; $Id$
;
; Copyright (c) 1992-1998, Research Systems, Inc.  All rights reserved.
;	Unauthorized reproduction prohibited.
;

;+
; NAME:
;	CALDAT
;
; PURPOSE:
;	Return the calendar date and time given julian date.
;	This is the inverse of the function JULDAY.
; CATEGORY:
;	Misc.
;
; CALLING SEQUENCE:
;	CALDAT, Julian, Month, Day, Year, Hour, Minute, Second
;	See also: julday, the inverse of this function.
;
; INPUTS:
;	JULIAN contains the Julian Day Number (which begins at noon) of the 
;	specified calendar date.  It should be a long integer.
;
; KEYWORD PARAMETERS:
;
;       NDAYSPM: developpe par eric, ca veut dire: nombre de jours par mois! 
;                par defaut c''est 30, sinon le specifier en donnant
;                une valeur a ndayspm
;                pour passer a un calendrier avec un nombre de jours constant par
;                mois. Utilise en particulier ds julday et caldat
;
; OUTPUTS:
;	(Trailing parameters may be omitted if not required.)
;	MONTH:	Number of the desired month (1 = January, ..., 12 = December).
;
;	DAY:	Number of day of the month.
;
;	YEAR:	Number of the desired year.
;
;	HOUR:	Hour of the day
;	Minute: Minute of the day
;	Second: Second (and fractions) of the day.
;
; COMMON BLOCKS:
;	None.
;
; SIDE EFFECTS:
;	None.
;
; RESTRICTIONS:
;	Accuracy using IEEE double precision numbers is approximately
;	1/10000th of a second.
;
; MODIFICATION HISTORY:
;	Translated from "Numerical Recipies in C", by William H. Press,
;	Brian P. Flannery, Saul A. Teukolsky, and William T. Vetterling.
;	Cambridge University Press, 1988 (second printing).
;
;	DMS, July 1992.
;	DMS, April 1996, Added HOUR, MINUTE and SECOND keyword
;	AB, 7 December 1997, Generalized to handle array input.
;       Eric Guilyardi, June 1999
;       Added key_work ndayspm for fixed number of days per months
;-
;


pro caldat_scalar, Julian, Month, Day, Year, Hour, Minute, Second, NDAYSPM = ndayspm
  ; Internal variant of CALDAT that does the actual work on a single
  ; value.

  ON_ERROR, 2		; Return to caller if errors

  IF NOT keyword_set(ndayspm) THEN BEGIN  

     IGREG = 2299161L           ;Beginning of Gregorian calendar

     IF julian GE 0 THEN jul = long(julian + .5d) $ ;Better be long
      ELSE jul = long(julian - .5d)
     f = julian + .5d - jul
     if f ne 0.0 then begin	;Get hours, minutes, seconds.
        hour = floor(f * 24.)
        f = f - hour / 24.d
        minute = floor(f*1440)
        second = (f - minute/1440.d0) * 86400.0d0
     endif else begin
        hour = 0L
        minute = 0L
        second = 0L
     endelse
     
     
     if jul ge igreg then begin
        jalpha = long(((jul - 1867216) - 0.25d0) / 36524.25)
        ja = jul + 1 + jalpha - long(0.25d0 * jalpha)
     endif else ja = jul
     
     jb = ja + 1524l
     jc = long(6680.0 + ((jb-2439870)-122.1d0)/365.25)
     jd = long(365 * jc + (0.25 * jc))
     je = long((jb - jd) / 30.6001)
     
     day = jb - jd - long(30.6001d * je)
     month = je -1
     if (month gt 12) then month = month - 12
     year = jc - 4715
     if month gt 2 then year = year - 1
     if year le 0 then year = year - 1

  ENDIF ELSE BEGIN

     jul = long(julian)
     f = (jul - floor(jul))
     IF f NE 0.0 THEN BEGIN	;Get hours, minutes, seconds.
        hour = floor(f*24.)
        f = f - hour / 24.d
        minute = floor(f*1440)
        second = (f - minute/1440.d0) * 86400.0d0
     ENDIF ELSE BEGIN
        hour = 0L
        minute = 0L
        second = 0L
     ENDELSE

     IF ndayspm EQ 1 THEN ndayspm = 30

     Z = floor(julian)
     X = Z / ndayspm
     day = Z - X*ndayspm 
     year = X / 12 
     month = X - year*12 + 1
     year = year + 1

  ENDELSE 

end




pro caldat, Julian, Month, Day, Year, Hour, Minute, Second, NDAYSPM = ndayspm

  ON_ERROR, 2		; Return to caller if errors

  ; Determine shape of input and construct longword output variables of
  ; the same shape.

  s = size(julian)
  if (s[0] eq 0) then begin
    ; Julian is scalar. Just call CALDAT_SCALAR and pass our arguments through.
    caldat_scalar, Julian, Month, Day, Year, Hour, Minute, Second, NDAYSPM = ndayspm
    return
  endif

  ; It's an array. Construct result variables
  ndim = s[0]		; Number or array dimensions
  n = s[ndim + 2]	; # of elements 
  s[ndim + 1] = 3	; Change the type to LONG
  MONTH = (DAY = (YEAR = (HOUR = (MINUTE = (SECOND = MAKE_ARRAY(SIZE=s))))))

  ; Loop over the input
  for i = 0, n-1 do begin
    caldat_scalar, julian[i], month_tmp, day_tmp, year_tmp, $
	hour_tmp, minute_tmp, second_tmp, NDAYSPM = ndayspm
    month[i]  = month_tmp
    day[i]    = day_tmp
    year[i]   = year_tmp
    hour[i]   = hour_tmp
    minute[i] = minute_tmp
    second[i] = second_tmp
  endfor
end