% (The MIT License)
%
% Copyright (c) 2021 Yegor Bugayenko
%
% Permission is hereby granted, free of charge, to any person obtaining a copy
% of this software and associated documentation files (the 'Software'), to deal
% in the Software without restriction, including without limitation the rights
% to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
% copies of the Software, and to permit persons to whom the Software is
% furnished to do so, subject to the following conditions:
%
% The above copyright notice and this permission notice shall be included in all
% copies or substantial portions of the Software.
%
% THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
% IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
% FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
% AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
% LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
% OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
% SOFTWARE.

\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{crumbs}[2021/09/12 0.3.0 Navigation Crumbs]

\makeatletter\newif\ifcrumbs@dry\makeatother
\makeatletter\DeclareOption{dry}{\crumbs@drytrue}\makeatother
\makeatletter\newif\ifcrumbs@increment\makeatother
\makeatletter\DeclareOption{increment}{\crumbs@incrementtrue}\makeatother
\ProcessOptions\relax

\RequirePackage{etoolbox}

% see https://tex.stackexchange.com/a/12414/1449
\makeatletter\newcommand\crumbs@back{\@backslashchar}\makeatother
% \makeatletter\newcommand\crumbs@percent{\@percentchar}\makeatother
\RequirePackage{catchfile}
  \newwrite\appendwrite
  \newcommand*\appendtofile[2]{%
    \begingroup
    \IfFileExists{#1}%
      {\CatchFileDef{\filecontent}{#1}{\endlinechar=`^^J\catcode\endlinechar=12\relax}}% keep existing end-of-lines
      {\let\filecontent\empty}%
    \immediate\openout\appendwrite=#1\relax
    \immediate\write\appendwrite{\unexpanded\expandafter{\filecontent} #2}%
    \immediate\closeout\appendwrite
    \endgroup
  }

\newcommand\subcrumbs{
  \ifnum\value{section}=0\else
    \expandafter\ifcsname crumbs\romannumeral\the\value{section}\endcsname
      \csname crumbs\romannumeral\the\value{section}\endcsname{}
    \fi
  \fi
}

\makeatletter\newcommand\crumbection[2][]{%
  \def\temp{#1}%
  \ifx\crumbs\empty%
    \appendtofile{\jobname.crumbs}{
      \crumbs@back ifx \crumbs@back crumbs \crumbs@back empty
        \crumbs@back gappto \crumbs@back crumbs{\crumbs@back setcounter{crumbi}{0}}
      \crumbs@back fi
      \crumbs@back gappto\crumbs@back crumbs{\crumbs@back stepcounter{crumbi}\crumbs@back crumb{\ifx\temp\empty #2\else #1\fi}{#2}}
    }%
  \fi%
  \ifcrumbs@increment\stepcounter{section}\fi%
}\makeatother

\makeatletter\newcommand\subcrumbection[2][]{%
  \def\temp{#1}%
  \ifx\crumbs\empty%
    \appendtofile{\jobname.crumbs}{
      \crumbs@back ifcsname crumbs\romannumeral\the\value{section}\crumbs@back endcsname\crumbs@back else
        \crumbs@back expandafter\crumbs@back newcommand\crumbs@back csname crumbs\romannumeral\the\value{section}\crumbs@back endcsname{%
          \crumbs@back setcounter{subcrumbi}{0}
        }
      \crumbs@back fi
      \crumbs@back expandafter\crumbs@back gappto\crumbs@back csname crumbs\romannumeral\the\value{section}\crumbs@back endcsname{%
        \crumbs@back stepcounter{subcrumbi}
        \crumbs@back subcrumb{\ifx\temp\empty #2\else #1\fi}{#2}
      }
    }%
  \fi%
  \ifcrumbs@increment\stepcounter{subsection}\fi%
}\makeatother

\makeatletter\ifcrumbs@dry
  \message{Since "dry" mode is ON we don't renew "section" and "subsection" commands}
\else
  \NewCommandCopy\crumbs@oldsection\section
  \renewcommand\section[2][]{%
    \crumbection[#1]{#2}%
    \crumbs@oldsection{#2}%
  }
  \NewCommandCopy\crumbs@oldsubsection\subsection
  \renewcommand\subsection[2][]{%
    \subcrumbection[#1]{#2}%
    \crumbs@oldsubsection{#2}%
  }
\fi\makeatletter

\ifcsname crumb\endcsname
  \message{The command "crumb" is already defined}
\else
  \newcommand\crumb[2]{#1}
\fi
\ifcsname subcrumb\endcsname
  \message{The command "subcrumb" is already defined}
\else
  \newcommand\subcrumb[2]{#1}
\fi

\newcommand*\crumbs{}
\newcounter{crumbi}
\newcounter{subcrumbi}
\AtBeginDocument{\IfFileExists{\jobname.crumbs}{\input{\jobname.crumbs}}{}}

\endinput
