## -*- texinfo -*-
## @deffn {Command} lookfor @var{str}
## @deffnx {Command} lookfor -all @var{str}
## @deffnx {Function} address@hidden, @var{helpstring}] = } lookfor (@var{str})
## @deffnx {Function} address@hidden, @var{helpstring}] = } lookfor ('-all', @var{str})
## Search for the string @var{str} in all of the functions found in the
## function search path.  By default @code{lookfor} searches for @var{str}
## in the first sentence of the help string of each function found. The entire
## help string of each function found in the path can be searched if
## the '-all' argument is supplied. All searches are case insensitive.
## 
## Called with no output arguments, @code{lookfor} prints the list of matching
## functions to the terminal. Otherwise the output arguments @var{fun} and
## @var{helpstring} define the matching functions and the first sentence of
## each of their help strings.
## 
## Note that the ability of @code{lookfor} to correctly identify the first
## sentence of the help of the functions is dependent on the format of the
## functions help. All of the functions in Octave itself will correctly
## find the first sentence, but the same can not be guaranteed for other
## functions. Therefore the use of the '-all' argument might be necessary
## to find related functions that are not part of Octave.
## @seealso{help, which}
## @end deffn

function [out_fun, out_help_text] = mylookfor (str, extra)
  if (strcmpi (str, "-all"))
    ## The difference between using '-all' and not, is which part of the caches
    ## we search. The cache is organised such that its first column contains
    ## the function name, its second column contains the full help text, and its
    ## third column contains the first sentence of the help text.
    str = extra;
    search_type = 2; # when using caches, search its second column
  else
    search_type = 3; # when using caches, search its third column
  endif
  str = lower (str);
  
  fun = help_text = {};
  p = path ();
  idx = find (p == pathsep ());
  prev_idx = 1;
  for n = 1:length (idx)
    f = p (prev_idx:idx (n)-1);
    cache_file = fullfile (f, "help_cache.mat");
    if (exist (cache_file, "file"))
      ## We have a cache. Read it and search it!
      load (cache_file);
      if (! isempty(cache))
        tmp = strfind (cache (search_type, :), str);
        cache_idx = find (!cellfun ("isempty", tmp));
        fun (end+1:end+length (cache_idx)) = cache (1, cache_idx);
        help_text (end+1:end+length (cache_idx)) = cache (3, cache_idx);
      endif
    else
      ## We don't have a cache. Search files
      funs_in_f = list_functions (f);
      for m = 1:length (funs_in_f)
        fn = funs_in_f {m}.name;
        
        ## Extract first sentence
        try
          first_sentence = get_first_help_sentence (fn);
          status = 0;
        catch
          status = 1;
        end_try_catch

        if (search_type == 2) # search entire help text
          [text, format] = get_help_text (fn);
    
          ## Take action depending on help text format
          switch (lower (format))
            case "plain text"
              status = 0;
            case "texinfo"
              [text, status] = makeinfo (text, "plaintext");
            otherwise
              status = 1;
          endswitch

        else # only search the first sentence of the help text
          text = first_sentence;
        endif
        
        ## Search the help text, if we can
        if (status == 0 && !isempty (strfind (text, str)))
          fun (end+1) = fn;
          help_text (end+1) = first_sentence;
        endif
      endfor
    endif
    prev_idx = idx (n) + 1;
  endfor
  
  if (nargout == 0)
    ## Print the results (XXX: improve this to make it look better.
    indent = 25;
    term_width = terminal_size() (2);
    desc_width = term_width - indent;
    indent_space = repmat (" ", 1, indent);
    for k = 1:length (fun)
      f = fun {k};
      f (end+1:indent) = " ";
      printf (f);
      desc = strtrim (strrep (help_text {k}, "\n", " "));
      ldesc = length (desc);
      printf ("%s\n", desc (1:min (desc_width, ldesc)));
      for start = desc_width+1:desc_width:ldesc
        stop = min (start + desc_width, ldesc);
        printf ("%s%s\n", indent_space, strtrim (desc (start:stop)));
      endfor
    endfor

  else
    ## Return the results instead of displaying them
    out_fun = fun;
    out_help_text = help_text;
  endif
endfunction