package bjc.utils.data.internals;

import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Supplier;

import bjc.utils.data.IHolder;
import bjc.utils.data.IPair;
import bjc.utils.data.Identity;
import bjc.utils.data.LazyPair;

/**
 * Implements a lazy pair that has been bound.
 *
 * @author Ben Culkin
 */
@SuppressWarnings("javadoc")
public class BoundLazyPair<OldLeft, OldRight, NewLeft, NewRight> implements IPair<NewLeft, NewRight> {
	/* The supplier of the left value. */
	private final Supplier<OldLeft> leftSupplier;
	/* The supplier of the right value. */
	private final Supplier<OldRight> rightSupplier;

	/* The binder to transform values. */
	private final BiFunction<OldLeft, OldRight, IPair<NewLeft, NewRight>> binder;

	/* The bound pair. */
	private IPair<NewLeft, NewRight> boundPair;

	/* Whether the pair has been bound yet. */
	private boolean pairBound;

	/**
	 * Create a new bound lazy pair.
	 *
	 * @param leftSupp
	 *        The supplier for the left value.
	 *
	 * @param rightSupp
	 *        The supplier for the right value.
	 *
	 * @param bindr
	 *        The function to use to bind the left and right into a new
	 *        pair.
	 */
	public BoundLazyPair(final Supplier<OldLeft> leftSupp, final Supplier<OldRight> rightSupp,
			final BiFunction<OldLeft, OldRight, IPair<NewLeft, NewRight>> bindr) {
		leftSupplier = leftSupp;
		rightSupplier = rightSupp;
		binder = bindr;
	}

	@Override
	public <BoundLeft, BoundRight> IPair<BoundLeft, BoundRight> bind(
			final BiFunction<NewLeft, NewRight, IPair<BoundLeft, BoundRight>> bindr) {
		if(bindr == null) throw new NullPointerException("Binder must not be null");

		final IHolder<IPair<NewLeft, NewRight>> newPair = new Identity<>(boundPair);
		final IHolder<Boolean> newPairMade = new Identity<>(pairBound);

		final Supplier<NewLeft> leftSupp = () -> {
			if(!newPairMade.getValue()) {
				/*
				 * If the pair hasn't been bound before, bind
				 * it.
				 */
				newPair.replace(binder.apply(leftSupplier.get(), rightSupplier.get()));

				newPairMade.replace(true);
			}

			return newPair.unwrap((pair) -> pair.getLeft());
		};

		final Supplier<NewRight> rightSupp = () -> {
			if(!newPairMade.getValue()) {
				/*
				 * If the pair hasn't been bound before, bind
				 * it.
				 */
				newPair.replace(binder.apply(leftSupplier.get(), rightSupplier.get()));

				newPairMade.replace(true);
			}

			return newPair.unwrap((pair) -> pair.getRight());
		};

		return new BoundLazyPair<>(leftSupp, rightSupp, bindr);
	}

	@Override
	public <BoundLeft> IPair<BoundLeft, NewRight> bindLeft(
			final Function<NewLeft, IPair<BoundLeft, NewRight>> leftBinder) {
		if(leftBinder == null) throw new NullPointerException("Left binder must not be null");

		final Supplier<NewLeft> leftSupp = () -> {
			IPair<NewLeft, NewRight> newPair = boundPair;

			if(!pairBound) {
				/*
				 * If the pair hasn't been bound before, bind
				 * it.
				 */
				newPair = binder.apply(leftSupplier.get(), rightSupplier.get());
			}

			return newPair.getLeft();
		};

		return new HalfBoundLazyPair<>(leftSupp, leftBinder);
	}

	@Override
	public <BoundRight> IPair<NewLeft, BoundRight> bindRight(
			final Function<NewRight, IPair<NewLeft, BoundRight>> rightBinder) {
		if(rightBinder == null) throw new NullPointerException("Right binder must not be null");

		final Supplier<NewRight> rightSupp = () -> {
			IPair<NewLeft, NewRight> newPair = boundPair;

			if(!pairBound) {
				/*
				 * If the pair hasn't been bound before, bind
				 * it.
				 */
				newPair = binder.apply(leftSupplier.get(), rightSupplier.get());
			}

			return newPair.getRight();
		};

		return new HalfBoundLazyPair<>(rightSupp, rightBinder);
	}

	@Override
	public <OtherLeft, OtherRight, CombinedLeft, CombinedRight> IPair<CombinedLeft, CombinedRight> combine(
			final IPair<OtherLeft, OtherRight> otherPair,
			final BiFunction<NewLeft, OtherLeft, CombinedLeft> leftCombiner,
			final BiFunction<NewRight, OtherRight, CombinedRight> rightCombiner) {
		if(otherPair == null) {
			throw new NullPointerException("Other pair must not be null");
		} else if(leftCombiner == null) {
			throw new NullPointerException("Left combiner must not be null");
		} else if(rightCombiner == null) {
			throw new NullPointerException("Right combiner must not be null");
		}

		return otherPair.bind((otherLeft, otherRight) -> {
			return bind((leftVal, rightVal) -> {
				CombinedLeft cLeft = leftCombiner.apply(leftVal, otherLeft);
				CombinedRight cRight = rightCombiner.apply(rightVal, otherRight);

				return new LazyPair<>(cLeft, cRight);
			});
		});
	}

	@Override
	public <NewLeftType> IPair<NewLeftType, NewRight> mapLeft(final Function<NewLeft, NewLeftType> mapper) {
		if(mapper == null) throw new NullPointerException("Mapper must not be null");

		final Supplier<NewLeftType> leftSupp = () -> {
			if(!pairBound) {
				final NewLeft leftVal = binder.apply(leftSupplier.get(), rightSupplier.get()).getLeft();

				return mapper.apply(leftVal);
			}

			return mapper.apply(boundPair.getLeft());
		};

		final Supplier<NewRight> rightSupp = () -> {
			if(!pairBound) return binder.apply(leftSupplier.get(), rightSupplier.get()).getRight();

			return boundPair.getRight();
		};

		return new LazyPair<>(leftSupp, rightSupp);
	}

	@Override
	public <NewRightType> IPair<NewLeft, NewRightType> mapRight(final Function<NewRight, NewRightType> mapper) {
		if(mapper == null) throw new NullPointerException("Mapper must not be null");

		final Supplier<NewLeft> leftSupp = () -> {
			if(!pairBound) return binder.apply(leftSupplier.get(), rightSupplier.get()).getLeft();

			return boundPair.getLeft();
		};

		final Supplier<NewRightType> rightSupp = () -> {
			if(!pairBound) {
				final NewRight rightVal = binder.apply(leftSupplier.get(), rightSupplier.get())
						.getRight();

				return mapper.apply(rightVal);
			}

			return mapper.apply(boundPair.getRight());
		};

		return new LazyPair<>(leftSupp, rightSupp);
	}

	@Override
	public <MergedType> MergedType merge(final BiFunction<NewLeft, NewRight, MergedType> merger) {
		if(merger == null) throw new NullPointerException("Merger must not be null");

		if(!pairBound) {
			/*
			 * If the pair isn't bound yet, bind it.
			 */
			boundPair = binder.apply(leftSupplier.get(), rightSupplier.get());

			pairBound = true;
		}

		return boundPair.merge(merger);
	}

	@Override
	public String toString() {
		if(pairBound) return boundPair.toString();

		return "(un-materialized)";
	}
}