% Font configuration and automatic Latin/Bangla font transitions.
% 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
\tl_new:N \l__latexbangla_text_family_tl
\tl_set:Nn \l__latexbangla_text_family_tl {rm}

% Siyam Rupali 1.070 reports a negative x-height. LaTeX uses ex units for
% heading spacing, so this can turn a display heading into a run-in heading.
% Repair only an invalid metric, using this face's actual x glyph at its final
% size. FontAdjustment runs for every size/face; the font file is untouched.
\cs_new_protected:Npn \__latexbangla_repair_xheight:
  {
    \dim_compare:nNnF {\tex_fontdimen:D 5\tex_font:D} > {0pt}
      {\tex_fontdimen:D 5\tex_font:D =
        \tex_fontcharht:D \tex_font:D `x\scan_stop:}
  }

% 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 and FreeSerif 3.5; SolaimanLipi and Siyam Rupali 4.5.
% Real bold faces never receive this synthetic-weight setting.
\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
    \str_case:Vn \l__latexbangla_font_profile_name_tl
      {
        {freeserif}{\tl_set:Nn \l__latexbangla_synthetic_bold_tl {3.5}}
        {kalpurush}{\tl_set:Nn \l__latexbangla_synthetic_bold_tl {3.5}}
        {fontkalpurush}{\tl_set:Nn \l__latexbangla_synthetic_bold_tl {3.5}}
        {solaimanlipi}{\tl_set:Nn \l__latexbangla_synthetic_bold_tl {4.5}}
        {solaimanlipi_20-04-07}{\tl_set:Nn \l__latexbangla_synthetic_bold_tl {4.5}}
        {siyamrupali}
          {\tl_set:Nn \l__latexbangla_synthetic_bold_tl {4.5}
           \tl_set:Nn \l__latexbangla_font_defaults_tl
            {Scale=0.8,WordSpace=1.2,
             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 a representative Bengali consonant before accepting a discovered face.
% 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_bengali: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:
            \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:}
  }

% 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 \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_bengali:nnTF {m}{n} {}
      {\msg_fatal:nnn {latexbangla} {non-bengali-font} {#2}}
    \tl_clear:N \l__latexbangla_fallback_features_tl
    \__latexbangla_face_has_bengali:nnTF {b}{n} {}
      {\tl_put_right:Ne \l__latexbangla_fallback_features_tl
        {BoldFont=*,BoldFeatures={FakeBold=\l__latexbangla_synthetic_bold_tl},}}
    \__latexbangla_face_has_bengali: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_bengali:nnTF {b}{it}
      {\__latexbangla_slant_upright_face:nn {b}{BoldItalicFeatures}}
      {\tl_put_right:Ne \l__latexbangla_fallback_features_tl
        {BoldItalicFont=*,BoldItalicFeatures=
          {FakeBold=\l__latexbangla_synthetic_bold_tl,FakeSlant=0.2},}}
    \tl_set:Ne \l__latexbangla_font_features_tl
      {Script=Bengali,\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 {bengalifont} {#1,#3} {#2}}
\NewDocumentCommand \setbanglasansfont {O{} m O{}}
  {\__latexbangla_set_font_role:nnn {bengalifontsf} {#1,#3} {#2}}
\NewDocumentCommand \setbanglamonofont {O{} m O{}}
  {\__latexbangla_set_font_role:nnn {bengalifonttt} {#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:NF \bengalifontsf
  {\cs_new_protected:Npn \bengalifontsf {\bengalifont}}
\cs_if_exist:NF \bengalifonttt
  {\cs_new_protected:Npn \bengalifonttt {\bengalifont}}

% Track public family switches using LaTeX command hooks. This avoids depending
% on Polyglossia's private family-state variable. Assignments are local, so a
% grouped \textsf or \texttt restores the enclosing family automatically.
\AddToHook{cmd/rmfamily/after}[latexbangla/family]
  {\tl_set:Nn \l__latexbangla_text_family_tl {rm}}
\AddToHook{cmd/sffamily/after}[latexbangla/family]
  {\tl_set:Nn \l__latexbangla_text_family_tl {sf}}
\AddToHook{cmd/ttfamily/after}[latexbangla/family]
  {\tl_set:Nn \l__latexbangla_text_family_tl {tt}}

\cs_new_protected:Npn \__latexbangla_select_latin_font:
  {
    \str_case:Vn \l__latexbangla_text_family_tl
      {
        {rm}{\rmfamilylatin}
        {sf}{\sffamilylatin}
        {tt}{\ttfamilylatin}
      }
  }

% ucharclasses inserts these groups only around Latin runs. Selecting a font
% family preserves size, weight and shape; normalfont would discard them.
% Devanagari is included in the block setup because danda (।) belongs there.
% Common typographic punctuation follows the companion English font, as ASCII
% punctuation already does. SolaimanLipi lacks these Unicode glyphs. Assign only
% visible punctuation, not the whole General Punctuation block: its joiners and
% format controls must remain available to Bengali shaping.
\clist_map_inline:nn {"2013,"2014,"2018,"2019,"201C,"201D,"2026}
  {\XeTeXcharclass #1 = \BasicLatinClass\scan_stop:}
\setTransitionsForLatin
  {\group_begin:\__latexbangla_select_latin_font:} {\group_end:}

% ucharclasses installs transitions only between its enabled blocks and the
% word boundary. Class 0 also needs transitions: characters outside the enabled
% blocks must close a Latin run before Bengali text resumes. Otherwise
% its font group leaks, causing missing glyphs and unbalanced author groups.
% Adjacent Latin blocks belong to the same run (as in café or Ānand);
% do not open another group when crossing between them.
% Reuse ucharclasses' Latin block inventory rather than duplicating its ranges.
\group_begin:
  \seq_clear_new:N \l__latexbangla_latin_classes_seq
  \cs_set:Npn \do #1
    {\cs_if_exist:cT {#1Class}
      {\seq_put_right:Nn \l__latexbangla_latin_classes_seq {#1Class}}}
  \LatinClasses
  \seq_map_inline:Nn \l__latexbangla_latin_classes_seq
    {
      \tex_global:D \XeTeXinterchartoks 0 \use:c {#1} =
        {\group_begin:\__latexbangla_select_latin_font:}
      \tex_global:D \XeTeXinterchartoks \use:c {#1} 0 = {\group_end:}
      \seq_map_inline:Nn \l__latexbangla_latin_classes_seq
        {\tex_global:D \XeTeXinterchartoks \use:c {#1} \use:c {##1} = {}}
    }
\group_end:

% 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_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_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:NF \bengalifont
      {\msg_fatal:nn {latexbangla} {missing-font}}
    \bool_gset_true:N \g__latexbangla_document_started_bool
  }
\endinput