% $Id: tex4ht-mathjax.tex 1302 2023-02-27 22:21:51Z karl $
% compile: latex tex4ht-mathjax
%
% Copyright 2018-2023 TeX Users Group
% Released under LPPL 1.3c+.
% See tex4ht-cpright.tex for license text.

\ifx \HTML\UnDef
   \def\HTML{mathjax-latex-4ht} 
   \def\CONFIG{\jobname}
   \def\MAKETITLE{\author{Michal Hoftich}}
   \def\next{\input mktex4ht.4ht  \endinput}
   \expandafter\next
\fi

\input{common-code}
\input{common}
\input{tex4ht-cpright}

\<mathjax-latex-4ht\><<<
% mathjax-latex-4ht.4ht (|version), generated from |jobname.tex
% Copyright 2018-2023 TeX Users Group
|<TeX4ht copywrite|>
|<required packages|>
|<defined commands|>
\AtBeginDocument{%
|<configurations|>
|<mhchem configurations|>
|<restore environments|>
}
\endinput
>>>

We don't require additional packages anymore, as everything necessary is included
in LaTeX kernel now.
% \RequirePackage{etoolbox,expl3,environ}
\<required packages\><<<
>>>

The \verb|\alteqtoks| command saves the used command in HTML. It uses detokenize command
to insert arguments verbatim. The side effect of this is that detokeize inserts space
after each control sequence. This is completely valid TeX code, but earlier versions of
MathJax didn't like that, rendering resulted in error.

Fortunatelly, MathJax 3 supports these spaces, so we can remove regular expressions for space handling.
The original code was this:

% % convert \ { to \:{ 
% \regex_replace_all:nnN { \x{5C} \x{20} \x{7B} } { \x{5C} \x{3A} \x{7B} } \l_tmpa_tl
% % delete spaces before left brackets
% \regex_replace_all:nnN { \x{20} \x{7B} } { \x{7B} } \l_tmpa_tl
% % replace \\:{ back to \\ { -- this can be introduced by the previous regex
% \regex_replace_all:nnN { \x{5C} \x{5C}  \x{3A} \x{7B} } { \x{5C} \x{5C} \x{20} \x{7B} } \l_tmpa_tl


We still use regula expressions to escape invalid XML characters to entities, so it works only with LaTeX.

\<defined commands\><<<
\ExplSyntaxOn
\cs_new_protected:Npn \alteqtoks #1
{
  \tl_set:Nx \l_tmpa_tl {\detokenize{#1}}
  % % replace < > and & with xml entities
  \regex_replace_all:nnN { \x{26} } { &amp; } \l_tmpa_tl
  \regex_replace_all:nnN { \x{3C} } { &lt; } \l_tmpa_tl 
  \regex_replace_all:nnN { \x{3E} } { &gt; } \l_tmpa_tl
  % replace \par command with blank lines
  \regex_replace_all:nnN { \x{5C}par\b } {\x{A}\x{A}} \l_tmpa_tl
  \tl_set:Nx \l_tmpb_tl{ \l_tmpa_tl }
  \HCode{\l_tmpb_tl}
}
\ExplSyntaxOff

>>>

Provide configuration for MathJax

\<defined commands\><<<
\NewConfigure{MathJaxConfig}{1}
>>>

The MathJaxMacros configuration includes a file with TeX macro 
definitions, and include them at the beginning of each HTML page.
MathJax then interprets them, so they are available in math. 
This is an alternative to JavaScript method using MathJaxConfig.

The file cannot contain any other commands than newcommand,
all characters that could cause issues in the HTML parsing must
be escaped, so \verb|<| should became \verb|&lt;|, for example.

\<defined commands\><<<
\NewConfigure{MathJaxMacros}[1]{%
\Configure{@BODY}{\bgroup\NoFonts\ttfamily\detokenize{\(}%
  \special{t4ht*<#1}%
\detokenize{\)}\EndNoFonts\egroup}%
}
>>>

The following commands are used for patching of the standard math commands and
environments. They will then keep the LaTeX code unchanged.

\<defined commands\><<<

\long\def\AltlMath#1\){\expandafter\alteqtoks{\(#1\)}\)}
\long\def\AltlDisplay#1\]{\alteqtoks{\[#1\]}\]}
\long\def\AltMathOne#1${\alteqtoks{\(#1\)}$}
% this seems a bit hacky -- we need to skip some code inserted at the 
% beginning of each display math
\long\def\AltlDisplayDollars#1$${\alteqtoks{\[#1\]}$$}

\newcommand\VerbMathToks[2]{%
  \alteqtoks{\begin{#2}
    #1
  \end{#2}}%
}
>>>

In pictures, we want to use the original version of the math environments. Because we use
an agressive verbatim method for the environments, we cannot use the usual \verb'\HLet' method.
Instead, we save the original meaning, and user needs to restore it manually, using
the \verb'\RestoreMathJaxEnvironments' command.

\<defined commands\><<<
\ExplSyntaxOn
\seq_new:N\:savedmathjaxenvs

\newcommand\:savemathjaxenv[1]{%
  \seq_gput_right:Nn\:savedmathjaxenvs{#1}
  \expandafter\let\csname mathjax-#1\expandafter\endcsname\csname #1\endcsname%
  \expandafter\let\csname mathjax-end#1\expandafter\endcsname\csname end#1\endcsname%
}

% we must not reintroduce the matrix environmeint in TikZ, because it interferes with the \matrix command
\newcommand\:ignoretikzmatrix{\seq_remove_all:Nn\:savedmathjaxenvs{matrix}}

\newcommand\RestoreMathJaxEnvironment[1]{%
  \expandafter\let\csname #1\expandafter\endcsname\csname mathjax-#1\endcsname%
  \expandafter\let\csname end#1\expandafter\endcsname\csname mathjax-end#1\endcsname%
}

\newcommand\RestoreMathJaxEnvironments{%
  \seq_map_function:NN\:savedmathjaxenvs\RestoreMathJaxEnvironment%
}
\ExplSyntaxOff
>>>

The \verb|\VerbMath| command redefines environments to pass their content
verbatim to the HTML output.

The optional command can contain name of the counter that should be updated.
It will also use LaTeX 3 regular expressions to search for label commands.
Thanks to that, cross-referencing to the math environments should work.
It is a bit limited, for example subequations cannot work. There can be also
issues in books, where equation numbers are based on chapters, but MathJax
numbers them consecutively. In these cases, other mechanisms may be necessary.

\<defined commands\><<<
\ExplSyntaxOn
\cs_generate_variant:Nn \regex_extract_once:nnNTF {nV}
\newcommand\VerbMath[2][]{%
  \cs_if_exist:cTF{#2}{
    \:savemathjaxenv{#2}%
    \RenewDocumentEnvironment{#2}{+!b}{%
      \NoFonts\expandafter\VerbMathToks\expandafter{\detokenize{##1}}{#2}\EndNoFonts%
      \ifx\relax#1\relax\else%
      \refstepcounter{#1}%
      \regex_extract_once:nVNTF { label\s* \x{7B}([^\x{7D}]*)\x{7D}} {\l_tmpb_tl} \l_tmp_seq {\label{\seq_item:Nn\l_tmp_seq{2}}} {}%
      \fi
    }{}
  }{}%
}
\ExplSyntaxOff
>>>

The \verb|\fixmathjaxtoc| command is used for patching commands which should
keep their verbatim appearance in the TOC

\<defined commands\><<<
\def\fixmathjaxtoc#1{\Configure{writetoc}{\def#1{\detokenize{#1}}}}
>>>

This was meant to fix some commands in sectioning commands, but it is not
a good solution. Better is to define the problematic commands as robust.

\<not defined commands\><<<
\def\fixmathjaxsec#1{\def#1{\detokenize{#1}}}
\fixmathjaxsec\right
\fixmathjaxsec\left
>>>

Require verbatim math environments.

\<configurations\><<<
\VerbMath{subarray}
\VerbMath{smallmatrix}
\VerbMath{matrix}
\VerbMath{pmatrix}
\VerbMath{bmatrix}
\VerbMath{Bmatrix}
\VerbMath{vmatrix}
\VerbMath{Vmatrix}
\VerbMath{cases}
\VerbMath{subequations}
\VerbMath{aligned}
\VerbMath{alignedat}
\VerbMath{gathered}
\VerbMath{gather}
\VerbMath{gather*}
\VerbMath{alignat}
\VerbMath{alignat*}
\VerbMath{xalignat}
\VerbMath{xalignat*}
\VerbMath{xxalignat}
\VerbMath{align}
\VerbMath{align*}
\VerbMath{flalign}
\VerbMath{flalign*}
\VerbMath{split}
\VerbMath{multline}
\VerbMath{multline*}
\VerbMath[equation]{equation}
\VerbMath{equation*}
\VerbMath{math}
\VerbMath{displaymath}
\VerbMath{eqnarray}
\VerbMath{eqnarray*}
>>>

It is necessary to reset env configurations for multiline 
environments, because default TeX4ht configurations turn
them into pictures.

\<configurations\><<<
\ConfigureEnv{gather}{}{}{}{}
\ConfigureEnv{gather*}{}{}{}{}
\ConfigureEnv{multline}{}{}{}{}
\ConfigureEnv{multline*}{}{}{}{}
>>>


Fixes for tables of contents.

\<configurations\><<<
\fixmathjaxtoc\int
\fixmathjaxtoc\,
\fixmathjaxtoc\sin
\fixmathjaxtoc\cos
\fixmathjaxtoc\tan
\fixmathjaxtoc\arcsin
\fixmathjaxtoc\arccos
\fixmathjaxtoc\arctan
\fixmathjaxtoc\csc
\fixmathjaxtoc\sec
\fixmathjaxtoc\cot
\fixmathjaxtoc\sinh
\fixmathjaxtoc\cosh
\fixmathjaxtoc\tanh
\fixmathjaxtoc\coth
\fixmathjaxtoc\log
\fixmathjaxtoc\ln
\fixmathjaxtoc\sum
\fixmathjaxtoc\(
\fixmathjaxtoc\)
\fixmathjaxtoc\begin
\fixmathjaxtoc\end
\fixmathjaxtoc\\
\fixmathjaxtoc\exp
\fixmathjaxtoc\left
\fixmathjaxtoc\right
>>>

\<mhchem configurations\><<<
\@ifpackageloaded{mhchem}{%
\def\ce#1{\texttt{\detokenize{\(\ce{#1}\)}}}
}{}
>>>

Restore environments redefined to produce verbatim output to their
original meaning in the picture mode. Otherwise math cannot work
inside TikZ etc.

\<restore environments\><<<
\@ifpackageloaded{tikz}{%
\tikzset{every picture/.append code={\:ignoretikzmatrix\RestoreMathJaxEnvironments}} 
}{}
>>>

\endinput