-module(shelf).
-export([rnt_init/0, titles/0, authors/0]).

-define(TITLES, [<<"karuta">>, <<"program">>, <<"titles">>]).
-define(BOOKS, {$b, [<<"karuta">>, <<"program">>, <<"books">>]}).

%% A FOL program over a beam program RNT holds, defined from the node.
rnt_init() ->
    rnt:define(?TITLES, <<"fol">>, project(?BOOKS, [<<"title">>])).

titles() -> rnt:invoke(?TITLES).

authors() -> rnt:evaluate(<<"fol">>, project(?BOOKS, [<<"author">>])).

project(Term, Attributes) ->
    bencode({$p, #{<<"term">> => Term, <<"attributes">> => Attributes}}).

bencode(Bytes) when is_binary(Bytes) -> [integer_to_binary(byte_size(Bytes)), $:, Bytes];
bencode(List) when is_list(List) -> [$l, [bencode(X) || X <- List], $e];
bencode(Map) when is_map(Map) ->
    [$d, [[bencode(K), bencode(V)] || {K, V} <- lists:sort(maps:to_list(Map))], $e];
bencode({Tag, Value}) -> [$t, Tag, bencode(Value)].