%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Module:    ZzTeX Tabbing Facilities
%
% Synopsis:  This module contains the definition of the block that is
%            used to format text with tab stops.
%
% Authors:   Paul C. Anagnostopoulos
% Created:   27 May 2016
%
% Copyright 1989--2020 by Paul C. Anagnostopoulos
% under The MIT License (opensource.org/licenses/MIT)
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%                       Tabbing Block
%                       ------- -----


\defineblock{\tabbing}{\endtabbing}{\false}{}
\resetinvcontext{\tabbing}

%~block tabbing Type
% \abovepenalty = integer               % Penalty above text.
% \aboveskip = glue                     % Space b/b above text.
% \setflag \autocallout = boolean       % Automatically number lines?
% \def \beginformat {...}               % Beginning of text formatter.
% \belowpenalty = integer               % Penalty below text.
% \belowskip = glue                     % Space b/b below text.
% \bodyfont = {font}                    % Body font.
% \def \calloutformat ##1{...}          % Callout formatter.
% \calloutnumber = integer              % Number of first callout.
% \def \callouttext {...}               % Callout text or \arg.
% \defaulttabwidth = dimen              % Default repeating tab width.
% \def \endformat {...}                 % End of text formatter.
% \leftindent = glue                    % Left indentation.
% \rightindent = glue                   % Right indentation.
% \tabbinggapskip = glue                % Standard tabbing gap.
% \textcolor = {...}                    % Color of text.
% \width = dimen                        % Line width.
%~end

\defineskip{\tabbinggapskip}{0pt}

\def \tabbing #1{%                                         {type}
  \blockcantbein{\tabbing}{\tabbing}%
  \beginblockscope{tabbing}%
  \global\increment \tabbingdepth
  \abovepenalty = \breakgood                            %~default hard
  \setflag \autocallout = \false                        %~default soft
  \def \beginformat {}%                                 %~default soft
  \belowpenalty = \breakgood                            %~default hard
  \calloutnumber = 1                                    %~default with
  \def \callouttext {\number\calloutnumber}%            %~default soft
  \defaulttabwidth = \mindimen                          %~default soft
  \def \endformat {}%                                   %~default soft
  \tabbinggapskip = \enclosingbaselineskip              %~default soft
  \textcolor = {}%                                      %~default soft
  \parindent = 0pt
  \parrag = 0pt
  \parskip = 0pt
  \processdesign{\tabbing}{#1}%
  \global\increment \tabbingnumber
  \tabbingformat
  \def \zarg {\arg}%
  \if \tokeqlp{\callouttext}{\zarg}%
    \defineatsigncommand @##{\ztbngatcallout}%
  \else
    \defineatsigncommand @##{\ztbngatcallout{\callouttext}}%
  \fi
  \if \emptytoksp{\textcolor}%          % Must have a group around \ztbnginit.
    \bgroup
  \else
    \color{\the\textcolor}%
  \fi
    \ztbnginit
    \ztbngstartline}

\def \endtabbing {%
    \ztbngfinal
  \if \emptytoksp{\textcolor}%
    \egroup % \tabbing group
  \else
    \endcolor
  \fi
  \futurelet\nexttoken \zendtabbing}

\def \zendtabbing {%
  \endtabbingformat
  \global\decrement \tabbingdepth
  \endblockscope{tabbing}%
  \parnext}

\def \tabbingformat {%
  \endgraf
  \the\bodyfont
  \bbskipabove{\abovepenalty}{\aboveskip}%
  \alterindentation{\leftindent}{\rightindent}%
  \settextwidth{\width}%
  \beginformat}

\def \endtabbingformat {%
  \endformat
  \bbskipbelowblockpar{\nexttoken}{\belowpenalty}{\belowskip}}

%~ Use this command in between lines in a |\tabbing| block to
%~ perform a vertical adjustment between those two lines. For example,
%~
%~   \adjusttabbing{\fullpagebreak}

\long\def \adjusttabbing #1{%                           {commands}
  \ztbngadjust{#1}}

%                       Initialize and Finalize
%                       ---------- --- --------


\definecount{\ztbngstopcount}{0}
\definecount{\ztbngstopindex}{0}

\definebox{\ztbngline}
\definebox{\ztbngfragment}


\def \ztbnginit {%
  \let \par = \ztbngshouldntbepar
  \def \nl {\ztbngfinishline{\false}}%
  \defineatsigncommand @.{\ztbngatsetstop}%
  \defineatsigncommand @>{\ztbngattab}%
  \defineatsigncommand @C{\ztbngatclear}%
  \defineatsigncommand @D{\ztbngatdiscard}%
  \ztbngsetdefaultstops{\defaulttabwidth}}

\def \ztbngsetdefaultstops #1{%                         {width}
  \global\ztbngstopcount = 0
  \def \ztbngstop {0pt}%
  \if \dimgtrp{#1}{0pt}%
    \tdimena = 0pt
    \loop
      \global\increment \ztbngstopcount
      \advance \tdimena by #1\relax
      \withname\edef {\ztbngstop\romannumeral\ztbngstopcount}{\the\tdimena}%
    \if \dimlssp{\tdimena}{\hsize}%
    \repeat
  \fi}

\def \ztbngfinal {%
  \ztbngfinishline{\true}}

%                       Build Lines
%                       ----- -----


\def \ztbngstartline {%
  \ztbngstopindex = 0
  \setbox\ztbngline = \hbox{}%
  \global\setflag \ztbngdiscardp = \false
  \settaginfo{\number\calloutnumber}{???title???}%
  \ztbngstartfragment}

\def \ztbngstartfragment {%
  \setbox \ztbngfragment = \hbox\bgroup
    \ignorespaces}

\def \ztbngfinishfragment {%
  \egroup % \ztbngfragment box
  \setbox\ztbngline = \hbox{%
    \unhbox\ztbngline
    \tdimena = \name{\ztbngstop\romannumeral\ztbngstopindex}%
    \hskip \tdimena
    \tdimenb = \hsize
    \advance \tdimenb by -\tdimena
    \hbox to \tdimenb{\copy\ztbngfragment \hfil}%
    \hskip -\tdimenb
    \hskip -\tdimena}}

\def \ztbngfinishline #1{%                              {end-of-block?}
  \ztbngfinishfragment
  \if \notp{\ztbngdiscardp}%
    \if \orp{\posp{\ztbngstopindex}}{\dimposp{\wd\ztbngfragment}}%
      \noindent
        \if \autocallout
          \llap{\calloutformat{\the\calloutnumber}}%
          \increment \calloutnumber
        \fi
        \box\ztbngline
      \endgraf
    \else\if \notp{#1}%
      \vspace{\tabbinggapskip}%
    \fi\fi
  \fi
  \if #1\let \znext = \relax \else \let \znext = \ztbngstartline \fi
  \znext}

%                       At-sign Commands
%                       ------- --------


% @#{callout}text...

\def \ztbngatcallout #1{%                               {callout}
  \ztbngfinishfragment
  \if \andp{\zerop{\ztbngstopindex}}{\dimzerop{\wd\ztbngfragment}}
    \setbox\ztbngfragment = \hbox\bgroup
      \llap{\calloutformat{#1}}%
    \ztbngfinishfragment
  \else
    \error{badtabcallout}{Callout command (\noexpand@##) must appear
                          at the beginning of the line}%
  \fi
  \increment \calloutnumber
  \ztbngstartfragment}

% text@.more text...

\def \ztbngatsetstop {%
  \ztbngfinishfragment
  \tdimena = \name{\ztbngstop\romannumeral\ztbngstopindex}%
  \advance \tdimena by \wd\ztbngfragment
  \increment \ztbngstopindex
  \if \gtrp{\ztbngstopindex}{\ztbngstopcount}%
    \withname\edef {\ztbngstop\romannumeral\ztbngstopindex}{\the\tdimena}%
    \increment \ztbngstopcount
  \else
    \error{badtabstop}{There is already a tab stop}%
  \fi
  \ztbngstartfragment}

% text@>more text...

\def \ztbngattab {%
  \ztbngfinishfragment
  \if \lssp{\ztbngstopindex}{\ztbngstopcount}%
    \increment \ztbngstopindex
  \else
    \warning{toomanytabs}{Too many tabs on line; extra tabs ignored}%
  \fi
  \ztbngstartfragment}

% @Ctext...\nl

\def \ztbngatclear {%
  \if \zerop{\ztbngstopindex}%
    \global\ztbngstopcount = 0\relax
  \else
    \error{badtabclear}{Tabs must be cleared at the beginning of the line}%
  \fi}

% text@D\nl

\def \ztbngatdiscard {%
  \global\setflag \ztbngdiscardp = \true \relax}

%                       Adjustment
%                       ----------


\long\def \ztbngadjust #1{%                             {commands}
  \ztbngfinishfragment
  \if \andp{\zerop{\ztbngstopindex}}{\dimzerop{\wd\ztbngfragment}}
    #1%
  \else
    \error{badtabadjust}{The \noexpand\adjusttabbing command must appear
                         in between lines}%
  \fi
  \ztbngstartfragment}
