% Copyright 2026 Open-Guji (https://github.com/open-guji)
%
% Licensed under the Apache License, Version 2.0 (the "License");
% you may not use this file except in compliance with the License.
% You may obtain a copy of the License at
%
%     http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS,
% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
% See the License for the specific language governing permissions and
% limitations under the License.

% luatex-cn-guji-cover.sty
% Cover page environment for guji (古籍) typesetting
% Provides: Cover / 封面 environment
%
\NeedsTeXFormat{LaTeX2e}
\RequirePackage{expl3}
\ProvidesExplPackage {guji/luatex-cn-guji-cover} {2026/02/26} {0.3.1} {Cover page support}

\RequirePackage{environ}
\RequirePackage{xcolor}

% ============================================================================
% Variables
% ============================================================================

\tl_new:N \l__luatexcn_cover_body_tl
\tl_new:N \l__luatexcn_cover_bg_color_tl
\tl_new:N \l__luatexcn_cover_saved_bg_tl

% ============================================================================
% Key-value Configuration
% ============================================================================

\keys_define:nn { luatexcn / cover }
  {
    background-color .tl_set:N = \l__luatexcn_cover_bg_color_tl,
    background-color .initial:n = {},
  }

% CJK key aliases
\keys_define:nn { luatexcn / cover }
  {
    底色 .tl_set:N = \l__luatexcn_cover_bg_color_tl,
  }

% ============================================================================
% Cover Environment
% ============================================================================

\NewEnviron{Cover}[1][]{%
  % Save BODY before nesting into another \NewEnviron (SinglePage)
  % to avoid infinite recursion (see MEMORY.md)
  \tl_set_eq:NN \l__luatexcn_cover_body_tl \BODY
  \keys_set:nn { luatexcn / cover } { #1 }%
  % Save the global page background color, then temporarily clear it so that
  % \begin{正文}'s apply_background does not override the cover's \pagecolor.
  \tl_set_eq:NN \l__luatexcn_cover_saved_bg_tl \l__luatexcn_page_background_color_tl
  \tl_clear:N \l__luatexcn_page_background_color_tl
  \begin{单页}
    % Apply cover-specific page background color
    \tl_if_empty:NF \l__luatexcn_cover_bg_color_tl
      {
        \tl_if_in:NnTF \l__luatexcn_cover_bg_color_tl { , }
          { \pagecolor[RGB]{\l__luatexcn_cover_bg_color_tl} }
          { \pagecolor{\l__luatexcn_cover_bg_color_tl} }
      }
    \keys_set:nn { luatexcn / content } { border = false, outer-border = false }
    \keys_set:nn { luatexcn / banxin } { banxin = false }
    \begin{正文}
      \char"200B\relax % Zero-width space placeholder to ensure page renders even when empty
      \l__luatexcn_cover_body_tl
    \end{正文}
  \end{单页}
  % Restore the global page background color
  \tl_set_eq:NN \l__luatexcn_page_background_color_tl \l__luatexcn_cover_saved_bg_tl
  % Re-apply the restored background: if template has a background-color, set it
  % back via \pagecolor; otherwise clear it.
  \tl_if_empty:NTF \l__luatexcn_page_background_color_tl
    { \nopagecolor }
    {
      \tl_if_in:NnTF \l__luatexcn_page_background_color_tl { , }
        { \pagecolor [RGB] { \l__luatexcn_page_background_color_tl } }
        { \pagecolor { \l__luatexcn_page_background_color_tl } }
    }
}

% ============================================================================
% CJK Aliases (中文别名)
% ============================================================================
% Simplified Chinese / 简体 (封面简繁同形)
\NewEnvironmentCopy{封面}{Cover}

\ExplSyntaxOff
\endinput