% LuaTeX font selection and the bridge to the pre-hyphenation node callback.
% Part of latexbangla, LPPL 1.3c or later; copyright 2026 Adib Hasan.

% HarfBuzz provides the Bengali shaping used by the tested XeTeX fonts too.
% This is a default for Bangla setters only; user features are applied last.
\tl_gset:Nn \g__latexbangla_renderer_features_tl {Renderer=HarfBuzz,}

% SolaimanLipi's fixed-pitch flag is wrong: its glyph advances are proportional.
% Use luaotfload's feature to retain normal space stretch/shrink before fontspec
% applies WordSpace. The shared SolaimanLipi profile alone requests this fix.
\tl_gset:Nn \g__latexbangla_proportional_spacing_features_tl {RawFeature={-fixedspace},}

% Lua's font resolver does not always substitute a bold face for missing bold
% italic. If bold has Bengali glyphs, slant that face instead of emboldening
% the regular face. Resolve its actual file through LuaTeX's font API; Path is
% local to this face, so both family-name and Path-based font loads work.
% Preserve a requested synthetic weight on bold too; never invent FakeBold=0,
% which LuaTeX renders with a nonzero PDF stroke.
\tl_new:N \l__latexbangla_bold_face_file_tl
\tl_new:N \l__latexbangla_bold_face_directory_tl
\tl_new:N \l__latexbangla_bold_face_weight_features_tl
\cs_new_eq:NN \__latexbangla_synthetic_bold_italic_fallback:
  \__latexbangla_supply_bold_italic_fallback:
\cs_set_protected:Npn \__latexbangla_supply_bold_italic_fallback:
  {
    \__latexbangla_face_has_language_glyphs:nnTF {b}{n}
      {
        \group_begin:
          \fontencoding{TU}\fontfamily{\l__latexbangla_font_family_tl}
          \fontseries{b}\fontshape{n}\selectfont
          \lua_now:n
            {
              local~selected~=~font.getfont(font.current());
              local~filename~=~selected.filename;
              filename~=~filename:gsub("^harfloaded:",~"");
              local~directory,~basename~=~filename:match("^(.-)([^/]+)$");
              token.set_macro("l__latexbangla_bold_face_file_tl",~basename);
              token.set_macro("l__latexbangla_bold_face_directory_tl",~directory);
              local~weight~=~selected.specification.features.normal.embolden;
              token.set_macro("l__latexbangla_bold_face_weight_features_tl",
                ~weight~and~("FakeBold="~..~weight~..~",")~or~"");
            }
          \use:e
            {
              \group_end:
              \tl_put_right:Nn \exp_not:N \l__latexbangla_fallback_features_tl
                {BoldItalicFont={\exp_not:V \l__latexbangla_bold_face_file_tl},
                 BoldItalicFeatures={Path={\exp_not:V \l__latexbangla_bold_face_directory_tl},
                   \exp_not:V \l__latexbangla_bold_face_weight_features_tl FakeSlant=0.2},}
            }
      }
      {\__latexbangla_synthetic_bold_italic_fallback:}
  }

% Nodes carry the selected companion font, not just a map from Bangla fonts.
% The same Bangla font can serve roman, sans and mono roles, each with a
% different English companion. Attributes are local to TeX groups and survive
% delayed paragraph shaping, boxes, footnotes and nested text styles.
\newattribute\g__latexbangla_latin_font_attribute
\int_const:Nn \c__latexbangla_latin_font_attribute_int {\allocationnumber}
\bool_new:N \l__latexbangla_capturing_latin_font_bool

% Capturing the companion's font ID calls selectfont again. This guard prevents
% recursive capture; the shared selection guard separately prevents recording
% our internal font selections as author overrides.
% Resolve it afresh so local changes to Polyglossia's Latin font commands work.
% NFSS already caches loaded fonts; a second cache would risk stale selections.
% Start as soon as a Bangla font exists, including saveboxes in the preamble.
% Math font setup can also call selectfont; it must not run text-family commands.
\cs_new_protected:Npn \__latexbangla_capture_latin_font:
  {
    \mode_if_math:F
      {
        \cs_if_exist:cT {\g__latexbangla_language_tl font}
          {
            \bool_if:NF \l__latexbangla_capturing_latin_font_bool
              {
                \group_begin:
                  \bool_set_true:N \l__latexbangla_capturing_latin_font_bool
                  \__latexbangla_select_latin_font:
                  \use:e
                    {\group_end:
                     \g__latexbangla_latin_font_attribute =
                       \int_eval:n {\tex_fontid:D \tex_font:D}\scan_stop:}
              }
          }
      }
  }
\AddToHook{selectfont}[latexbangla/latin-font]{\__latexbangla_capture_latin_font:}
\DeclareHookRule{selectfont}{latexbangla/latin-font}{after}{latexbangla/local-font}
% Shared family tracking runs before rmfamily/sffamily/ttfamily select a font,
% so their normal selectfont hook already captures the correct companion.
\AddToHook{begindocument/end}[latexbangla/latin-font]{\__latexbangla_capture_latin_font:}

\lua_now:e
  {
    local~install~=~dofile(kpse.find_file("code/engines/latexbangla-switching-luatex.lua",~"tex"));
    install(\int_use:N \c__latexbangla_latin_font_attribute_int);
  }
\endinput