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########################################################################
##
## Copyright (C) 2013-2024 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## 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
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {@var{varargout} =} imageIO (@var{fcn}, @var{core_fcn}, @var{fieldname}, @var{filename}, @var{varargin})
##
## This function bridges the image input functions @code{imread} and
## @code{imfinfo} to the functions that will actually be used, based on their
## format. See below for the details on how it identifies the format, and what
## the defaults are.
##
## It will change the input arguments that were passed to @code{imread} and
## @code{imfinfo}. It will change the filename to provide the absolute
## filepath for the file, it will extract the possible format name from the
## rest of the input arguments (in case there was one), and will give an error
## if the file can't be found.
##
## Usage:
##
## @table @var
## @item fcn
## Function name to use in error message.
##
## @item core_fcn
## Function handle for the default function to use if we can't find the format
## in imformats.
##
## @item fieldname
## Name of the field in the struct returned by imformats that has the function
## to use.
##
## @item filename
## Most likely the first input argument from the function that called this.
## May be missing the file extension which can be on varargin.
##
## @item varargin
## Followed by all the OTHER arguments passed to imread and imfinfo.
## @end table
##
## @seealso{imread, imwrite}
## @end deftypefn
function varargout = imageIO (fcn, core_fcn, fieldname, filename, varargin)
## First thing: figure out the filename and possibly download it.
## The first attempt is to try the filename and see if it exists. If it
## does not, we try to add the next argument since the file extension can
## be given as a separate argument. If we still can't find the file, it
## can be a URL. Lastly, if we still didn't found a file, try adding the
## extension to the URL
file_2_delete = false; # will we have to remove the file in the end?
persistent abs_path = @(x) file_in_path (IMAGE_PATH, tilde_expand (x));
## Filename was given with file extension
fn = abs_path (filename);
if (isempty (fn) && ! isempty (varargin))
## Maybe if we add a file extension?
fn = abs_path ([filename "." varargin{1}]);
endif
## Maybe we have a URL
if (isempty (fn)
&& ! isempty (regexp (filename, '^[a-zA-Z][a-zA-Z0-9.+-]+:')))
file_2_delete = true; # mark file for deletion
[fn, ~] = urlwrite (filename, tempname ());
## Maybe the URL is missing the file extension?
if (isempty (fn) && ! isempty (varargin))
[fn, ~] = urlwrite ([filename "." varargin{1}], tempname ());
endif
endif
if (isempty (fn))
error ([fcn ": unable to find file '" filename "'"]);
endif
## unwind_protect block because we may have a file to remove in the end
unwind_protect
## When guessing the format to use, we first check if the second
## argument is a format defined in imformats. If so, we remove it
## from the rest of arguments before passing them on. If not, we
## try to guess the format from the file extension. Finally, if
## we still don't know the format, we use the Octave core functions
## which is the same for all formats.
hfcn = []; # the function we will use
## We check if the call to imformats (ext) worked using
## "numfields (fmt) > 0 because when it fails, the returned
## struct is not considered empty.
## try the second input argument
if (! isempty (varargin) && ischar (varargin{1}))
fmt = imformats (varargin{1});
if (numfields (fmt) > 0)
hfcn = fmt.(fieldname);
varargin(1) = []; # remove format name from arguments
endif
endif
## try extension from filename
if (isempty (hfcn))
[~, ~, ext] = fileparts (fn);
if (! isempty (ext))
## remove dot from extension
ext = ext(2:end);
endif
fmt = imformats (ext);
if (numfields (fmt) > 0)
hfcn = fmt.(fieldname);
endif
endif
## use the core function
if (isempty (hfcn))
hfcn = core_fcn;
endif
[varargout{1:nargout}] = hfcn (fn, varargin{:});
unwind_protect_cleanup
if (file_2_delete)
unlink (fn);
endif
end_unwind_protect
endfunction
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