%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                   %
%      Made by Gabriel Ruprecht     %
%                                   %
% This work is published under the  %
% LaTeX project public license 1.3  %
%                                   %
%       Package version 1.0.1       %
%            2025-01-10             %
%                                   %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\ProvidesPackage{fillpages}[version 1.0.1]

%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Number definitions %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%

% How many pages were inserted in the last run
% (at begin document) and how many pages are already
% inserted in this run (after begin document). The
% default value is overwritten with the content from
% the aux file (if there had ever be a run).
\newcount\GFM@FiPa@numberOfInsertedPages\relax
\GFM@FiPa@numberOfInsertedPages=0\relax

% To distribute the fill pages on evenly on all 
% insertion points, they must be counted. Default
% value must be 1 to avoid division by 0. It will
% be overwritten by the aux file value.
\newcount\GFM@FiPa@numberOfFillPagePositions\relax
\GFM@FiPa@numberOfFillPagePositions=1\relax

% Number of pages, if there weren't any fill pages.
\newcount\GFM@FiPa@pageCountWithoutFillPages\relax
\GFM@FiPa@pageCountWithoutFillPages=0\relax

% Self-explaining. Will be calculated. It is a
% float number, therefore realized as a length.
\newdimen\GFM@FiPa@pagesPerFillPosition\relax
\GFM@FiPa@pagesPerFillPosition=0pt\relax

% The currentLimit defines, how many new fill pages
% are inserted. If there were over all 3 and current
% limit is 5, 2 fill pages will be inserted at the
% current insertion point.
\newdimen\GFM@FiPa@currentLimit\relax
\GFM@FiPa@currentLimit=0pt\relax

% The number, by which the page number must be
% divisible.
\newcount\GFM@FiPa@Divisor\relax
\GFM@FiPa@Divisor=4\relax

% An offset, if the numbers must be i.e. divisible
% by 4 and have 2 extra pages.
\newcount\GFM@FiPa@DivisibleOffset\relax
\GFM@FiPa@DivisibleOffset=0\relax



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Set the number by which the  %%%
%%% page count must be divisible %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\NewDocumentCommand\pagesDivisibleBy{m O{0}}{%
\GFM@FiPa@Divisor=#1\relax%
\ifnum\GFM@FiPa@Divisor<1\relax%
    \PackageError{fillpages.sty}{line 31: Illegal number}{You can't divide a page count by zero. Replaced with 1.}%
    \GFM@FiPa@Divisor=1\relax%
\fi%
\ifnum\GFM@FiPa@Divisor>50\relax%
    \PackageWarning{fillpages.sty}{Strange number. You want your pages divisible by a number greater than 50}%
\fi%
\GFM@FiPa@DivisibleOffset=#2\relax%
}



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Defines a custom fillpage              %%%
%%%                                        %%%
%%% i.e. \setFillPage{1}{custom Text} lets %%%
%%% appear "custom Text" on fillpage no. 1 %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\long\def\setFillPage#1#2{
\expandafter\global\expandafter\def\csname GFM@FiPa@AusgleichSeite#1\endcsname {
#2%
}%\def\csname...
}%\def\setFillPage



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Do the calculations, after  %%%
%%% the aux file had been read. %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\AtBeginDocument{
% From aux-file: 
% GFM@FiPa@numberOfFillPagePositions
% GFM@FiPa@numberOfInsertedPages

% Calculate pagesCountWithoutFillPages
\GFM@FiPa@pageCountWithoutFillPages=\PreviousTotalPages\relax
\advance\GFM@FiPa@pageCountWithoutFillPages by -\GFM@FiPa@numberOfInsertedPages\relax
% Reset to 0 for the next counting round.
\GFM@FiPa@numberOfInsertedPages=0\relax

\GFM@FiPa@pagesPerFillPosition=\the\GFM@FiPa@pageCountWithoutFillPages pt\relax
\advance\GFM@FiPa@pagesPerFillPosition by -\GFM@FiPa@DivisibleOffset pt\relax

\ifdim\GFM@FiPa@pagesPerFillPosition>0 pt%
\loop%
\advance\GFM@FiPa@pagesPerFillPosition by -\GFM@FiPa@Divisor pt\relax%
\ifdim\GFM@FiPa@pagesPerFillPosition>0 pt\repeat%
%loop%
\fi

\multiply\GFM@FiPa@pagesPerFillPosition by -1\relax%

\divide\GFM@FiPa@pagesPerFillPosition by \GFM@FiPa@numberOfFillPagePositions\relax%

\GFM@FiPa@numberOfFillPagePositions=0\relax
}%AtBeginDocument



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% This defines an insertion point   %%%
%%% where the fill pages will appear. %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\insertFillPages{%
% i++ for GFM@FiPa@numberOfFillPagePositions%
\advance\GFM@FiPa@numberOfFillPagePositions by 1\relax%
%
% calculate the GFM@FiPa@currentLimit for insertion%
\GFM@FiPa@currentLimit=\GFM@FiPa@pagesPerFillPosition\relax%
\multiply\GFM@FiPa@currentLimit by \GFM@FiPa@numberOfFillPagePositions\relax%
\advance\GFM@FiPa@currentLimit by -0.98pt\relax%
%
% insert pages%
\ifdim\GFM@FiPa@numberOfInsertedPages pt<\GFM@FiPa@currentLimit%
    \loop%
        \advance\GFM@FiPa@numberOfInsertedPages by 1\relax%
        \clearpage%
        % choose the content of a predefined page. If it doesn't exist, csname expands to nothing.
        \csname % 
        GFM@FiPa@AusgleichSeite\the\GFM@FiPa@numberOfInsertedPages
        \endcsname%
        \mbox{}%
        \clearpage%
        \ifnum\GFM@FiPa@numberOfInsertedPages>1000\relax%
            \PackageError{fillpages.sty}{line 101: More than 1000 fill pages produced.}{You tried to insert more than 1000 fill pages. This must be an infinite loop.}%
            \errmessage{Infinite loop detected}
        \fi%
    \ifdim\GFM@FiPa@numberOfInsertedPages pt<\GFM@FiPa@currentLimit\repeat%
    %end loop%
\fi%ifdim
}%insertFillPages



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Do a calculation and write %%%
%%% numbers to the aux file.   %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\AtEndDocument{
% Write to aux
\ifnum\GFM@FiPa@numberOfFillPagePositions > 0\relax
    \write\@auxout{%
            \noexpand\global%
            \noexpand\GFM@FiPa@numberOfFillPagePositions=%
            \the\GFM@FiPa@numberOfFillPagePositions%
            \noexpand\relax}
\fi

\write\@auxout{%
        \noexpand\global%
        \noexpand\GFM@FiPa@numberOfInsertedPages=%
        \the\GFM@FiPa@numberOfInsertedPages%
        \noexpand\relax}

% Write to log:
\wlog{Number of fill page positions: \the\GFM@FiPa@pagesPerFillPosition\relax}%
\wlog{Number of inserted fill pages: \the\GFM@FiPa@numberOfInsertedPages\relax}%

}%AtEndDocument

