package testsupport.assertion;

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.functions.Fn2;

import com.jnape.palatable.lambda.functions.builtin.fn2.Map;

import com.jnape.palatable.lambda.functor.Functor;

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

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

import com.jnape.palatable.lambda.optics.Optic;

import java.util.Objects;

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.CatMaybes.catMaybes;

import static com.jnape.palatable.lambda.functions.builtin.fn2.CartesianProduct.cartesianProduct;

import static com.jnape.palatable.lambda.functions.builtin.fn2.Into.into;

import static com.jnape.palatable.lambda.functions.builtin.fn2.ReduceLeft.reduceLeft;

import static com.jnape.palatable.lambda.optics.functions.Set.set;

import static com.jnape.palatable.lambda.optics.functions.View.view;

import static java.lang.String.format;

import static java.lang.String.join;

import static java.util.Arrays.asList;

public final class LensAssert {

public static <S, A> void assertLensLawfulness(Optic<? super Fn1<?, ?>, Functor<?, ?>, S, S, A, A> lens,

Iterable<S> ss,

Iterable<A> bs) {

Iterable<Tuple2<S, A>> cases = cartesianProduct(ss, bs);

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

.reduceLeft(asList(falsify("You get back what you put in", (s, b) -> view(lens, set(lens, b, s)), (s, b) -> b, cases),

falsify("Putting back what you got changes nothing", (s, b) -> set(lens, view(lens, s), s), (s, b) -> s, cases),

falsify("Setting twice is equivalent to setting once", (s, b) -> set(lens, b, set(lens, b, s)), (s, b) -> set(lens, b, s), cases)))

.match(IO::io, failures -> IO.throwing(new AssertionError("Lens law failures\n\n" + failures)))

.unsafePerformIO();

}

private static <S, A, X> Maybe<String> falsify(String label, Fn2<S, A, X> l, Fn2<S, A, X> r,

Iterable<Tuple2<S, A>> cases) {

return Map.<Tuple2<S, A>, Maybe<String>>map(into((s, b) -> {

X x = l.apply(s, b);

X y = r.apply(s, b);

return Objects.equals(x, y) ? nothing() : just(format("S <%s>, B <%s> (%s != %s)", s, b, x, y));

}))

.fmap(catMaybes())

.fmap(reduceLeft((x, y) -> x + "\n\t - " + y))

.fmap(maybeFailures -> maybeFailures.fmap(failures -> "\"" + label + "\" failed for the following cases:\n\n\t - " + failures))

.apply(cases);

}

}