/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
 *  with the License.  You may obtain a copy of the License at
 *
 *    https://www.apache.org/licenses/LICENSE-2.0
 *
 *  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 grails.util;

import java.util.Optional;
import java.util.function.Supplier;

/**
 * Helper methods for dealing with {@link Supplier}.
 *
 * @author James Kleeh
 * @since 1.0
 */
public class SupplierUtil {

    /**
     * Caches the result of supplier in a thread safe manner.
     *
     * @param actual The supplier providing the result
     * @param <T> The type of result
     * @return A new supplier that will cache the result
     */
    public static <T> Supplier<T> memoized(Supplier<T> actual) {
        return new Supplier<>() {
            Supplier<T> delegate = this::initialize;
            boolean initialized;

            public T get() {
                return delegate.get();
            }

            private synchronized T initialize() {
                if (!initialized) {
                    T value = actual.get();
                    delegate = () -> value;
                    initialized = true;
                }
                return delegate.get();
            }
        };
    }

    /**
     * Caches the result of supplier in a thread safe manner. The result
     * is only cached if it is non null or non empty if an optional.
     *
     * @param actual The supplier providing the result
     * @param <T> The type of result
     * @return A new supplier that will cache the result
     */
    public static <T> Supplier<T> memoizedNonEmpty(Supplier<T> actual) {
        return new Supplier<>() {
            Supplier<T> delegate = this::initialize;
            boolean initialized;

            public T get() {
                return delegate.get();
            }

            private synchronized T initialize() {
                if (!initialized) {
                    T value = actual.get();
                    if (value == null) {
                        return null;
                    }
                    if (value instanceof Optional) {
                        if (!((Optional) value).isPresent()) {
                            return value;
                        }
                    }
                    delegate = () -> value;
                    initialized = true;
                }
                return delegate.get();
            }
        };
    }
}
