/*
 * 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
 *
 *   http://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 org.apache.jackrabbit.vault.util;

import java.util.function.Supplier;

import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

/**
 * A supplier wrapper which caches the supplied values. This class is not threadsafe!
 * @param <T>
 * @since FileVault 4.0.2
 */
public class CachingSupplier<T> implements Supplier<T> {

    T resolvedValue = null;
    Supplier<T> delegate;

    private CachingSupplier(Supplier<T> supplier) {
        delegate = supplier;
    }

    public static <T> CachingSupplier<T> of(@NotNull Supplier<T> supplier) {
        return new CachingSupplier<T>(supplier);
    }

    /**
     * Uses the cached value from previous get() calls instead of contacting the underlying delegate
     * @return the resolved value (can be null);
     */
    public @Nullable T get() {
        if (resolvedValue == null) {
            resolvedValue = delegate.get();
        }
        return resolvedValue;
    }
}
