% Shared Latin family selection and scoped fontspec overrides.
% Part of latexbangla, LPPL 1.3c or later; copyright 2026 Adib Hasan.

\tl_new:N \l__latexbangla_text_family_tl
\tl_set:Nn \l__latexbangla_text_family_tl {rm}
\tl_new:N \l__latexbangla_local_latin_family_tl
\bool_new:N \l__latexbangla_selecting_font_bool
\bool_new:N \g__latexbangla_track_local_fonts_bool

% Public family commands deliberately return to a document family. Clear a
% local fontspec selection before Polyglossia selects that family's Bangla
% font. TeX grouping restores both choices when a nested text command ends.
\clist_map_inline:nn {rm,sf,tt}
  {
    \AddToHook{cmd/#1family/before}[latexbangla/family]
      {\tl_set:Nn \l__latexbangla_text_family_tl {#1}
       \tl_clear:N \l__latexbangla_local_latin_family_tl}
  }

% Keep our automatic selections out of the author-selection hook. Do not use
% a TeX group here: callers need the chosen font to remain selected. Nested
% calls inherit the guard and leave its enclosing value intact.
\cs_new_protected:Npn \__latexbangla_select_font_guarded:n #1
  {
    \bool_if:NTF \l__latexbangla_selecting_font_bool
      {#1}
      {\bool_set_true:N \l__latexbangla_selecting_font_bool
       #1
       \bool_set_false:N \l__latexbangla_selecting_font_bool}
  }

\cs_new_protected:Npn \__latexbangla_select_latin_font:
  {
    \__latexbangla_select_font_guarded:n
      {
        \tl_if_empty:NTF \l__latexbangla_local_latin_family_tl
          {\str_case:Vn \l__latexbangla_text_family_tl
            {{rm}{\rmfamilylatin} {sf}{\sffamilylatin} {tt}{\ttfamilylatin}}}
          {\fontencoding{TU}
           \exp_args:NV \fontfamily \l__latexbangla_local_latin_family_tl
           \selectfont}
      }
  }

% A fontspec family selected for Latin text becomes the local companion. Keep
% the Bangla family as the enclosing text font so mixed text still shapes in
% Bangla; the engine selects the companion only for Latin runs. Store a family,
% not a fixed face, so later bold/italic/size changes retain ordinary NFSS rules.
% Script selection, rather than glyph coverage, distinguishes a Latin FreeSerif
% declaration from a Bengali FreeSerif declaration of the very same font.
\cs_new_protected:Npn \__latexbangla_remember_local_latin_font:
  {
    \bool_lazy_or:nnT
      {\bool_if_p:N \g__latexbangla_track_local_fonts_bool}
      {\mode_if_horizontal_p:}
      {
        \bool_if:NF \l__latexbangla_selecting_font_bool
          {
            \mode_if_math:F
              {
                \fontspec_if_current_script:nT {latn}
                  {
                    \tl_set:Ne \l__latexbangla_local_latin_family_tl {\f@family}
                    \__latexbangla_select_font_guarded:n
                      {
                        \str_case:Vn \l__latexbangla_text_family_tl
                          {
                            {rm}{\use:c {\g__latexbangla_language_tl font}}
                            {sf}{\use:c {\g__latexbangla_language_tl fontsf}}
                            {tt}{\use:c {\g__latexbangla_language_tl fonttt}}
                          }
                      }
                  }
              }
          }
      }
  }
\AddToHook{selectfont}[latexbangla/local-font]{\__latexbangla_remember_local_latin_font:}
% Font discovery and mathematics setup in the preamble must see their actual
% selected font. Track preamble selections only inside actual text boxes;
% activate general author tracking after document initialization finishes.
\AddToHook{begindocument/end}[latexbangla/local-font]
  {\bool_gset_true:N \g__latexbangla_track_local_fonts_bool}
% With a local Latin selection, fontspec features belong to that companion,
% even though the enclosing font remains Bangla for automatic script switching.
\clist_map_inline:nn {addfontfeatures,addfontfeature}
  {
    \AddToHook{cmd/#1/before}[latexbangla/local-font]
      {\tl_if_empty:NF \l__latexbangla_local_latin_family_tl
        {\__latexbangla_select_latin_font:}}
  }

\endinput