% -*- coding: utf-8 -*-
% ----------------------------------------------------------------------------
% Author:  Jianrui Lyu <tolvjr@163.com>
% License: The LaTeX Project Public License 1.3c
% ----------------------------------------------------------------------------

\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{freealign}[2024-01-01 v2024A Align math formulas in different lines]

\RequirePackage{etoolbox,zref-savepos}

\@ifundefined{zsaveposx}{\let\zsaveposx\zsavepos}{} % 旧版本无 \zsaveposx 命令

\newcounter{saveposcnt}
\newcounter{useposcnt}
\renewcommand*{\thesaveposcnt}{savepos\number\value{saveposcnt}}
\renewcommand*{\theuseposcnt}{usepos\number\value{useposcnt}}

\def\my@alignment@offset{}

\def\my@alignment@list{}
\forcsvlist{\listadd\my@alignment@list}{=,<,>,\le,\ge,\leq,\geq,\approx}

\newlength{\my@alignment@kern}

\newcommand*{\my@alignment@check}[1]{%
  \ifx\my@let@token #1%
    \def\my@alignment@offset{5}%
    \expandafter\listbreak
  \fi
}

\newcommand{\my@alignment@next}{%
  \ifdefempty{\my@alignment@offset}{%
    \def\my@alignment@offset{0}%
    \forlistloop{\my@alignment@check}{\my@alignment@list}%
  }{}%
  \settowidth{\my@alignment@kern}{$\mkern\my@alignment@offset mu$}%
  \stepcounter{saveposcnt}%
  \rlap{\kern\my@alignment@kern\zsaveposx{\thesaveposcnt}}%
}

\newcommand*{\tabpoint}[1][]{%
  \leavevmode
  \def\my@alignment@offset{#1}%
  \futurelet\my@let@token\my@alignment@next
}
\let \? = \tabpoint

\newcommand*{\tabto}{%
  \stepcounter{useposcnt}%
  \zsaveposx{\theuseposcnt}%
  \noindent
  \hskip\zposx{\thesaveposcnt}sp\relax
  \hskip-\zposx{\theuseposcnt}sp\relax
  \ignorespaces
}
\let \+ = \tabto

\newcommand*{\tableft}{%
  \settowidth{\my@alignment@kern}{$=\mkern5mu$}%
  \stepcounter{useposcnt}%
  \zsaveposx{\theuseposcnt}%
  \noindent
  \hskip\zposx{\thesaveposcnt}sp\relax
  \hskip-\zposx{\theuseposcnt}sp\relax
  \hskip-\my@alignment@kern
  \ignorespaces
}
\let \< = \tableft