/* 
 * 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.Function;
import java.util.function.UnaryOperator;

/**
 * Simple implementation of IHolder that has no hidden behavior.
 *
 * @author ben
 *
 * @param <ContainedType>
 *                        The type contained in the holder.
 */
public class Identity<ContainedType> implements Holder<ContainedType> {
	/* The held value. */
	private ContainedType heldValue;

	/** Create a holder holding null */
	public Identity() {
		heldValue = null;
	}

	/**
	 * Create a holder holding the specified value.
	 *
	 * @param value
	 *              The value to hold.
	 */
	public Identity(final ContainedType value) {
		heldValue = value;
	}

	@Override
	public <BoundType> Holder<BoundType>
			bind(final Function<ContainedType, Holder<BoundType>> binder) {
		return binder.apply(heldValue);
	}

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

		result = prime * result + (heldValue == null ? 0 : heldValue.hashCode());

		return result;
	}

	@Override
	public boolean equals(final Object obj) {
		if (this == obj)                return true;
		if (obj == null)                return false;
		if (!(obj instanceof Identity)) return false;

		final Identity<?> other = (Identity<?>) obj;

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

		return true;
	}

	@Override
	public <NewType> Function<ContainedType, Holder<NewType>>
			lift(final Function<ContainedType, NewType> func) {
		return val -> {
			return new Identity<>(func.apply(val));
		};
	}

	@Override
	public <MappedType> Holder<MappedType>
			map(final Function<ContainedType, MappedType> mapper) {
		return new Identity<>(mapper.apply(heldValue));
	}

	@Override
	public String toString() {
		return String.format("Identity [heldValue=%s]", heldValue);
	}

	@Override
	public Holder<ContainedType>
			transform(final UnaryOperator<ContainedType> transformer) {
		heldValue = transformer.apply(heldValue);

		return this;
	}

	@Override
	public <UnwrappedType> UnwrappedType
			unwrap(final Function<ContainedType, UnwrappedType> unwrapper) {
		return unwrapper.apply(heldValue);
	}

	/**
	 * Create a new identity container.
	 *
	 * @param <ContainedType> The type of the contained value.
	 * @param val The contained value.
	 *
	 * @return A new identity container.
	 */
	public static <ContainedType> Identity<ContainedType> id(final ContainedType val) {
		return new Identity<>(val);
	}

	/**
	 * Create a new empty identity container.
	 * 
	 * @param <ContainedType> The type of the contained value.
	 * 
	 * @return A new empty identity container.
	 */
	public static <ContainedType> Identity<ContainedType> id() {
		return new Identity<>();
	}
}