% babelbidi-fontfallback.def
%
% Babelbidi: Bidi extensions for Babel.
%
% Copyright (C) 2026 Amer Amikhteh
%
% This file is part of the Babelbidi package.
%
% This work is free software: you may redistribute it and/or modify
% it under the terms of the LaTeX Project Public License as published
% by the LaTeX Project, either version 1.3c of the License, or
% (at your option) any later version.
%
% This work 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.
%
% The full license text is available at:
% https://www.latex-project.org/lppl/
%
% This work is "maintained" by Amer Amikhteh.
%
% The current maintainer of this work is Amer Amikhteh.

\ProvidesFile{babelbidi-fontfallback.def}
[2026/10/14 v0.3.0 Language-aware font fallbacks for Babelbidi]


\directlua{babelbidi_font_fallback = dofile(kpse.find_file('babelbidi-fontfallback.lua'))}

\makeatletter
\ExplSyntaxOn
\prop_new:N \g__bbd_fallback_prop
\seq_new:N \g__bbd_fallback_targets_seq
\bool_new:N \g__bbd_fallback_active_bool
\tl_new:N \l__bbd_fallback_source_tl
\tl_new:N \l__bbd_fallback_ids_tl
\clist_new:N \l__bbd_fallback_clist

% Declarations may precede babelprovide and babelfont. A later declaration
% replaces the source's chain; an empty list disables it.
\NewDocumentCommand \fontfallback { m m }
{
    \tl_set:Nx \l__bbd_fallback_source_tl { \tl_trim_spaces:n {#1} }
    \clist_set:Nn \l__bbd_fallback_clist {#2}
    \prop_gput:NVV \g__bbd_fallback_prop
    \l__bbd_fallback_source_tl \l__bbd_fallback_clist
}

\cs_new_protected:Npn \bbd_fontfallback_setup:
{
    \prop_map_inline:Nn \g__bbd_fallback_prop
    {
        \cs_if_exist:cTF { bbl@id@@##1 }
        {
            \seq_if_in:NnF \g__bbd_fallback_targets_seq {##1}
            { \seq_gput_right:Nn \g__bbd_fallback_targets_seq {##1} }
            \tl_clear:N \l__bbd_fallback_ids_tl
            \clist_map_inline:nn {##2}
            {
                \cs_if_exist:cTF { bbl@id@@####1 }
                {
                    \str_if_eq:nnF {##1} {####1}
                    {
                        \bool_gset_true:N \g__bbd_fallback_active_bool
                        \tl_put_right:Nx \l__bbd_fallback_ids_tl
                        { \int_use:c { bbl@id@@####1 } , }
                        \seq_if_in:NnF \g__bbd_fallback_targets_seq {####1}
                        { \seq_gput_right:Nn \g__bbd_fallback_targets_seq {####1} }
                    }
                }
                { \PackageWarning{babelbidi}{Unknown~fallback~target~locale~'####1'} }
            }
            \directlua{babelbidi_font_fallback.set(
                \int_use:c { bbl@id@@##1 }, {\l__bbd_fallback_ids_tl})}
        }
        { \PackageWarning{babelbidi}{Unknown~fallback~source~locale~'##1'} }
    }
    \bool_if:NT \g__bbd_fallback_active_bool
    {
        % Reuse the upstream mapper already retained by babelbidi's cache.
        % This creates mappings without enabling automatic onchar selection.
        \cs_if_exist:NF \bbl@mapdir
        { \cs_set_eq:NN \bbl@mapdir \bbd@fontcache@expected@mapdir }
        \AddToHook{selectfont}[babelbidi/font-fallback]{\bbd@fontfallback@mapcurrent}
        \bbd@fontfallback@mapcurrent
        \directlua{babelbidi_font_fallback.install()}
    }
}

\cs_new_protected:Npn \bbd_fontfallback_maptargets:
{
    \seq_map_inline:Nn \g__bbd_fallback_targets_seq
    { \bbd@fontfallback@maptarget{##1} }
}
\ExplSyntaxOff

\makeatletter
\@onlypreamble\fontfallback
\newif\ifbbd@fontfallback@mapping
\newattribute\bbd@fontfallback@context
\directlua{babelbidi_font_fallback.attribute =
    luatexbase.registernumber('bbd@fontfallback@context')}

% Reuse Babel's mapper, including babelbidi's cache once it is installed.
\def\bbd@fontfallback@maptarget#1{%
    \begingroup
    \edef\bbl@prefontid{\bbd@fontfallback@sourcefont}%
    \bbl@mapdir{#1}%
    \endgroup
}

\def\bbd@fontfallback@mapcurrent{%
    \ifbbd@fontfallback@mapping\else
        \ifnum\fontid\font>\z@
            \edef\bbd@fontfallback@sourcefont{\fontid\font}%
            \begingroup
            \bbd@fontfallback@mappingtrue
            \let\bbl@mapselect\relax
            \csname bbd_fontfallback_maptargets:\endcsname
            \endgroup
            \directlua{babelbidi_font_fallback.capture(\bbd@fontfallback@sourcefont)}%
        \fi
    \fi
}

\AddToHook{begindocument/end}[babelbidi/font-fallback]{%
    \@ifundefined{bbl@switchfont}{%
        \PackageWarningNoLine{babelbidi}{Font~fallback~requires~Babel's~font~resolver}%
    }{\csname bbd_fontfallback_setup:\endcsname}%
}
\DeclareHookRule{begindocument/end}{babelbidi/font-fallback}{before}{babelbidi/font-cache}
\makeatother
\endinput