%D \module
%D   [       file=spac-par,
%D        version=2009.10.16, % 1997.03.31, was core-spa.tex
%D          title=\CONTEXT\ Spacing Macros,
%D       subtitle=Paragraphs,
%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 / Paragraphs}

\unprotect

%D The dreadful sequence \type {\bgroup} \unknown\
%D \type {\carryoverpar} \unknown\ \type {\egroup} is needed
%D when for instance sidefloats are used in combination with
%D something that starts with a group. This is because
%D otherwise the indentation as set (by the output routine)
%D inside the group are forgotten afterwards. (I must
%D not forget its existence).

\def\carryoverpar#1% #1 can be \endgroup or \egroup or ... expandable !
  {\normalexpanded
     {\noexpand#1%
      \hangindent\the\hangindent
      \hangafter \the\hangafter
      \parskip   \the\parskip
      \leftskip  \the\leftskip
      \rightskip \the\rightskip}}

\unexpanded\def\pushparagraphproperties
  {\edef\currentparagraphproperties{\carryoverpar\relax}%
   \pushmacro\currentparagraphproperties}

\unexpanded\def\popparagraphproperties
  {\popmacro\currentparagraphproperties
   \currentparagraphproperties}

\unexpanded\def\flushparagraphproperties
  {\popmacro\currentparagraphproperties}

% Beware, changing this will break some code (like pos/backgrounds) but
% it has been changed anyway so let's see where things go wrong.

\installcorenamespace{paragraphintro}

\let\insertparagraphintro\relax % hook into everypar

\newtoks\t_spac_paragraphs_intro_first
\newtoks\t_spac_paragraphs_intro_next
\newtoks\t_spac_paragraphs_intro_each

\newconditional\c_spac_paragraphs_intro_first
\newconditional\c_spac_paragraphs_intro_next
\newconditional\c_spac_paragraphs_intro_each

\unexpanded\def\setupparagraphintro
  {\dodoubleempty\spac_paragraphs_intro}

\unexpanded\def\spac_paragraphs_intro[#1][#2]%
  {\def\spac_paragraphs_intro_step##1%
     {\csname\??paragraphintro\ifcsname\??paragraphintro##1\endcsname##1\fi\endcsname{#2}}%
   \processcommacommand[#1]\spac_paragraphs_intro_step}

\letvalue{\??paragraphintro\empty}\gobbleoneargument

\setvalue{\??paragraphintro\v!reset}#1%
  {\global\setfalse\c_spac_paragraphs_intro_first
   \global\setfalse\c_spac_paragraphs_intro_next
   \global\setfalse\c_spac_paragraphs_intro_each
   \global\t_spac_paragraphs_intro_first\emptytoks
   \global\t_spac_paragraphs_intro_next \emptytoks
   \global\t_spac_paragraphs_intro_each \emptytoks
   \glet\insertparagraphintro\relax}

\setvalue{\??paragraphintro\v!first}#1%
  {\global\settrue\c_spac_paragraphs_intro_first
   \global\t_spac_paragraphs_intro_first\expandafter{\the\t_spac_paragraphs_intro_first#1}%
   \glet\insertparagraphintro\spac_paragraphs_flush_intro}

\setvalue{\??paragraphintro\v!next}#1%
  {\global\settrue\c_spac_paragraphs_intro_next
   \global\t_spac_paragraphs_intro_next\expandafter{\the\t_spac_paragraphs_intro_next#1}%
   \glet\insertparagraphintro\spac_paragraphs_flush_intro}

\setvalue{\??paragraphintro\v!each}#1%
  {\global\settrue\c_spac_paragraphs_intro_each
   \global\t_spac_paragraphs_intro_each\expandafter{\the\t_spac_paragraphs_intro_each#1}%
   \glet\insertparagraphintro\spac_paragraphs_flush_intro}

%D We can say:
%D
%D \starttyping
%D \setupparagraphintro[first][\index{Knuth}]
%D \stoptyping
%D
%D Maybe more convenient is:
%D
%D \starttyping
%D \flushatparagraph{\index{Zapf}}
%D \stoptyping
%D
%D \starttyping
%D \setupparagraphintro[first][\hbox to 3.5em{\tt FIRST \hss}]
%D \setupparagraphintro[first][\hbox to 3.5em{\tt TSRIF \hss}]
%D \setupparagraphintro[next] [\hbox to 3.5em{\tt NEXT  \hss}]
%D \setupparagraphintro[next] [\hbox to 3.5em{\tt TXEN  \hss}]
%D \setupparagraphintro[each] [\hbox to 3.0em{\tt EACH  \hss}]
%D \setupparagraphintro[each] [\hbox to 3.0em{\tt HCEA  \hss}]
%D
%D some paragraph \par
%D some paragraph \par
%D some paragraph \par
%D some paragraph \par
%D
%D \setupparagraphintro[first][\hbox to 3.5em{\tt FIRST \hss}]
%D \setupparagraphintro[first][\hbox to 3.5em{\tt TSRIF \hss}]
%D
%D some paragraph \par
%D some paragraph \par
%D
%D \setupparagraphintro[reset]
%D
%D some paragraph \par
%D \stoptyping

\unexpanded\def\flushatparagraph#1%
  {\global\c_spac_paragraphs_intro_first\plusone
   \global\t_spac_paragraphs_intro_first\expandafter{\the\t_spac_paragraphs_intro_first#1}%
   \glet\insertparagraphintro\spac_paragraphs_flush_intro}

%D Here comes the flusher (we misuse the one level expansion of token
%D registers to feed a nice stream into the paragraph.)

\unexpanded\def\spac_paragraphs_flush_intro % we make sure that the token lists expand directly after another
  {\normalexpanded{%                            % so the first code is there twice
     \ifconditional\c_spac_paragraphs_intro_each
       \ifconditional\c_spac_paragraphs_intro_next
         \glet\insertparagraphintro\spac_paragraphs_flush_intro_next
       \else
         \glet\insertparagraphintro\spac_paragraphs_flush_intro_each
       \fi
       \ifconditional\c_spac_paragraphs_intro_first
         \global\setfalse\c_spac_paragraphs_intro_first
         \global\t_spac_paragraphs_intro_first\emptytoks
         \the\t_spac_paragraphs_intro_first
       \fi
       \the\t_spac_paragraphs_intro_each
     \else
       \ifconditional\c_spac_paragraphs_intro_next
         \glet\insertparagraphintro\spac_paragraphs_flush_intro_next
       \fi
       \ifconditional\c_spac_paragraphs_intro_first
         \global\setfalse\c_spac_paragraphs_intro_first
         \global\t_spac_paragraphs_intro_first\emptytoks
         \the\t_spac_paragraphs_intro_first
       \fi
     \fi}}

\unexpanded\def\spac_paragraphs_flush_intro_next
  {\normalexpanded{%
     \global\setfalse\c_spac_paragraphs_intro_next
     \global\t_spac_paragraphs_intro_next\emptytoks
     \ifconditional\c_spac_paragraphs_intro_each
       \glet\insertparagraphintro\spac_paragraphs_flush_intro_each
       \the\t_spac_paragraphs_intro_next
       \the\t_spac_paragraphs_intro_each
     \else
       \glet\insertparagraphintro\relax
       \the\t_spac_paragraphs_intro_next
     \fi}}

\unexpanded\def\spac_paragraphs_flush_intro_each
  {\the\t_spac_paragraphs_intro_each}

%D \macros
%D   {flushatnextpar}
%D
%D This macro collects data that will be flushed at the next paragraph.
%D By using this macro you can avoid interfering nodes (writes, etc).

\let\flushpostponednodedata\relax % hook into everypar

\newbox\b_spac_postponed_data

\unexpanded\def\flushatnextpar
  {\begingroup
   \glet\flushpostponednodedata\spac_postponed_flush
   \dowithnextboxcs\spac_postponed_finish\hbox}

\def\spac_postponed_finish
  {\global\setbox\b_spac_postponed_data\hbox % to\zeropoint
     {\box\b_spac_postponed_data\box\nextbox}%
   \endgroup}

\def\spac_postponed_flush
  {\ifvoid\b_spac_postponed_data\else
     \hbox{\smashedbox\b_spac_postponed_data}% \box\b_spac_postponed_data
   \fi
   \glet\flushpostponednodedata\relax}

\unexpanded\def\doflushatpar
  {\ifvmode
     \expandafter\flushatnextpar
   \else
     \expandafter\firstofoneargument
   \fi}

\protect \endinput
