## Copyright (C) 1996-2012 John W. Eaton
##
## 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{h}, @var{varargin}, @var{narg}] =} __plt_get_axis_arg__ (@var{caller}, @var{varargin})
## Undocumented internal function.
## @end deftypefn

## Author: jwe

function [h, varargin, narg] = __plt_get_axis_arg__ (caller, varargin)

  ## First argument can be a boolean which determines whether a new
  ## axis will be created if none exists.
  if (islogical (caller))
    nogca = caller;
    caller = varargin{1};
    varargin(1) = [];
  else
    nogca = false;
  endif

  ## Search for parent property
  parent = find (strcmpi (varargin, "parent"), 1);
  
  ## Look for numeric scalar which is a graphics handle but not the
  ## Root Figure (0) or an ordinary figure (integer).
  if (numel (varargin) > 0 && isnumeric (varargin{1})
      && isscalar (varargin{1}) && ishandle (varargin{1})
      && varargin{1} != 0 && ! isfigure (varargin{1}))
    htmp = varargin{1};
    obj = get (htmp);
    if ((strcmp (obj.type, "axes") && ! strcmp (obj.tag, "legend"))
        || strcmp (obj.type, "hggroup"))
      h = ancestor (htmp, "axes");
      varargin(1) = [];
    else
      error ("%s: expecting first argument to be axes handle", caller);
    endif
  elseif (numel (varargin) > 1 && ! isempty (parent))
    if (parent < numel (varargin) && ishandle (varargin{parent+1}))
      htmp = varargin{parent+1};
      obj = get (htmp);
      if ((strcmp (obj.type, "axes") && ! strcmp (obj.tag, "legend"))
          || strcmp (obj.type, "hggroup"))
        h = ancestor (htmp, "axes");
        varargin(parent:parent+1) = [];
      else
        error ("%s: expecting parent value to be axes handle", caller);
      endif
    else
      error ("%s: expecting parent value to be axes handle", caller);
    endif
  else
    ## No axis specified.  Use current axis or create one as necessary.
    f = get (0, "currentfigure");
    if (isempty (f))
      h = [];
    else
      h = get (f, "currentaxes");
    endif
    if (isempty (h))
      if (nogca)
        h = NaN;
      else
        h = gca ();
      endif
    endif
    if (nargin < 2)
      varargin = {};
    endif
  endif

  if (ishandle (h) && strcmp (get (h, "nextplot"), "new"))
    h = axes ();
  endif

  narg = length (varargin);

endfunction


## No test needed for internal helper function.
%!assert (1)