## Copyright (C) 2006-2012 Paul Kienzle
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or (at
## your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn  {Function File} {@var{days} =} datenum (@var{datevec})
## @deftypefnx {Function File} {@var{days} =} datenum (@var{year}, @var{month}, @var{day})
## @deftypefnx {Function File} {@var{days} =} datenum (@var{year}, @var{month}, @var{day}, @var{hour})
## @deftypefnx {Function File} {@var{days} =} datenum (@var{year}, @var{month}, @var{day}, @var{hour}, @var{minute})
## @deftypefnx {Function File} {@var{days} =} datenum (@var{year}, @var{month}, @var{day}, @var{hour}, @var{minute}, @var{second})
## @deftypefnx {Function File} {@var{days} =} datenum ("datestr")
## @deftypefnx {Function File} {@var{days} =} datenum ("datestr", @var{p})
## @deftypefnx {Function File} {[@var{days}, @var{secs}] =} datenum (@dots{})
## Return the date/time input as a serial day number, with Jan 1, 0000
## defined as day 1.
##
## The integer part, @code{floor (@var{days})} counts the number of
## complete days in the date input.
##
## The fractional part, @code{rem (@var{days}, 1)} corresponds to the time
## on the given day.
##
## The input may be a date vector (see @code{datevec}), 
## datestr (see @code{datestr}), or directly specified as input.
##
## When processing input datestrings, @var{p} is the year at the start of the
## century to which two-digit years will be referenced.  If not specified, it
## defaults to the current year minus 50.
##
## The optional output @var{secs} holds the time on the specified day with
## greater precision than @var{days}.
##
## Notes:
##
## @itemize
## @item
## Years can be negative and/or fractional.
##
## @item
## Months below 1 are considered to be January.
##
## @item
## Days of the month start at 1.
##
## @item
## Days beyond the end of the month go into subsequent months.
##
## @item
## Days before the beginning of the month go to the previous month.
##
## @item
## Days can be fractional.
## @end itemize
##
## @strong{Caution:} this function does not attempt to handle Julian
## calendars so dates before Octave 15, 1582 are wrong by as much
## as eleven days.  Also, be aware that only Roman Catholic countries
## adopted the calendar in 1582.  It took until 1924 for it to be
## adopted everywhere.  See the Wikipedia entry on the Gregorian
## calendar for more details.
##
## @strong{Warning:} leap seconds are ignored.  A table of leap seconds
## is available on the Wikipedia entry for leap seconds.
## @seealso{datestr, datevec, now, clock, date}
## @end deftypefn

## Algorithm: Peter Baum (http://vsg.cape.com/~pbaum/date/date0.htm)
## Author: pkienzle <pkienzle@users.sf.net>

function [days, secs] = datenum (year, month = [], day = [], hour = 0, minute = 0, second = 0)

  ## Days until start of month assuming year starts March 1.
  persistent monthstart = [306; 337; 0; 31; 61; 92; 122; 153; 184; 214; 245; 275];

  if (nargin == 0 || nargin > 6 || 
     (nargin > 2 && (ischar (year) || iscellstr (year))))
    print_usage ();
  endif

  if (ischar (year) || iscellstr (year))
    [year, month, day, hour, minute, second] = datevec (year, month);
  else
    if (nargin == 1)
      nc = columns (year);
      if (nc > 6 || nc < 3)
        error ("datenum: expected date vector containing [YEAR, MONTH, DAY, HOUR, MINUTE, SECOND]");
      endif
      if (nc >= 6) second = year(:,6); endif
      if (nc >= 5) minute = year(:,5); endif
      if (nc >= 4) hour   = year(:,4); endif
      day   = year(:,3);
      month = year(:,2);
      year  = year(:,1);
    endif
  endif

  month(month<1) = 1; ## For compatibility.  Otherwise allow negative months.

  ## Set start of year to March by moving Jan. and Feb. to previous year.
  ## Correct for months > 12 by moving to subsequent years.
  year += fix ((month-14)/12);

  ## Lookup number of days since start of the current year.
  if (numel (month) == 1 || numel (day) == 1)
    ## Allow month or day to be scalar while other values may be vectors or
    ## matrices.
    day += monthstart (mod (month-1,12) + 1) + 60;
    if (numel (month) > 1)
      day = reshape (day, size (month));
    endif
  else
    day += reshape (monthstart (mod (month-1,12) + 1), size (day)) + 60;
  endif

  ## Add number of days to the start of the current year. Correct
  ## for leap year every 4 years except centuries not divisible by 400.
  day += 365*year + floor (year/4) - floor (year/100) + floor (year/400);

  ## Add fraction representing current second of the day.
  days = day + (hour + (minute + second/60)/60)/24;

  ## Output seconds if asked so that etime can be more accurate
  if (isargout (2))
    secs = day*86400 + hour*3600 + minute*60 + second;
  endif

endfunction


%!shared part
%! part = 0.514623842592593;
%!assert (datenum (2001,5,19), 730990)
%!assert (datenum ([1417,6,12]), 517712)
%!assert (datenum ([2001,5,19;1417,6,12]), [730990;517712])
%!assert (datenum (2001,5,19,12,21,3.5), 730990+part, eps)
%!assert (datenum ([1417,6,12,12,21,3.5]), 517712+part, eps)
## Test vector inputs
%!test
%! t = [2001,5,19,12,21,3.5; 1417,6,12,12,21,3.5];
%! n = [730990; 517712] + part;
%! assert (datenum (t), n, 2*eps);
%! ## Check that vectors can have either orientation
%! t = t';
%! n = n';
%! assert (datenum (t(1,:), t(2,:), t(3,:), t(4,:), t(5,:), t(6,:)), n, 2*eps);

## Test mixed vectors and scalars
%!assert (datenum ([2008;2009],1,1), [datenum(2008,1,1);datenum(2009,1,1)])
%!assert (datenum (2008, [1;2], 1), [datenum(2008,1,1);datenum(2008,2,1)])
%!assert (datenum (2008, 1, [1;2]), [datenum(2008,1,1);datenum(2008,1,2)])
%!assert (datenum ([2008;2009], [1;2], 1), [datenum(2008,1,1);datenum(2009,2,1)])
%!assert (datenum ([2008;2009], 1, [1;2]), [datenum(2008,1,1);datenum(2009,1,2)])
%!assert (datenum (2008, [1;2], [1;2]), [datenum(2008,1,1);datenum(2008,2,2)])
## And the other orientation
%!assert (datenum ([2008 2009], 1, 1), [datenum(2008,1,1) datenum(2009,1,1)])
%!assert (datenum (2008, [1 2], 1), [datenum(2008,1,1) datenum(2008,2,1)])
%!assert (datenum (2008, 1, [1 2]), [datenum(2008,1,1) datenum(2008,1,2)])
%!assert (datenum ([2008 2009], [1 2], 1), [datenum(2008,1,1) datenum(2009,2,1)])
%!assert (datenum ([2008 2009], 1, [1 2]), [datenum(2008,1,1) datenum(2009,1,2)])
%!assert (datenum (2008, [1 2], [1 2]), [datenum(2008,1,1) datenum(2008,2,2)])
## Test string and cellstr inputs
%!assert (datenum ("5/19/2001"), 730990)
%!assert (datenum ({"5/19/2001"}), 730990)
%!assert (datenum (char ("5/19/2001", "6/6/1944")), [730990; 710189])
%!assert (datenum ({"5/19/2001", "6/6/1944"}), [730990; 710189])

%% Test input validation
%!error datenum ()
%!error datenum (1,2,3,4,5,6,7)
%!error datenum ([1, 2])
%!error datenum ([1,2,3,4,5,6,7])