## Copyright (C) 2000-2012 Paul Kienzle
##
## 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
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn  {Command} {} demo @var{name}
## @deftypefnx {Command} {} demo @var{name} @var{n}
## @deftypefnx {Function File} {} demo ('@var{name}')
## @deftypefnx {Function File} {} demo ('@var{name}', @var{n})
##
## Run example code block @var{n} associated with the function @var{name}.
## If @var{n} is not specified, all examples are run.
##
## Examples are stored in the script file, or in a file with the same
## name but no extension located on Octave's load path.  To keep examples
## separate from regular script code, all lines are prefixed by @code{%!}.  Each
## example must also be introduced by the keyword 'demo' flush left to the
## prefix with no intervening spaces.  The remainder of the example can
## contain arbitrary Octave code.  For example:
##
## @example
## @group
##   %!demo
##   %! t=0:0.01:2*pi; x = sin(t);
##   %! plot (t,x)
##   %! %-------------------------------------------------
##   %! % the figure window shows one cycle of a sine wave
## @end group
## @end example
##
## Note that the code is displayed before it is executed, so a simple
## comment at the end suffices for labeling what is being shown.  It is
## generally not necessary to use @code{disp} or @code{printf} within the demo.
##
## Demos are run in a function environment with no access to external
## variables.  This means that every demo must have separate initialization
## code.  Alternatively, all demos can be combined into a single large demo
## with the code
##
## @example
##    %! input("Press <enter> to continue: ","s");
## @end example
##
## @noindent
## between the sections, but this is discouraged.  Other techniques
## to avoid multiple initialization blocks include using multiple plots
## with a new @code{figure} command between each plot, or using @code{subplot}
## to put multiple plots in the same window.
##
## Also, because demo evaluates within a function context, you cannot
## define new functions inside a demo.  If you must have function blocks,
## rather than just anonymous functions or inline functions, you will have to
## use @code{eval(example('function',n))} to see them.  Because eval only
## evaluates one line, or one statement if the statement crosses
## multiple lines, you must wrap your demo in "if 1 <demo stuff> endif"
## with the 'if' on the same line as 'demo'.  For example:
##
## @example
## @group
##   %!demo if 1
##   %!  function y=f(x)
##   %!    y=x;
##   %!  endfunction
##   %!  f(3)
##   %! endif
## @end group
## @end example
##
## @seealso{test, example}
## @end deftypefn

## FIXME: modify subplot so that gnuplot_has_multiplot == 0 causes it to
## use the current figure window but pause if not plotting in the
## first subplot.

function demo (name, n)

  if (nargin < 1 || nargin > 2)
    print_usage ();
  endif

  if (nargin < 2)
    n = 0;
  elseif (ischar (n))
    n = str2double (n);
  endif

  [code, idx] = test (name, "grabdemo");
  if (isempty (idx))
    warning ("no demo available for %s", name);
    return;
  elseif (n >= length (idx))
    warning ("only %d demos available for %s", length (idx) - 1, name);
    return;
  endif

  if (n > 0)
    doidx = n;
  else
    doidx = 1:length(idx)-1;
  endif
  for i = 1:length (doidx)
    ## Pause between demos
    if (i > 1)
      input ("Press <enter> to continue: ", "s");
    endif

    ## Process each demo without failing
    try
      block = code(idx(doidx(i)):idx(doidx(i)+1)-1);
      ## FIXME: need to check for embedded test functions, which cause
      ## segfaults, until issues with subfunctions in functions are resolved.
      embed_func = regexp (block, '^\s*function ', 'once', 'lineanchors');
      if (isempty (embed_func))
        ## Use an environment without variables
        eval (cstrcat ("function __demo__()\n", block, "\nendfunction"));
        ## Display the code that will be executed before executing it
        printf ("%s example %d:%s\n\n", name, doidx(i), block);
        __demo__;
      else
        error (["Functions embedded in %!demo blocks are not allowed.\n", ...
                "Use the %!function/%!endfunction syntax instead to define shared functions for testing.\n"]);
      endif
    catch
      ## Let the programmer know which demo failed.
      printf ("%s example %d: failed\n%s\n", name, doidx(i), lasterr ());
    end_try_catch
    clear __demo__;
  endfor

endfunction

%!demo
%! t=0:0.01:2*pi; x = sin(t);
%! plot (t,x)
%! %-------------------------------------------------
%! % the figure window shows one cycle of a sine wave

%!error demo ();
%!error demo (1, 2, 3);