/*
 *      Copyright (c) 2018-2028, DreamLu All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions are met:
 *
 *  Redistributions of source code must retain the above copyright notice,
 *  this list of conditions and the following disclaimer.
 *  Redistributions in binary form must reproduce the above copyright
 *  notice, this list of conditions and the following disclaimer in the
 *  documentation and/or other materials provided with the distribution.
 *  Neither the name of the dreamlu.net developer nor the names of its
 *  contributors may be used to endorse or promote products derived from
 *  this software without specific prior written permission.
 *  Author: DreamLu 卢春梦 (596392912@qq.com)
 */
package org.springblade.core.tool.utils;

import org.springframework.lang.Nullable;

import java.io.Serializable;
import java.util.function.Supplier;

/**
 * Holder of a value that is computed lazy.
 *
 * @author L.cm
 */
public class Lazy<T> implements Supplier<T>, Serializable {

	@Nullable
	private transient volatile Supplier<? extends T> supplier;
	@Nullable
	private T value;

	/**
	 * Creates new instance of Lazy.
	 *
	 * @param supplier Supplier
	 * @param <T>      泛型标记
	 * @return Lazy
	 */
	public static <T> Lazy<T> of(final Supplier<T> supplier) {
		return new Lazy<>(supplier);
	}

	private Lazy(final Supplier<T> supplier) {
		this.supplier = supplier;
	}

	/**
	 * Returns the value. Value will be computed on first call.
	 *
	 * @return lazy value
	 */
	@Nullable
	@Override
	public T get() {
		return (supplier == null) ? value : computeValue();
	}

	@Nullable
	private synchronized T computeValue() {
		final Supplier<? extends T> s = supplier;
		if (s != null) {
			value = s.get();
			supplier = null;
		}
		return value;
	}

}