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% Copyright (C) 2010-2014 by Ulrich M. Schwarz
% Copyright (C) 2019      by Frank Mittelbach
% Copyright (C) 2020-     by Yukai Chou
%
% This file may be distributed and/or modified under the conditions of
% the LaTeX Project Public License, version 1.3c.
% The license can be obtained from
% http://www.latex-project.org/lppl/lppl-1-3c.txt
%
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%
% Mostly, this key wraps the theorem in a |shadebox| environment.
% The parameters are set by treating the value we are given as
% a new key-val list, see below.
%
%    \begin{macrocode}
  \define@key{thmdef}{shaded}[{}]{%
  \thmt@trytwice{}{%
    \RequirePackage{shadethm}%
    \RequirePackage{thm-patch}%
    \addtotheorempreheadhook[\thmt@envname]{%
      \setlength\shadedtextwidth{\linewidth}%
      \kvsetkeys{thmt@shade}{#1}\begin{shadebox}}%
    \addtotheorempostfoothook[\thmt@envname]{\end{shadebox}}%
    }%
  }
%    \end{macrocode}
% The docs for |shadethm| say:
% \begin{quote}
%   There are some parameters you could set the default for (try them as is,
% first).
% \begin{itemize}
%    \item |shadethmcolor|\quad  The shading color of the background.  See the
%      documentation for the color package, but with a `gray' model, I find .97
%      looks good out of my printer, while a darker shade like .92 is needed
%      to make it copy well.  (Black is  0, white is 1.)
%    \item |shaderulecolor|\quad  The shading color of the border of the shaded box.
%      See (i).  If shadeboxrule is set to 0pt then this won't print anyway.
%    \item |shadeboxrule|\quad  The width of the border around the shading.  Set it to
%      0pt (not just 0) to make it disappear.
%    \item |shadeboxsep|\quad  The length by which the shade box surrounds the text.
% \end{itemize}
% \end{quote}
%
% So, let's just define keys for all of these.
%
%    \begin{macrocode}
\define@key{thmt@shade}{textwidth}  {\setlength\shadedtextwidth{#1}}
\define@key{thmt@shade}{bgcolor}    {\thmt@definecolor{shadethmcolor}{#1}}
\define@key{thmt@shade}{rulecolor}  {\thmt@definecolor{shaderulecolor}{#1}}
\define@key{thmt@shade}{rulewidth}  {\setlength\shadeboxrule{#1}}
\define@key{thmt@shade}{margin}     {\setlength\shadeboxsep{#1}}
\define@key{thmt@shade}{padding}    {\setlength\shadeboxsep{#1}}
\define@key{thmt@shade}{leftmargin} {\setlength\shadeleftshift{#1}}
\define@key{thmt@shade}{rightmargin}{\setlength\shaderightshift{#1}}
%    \end{macrocode}
%
% What follows is wizardry you don't have to understand. In essence,
% we want to support two notions of color: one is ``everything that goes
% after |\definecolor{shadethmcolor}|'', such as 
% |{rgb}{0.8,0.85,1}|. On the other hand, we'd also like
% to recognize an already defined color name such as |blue|.
%
% To handle the latter case, we need to copy the definition of one color
% into another. The \pkg{xcolor} package offers |\colorlet| for that, 
% for the \pkg{color} package, we just cross our fingers.
%    \begin{macrocode}
\def\thmt@colorlet#1#2{%
  %\typeout{don't know how to let color `#1' be like color `#2'!}%
  \@xa\let\csname\string\color@#1\@xa\endcsname
    \csname\string\color@#2\endcsname
  % this is dubious at best, we don't know what a backend does.
}
\AtBeginDocument{%
  \ifcsname colorlet\endcsname
    \let\thmt@colorlet\colorlet
  \fi
}
%    \end{macrocode}
% Now comes the interesting part: we assume that a simple color name
% must not be in braces, and a color definition starts with an opening
% curly brace. (So, if |\definecolor| ever gets an optional arg,
% we are in a world of pain.)
%
% If the second argument to |\thmt@definecolor| (the key) starts
% with a brace,
% then |\thmt@def@color| will have an empty second argument,
% delimited by the brace of the key. Hopefully, the key will have exactly
% enough arguments to satisfy |\definecolor|. Then, 
% |thmt@drop@relax| will be executed and gobble the fallback
% values and the |\thmt@colorlet|.
%
% If the key does not contain an opening brace, |\thmt@def@color|
% will drop everything up to |{gray}{0.5}|. So, first the color
% gets defined to a medium gray, but then, it immediately gets overwritten
% with the definition corresponding to the color name.
%    \begin{macrocode}
\def\thmt@drop@relax#1\relax{}
\def\thmt@definecolor#1#2{%
  \thmt@def@color{#1}#2\thmt@drop@relax 
    {gray}{0.5}%
    \thmt@colorlet{#1}{#2}%
  \relax
}
\def\thmt@def@color#1#2#{%
  \definecolor{#1}}
%    \end{macrocode}
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