% 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} {2026/10/29} {0.4.3} {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 } }
    }
}


% ============================================================================
% 线装书封面 (issue #170)
% ============================================================================
% 现代蓝色线装书封面（中华书局、广陵书社等影印古籍常见样式），参照
% CY/T 247—2021《线装书籍要求》图 1、图 2：
%   藏青色封面，左上角贴一条米色签条；签条内为「文武线」双框（外粗内细），
%   框外留一圈纸边；书名大字自上而下；册次、卷次等小字排在签条下部
%  （或紧随书名之后）。封面上不印作者、出版者。
%
%   \线装书封面[键值]{书名}
%
% 签条宽、位置、书名字号默认按页面尺寸比例取值；签条高度取「最小高度」与
% 「书名 + 小字所需高度」中的较大者，书名越长签条越高。
%
% 实现：签条由三层悬浮文本框叠成——底纸（仅底色）、文武线框 + 书名、小字。
% 悬浮框按注册先后绘制（见 render-page.lua），后者叠在前者之上。

\tl_new:N \l__luatexcn_tcover_title_tl
\tl_new:N \l__luatexcn_tcover_volume_tl
\tl_new:N \l__luatexcn_tcover_juan_tl
\tl_new:N \l__luatexcn_tcover_small_pos_tl
\tl_new:N \l__luatexcn_tcover_bg_tl
\tl_new:N \l__luatexcn_tcover_label_bg_tl
\tl_new:N \l__luatexcn_tcover_ink_tl
\dim_new:N \l__luatexcn_tcover_pw_dim          % 页宽（逻辑页）
\dim_new:N \l__luatexcn_tcover_ph_dim          % 页高
\dim_new:N \l__luatexcn_tcover_w_dim           % 签条宽
\dim_new:N \l__luatexcn_tcover_left_dim        % 签条左距
\dim_new:N \l__luatexcn_tcover_top_dim         % 签条上距
\dim_new:N \l__luatexcn_tcover_minh_dim        % 签条最小高
\dim_new:N \l__luatexcn_tcover_fs_dim          % 书名字号
\dim_new:N \l__luatexcn_tcover_sfs_dim         % 小字字号
\dim_new:N \l__luatexcn_tcover_h_dim           % 签条实际高
\dim_new:N \l__luatexcn_tcover_m_dim           % 纸边
\dim_new:N \l__luatexcn_tcover_thick_dim       % 外粗线
\dim_new:N \l__luatexcn_tcover_thin_dim        % 内细线
\dim_new:N \l__luatexcn_tcover_sep_dim         % 粗细线间距
\dim_new:N \l__luatexcn_tcover_pad_dim         % 内框到书名的上下留白
\dim_new:N \l__luatexcn_tcover_ext_dim         % 内框外扩（细线半宽 + 间距 + 粗线）
\dim_new:N \l__luatexcn_tcover_gw_dim          % 字格宽
\dim_new:N \l__luatexcn_tcover_need_dim
\dim_new:N \l__luatexcn_tcover_small_h_dim
\dim_new:N \l__luatexcn_tcover_x_dim
\dim_new:N \l__luatexcn_tcover_y_dim
\bool_new:N \l__luatexcn_tcover_thread_bool
\tl_new:N \l__luatexcn_tcover_thread_color_tl
\int_new:N \l__luatexcn_tcover_holes_int
\dim_new:N \l__luatexcn_tcover_thread_x_dim
\dim_new:N \l__luatexcn_tcover_thread_w_dim
\int_new:N \l__luatexcn_tcover_nt_int
\int_new:N \l__luatexcn_tcover_nv_int
\dim_new:N \l__luatexcn_tcover_title_h_dim
\dim_new:N \l__luatexcn_tcover_maxh_dim
\fp_new:N \l__luatexcn_tcover_ratio_fp
\int_new:N \l__luatexcn_tcover_nj_int

\keys_define:nn { luatexcn / threadcover }
  {
    background-color .tl_set:N = \l__luatexcn_tcover_bg_tl,
    background-color .initial:n = { 30, 50, 90 },
    label-color .tl_set:N = \l__luatexcn_tcover_label_bg_tl,
    label-color .initial:n = { 232, 228, 212 },
    ink-color .tl_set:N = \l__luatexcn_tcover_ink_tl,
    ink-color .initial:n = { 25, 25, 25 },
    % 以下长度取 0pt 表示「按页面比例自动」
    label-width .dim_set:N = \l__luatexcn_tcover_w_dim,
    label-left .dim_set:N = \l__luatexcn_tcover_left_dim,
    label-top .dim_set:N = \l__luatexcn_tcover_top_dim,
    label-min-height .dim_set:N = \l__luatexcn_tcover_minh_dim,
    title-font-size .dim_set:N = \l__luatexcn_tcover_fs_dim,
    small-font-size .dim_set:N = \l__luatexcn_tcover_sfs_dim,
    volume .tl_set:N = \l__luatexcn_tcover_volume_tl,
    juan .tl_set:N = \l__luatexcn_tcover_juan_tl,
    small-position .choices:nn = { bottom, follow }
      { \tl_set_eq:NN \l__luatexcn_tcover_small_pos_tl \l_keys_choice_tl },
    small-position .initial:n = bottom,
    % 订线（仅供预览：印制封面时不印）
    binding-thread .bool_set:N = \l__luatexcn_tcover_thread_bool,
    binding-thread .default:n = true,
    binding-thread .initial:n = false,
    thread-color .tl_set:N = \l__luatexcn_tcover_thread_color_tl,
    thread-color .initial:n = { 236, 236, 230 },
    thread-holes .int_set:N = \l__luatexcn_tcover_holes_int,
    thread-holes .initial:n = 4,
    thread-distance .dim_set:N = \l__luatexcn_tcover_thread_x_dim,
    % 简体
    订线 .meta:n = { binding-thread = {#1} },
    订线 .default:n = true,
    订线颜色 .meta:n = { thread-color = {#1} },
    订线眼数 .meta:n = { thread-holes = {#1} },
    订线距 .meta:n = { thread-distance = {#1} },
    底色 .meta:n = { background-color = {#1} },
    签条底色 .meta:n = { label-color = {#1} },
    墨色 .meta:n = { ink-color = {#1} },
    签条宽 .meta:n = { label-width = {#1} },
    签条左距 .meta:n = { label-left = {#1} },
    签条上距 .meta:n = { label-top = {#1} },
    签条最小高 .meta:n = { label-min-height = {#1} },
    书名字号 .meta:n = { title-font-size = {#1} },
    小字字号 .meta:n = { small-font-size = {#1} },
    册次 .meta:n = { volume = {#1} },
    卷次 .meta:n = { juan = {#1} },
    小字位置 .choice:,
    小字位置 / 底部 .meta:n = { small-position = bottom },
    小字位置 / 随后 .meta:n = { small-position = follow },
    % 繁體
    簽條底色 .meta:n = { label-color = {#1} },
    簽條寬 .meta:n = { label-width = {#1} },
    簽條左距 .meta:n = { label-left = {#1} },
    簽條上距 .meta:n = { label-top = {#1} },
    簽條最小高 .meta:n = { label-min-height = {#1} },
    書名字號 .meta:n = { title-font-size = {#1} },
    小字字號 .meta:n = { small-font-size = {#1} },
    冊次 .meta:n = { volume = {#1} },
    訂線 .meta:n = { binding-thread = {#1} },
    訂線 .default:n = true,
    訂線顏色 .meta:n = { thread-color = {#1} },
    訂線眼數 .meta:n = { thread-holes = {#1} },
    訂線距 .meta:n = { thread-distance = {#1} },
    小字位置 / 隨後 .meta:n = { small-position = follow },
  }

% 当前逻辑页宽 / 页高（对开模式下取半页宽；悬浮框 x 以逻辑页右边计）
\cs_new:Npn \__luatexcn_tcover_page_width:
  {
    \lua_now:n
      {
        local~sp = require('core.luatex-cn-core-page').split ;
        local~w = _G.page.paper_width~or~0 ;
        if~sp.is_enabled()~and~sp.get_target_width()~>~0~then~
          w = sp.get_target_width() ;
        end ;
        tex.sprint((w~/~65536)~..~'pt') ;
      }
  }
\cs_new:Npn \__luatexcn_tcover_page_height:
  { \lua_now:n { tex.sprint(((_G.page.paper_height~or~0)~/~65536)~..~'pt') } }

% 放一个悬浮文本框：#1 = 左距, #2 = 上距, #3 = 盒宽（含边框外扩）, #4 = 其余键值, #5 = 内容
\cs_new_protected:Npn \__luatexcn_tcover_float:nnnnn #1 #2 #3 #4 #5
  {
    \tl_set:Nx \l_tmpa_tl
      {
        [
          floating = true,
          x = \dim_eval:n { \l__luatexcn_tcover_pw_dim - (#1) - (#3) },
          y = \dim_eval:n {#2},
          #4
        ]
      }
    \exp_after:wN \TextBox \l_tmpa_tl {#5}
  }

% 竖排小字一列：#1 = 列中心距页面左边, #2 = 上距, #3 = 文字
\cs_new_protected:Npn \__luatexcn_tcover_small:nnn #1 #2 #3
  {
    \tl_if_blank:nF {#3}
      {
    \__luatexcn_tcover_float:nnnnn
      { (#1) - 0.6 \l__luatexcn_tcover_sfs_dim } {#2} { 1.2 \l__luatexcn_tcover_sfs_dim }
      {
        font-size = \dim_use:N \l__luatexcn_tcover_sfs_dim,
        grid-height = \dim_eval:n { 1.1 \l__luatexcn_tcover_sfs_dim },
        grid-width = \dim_eval:n { 1.2 \l__luatexcn_tcover_sfs_dim },
        height = \int_eval:n { \tl_count:n {#3} },
        column-align = center,
        font-color = { \l__luatexcn_tcover_ink_tl },
      }
      {#3}
      }
  }
\cs_generate_variant:Nn \__luatexcn_tcover_small:nnn { nnV }

% 订线：一条竖线 + 每个订眼一条横线（绕到书背），用纯色悬浮框画出。
% 位置参照 CY/T 247—2021 图 2：订线距右边约页宽 8%，首末订眼距上下边约页高 11.5%，
% 其余订眼等分。
\cs_new_protected:Npn \__luatexcn_tcover_bar:nnnn #1 #2 #3 #4
  {
    % #1 左距, #2 上距, #3 宽, #4 高
    \__luatexcn_tcover_float:nnnnn {#1} {#2} {#3}
      {
        grid-width = \dim_eval:n {#3},
        grid-height = \dim_eval:n {#4},
        height = 1,
        background-color = { \l__luatexcn_tcover_thread_color_tl },
      }
      { \char"200B }
  }
\cs_new_protected:Npn \__luatexcn_tcover_thread:
  {
    \dim_compare:nNnT \l__luatexcn_tcover_thread_x_dim = \c_zero_dim
      { \dim_set:Nn \l__luatexcn_tcover_thread_x_dim { 0.08 \l__luatexcn_tcover_pw_dim } }
    \dim_set:Nn \l__luatexcn_tcover_thread_w_dim
      { \dim_max:nn { 0.8pt } { 0.0022 \l__luatexcn_tcover_pw_dim } }
    % 竖线
    \__luatexcn_tcover_bar:nnnn
      { \l__luatexcn_tcover_pw_dim - \l__luatexcn_tcover_thread_x_dim - 0.5 \l__luatexcn_tcover_thread_w_dim }
      { 0pt } { \l__luatexcn_tcover_thread_w_dim } { \l__luatexcn_tcover_ph_dim }
    % 横线（订眼）
    \int_step_inline:nn { \int_max:nn { 2 } { \l__luatexcn_tcover_holes_int } }
      {
        \__luatexcn_tcover_bar:nnnn
          { \l__luatexcn_tcover_pw_dim - \l__luatexcn_tcover_thread_x_dim }
          {
            \fp_eval:n
              { 0.115 + 0.77 * ( ##1 - 1 ) / ( \int_max:nn { 2 } { \l__luatexcn_tcover_holes_int } - 1 ) }
              \l__luatexcn_tcover_ph_dim
            - 0.5 \l__luatexcn_tcover_thread_w_dim
          }
          { \l__luatexcn_tcover_thread_x_dim }
          { \l__luatexcn_tcover_thread_w_dim }
      }
  }

% 由字号推出：上下留白、书名列高、小字区高、所需签条高
\cs_new_protected:Npn \__luatexcn_tcover_measure:
  {
    \dim_set:Nn \l__luatexcn_tcover_pad_dim { 0.2 \l__luatexcn_tcover_fs_dim }
    \dim_set:Nn \l__luatexcn_tcover_title_h_dim
      { \fp_eval:n { 1.05 * \l__luatexcn_tcover_nt_int } \l__luatexcn_tcover_fs_dim }
    \dim_set:Nn \l__luatexcn_tcover_small_h_dim
      {
        \fp_eval:n { 1.1 * max ( \l__luatexcn_tcover_nv_int , \l__luatexcn_tcover_nj_int ) }
          \l__luatexcn_tcover_sfs_dim
      }
    \dim_set:Nn \l__luatexcn_tcover_need_dim
      {
        \l__luatexcn_tcover_title_h_dim + \l__luatexcn_tcover_small_h_dim
        + \dim_compare:nNnTF \l__luatexcn_tcover_small_h_dim > \c_zero_dim
            { 0.45 \l__luatexcn_tcover_fs_dim } { 0pt }
        + 2 \l__luatexcn_tcover_pad_dim
        + 2 \l__luatexcn_tcover_ext_dim + 2 \l__luatexcn_tcover_m_dim
      }
  }

\cs_new_protected:Npn \__luatexcn_tcover_body:
  {
    \dim_set:Nn \l__luatexcn_tcover_pw_dim { \__luatexcn_tcover_page_width: }
    \dim_set:Nn \l__luatexcn_tcover_ph_dim { \__luatexcn_tcover_page_height: }
    % ---- 自动比例（参照标准图 1/2 与实物量取）----
    \dim_compare:nNnT \l__luatexcn_tcover_w_dim = \c_zero_dim
      { \dim_set:Nn \l__luatexcn_tcover_w_dim { 0.23 \l__luatexcn_tcover_pw_dim } }
    \dim_compare:nNnT \l__luatexcn_tcover_left_dim = \c_zero_dim
      { \dim_set:Nn \l__luatexcn_tcover_left_dim { 0.05 \l__luatexcn_tcover_pw_dim } }
    \dim_compare:nNnT \l__luatexcn_tcover_top_dim = \c_zero_dim
      { \dim_set:Nn \l__luatexcn_tcover_top_dim { 0.04 \l__luatexcn_tcover_ph_dim } }
    \dim_compare:nNnT \l__luatexcn_tcover_minh_dim = \c_zero_dim
      { \dim_set:Nn \l__luatexcn_tcover_minh_dim { 0.5 \l__luatexcn_tcover_ph_dim } }
    \dim_compare:nNnT \l__luatexcn_tcover_fs_dim = \c_zero_dim
      { \dim_set:Nn \l__luatexcn_tcover_fs_dim { 0.56 \l__luatexcn_tcover_w_dim } }
    \dim_compare:nNnT \l__luatexcn_tcover_sfs_dim = \c_zero_dim
      { \dim_set:Nn \l__luatexcn_tcover_sfs_dim { 0.3 \l__luatexcn_tcover_fs_dim } }
    % ---- 签条内部尺寸 ----
    \dim_set:Nn \l__luatexcn_tcover_m_dim { 0.055 \l__luatexcn_tcover_w_dim }
    \dim_set:Nn \l__luatexcn_tcover_thick_dim { 0.013 \l__luatexcn_tcover_w_dim }
    \dim_set:Nn \l__luatexcn_tcover_thin_dim { 0.004 \l__luatexcn_tcover_w_dim }
    \dim_set:Nn \l__luatexcn_tcover_sep_dim { 0.025 \l__luatexcn_tcover_w_dim }
    \dim_set:Nn \l__luatexcn_tcover_ext_dim
      { 0.5 \l__luatexcn_tcover_thin_dim + \l__luatexcn_tcover_sep_dim + \l__luatexcn_tcover_thick_dim }
    \dim_set:Nn \l__luatexcn_tcover_gw_dim
      { \l__luatexcn_tcover_w_dim - 2 \l__luatexcn_tcover_m_dim - 2 \l__luatexcn_tcover_ext_dim }
    % ---- 高度：书名 + 小字 + 留白，与最小高取大 ----
    \int_set:Nn \l__luatexcn_tcover_nv_int { \tl_count:V \l__luatexcn_tcover_volume_tl }
    \int_set:Nn \l__luatexcn_tcover_nj_int { \tl_count:V \l__luatexcn_tcover_juan_tl }
    \int_set:Nn \l__luatexcn_tcover_nt_int { \tl_count:V \l__luatexcn_tcover_title_tl }
    \__luatexcn_tcover_measure:
    % 书名过长、签条超出页面时，按比例缩小书名与小字
    \dim_set:Nn \l__luatexcn_tcover_maxh_dim
      { \l__luatexcn_tcover_ph_dim - 2 \l__luatexcn_tcover_top_dim }
    \dim_compare:nNnT \l__luatexcn_tcover_need_dim > \l__luatexcn_tcover_maxh_dim
      {
        \fp_set:Nn \l__luatexcn_tcover_ratio_fp
          { \dim_to_fp:n \l__luatexcn_tcover_maxh_dim / \dim_to_fp:n \l__luatexcn_tcover_need_dim }
        \dim_set:Nn \l__luatexcn_tcover_fs_dim
          { \fp_use:N \l__luatexcn_tcover_ratio_fp \l__luatexcn_tcover_fs_dim }
        \dim_set:Nn \l__luatexcn_tcover_sfs_dim
          { \fp_use:N \l__luatexcn_tcover_ratio_fp \l__luatexcn_tcover_sfs_dim }
        \__luatexcn_tcover_measure:
      }
    \dim_set:Nn \l__luatexcn_tcover_h_dim
      { \dim_max:nn \l__luatexcn_tcover_minh_dim \l__luatexcn_tcover_need_dim }
    \bool_if:NT \l__luatexcn_tcover_thread_bool { \__luatexcn_tcover_thread: }
    % ---- 第一层：底纸 ----
    \__luatexcn_tcover_float:nnnnn
      { \l__luatexcn_tcover_left_dim } { \l__luatexcn_tcover_top_dim } { \l__luatexcn_tcover_w_dim }
      {
        grid-width = \dim_use:N \l__luatexcn_tcover_w_dim,
        grid-height = \dim_use:N \l__luatexcn_tcover_h_dim,
        height = 1,
        background-color = { \l__luatexcn_tcover_label_bg_tl },
      }
      { \char"200B }
    % ---- 第二层：文武线框 + 书名 ----
    \__luatexcn_tcover_float:nnnnn
      { \l__luatexcn_tcover_left_dim + \l__luatexcn_tcover_m_dim }
      { \l__luatexcn_tcover_top_dim + \l__luatexcn_tcover_m_dim }
      { \l__luatexcn_tcover_w_dim - 2 \l__luatexcn_tcover_m_dim }
      {
        font-size = \dim_use:N \l__luatexcn_tcover_fs_dim,
        grid-height = \dim_eval:n { 1.05 \l__luatexcn_tcover_fs_dim },
        grid-width = \dim_use:N \l__luatexcn_tcover_gw_dim,
        height = \dim_eval:n
          { \l__luatexcn_tcover_h_dim - 2 \l__luatexcn_tcover_m_dim - 2 \l__luatexcn_tcover_ext_dim },
        padding-top = \dim_use:N \l__luatexcn_tcover_pad_dim,
        column-align = center,
        font-color = { \l__luatexcn_tcover_ink_tl },
        border-color = { \l__luatexcn_tcover_ink_tl },
        border-shape = rect,
        border-width = \dim_use:N \l__luatexcn_tcover_thin_dim,
        border-margin = 0pt,
        outer-border = true,
        outer-border-thickness = \dim_use:N \l__luatexcn_tcover_thick_dim,
        outer-border-sep = \dim_use:N \l__luatexcn_tcover_sep_dim,
      }
      { \l__luatexcn_tcover_title_tl }
    % ---- 第三层：册次 / 卷次 ----
    \dim_compare:nNnT \l__luatexcn_tcover_small_h_dim > \c_zero_dim
      {
        \str_if_eq:VnTF \l__luatexcn_tcover_small_pos_tl { follow }
          {
            \dim_set:Nn \l__luatexcn_tcover_y_dim
              {
                \l__luatexcn_tcover_top_dim + \l__luatexcn_tcover_m_dim + \l__luatexcn_tcover_ext_dim
                + \l__luatexcn_tcover_pad_dim + \l__luatexcn_tcover_title_h_dim
                + 0.3 \l__luatexcn_tcover_fs_dim
              }
          }
          {
            \dim_set:Nn \l__luatexcn_tcover_y_dim
              {
                \l__luatexcn_tcover_top_dim + \l__luatexcn_tcover_h_dim
                - \l__luatexcn_tcover_m_dim - \l__luatexcn_tcover_ext_dim
                - \l__luatexcn_tcover_pad_dim - \l__luatexcn_tcover_small_h_dim
              }
          }
        \dim_set:Nn \l__luatexcn_tcover_x_dim
          { \l__luatexcn_tcover_left_dim + 0.5 \l__luatexcn_tcover_w_dim }
        \bool_lazy_and:nnTF
          { \int_compare_p:nNn \l__luatexcn_tcover_nv_int > 0 }
          { \int_compare_p:nNn \l__luatexcn_tcover_nj_int > 0 }
          {
            % 两列：册次在右，卷次在左
            \__luatexcn_tcover_small:nnV
              { \l__luatexcn_tcover_x_dim + 0.7 \l__luatexcn_tcover_sfs_dim }
              { \l__luatexcn_tcover_y_dim } \l__luatexcn_tcover_volume_tl
            \__luatexcn_tcover_small:nnV
              { \l__luatexcn_tcover_x_dim - 0.7 \l__luatexcn_tcover_sfs_dim }
              { \l__luatexcn_tcover_y_dim } \l__luatexcn_tcover_juan_tl
          }
          {
            \__luatexcn_tcover_small:nnV
              { \l__luatexcn_tcover_x_dim } { \l__luatexcn_tcover_y_dim } \l__luatexcn_tcover_volume_tl
            \__luatexcn_tcover_small:nnV
              { \l__luatexcn_tcover_x_dim } { \l__luatexcn_tcover_y_dim } \l__luatexcn_tcover_juan_tl
          }
      }
  }

\NewDocumentCommand \ThreadBoundCover { O{} m }
  {
    \group_begin:
      \keys_set:nn { luatexcn / threadcover } {#1}
      \tl_set:Nn \l__luatexcn_tcover_title_tl {#2}
      \tl_set:Nx \l_tmpb_tl
        { \exp_not:N \begin{Cover} [ background-color = { \l__luatexcn_tcover_bg_tl } ] }
      \exp_last_unbraced:No \use:n \l_tmpb_tl
        \__luatexcn_tcover_body:
      \end{Cover}
    \group_end:
  }

% ============================================================================
% CJK Aliases (中文别名)
% ============================================================================
% Simplified Chinese / 简体 (封面简繁同形)
\NewEnvironmentCopy{封面}{Cover}
\NewCommandCopy{\线装书封面}{\ThreadBoundCover}
% Traditional / 繁體
\NewCommandCopy{\線裝書封面}{\ThreadBoundCover}

\ExplSyntaxOff
\endinput