINE day_rst( kt, cdrw )
      !!---------------------------------------------------------------------
      !!                   ***  ROUTINE ts_rst  ***
      !!
      !!  ** Purpose : Read or write calendar in restart file:
      !!
      !!  WRITE(READ) mode:
      !!       kt        : number of time step since the begining of the experiment at the
      !!                   end of the current(previous) run
      !!       adatrj(0) : number of elapsed days since the begining of the experiment at the
      !!                   end of the current(previous) run (REAL -> keep fractions of day)
      !!       ndastp    : date at the end of the current(previous) run (coded as yyyymmdd integer)
      !!
      !!   According to namelist parameter nrstdt,
      !!       nrstdt = 0  no control on the date (nit000 is  arbitrary).
      !!       nrstdt = 1  we verify that nit000 is equal to the last
      !!                   time step of previous run + 1.
      !!       In both those options, the  exact duration of the experiment
      !!       since the beginning (cumulated duration of all previous restart runs)
      !!       is not stored in the restart and is assumed to be (nit000-1)*rdt.
      !!       This is valid is the time step has remained constant.
      !!
      !!       nrstdt = 2  the duration of the experiment in days (adatrj)
      !!                    has been stored in the restart file.
      !!----------------------------------------------------------------------
      INTEGER         , INTENT(in) ::   kt         ! ocean time-step
      CHARACTER(len=*), INTENT(in) ::   cdrw       ! "READ"/"WRITE" flag
      !
      REAL(wp) ::   zkt, zndastp
      !!----------------------------------------------------------------------

      IF( TRIM(cdrw) == 'READ' ) THEN

         IF( iom_varid( numror, 'kt', ldstop = .FALSE. ) > 0 ) THEN
            ! Get Calendar informations
            CALL iom_get( numror, 'kt', zkt )   ! last time-step of previous run
            IF(lwp) THEN
               WRITE(numout,*) ' *** Info read in restart : '
               WRITE(numout,*) '   previous time-step                               : ', NINT( zkt )
               WRITE(numout,*) ' *** restart option'
               SELECT CASE ( nrstdt )
               CASE ( 0 )   ;   WRITE(numout,*) ' nrstdt = 0 : no control of nit000'
               CASE ( 1 )   ;   WRITE(numout,*) ' nrstdt = 1 : no control the date at nit000 (use ndate0 read in the namelist)'
               CASE ( 2 )   ;   WRITE(numout,*) ' nrstdt = 2 : calendar parameters read in restart'
               END SELECT
               WRITE(numout,*)
            ENDIF
            ! Control of date
            IF( nit000 - NINT( zkt ) /= 1 .AND. nrstdt /= 0 )                                         &
                 &   CALL ctl_stop( ' ===>>>> : problem with nit000 for the restart',                 &
                 &                  ' verify the restart file or rerun with nrstdt = 0 (namelist)' )
            ! define ndastp and adatrj
            IF ( nrstdt == 2 ) THEN
               ! read the parameters correspondting to nit000 - 1 (last time step of previous run)
               CALL iom_get( numror, 'ndastp', zndastp )
               ndastp = NINT( zndastp )
               CALL iom_get( numror, 'adatrj', adatrj  )
            ELSE
               ! parameters correspondting to nit000 - 1 (as we start the step loop with a call to day)
               ndastp = ndate0 - 1     ! ndate0 read in the namelist in dom_nam, we assume that we start run at 00:00
               adatrj = ( REAL( nit000-1, wp ) * rdttra(1) ) / rday
               ! note this is wrong if time step has changed during run
            ENDIF
         ELSE
            ! parameters correspondting to nit000 - 1 (as we start the step loop with a call to day)
            ndastp = ndate0 - 1        ! ndate0 read in the namelist in dom_nam, we assume that we start run at 00:00
            adatrj = ( REAL( nit000-1, wp ) * rdttra(1) ) / rday
         ENDIF
         IF( ABS(adatrj  - REAL(NINT(adatrj),wp)) < 0.1 / rday )   adatrj = REAL(NINT(adatrj),wp)   ! avoid truncation error
         !
         IF(lwp) THEN
            WRITE(numout,*) ' *** Info used values : '
            WRITE(numout,*) '   date ndastp                                      : ', ndastp
            WRITE(numout,*) '   number of elapsed days since the begining of run : ', adatrj
            WRITE(numout,*)
         ENDIF
         !
      ELSEIF( TRIM(cdrw) == 'WRITE' ) THEN
         !
         IF( kt == nitrst ) THEN
            IF(lwp) WRITE(numout,*)
            IF(lwp) WRITE(numout,*) 'rst_write : write oce restart file  kt =', kt
            IF(lwp) WRITE(numout,*) '~~~~~~~'
         ENDIF
         ! calendar control
         CALL iom_rstput( kt, nitrst, numrow, 'kt'     , REAL( kt    , wp) )   ! time-step
         CALL iom_rstput( kt, nitrst, numrow, 'ndastp' , REAL( ndastp, wp) )   ! date
         CALL iom_rstput( kt, nitrst, numrow, 'adatrj' , adatrj            )   ! number of elapsed days since
         !                                                                     ! the begining of the run [s]
      ENDIF
      !
   END SUBROUTINE day_rst

   !!======================================================================
END MODULE daymod
