%%
%% tcbpagefootnote.sty
%% ===================
%% Page footnotes from inside tcolorbox.
%%
%% Copyright (c) 2026 Munehiro Yamamoto <munepixyz@gmail.com>
%%
%% This package is licensed under the conditions of the LaTeX Project
%% Public License, either version 1.3c of this license or (at your
%% option) any later version.  The latest version of this license is in
%%   https://www.latex-project.org/lppl.txt
%%
%% This work has the LPPL maintenance status `maintained'.
%% The Current Maintainer of this work is Munehiro Yamamoto.
%%
%% Background
%%   tcolorbox typesets the content of a box like a minipage: \footnote
%%   uses the mpfootnote counter and the footnote text is put at the
%%   bottom of the box.
%%
%% What this package does
%%   The tcolorbox key "page footnote" makes \footnote inside the box
%%   (title, upper and lower part) behave as in the body text:
%%     (1) the footnote counter and \thefootnote are used for the mark;
%%     (2) the footnote text is collected, together with its mark, while
%%         the box is typeset, and is put into the ordinary footnote
%%         insertion right after the box ("after pre" of the hooks
%%         library), i.e. at the bottom of the page where the box is.
%%   With hyperref, each footnote text keeps the anchor of its own mark.
%%
%% Limitations
%%   * A breakable box that is broken across pages puts all its footnote
%%     texts on the page where the box ends; a warning is issued.
%%   * "page footnote" cannot be used with "float".
%%   * Keys that set the "after" code (after, after skip, nobeforeafter,
%%     ...) must come before "page footnote" in the option list.
%%   * Vertical writing (tate) is out of the scope of this version.
%%
%% Supported formats/engines: pdfLaTeX, XeLaTeX, LuaLaTeX, pLaTeX and
%% upLaTeX (+ dvipdfmx).
%%
\RequirePackage{expl3}
\ProvidesExplPackage{tcbpagefootnote}
  {2026/10/25}{1.0}{Page footnotes from inside tcolorbox}

\RequirePackage{tcolorbox}
\tcbuselibrary{hooks}

%% The footnotes collected inside the box(es), output after the box
\tl_new:N \g__tcbpagefootnote_notes_tl
\tl_new:N \l__tcbpagefootnote_notes_tl

%% -----------------------------------------------------------------
%% Messages
%% -----------------------------------------------------------------
\msg_new:nnn { tcbpagefootnote } { key-defined }
  {
    The~tcolorbox~key~'page~footnote'~is~already~defined.\\
    tcbpagefootnote~will~not~redefine~it.
  }
\msg_new:nnn { tcbpagefootnote } { after-overwritten }
  {
    The~'after'~code~of~this~box~no~longer~flushes~the~page~footnotes.\\
    Put~'page~footnote'~after~'after',~'after~skip',~etc.~in~the~option~list.
  }
\msg_new:nnn { tcbpagefootnote } { float }
  { The~key~'page~footnote'~cannot~be~used~with~'float'. }
\msg_new:nnn { tcbpagefootnote } { broken }
  {
    This~box~is~broken~across~pages.\\
    Its~footnote~texts~are~put~on~the~page~where~the~box~ends.
  }

%% -----------------------------------------------------------------
%% 1. Inside the box, switch the footnotes back from the minipage
%%    setting to the page setting
%% -----------------------------------------------------------------
\cs_new_protected:Npn \__tcbpagefootnote_restore:
  {
    \cs_set:Npn \@mpfn { footnote }
    \cs_set:Npn \thempfn { \thefootnote }
    \cs_set_eq:NN \@footnotetext \__tcbpagefootnote_collect:n
  }

%% -----------------------------------------------------------------
%% 2. Collect the footnote text together with its mark
%%    The mark is saved as the string formatted by \thefootnote:
%%    \footnotetext[...] is not used since it assigns a number to the
%%    counter.  With hyperref, the anchor of the mark
%%    (\Hy@footnote@currentHref) is saved as well, since it is
%%    overwritten by the next mark.
%% -----------------------------------------------------------------
\cs_new_protected:Npn \__tcbpagefootnote_collect:n #1
  {
    \tl_gput_right:Ne \g__tcbpagefootnote_notes_tl
      {
        \__tcbpagefootnote_output:nnn
          { \exp_not:o { \@thefnmark } }
          {
            \cs_if_exist:NT \Hy@footnote@currentHref
              { \exp_not:o { \Hy@footnote@currentHref } }
          }
          { \exp_not:n {#1} }
      }
  }

\cs_new_protected:Npn \__tcbpagefootnote_output:nnn #1#2#3
  {
    \tl_gset:Nn \@thefnmark {#1}
    \cs_if_exist:NT \Hy@footnote@currentHref
      { \tl_gset:Nn \Hy@footnote@currentHref {#2} }
    \@footnotetext {#3}
  }

%% -----------------------------------------------------------------
%% 3. Output the collected footnotes and clear the list
%%    Called from "after pre", so that the footnotes are inserted
%%    right after the box.  The list is cleared before its content is
%%    used: a box with "page footnote" inside another one collects its
%%    footnotes again into the list of the outer box.
%% -----------------------------------------------------------------
\cs_new_protected:Npn \__tcbpagefootnote_flush:
  {
    \tl_set_eq:NN \l__tcbpagefootnote_notes_tl \g__tcbpagefootnote_notes_tl
    \tl_gclear:N \g__tcbpagefootnote_notes_tl
    \tl_if_empty:NF \l__tcbpagefootnote_notes_tl
      {
        \cs_if_exist:NT \c@tcbbreakpart
          {
            \int_compare:nNnT { \c@tcbbreakpart } > { 1 }
              { \msg_warning:nn { tcbpagefootnote } { broken } }
          }
      }
    \tl_use:N \l__tcbpagefootnote_notes_tl
  }

%% -----------------------------------------------------------------
%% 4. Check the settings under which the footnotes cannot be output
%%    - a float box does not use \kvtcb@afterbox
%%    - after, after skip, etc. given later remove the "after pre" code
%%    The tcbbreakpart counter of the breakable library is reset here:
%%    a broken box sets it to the number of its parts while it is drawn
%%    (after its content is typeset), and an unbreakable box does not
%%    touch it.
%% -----------------------------------------------------------------
\cs_new_protected:Npn \__tcbpagefootnote_check:
  {
    \tl_if_empty:NF \kvtcb@float
      { \msg_error:nn { tcbpagefootnote } { float } }
    \tl_if_in:NnF \kvtcb@afterbox { \__tcbpagefootnote_flush: }
      { \msg_error:nn { tcbpagefootnote } { after-overwritten } }
    \cs_if_exist:NT \c@tcbbreakpart
      { \int_gzero:N \c@tcbbreakpart }
  }

%% -----------------------------------------------------------------
%% 5. The tcolorbox key
%% -----------------------------------------------------------------
\pgfkeysifdefined { /tcb/page~footnote/.@cmd }
  { \msg_error:nn { tcbpagefootnote } { key-defined } }
  {
    \tcbset
      {
        page~footnote/.style =
          {
            before~title~pre = \__tcbpagefootnote_restore: ,
            before~upper~pre = \__tcbpagefootnote_check:
                               \__tcbpagefootnote_restore: ,
            before~lower~pre = \__tcbpagefootnote_restore: ,
            after~pre        = \__tcbpagefootnote_flush: ,
          }
      }
  }

\endinput