package fj.data;

import fj.F0;

import fj.F2;

import org.junit.Assert;

import org.junit.Test;

import java.util.Iterator;

public class EvalTest {

@Test

public void testNow() {

Eval<Integer> eval = Eval.now(1);

Assert.assertEquals(eval.value().intValue(), 1);

Assert.assertEquals(eval.map(a -> a.toString()).value(), "1");

Assert.assertEquals(eval.bind(a -> Eval.now(a * 3)).value().intValue(), 3);

}

@Test

public void testLater() {

InvocationTrackingF<Integer> tracker = new InvocationTrackingF<>(1);

Eval<Integer> eval = Eval.later(tracker);

Assert.assertEquals(tracker.getInvocationCounter(), 0);

Assert.assertEquals(eval.value().intValue(), 1);

Assert.assertEquals(tracker.getInvocationCounter(), 1);

eval.value();

Assert.assertEquals(tracker.getInvocationCounter(), 1);

}

@Test

public void testAlways() {

InvocationTrackingF<Integer> tracker = new InvocationTrackingF<>(1);

Eval<Integer> eval = Eval.always(tracker);

Assert.assertEquals(tracker.getInvocationCounter(), 0);

Assert.assertEquals(eval.value().intValue(), 1);

Assert.assertEquals(tracker.getInvocationCounter(), 1);

eval.value();

eval.value();

Assert.assertEquals(tracker.getInvocationCounter(), 3);

}

@Test

public void testDefer() {

// Make sure that a recursive computation is actually stack-safe.

int targetValue = 200000;

Iterator<Integer> it = Enumerator.intEnumerator.toStream(0).iterator();

Eval<Boolean> result = foldRight(it, (v, acc) -> v == targetValue ? Eval.now(true) : acc, false);

Assert.assertTrue(result.value());

}

private static <A, T> Eval<A> foldRight(Iterator<T> iterator,

F2<T, Eval<A>, Eval<A>> f,

A zero) {

if (!iterator.hasNext()) {

return Eval.now(zero);

}

return f.f(iterator.next(), Eval.defer(() -> foldRight(iterator, f, zero)));

}

private static class InvocationTrackingF<A> implements F0<A> {

private final A value;

private int invocationCounter;

public InvocationTrackingF(A value) {

this.value = value;

this.invocationCounter = 0;

}

@Override

public A f() {

invocationCounter++;

return value;

}

public int getInvocationCounter() {

return invocationCounter;

}

}

}