## Copyright (C) 2008 Soren Hauberg
##
## This program 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.
##
## This program 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 this program; see the file COPYING.  If not, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} address@hidden =} get_first_help_sentence (@var{name}, @var{max_len})
## Return the first sentence of a function help text.
##
## The function reads the first sentence of the help text of the function
## @var{name}. The first sentence is defined as the text after the function
## declaration until either the first period (".") or the first appearance of
## two consecutive end-lines ("\n\n"). The text is truncated to a maximum length
## of @var{max_len}, which defaults to 80.
##
## As an example, the first sentence of this help text is
##
## @example
## get_first_help_sentence ("get_first_help_sentence")
## @print{} ans = Return the first sentence of a function help text.
## @end example
## @end deftypefn

function retval = get_first_help_sentence (name, max_len = 80)
  ## Check input
  if (nargin == 0)
    error ("get_first_help_sentence: not enough input arguments");
  endif
  
  if (!ischar (name))
    error ("get_first_help_sentence: first input must be a string");
  endif
  
  if (!isnumeric (max_len) || max_len <= 0 || max_len != round (max_len))
    error ("get_first_help_sentence: second input must be positive integer");
  endif

  ## First, we get the raw help text
  [help_text, format] = get_help_text (name);
  
  ## Then, we take action depending on the format
  switch (lower (format))
    case "plain text"
      retval = first_sentence_plain_text (help_text, max_len);
    case "texinfo"
      retval = first_sentence_texinfo (help_text, max_len);
    case "not found"
      error ("get_first_help_sentence: `%s' not found\n", name);
    otherwise
      error ("get_first_help_sentence: internal error: unsupported help text format: '%s'\n", format);
  endswitch
endfunction

## This function extracts the first sentence from a plain text help text
function retval = first_sentence_plain_text (help_text, max_len)
  ## Extract first line by searching for a period or a double line-end.
  period_idx = find (help_text == ".", 1);
  line_end_idx = strfind (help_text, "\n\n");
  retval = help_text (1:min ([period_idx, line_end_idx , max_len, length(help_text)]));
endfunction

## This function extracts the first sentence from a Texinfo help text.
## The function works by removing @def* from the texinfo text. After this, we
## render the text to plain text using makeinfo, and then extract the first line.
function retval = first_sentence_texinfo (help_text, max_len)
  ## Find, and remove, lines that start with @def. This should remove things
  ## such as @deftypefn, @deftypefnx, @defvar, etc.
  keep = true (size (help_text));
  def_idx = strfind (help_text, "@def");
  if (!isempty (def_idx))
    endl_idx = find (help_text == "\n");
    for k = 1:length (def_idx)
      endl = endl_idx (find (endl_idx > def_idx (k), 1));
      if (isempty (endl))
        keep (def_idx (k):end) = false;
      else
        keep (def_idx (k):endl) = false;
      endif
    endfor
  
    ## Remove the @end ... that corresponds to the @def we removed above
    def1 = def_idx (1);
    space_idx = find (help_text == " ");
    space_idx = space_idx (find (space_idx > def1, 1));
    bracket_idx = find (help_text == "{" | help_text == "}");
    bracket_idx = bracket_idx (find (bracket_idx > def1, 1));
    if (isempty (space_idx) && isempty (bracket_idx))
      error ("get_first_help_sentence: couldn't parse texinfo");
    endif
    sep_idx = min (space_idx, bracket_idx);
    def_type = help_text (def1+1:sep_idx-1);

    end_idx = strfind (help_text, sprintf ("@end %s", def_type));
    if (isempty (end_idx))
      error ("get_first_help_sentence: couldn't parse texinfo");
    endif
    endl = endl_idx (find (endl_idx > end_idx, 1));
    if (isempty (endl))
      keep (end_idx:end) = false;
    else
      keep (end_idx:endl) = false;
    endif
    
    help_text = help_text (keep);
  endif
  
  ## Run makeinfo to generate plain text
  [help_text, status] = makeinfo (help_text, "plaintext");
  if (status != 0)
    error ("get_first_help_sentence: couldn't run makeinfo");
  endif
  
  ## Extract first line with plain text method.
  retval = first_sentence_plain_text (help_text, max_len);
endfunction