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## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
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## -*- texinfo -*-
## @deftypefn  {} {@var{c} =} calendar ()
## @deftypefnx {} {@var{c} =} calendar (@var{d})
## @deftypefnx {} {@var{c} =} calendar (@var{y}, @var{m})
## @deftypefnx {} {} calendar (@dots{})
## Return the current monthly calendar in a 6x7 matrix.
##
## If @var{d} is specified, return the calendar for the month containing the
## date @var{d}, which must be a serial date number or a date string.
##
## If @var{y} and @var{m} are specified, return the calendar for year @var{y}
## and month @var{m}.
##
## If no output arguments are specified, print the calendar on the screen
## instead of returning a matrix.
## @seealso{datenum, datestr}
## @end deftypefn

function c = calendar (y, m)

  switch (nargin)
    case 0
      v = clock ();
      y = v(1);
      m = v(2);
      d = v(3);

    case 1
      v = datevec (y);
      y = v(1);
      m = v(2);
      d = v(3);

    case 2
      d = [];

  endswitch

  cal = zeros (7, 6);
  dayone = datenum (y, m, 1);
  ndays = eomday (y, m);
  cal(weekday (dayone) - 1 + [1:ndays]) = 1:ndays;

  if (nargout > 0)
    c = cal';
  else
    ## Layout the calendar days, 6 columns per day, 7 days per row.
    str = sprintf ("    %2d    %2d    %2d    %2d    %2d    %2d    %2d\n", cal);

    ## Print an asterisk before the specified date.
    if (! isempty (d))
      pos = weekday (dayone) + d - 1;
      idx = 6*pos + fix (pos / 7.1) - ifelse (d < 10, 1, 2);
      str(idx) = "*";
    endif

    ## Display the calendar.
    s.year = y - 1900;
    s.mon = m - 1;
    puts (strftime ("                    %b %Y\n", s));
    puts ("     S     M    Tu     W    Th     F     S\n");
    puts (str);
  endif

endfunction


%!demo
%! ## Calendar for current month
%! calendar ()

%!demo
%! ## Calendar for October, 1957
%! calendar (1957, 10)

%!assert ((calendar(2000,2))'(2:31), [0:29])
%!assert ((calendar(1957,10))'(2:33), [0:31])