;+
;
; @file_comments
; get the time axis from a netcdf_file and transforms it in
; Julian days of IDL.
;
; @categories
; Reading
;
; @param CDFID {in}{required}
; the ID of the ncdf_file, which is already open
;
; @param TIMEID {in}{required}
; the ID or the name of the variable which describe the calendar
;
; @keyword YYYYMMDD
; active to obtain the date as a long integer with
; the format YearYearYearYearMonthMonthDayDay
;
; @keyword _EXTRA
; the keyword parameters of ncdf_varget
;
; @returns
; a long array of IDL Julian days
;
; @restrictions
; the calendar variable must have the units attribute
; following the syntax bellow:
;
; time_counter:units = "seconds since 0001-01-01 00:00:00" ;
; time_counter:units = "hours since 0001-01-01 00:00:00" ;
; time_counter:units = "days since 1979-01-01 00:00:00" ;
; time_counter:units = "months since 1979-01-01 00:00:00" ;
; time_counter:units = "years since 1979-01-01 00:00:00" ;
;
; @history
; Sebastien Masson (smasson\@lodyc.jussieu.fr)
;                      June 2001
; @version
; $Id$
;-
;
FUNCTION ncdf_timeget, cdfid, timeid, YYYYMMDD = yyyymmdd, _EXTRA = ex
;
  compile_opt idl2, strictarrsubs
;

   insidetime=ncdf_varinq(cdfid,timeid)
   if insidetime.natts NE 0 then begin
      attnames = strarr(insidetime.natts)
      for attiq=0,insidetime.natts-1 do attnames[attiq]=strlowcase(ncdf_attname(cdfid,timeid,attiq))
   ENDIF ELSE return, report('the variable '+timeid+' must have the units attribut')
; reading of the time axis
   ncdf_varget, cdfid, timeid, time, _extra = ex
;
; time_counter:units = "seconds since 0001-01-01 00:00:00" ;
; time_counter:units = "hours since 0001-01-01 00:00:00" ;
; time_counter:units = "days since 1979-01-01 00:00:00" ;
; time_counter:units = "months since 1979-01-01 00:00:00" ;
; time_counter:units = "years since 1979-01-01 00:00:00" ;
;
   if (where(attnames EQ 'units'))[0] NE -1 then begin
      ncdf_attget,cdfid,timeid,'units',value
      value = strtrim(strcompress(string(value)), 2)
      words = str_sep(value, ' ')
      unite = words[0]
      start = str_sep(words[2], '-')
      case strlowcase(unite) of
         'seconds':time = julday(start[1], start[2], start[0])+time/(long(24)*3600)
         'hours':time = julday(start[1], start[2], start[0])+time/long(24)
         'days':time = julday(start[1], start[2], start[0])+time
         'months':BEGIN
            for t = 0, n_elements(time)-1  do begin
               time[t] = julday(start[1]+time[t], start[2], start[0])
            endfor
         END
         'years':BEGIN
            for t = 0, n_elements(time)-1  do begin
               time[t] = julday(start[1], start[2], start[0]+time[t])
            endfor
         END
         ELSE:return, report('bad syntax of the units attribut of the variable '+timeid)
      ENDCASE
   ENDIF ELSE return, report('the variable '+timeid+' must have the units attribut')
   if keyword_set(yyyymmdd) then time = jul2date(time)
   return, time
end