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package au.id.zancanaro;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.function.Predicate;
public class Generators {
public static <T> Generator<T> suchThat(Generator<T> gen, Predicate<T> pred) {
return (random, size) -> {
RoseTree<T> result = gen.generate(random, size);
if (pred.test(result.getValue())) {
return result.filter(pred);
} else {
return suchThat(gen, pred).generate(random, size);
}
};
}
@SafeVarargs
public static <T> Generator<T> oneOf(Generator<T>... gens) {
return integer(0, gens.length).flatMap(index -> gens[index]);
}
public static Generator<Integer> integer(int lower, int upper) {
return (random, size) -> {
int value = lower + random.nextInt(upper - lower);
int bound = lower > 0 ? lower : (upper < 0 ? upper : 0);
return new RoseTree<>(value, intShrinkingIterable(value, bound));
};
}
public static Generator<Integer> integer() {
return (random, size) -> integer(-size, size).generate(random, size);
}
public static Generator<Integer> natural() {
return (random, size) -> integer(0, size).generate(random, size);
}
private static Iterable<RoseTree<Integer>> intShrinkingIterable(final int value, final int bound) {
return () -> new Iterator<RoseTree<Integer>>() {
int curr = value - bound;
@Override
public boolean hasNext() {
return curr != 0;
}
@Override
public RoseTree<Integer> next() {
int prevCurr = curr;
curr = curr / 2;
return new RoseTree<>(value - prevCurr, intShrinkingIterable(value - prevCurr, bound));
}
};
}
public static <T> Generator<List<T>> listOf(Generator<T> gen) {
return (random, size) -> integer(0, size).flatMap(count -> {
@SuppressWarnings("unchecked")
Generator<T>[] gens = (Generator<T>[]) new Generator[count];
Arrays.fill(gens, gen);
return Generator.tuple(gens).fmap(Arrays::asList);
}).generate(random, size);
}
}
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