%
% switcheml.sty
%
% Charles Duan (2004/02/10)
%
% Obfuscates an e-mail address so that it is unreadable by automated document
% crawlers but appears correct when displayed.
%
% Commands provided by this package are:
%
% \switchemail{EMAIL}
%   Obfuscates EMAIL by reversing on the @ and . symbols, so
%       some@one.place.com
%   will be written to the document as:
%       com place. one. some@
%   but it will appear properly on the document page.
%
% \switch{DELIM}{TEXT}
%   Obfuscates TEXT by reversing values around DELIM, so
%       \switch{,}{abc,def,ghi,jkl}
%   will be written to the document as:
%       jkl ghi, def, abc
%   but it will appear on the document page as:
%       abc,def,ghi,jkl
%
% \kernhack{A}{B}
%   Produces a kern equivalent to the kern that would normally appear between A
%   and B.
%   
\ProvidesPackage{switcheml}[2004/02/10 Obfuscate e-mail addresses]
% Produce a kern equivalent to the kern between #1 and #2
\def\kernhack#1#2{%
    \begingroup
	\setbox\z@\hbox{#1#2}%
	\dimen@\wd\z@
	\setbox\z@\hbox{#1{}#2}\advance\dimen@-\wd\z@
	\ifdim\dimen@=\z@\else\kern\dimen@\fi
    \endgroup
}
% Given a character to find (e.g., period) and a string of text, obfuscate the
% text so that the last part of the text is placed first, etc., so everything
% comes up in reverse order when you try to copy/paste but it looks fine on
% screen. For instance,
%
% some.domain.com
%
% is rewritten as:
%
% box{com} box{domain.} box{some.}
%
% with each of the boxes placed such that they print out properly.
%
\def\switch#1#2{%
    \begingroup
	\def\@switch##1#1##2\@nil#1##3\@stop{%
	    \def\reserved@a{##3}%
	    \ifx\reserved@a\@empty#2\else
		\setbox\z@\hbox{##1#1}%
		\setbox\tw@\hbox{\kernhack{#1}{##2}\switch{#1}{##2}}%
		\dimen@\wd\tw@\advance\dimen@\wd\z@%
		\wd\z@\dimen@%
		\rlap{\hb@xt@\dimen@{\hfil\unhbox\tw@}}%
		\box\z@
	    \fi
	}%
	\@switch#2\@nil#1\@nil#1\@stop
    \endgroup
}
% Given an e-mail address of the form abc@def.ghi.jkl, reverses it to be jkl
% ghi. def. abc@
\def\switchemail#1{%
    \expandafter\@switchemail#1\@stop
}
% Helper function for \switchemail. Note the \copy, because \kernhack will
% destroy the box otherwise. Need to do some funky stuff because of catcodes.
\begingroup
    \makeatother
    \def\tmp#1#2#3{%
	\gdef#1##1@##2#2{%
	    \begingroup
		\setbox#3\hbox{\switch{.}{##2}}%
		\switch{@}{##1@\copy#3}%
	    \endgroup
	}%
    }
    \makeatletter
    \tmp\@switchemail\@stop\@tempboxa
\endgroup

\endinput