;+
;
; @file_comments
; gives Julian day equivalent of a date given in yyyymmdd format
; This is the inverse of the function <pro>jul2date</pro>.
;
; @categories
; Calendar
;
; @param date {in}{required} {type=long or double, scalar or array}
; longword integer with yyyymmdd format or double-precision
; floating-point with yyyymmdd.xx where xx is the fraction of the day
; (xx=0 at 0am and 5 at 12am) 
;
; @keyword GRADS
; if  1 <= year <= 49 --> year = 2000 + year
; if 50 <= year <= 99 --> year = 1900 + year
;
; @keyword MONTH
; Set this keyword equal to a named variable that will receive a
; longword integer or longword integer array representing the number of
; the desired month (1 = January, ..., 12 = December). 
;
; @keyword DAY
; Set this keyword equal to a named variable that will receive a
; longword integer or longword integer array representing the number of
; the day of the month (1-31).  
;
; @keyword YEAR
; Set this keyword equal to a named variable that will receive a
; longword integer or longword integer array representing the number of
; the desired year (e.g., 1994).  
;
; @keyword HOUR
; Set this keyword equal to a named variable that will receive a
; longword integer or longword integer array representing the number of
; the hour of the day (0-23).  
; 
; @keyword MINUTE
; Set this keyword equal to a named variable that will receive a
; longword integer or longword integer array representing the number of
; the minute of the hour (0-59).  
;  
; @keyword SECOND
; Set this keyword equal to a named variable that will receive a
; double-precision floating-point value or a double-precision
; floating-point array representing the number of the second of the
; minute (0-59).
;
; @returns
; Julian day with the same format (long or double) as the input parameter
;
; @restrictions
; Input param must be longword integer or double-precision floating-point
; 
; @examples
;
;   IDL> jday = juldate(19930124)
;   IDL> print, date2jul(19931205) EQ julday(12,5,1993)
;       1
;   IDL> print, date2jul(931205,/grads) EQ julday(12,5,1993)
;       1
;   IDL> print, date2jul(19931205.5d) EQ julday(12,5,1993,12,0,0)
;       1
;   IDL> print, date2jul(19931205.0d) EQ julday(12,5,1993,0,0,0)
;       1
;
; @history
; Sebastien Masson (smasson\@lodyc.jussieu.fr) June 2005
;
; @version
; $Id$
;
;-
FUNCTION date2jul, date, GRADS=grads, MONTH=month, DAY=day, YEAR=year $
                 , HOUR=hour, MINUTE=minute, SECOND=second
;
  compile_opt idl2, strictarrsubs
;
; check parameters
  if (N_PARAMS() EQ 0) then return, report(['ERROR, No input parameter', 'Usage : ' $
                                            , 'res = date2jul( date[, GRADS = grads][, MONTH = month][, DAY = day]' $
                                            + '[, YEAR = year][, HOUR = hour][, MINUTE = minute][, SECOND = second] )'])
;
  sztype = size(date, /type)
  IF sztype NE 3 AND sztype NE 5 AND sztype LT 13 THEN BEGIN
    dummy = report('Beware of input type, date must be long or double')
    stop
  ENDIF
;
  year = long(date) / 10000
  month = long(abs(date)/100) MOD 100
  day = long(abs(date)) MOD 100
;------------------------------------------------------------
  if keyword_set(grads) then $
     year = year + 1900L * (year GE 50 AND year LE 99) $
                 + 2000L * (year GE  1 AND year LE 49)
;------------------------------------------------------------
  IF sztype NE 5 THEN return, julday(month, day, year)

  fraction = date - long(date)
  hour = floor(fraction * 24d)
  fraction = temporary(fraction) - hour/24d
  minute = floor(fraction*1440d)
  second = (temporary(fraction) - minute/1440d) * 86400d

  return, julday(month, day, year, hour, minute, second)

end