/*
 * Copyright (c) 2019-2029, Dreamlu 卢春梦 (596392912@qq.com & www.dreamlu.net).
 * <p>
 * Licensed under the GNU LESSER GENERAL PUBLIC LICENSE 3.0;
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p>
 * http://www.gnu.org/licenses/lgpl.html
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.dreamlu.mica.core.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 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;
	}

}
