% Shared font configuration, face fallbacks and text-symbol support.
% Part of latexbangla, LPPL 1.3c or later; copyright 2026 Adib Hasan.

\bool_new:N \g__latexbangla_document_started_bool
\tl_new:N \l__latexbangla_font_family_tl
\tl_new:N \l__latexbangla_font_name_tl
\tl_new:N \l__latexbangla_font_features_tl
\tl_new:N \l__latexbangla_fallback_features_tl
\tl_new:N \l__latexbangla_font_profile_name_tl
\tl_new:N \l__latexbangla_font_defaults_tl
\tl_new:N \l__latexbangla_synthetic_bold_tl

% Siyam Rupali 1.070 and Mukti 3 report invalid x-heights. LaTeX uses ex
% units for heading spacing, so these metrics can distort document layout.
% Repair only an invalid metric from the actual x glyph, or Bengali ka when
% the face has no Latin alphabet. FontAdjustment runs at each size and face;
% the font file is untouched.
\cs_new_protected:Npn \__latexbangla_repair_xheight:
  {
    \bool_lazy_or:nnT
      {\dim_compare_p:nNn {\tex_fontdimen:D 5\tex_font:D} < {0.01pt}}
      {\dim_compare_p:nNn {\tex_fontdimen:D 5\tex_font:D} > {\tex_fontdimen:D 6\tex_font:D}}
      {
        \tex_iffontchar:D \tex_font:D `x\scan_stop:
          \tex_fontdimen:D 5\tex_font:D =
            \tex_fontcharht:D \tex_font:D `x\scan_stop:
        \else:
          \tex_fontdimen:D 5\tex_font:D =
            \tex_fontcharht:D \tex_font:D "0995\scan_stop:
        \fi:
      }
  }

% Known-font adjustments are deliberately small. Unlisted fonts retain native
% scale/spacing and synthetic weight 2.5. Recognize family names and standard
% filenames, including Path= loads; renamed files use the generic defaults.
% Reviewed weights: Kalpurush, SolaimanLipi and Anek Bangla 4;
% FreeSerif, Tiro Bangla, Galada, Nikosh, Likhan and Shimanto 3.5; Siyam Rupali and Lohit Bengali 4.5.
% Real bold faces never receive this synthetic-weight setting.
% Word-space presets were measured against default Latin Modern Roman and
% checked in mixed paragraphs with Pagella and Termes. They bring narrow spaces
% near the default English width, rather than tracking the chosen English font.
% Keep Kalpurush's already generous spacing. Explicit fontspec options win.
\cs_new_protected:Npn \__latexbangla_select_font_defaults:n #1
  {
    \tl_clear:N \l__latexbangla_font_defaults_tl
    \tl_set:Nn \l__latexbangla_synthetic_bold_tl {2.5}
    \tl_set:Ne \l__latexbangla_font_profile_name_tl {\str_lowercase:f {#1}}
    \regex_replace_once:nnN {\A .* [/\\]} {} \l__latexbangla_font_profile_name_tl
    \regex_replace_once:nnN {\.(ttf|otf|ttc)\Z} {} \l__latexbangla_font_profile_name_tl
    \regex_replace_all:nnN {\s+} {} \l__latexbangla_font_profile_name_tl
    % Resolve the filenames used by supported font downloads to their families.
    \str_case:Vn \l__latexbangla_font_profile_name_tl
      {
        {jamrulnormal}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {jamrul}}
        {likhannormal}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {likhan}}
        {fontkalpurush}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {kalpurush}}
        {solaimanlipi_20-04-07}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {solaimanlipi}}
        {notoserifbengali-regular}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {notoserifbengali}}
        {notoserifbengali-bold}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {notoserifbengali}}
        {notosansbengali-regular}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {notosansbengali}}
        {notosansbengali-bold}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {notosansbengali}}
        {hindsiliguri-regular}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {hindsiliguri}}
        {hindsiliguri-bold}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {hindsiliguri}}
        {balooda2-regular}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {balooda2}}
        {balooda2-bold}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {balooda2}}
        {lohit-bengali}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {lohitbengali}}
        {galada-regular}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {galada}}
        {tirobangla-regular}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {tirobangla}}
        {tirobangla-italic}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {tirobangla}}
        {anekbangla-vf}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {anekbangla}}
        {anekbangla[wdth,wght]}{\tl_set:Nn \l__latexbangla_font_profile_name_tl {anekbangla}}
      }
    \str_case:Vn \l__latexbangla_font_profile_name_tl
      {
        {freeserif}
          {\tl_set:Nn \l__latexbangla_synthetic_bold_tl {3.5}
           \tl_set:Nn \l__latexbangla_font_defaults_tl {WordSpace=1.33,}}
        % Jamrul uses the shared synthetic weight; the other single-face fonts
        % below have individually reviewed weights.
        % Jamrul's native space is over twice Latin Modern's; reduce it rather
        % than reducing the glyph size. Likhan and Shimanto need smaller changes.
        {jamrul}{\tl_set:Nn \l__latexbangla_font_defaults_tl {WordSpace=0.43,}}
        {likhan}
          {\tl_set:Nn \l__latexbangla_synthetic_bold_tl {3.5}
           \tl_set:Nn \l__latexbangla_font_defaults_tl {Scale=0.9,WordSpace=0.97,}}
        {shimanto}
          {\tl_set:Nn \l__latexbangla_synthetic_bold_tl {3.5}
           \tl_set:Nn \l__latexbangla_font_defaults_tl {WordSpace=1.11,}}
        {kalpurush}{\tl_set:Nn \l__latexbangla_synthetic_bold_tl {4}}
        {solaimanlipi}
          {\tl_set:Nn \l__latexbangla_synthetic_bold_tl {4}
           \tl_set:Ne \l__latexbangla_font_defaults_tl
             {Scale=0.9,WordSpace=1.33,\exp_not:V \g__latexbangla_proportional_spacing_features_tl}}
        {notoserifbengali}{\tl_set:Nn \l__latexbangla_font_defaults_tl {WordSpace=1.3,}}
        {notosansbengali}{\tl_set:Nn \l__latexbangla_font_defaults_tl {WordSpace=1.2,}}
        {hindsiliguri}{\tl_set:Nn \l__latexbangla_font_defaults_tl {Scale=0.9,WordSpace=1.64,}}
        {nikosh}
          {\tl_set:Nn \l__latexbangla_synthetic_bold_tl {3.5}
           \tl_set:Nn \l__latexbangla_font_defaults_tl {WordSpace=1.37,}}
        {mukti}
          {
            \tl_set:Nn \l__latexbangla_font_defaults_tl
              {Scale=0.9,WordSpace=1.33,FontAdjustment={\__latexbangla_repair_xheight:},}
            % Mukti 3 has inconsistent style names. Select available companions
            % by full face name so bold and bold italic cannot be interchanged.
            \str_if_eq:eeT {\str_lowercase:f {#1}} {mukti}
              {
                \fontspec_font_if_exist:nT {Mukti~Bold}
                  {\tl_put_right:Nn \l__latexbangla_font_defaults_tl
                    {BoldFont={Mukti~Bold},}}
                \fontspec_font_if_exist:nT {Mukti~Italic}
                  {\tl_put_right:Nn \l__latexbangla_font_defaults_tl
                    {ItalicFont={Mukti~Italic},}}
                \fontspec_font_if_exist:nT {Mukti~Bold~Italic}
                  {\tl_put_right:Nn \l__latexbangla_font_defaults_tl
                    {BoldItalicFont={Mukti~Bold~Italic},}}
              }
          }
        {kohinoorbangla}
          {
            \tl_set:Nn \l__latexbangla_font_defaults_tl {Scale=0.9,WordSpace=1.29,}
            % Collection style lookup can return semibold for bold, or regular
            % for bold italic. Name the bold face; the fallback supplies slant.
            \str_if_eq:eeT {\str_lowercase:f {#1}} {kohinoor~bangla}
              {
                \fontspec_font_if_exist:nT {Kohinoor~Bangla~Bold}
                  {\tl_put_right:Nn \l__latexbangla_font_defaults_tl
                    {BoldFont={Kohinoor~Bangla~Bold},
                     BoldItalicFont={Kohinoor~Bangla~Bold},}}
              }
          }
        {balooda2}{\tl_set:Nn \l__latexbangla_font_defaults_tl {Scale=0.9,WordSpace=1.86,}}
        {lohitbengali}
          {\tl_set:Nn \l__latexbangla_synthetic_bold_tl {4.5}
           \tl_set:Nn \l__latexbangla_font_defaults_tl {Scale=0.9,WordSpace=1.33,}}
        {galada}
          {\tl_set:Nn \l__latexbangla_synthetic_bold_tl {3.5}
           \tl_set:Nn \l__latexbangla_font_defaults_tl {Scale=0.9,WordSpace=1.67,}}
        {tirobangla}
          {
            \tl_set:Nn \l__latexbangla_synthetic_bold_tl {3.5}
            \tl_set:Nn \l__latexbangla_font_defaults_tl {Scale=0.9,WordSpace=1.39,}
            % Tiro has a real italic but no bold italic. Name that companion
            % explicitly for installed-family loads: engine substitutions differ.
            % A regular-only installation keeps the ordinary synthetic fallbacks.
            % File loads use fontspec's explicit face options, as with Noto.
            \str_if_eq:eeT {\str_lowercase:f {#1}} {tiro~bangla}
              {
                \fontspec_font_if_exist:nT {Tiro~Bangla~Italic}
                  {\tl_put_right:Ne \l__latexbangla_font_defaults_tl
                    {BoldItalicFont={Tiro~Bangla~Italic},
                     BoldItalicFeatures={FakeBold=\l__latexbangla_synthetic_bold_tl},}}
              }
          }
        {anekbangla}
          {\tl_set:Nn \l__latexbangla_synthetic_bold_tl {4}
           \tl_set:Nn \l__latexbangla_font_defaults_tl {Scale=0.9,WordSpace=2.1,}}
        {siyamrupali}
          {\tl_set:Nn \l__latexbangla_synthetic_bold_tl {4.5}
           \tl_set:Nn \l__latexbangla_font_defaults_tl
            {Scale=0.8,WordSpace=1.12,
             FontAdjustment={\__latexbangla_repair_xheight:},}}
      }
  }

% A discovered face is useful only if it includes Bengali. For example, some
% broad Unicode families include Bengali in their regular face but not in bold.
% Check ka in both languages, and Assamese ra/wa in Assamese mode, before
% accepting a discovered face. Missing letters trigger the same style fallback.
% The NFSS shape registry is the one low-level interface inspected here; testing
% existence first avoids triggering NFSS's own warning/substitution machinery.
\prg_new_protected_conditional:Npnn \__latexbangla_face_has_language_glyphs:nn #1#2 {TF}
  {
    \cs_if_exist:cTF {TU/\l__latexbangla_font_family_tl/#1/#2}
      {
        \group_begin:
          \fontencoding{TU}\fontfamily{\l__latexbangla_font_family_tl}
          \fontseries{#1}\fontshape{#2}\selectfont
          \tex_iffontchar:D \tex_font:D "0995\scan_stop:
            \str_if_eq:VnTF \g__latexbangla_language_tl {assamese}
              {
                \tex_iffontchar:D \tex_font:D "09F0\scan_stop:
                  \tex_iffontchar:D \tex_font:D "09F1\scan_stop:
                    \group_end:\prg_return_true:
                  \else:\group_end:\prg_return_false:\fi:
                \else:\group_end:\prg_return_false:\fi:
              }
              {\group_end:\prg_return_true:}
          \else:
            \group_end:\prg_return_false:
          \fi:
      }
      {\prg_return_false:}
  }

% A successful font lookup can still return an upright substitute: in the
% tested Noto families, the system resolves /BI to the ordinary bold font.
% For a face with Bengali coverage, inspect its actual slant (fontdimen 1).
% Keep that face and add only the missing slant, preserving real bold weight.
% Arguments: NFSS series, fontspec feature key for the italic face.
\cs_new_protected:Npn \__latexbangla_slant_upright_face:nn #1#2
  {
    \group_begin:
      \fontencoding{TU}\fontfamily{\l__latexbangla_font_family_tl}
      \fontseries{#1}\fontshape{it}\selectfont
      \dim_compare:nNnTF {\tex_fontdimen:D 1\tex_font:D} = {0pt}
        {
          \group_end:
          \tl_put_right:Nn \l__latexbangla_fallback_features_tl
            {#2={FakeSlant=0.2},}
        }
        {\group_end:}
  }

% Engine defaults are kept out of user feature lists. Explicit features still
% win, and an engine backend may refine face lookup without duplicating setters.
\tl_new:N \g__latexbangla_renderer_features_tl
\tl_new:N \g__latexbangla_proportional_spacing_features_tl
\cs_new_protected:Npn \__latexbangla_supply_bold_italic_fallback:
  {
    \tl_put_right:Ne \l__latexbangla_fallback_features_tl
      {BoldItalicFont=*,BoldItalicFeatures=
        {FakeBold=\l__latexbangla_synthetic_bold_tl,FakeSlant=0.2},}
  }

% Arguments: fontspec features, font name. The result is stored in
% \l__latexbangla_font_family_tl for the calling role setter.
% Ask fontspec to discover real faces first. Supply synthetic features for
% missing faces or slant, preserving each usable real face.
% Explicit user features are applied last and remain authoritative. Check the
% combined face independently: having bold and italic does not imply that a
% family also supplies a Bengali bold-italic face.
% Apply tested font defaults before explicit features in both declarations.
\cs_new_protected:Npn \__latexbangla_define_font_family:nn #1#2
  {
    \__latexbangla_select_font_defaults:n {#2}
    % Old documents used the PostScript name SiyamRupali. In the tested XeTeX,
    % that lookup also disrupts later English bold-face discovery, even with
    % plain fontspec. Resolve this exact legacy alias to the family name;
    % leave filenames and every other font request untouched.
    \tl_set:Nn \l__latexbangla_font_name_tl {#2}
    \str_if_eq:nnT {#2} {SiyamRupali}
      {\tl_set:Nn \l__latexbangla_font_name_tl {Siyam~Rupali}}
    % WordSpace multiplies the font's existing space dimensions globally.
    % Neutralize it while discovering faces, then apply the requested value
    % only in the final declaration below. Otherwise a fallback rebuild turns
    % WordSpace=1.1 into 1.21, even though the author requested a 10% increase.
    \tl_set:Ne \l__latexbangla_font_features_tl
      {Script=Bengali,\exp_not:V \g__latexbangla_renderer_features_tl
       \exp_not:V \l__latexbangla_font_defaults_tl,
       \exp_not:n {#1},WordSpace=1}
    \fontspec_set_family:NVV \l__latexbangla_font_family_tl
      \l__latexbangla_font_features_tl \l__latexbangla_font_name_tl
    \__latexbangla_face_has_language_glyphs:nnTF {m}{n} {}
      {\str_if_eq:VnTF \g__latexbangla_language_tl {assamese}
        {\msg_fatal:nnn {latexbangla} {incomplete-assamese-font} {#2}}
        {\msg_fatal:nnn {latexbangla} {non-bengali-font} {#2}}}
    % Many Bengali-script fonts use only a default language system. Request
    % Assamese shaping when advertised; otherwise retain the font's default.
    % The explicit feature list still wins in the final declaration below.
    \str_if_eq:VnT \g__latexbangla_language_tl {assamese}
      {
        \group_begin:
          \fontencoding{TU}\fontfamily{\l__latexbangla_font_family_tl}\selectfont
          \fontspec_if_language:nTF {ASM}
            {\group_end:
             \tl_put_right:Nn \l__latexbangla_font_defaults_tl {Language=Assamese,}}
            {\group_end:}
      }
    \tl_clear:N \l__latexbangla_fallback_features_tl
    \__latexbangla_face_has_language_glyphs:nnTF {b}{n} {}
      {\tl_put_right:Ne \l__latexbangla_fallback_features_tl
        {BoldFont=*,BoldFeatures={FakeBold=\l__latexbangla_synthetic_bold_tl},}}
    \__latexbangla_face_has_language_glyphs:nnTF {m}{it}
      {\__latexbangla_slant_upright_face:nn {m}{ItalicFeatures}}
      {\tl_put_right:Nn \l__latexbangla_fallback_features_tl
        {ItalicFont=*,ItalicFeatures={FakeSlant=0.2},}}
    \__latexbangla_face_has_language_glyphs:nnTF {b}{it}
      {\__latexbangla_slant_upright_face:nn {b}{BoldItalicFeatures}}
      {\__latexbangla_supply_bold_italic_fallback:}
    \tl_set:Ne \l__latexbangla_font_features_tl
      {Script=Bengali,\exp_not:V \g__latexbangla_renderer_features_tl
       \exp_not:V \l__latexbangla_font_defaults_tl,
       \exp_not:V \l__latexbangla_fallback_features_tl,\exp_not:n {#1}}
    \fontspec_set_family:NVV \l__latexbangla_font_family_tl
      \l__latexbangla_font_features_tl \l__latexbangla_font_name_tl
  }
\cs_generate_variant:Nn \fontspec_set_family:Nnn {NVV}

% Arguments: Polyglossia font-command name, fontspec features, font name.
% Polyglossia selects these named font commands itself. Freeze the NFSS family
% in each command; do not store a reference to the scratch family variable.
\cs_new_protected:Npn \__latexbangla_set_font_role:nnn #1#2#3
  {
    \bool_if:NT \g__latexbangla_document_started_bool
      {\msg_fatal:nn {latexbangla} {preamble-only}}
    \tl_if_blank:nTF {#3}
      {\msg_error:nn {latexbangla} {empty-font}}
      {
        \__latexbangla_define_font_family:nn {#2} {#3}
        \cs_gset_protected:cpe {#1}
          {
            \exp_not:N \fontencoding {TU}
            \exp_not:N \fontfamily {\l__latexbangla_font_family_tl}
            \exp_not:N \selectfont
          }
      }
  }

% Match fontspec's familiar optional-feature syntax, including the optional
% feature list after the font name. Both lists are forwarded without parsing
% or restricting fontspec's feature vocabulary.
\NewDocumentCommand \setbanglamainfont {O{} m O{}}
  {\__latexbangla_set_font_role:nnn {\g__latexbangla_language_tl font} {#1,#3} {#2}}
\NewDocumentCommand \setbanglasansfont {O{} m O{}}
  {\__latexbangla_set_font_role:nnn {\g__latexbangla_language_tl fontsf} {#1,#3} {#2}}
\NewDocumentCommand \setbanglamonofont {O{} m O{}}
  {\__latexbangla_set_font_role:nnn {\g__latexbangla_language_tl fonttt} {#1,#3} {#2}}

% Dynamic fallbacks follow later changes to the main font. A direct fontspec
% declaration made before package loading is respected; a later setter replaces
% only its own role. No second font is loaded simply to provide a fallback.
\cs_if_exist:cF {\g__latexbangla_language_tl fontsf}
  {\cs_new_protected:cpn {\g__latexbangla_language_tl fontsf}
    {\use:c {\g__latexbangla_language_tl font}}}
\cs_if_exist:cF {\g__latexbangla_language_tl fonttt}
  {\cs_new_protected:cpn {\g__latexbangla_language_tl fonttt}
    {\use:c {\g__latexbangla_language_tl font}}}

% TU text-symbol definitions are the shared dispatch point for standard lists,
% enumitem labels, direct symbol commands and aliases such as
% \let\labelitemi\textbullet. Adapting them avoids inspecting or expanding an
% author's label macro. Other encodings and author-defined label layouts remain
% untouched. Preserve each existing TU definition, including its formatting.
% The current font wins when it contains the glyph; otherwise use the configured
% Latin family, with the current weight, shape and size.
\cs_new_protected:Npn \__latexbangla_typeset_symbol:nn #1#2
  {
    \group_begin:
      \tex_iffontchar:D \tex_font:D #1\scan_stop:
      \else:
        \__latexbangla_select_latin_font:
      \fi:
      #2
    \group_end:
  }
% #1 is a public text-symbol command; #2 is its Unicode code point.
% TU\<command> is LaTeX's encoding-specific text-command registry entry.
\prop_new:N \g__latexbangla_symbol_codepoints_prop
\tl_new:N \l__latexbangla_symbol_codepoint_tl
\cs_new_protected:Npn \__latexbangla_install_symbol_fallback:Nn #1#2
  {
    \prop_gput:Nen \g__latexbangla_symbol_codepoints_prop
      {\tl_to_str:n {#1}} {#2}
    \cs_new_eq:cc {__latexbangla_original_\cs_to_str:N #1 :}
      {TU\token_to_str:N #1}
    \DeclareTextCommand #1 {TU}
      {
        \__latexbangla_typeset_symbol:nn {#2}
          {\use:c {__latexbangla_original_\cs_to_str:N #1 :}}
      }
  }
\__latexbangla_install_symbol_fallback:Nn \textbullet {"2022}
\__latexbangla_install_symbol_fallback:Nn \textendash {"2013}
\__latexbangla_install_symbol_fallback:Nn \textasteriskcentered {"2217}
\__latexbangla_install_symbol_fallback:Nn \textperiodcentered {"00B7}
% Complete the standard \fnsymbol inventory too: symbolic footnotes must not
% disappear merely because the main Bengali font lacks dagger or bar glyphs.
\__latexbangla_install_symbol_fallback:Nn \textdagger {"2020}
\__latexbangla_install_symbol_fallback:Nn \textdaggerdbl {"2021}
\__latexbangla_install_symbol_fallback:Nn \textsection {"00A7}
\__latexbangla_install_symbol_fallback:Nn \textparagraph {"00B6}
\__latexbangla_install_symbol_fallback:Nn \textbardbl {"2016}

% A TU composite stores "\iffontchar\font<number> <Unicode letter> ...".
% microtype expands that test to discover the letter, which fails in Bengali
% fonts without Latin accents. Resolve the encoded letter without testing font
% coverage; microtype's normal width check then skips glyphs the font lacks.
% Only the standard TU form is decoded; other definitions stay upstream.
\cs_new_protected:Npn \__latexbangla_extract_microtype_composite:w \font #1~#2\q_stop
  {\cs_set:Npn \MT@char {#2}}
\AddToHook{package/microtype/after}[latexbangla/character-slots]
  {
    \cs_new_eq:NN \__latexbangla_original_microtype_composite: \MT@is@uni@comp
    \cs_set_protected:Npn \MT@is@uni@comp #1\iffontchar#2\else#3\fi\relax
      {
        \bool_lazy_all:nTF
          {
            {\str_if_eq_p:ee {\MT@encoding} {TU}}
            {\tl_if_empty_p:n {#1}}
            {\tl_if_head_eq_meaning_p:nN {#2} \font}
          }
          {
            \tl_if_in:nnTF {#2} {~}
              {\__latexbangla_extract_microtype_composite:w #2\q_stop}
              {\__latexbangla_original_microtype_composite:
                #1\iffontchar#2\else#3\fi\relax}
          }
          {\__latexbangla_original_microtype_composite:
            #1\iffontchar#2\else#3\fi\relax}
      }
    % Fallback symbols keep their Unicode identity, even though their wrapped
    % definitions no longer look like simple character commands to microtype.
    \cs_new_eq:NN \__latexbangla_original_microtype_symbol: \MT@is@symbol
    \cs_set_protected:Npn \MT@is@symbol
      {
        \__latexbangla_original_microtype_symbol:
        \str_if_eq:eeT {\MT@encoding} {TU}
          {
            \int_compare:nNnT {\MT@char@} < {0}
              {
                \prop_get:NeNT \g__latexbangla_symbol_codepoints_prop
                  {\tl_to_str:V \@tempa} \l__latexbangla_symbol_codepoint_tl
                  {\cs_set:Npe \MT@char@
                    {\int_eval:n {\l__latexbangla_symbol_codepoint_tl}}}
              }
          }
      }
  }

\AddToHook{begindocument/before}[latexbangla/fonts]
  {
    \cs_if_exist:cF {\g__latexbangla_language_tl font}
      {\msg_fatal:nn {latexbangla} {missing-font}}
    \bool_gset_true:N \g__latexbangla_document_started_bool
  }
\endinput