fill_grads_template Subroutine

   subroutine fill_grads_template(output_string,template,unusable,experiment_id,nymd,nhms,time,preserve,rc)
      character(len=*), intent(out) :: output_string
      character(len=*), intent(in)  :: template
      class(keywordEnforcer), optional, intent(in) :: unusable
      character(len=*), intent(in), optional :: experiment_id
      integer, intent(in), optional :: nymd
      integer, intent(in), optional :: nhms
      type(ESMF_Time), intent(in), optional :: time
      logical, intent(in), optional :: preserve
      integer, intent(out), optional :: rc

      integer :: year,month,day,hour,minute,second,tmpl_length,output_length
      integer  :: i, m, istp, k, kstp, i1, i2
      character(len=1) :: c0,c1,c2
      character(len=4) :: sbuf
      logical :: valid_token,preserve_
      integer :: status
     
      _UNUSED_DUMMY(unusable)
      if (present(preserve)) then
         preserve_=preserve
      else
         preserve_=.false.
      end if
      year=uninit_time
      month=uninit_time
      day=uninit_time
      hour=uninit_time
      minute=uninit_time
      second=uninit_time
      if (present(time)) then
         _ASSERT(.not.present(nymd),'can not specify an ESMF_Time and an integer time')
         _ASSERT(.not.present(nhms),'can not specify an ESMF_Time and an integer time')
         call ESMF_TimeGet(time,yy=year,mm=month,dd=day,h=hour,m=minute,s=second,rc=status)
         _VERIFY(status)
      end if
      if (present(nymd)) then
         _ASSERT(.not.present(time),'can not specify an ESMF_Time and an integer time')
         year = nymd/10000
         month = mod(nymd/100,100)
         day = mod(nymd,100)
      end if
      if (present(nhms)) then
         _ASSERT(.not.present(time),'can not specify an ESMF_Time and an integer time')
         hour = nhms/10000
         minute = mod(nhms/100,100)
         second = mod(nhms,100)  
      end if
      output_string = ""

      output_length=len(output_string)
      tmpl_length=len_trim(template)
      i=0
      istp=1
      k=1
      kstp=1
      do while(i+istp <= tmpl_length)
         i=i+istp
         c0 = template(i:i)
         if (c0 == "%") then
            i1=i+1
            c1=""
            if (i1<=tmpl_length) c1=template(i1:i1)
            select case(c1)
            case("s")
               if (present(experiment_id)) then
                  istp=2
                  m=min(k+len_trim(experiment_id)-1,output_length)
                  output_string(k:m)=experiment_id
                  k=m+1
                  cycle
               else if (preserve_) then
                  output_string(k:k+1)="%s"
                  k=k+1
               else
                  _FAIL("Using %s token with no experiment id")
               end if
            case("%")
               istp=2
               output_string(k:k)=c1
               k=k+1
               cycle
            case default
               c2=""
               i2=i1+1
               if(i2 <= tmpl_length) c2=template(i2:i2)
               valid_token = check_token(c1//c2) 
               if (valid_token) then
                  istp=3
                  if (.not.preserve_) then
                     _ASSERT(present(nymd) .or. present(nhms) .or. present(time),'Using token with no time')
                  end if
                  sbuf = evaluate_token(c1//c2,year,month,day,hour,minute,second,preserve_)
                  kstp = len_trim(sbuf)
                  m=k+kstp-1
                  output_string(k:m)=sbuf
                  k=m+1
               else
                  _FAIL("Invalid token in file template: "//c1//c2)
               end if
            end select
         else
            istp=1
            output_string(k:k)=template(i:i)
            k=k+1
         end if
      enddo
      _RETURN(_SUCCESS)

   end subroutine fill_grads_template