% --------------------------------------------------------------------------
% the LEADSHEETS package
% 
%   typesetting leadsheets and songbooks
%
% --------------------------------------------------------------------------
% Clemens Niederberger
% E-Mail: contact@mychemistry.eu
% --------------------------------------------------------------------------
% Copyright 2014-2017 Clemens Niederberger
%
% This work may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either version 1.3
% of this license or (at your option) any later version.
% The latest version of this license is in
%   http://www.latex-project.org/lppl.txt
% and version 1.3 or later is part of all distributions of LaTeX
% version 2005/12/01 or later.
%
% This work has the LPPL maintenance status `maintained'.
%
% The Current Maintainer of this work is Clemens Niederberger.
% --------------------------------------------------------------------------
\LeadsheetsExplLibrary{external}
  {2016/08/18 include external leadsheets into a main file}

\msg_new:nnn {leadsheets} {class-not-registered}
  {
    You've~ tried~ to~ include~ the~ leadsheet~ `#1'~ which~ uses~ the~
    document~ class~ `#2'.~ However,~ this~ class~ is~ not~ yet~ registered.~
    You~ can~ register~ it~ using~ the~ option~ `register-class'.
  }

\msg_new:nnn {leadsheets} {file-not-found}
  {
    You've~ tried~ to~ include~ the~ leadsheet~ `#1'.~ However,~ I~ can't~
    find~ the~ file~ `#1'.~ Please~ make~ sure~ the~ file~ exists~ in~ a~
    path~ where~ TeX~ can~ find~ it.
  }

\cs_generate_variant:Nn \msg_error:nnnn {nnV}
  
\cs_new_protected:Npn \__leadsheets_disable_document_env:
  {
    \cs_set_protected:Npn \document
      {
        \cs_set_protected:Npn \enddocument
          { \tex_endinput:D }
      }
  }

% --------------------------------------------------------------------------
% don't allow any class per default
\seq_new:N \l__leadsheets_external_classes_seq

\cs_new_protected:Npn \leadsheets_add_external_class:n #1
  {
    \seq_put_right:Nn \l__leadsheets_external_classes_seq {#1}
    \seq_remove_duplicates:N \l__leadsheets_external_classes_seq
  }
\cs_generate_variant:Nn \leadsheets_add_external_class:n {V}

\leadsheets_add_external_class:n {leadsheet}
  
\prg_new_conditional:Npnn \leadsheets_if_is_external_class:n #1 {p,T,F,TF}
  {
    \seq_if_in:NnTF \l__leadsheets_external_classes_seq {#1}
      { \prg_return_true: }
      { \prg_return_false: }
  }

\bool_new:N \l__leadsheets_gobble_preamble_bool

\keys_define:nn {leadsheets}
  {
    gobble-preamble .bool_set:N = \l__leadsheets_gobble_preamble_bool ,
    gobble-preamble .initial:n  = true ,
    register-class  .code:n     =
      \clist_map_inline:nn {#1}
        {
          \tl_set:Nx \l__leadsheets_tmpa_tl { \tl_trim_spaces:n {##1} }
          \leadsheets_add_external_class:V \l__leadsheets_tmpa_tl
        }
  }

\cs_new_protected:Npn \leadsheets_documentclass:wnw
  {
    \peek_meaning:NTF [ % ]
      { \__leadsheets_documentclass:wnw }
      { \__leadsheets_documentclass:nw }
  }

\cs_new_protected:Npn \__leadsheets_documentclass:wnw [#1]
  { \__leadsheets_documentclass:nw }

\cs_new_protected:Npn \__leadsheets_documentclass:nw #1
  {
    \peek_meaning:NTF [ % ]
      { \__leadsheets_documentclass_aux:nw {#1} }
      { \__leadsheets_documentclass:n {#1} }
  }

\cs_new_protected:Npn \__leadsheets_documentclass_aux:nw #1[#2]
  { \__leadsheets_documentclass:n {#1} }

\cs_new_protected:Npn \__leadsheets_documentclass:n #1
  {
    \leadsheets_if_is_external_class:nF {#1}
      {
        \msg_error:nnVn {leadsheets} {class-not-registered}
          \l__leadsheets_current_leadsheet_tl
          {#1}
      }
    \RenewDocumentCommand \usepackage {omo} {}
    \RenewDocumentCommand \RequirePackage {omo} {}
    \__leadsheets_disable_document_env:
    \bool_if:NT \l__leadsheets_gobble_preamble_bool
      { \__leadsheets_gobble_preamble:wn }
  }

% include a file into a leadsheet only reading code between \LeadsheetSurvive
% and \LeadsheetEndSurvive
\cs_new_protected:Npn \leadsheets_include_external_file:nn #1#2
  {
    \tl_set_from_file:Nnn \l__leadsheets_tmpa_tl
      {}
      { #1 \tl_if_blank:nF {#2} {.} #2 }
    \cs_set:Npn \LeadsheetSurvive ##1 \LeadsheetEndSurvive ##2 \q_stop
      { ##1 \__leadsheets_extract_survival:ww ##2 \q_stop }
    \__leadsheets_include_external_file_aux:V \l__leadsheets_tmpa_tl
  }

\cs_new_protected:Npn \__leadsheets_include_external_file_aux:n #1
  { \__leadsheets_extract_survival:ww #1 \LeadsheetSurvive\LeadsheetSurvive \q_stop }
\cs_generate_variant:Nn \__leadsheets_include_external_file_aux:n {V}

\cs_new_protected:Npn \__leadsheets_extract_survival:ww
  #1 \LeadsheetSurvive #2 \LeadsheetSurvive #3 \q_stop
  {
    \tl_if_blank:nF {#3}
      { \LeadsheetSurvive #2 \LeadsheetSurvive #3 \q_stop }
  }

\NewDocumentCommand \AddExternalFile {mm}
  { \leadsheets_include_external_file:nn {#1} {#2} }
\NewDocumentCommand \AddExternalClass {m}
  { \leadsheets_include_external_file:nn {#1} {cls} }
\NewDocumentCommand \AddExternalPackage {m}
  { \leadsheets_include_external_file:nn {#1} {sty} }

\cs_new_protected:Npn \__leadsheets_gobble_preamble:wn #1 \begin #2
  {
    \str_if_eq:nnTF {#2} {document}
      { \begin {#2} }
      { \__leadsheets_gobble_preamble:wn }
  }

\cs_new_protected:Npn \leadsheets_include_leadsheet:nn #1#2
  {
    \file_if_exist:nTF {#2}
      {
        \group_begin:
          \keys_set:nn {leadsheets} {#1}
          \tl_set:Nn \l__leadsheets_current_leadsheet_tl {#2}
          \cs_set_eq:NN \documentclass \leadsheets_documentclass:wnw
          \file_input:n {#2}
        \group_end:
      }
      { \msg_error:nnn {leadsheets} {file-not-found} {#2} }
  }

\NewDocumentCommand \includeleadsheet {sO{}m}
  {
    \IfBooleanF {#1}
      { \leadsheets_include_external_file:nn {leadsheet} {cls} }
    \leadsheets_include_leadsheet:nn {#2} {#3}
  }
  
\endinput

2016/08/18 - first version