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## Copyright (C) 2013-2025 The Octave Project Developers
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## -*- texinfo -*-
## @deftypefn {} {[filename, ext, cmap, options] =} imwrite_filename (@var{varargin})
##
## The input check for @code{imwrite} needs to be done twice, once when
## @code{imwrite} is called the first time to find where the filename is, and a
## second time by @code{__imwrite__} after imformats decides what function to
## use.  Because a user can, and is encouraged to, get a function handle to
## @code{__imwrite__}, the input check is also done there.
##
## In addition, the input check for @code{imwrite} is not that straightforward
## in order to support the multiple ways the function can be called, and
## interpretations of @sc{matlab} documentation.
##
## Anyway, this will only do the input check until it finds the filename
## to be used, the only part that @code{imwrite} actually needs.
## @seealso{imwrite}
## @end deftypefn

function [filename, ext, cmap, options] = imwrite_filename (varargin)

  ## First, we check if the first argument is a colormap or a filename.
  cmap = [];
  if (ischar (varargin{1}))
    filename_idx = 1;
  elseif (numel (varargin) >= 2
          && iscolormap (varargin{1}) && ischar (varargin{2}))
    filename_idx = 2;
    cmap = varargin{1};
  else
    error ("imwrite: no FILENAME specified");
  endif
  filename = tilde_expand (varargin{filename_idx});

  ## Next, we get the file extension.
  ## if we have an odd number of leftover arguments, and the next argument
  ## is a string, we consider it the file extension.  Otherwise we will
  ## extract what we can from the previously found filename.
  options_idx = filename_idx + 1;
  if (numel (varargin) > filename_idx
      && rem (length (varargin) - filename_idx, 2) != 0
      && ischar (varargin{filename_idx + 1}))
    ext = varargin{filename_idx + 1};
    options_idx += 1;
  else
    [~, ~, ext] = fileparts (filename);
    if (! isempty (ext))
      ## remove dot from extension
      ext = ext(2:end);
    endif
  endif

  ## After all the work finding where the filename was, we might as well
  ## send the leftovers list (they should be in key value pairs)
  options = varargin(options_idx:end);

endfunction
