%D \module
%D   [       file=page-blk,
%D        version=2022.06.04,
%D          title=\CONTEXT\ Page Macros,
%D       subtitle=Shuffling 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 Page Macros / Shuffling pages}

%D This is a somewhat tricky module and although we have a somewhat abstract
%D interface we are pretty much bound to \PDF\ output here. When large amounts of
%D documents are to be generated and|/|or when saving a run makes sense the table
%D of contents can be typeset at the end and moved to the beginning. However, it
%D assumes a rather stable and predictable rendering. Don't use this without
%D checking it really works out well.
%D
%D The low level backend code has been around for quite a while but we never had
%D a real (need and therefore) interface for it. There actually is not that much
%D code involved anyway. There is no need to backport it to \MKIV.

\registerctxluafile{page-blk}{autosuffix}

% Musical timestamp: end May 2022 xpropaganda (in loop mode to keep the pace).

% pitfalls: we need to keep the toc in order (or generate it 'manually' based on
% deltas but even then we get the numbers wrong)

\unprotect

\newinteger\c_pages_prerolled

\permanent\protected\def\startpageblock[#1]%
  {\page
   \clf_startpageblock{#1}}

\permanent\protected\def\stoppageblock
  {\page
   \clf_stoppageblock}

\permanent\protected\def\flushpageblocks[#1]%
  {\page
   \clf_flushpageblocks{#1}}

\permanent\def\pageblockrealpage#1%
  {\clf_pageblockrealpage{#1}}

\tolerant\permanent\protected\def\startprerollpageblock[#1]%
  {\page
   \clf_startprerollpageblock{#1}%
   \global\c_pages_prerolled\realpageno % hack
   \setuppaper[\c!method=\v!none]}

\permanent\protected\def\stopprerollpageblock
  {\page
   \clf_stopprerollpageblock
   \setcounter[realpage][\c_pages_prerolled]% hack
   \setuppaper[\c!method=\v!normal]}

\permanent\def\prerolledpages#1%
  {\clf_prerolledpages{#1}}

\protect \endinput

\usemodule[article-basic]

\setupinteraction[state=start]

% \enabletrackers[*reference*]
% \enabletrackers[*destination*]

\useMPlibrary[dum]

\starttext

\def\AlphaOffset{0}
\def\BetaOffset {0}

% the flexible ones (can come from files)

\startbuffer[alpha]
    \startchapter[title=Alpha]
        \dorecurse{20}{\samplefile{tufte}\par}
    \stopchapter
\stopbuffer

\startbuffer[beta]
    \startchapter[title=Beta]
        \dorecurse{6}{\samplefile{tufte}\par}
    \stopchapter
\stopbuffer

% the fixed ones

\startbuffer[gamma]
    \startchapter[title=Gamma]
        \externalfigure[whatever-dummy-3][width=\textwidth]
    \stopchapter
\stopbuffer

\startbuffer[rest]
    \startchapter[title=Rest A]
        \samplefile{tufte}
    \stopchapter
    \startchapter[title=Rest B]
        \samplefile{tufte}
        \blank
        Alpha : \goto{page \AlphaPages}[realpage(\AlphaPages)]\par
        Beta  : \goto{page \BetaPages }[realpage(\BetaPages )]
    \stopchapter
\stopbuffer

\startbuffer[contents]
    \starttitle[title=Contents]
        \placelist[chapter][criterium=text]
    \stoptitle
\stopbuffer

% Preroll.

\startprerollpageblock[alpha]
    \start
        \setuphead[chapter][incrementnumber=no]
        \getbuffer[alpha]
    \stop
\stopprerollpageblock

% \writestatus{!!!!!}{nofalphapages: \prerolledpages{alpha}}

\startprerollpageblock[beta]
    \start
        \setuphead[chapter][incrementnumber=no]
        \getbuffer[beta]
    \stop
\stopprerollpageblock

% \writestatus{!!!!!}{nofbetapages: \prerolledpages{beta}}

% Some titling.

\startpageblock[titlepage]
    \startstandardmakeup
        \externalfigure[whatever-dummy-1][height=\textheight,width=\textwidth]
    \stopstandardmakeup
\stoppageblock

\startpageblock[boguspage]
    \startstandardmakeup
        \externalfigure[whatever-dummy-2][height=\textheight,width=\textwidth]
    \stopstandardmakeup
\stoppageblock

% The contents will end up here.

% page 1

% The main document.

\setuppagenumber[number=2]

\startpageblock[chapters]
    % we have a predictable rest:

    \edef\AlphaPages{\the\numexpr 4 \relax}
    \edef\BetaPages {\the\numexpr 4 + \prerolledpages{alpha} \relax}

    \getbuffer[rest]
    \getbuffer[alpha]
    \getbuffer[beta]
    \getbuffer[gamma]
\stoppageblock

% This one will move:

\setuppagenumber[number=1]

\startpageblock[contents]
    \getbuffer[contents]
\stoppageblock

\flushpageblocks
  [titlepage,
   boguspage,
   contents,
   chapters]

\stoptext