package testsupport.traits;

import com.jnape.palatable.lambda.adt.Maybe;

import com.jnape.palatable.lambda.adt.hlist.Tuple2;

import com.jnape.palatable.lambda.functions.Fn1;

import com.jnape.palatable.lambda.io.IO;

import com.jnape.palatable.lambda.monad.MonadWriter;

import com.jnape.palatable.lambda.monoid.builtin.Present;

import static com.jnape.palatable.lambda.adt.Maybe.just;

import static com.jnape.palatable.lambda.adt.Maybe.nothing;

import static com.jnape.palatable.lambda.functions.builtin.fn1.Id.id;

import static com.jnape.palatable.lambda.io.IO.throwing;

import static java.util.Arrays.asList;

public class MonadWriterLaws<W, A, M extends MonadWriter<W, ?, M>> implements EquivalenceTrait<MonadWriter<W, A, M>> {

@Override

public Class<? super MonadWriter<?, ?, M>> type() {

return MonadWriter.class;

}

@Override

public void test(Equivalence<MonadWriter<W, A, M>> equivalence) {

Present.<String>present((x, y) -> x + "\n\t - " + y)

.<Fn1<Equivalence<MonadWriter<W, A, M>>, Maybe<String>>>foldMap(

f -> f.apply(equivalence), asList(

this::testCensor,

this::testListens)

)

.match(IO::io,

s -> throwing(new AssertionError("The following MonadWriter laws did not hold for instance" +

" of " + equivalence + ": \n\t - " + s)))

.unsafePerformIO();

}

private Maybe<String> testCensor(Equivalence<MonadWriter<W, A, M>> equivalence) {

return equivalence.invMap(mw -> mw.censor(id())).equals(equivalence)

? nothing()

: just("censor (mw.censor(id()).equals(mw))");

}

private Maybe<String> testListens(Equivalence<MonadWriter<W, A, M>> equivalence) {

return equivalence.invMap(mw -> mw.listens(id()).fmap(Tuple2::_1)).equals(equivalence)

? nothing()

: just("censor (mw.censor(id()).equals(mw))");

}

}