%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 ADE \& \CONTEXT\ Development Team}]
%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 The code here has evolved over time and might not be the best
%D around. Maybe much will be gone a some point.

\installcorenamespace {alignswitch}

\letvalue{\??alignswitch\v!left  }\zerocount
\letvalue{\??alignswitch\v!middle}\plusone
\letvalue{\??alignswitch\v!right }\plustwo

\def\setalignmentswitch#1%
  {\chardef\alignmentswitch\csname\??alignswitch\ifcsname\??alignswitch#1\endcsname#1\else\v!left\fi\endcsname}

\newcount   \noftrackedpagestates
\newif      \ifpagestatemismatch
\newcount   \realpagestateno
\newconstant\frozenpagestate

\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% not expandable !
  {\ifcase\frozenpagestate
     \pagestatemismatchfalse
     \realpagestateno\realfolio
     \ifinpagebody
       \ifdoublesided
         \ifodd\realpageno\relax
           \syst_twopass_set_found
         \else
           \syst_twopass_set_not_found
         \fi
       \else
         \syst_twopass_set_found
       \fi
     \else\ifdoublesided
       \findtwopassdata{#1}{\number#2}%
       \ifconditional\twopassdatafound
         \realpagestateno\twopassdata\relax
         \ifnum\twopassdata=\realpageno \else
           \pagestatemismatchtrue
         \fi
         \ifodd\twopassdata\relax
           \syst_twopass_set_found
         \else
           \syst_twopass_set_not_found
         \fi
       \else
         \ifodd\realpageno\relax
           \syst_twopass_set_found
         \else
           \syst_twopass_set_not_found
         \fi
       \fi
     \else
       \syst_twopass_set_found
     \fi\fi
   \else
     \ifodd\realpagestateno\relax
       \syst_twopass_set_found
     \else
       \syst_twopass_set_not_found
     \fi
   \fi
   \ifconditional\twopassdatafound
     \expandafter\firstoftwoarguments
   \else
     \expandafter\secondoftwoarguments
   \fi}

\def\doifforcedrightpagestateelse#1#2%
  {\ifcase\frozenpagestate
     \pagestatemismatchfalse
     \realpagestateno\realfolio
     \findtwopassdata{#1}{\number#2}%
     \ifconditional\twopassdatafound
       \realpagestateno\twopassdata\relax
       \ifnum\twopassdata=\realpageno \else
         \pagestatemismatchtrue
       \fi
       \ifodd\twopassdata\relax
         \syst_twopass_set_found
       \else
         \syst_twopass_set_not_found
       \fi
     \else
       \ifodd\realpageno\relax
         \syst_twopass_set_found
       \else
         \syst_twopass_set_not_found
       \fi
     \fi
   \else
     \ifodd\realpagestateno\relax
       \syst_twopass_set_found
     \else
       \syst_twopass_set_not_found
     \fi
   \fi
   \ifconditional\twopassdatafound
     \expandafter\firstoftwoarguments
   \else
     \expandafter\secondoftwoarguments
   \fi}

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

% no longer used
%
% \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}
%
% \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

\installcorenamespace{pagechanges}

\newif\ifpagechanged \let\lastchangedpage\empty

\def\spac_pagechanges_check#1#2#3%
  {\pagechangedfalse
   \doforcedtrackpagestate{#2}{#3}%
   \findtwopassdata{#2}{\number#3}%
   \ifconditional\twopassdatafound
     \ifnum\twopassdata>0\getvalue{\??pagechanges#2:#1}\relax
       \pagechangedtrue
     \fi
   \fi
   \ifpagechanged
     \letgvalue{\??pagechanges#2:#1}\twopassdata
     \globallet\lastchangedpage\twopassdata
   \else
     \globallet\lastchangedpage\realfolio
   \fi}

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

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

\protect \endinput