namespace.sty

\RequirePackage{expl3}
\RequirePackage{xparse}

\ProvidesExplPackage {namespace} {2020/08/31} {0.1} {Compositional namespaces for labels}

\tl_new:N \l_ns_stk

\cs_new:Npn \ns_push:n #1 {
  \tl_put_right:Nn \l_ns_stk {#1}
  \tl_put_right:Nn \l_ns_stk {/}
}


\cs_new:Npn \ns_resolve:Nn #1 #2 {
  \regex_match:nnTF {^/} {#2} {
    \tl_put_right:Nn #1 {\tl_tail:n {#2}}
  } {
    \tl_put_right:Nn #1 {\l_ns_stk}
    \tl_put_right:Nn #1 {#2}
  }
}

% Map over a sequence with special behavior for the last item
\cs_new:Npn \ns_seq_map_inline_last:Nnn #1 #2 #3 {
  \int_zero:N \l_tmpa_int
  \seq_map_inline:Nn #1 {
    \int_incr:N \l_tmpa_int
    \int_compare:nNnTF {\l_tmpa_int} < {\seq_count:N #1} {#2} {#3}
  }
}

\seq_new:N \l_ns_resolve_multi_split 
\cs_new:Npn \ns_resolve_multi:Nn #1 #2 {
  \seq_set_split:Nnn \l_ns_resolve_multi_split {,} {#2}
  \ns_seq_map_inline_last:Nnn \l_ns_resolve_multi_split {
    \ns_resolve:Nn #1 {##1}
    \tl_put_right:Nn #1 {,}
  } {
    \ns_resolve:Nn #1 {##1}
  }
}

\NewDocumentEnvironment{namespace}{m}{
  \group_begin:
  \ns_push:n {#1}
}{
  \group_end:
}

\tl_new:N \l_ns_resolve_tl
\NewDocumentCommand\nslabel{om}{
  \tl_clear:N \l_ns_resolve_tl
  \ns_resolve:Nn \l_ns_resolve_tl {#2}
  \IfValueTF{#1}{\label[#1]{\l_ns_resolve_tl}}{\label{\l_ns_resolve_tl}}
}

\NewDocumentCommand\nsref{m}{
  \tl_clear:N \l_ns_resolve_tl
  \ns_resolve_multi:Nn \l_ns_resolve_tl {#1}
  \ref{\l_ns_resolve_tl}
}

\NewDocumentCommand\nscref{m}{
  \tl_clear:N \l_ns_resolve_tl
  \ns_resolve_multi:Nn \l_ns_resolve_tl {#1}
  %[\tl_use:N \l_ns_resolve_tl]
  \cref{\l_ns_resolve_tl}
}