package au.id.zancanaro.javacheck;

import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.function.Function;
import java.util.function.Predicate;

public final class Generators {
    private Generators() {
    }

    public static <T> Generator<T> sized(Function<Integer, Generator<T>> makeGenerator) {
        return (random, size) -> makeGenerator.apply(size).generate(random, size);
    }

    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 <T> Generator<T> elements(T[] elements) {
        return elements(Arrays.asList(elements));
    }

    public static <T> Generator<T> elements(List<T> elements) {
        return integer(0, elements.size()).fmap(elements::get);
    }

    public static Generator<Boolean> bool() {
        return (random, size) ->
                random.nextBoolean() ?
                        new RoseTree<>(true, Collections.singletonList(new RoseTree<>(false, Collections.emptyList()))) :
                        new RoseTree<>(false, Collections.emptyList());
    }

    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 sized(size -> integer(-size, size));
    }

    public static Generator<Integer> natural() {
        return sized(size -> integer(0, 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) -> {
            Generator<Integer> countGen = sized(s -> integer(0, s));
            int count = countGen.generate(random, size).getValue();
            return Generator.list(count, gen).generate(random, size);
        };
    }

    public static Generator<Character> character() {
        return integer(0, 256).fmap(i -> (char) i.intValue());
    }

    public static Generator<Character> asciiCharacter() {
        return integer(32, 127).fmap(i -> (char) i.intValue());
    }

    public static Generator<Character> alphaNumericCharacter() {
        return oneOf(
                integer(48, 58),
                integer(65, 91),
                integer(97, 123)).fmap(i -> (char) i.intValue());
    }

    public static Generator<Character> alphaCharacter() {
        return oneOf(
                integer(65, 91),
                integer(97, 123)).fmap(i -> (char) i.intValue());
    }

    private static String makeString(Character[] arr) {
        StringBuilder builder = new StringBuilder(arr.length);
        for (Character c : arr) {
            builder.append(c);
        }
        return builder.toString();
    }

    public static Generator<String> string() {
        return stringOf(character());
    }

    public static Generator<String> stringOf(Generator<Character> charGen) {
        return listOf(charGen).fmap(list -> {
            char[] chars = new char[list.size()];
            int i = 0;
            for (Character c : list) {
                chars[i++] = c;
            }
            return String.valueOf(chars);
//            return new String(chars);
        });
    }
}