## Copyright (C) 2012-2013 Rik Wehbring
##
## 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{names} =} fieldnames (@var{struct})
## @deftypefnx {Function File} {@var{names} =} fieldnames (@var{obj})
## @deftypefnx {Function File} {@var{names} =} fieldnames (@var{javaobj})
## @deftypefnx {Function File} {@var{names} =} fieldnames ("@var{jclassname}")
## Return a cell array of strings with the names of the fields in the
## specified input.
##
## When the input is a structure @var{struct}, the names are the elements
## of the structure.
##
## When the input is an Octave object @var{obj}, the names are the public
## properties of the object.
##
## When the input is a Java object @var{javaobj} or Java classname
## @var{jclassname} the name are the public data elements of the object or
## class.
## @seealso{nfields, isfield, orderfields, struct, methods}
## @end deftypefn

function names = fieldnames (obj)
  
  if (nargin != 1)
    print_usage ();
  endif
  
  if (isstruct (obj) || isobject (obj))
    ## Call internal C++ function for structs or Octave objects
    names = __fieldnames__ (obj);
  elseif (isjava (obj) || ischar (obj))
    ## FIXME: Function prototype that excepts java obj exists, but doesn't
    ##        work if obj is java.lang.String.  Convert obj to classname.
    if (! ischar (obj))
      obj = class (obj);
    endif
    names_str = javaMethod ("getFields", "org.octave.ClassHelper", obj);
    names = ostrsplit (names_str, ';');
  else
    error ("fieldnames: Invalid input argument"); 
  endif

endfunction


## test preservation of fieldname order
%!test
%! x(3).d=1;  x(2).a=2;  x(1).b=3;  x(2).c=3;
%! assert (fieldnames (x), {"d"; "a"; "b"; "c"});

## test empty structure
%!test
%! s = struct ();
%! assert (fieldnames (s), cell (0, 1));

## test Java classname
%!testif HAVE_JAVA 
%! names = fieldnames ("java.lang.Double");
%! search = strfind (names, "java.lang.Double.MAX_VALUE");
%! assert (! isempty ([search{:}]));