package bjc.utils.data;

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

/**
 * A holder that may or may not contain a value
 *
 * @author ben
 *
 * @param <ContainedType>
 *                The type of the value that may or may not be held
 */
public class Option<ContainedType> implements IHolder<ContainedType> {
	private ContainedType held;

	/**
	 * Create a new optional, using the given initial value
	 *
	 * @param seed
	 *                The initial value for the optional
	 */
	public Option(ContainedType seed) {
		held = seed;
	}

	@Override
	public <BoundType> IHolder<BoundType> bind(Function<ContainedType, IHolder<BoundType>> binder) {
		if(held == null) return new Option<>(null);

		return binder.apply(held);
	}

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

	@Override
	public <MappedType> IHolder<MappedType> map(Function<ContainedType, MappedType> mapper) {
		if(held == null) return new Option<>(null);

		return new Option<>(mapper.apply(held));
	}

	@Override
	public IHolder<ContainedType> transform(UnaryOperator<ContainedType> transformer) {
		if(held != null) {
			held = transformer.apply(held);
		}

		return this;
	}

	@Override
	public <UnwrappedType> UnwrappedType unwrap(Function<ContainedType, UnwrappedType> unwrapper) {
		if(held == null) return null;

		return unwrapper.apply(held);
	}

	@Override
	public String toString() {
		StringBuilder builder = new StringBuilder();

		builder.append("Option [");

		if(held != null) {
			builder.append("held=");
			builder.append(held);
		}

		builder.append("]");
		return builder.toString();
	}

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

		int result = 1;
		result = prime * result + ((held == null) ? 0 : held.hashCode());

		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if(this == obj) return true;
		if(obj == null) return false;
		if(getClass() != obj.getClass()) return false;

		Option<?> other = (Option<?>) obj;

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

		return true;
	}
}