/* 
 * esodata - data structures and other things, of varying utility
 * Copyright 2022, Ben Culkin
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *   
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
package bjc.data;

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

import bjc.data.internals.BoundLazyPair;
import bjc.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 Pair<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> Pair<BoundLeft, BoundRight> bind(
			final BiFunction<LeftType, RightType, Pair<BoundLeft, BoundRight>> binder) {
		return new BoundLazyPair<>(leftSupplier, rightSupplier, binder);
	}

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

			return leftSupplier.get();
		};

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

	@Override
	public <BoundRight> Pair<LeftType, BoundRight> bindRight(
			final Function<RightType, Pair<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>
			Pair<CombinedLeft, CombinedRight>
			combine(final Pair<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> Pair<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> Pair<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;
	}
}