Question about zref bundle (changing the behaviour of footnote rule)

Question

In bidi package, we have three footnote commands \footnote (typesetting RTL footnotes in RTL mode and typesetting LTR footnotes in LTR modes), \RTLfootnote (always typeset RTL footnote), and \LTRfootnote (always typeset LTR footnotes). Currently bidi package has a complicated way to detect what is the first footnote command in a page and it failed when footnotes are split.

Hence my question is that is it possible (with using zref bundle) to detect what is the first footnote command used in a page and accordingly (if the first footnote in a page is RTL, put the footnote rule to be on the right hand side and if the first footnote in a page is LTR, put the footnote rule on the left hand side), change the behaviour of footnote rule.

Here is an example which seems to work correctly:

\documentclass{article}
\usepackage{zref-perpage}
\usepackage{bidi}
\makeatletter
\@definecounter{bidifootnote}

\zmakeperpage{bidifootnote}
\long\def\@RTLfootnotetext#1{\insert\footins{%
    \stepcounter{bidifootnote}\@RTLtrue
    \ifnum\c@bidifootnote=1\if@RTL\global\let\footnoterule\right@footnote\else\global\let\footnoterule\left@footnote\fi\fi
    \reset@font\footnotesize
    \interlinepenalty\interfootnotelinepenalty
    \splittopskip\footnotesep
    \splitmaxdepth \dp\strutbox \floatingpenalty \@MM
    \hsize\columnwidth \@parboxrestore
    \protected@edef\@currentlabel{%
       \csname p@footnote\endcsname\@thefnmark
    }%
    \color@begingroup
      \@makefntext{%
        \rule\z@\footnotesep\ignorespaces#1\@finalstrut\strutbox}%
    \color@endgroup}}%


\long\def\@LTRfootnotetext#1{\insert\footins{\stepcounter{bidifootnote}\@RTLfalse%
    \ifnum\c@bidifootnote=1\if@RTL\global\let\footnoterule\right@footnote\else\global\let\footnoterule\left@footnote\fi\fi
    \reset@font\footnotesize
    \interlinepenalty\interfootnotelinepenalty
    \splittopskip\footnotesep
    \splitmaxdepth \dp\strutbox \floatingpenalty \@MM
    \hsize\columnwidth \@parboxrestore
    \protected@edef\@currentlabel{%
       \csname p@footnote\endcsname\@thefnmark
    }%
    \color@begingroup
      \@makefntext{%
        \rule\z@\footnotesep\ignorespaces#1\@finalstrut\strutbox}%
    \color@endgroup}}%



\long\def\@footnotetext#1{\insert\footins{%
    \stepcounter{bidifootnote}\if@RTL@footnote\@RTLtrue\else\@RTLfalse\fi
    \ifnum\c@bidifootnote=1\if@RTL\global\let\footnoterule\right@footnote\else\global\let\footnoterule\left@footnote\fi\fi
    \reset@font\footnotesize
    \interlinepenalty\interfootnotelinepenalty
    \splittopskip\footnotesep
    \splitmaxdepth \dp\strutbox \floatingpenalty \@MM
    \hsize\columnwidth \@parboxrestore
    \protected@edef\@currentlabel{%
       \csname p@footnote\endcsname\@thefnmark
    }%
    \color@begingroup
      \@makefntext{%
        \rule\z@\footnotesep\ignorespaces#1\@finalstrut\strutbox}%
    \color@endgroup}}%
\makeatother
\begin{document}
\RTLfootnote{This is a test.}\LTRfootnote{This is a test.}
\newpage
\LTRfootnotetext[3]{This is a test.}\RTLfootnote[4]{This is a footnote.}
\end{document}

Answer 1

The following solutions uses labels to know the page, where a footnote command is executed. The first executed footnote (\@LTRfootnotetext or \@RTLfootnotetext) globally defines the macro \footdir@<absolute page number> with L/R for the rule left or right. \footnoterule checks that macro to print the right rule.

\documentclass{article}
\usepackage{zref-abspage}[2010/03/26]
\usepackage{auxhook}
\usepackage{ltxcmds}[2010/11/12]
\usepackage{bidi}

\makeatletter
\newcounter{footdir@label}
\renewcommand*{\thefootdir@label}{footdir@\the\value{footdir@label}}
\newcommand*{\footdir@write}{%
  \stepcounter{footdir@label}%
  \zref@labelbyprops{\thefootdir@label}{abspage}%
}
\newif\iffootdir@debug
\footdir@debugtrue
\newcommand*{\footdir@debug}[1]{%
  \iffootdir@debug
    \typeout{[footdir] #1}%
  \fi
}
\@ifpackagelater{zref-abspage}{2012/10/27}{%
  % this version is not yet released
  \newcommand*{\footdir@LeftRightElse}{%
    \ltx@ifundefined{footdir@\the\value{zabspage}}{%
      \footdir@debug{abspage \the\value{zabspage}: else}%
      \ltx@thirdofthree
    }{%
      \if\csname footdir@\the\value{zabspage}\endcsname L%
        \footdir@debug{abspage \the\value{zabspage}: left}%
        \expandafter\ltx@firstofthree
      \else
        \footdir@debug{abspage \the\value{zabspage}: right}%
        \expandafter\ltx@secondofthree
      \fi
    }%
  }%
}{%
  \providecommand*{\c@zabspage}{\c@abspage}%
  \newcommand*{\footdir@LeftRightElse}{%
    \footdir@write
    \zifrefundefined{\thefootdir@label}{%
      \footdir@debug{abspage ??: else}%  
      \ltx@thirdofthree
    }{%
      \edef\footdir@abspage{%
        \zref@extractdefault{\thefootdir@label}{abspage}{0}%
      }%
      \ltx@ifundefined{footdir@\footdir@abspage}{%
        \footdir@debug{\footdir@abspage: else}%   
        \ltx@thirdofthree
      }{%
        \if\csname footdir@\footdir@abspage\endcsname L%
          \footdir@debug{\footdir@abspage: left}%
          \expandafter\ltx@firstofthree
        \else
          \footdir@debug{\footdir@abspage: right}%
          \expandafter\ltx@secondofthree
        \fi
      }%   
    }%     
  }%       
}          
\newcommand*{\footdir@fntext}[1]{%
  \footdir@write
  \zifrefundefined{\thefootdir@label}{%
  }{%
    \edef\footdir@name{%
      footdir@\zref@extractdefault{\thefootdir@label}{abspage}{0}%
    }%
    \@ifundefined{\footdir@name}{%
      \expandafter\gdef\csname\footdir@name\endcsname{#1}%
    }{}%
  }%
}   
\@ifdefinable{\footdir@ORG@RTLfootnotetext}{%
  \let\footdir@ORG@RTLfootnotetext\@RTLfootnotetext
  \def\@RTLfootnotetext{%
    \footdir@fntext{R}%  
    \footdir@ORG@RTLfootnotetext
  }%
}   
\@ifdefinable{\footdir@ORG@LTRfootnotetext}{%
  \let\footdir@ORG@LTRfootnotetext\@LTRfootnotetext
  \def\@LTRfootnotetext{%
    \footdir@fntext{L}%  
    \footdir@ORG@LTRfootnotetext
  }%
}   
\def\footnoterule{%
  \footdir@LeftRightElse
    \left@footnoterule  
    \right@footnoterule 
    \left@footnoterule  
}
\makeatother

\begin{document}
\RTLfootnote{This is a test.}\LTRfootnote{This is a test.}
\newpage
\LTRfootnotetext[3]{This is a test.}\RTLfootnote[4]{This is a footnote.}
\newpage
\beginR 
\RTLfootnote{This is a test.}\LTRfootnote{This is a test.}
\endR
\newpage
\beginR 
\LTRfootnotetext[3]{This is a test.}\RTLfootnote[4]{This is a footnote.}
\endR
\end{document}

The debug output:

[footdir] abspage 1: right
[1]
[footdir] abspage 2: left
[2]
[footdir] abspage 3: right
[3]
[footdir] abspage 4: left
[4]

Extension for footnotes, split over two pages

\documentclass{article}
\usepackage{lipsum}
\usepackage{zref-abspage}[2010/03/26]
\usepackage{auxhook}
\usepackage{ltxcmds}[2010/11/12]
\usepackage{bidi}

\makeatletter
\newcounter{footdir@label}
\renewcommand*{\thefootdir@label}{footdir@\the\value{footdir@label}}
\newcommand*{\footdir@write}{%
  \stepcounter{footdir@label}%
  \zref@labelbyprops{\thefootdir@label}{abspage}%
}
\newif\iffootdir@debug
\footdir@debugtrue
\newtoks\footdir@toks
\newcommand*{\footdir@debug}[1]{%
  \iffootdir@debug
    \typeout{[footdir] #1}%
  \fi
}
\@ifpackagelater{zref-abspage}{2012/10/27}{%
  \newcommand*{\footdir@LeftRightElse}{%
    \ltx@ifundefined{footdir@\the\value{zabspage}}{%
      \footdir@debug{abspage \the\value{zabspage}: else}%
      \ltx@thirdofthree
    }{%
      \if\csname footdir@\the\value{zabspage}\endcsname L%
        \footdir@debug{abspage \the\value{zabspage}: left}%
        \expandafter\ltx@firstofthree
      \else
        \footdir@debug{abspage \the\value{zabspage}: right}%
        \expandafter\ltx@secondofthree
      \fi
    }%
  }%
}{%
  \providecommand*{\c@zabspage}{\c@abspage}%
  \newcommand*{\footdir@LeftRightElse}{%
    \footdir@write
    \zifrefundefined{\thefootdir@label}{%
      \footdir@debug{abspage ??: else}%  
      \ltx@thirdofthree
    }{%
      \edef\footdir@abspage{%
        \zref@extractdefault{\thefootdir@label}{abspage}{0}%
      }%
      \ltx@ifundefined{footdir@\footdir@abspage}{%
        \footdir@debug{\footdir@abspage: else}%   
        \ltx@thirdofthree
      }{%
        \if\csname footdir@\footdir@abspage\endcsname L%
          \footdir@debug{\footdir@abspage: left}%
          \expandafter\ltx@firstofthree
        \else
          \footdir@debug{\footdir@abspage: right}%
          \expandafter\ltx@secondofthree
        \fi
      }%   
    }%     
  }%       
}          
\newcommand*{\footdir@fntext}[1]{%
  \zifrefundefined{\thefootdir@label}{%
  }{%
    \edef\footdir@name{%
      footdir@\zref@extractdefault{\thefootdir@label}{abspage}{0}%
    }%
    \@ifundefined{\footdir@name}{%
      \expandafter\gdef\csname\footdir@name\endcsname{#1}%
    }{}%
  }%
}   
\newcommand*{\footdir@temp}[3]{%
  \@ifdefinable{#1}{%
    \let#1#2%
    \renewcommand{#2}[1]{%
      \footdir@write
      \footdir@fntext{#3}%
      \stepcounter{footdir@label}%
      \footdir@fntext{#3}%
      \footdir@toks{##1}% 
      \footdir@toks\expandafter{%
        \the\expandafter\footdir@toks
        \expandafter
        \zref@labelbyprops\expandafter{\thefootdir@label}{abspage}%
      }%
      \expandafter#1\expandafter{\the\footdir@toks}%
    }%
  }%  
}     
\footdir@temp\footdir@ORG@RTLfootnotetext\@RTLfootnotetext{R}%
\footdir@temp\footdir@ORG@LTRfootnotetext\@LTRfootnotetext{L}%
\def\footnoterule{%
  \footdir@LeftRightElse
    \left@footnoterule  
    \right@footnoterule 
    \left@footnoterule  
}
\makeatother

\begin{document}
\RTLfootnote{This is a test.}\LTRfootnote{This is a test.}
\newpage
\lipsum[1-4]
\LTRfootnotetext[3]{This is a test.}\RTLfootnote[4]{\lipsum[1-2]}
\newpage
Test with split footnote.
\newpage
\beginR 
\RTLfootnote{This is a test.}\LTRfootnote{This is a test.}
\endR
\newpage
\beginR 
\LTRfootnotetext[3]{This is a test.}\RTLfootnote[4]{This is a footnote.}
\endR
\end{document}

In this example, also the end of a footnote gets a label. If the end of the footnote falls on the next page, then \footdir@<absolute page number> is defined for that page.

Unsupported is the case, when a footnote split over more than two pages. This is much more complicate, because also the direction of the last footnote must be remembered and the page with the last footnote needs to be found.

Answer 2

Due to lack of time, here is a first draft of numbering elements on a page.

\onopSet{<class>}{<id>}

The type of elements is given in <class> and the element is identified by <id> inside the class. \onopSet writes/constructs a zref label in the .aux file.

\onopGet{<class>}{<id>}

Expandable macro \onopGet expands to the ordinal number of the element <id> of class <class> on its page.

\onopUsed{<class>}{<id>}

is the companion macro for the expandable macro \onopGet and marks the reference as used in order to allow LaTeX to print an undefined reference warning if the reference do not yet exist.

\documentclass{article}
\usepackage{zref-abspage}
\usepackage{auxhook}

% Ordinal Number On Page/ OrdNumOnPage / onop

\makeatletter
\providecommand*{\c@zabspage}{\c@abspage}
\newcommand*{\onop@abspage}{\the\value{zabspage}}

\zref@newprop{OrdinalNumberOnPage}[0]{0}
\newcommand*{\onopSet}[2]{%
  \if@filesw
    \protected@write\@auxout{%
      \let\onop@abspage\relax
    }{%
      \protect\onopLabel{#1}{#2}{\onop@abspage}%
    }%
  \fi
}
\AddLineBeginAux{%
  \string\providecommand{\string\onopLabel}[3]{}%
}
\newcommand*{\onopLabel}[3]{%
  \@ifundefined{onop:#1:#3}{%
    \expandafter\xdef\csname onop:#1:#3\endcsname{1}%
    \onop@Clear{#1}{#3}%
  }{%
    \begingroup
      \count@=\csname onop:#1:#3\endcsname\relax
      \advance\count@\@ne
      \expandafter\xdef\csname onop:#1:#3\endcsname{\the\count@}%
    \endgroup
  }%
  \begingroup
  \edef\onop@tmp{\endgroup
    \noexpand\zref@newlabel{onop@#1@#2}{%
      \noexpand\abspage{#3}%
      \noexpand\OrdinalNumberOnPage{\csname onop:#1:#3\endcsname}%
    }%
  }\onop@tmp
}
\let\onop@AtBeginDocument\@empty
\newcommand*{\onop@Clear}[2]{%
  \expandafter
  \g@addto@macro\expandafter\onop@AtBeginDocument\expandafter{%
    \expandafter
    \global\expandafter\let\csname onop:#1:#2\endcsname\@undefined
  }%
}
\AtBeginDocument{%
  \onop@AtBeginDocument
  \let\onop@Clear\@gobbletwo 
}
\newcommand*{\onopUsed}[2]{%
  \zref@refused{onop@#1@#2}%
}
\newcommand*{\onopGet}[2]{%
  \zref@extract{onop@#1@#2}{OrdinalNumberOnPage}%
}
\newcommand*{\onopLabelName}[2]{%
  onop@#1@#2%
}   
\newcommand*{\onopGetAbsPage}[2]{%
  \zref@extract{onop@#1@#2}{abspage}%
}
\makeatother

\begin{document}
\section{Test}
\onopSet{footnote}{a}
\onopSet{footnote}{b}

\onopUsed{footnote}{a}
\onopUsed{footnote}{b}

a: \onopGet{footnote}{a}%
\ifnum\onopGet{footnote}{a}=1 %
  ~(first)%
\fi
,
b: \onopGet{footnote}{b}%   
\ifnum\onopGet{footnote}{b}=1 %
  ~(first)%
\fi
\end{document}