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## -*- texinfo -*-
## @deftypefn  {} {@var{h} =} hgload (@var{filename})
## @deftypefnx {} {[@var{h}, @var{old_prop}] =} hgload (@var{filename}, @var{prop_struct})
## Load the graphics objects in @var{filename} into a vector of graphics
## handles @var{h}.
##
## If @var{filename} has no extension, Octave will try to find the file with
## and without the default extension @file{.ofig}.
##
## If provided, the elements of structure @var{prop_struct} will be used to
## override the properties of top-level objects stored in @var{filename}, and
## the saved values from @var{filename} will be stored in @var{old_prop}.
## @var{old_prop} is a cell array matching the size of @var{h}; each cell
## contains a structure of the existing property names and values before being
## overridden.
##
## @seealso{openfig, hgsave, struct2hdl}
## @end deftypefn

function [h, old_prop] = hgload (filename, prop_struct = struct ())

  ## Check number of input arguments
  if (nargin == 0)
    print_usage ();
  endif

  ## Check type of second input argument
  if (! isstruct (prop_struct))
    error ("hgload: PROP_STRUCT must be a struct");
  endif

  ## Check file existence
  [~, ~, ext] = fileparts (filename);
  if (isempty (ext))
    if (! isempty (file_in_loadpath ([filename ".ofig"])))
      filename = [filename ".ofig"];
    elseif (isempty (file_in_loadpath (filename)))
      error ("hgload: unable to locate file %s", filename);
    endif
  else
    if (isempty (file_in_loadpath (filename)))
      error ("hgload: unable to locate file %s", filename);
    endif
  endif

  ## Load the handle structure
  hgs = {"s_oct40", "hgS_050200", "hgS_070000"};
  hg = load (filename);
  fig_file_version = isfield (hg, hgs);
  if (nnz (fig_file_version) != 1)
    error ("hgload: could not load hgsave-formatted object in file %s", filename);
  endif
  hg = hg.(hgs{fig_file_version});

  ## Override properties of top-level objects
  calc_old_prop = false;
  if (isargout (2))
    calc_old_prop = true;
    old_prop = repmat ({[]}, 1, numel (hg));
  endif
  fn_new = fieldnames (prop_struct);
  if (! isempty (fn_new))
    for i = 1:numel (hg)
      fn_old = fieldnames (hg(i).properties);
      for j = 1:numel (fn_new)
        idx = ismember (tolower (fn_old), tolower (fn_new{j}));
        if (any (idx))
          if (calc_old_prop)
            old_prop{i}.(fn_new{j}) = hg(i).properties.(fn_old{idx});
          endif
          hg(i).properties.(fn_old{idx}) = prop_struct.(fn_new{j});
        endif
      endfor
    endfor
  endif

  ## Build the graphics handle object
  h = zeros (1, numel (hg));
  for i = 1:numel (hg)
    h(i) = struct2hdl (hg(i));
  endfor

endfunction


## Functional test for hgload/hgsave pair is in hgsave.m

## Test overriding saved properties with second input
%!test
%! unwind_protect
%!   h1 = figure ("visible", "off");
%!   col = get (h1, "color");
%!   ftmp = [tempname() ".ofig"];
%!   hgsave (h1, ftmp);
%!   close (h1);
%!   [h2, old] = hgload (ftmp);
%!   assert (old, {[]});
%!   [h3, old] = hgload (ftmp, struct ("color", [1 0 0]));
%!   assert (get (h3, "color"), [1 0 0]);
%!   assert (iscell (old) && numel (old) == 1);
%!   assert (isstruct (old{1}) && isfield (old{1}, "color"));
%!   assert (old{1}.color, col);
%! unwind_protect_cleanup
%!   unlink (ftmp);
%!   try, close (h1); end_try_catch
%!   try, close (h2); end_try_catch
%!   try, close (h3); end_try_catch
%! end_unwind_protect

## Test input validation
%!error <Invalid call> hgload ()
%!error <PROP_STRUCT must be a struct> hgload (1, {})
%!error <unable to locate file> hgload ("%%_A_REALLY_UNLIKELY_FILENAME_%%")
%!error <unable to locate file> hgload ("%%_A_REALLY_UNLIKELY_FILENAME_%%.fig")
