/*
 * 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.skywalking.apm.agent.core.plugin;

import java.util.HashMap;
import java.util.Map;
import net.bytebuddy.pool.TypePool;

/**
 * The <code>WitnessClassFinder</code> represents a pool of {@link TypePool}s,
 * each {@link TypePool} matches a {@link ClassLoader},
 * which helps to find the class define existed or not.
 *
 * @author wusheng
 */
public enum WitnessClassFinder {
    INSTANCE;

    private Map<ClassLoader, TypePool> poolMap = new HashMap<ClassLoader, TypePool>();

    /**
     * @param witnessClass
     * @param classLoader for finding the witnessClass
     * @return true, if the given witnessClass exists, through the given classLoader.
     */
    public boolean exist(String witnessClass, ClassLoader classLoader) {
        ClassLoader mappingKey = classLoader == null ? NullClassLoader.INSTANCE : classLoader;
        if (!poolMap.containsKey(mappingKey)) {
            synchronized (poolMap) {
                if (!poolMap.containsKey(mappingKey)) {
                    TypePool classTypePool = classLoader == null ? TypePool.Default.ofClassPath() : TypePool.Default.of(classLoader);
                    poolMap.put(mappingKey, classTypePool);
                }
            }
        }
        TypePool typePool = poolMap.get(mappingKey);
        TypePool.Resolution witnessClassResolution = typePool.describe(witnessClass);
        return witnessClassResolution.isResolved();
    }
}

final class NullClassLoader extends ClassLoader {
    static NullClassLoader INSTANCE = new NullClassLoader();
}
