%D \module
%D   [       file=spac-pag,
%D        version=2009.10.16, % 1997.03.31, was core-spa.tex
%D          title=\CONTEXT\ Spacing Macros,
%D       subtitle=Pages,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA / Hans Hagen \& Ton Otten}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

\writestatus{loading}{ConTeXt Spacing Macros / Pages}

\unprotect

%D A quick way to determine left|/|middle|/|right states
%D (experimental).

\setvalue{\??as\v!left  }{0}
\setvalue{\??as\v!middle}{1}
\setvalue{\??as\v!right }{2}

\def\setalignmentswitch#1%
  {\chardef\alignmentswitch0\csname\??as#1\endcsname\relax}

\newcount \noftrackedpagestates
\newif    \ifpagestatemismatch
\newcount \realpagestateno
\chardef  \frozenpagestate      \zerocount

\def\dotrackpagestate#1#2%
  {\ifdoublesided \ifinpagebody \else
     \doforcedtrackpagestate{#1}{#2}%
   \fi \fi}

\def\doforcedtrackpagestate#1#2%
  {\ifcase\frozenpagestate
     \global\advance\noftrackedpagestates\plusone
     \global\advance#2\plusone
     \lazysavetaggedtwopassdata{#1}{\number\noftrackedpagestates}{\number#2}{\noexpand\realfolio}%
     %\llap{\infofont\number\noftrackedpagestates/\number#2}% tracing
   \fi}

\def\doifrightpagestateelse#1#2%
  {\ifcase\frozenpagestate
     \pagestatemismatchfalse
     \realpagestateno\realfolio
     \ifinpagebody
       \ifdoublesided
         \ifodd\realpageno\relax
           \twopassdatafoundtrue \else \twopassdatafoundfalse
         \fi
       \else
         \twopassdatafoundtrue
       \fi
     \else\ifdoublesided
       \findtwopassdata{#1}{\number#2}%
       \iftwopassdatafound
         \realpagestateno\twopassdata\relax
         \ifnum\twopassdata=\realpageno \else
           \pagestatemismatchtrue
         \fi
         \ifodd\twopassdata\relax
           \twopassdatafoundtrue \else \twopassdatafoundfalse
         \fi
       \else
         \ifodd\realpageno\relax
           \twopassdatafoundtrue \else \twopassdatafoundfalse
         \fi
       \fi
     \else
       \twopassdatafoundtrue
     \fi\fi
   \else
     \ifodd\realpagestateno\relax
       \twopassdatafoundtrue \else \twopassdatafoundfalse
     \fi
   \fi
   \iftwopassdatafound
     \@EA\firstoftwoarguments
   \else
     \@EA\secondoftwoarguments
   \fi}

\def\doifforcedrightpagestateelse#1#2%
  {\ifcase\frozenpagestate
     \pagestatemismatchfalse
     \realpagestateno\realfolio
     \findtwopassdata{#1}{\number#2}%
     \iftwopassdatafound
       \realpagestateno\twopassdata\relax
       \ifnum\twopassdata=\realpageno \else
         \pagestatemismatchtrue
       \fi
       \ifodd\twopassdata\relax
         \twopassdatafoundtrue \else \twopassdatafoundfalse
       \fi
     \else
       \ifodd\realpageno\relax
         \twopassdatafoundtrue \else \twopassdatafoundfalse
       \fi
     \fi
   \else
     \ifodd\realpagestateno\relax
       \twopassdatafoundtrue \else \twopassdatafoundfalse
     \fi
   \fi
   \iftwopassdatafound
     \@EA\firstoftwoarguments
   \else
     \@EA\secondoftwoarguments
   \fi}

\def\freezepagestate {\chardef\frozenpagestate\plusone  }
\def\defrostpagestate{\chardef\frozenpagestate\zerocount}

% we can make more of these on top, but how to deal with mixed frozen states

\definetwopasslist\s!paragraph \newcount \nofraggedparagraphs

\def\signalrightpage  {\dotrackpagestate      \s!paragraph\nofraggedparagraphs}
\def\doifrightpageelse{\doifrightpagestateelse\s!paragraph\nofraggedparagraphs}

\newcount\pagesignallevel

\unexpanded\def\startsignalrightpage % one may do a \postsignalrightplace
  {\advance\pagesignallevel\plusone
   \presignalrightpage
   \let\signalrightpage\relax
   \let\presignalrightpage\relax
   \let\startsignalrightpage\relax
   \doifrightpageelse\donothing\donothing
   \freezepagestate}

\unexpanded\def\stopsignalrightpage
  {\ifcase\pagesignallevel\or\postsignalrightpage\fi
   \advance\pagesignallevel\minusone}

\def\setraggedparagraphmode
  {\signalrightpage\doifrightpageelse} % move it there

\ifx\swapmargins\undefined \let\swapmargins\undefined \fi % todo

\def\doifswappedrightpageelse#1#2% alleen in box construction !
  {\doifrightpageelse
     {#1}
     {\scratchcounter\realpageno
      \realpageno\realpagestateno\relax
      \swapmargins
      \realpageno\scratchcounter
      #2}}

\newbox\signaledrightpage % this way we can avoid interference, i.e. postpone placement

\def\presignalrightpage {\global\setbox\signaledrightpage\hbox{\signalrightpage}}
\def\postsignalrightpage{\ifvoid\signaledrightpage\else\box\signaledrightpage\fi}

% The next feature is is used in:
%
% \definenumber[test][way=bypage]
%
% \def\Test
%   {\incrementnumber[test]\rawnumber[test]/%
%    \incrementnumber[test]\rawnumber[test]/%
%    \incrementnumber[test]\rawnumber[test]\space
%    \checkpagechange{oeps}\changedpage{oeps}\space
%    \ifpagechanged TRUE\else FALSE\fi}
%
% \Test\page \Test\par \Test\page \Test\par \Test\page \Test\page
%
% (adapted from cont-new.tex:)

\newif\ifpagechanged \let\lastchangedpage\empty

\def\docheckpagestatechange#1#2#3%
  {\pagechangedfalse
   \doforcedtrackpagestate{#2}{#3}%
   \findtwopassdata{#2}{\number#3}%
   \iftwopassdatafound
     \ifnum\twopassdata>0\getvalue{#2:p:#1}\relax
       \pagechangedtrue
     \fi
   \fi
   \ifpagechanged
     \letgvalue{#2:p:#1}\twopassdata
     \globallet\lastchangedpage\twopassdata
   \else
     \globallet\lastchangedpage\realfolio
   \fi}

\def\changedpagestate#1#2%
  {\executeifdefined{#2:p:#1}{0}}

\def\checkpagechange#1{\docheckpagestatechange{#1}\s!paragraph\nofraggedparagraphs}
\def\changedpage    #1{\changedpagestate{#1}\s!paragraph}

\protect \endinput