package au.id.zancanaro;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.function.Function;

public interface Generator<T> {
    RoseTree<T> generate(Random random, int size);

    static <T> Generator<T> pure(T value) {
        return (random, size) -> RoseTree.pure(value);
    }

    default <R> Generator<R> genFlatmap(Function<RoseTree<T>, Generator<R>> f) {
        return (random, size) -> {
            RoseTree<T> inner = this.generate(random, size);
            Generator<R> generator = f.apply(inner);
            return generator.generate(random, size);
        };
    }

    default <R> Generator<R> genFmap(Function<RoseTree<T>, RoseTree<R>> f) {
        return (random, size) -> f.apply(this.generate(random, size));
    }

    @SafeVarargs
    static <T> Generator<T[]> tuple(Generator<T>... generators) {
        return (random, size) -> {
            @SuppressWarnings("unchecked")
            RoseTree<T>[] result = (RoseTree<T>[]) new RoseTree[generators.length];
            int index = 0;
            for (Generator<T> generator : generators) {
                result[index++] = generator.generate(random, size);
            }
            return RoseTree.zip(Function.identity(), result);
        };
    }

    default <R> Generator<R> fmap(Function<T, R> f) {
        return (random, size) -> this.generate(random, size).fmap(f);
    }

    default <R> Generator<R> flatMap(Function<T, Generator<R>> action) {
        return this.genFlatmap(rose -> {
            Generator<RoseTree<R>> generator = (random, size) ->
                    rose.fmap(action).fmap(g -> g.generate(random, size));
            return generator.<R>genFmap(RoseTree::join);
        });
    }
}