## Copyright (C) 2009-2018 Søren Hauberg
##
## 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  {} {} print_usage ()
## @deftypefnx {} {} print_usage (@var{name})
## Print the usage message for the function @var{name}.
##
## When called with no input arguments the @code{print_usage} function displays
## the usage message of the currently executing function.
## @seealso{help}
## @end deftypefn

function print_usage (name)

  x = dbstack ();
  ## Handle input
  if (nargin == 0)
    ## Determine the name of the calling function
    if (numel (x) > 1)
      name = x(2).name;
    else
      error ("Octave:invalid-context", "print_usage: invalid function\n");
    endif
    fullpath = evalin ("caller", 'mfilename ("fullpath")');
    if (strcmp (fullpath(end-length(name)+1:end), name))
      fullname = [fullpath ".m"];
    endif
  elseif (! ischar (name))
    error ("Octave:invalid-input-arg",
           "print_usage: input argument must be a string");
  else
    fullname = name;
  endif

  ## Determine if we were called from top level.
  at_toplev = length (x) < 2 || (length (x) == 2 && strcmp (x(2).name, name));

  ## Do the actual work
  [text, format] = get_help_text (fullname);
  max_len = 80;
  switch (lower (format))
    case "plain text"
      [usage_string, status] = get_usage_plain_text (text, max_len);
    case "texinfo"
      [usage_string, status] = get_usage_texinfo (text, max_len);
    case "html"
      [usage_string, status] = get_usage_html (text, max_len);
    case "not documented"
      error ("print_usage: '%s' is not documented\n", name);
    case "not found"
      error ("print_usage: '%s' not found\n", name);
    otherwise
      error ("print_usage: internal error: unsupported help text format: '%s'\n", format);
  endswitch

  ## Raise the final error
  if (status != 0)
    warning ("print_usage: Texinfo formatting filter exited abnormally");
    warning ("print_usage: raw Texinfo source of help text follows...\n");
  endif

  if (at_toplev)
    error ("Octave:invalid-fun-call",
           "Invalid call to %s.  Correct usage is:\n\n%s\n%s",
           name, usage_string, __additional_help_message__ ());
  else
    msg = sprintf ("Invalid call to %s.  Correct usage is:\n\n%s",
                   name, usage_string);
    ## Ensure that the error doesn't end up with a newline, as that disables
    ## backtraces.
    if (msg(end) == "\n")
      msg(end) = " ";
    endif

    error ("Octave:invalid-fun-call", msg);
  endif

endfunction

function [retval, status] = get_usage_plain_text (help_text, max_len)
  ## Extract first line by searching for a double line-end.
  line_end_idx = strfind (help_text, "\n\n");
  retval = help_text (1:min ([line_end_idx , max_len, length(help_text)]));
  status = 0;
endfunction

function [retval, status] = get_usage_texinfo (help_text, max_len)

  ## Lines ending with "@\n" are continuation lines, so they should be
  ## concatenated with the following line.
  help_text = strrep (help_text, "@\n", " ");

  ## Find, and keep, lines that start with @def or @end def.  This should
  ## include things such as @deftypefn, @deftypefnx, @defvar, etc. and their
  ## corresponding @end's.
  def_idx = strfind (help_text, "@def");
  if (! isempty (def_idx))
    endf_idx = strfind (help_text, "@end def");
    def_idx = sort ([def_idx, endf_idx]);
    endl_idx = find (help_text == "\n");
    buffer = "";
    for k = 1:length (def_idx)
      endl = endl_idx(find (endl_idx > def_idx(k), 1));
      if (isempty (endl))
        buffer = [buffer, help_text(def_idx(k):end), "\n"];
      else
        buffer = [buffer, help_text(def_idx(k):endl)];
      endif
    endfor
  else
    [retval, status] = get_usage_plain_text (help_text, max_len);
  endif

  ## Run makeinfo to generate plain text
  [retval, status] = __makeinfo__ (buffer, "plain text");

endfunction

function [retval, status] = get_usage_html (help_text, max_len)
  ## Strip tags
  [help_text, status] = strip_html_tags (help_text);

  ## Extract first line with plain text method.
  retval = get_usage_plain_text (help_text, max_len);
endfunction


## Stop reporting function as missing tests.  No good tests possible.
%!assert (1)
