package bjc.utils.data;

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

import bjc.utils.data.internals.BoundLazyPair;
import bjc.utils.data.internals.HalfBoundLazyPair;

/**
 * A lazy implementation of a pair.
 *
 * @author ben
 *
 * @param <LeftType>
 * 	The type on the left side of the pair.
 *
 * @param <RightType>
 * 	The type on the right side of the pair.
 */
public class LazyPair<LeftType, RightType> implements IPair<LeftType, RightType> {
	/* The supplier for the left value. */
	private Supplier<LeftType>  leftSupplier;
	/* The left value. */
	private LeftType leftValue;
	/* Whether the left value has been created. */
	private boolean	leftMaterialized;

	/* The supplier for the right value. */
	private Supplier<RightType> rightSupplier;
	/* The right value. */
	private RightType rightValue;
	/* Whether the right value has been created. */
	private boolean	rightMaterialized;

	/**
	 * Create a new lazy pair, using the set values.
	 *
	 * @param leftVal
	 * 	The value for the left side of the pair.
	 *
	 * @param rightVal
	 * 	The value for the right side of the pair.
	 */
	public LazyPair(final LeftType leftVal, final RightType rightVal) {
		leftValue  = leftVal;
		rightValue = rightVal;

		leftMaterialized  = true;
		rightMaterialized = true;
	}

	/**
	 * Create a new lazy pair from the given value sources.
	 *
	 * @param leftSupp
	 * 	The source for a value on the left side of the pair.
	 *
	 * @param rightSupp
	 * 	The source for a value on the right side of the pair.
	 */
	public LazyPair(final Supplier<LeftType> leftSupp, final Supplier<RightType> rightSupp) {
		/* Use single suppliers to catch double-instantiation bugs. */
		leftSupplier  = new SingleSupplier<>(leftSupp);
		rightSupplier = new SingleSupplier<>(rightSupp);

		leftMaterialized  = false;
		rightMaterialized = false;
	}

	@Override
	public <BoundLeft, BoundRight> IPair<BoundLeft, BoundRight> bind(
			final BiFunction<LeftType, RightType, IPair<BoundLeft, BoundRight>> binder) {
		return new BoundLazyPair<>(leftSupplier, rightSupplier, binder);
	}

	@Override
	public <BoundLeft> IPair<BoundLeft, RightType> bindLeft(
			final Function<LeftType, IPair<BoundLeft, RightType>> leftBinder) {
		final Supplier<LeftType> leftSupp = () -> {
			if (leftMaterialized) return leftValue;

			return leftSupplier.get();
		};

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

	@Override
	public <BoundRight> IPair<LeftType, BoundRight> bindRight(
			final Function<RightType, IPair<LeftType, BoundRight>> rightBinder) {
		final Supplier<RightType> rightSupp = () -> {
			if (rightMaterialized) return rightValue;

			return rightSupplier.get();
		};

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

	@Override
	public <OtherLeft, OtherRight, CombinedLeft, CombinedRight> IPair<CombinedLeft, CombinedRight> combine(
			final IPair<OtherLeft, OtherRight> otherPair,
			final BiFunction<LeftType, OtherLeft, CombinedLeft> leftCombiner,
			final BiFunction<RightType, OtherRight, CombinedRight> rightCombiner) {
		return otherPair.bind((otherLeft, otherRight) -> {
			return bind((leftVal, rightVal) -> {
				final CombinedLeft left   = leftCombiner.apply(leftVal, otherLeft);
				final CombinedRight right = rightCombiner.apply(rightVal, otherRight);

				return new LazyPair<>(left, right);
			});
		});
	}

	@Override
	public LeftType getLeft() {
		if (!leftMaterialized) {
			leftValue = leftSupplier.get();

			leftMaterialized = true;
		}

		return leftValue;
	}

	@Override
	public RightType getRight() {
		if (!rightMaterialized) {
			rightValue = rightSupplier.get();

			rightMaterialized = true;
		}

		return rightValue;
	}

	@Override
	public <NewLeft> IPair<NewLeft, RightType> mapLeft(final Function<LeftType, NewLeft> mapper) {
		final Supplier<NewLeft> leftSupp = () -> {
			if (leftMaterialized) return mapper.apply(leftValue);

			return mapper.apply(leftSupplier.get());
		};

		final Supplier<RightType> rightSupp = () -> {
			if (rightMaterialized) return rightValue;

			return rightSupplier.get();
		};

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

	@Override
	public <NewRight> IPair<LeftType, NewRight> mapRight(final Function<RightType, NewRight> mapper) {
		final Supplier<LeftType> leftSupp = () -> {
			if (leftMaterialized) return leftValue;

			return leftSupplier.get();
		};

		final Supplier<NewRight> rightSupp = () -> {
			if (rightMaterialized) return mapper.apply(rightValue);

			return mapper.apply(rightSupplier.get());
		};

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

	@Override
	public <MergedType> MergedType merge(final BiFunction<LeftType, RightType, MergedType> merger) {
		if (!leftMaterialized) {
			leftValue = leftSupplier.get();

			leftMaterialized = true;
		}

		if (!rightMaterialized) {
			rightValue = rightSupplier.get();

			rightMaterialized = true;
		}

		return merger.apply(leftValue, rightValue);
	}

	@Override
	public String toString() {
		String leftVal;
		String rightVal;

		if (leftMaterialized) {
			leftVal = leftValue.toString();
		} else {
			leftVal = "(un-materialized)";
		}

		if (rightMaterialized) {
			rightVal = rightValue.toString();
		} else {
			rightVal = "(un-materialized)";
		}

		return String.format("pair[l=%s,r=%s]", leftVal, rightVal);
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;

		result = prime * result + (leftMaterialized ? 1231 : 1237);
		result = prime * result + (leftValue == null ? 0 : leftValue.hashCode());
		result = prime * result + (rightMaterialized ? 1231 : 1237);
		result = prime * result + (rightValue == null ? 0 : rightValue.hashCode());

		return result;
	}

	@Override
	public boolean equals(final Object obj) {
		if (this == obj) return true;
		if (obj == null) return false;
		if (!(obj instanceof LazyPair<?, ?>)) return false;

		final LazyPair<?, ?> other = (LazyPair<?, ?>) obj;

		if (leftMaterialized != other.leftMaterialized) return false;

		if (leftMaterialized) {
			if (leftValue == null) {
				if (other.leftValue != null) return false;
			} else if (!leftValue.equals(other.leftValue)) return false;
		} else return false;

		if (rightMaterialized != other.rightMaterialized) return false;
		if (rightMaterialized) {
			if (rightValue == null) {
				if (other.rightValue != null) return false;
			} else if (!rightValue.equals(other.rightValue)) return false;
		} else return false;

		return true;
	}
}