-module(fp2@monoid).
-compile(no_auto_import).

-export([monoid_string/0, concat_all/1, to_semigroup/1, from_semigroup/2]).
-export_type([monoid/1]).

-type monoid(EOC) :: {monoid, fun((EOC, EOC) -> EOC), EOC}.

-spec monoid_string() -> monoid(binary()).
monoid_string() ->
    {monoid, fun(A, B) -> gleam@string:concat([A, B]) end, <<""/utf8>>}.

-spec concat_all(monoid(EOE)) -> fun((list(EOE)) -> EOE).
concat_all(M) ->
    fun(Ass) ->
        gleam@list:fold(Ass, erlang:element(3, M), erlang:element(2, M))
    end.

-spec to_semigroup(monoid(EOH)) -> fp2@semigroup:semigroup(EOH).
to_semigroup(M) ->
    {semigroup, erlang:element(2, M)}.

-spec from_semigroup(fp2@semigroup:semigroup(EOK), EOK) -> monoid(EOK).
from_semigroup(S, Empty) ->
    {monoid, erlang:element(2, S), Empty}.