%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                         %
%  easyformat  Easily add boldface, italics and smallcaps in LaTeX.       %
%  Copyright (C) 2017  Evert Provoost <evert.provoost@gmail.com>          %
%                                                                         %
%  This program is free software: you can redistribute it and/or modify   %
%  it under the terms of the GNU General Public License as published by   %
%  the Free Software Foundation, either version 3 of the License, or      %
%  (at your option) any later version.                                    %
%                                                                         %
%  This program is distributed in the hope that it will be useful,        %
%  but WITHOUT ANY WARRANTY; without even the implied warranty of         %
%  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the          %
%  GNU General Public License for more details.                           %
%                                                                         %
%  You should have received a copy of the GNU General Public License      %
%  along with this program.  If not, see <http://www.gnu.org/licenses/>.  %
%                                                                         %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


%% NOTE TO THE FUTURE:
%    In LaTeX3 the `New Font Selection Scheme' is replaced
%    by XFSS (xfont). Moving will require some research.


%% Administration...
\RequirePackage{expl3}[2016/04/21]
\ProvidesExplPackage
  {easyformat}
  {2017/06/03}
  {1.4.0}
  {Easily add boldface, italics and smallcaps.}


%% Public macros
% Add macros to switch the syntax on or off.
\cs_new:Npn \enableeasyformat
  {
    \char_set_catcode_active:N _
    \char_set_catcode_active:N ^
  }

\cs_new:Npn \disableeasyformat
  {
    \char_set_catcode_math_subscript:N _
    \char_set_catcode_math_superscript:N ^
  }

% Add a macro LaTeX should have...
% Which is protected to fix the double superscript error
% and able to give correct kerning in mathmode.
\cs_new_protected:Npn \cir
  {
    \mode_if_math:TF
      { \hat{} }
      { \c_circumflex_str }
  }


%% Variables
% Remember the style before changing to italics/boldface/smallcaps.
\str_new:N \l__prev_shape_str
\str_set_eq:NN \l__prev_shape_str \shapedefault

\str_new:N \l__prev_case_str
% Case is the option used in XFSS, however do note that in
% LaTeX2e's NFSS, smallcaps is a kind of shape.
\str_set_eq:NN \l__prev_case_str \shapedefault

\str_new:N \l__prev_series_str
\str_set_eq:NN \l__prev_series_str \seriesdefault


%% Formating handling
% Add macros which change the font shape and font series.
\cs_new:Npn \__font_set_shape:n #1
  {
    \fontshape {#1}
    \selectfont
  }

\cs_new:Npn \__font_set_series:n #1
  {
    \fontseries {#1}
    \selectfont
  }

% Switch italics on or off.
\cs_new:Npn \__handle_italics:
  {
    \str_if_eq:NNTF \f@shape \itdefault
      {
        \__font_set_shape:n {\l__prev_shape_str}
        \str_set_eq:NN \l__prev_shape_str \shapedefault
        % \maybe@ic adds italics correction if needed.
        % Probably becomes \xfss_maybe_ic: in LaTeX3.
        \maybe@ic
      }
      {
        \str_set_eq:NN \l__prev_shape_str \f@shape
        \itshape
      }
  }

% Switch smallcaps on or off.
\cs_new:Npn \__handle_smallcaps:
  {
    \str_if_eq:NNTF \f@shape \scdefault
      {
        \__font_set_shape:n {\l__prev_case_str}
        \str_set_eq:NN \l__prev_case_str \shapedefault
      }
      {
        \str_set_eq:NN \l__prev_case_str \f@shape
        \scshape
      }
  }

% Switch boldface on or off.
\cs_new:Npn \__handle_boldface:
  {
    \str_if_eq:NNTF \f@series \bfdefault
      {
        \__font_set_series:n {\l__prev_series_str}
        \str_set_eq:NN \l__prev_series_str \seriesdefault
      }
      {
        \str_set_eq:NN \l__prev_series_str \f@series
        \bfseries
      }
  }


%% Handling the syntax
% This is where the magic happens (also differentiates between
% text- and mathmode.)
% These are protected because they should also work in eg. \section{}

% Syntax handling for the underscore: italics and boldface.
\cs_new_protected:Npn \__syntax_underscore:
  {
    \mode_if_math:TF
      { \c_math_subscript_token }
      {
        \peek_charcode_remove:NTF _
          % The second underscore is removed when detected.
          { \__handle_boldface: }
          { \__handle_italics: }
      }
  }

% Syntax handling for the circumflex: smallcaps.
\cs_new_protected:Npn \__syntax_circumflex:
  {
    \mode_if_math:TF
      { \c_math_superscript_token }
      { \__handle_smallcaps: }
  }

% Now give the underscore and the circumflex their behaviour.
\char_set_active_eq:NN _ \__syntax_underscore:
\char_set_active_eq:NN ^ \__syntax_circumflex:


%% Activate the systems.
% First disable the Expl3 syntax as it will only cause trouble.
\ExplSyntaxOff

% Now enable the easyformat syntax.
\enableeasyformat

% DONE!!!


%% IMPLEMENTATION DETAILS:
%% Why not \textit/bf/sc\bgroup and \egroup?
%      Well actualy that was the original solution. However this
%      doesn't differentiate between ending itallics or ending
%      boldface. The current solution does and this makes the
%      syntax more predictable and generally more useful.

%% Why no ^^typewriter^^?
%     because this doesn't add much value, in most contexts
%     where a monospace font is useful there is already
%     other syntax available.