% \iffalse
% This is versonotes.dtx, which supports adding notes on verso pages,
% opposite annotation on the recto pages.  Still sketchy
%%
%% Release version 0.2, 2015 February 16.
%%
%% Copyright 2014, 2015 Norman Gray <http://nxg.me.uk>
%% 
%% This work may be distributed and/or modified under the
%% conditions of the LaTeX Project Public License, either version 1.3
%% of this license or (at your option) any later version.
%% The latest version of this license is in
%%     http://www.latex-project.org/lppl.txt
%% and version 1.3 or later is part of all distributions of LaTeX
%% version 2005/12/01 or later.
%% 
%% This work has the LPPL maintenance status `maintained'.
%% 
%% The Current Maintainer of this work is Norman Gray
%% 
%% This work consists of the files versonotes.dtx and versonotes.ins
%% and the derived file versonotes.sty.
%%
%%%% File: versonotes.dtx

%<+package|driver|example>%%%% Source: c64b7a550082, 2015-02-16T18:33:46+00:00
%%
%<+package>\NeedsTeXFormat{LaTeX2e}
%<+package>\ProvidesPackage{versonotes}[2015/02/16 v0.2]
%
%<*driver>
\documentclass{ltxdoc}
\title{versonotes: Notes on verso pages}
\author{Norman Gray\\\url{http://nxg.me.uk}}
\date{Release 0.2}
\usepackage{url}
\newcommand\Lopt[1]{\textsf {#1}} % options
\newcommand\file[1]{\texttt {#1}}
\newcommand\Lcount[1]{\textsl {\small#1}}
\newcommand\Lenv[1]{\texttt{\{#1\}}} %environments
\newcommand\Lpackage[1]{\{\textsf{#1}\}} %packages
%Make command strings easier to write
%{\catcode`\<=\active \gdef<#1>{\meta{#1}}}
{\catcode`\<=\active
  \gdef<#1>{{\ensuremath\langle\normalfont\textsl{#1}\ensuremath\rangle}}}
\def\cmd{\begingroup
 \catcode`\\=12 \catcode`\{=12 \catcode`\}=12
 \catcode`\<=\active \catcode`\|=12
 \docmd}
\def\docmd|#1|{\texttt{#1}\endgroup}
%%% \url macro (url.sty does this better)
%\def\setpathdots{\discretionary{.}{}{.}}
%\def\setpathslash{\discretionary{/}{}{/}}
%{\catcode`\.=\active
% \catcode`\/=\active
%  \gdef\pathcats{%
%    \catcode`\%=12      \catcode`\~=12
%    \catcode`\.=\active  \let.\setpathdots
%    \catcode`\/=\active \let/\setpathslash
%    \catcode`\#=12      \catcode`\_=12}%
%    }
%\def\setpath#1{\ttfamily <\nobreak #1\nobreak>\endgroup}
%\def\url{\begingroup\pathcats\setpath}

\def\bs{$\backslash$}

% Uncomment \OnlyDescription to skip the implementation
\OnlyDescription
\begin{document}
\maketitle
%\tableofcontents
%\bigskip
\DocInput{versonotes.dtx}
\end{document}
%</driver>
%
% \fi
%
% \noindent This package allows you to place notes on the verso pages
% of an otherwise single-sided document.  If, in the run
% of text, you include a call to the macro
% |\versonote{This is a remark}|,
% then that text will be placed on the opposite (ie, `verso') page,
% lined up with the macro call.
% The notes may contain more than one paragraph.
%
% All the pages in the document appear as recto pages
% (ie, right-hand pages),
% and are numbered as such;
% the document should be formatted with that in mind.
%
% Since there is no page opposite the first page, any notes which are
% positioned to appear opposite page 1 are silently discarded.
%
% To invoke the package, use the command |\usepackage{versonotes}|.
%
% The dimensions |\versoleftmargin| and |\versotextwidth| specify the
% position of the text block on the verso page.  The defaults for
% these are based on the |\textwidth| and |\evensidemargin| of the
% document at the time the package is loaded.
% By default, verso paragraphs are set ragged-left; with the
% declarations in |\versolayout| setting the paragraph parameters.
% You may reset the first two dimensions with for example
% |\versoleftmargin=4cm|, and use |\renewcommand\versolayout{...}| to
% override the paragraph formatting (this will typically require
% changing |\rightskip|, |\leftskip| and |\parfillskip|).  For more
% elaborate effects (for example changing the note font size and
% spacing), you will need to redefine |\versolayout|.
%
% If two notes come too close after one another, the second would
% overprint the first if we did not take steps to avoid this.  By
% default, they are separated from each other by a short horizontal
% line, but if the \Lopt{mergecollisions} option is provided when
% loading the package, then such notes are instead merged into a
% single block of text.  If a sequence of notes needs to be merged,
% then they will be added to the merged block one at a time in
% successive \LaTeX\ runs, since merging one note may make it
% unnecessary to merge the next.  If a large block of such notes need
% to be merged, it will therefore take several runs before the package
% finds a stable state.  If you find yourself inconvenienced by this,
% it sounds as if you are preparing a critical edition, and you might
% want to venture into a closer relationship with the
% \Lpackage{eledmac}
% package.\footnote{\texttt{http://www.ctan.org/pkg/eledmac}}
%
% \subsection*{Notes}
% \begin{itemize}
% \item The package uses the |\pdfsavepos| primitive, and so requires
% \texttt{pdflatex} or \texttt{xelatex} (and \texttt{luatex}?).
%
% \item The notes are handled using the |.aux| file, and so (i) they will
% only appear on the second and subsequent runs; and (ii) they will be
% located opposite the position where the |\versonote| macro was
% called on the \emph{previous} run.
%
% \end{itemize}
% \StopEventually{}

% \newpage
% \section{Implementation}
%
%    \begin{macrocode}
%<*package>
%    \end{macrocode}
%
% The package contains a single user-visible command, and three
% configuration parameters.
%
% Configuration options:
%    \begin{macrocode}
\def\verso@resetmergestate{\verso@mergestate=2}
\DeclareOption{mergecollisions}{\def\verso@resetmergestate{\verso@mergestate=0}}
\ProcessOptions
%    \end{macrocode}
%
% The single user-visible command is |\versonote|.
% Use |\unexpanded| (from e-\TeX) so that macros in the argument are
% not expanded into the aux file.
%    \begin{macrocode}
\long\def\versonote#1{\@bsphack
  \pdfsavepos
  \write\@auxout{\string\verso@note{\the\c@page}{\the\pdflastypos sp}\unexpanded{{#1}}}%
  \@esphack}
%    \end{macrocode}
%
% Now the layout parameters, and defaults.
% The dimensions |\versoleftmargin| and |\versotextwidth| specify the
% position of the text block on the verso page, and the declarations
% in |\versolayout| set the paragraph parameters.
%    \begin{macrocode}
\newdimen\versotextwidth
  \versotextwidth=\textwidth
\newdimen\versoleftmargin
  \versoleftmargin=\paperwidth
  \advance\versoleftmargin -\textwidth
  \advance\versoleftmargin -\evensidemargin
  \advance\versoleftmargin -\hoffset
  \advance\versoleftmargin -1in
\def\versolayout{
  \leftskip=0pt plus 1fil
  \rightskip=0pt
  \parfillskip=0pt
  \parindent=0pt
  \parskip=\medskipamount
}
%    \end{macrocode}
%
% Add a sentinel at the end of the document
%    \begin{macrocode}
\def\end@versonote{%
  \write\@auxout{\string\verso@note{\the\c@page}{-1pt}{}}}
\AtEndDocument{\end@versonote}
%    \end{macrocode}
%
% Define various bits of working storage.
%    \begin{macrocode}
\newtoks\verso@pages
\newtoks\verso@currentpage
\newcount\verso@currentpagenum
  \verso@currentpagenum=1
\newcount\verso@currentnotenum
  \verso@currentnotenum=0
\newdimen\verso@spacerskip
  \verso@spacerskip=10pt
%    \end{macrocode}
% Flag |\if@verso@processversonotes| is set true if there are any
% |\verso@note|s found in the aux file.  If there are none -- so that
% this is still false at the first |\shipout| -- then the package
% carefully does nothing.
%    \begin{macrocode}
\newif\if@verso@processversonotes
  \@verso@processversonotesfalse
%    \end{macrocode}
%
% We need to be able to calculate our position on the page.
% The |\verso@pagebottom| is the position of the bottom of the page,
% in the same coordinates as |\verso@currentposition|, and is
% (textheight + top margin + \dots).
%    \begin{macrocode}
\newdimen\verso@pagebottom
  \verso@pagebottom=1in
  \advance\verso@pagebottom \topskip
  \advance\verso@pagebottom \topmargin
  \advance\verso@pagebottom \headheight
  \advance\verso@pagebottom \headsep
  \advance\verso@pagebottom \textheight
\newdimen\verso@currentposition
%    \end{macrocode}
% The paper size options to class files set |\paperheight| but not (or
% not necessarily) |\pdfpageheight|.  If we don't set this, then
% output vertical positions will come out incorrectly if the latter
% parameter doesn't default to the right value.  The code in this package is
% specific to pdf\TeX and friends, so we don't have to conditionalise.
%    \begin{macrocode}
\pdfpageheight=\paperheight
%    \end{macrocode}
%
% Macro |\verso@note| is what's written to the aux file, and so is
% what we process on the next run, to discover the set of verso-notes
% we need to produce.
%    \begin{macrocode}
\long\def\verso@note#1#2#3{%
  \global\@verso@processversonotestrue
%    \end{macrocode}
% Store the target page number, and issue a warning if this was
% indicated to appear on the (ignored) first page; such notes are
% silently discarded below.
%    \begin{macrocode}
  \@tempcnta=#1
  \ifnum\@tempcnta=1
    \PackageWarning{versopages}{page 1 verso text will be ignored}
  \fi
%    \end{macrocode}
% Gather pages from the .aux file, assembling them into a single list
% in |\verso@pages| with one group per page, each containing a
% sequence of |\\{...}| note specifications.  This inserts empty
% groups for pages which have no verso-notes.
%    \begin{macrocode}
  \@tempdima=#2 % #2 < 0pt is the end-of-document flag
  \loop
    \@tempswafalse
    \ifnum\@tempcnta>\verso@currentpagenum \@tempswatrue \fi
    \ifdim\@tempdima < 0pt \@tempswatrue \@tempdima=0pt \fi
    \if@tempswa
      \edef\@tempa{\the\verso@pages {\the\verso@currentpage}}
      \global\verso@pages=\expandafter{\@tempa}
      \advance\verso@currentpagenum 1
      \verso@currentpage={}
  \repeat
  \verso@currentpage=\expandafter{\the\verso@currentpage \\{{#1}{#2}{#3}}}
}
%    \end{macrocode}
%
% Disable |\verso@note| in time for the end-document aux reading.
% This isn't quite necessary, but it's tidy.
%    \begin{macrocode}
\AtEndDocument{\long\def\verso@note#1#2#3{}}
%    \end{macrocode}
%
% Test whether we want to merge the current note with the following
% one.  The arguments to this macro are the contents of
% |\verso@mergenotelist|, which is assembled from the
% |\verso@mergenote| commands read from the aux file.
%    \begin{macrocode}
\def\verso@testmergenote#1,#2\@nil{
  \def\@tempa{#1}
  \ifx\@tempa\@empty
    \@tempcnta=-1
  \else
    \@tempcnta=#1
  \fi
  \advance\@tempcnta -1
  \ifnum\@tempcnta=\verso@currentnotenum
%    \end{macrocode}
% Set |\if@tempswa| true, set |\verso@mergenotelist| to the tail of
% the list, and ensure that this note is merged next time round.
%    \begin{macrocode}
    \@tempswatrue
    \xdef\verso@mergenotelist{#2}
    \immediate\write\@auxout{\string\verso@mergenote{#1}}
  \else
    \@tempswafalse
  \fi
}
%    \end{macrocode}
%
% The macro |\verso@setnote| is the one which does the work of
% positioning a single note on the (verso) page.  We potentially work
% quite hard to avoid notes overwriting each other here.  If
% |\verso@mergestate| is greater than one (by default, it's
% initialised to~2, but any number greater than~1 would be equivalent)
% then when two notes collide, we simply put a horizontal bar between
% them, and hope for the best.  Each time we have a collision we
% increment this number, and if we find it has a value~1 (ie, the
% first collision) we we record in the aux file that this note should
% be merged with its predecessor, by writing a |\verso@mergenote|
% command.  Next time round, when we are about to set the note
% \emph{before} that one, we avoid setting it, and instead start
% accumulating the text of such merged notes, in the token register
% |\verso@accumulatenote|.  We only add a single note to the list of
% merged notes on each \LaTeX\ run, since merging one note may make it
% unnecessary to merge any more.  The only way to delete the
% collections of merged notes is to delete the aux file.
%    \begin{macrocode}
\newcount\verso@mergestate
  \verso@resetmergestate
\newtoks\verso@accumulatenote
  \verso@accumulatenote={}
%    \end{macrocode}
%
% Set the note.  The arguments are (1) the page number, (2) the
% position on the page, and (3) the text of the note.
%    \begin{macrocode}
\long\def\verso@setnote#1#2#3{
  \@tempdima=\paperheight \advance\@tempdima -#2
  % target position; will become skip to add
  \@tempdimb=\verso@currentposition
  \global\advance\verso@currentnotenum 1
%    \end{macrocode}
% Check whether we're to merge the following note into this one.
%    \begin{macrocode}
  \expandafter\verso@testmergenote\verso@mergenotelist,\@nil
  \if@tempswa
    \verso@accumulatenote=\expandafter{%
      \the\verso@accumulatenote
      #3%
      \quad\P~\nobreak}
    %\PackageInfo{versonotes}{\typeout{Merging notes on p#1}}
  \else
%    \end{macrocode}
% No merging: set the current note, possibly along with any
% accumulated notes, in a box, and then start to work out where to put it.
%    \begin{macrocode}
    \setbox0=\vtop{
      \versolayout
      \the\verso@accumulatenote 
      #3\par}
    \verso@accumulatenote={}
%    \end{macrocode}
% We now know how big this box is (|\ht0|), how far down the page the
% accumulated boxes are (|\verso@currentposition|), and where the box
% is to appear, as an offset from the top of the paper (|\@tempdima|).
% Work how how much of a skip we have to add to get there.
%    \begin{macrocode}
    \ifdim\@tempdima>\verso@currentposition
%    \end{macrocode}
% The target position is below the current position; add a skip.  This
% is the straightforward case, and leaves the skip in |\@tempdima| and
% the new current position in |\@tempdimb|.
%    \begin{macrocode}
      \advance\@tempdima -\verso@currentposition
      \advance\@tempdima -\ht0
      \advance\@tempdimb \@tempdima
      \verso@resetmergestate
    \else
%    \end{macrocode}
% Or the target position is above the current position;
% thus the new material will have to be moved down
% (I'm not sure how best to handle the case where this skip results
% in the note hitting the bottom of the page.  Should it be merged
% with that case below, somehow?).
%    \begin{macrocode}
      % note: \PackageWarning seems to produce odd effects here
      \message{^^Jversonotes warning: Moved versonote text on p.#1.}
      \advance\verso@mergestate 1
      \ifnum\verso@mergestate=1
        \immediate\write\@auxout{\string\verso@mergenote{\the\verso@currentnotenum}}
      \fi
      \nointerlineskip
      \vbox to \verso@spacerskip{\vfil
        \hbox to \hsize{\hfil\vrule height 0.4pt width 10em}
        \vfil}
      \advance\@tempdimb \verso@spacerskip
      \@tempdima=0pt % ...so don't add any more skip
    \fi
    \advance\@tempdimb \ht0
    \advance\@tempdimb \dp0
%    \end{macrocode}
% Parameter |\@tempdimb| now holds the expected new value of
% |\verso@currentposition|.  Check to see if this would be beyond the bottom
% of the page, and move the text upwards in that case.
%    \begin{macrocode}
    \ifdim\@tempdimb>\verso@pagebottom
      \message{^^Jversonotes warning: versonote text on p.#1 hit bottom of page.}
      \advance\@tempdima -\@tempdimb
      \advance\@tempdima \verso@pagebottom
      \@tempdimb=\verso@pagebottom
    \fi
%    \end{macrocode}
% Finally, do the skip and add the box.
%    \begin{macrocode}
    \vskip\@tempdima
    \verso@currentposition=\@tempdimb
    \nointerlineskip
    \box0
  \fi
}
%    \end{macrocode}
%
% Log notes where a previous run has discovered they collide.
%    \begin{macrocode}
\def\verso@mergenotelist{}
\def\verso@mergenote#1{\xdef\verso@mergenotelist{\verso@mergenotelist #1,}}
%    \end{macrocode}
%
% Save the original definition of |\shipout|, prior to our
% redefining it below.  We could do this perfectly well using the
% \Lpackage{everyshi} package, but we do it by hand in order to avoid
% the extra dependency.
%    \begin{macrocode}
\let\verso@orig@shipout\shipout
%    \end{macrocode}
%
%
% Process a single page of verso-notes.
% Macro |\verso@processonepage@| consumes the next group in the
% |\verso@pages| list.  This is invoked as part of the redefined |\shipout|.
%    \begin{macrocode}
\long\def\verso@processonepage@#1#2\@nil{
  \def\@tempa{#1}
%    \end{macrocode}
% We can't have verso-notes opposite the first page.  Any notes
% which would appear in such a position are silently discarded.
%    \begin{macrocode}
  \ifnum\c@page>1
%    \end{macrocode}
% If there are no verso-notes on this page, then ship out an empty box.
%    \begin{macrocode}
    \ifx\@tempa\@empty
      \verso@orig@shipout\vbox{}
%    \end{macrocode}
% This is the normal case:
% create a box containing the |\\{...}| contents of the
% current page's verso-notes
%    \begin{macrocode}
    \else
      \begingroup
%    \end{macrocode}
% Within the box we're about to create, we have to `un-protect' things.
% Robust commands (including for example |\emph| and other font-changing commands) are
% defined using |\protect|, which in the present context, inside
% |\@outputpage|, is |\let| equal to |\noexpand|.
% We must set this to be simply |\relax|,
% as it is in the normal run of text elsewhere
% (see \url{http://tex.stackexchange.com/questions/206673/}).
%    \begin{macrocode}
        \let\protect\relax
%    \end{macrocode}
% Set everything up for setting the verso page.
%    \begin{macrocode}
        \hoffset=-1in \advance\hoffset \versoleftmargin
        \voffset=-1in
        \hsize=\versotextwidth
        \topskip=0pt
        \topmargin=0pt
        \headheight=0pt
        \headsep=0pt
        \vsize=1000mm % larger than any actual note
        \normalfont\normalsize
%    \end{macrocode}
% Construct and ship out the page contents.
%    \begin{macrocode}
        \long\def\\##1{\verso@setnote ##1}
        \verso@orig@shipout\vbox{
          \verso@currentposition=0pt
          #1}
      \endgroup
    \fi
  \fi
%    \end{macrocode}
% Finally, set |\verso@pages| to the tail of the list.
%    \begin{macrocode}
  \global\verso@pages={#2}}
%    \end{macrocode}
%
% The command |\verso@processonepage| is invoked once on every |\shipout|.
%    \begin{macrocode}
\def\verso@processonepage{
  \if@verso@processversonotes
    \expandafter\verso@processonepage@\the\verso@pages{}{}\@nil
  \else
    % we don't seem to have any versonotes in this file: don't come here again
    \global\let\verso@processonepage\relax
  \fi
}
%    \end{macrocode}
%
% And finally, redefine |\shipout|.
%    \begin{macrocode}
\def\shipout{\verso@processonepage \verso@orig@shipout}
%    \end{macrocode}
%
% That's all.
%    \begin{macrocode}
%</package>
%    \end{macrocode}
% \Finale
%
\endinput