package testsupport.traits;

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

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

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

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

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.Collections.singletonList;

public class MonadReaderLaws<M extends MonadReader<?, ?, M>> implements EquivalenceTrait<MonadReader<?, ?, M>> {

@Override

public Class<? super MonadReader<?, ?, ?>> type() {

return MonadReader.class;

}

@Override

public void test(Equivalence<MonadReader<?, ?, M>> equivalence) {

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

.<Fn1<Equivalence<MonadReader<?, ?, M>>, Maybe<String>>>foldMap(

f -> f.apply(equivalence),

singletonList(this::testLocalIdentity)

)

.match(IO::io,

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

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

.unsafePerformIO();

}

private Maybe<String> testLocalIdentity(Equivalence<MonadReader<?, ?, M>> equivalence) {

return equivalence.invMap(mr -> mr.local(id())).equals(equivalence)

? nothing()

: just("local identity (mr.local(id()).equals(mr))");

}

}