pro head_format, filnam, index
;
; This is to examine date string and decide the head format for the specific date;
; the reason for this is that we have used three different types of date string format
; in the FITS header, and an user-friendly program has to be able to tell which
; format to use to extract date information for the subsequent analysis.
; 
; This is the version just for the old (93/94/95) data.
;
; The input is the filename string which contains date information.
;

fnam = filnam(0)
fil_len = strlen(fnam)
;sign = strmid(fnam, fil_len -2, 2)
;if (sign eq 'gz') then date = strmid(fnam, fil_len - 17, 7) $
;                  else date = strmid(fnam, fil_len - 14, 7)
date = strmid(fnam(0), fil_len - 7, 7)

day = fix(strmid(date, 5, 2))
year = fix(strmid(date, 0, 2))
if year le 93 then year = year + 1900 else year = year + 2000
mon = strmid(date, 2, 3)
case mon of
  'jan':	month = 1
  'feb':	month = 2
  'mar':	month = 3
  'apr':	month = 4
  'may':	month = 5
  'jun':	month = 6
  'jul':	month = 7
  'aug':	month = 8
  'sep':	month = 9
  'oct':	month = 10
  'nov':	month = 11
  'dec':	month = 12
endcase

if (year le 1999 and month le 9) or (year eq 1999 and month eq 9 and day le 6) or (year le 1998) then index = 1		; >98dec03 and <99sep06
if (year eq 1999 and month gt 9) or (year eq 1999 and month eq 9 and day ge 13) then index = 2				; >99sep13 and <99dec30
if (year ge 2000) then index = 3							; >00jan11 
if (year eq 2000 and month eq 1 and day eq 3) then index = 4				; 00jan03 

end