### Mode:octave
## -*- texinfo -*-
## @deftypefn {Function File} {V =} datevec(date)
## @deftypefnx {Function File} {[Y,M,D,h,m,s] =} datevec(date, P)
## Breaks the number of days since Jan 1, 0000 into a year-month-day
## hour-minute-second format. By this reckoning, Jan 1, 1970 is day
## number 719529.  The fractional portion of @code{date} corresponds to the
## portion of the given day. If a single return value is requested,
## then the components of the date are columns of the matrix @code{V}.
##
## Note: 32-bit architectures only handle times between Dec 14, 1901 
## and Jan 19, 2038, with special handling for 0000-01-01.  datenum
## returns -1 in case of a range error.
##
## The parameter @code{P} is needed to convert date strings with 2 digit
## years into dates with 4 digit years.  2 digit years are assumed to be
## between @code{P} and @code{P+99}. If @code{P} is not given then the 
## current year - 50 is used, so that dates are centered on the present.
## For birthdates, you would want @code{P} to be current year - 99.  For
## appointments, you would want @code{P} to be current year.
##
## Dates must be represented as an integer date code or in a format
## recognisable by datesplit as either a string, string array, cell, or
## cell string array.
##
## @seealso{date,clock,now,datestr,datenum,calendar,weekday,datesplit} 
## @end deftypefn

## Algorithm: Peter Baum (http://vsg.cape.com/~pbaum/date/date0.htm)
## Author: Paul Kienzle
## This program is granted to the public domain.
## Modified-by: Bill Denney <bill@givebillmoney.com>

function [Y,M,D,h,m,s] = datevec(date,P)

  if nargin == 0 || nargin > 2
    usage("V=datevec(n) or [Y,M,D,h,m,s]=datevec(n)");
  endif
  if nargin < 2, P = []; endif

  if (ischar(date) || iscellstr(date))
    ## handle strings
    if isempty(P)
      tm = localtime(time);
      P = tm.year+1900-50;
    endif

    global __month_names = ["Jan";"Feb";"Mar";"Apr";"May";"Jun";...
			    "Jul";"Aug";"Sep";"Oct";"Nov";"Dec"];
    global __time_names = ["AM";"PM"];

    Y = h = m = s = zeros(rows(date),1);
    M = D = ones(size(Y));

    for i = 1:size(date,1)
      if (iscellstr(date))
	thisdate = date{i};
      else
	thisdate = date(i,:);
      endif
      [Y(i) M(i) D(i) h(i) m(i) s(i)] = datesplit(date(i,:), P);
    endfor
  else
    ## handle date numbers

    ## Move day 0 from midnight -0001-12-31 to midnight 0001-3-1
    z = floor(date) - 60; 
    ## Calculate number of centuries; K1=0.25 is to avoid rounding problems.
    a = floor((z-0.25)/36524.25);
    ## Days within century;  K2=0.25 is to avoid rounding problems.
    b = z - 0.25 + a - floor(a/4);
    ## Calculate the year (year starts on March 1).
    Y = floor(b/365.25);
    ## Calculate day in year.
    c = fix(b-floor(365.25*Y)) + 1;
    ## Calculate month in year.
    M = fix((5*c + 456)/153);
    D = c - fix((153*M-457)/5);
    ## Move to Jan 1 as start of year.
    Y(M>12)++;
    M(M>12)-=12;

    ## Convert hour-minute-seconds
    s = 86400*(date-floor(date));
    h = floor(s/3600);
    s = s - 3600*h;
    m = floor(s/60);
    s = s - 60*m;
  endif

  if nargout <= 1
    Y = [ Y(:), M(:), D(:), h(:), m(:), s(:) ];
  endif
endfunction

%!assert(all(datenum(datevec([-1e4:1e4]))==[-1e4:1e4]'))
%!test
%! t=linspace(-2e5,2e5,10993);
%! assert(all(datenum(datevec(t))==t'));