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%D \module
%D   [     file=t-filter,
%D      version=2011.02.21,
%D        title=\CONTEXT\ User Module,
%D     subtitle=Filter,
%D       author=Aditya Mahajan,
%D         date=\currentdate,
%D    copyright=Aditya Mahajan,
%D        email=adityam <at> umich <dot> edu,
%D      license=Simplified BSD License]

\writestatus{loading}{ConTeXt User Module / Filter}

\startmodule    [filter]

\unprotect

%D \section {Initialization}
%D
%D \subsubject {Interface}
%D
%D The first step is to set the interface variables. This allows me to use 
%D \type{\c!filter} etc. in the module definition, and thereby reduces the risk
%D of a typo. Currently, only English names are provided. If someone wants, I
%D can also add other multi-lingual names.

\startinterface all
  \setinterfaceconstant {filter}           {filter}
  \setinterfaceconstant {filtercommand}    {filtercommand}
  \setinterfaceconstant {output}           {output} 
  \setinterfaceconstant {read}             {read} 
  \setinterfaceconstant {readcommand}      {readcommand} 
\stopinterface

\def\m!externalfilter{t-filter}

%D \subsubject {Messages}

\setinterfacemessage{externalfilter}{title}     {\m!externalfilter}
\setinterfacemessage{externalfilter}{notfound}  {file -- cannot be found}
\setinterfacemessage{externalfilter}{missing}   {output file missing}
\setinterfacemessage{externalfilter}{forbidden} {Fatal Error: Cannot use absolute path -- as directory}
\setinterfacemessage{externalfilter}{slash}     {Appending / to directory -- }

%D \subsubject {Name space}

\def\????externalfilter{@@@@externalfilter}
\def\!!!!externalfilter{externalfilter}
\def\currentexternalfilter{}
\def\externalfiltercountername{\????externalfilter-\currentexternalfilter-counter}

\ifx\undefined\normalexpanded \let\normalexpanded\expanded \fi

\installparameterhandler     \????externalfilter \!!!!externalfilter
\installparameterhashhandler \????externalfilter \!!!!externalfilter
\installsetuphandler         \????externalfilter {externalfilters} %Note the plural

\doifmode\s!mkiv
  {\installattributehandler \????externalfilter \!!!!externalfilter}

%D \section {Tracing Macros}

\newif\iftraceexternalfilters

\let\traceexternalfilters\traceexternalfilterstrue

\starttexdefinition doshowfilterstate
  \iftraceexternalfilters
    \writestatus\m!externalfilter{current filter : \currentexternalfilter}
    \writestatus\m!externalfilter{base file : \externalfilterbasefile}
    \writestatus\m!externalfilter{input file : \externalfilterinputfile}
    \writestatus\m!externalfilter{output file : \externalfilteroutputfile}
  \fi
\stoptexdefinition

\def\doshowfilterstatus#1%
  {\iftraceexternalfilters
    \writestatus\m!externalfilter{#1}%
  \fi}

\starttexdefinition doshowfiltercommand
    \writestatus\m!externalfilter{command : \externalfilterparameter\c!filtercommand}
\stoptexdefinition

%D \section {The main user macros}

%D \subsubject {Define a new filter}

\def\defineexternalfilter
  {\dodoubleargument\dodefineexternalfilter}

\def\dodefineexternalfilter[#1][#2]%
  {\doshowfilterstatus{defining filter : #1}%
   \edef\currentexternalfilter{#1}%
   \getparameters[\????externalfilter#1][\s!parent=\????externalfilter,#2]%
   \doif{\externalfilterparameter\c!continue}\v!yes
      {\expandafter\newcounter\csname\externalfiltercountername\endcsname}%
   \setvalue{\e!start#1}{\bgroup\obeylines\dodoubleargument\dostartexternalfilter[#1]}%
   \setvalue{\e!stop#1}{\doprocessexternalfilter}%
   \setvalue{process#1file}{\dodoubleargument\doprocessexternalfilterfile[#1]}%
   \setvalue{inline#1}{\doinlineexternalfilter[#1]}
   }

\def\dostartexternalfilter[#1][#2]% filter options
  {% Initializations
   \egroup %\bgroup in \start#1 
   \edef\currentexternalfilter   {#1}%
   \begingroup % to keep assignments local
   \getparameters[\????externalfilter#1][\c!name=,#2]%
   \setexternalfilterfilenames
   % Capture the contents of the buffer
   \dostartbuffer[\externalfiltertmpfile][\e!start#1][\e!stop#1]}

\def\doprocessexternalfilterfile[#1][#2]#3%
  {\begingroup
   \edef\currentexternalfilter    {#1}%
   \getparameters[\????externalfilter#1][\c!name=,\c!continue=\v!yes,#2]% 
   %NOTE: Currently filters with a pipe (|) fail with continue=yes
   \setexternalfilterdirectory
   \edef\externalfilterinputfile  {#3}%
   \splitfilename {#3}%
   %NOTE: \edef doesn not work
   \def\externalfilterbasefile   {\splitoffname}%
   % The output is always in the directory specified by 
   % \c!directory; even if the input is from some other directory
   \def\externalfilteroutputfile{\getexternalfilterdirectory\externalfilterparameter\c!output}%
   \doshowfilterstate
   \doexecuteexternalfilter
   \doreadprocessedfile
   \endgroup}
   
\def\doinlineexternalfilter[#1]%
  {\edef\currentexternalfilter {#1}%
   \begingroup % to keep assignments local
   \getparameters[\????externalfilter#1][\c!name=]% 
   \setexternalfilterfilenames
   \pushcatcodetable
   \futurelet\next\dodoinlineexternalfilter}

%D \subsubject {Catcode tables}
%D 
%D Just to be sure, I define all catcode tables that are needed within the
%D module. Some of these are repetition of what is defined in ConTeXt, but the
%D internal names keep on changing which is a  maintenance nightmare.

\newcatcodetable \externalfilterreadcatcodes
\newcatcodetable \externalfilterwritecatcodes
\newcatcodetable \externalfilterverbcatcodes

\startcatcodetable \externalfilterreadcatcodes % same as typcatcodesa
    \catcode\tabasciicode       \othercatcode
    \catcode\endoflineasciicode \othercatcode
    \catcode\formfeedasciicode  \othercatcode
    \catcode\spaceasciicode     \othercatcode
    \catcode\endoffileasciicode \othercatcode
    \catcode\leftbraceasciicode \begingroupcatcode
    \catcode\rightbraceasciicode\endgroupcatcode
\stopcatcodetable

\startcatcodetable \externalfilterwritecatcodes
  \catcode\backslashasciicode  = \escapecatcode
  \catcode\leftbraceasciicode  = \begingroupcatcode  
  \catcode\rightbraceasciicode = \endgroupcatcode
  \catcode\endoflineasciicode  = \activecatcode
  \catcode\formfeedasciicode   = \activecatcode
  \catcode\spaceasciicode      = \activecatcode
\stopcatcodetable 

\startcatcodetable \externalfilterverbcatcodes % same as vrbcatcodes
    \catcode\tabasciicode      \othercatcode
    \catcode\endoflineasciicode\othercatcode
    \catcode\formfeedasciicode \othercatcode
    \catcode\spaceasciicode    \othercatcode
    \catcode\endoffileasciicode\othercatcode
\stopcatcodetable

%D \subsubject {Write argument to file verbatim}
%D
%D Surprisingly, there is nothing in the core to define a function that write its
%D argument to a file verbatim. I basically copied the \type{\type} macro.

\def\dodoinlineexternalfilter
  {\ifx\next\bgroup
     \expandafter\dodoinlineexternalfilterA
   \else
     \expandafter\dodoinlineexternalfilterB
   \fi}

\def\dodoinlineexternalfilterA
  {\setcatcodetable \externalfilterreadcatcodes
   \redoinlineexternalfilter}

\def\dodoinlineexternalfilterB#1%
  {\setcatcodetable \externalfilterverbcatcodes
   \def\dododoinlineexternalfilterB##1#1{\redoinlineexternalfilter{##1}}%
   \dododoinlineexternalfilterB}

\newwrite\externalfilterwrite

\def\redoinlineexternalfilter#1%
  {\immediate\openout \externalfilterwrite\externalfilterinputfile
   \immediate\write   \externalfilterwrite{\detokenize{#1}}%
   \immediate\closeout\externalfilterwrite
   \popcatcodetable
   \doexecuteexternalfilter
   \doreadprocessedfile
   % Finalization
   \doif{\externalfilterparameter\c!continue}\v!yes
        {\doglobal\expandafter\increment\csname\externalfiltercountername\endcsname}%
   \endgroup}



%D \section {Helper Functions}
%D
%D \subsubject {First and last character of a string}

\def\getfirstcharacter#1%
  {\dogetfirstcharacter#1\relax}

\def\dogetfirstcharacter#1#2\relax{#1}

\def\getlastcharacter#1%
  {\@EA\dogetlastcharacter#1\relax}

\def\dogetlastcharacter#1#2%
  {\ifx#2\relax#1\else\@EA\dogetlastcharacter\@EA#2\fi}

%D \subsubject {Set the name of output directory}

\def\setexternalfilterdirectory
  {\edef\getexternalfilterdirectory{\externalfilterparameter\c!directory}%
   \doifsomething{\getexternalfilterdirectory}\dosetexternalfilterdirectory}
   
\def\dosetexternalfilterdirectory
  {\doif{\getfirstcharacter\getexternalfilterdirectory}{/}
      {\writeline
       \showmessage\!!!!externalfilter{forbidden}\getexternalfilterdirectory
       \batchmode
       \errmessage{}
       \normalend}
   \doifnot{\getlastcharacter\getexternalfilterdirectory}{/}
      {\showmessage\!!!!externalfilter{slash}\getexternalfilterdirectory
       \edef\getexternalfilterdirectory{\getexternalfilterdirectory/}}}
  


%D \subsubject {Set file names}
%D
%D \type{\externalfilterbasefile} is the name of the temporary file without
%D extension. Its actual value depends on the state of \type{continue} key as
%D well as the value of \type{name} key.

\def\setexternalfilterfilenames
  {\setexternalfilterdirectory
   % Set the name of temp file for the filter
   \doifelse{\externalfilterparameter\c!continue}\v!yes
       {\edef\externalfiltertmpfile{\!!!!externalfilter-\currentexternalfilter-\csname\externalfiltercountername\endcsname}}
       {\edef\externalfiltertmpfile{\!!!!externalfilter-\currentexternalfilter}}
   \doifsomething{\externalfilterparameter\c!name}
       {\edef\externalfiltertmpfile{\!!!!externalfilter-\currentexternalfilter-\externalfilterparameter\c!name}}
   % The following  macros are useful for filter= and filtercommand= options
   % The basename of the external file 
   \edef\externalfilterbasefile  {\jobname-\externalfiltertmpfile}%
   % In MkII, the buffer output is written to \TEXbufferfile{buffername} where
   % the macro \TEXbufferfile is defined as
   %
   %        \def\TEXbufferfile   #1{\bufferprefix#1.\f!temporaryextension}
   %
   % We redefine bufferprefix to include the directory name.
   \doifmode{\s!mkii}
      {\edef\bufferprefix{\getexternalfilterdirectory\jobname-}}
   % In MkIV, we do not need to do such jugglary, because we can specify the
   % name of the file where the buffer has to be saved. This file is
   % \externalfilterinputfile (because it is the input to the filter).
   \edef\externalfilterinputfile {\getexternalfilterdirectory\externalfilterbasefile.\f!temporaryextension}%
   % The name of the file to which the filter output is written
   \edef\externalfilteroutputfile{\getexternalfilterdirectory\externalfilterparameter\c!output}%
   \doshowfilterstate
  }


%D \subsubject {Process Filter}
%D
%D Execute filter, read the output and do book-keeping if needed.

\def\doprocessexternalfilter
  {% By defualt, buffers are in memory in MkIV
   \doifmode\s!mkiv{\savebuffer[\externalfiltertmpfile][\externalfilterinputfile]}%
   % Run external command
   \doexecuteexternalfilter
   \doreadprocessedfile
   \endgroup 
   % Finalization
   \doif{\externalfilterparameter\c!continue}\v!yes
        {\doglobal\expandafter\increment\csname\externalfiltercountername\endcsname}%
   }

%D \subsubject {Execute Filter}   

\def\doexecuteexternalfilter
  {\doshowfiltercommand
   \doifelse{\externalfilterparameter\c!continue}\v!yes
     {\doifmode{*first}
       {\executesystemcommand
        {mtxrun --ifchanged=\externalfilterinputfile\space 
            --direct \externalfilterparameter\c!filtercommand}}}
     {\executesystemcommand
        {\externalfilterparameter\c!filtercommand}}}

%D \subsubject {Read output}

\def\doreadprocessedfile
  {\doif{\externalfilterparameter\c!read}\v!yes
      {\doiffileelse{\externalfilteroutputfile}
          {\dodoreadprocessedfile}
          {\showmessage\!!!!externalfilter{notfound}\externalfilteroutputfile 
           \blank
           {\tttf [[\getmessage\!!!!externalfilter{missing}]]}%
           \blank
          }}}

\def\dodoreadprocessedfile
  {\externalfilterparameter\c!before
   \begingroup
   \doifmode\s!mkiv
      {\dosetexternalfilterattributes\c!style\c!color}
   \processcommacommand[\externalfilterparameter\c!setups]\directsetup
   \externalfilterparameter\c!readcommand\externalfilteroutputfile
   \endgroup
   \externalfilterparameter\c!after}

%D \section {Default Values}

\setupexternalfilters
  [
   \c!before=,
   \c!after=,
   \c!style=,
   \c!color=,
   \c!setups=,
   \c!continue=\v!no,
   \c!read=\v!yes,
   \c!readcommand=\ReadFile,
   \c!directory=,
   \c!output=\externalfilterbasefile.tex,
   \c!filter=,
   \c!filtercommand={\externalfilterparameter\c!filter\space \externalfilterinputfile},
 ]
   
\protect
\stopmodule