%D \module
%D   [       file=page-flw,
%D        version=2003.04.19, % from test-002 (1997) profile experiment
%D          title=\CONTEXT\ Page Macros,
%D       subtitle=Text Flows,
%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 Page Macros / Text Flows}

%D This is high experimental and especially flushing may change (proper
%D spacing is the driving force here). It's an old mechanism used for
%D playing with stepping through document threads. As it's a simple and
%D effective mechanism we keep it around. It's not to be confused with
%D upcoming stream support.
%D
%D \starttyping
%D \setuppapersize [S6]
%D \setuptolerance [verytolerant,stretch]
%D \setupfooter    [strut=no]
%D \setupwhitespace[big]
%D
%D \setuplayout
%D   [rightedge=5cm,width=fit,margin=0pt,edgedistance=1cm,
%D    footer=4cm,footerdistance=1cm,header=0cm]
%D
%D \setuptexttexts  [edge][][\vbox{\flushtextflow{alpha}}]
%D \setupfootertexts[edge][][\vbox{\flushtextflow{beta}}]
%D \setupfootertexts        [\vbox{\flushtextflow{gamma}}][]
%D
%D \definetextflow [alfa]  [width=\rightedgewidth]
%D \definetextflow [beta]  [width=\rightedgewidth]
%D \definetextflow [gamma] [width=\footerheight]
%D
%D \starttext
%D
%D \dorecurse{50}
%D   {\getrandomnumber{\funny}{0}{8}
%D    \ifcase\funny \starttextflow[alfa]  \input tufte.tex   \stoptextflow
%D    \or           \starttextflow[beta]  \input knuth.tex   \stoptextflow
%D    \or           \starttextflow[gamma] \input materie.tex \stoptextflow
%D    \or          {\bf   TUFTE}\quad \input tufte   \par
%D    \or          {\bf   TUFTE}\quad \input tufte   \par
%D    \or          {\bf   KNUTH}\quad \input knuth   \par
%D    \or          {\bf   KNUTH}\quad \input knuth   \par
%D    \or          {\bf MATERIE}\quad \input materie \par
%D    \else        {\bf MATERIE}\quad \input materie \par
%D    \fi}
%D
%D \stoptext
%D \stoptyping

\unprotect

\installcorenamespace{textflow}
\installcorenamespace{textflowbox}

\installcommandhandler \??textflow {textflow} \??textflow

\setuptextflow
  [%c!style=,
   %c!color=,
   \c!width=\availablehsize]

\appendtoks
    \ifcsname\??textflowbox\currenttextflow\endcsname
       \setbox\csname\??textflowbox\currenttextflow\endcsname\emptybox
    \else
       \expandafter\newbox\csname\??textflowbox\currenttextflow\endcsname
    \fi
\to \everydefinetextflow

\newcount\b_page_textflow_box

\def\textflowcollector#1%
  {\csname\??textflowbox#1\endcsname}

\unexpanded\def\doifelsetextflowcollector#1%
  {\ifcsname\??textflowbox#1\endcsname
     \expandafter\firstoftwoarguments
   \else
     \expandafter\secondoftwoarguments
   \fi}

\unexpanded\def\doifelsetextflow#1%
  {\ifcsname\??textflowbox#1\endcsname
     \ifvoid\csname\??textflowbox#1\endcsname
       \doubleexpandafter\secondoftwoarguments
     \else
       \doubleexpandafter\firstoftwoarguments
     \fi
   \else
     \expandafter\secondoftwoarguments
   \fi}

\let\doiftextflowcollectorelse\doifelsetextflowcollector
\let\doiftextflowelse         \doifelsetextflow

% \unexpanded\def\doiftextflow#1%
%   {\doiftextflowelse{#1}\firstofoneargument\gobbleoneargument}

\unexpanded\def\starttextflow[#1]%
  {\begingroup
   \edef\currenttextflow{#1}%
   \ifcsname\??textflowbox\currenttextflow\endcsname
     \b_page_textflow_box\csname\??textflowbox\currenttextflow\endcsname
     \global\setbox\b_page_textflow_box\vbox
       \bgroup
       \dontcomplain
       \ifvoid\b_page_textflow_box\else
         \unvbox\b_page_textflow_box
       \fi
       \hsize\textflowparameter\c!width\relax
       \usetextflowstyleandcolor\c!style\c!color
       \unexpanded\def\stoptextflow{\endgraf\egroup\endgroup}%
   \else
     \let\stoptextflow\endgroup
   \fi}

\unexpanded\def\flushtextflow#1%
  {\begingroup
   \edef\currenttextflow{#1}%
   \ifcsname\??textflowbox\currenttextflow\endcsname
     \b_page_textflow_box\csname\??textflowbox\currenttextflow\endcsname
     \ifvoid\b_page_textflow_box
       % sorry
     \else\ifdim\ht\b_page_textflow_box>\vsize
        \setbox\scratchbox\vsplit\b_page_textflow_box to \vsize
        \ifvoid\scratchbox\else
          \unvbox\scratchbox
        \fi
      \else
        \unvbox\b_page_textflow_box
      \fi\fi
   \fi
   \endgroup}

\protect \endinput

% \setuppapersize [A6]
% \setupbodyfont [pagella, 12pt]
%
% \definetextflow [even]  [width=\textwidth]
% \definetextflow [odd]   [width=\textwidth]
%
% \starttextflow [even] \dorecurse{15}{\input bryson} \stoptextflow
% \starttextflow [odd]  \dorecurse {5}{\input knuth } \stoptextflow
%
% \starttext
%
% \doloop {
%     \ifodd\realpageno
%         \doiftextflowelse{odd} {
%             \bgroup
%             \vsize\dimexpr\textheight-\strutdp\relax
%             \flushtextflow{odd}
%             \egroup
%         } {
%             \null
%         }
%         \page
%     \else
%         \doiftextflowelse{even} {
%             \bgroup
%             \vsize\dimexpr\textheight-\strutdp\relax
%             \flushtextflow{even}
%             \egroup
%         } {
%           \null
%         }
%         \page
%     \fi
%     \doiftextflowelse{even}\donothing{\doiftextflowelse{odd}\donothing\exitloop}
% }
%
% \stoptext