wtxsection.sty

%%
%% This is file 'wtxsection.sty'.
%%
%% Copyright 2019 Takuto ASAKURA (wtsnjp)
%%   GitHub:   https://github.com/wtsnjp
%%   Twitter:  @wtsnjp
%%
%% This package is distributed under the MIT License.
%%

% Note: This package is a conceptual TOY package. Don't be so serious.

% -------------------------------------------------- declarations

\RequirePackage{xparse}
\ProvidesExplPackage {wtxsection} {2019/09/23} {0.1.0}
  {LaTeX section extencion for begin-end balancing}

% -------------------------------------------------- variables

\seq_new:N \g_wtxs_sections_seq

\str_new:N \l_wtxs_cur_type_str
\str_new:N \l_wtxs_cur_name_str

% -------------------------------------------------- messages

\msg_new:nnn { wtxsection } { already-declared }
  {
    Section~type~"#1"~is~already~declared.
  }
\msg_new:nnn { wtxsection } { not-declared }
  {
    Section~type~"#1"~has~not~been~declared.
  }
\msg_new:nnn { wtxsection } { seq-emtpy }
  {
    End~of~section~is~declared~\msg_line_context:,~
    but~no~section~has~been~begun.
  }
\msg_new:nnn { wtxsection } { bad-end }
  {
    End~of~#1~is~declared~\msg_line_context:,~
    but~you~must~declare~the~end~of~#2~"#3"~first.
  }
\msg_new:nnn { wtxsection } { unclosed-section }
  {
    End~of~document~is~declared~before~the~end~of~
    #1~"#2"~is~declared.
  }

% -------------------------------------------------- utility

% LaTeX2e stuff
%% \__wtxs_only_preamble:N \CS
\cs_new_eq:Nc \__wtxs_only_preamble:N { @onlypreamble }

%% \__wtxs_at_end_document:n { <code> }
\cs_new_eq:NN \__wtxs_at_end_document:n \AtEndDocument

% -------------------------------------------------- LaTeX2e interface

%% \xDeclareNewSection { <type> } { <command> }
\NewDocumentCommand \xDeclareNewSection { m m }
  {
    \str_if_exist:cTF { c_wtxs_#1_str }
      {
        \msg_critical:nnn { wtxsection } { already-declared } {#1}
      }
      {
        \wtxs_declare_new_section:nn {#1} {#2}
      }
  }
\__wtxs_only_preamble:N \xDeclareNewSection

%% \xBegin { <type> } (*) [<toc name>] { <name> }
\NewDocumentCommand \xBegin { m s o m }
  {
    \str_if_exist:cTF { c_wtxs_#1_str }
      {
        \IfBooleanTF {#2}
          {
            % begin xsection
            \use:c { wtxs_begin_#1:n } {#4}

            % execute actual LaTeX2e section with star
            \use:c { wtxs_cmd_#1: } * {#4}
          }
          {
            \IfNoValueTF {#3}
              {
                % begin xsection
                \use:c { wtxs_begin_#1:n } {#4}

                % execute actual LaTeX2e section
                \use:c { wtxs_cmd_#1: } {#4}
              }
              {
                % begin xsection
                \use:c { wtxs_begin_#1:n } {#3}

                % execute actual LaTeX2e section with an optional argument
                \use:c { wtxs_cmd_#1: } [#3] {#4}
              }
          }
      }
      {
        \msg_critical:nnn { wtxsection } { not-declared } {#1}
      }
  }

%% \xEnd { <type> }
\NewDocumentCommand \xEnd { m }
  {
    \str_if_exist:cTF { c_wtxs_#1_str }
      {
        \use:c { wtxs_end_#1: }
      }
      {
        \msg_critical:nnn { wtxsection } { not-declared } {#1}
      }
  }

% -------------------------------------------------- implementation

%% \wtxs_declare_new_section:nn { <type> } { <command> }
\cs_new:Npn \wtxs_declare_new_section:nn #1#2
  {
    % declare the section
    \str_const:cn { c_wtxs_#1_str } { #1 }

    % copy the actual command
    \cs_new_eq:cN { wtxs_cmd_#1: } #2

    % begin section
    \cs_new:cpn { wtxs_begin_#1:n } ##1
      {
        \seq_gput_left:Nn \g_wtxs_sections_seq { {#1} ##1 }
      }

    % end section
    \cs_new:cn { wtxs_end_#1: }
      {
        \seq_gpop_left:NNTF \g_wtxs_sections_seq \l_tmpa_tl
          {
            \str_set:Nx \l_wtxs_cur_type_str { \tl_head:V \l_tmpa_tl }
            \str_set:Nx \l_wtxs_cur_name_str { \tl_tail:V \l_tmpa_tl }

            \str_if_eq:NcF \l_wtxs_cur_type_str { c_wtxs_#1_str }
              {
                \msg_critical:nnxxx { wtxsection } { bad-end } { #1 }
                  { \str_use:N \l_wtxs_cur_type_str }
                  { \str_use:N \l_wtxs_cur_name_str }
              }
          }
          { \msg_critical:nn { wtxsection } { seq-emtpy } }
      }
  }

\cs_new:Nn \wtxs_check_end_of_document:
  {
    \seq_gpop_left:NNT \g_wtxs_sections_seq \l_tmpa_tl
      {
        \str_set:Nx \l_wtxs_cur_type_str { \tl_head:V \l_tmpa_tl }
        \str_set:Nx \l_wtxs_cur_name_str { \tl_tail:V \l_tmpa_tl }

        \msg_critical:nnxx { wtxsection } { unclosed-section }
          { \str_use:N \l_wtxs_cur_type_str }
          { \str_use:N \l_wtxs_cur_name_str }
      }
  }
\__wtxs_at_end_document:n { \wtxs_check_end_of_document: }

% vim: ft=expl3 nospell:
%% EOF