%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Copyright © 2021 Maximilian Keßler
% 
% 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.
% 
% This LaTeX package is free software and distributed under the MIT License. You
% may use it freely for your purposes. The latest version of the package can be
% obtained via GitHub under
%    https://github.com/kesslermaximilian/LatexPackages
% For further information see the url above.
% Reportings of bugs, suggestions and improvements are welcome, see the README
% at the Git repository for further information.
% 
% This package has been generated by PyTeX, available at
%    https://github.com/kesslermaximilian/PyTeX
% and built from source file 'findpackage.pysty'.
% It is STRONGLY DISCOURAGED to edit this source file directly, since local
% changes will not be versioned by Git and overwritten by the next build. Always
% edit the source file and build the package again.
% 
% Build details:
%   Build time: 2021/10/17 14:13
%   PyTeX version: v1.0.0-3 (commit 4409c94)
%   LatexPackages version: v2.2.1 (commit db62b98)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{mkessler-findpackage}[2021/10/17 - Find a package that provides some command]


% This is just a quick packaging of the post by
%   'Martin Nyolt' (https://tex.stackexchange.com/users/78783/martin-nyolt)
% found at
%   https://tex.stackexchange.com/users/78783/martin-nyolt
% Note that SO answers are by default CC BY-SA 3.0 licensed, see
%   https://creativecommons.org/licenses/by-sa/3.0/

\def\find@load#1[#2]#3[#4]{%
    % load the package
    \find@fileswith@pti@ns{#1}[#2]{#3}[#4]%
    % check if commands exists now
    \ifcsname\find@command\endcsname
        \typeout{Package #3 introduces command \find@command.}%
        % command has been found, revert to original version without checks
        \let\@fileswith@pti@ns\find@fileswith@pti@ns
    \else
        % somehow, \@fileswith@pti@ns is restored after loading a package
        % thus, patch it again
        \let\@fileswith@pti@ns\find@load
    \fi
}%

\newcommand*{\findpackagebycommand}[1]{%
    % using this multiple times - esp. when the package has not been found yet -
    % will break things. Thus, check first that \find@command has never been defined before
    \ifx\find@command\undefined
        \def\find@command{#1}%
        % first, check if this command is already defined
        \ifcsname\find@command\endcsname
            % in this case, just issue a warning and do nothing
            \@latex@warning@no@line{Command \find@command \space is already defined}%
        \else
            % overwrite the internal \@fileswith@pti@ns command, which does the actual loading
            % \@fileswith@pti@ns is used internally by \usepackage and \RequirePackage
            \let\find@fileswith@pti@ns\@fileswith@pti@ns
            \let\@fileswith@pti@ns\find@load
        \fi
    \else
        % used multiple times - prevent and give a warning
        \@latex@warning@no@line{You can use \protect\findpackagebycommand \space only once}%
        \errmessage{Invalid use of command findpackagebycommand.}%
    \fi
}