module Module_Date_utilities_rt
contains
  subroutine geth_newdate (ndate, odate, idt)
    implicit none

    !  From old date ("YYYY-MM-DD HH:MM:SS.ffff" or "YYYYMMDDHHMMSSffff") and 
    !  delta-time, compute the new date.

    !  on entry     -  odate  -  the old hdate.
    !                  idt    -  the change in time

    !  on exit      -  ndate  -  the new hdate.

    integer, intent(in)           :: idt
    character (len=*), intent(out) :: ndate
    character (len=*), intent(in)  :: odate

    !  Local Variables

    !  yrold    -  indicates the year associated with "odate"
    !  moold    -  indicates the month associated with "odate"
    !  dyold    -  indicates the day associated with "odate"
    !  hrold    -  indicates the hour associated with "odate"
    !  miold    -  indicates the minute associated with "odate"
    !  scold    -  indicates the second associated with "odate"

    !  yrnew    -  indicates the year associated with "ndate"
    !  monew    -  indicates the month associated with "ndate"
    !  dynew    -  indicates the day associated with "ndate"
    !  hrnew    -  indicates the hour associated with "ndate"
    !  minew    -  indicates the minute associated with "ndate"
    !  scnew    -  indicates the second associated with "ndate"

    !  mday     -  a list assigning the number of days in each month

    !  i        -  loop counter
    !  nday     -  the integer number of days represented by "idt"
    !  nhour    -  the integer number of hours in "idt" after taking out
    !              all the whole days
    !  nmin     -  the integer number of minutes in "idt" after taking out
    !              all the whole days and whole hours.
    !  nsec     -  the integer number of minutes in "idt" after taking out
    !              all the whole days, whole hours, and whole minutes.

    integer :: newlen, oldlen
    integer :: yrnew, monew, dynew, hrnew, minew, scnew, frnew
    integer :: yrold, moold, dyold, hrold, miold, scold, frold
    integer :: nday, nhour, nmin, nsec, nfrac, i, ifrc
    logical :: opass
    character (len=10) :: hfrc
    character (len=1) :: sp
    logical :: punct
    integer :: yrstart, yrend, mostart, moend, dystart, dyend
    integer :: hrstart, hrend, mistart, miend, scstart, scend, frstart
    integer :: units
    integer, dimension(12) :: mday = (/31,28,31,30,31,30,31,31,30,31,30,31/)

    ! Determine if odate is "YYYY-MM-DD_HH ... " or "YYYYMMDDHH...."
    if (odate(5:5) == "-") then
       punct = .TRUE.
    else
       punct = .FALSE.
    endif

    !  Break down old hdate into parts

    hrold = 0
    miold = 0
    scold = 0
    frold = 0
    oldlen = LEN(odate)
    if (punct) then
       yrstart = 1
       yrend = 4
       mostart = 6
       moend = 7
       dystart = 9
       dyend = 10
       hrstart = 12
       hrend = 13
       mistart = 15
       miend = 16
       scstart = 18
       scend = 19
       frstart = 21
       select case (oldlen)
       case (10)
          ! Days
          units = 1
       case (13)
          ! Hours
          units = 2
       case (16)
          ! Minutes
          units = 3
       case (19)
          ! Seconds
          units = 4
       case (21)
          ! Tenths
          units = 5
       case (22)
          ! Hundredths
          units = 6
       case (23)
          ! Thousandths
          units = 7
       case (24)
          ! Ten thousandths
          units = 8
       case default
#ifdef HYDRO_D
          write(*,*) 'ERROR: geth_newdate:  odd length: #'//trim(odate)//'#'
          call hydro_stop("geth_newdate")
#endif
       end select

       if (oldlen.ge.11) then
          sp = odate(11:11)
       else
          sp = ' '
       end if

    else

       yrstart = 1
       yrend = 4
       mostart = 5
       moend = 6
       dystart = 7
       dyend = 8
       hrstart = 9
       hrend = 10
       mistart = 11
       miend = 12
       scstart = 13
       scend = 14
       frstart = 15

       select case (oldlen)
       case (8)
          ! Days
          units = 1
       case (10)
          ! Hours
          units = 2
       case (12)
          ! Minutes
          units = 3
       case (14)
          ! Seconds
          units = 4
       case (15)
          ! Tenths
          units = 5
       case (16)
          ! Hundredths
          units = 6
       case (17)
          ! Thousandths
          units = 7
       case (18)
          ! Ten thousandths
          units = 8
       case default
#ifdef HYDRO_D
          write(*,*) 'ERROR: geth_newdate:  odd length: #'//trim(odate)//'#'
          call hydro_stop("geth_newdate")
#endif
       end select
    endif

    !  Use internal READ statements to convert the CHARACTER string
    !  date into INTEGER components.

    read(odate(yrstart:yrend),  '(i4)') yrold
    read(odate(mostart:moend),  '(i2)') moold
    read(odate(dystart:dyend), '(i2)') dyold
    if (units.ge.2) then
       read(odate(hrstart:hrend),'(i2)') hrold
       if (units.ge.3) then
          read(odate(mistart:miend),'(i2)') miold
          if (units.ge.4) then
             read(odate(scstart:scend),'(i2)') scold
             if (units.ge.5) then
                read(odate(frstart:oldlen),*) frold
             end if
          end if
       end if
    end if

    !  Set the number of days in February for that year.

    mday(2) = nfeb(yrold)

    !  Check that ODATE makes sense.

    opass = .TRUE.

    !  Check that the month of ODATE makes sense.

    if ((moold.gt.12).or.(moold.lt.1)) then
#ifdef HYDRO_D
       write(*,*) 'GETH_NEWDATE:  Month of ODATE = ', moold
#endif
       opass = .FALSE.
    end if

    !  Check that the day of ODATE makes sense.

    if ((dyold.gt.mday(moold)).or.(dyold.lt.1)) then
#ifdef HYDRO_D
       write(*,*) 'GETH_NEWDATE:  Day of ODATE = ', dyold
#endif
       opass = .FALSE.
    end if

    !  Check that the hour of ODATE makes sense.

    if ((hrold.gt.23).or.(hrold.lt.0)) then
#ifdef HYDRO_D
       write(*,*) 'GETH_NEWDATE:  Hour of ODATE = ', hrold
#endif
       opass = .FALSE.
    end if

    !  Check that the minute of ODATE makes sense.

    if ((miold.gt.59).or.(miold.lt.0)) then
#ifdef HYDRO_D
       write(*,*) 'GETH_NEWDATE:  Minute of ODATE = ', miold
#endif
       opass = .FALSE.
    end if

    !  Check that the second of ODATE makes sense.

    if ((scold.gt.59).or.(scold.lt.0)) then
#ifdef HYDRO_D
       write(*,*) 'GETH_NEWDATE:  Second of ODATE = ', scold
#endif
       opass = .FALSE.
    end if

    !  Check that the fractional part  of ODATE makes sense.


    if (.not.opass) then
#ifdef HYDRO_D
       write(*,*) 'Crazy ODATE: ', odate(1:oldlen), oldlen
       stop
#endif
    end if

    !  Date Checks are completed.  Continue.


    !  Compute the number of days, hours, minutes, and seconds in idt

    if (units.ge.5) then !idt should be in fractions of seconds
       ifrc = oldlen-(frstart)+1
       ifrc = 10**ifrc
       nday   = abs(idt)/(86400*ifrc)
       nhour  = mod(abs(idt),86400*ifrc)/(3600*ifrc)
       nmin   = mod(abs(idt),3600*ifrc)/(60*ifrc)
       nsec   = mod(abs(idt),60*ifrc)/(ifrc)
       nfrac = mod(abs(idt), ifrc)
    else if (units.eq.4) then  !idt should be in seconds
       ifrc = 1
       nday   = abs(idt)/86400 ! integer number of days in delta-time
       nhour  = mod(abs(idt),86400)/3600
       nmin   = mod(abs(idt),3600)/60
       nsec   = mod(abs(idt),60)
       nfrac  = 0
    else if (units.eq.3) then !idt should be in minutes
       ifrc = 1
       nday   = abs(idt)/1440 ! integer number of days in delta-time
       nhour  = mod(abs(idt),1440)/60
       nmin   = mod(abs(idt),60)
       nsec   = 0
       nfrac  = 0
    else if (units.eq.2) then !idt should be in hours
       ifrc = 1
       nday   = abs(idt)/24 ! integer number of days in delta-time
       nhour  = mod(abs(idt),24)
       nmin   = 0
       nsec   = 0
       nfrac  = 0
    else if (units.eq.1) then !idt should be in days
       ifrc = 1
       nday   = abs(idt)    ! integer number of days in delta-time
       nhour  = 0
       nmin   = 0
       nsec   = 0
       nfrac  = 0
    else
#ifdef HYDRO_D
       write(*,'(''GETH_NEWDATE: Strange length for ODATE: '', i3)') &
            oldlen
       write(*,*) '#'//odate(1:oldlen)//'#'
       call hydro_stop("geth_newdate")
#endif
    end if

    if (idt.ge.0) then

       frnew = frold + nfrac
       if (frnew.ge.ifrc) then
          frnew = frnew - ifrc
          nsec = nsec + 1
       end if

       scnew = scold + nsec
       if (scnew .ge. 60) then
          scnew = scnew - 60
          nmin  = nmin + 1
       end if

       minew = miold + nmin
       if (minew .ge. 60) then
          minew = minew - 60
          nhour  = nhour + 1
       end if

       hrnew = hrold + nhour
       if (hrnew .ge. 24) then
          hrnew = hrnew - 24
          nday  = nday + 1
       end if

       dynew = dyold
       monew = moold
       yrnew = yrold
       do i = 1, nday
          dynew = dynew + 1
          if (dynew.gt.mday(monew)) then
             dynew = dynew - mday(monew)
             monew = monew + 1
             if (monew .gt. 12) then
                monew = 1
                yrnew = yrnew + 1
                ! If the year changes, recompute the number of days in February
                mday(2) = nfeb(yrnew)
             end if
          end if
       end do

    else if (idt.lt.0) then

       frnew = frold - nfrac
       if (frnew .lt. 0) then
          frnew = frnew + ifrc
          nsec = nsec + 1
       end if

       scnew = scold - nsec
       if (scnew .lt. 00) then
          scnew = scnew + 60
          nmin  = nmin + 1
       end if

       minew = miold - nmin
       if (minew .lt. 00) then
          minew = minew + 60
          nhour  = nhour + 1
       end if

       hrnew = hrold - nhour
       if (hrnew .lt. 00) then
          hrnew = hrnew + 24
          nday  = nday + 1
       end if

       dynew = dyold
       monew = moold
       yrnew = yrold
       do i = 1, nday
          dynew = dynew - 1
          if (dynew.eq.0) then
             monew = monew - 1
             if (monew.eq.0) then
                monew = 12
                yrnew = yrnew - 1
                ! If the year changes, recompute the number of days in February
                mday(2) = nfeb(yrnew)
             end if
             dynew = mday(monew)
          end if
       end do
    end if

    !  Now construct the new mdate

    newlen = LEN(ndate)

    if (punct) then

       if (newlen.gt.frstart) then
          write(ndate(1:scend),19) yrnew, monew, dynew, hrnew, minew, scnew
          write(hfrc,'(i10)') frnew+1000000000
          ndate = ndate(1:scend)//'.'//hfrc(31-newlen:10)

       else if (newlen.eq.scend) then
          write(ndate(1:scend),19) yrnew, monew, dynew, hrnew, minew, scnew
19        format(i4,'-',i2.2,'-',i2.2,'_',i2.2,':',i2.2,':',i2.2)

       else if (newlen.eq.miend) then
          write(ndate,16) yrnew, monew, dynew, hrnew, minew
16        format(i4,'-',i2.2,'-',i2.2,'_',i2.2,':',i2.2)

       else if (newlen.eq.hrend) then
          write(ndate,13) yrnew, monew, dynew, hrnew
13        format(i4,'-',i2.2,'-',i2.2,'_',i2.2)

       else if (newlen.eq.dyend) then
          write(ndate,10) yrnew, monew, dynew
10        format(i4,'-',i2.2,'-',i2.2)

       end if

    else

       if (newlen.gt.frstart) then
          write(ndate(1:scend),119) yrnew, monew, dynew, hrnew, minew, scnew
          write(hfrc,'(i10)') frnew+1000000000
          ndate = ndate(1:scend)//'.'//hfrc(31-newlen:10)

       else if (newlen.eq.scend) then
          write(ndate(1:scend),119) yrnew, monew, dynew, hrnew, minew, scnew
119       format(i4,i2.2,i2.2,i2.2,i2.2,i2.2)

       else if (newlen.eq.miend) then
          write(ndate,116) yrnew, monew, dynew, hrnew, minew
116       format(i4,i2.2,i2.2,i2.2,i2.2)

       else if (newlen.eq.hrend) then
          write(ndate,113) yrnew, monew, dynew, hrnew
113       format(i4,i2.2,i2.2,i2.2)

       else if (newlen.eq.dyend) then
          write(ndate,110) yrnew, monew, dynew
110       format(i4,i2.2,i2.2)

       end if

    endif

    if (punct .and. (oldlen.ge.11) .and. (newlen.ge.11)) ndate(11:11) = sp

  end subroutine geth_newdate

  subroutine geth_idts (newdate, olddate, idt)

    implicit none

    !  From 2 input mdates ('YYYY-MM-DD HH:MM:SS.ffff'), 
    !  compute the time difference.

    !  on entry     -  newdate  -  the new hdate.
    !                  olddate  -  the old hdate.

    !  on exit      -  idt    -  the change in time.
    !                            Units depend on length of date strings.

    character (len=*) , intent(in) :: newdate, olddate
    integer           , intent(out)   :: idt


    !  Local Variables

    !  yrnew    -  indicates the year associated with "ndate"
    !  yrold    -  indicates the year associated with "odate"
    !  monew    -  indicates the month associated with "ndate"
    !  moold    -  indicates the month associated with "odate"
    !  dynew    -  indicates the day associated with "ndate"
    !  dyold    -  indicates the day associated with "odate"
    !  hrnew    -  indicates the hour associated with "ndate"
    !  hrold    -  indicates the hour associated with "odate"
    !  minew    -  indicates the minute associated with "ndate"
    !  miold    -  indicates the minute associated with "odate"
    !  scnew    -  indicates the second associated with "ndate"
    !  scold    -  indicates the second associated with "odate"
    !  i        -  loop counter
    !  mday     -  a list assigning the number of days in each month

    ! ndate, odate: local values of newdate and olddate
    character(len=24) :: ndate, odate

    integer :: oldlen, newlen
    integer :: yrnew, monew, dynew, hrnew, minew, scnew, frnew
    integer :: yrold, moold, dyold, hrold, miold, scold, frold
    integer :: i, newdys, olddys
    logical :: npass, opass
    integer :: timesign
    integer :: ifrc
    integer, dimension(12) :: mday = (/31,28,31,30,31,30,31,31,30,31,30,31/)
    logical :: punct
    integer :: yrstart, yrend, mostart, moend, dystart, dyend
    integer :: hrstart, hrend, mistart, miend, scstart, scend, frstart
    integer :: units

    oldlen = len(olddate)
    newlen = len(newdate)
    if (newlen.ne.oldlen) then
#ifdef HYDRO_D
       write(*,'("GETH_IDTS: NEWLEN /= OLDLEN: ", A, 3x, A)') newdate(1:newlen), olddate(1:oldlen)
       call hydro_stop("geth_newdate")
#endif
    endif

    if (olddate.gt.newdate) then
       timesign = -1

       ifrc = oldlen
       oldlen = newlen
       newlen = ifrc

       ndate = olddate
       odate = newdate
    else
       timesign = 1
       ndate = newdate
       odate = olddate
    end if

    ! Break down old hdate into parts

    ! Determine if olddate is punctuated or not
    if (odate(5:5) == "-") then
       punct = .TRUE.
       if (ndate(5:5) /= "-") then
#ifdef HYDRO_D
          write(*,'("GETH_IDTS: Dates appear to be different formats: ", A, 3x, A)') &
               ndate(1:newlen), odate(1:oldlen)
          call hydro_stop("geth_idts")
#endif
       endif
    else
       punct = .FALSE.
       if (ndate(5:5) == "-") then
#ifdef HYDRO_D
          write(*,'("GETH_IDTS: Dates appear to be different formats: ", A, 3x, A)') &
               ndate(1:newlen), odate(1:oldlen)
          call hydro_stop("geth_idts")
#endif
       endif
    endif

    if (punct) then
       yrstart = 1
       yrend = 4
       mostart = 6
       moend = 7
       dystart = 9
       dyend = 10
       hrstart = 12
       hrend = 13
       mistart = 15
       miend = 16
       scstart = 18
       scend = 19
       frstart = 21
       select case (oldlen)
       case (10)
          ! Days
          units = 1
       case (13)
          ! Hours
          units = 2
       case (16)
          ! Minutes
          units = 3
       case (19)
          ! Seconds
          units = 4
       case (21)
          ! Tenths
          units = 5
       case (22)
          ! Hundredths
          units = 6
       case (23)
          ! Thousandths
          units = 7
       case (24)
          ! Ten thousandths
          units = 8
       case default
#ifdef HYDRO_D
          write(*,*) 'ERROR: geth_idts:  odd length: #'//trim(odate)//'#'
          call hydro_stop("geth_idts")
#endif
       end select
    else

       yrstart = 1
       yrend = 4
       mostart = 5
       moend = 6
       dystart = 7
       dyend = 8
       hrstart = 9
       hrend = 10
       mistart = 11
       miend = 12
       scstart = 13
       scend = 14
       frstart = 15

       select case (oldlen)
       case (8)
          ! Days
          units = 1
       case (10)
          ! Hours
          units = 2
       case (12)
          ! Minutes
          units = 3
       case (14)
          ! Seconds
          units = 4
       case (15)
          ! Tenths
          units = 5
       case (16)
          ! Hundredths
          units = 6
       case (17)
          ! Thousandths
          units = 7
       case (18)
          ! Ten thousandths
          units = 8
       case default
#ifdef HYDRO_D
          write(*,*) 'ERROR: geth_idts:  odd length: #'//trim(odate)//'#'
          call hydro_stop("geth_idts")
#endif
       end select
    endif


    hrold = 0
    miold = 0
    scold = 0
    frold = 0

    read(odate(yrstart:yrend), '(i4)') yrold
    read(odate(mostart:moend), '(i2)') moold
    read(odate(dystart:dyend), '(i2)') dyold
    if (units.ge.2) then
       read(odate(hrstart:hrend),'(i2)') hrold
       if (units.ge.3) then
          read(odate(mistart:miend),'(i2)') miold
          if (units.ge.4) then
             read(odate(scstart:scend),'(i2)') scold
             if (units.ge.5) then
                read(odate(frstart:oldlen),*) frold
             end if
          end if
       end if
    end if

    !  Break down new hdate into parts

    hrnew = 0
    minew = 0
    scnew = 0
    frnew = 0

    read(ndate(yrstart:yrend), '(i4)') yrnew
    read(ndate(mostart:moend), '(i2)') monew
    read(ndate(dystart:dyend), '(i2)') dynew
    if (units.ge.2) then
       read(ndate(hrstart:hrend),'(i2)') hrnew
       if (units.ge.3) then
          read(ndate(mistart:miend),'(i2)') minew
          if (units.ge.4) then
             read(ndate(scstart:scend),'(i2)') scnew
             if (units.ge.5) then
                read(ndate(frstart:newlen),*) frnew
             end if
          end if
       end if
    end if

    !  Check that the dates make sense.

    npass = .true.
    opass = .true.

    !  Check that the month of NDATE makes sense.
    
    if ((monew.gt.12).or.(monew.lt.1)) then
#ifdef HYDRO_D
       write(*,*) 'GETH_IDTS:  Month of NDATE = ', monew
#endif
       npass = .false.
    end if

    !  Check that the month of ODATE makes sense.

    if ((moold.gt.12).or.(moold.lt.1)) then
#ifdef HYDRO_D
       print*, 'GETH_IDTS:  Month of ODATE = ', moold
#endif
       opass = .false.
    end if

    !  Check that the day of NDATE makes sense.

    if (monew.ne.2) then
       ! ...... For all months but February
       if ((dynew.gt.mday(monew)).or.(dynew.lt.1)) then
#ifdef HYDRO_D
          print*, 'GETH_IDTS:  Day of NDATE = ', dynew
#endif
          npass = .false.
       end if
    else if (monew.eq.2) then
       ! ...... For February
       if ((dynew > nfeb(yrnew)).or.(dynew < 1)) then
#ifdef HYDRO_D
          print*, 'GETH_IDTS:  Day of NDATE = ', dynew
#endif
          npass = .false.
       end if
    endif

    !  Check that the day of ODATE makes sense.

    if (moold.ne.2) then
       ! ...... For all months but February
       if ((dyold.gt.mday(moold)).or.(dyold.lt.1)) then
#ifdef HYDRO_D
          print*, 'GETH_IDTS:  Day of ODATE = ', dyold
#endif
          opass = .false.
       end if
    else if (moold.eq.2) then
       ! ....... For February
       if ((dyold > nfeb(yrold)).or.(dyold < 1)) then
#ifdef HYDRO_D
          print*, 'GETH_IDTS:  Day of ODATE = ', dyold
#endif
          opass = .false.
       end if
    end if

    !  Check that the hour of NDATE makes sense.

    if ((hrnew.gt.23).or.(hrnew.lt.0)) then
#ifdef HYDRO_D
       print*, 'GETH_IDTS:  Hour of NDATE = ', hrnew
#endif
       npass = .false.
    end if

    !  Check that the hour of ODATE makes sense.

    if ((hrold.gt.23).or.(hrold.lt.0)) then
#ifdef HYDRO_D
       print*, 'GETH_IDTS:  Hour of ODATE = ', hrold
#endif
       opass = .false.
    end if

    !  Check that the minute of NDATE makes sense.

    if ((minew.gt.59).or.(minew.lt.0)) then
#ifdef HYDRO_D
       print*, 'GETH_IDTS:  Minute of NDATE = ', minew
#endif
       npass = .false.
    end if

    !  Check that the minute of ODATE makes sense.

    if ((miold.gt.59).or.(miold.lt.0)) then
#ifdef HYDRO_D
       print*, 'GETH_IDTS:  Minute of ODATE = ', miold
#endif
       opass = .false.
    end if

    !  Check that the second of NDATE makes sense.

    if ((scnew.gt.59).or.(scnew.lt.0)) then
#ifdef HYDRO_D
       print*, 'GETH_IDTS:  SECOND of NDATE = ', scnew
#endif
       npass = .false.
    end if

    !  Check that the second of ODATE makes sense.

    if ((scold.gt.59).or.(scold.lt.0)) then
#ifdef HYDRO_D
       print*, 'GETH_IDTS:  Second of ODATE = ', scold
#endif
       opass = .false.
    end if

    if (.not. npass) then
#ifdef HYDRO_D
       print*, 'Screwy NDATE: ', ndate(1:newlen)
       call hydro_stop("geth_idts")
#endif
    end if

    if (.not. opass) then
#ifdef HYDRO_D
       print*, 'Screwy ODATE: ', odate(1:oldlen)
       call hydro_stop("geth_idts")
#endif
    end if

    !  Date Checks are completed.  Continue.

    !  Compute number of days from 1 January ODATE, 00:00:00 until ndate
    !  Compute number of hours from 1 January ODATE, 00:00:00 until ndate
    !  Compute number of minutes from 1 January ODATE, 00:00:00 until ndate

    newdys = 0
    do i = yrold, yrnew - 1
       newdys = newdys + 337 + nfeb(i)
    end do

    if (monew .gt. 1) then
       mday(2) = nfeb(yrnew)
       do i = 1, monew - 1
          newdys = newdys + mday(i)
       end do
       mday(2) = 28
    end if

    newdys = newdys + dynew - 1

    !  Compute number of hours from 1 January ODATE, 00:00:00 until odate
    !  Compute number of minutes from 1 January ODATE, 00:00:00 until odate

    olddys = 0

    if (moold .gt. 1) then
       mday(2) = nfeb(yrold)
       do i = 1, moold - 1
          olddys = olddys + mday(i)
       end do
       mday(2) = 28
    end if

    olddys = olddys + dyold -1

    !  Determine the time difference

    idt = (newdys - olddys)
    if (units.ge.2) then
       idt = idt*24 + (hrnew - hrold)
       if (units.ge.3) then
          idt = idt*60 + (minew - miold)
          if (units.ge.4) then
             idt = idt*60 + (scnew - scold)
             if (units.ge.5) then
                ifrc = oldlen-(frstart-1)
                ifrc = 10**ifrc
                idt = idt * ifrc + (frnew-frold)
             endif
          endif
       endif
    endif

    if (timesign .eq. -1) then
       idt = idt * timesign
    end if

  end subroutine geth_idts


  integer function nfeb(year)
    !
    ! Compute the number of days in February for the given year.
    !
    implicit none
    integer, intent(in) :: year ! Four-digit year

    nfeb = 28 ! By default, February has 28 days ...
    if (mod(year,4).eq.0) then  
       nfeb = 29  ! But every four years, it has 29 days ...
       if (mod(year,100).eq.0) then
          nfeb = 28  ! Except every 100 years, when it has 28 days ...
          if (mod(year,400).eq.0) then
             nfeb = 29  ! Except every 400 years, when it has 29 days ...
             if (mod(year,3600).eq.0) then
                nfeb = 28  ! Except every 3600 years, when it has 28 days.
             endif
          endif
       endif
    endif
  end function nfeb

  integer function nmdays(hdate)
    !
    ! Compute the number of days in the month of given date hdate.
    !
    implicit none
    character(len=*), intent(in) :: hdate

    integer :: year, month
    integer, dimension(12), parameter :: ndays = (/ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 /)

    read(hdate(1:7), '(I4,1x,I2)') year, month

    if (month == 2) then
       nmdays = nfeb(year)
    else
       nmdays = ndays(month)
    endif
  end function nmdays

  function monthabbr_to_mm(mon) result(mm)
    implicit none

    character(len=3), intent(in) :: mon

    integer :: mm

    if (mon == "Jan") then
       mm = 1
    elseif (mon == "Feb") then
       mm = 2
    elseif (mon == "Mar") then
       mm = 3
    elseif (mon == "Apr") then
       mm = 4
    elseif (mon == "May") then
       mm = 5
    elseif (mon == "Jun") then
       mm = 6
    elseif (mon == "Jul") then
       mm = 7
    elseif (mon == "Aug") then
       mm = 8
    elseif (mon == "Sep") then
       mm = 9
    elseif (mon == "Oct") then
       mm = 10
    elseif (mon == "Nov") then
       mm = 11
    elseif (mon == "Dec") then
       mm = 12
    else
#ifdef HYDRO_D
       write(*, '("Function monthabbr_to_mm:  mon = <",A,">")') mon
       print*,  "Function monthabbr_to_mm:  Unrecognized mon"
       call hydro_stop("monthabbr_to_mm")
#endif
    endif
  end function monthabbr_to_mm

  subroutine swap_date_format(indate, outdate)
    implicit none
    character(len=*), intent(in)  :: indate
    character(len=*), intent(out) :: outdate
    integer :: inlen

    inlen = len(indate)
    if (indate(5:5) == "-") then
       select case (inlen)
       case (10)
          ! YYYY-MM-DD
          outdate = indate(1:4)//indate(6:7)//indate(9:10)
       case (13)
          ! YYYY-MM-DD_HH
          outdate = indate(1:4)//indate(6:7)//indate(9:10)//indate(12:13)
       case (16)
          ! YYYY-MM-DD_HH:mm
          outdate = indate(1:4)//indate(6:7)//indate(9:10)//indate(12:13)//indate(15:16)
       case (19)
          ! YYYY-MM-DD_HH:mm:ss
          outdate = indate(1:4)//indate(6:7)//indate(9:10)//indate(12:13)//indate(15:16)//&
               indate(18:19)
       case (21,22,23,24)
          ! YYYY-MM-DD_HH:mm:ss.f[f[f[f]]]
          outdate = indate(1:4)//indate(6:7)//indate(9:10)//indate(12:13)//indate(15:16)//&
               indate(18:19)//indate(21:inlen)
       case default
#ifdef HYDRO_D
          write(*,'("Unrecognized length: <", A,">")') indate
         call hydro_stop("swap_date_format")
#endif
       end select
    else
       select case (inlen)
       case (8)
          ! YYYYMMDD
          outdate = indate(1:4)//"-"//indate(5:6)//"-"//indate(7:8)
       case (10)
          ! YYYYMMDDHH
          outdate = indate(1:4)//"-"//indate(5:6)//"-"//indate(7:8)//"_"//&
               indate(9:10)
       case (12)
          ! YYYYMMDDHHmm
          outdate = indate(1:4)//"-"//indate(5:6)//"-"//indate(7:8)//"_"//&
               indate(9:10)//":"//indate(11:12)
       case (14)
          ! YYYYMMDDHHmmss
          outdate = indate(1:4)//"-"//indate(5:6)//"-"//indate(7:8)//"_"//&
               indate(9:10)//":"//indate(11:12)//":"//indate(13:14)
       case (15,16,17,18)
          ! YYYYMMDDHHmmssf[f[f[f]]]
          outdate = indate(1:4)//"-"//indate(5:6)//"-"//indate(7:8)//"_"//&
               indate(9:10)//":"//indate(11:12)//":"//indate(13:14)//"."//indate(15:inlen)
       case default
#ifdef HYDRO_D
          write(*,'("Unrecognized length: <", A,">")') indate
          call hydro_stop("swap_date_format")
#endif
       end select
    endif

  end subroutine swap_date_format

  character(len=3) function mm_to_monthabbr(ii) result(mon)
    implicit none
    integer, intent(in) :: ii
    character(len=3), parameter, dimension(12) :: month = (/ &
         "Jan", "Feb", "Mar", "Apr", "May", "Jun", &
         "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" /)
    if (ii > 0 .and. ii < 13 ) then
       mon = month(ii)
    else
#ifdef HYDRO_D
       print*, "mm_to_monthabbr"
       call hydro_stop("mm_to_monthabbr")
#endif
    endif
  end function mm_to_monthabbr

end module Module_Date_utilities_rt
