/*
 * 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.axiom.testutils;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Utility class that counts the number of invocations on one or more objects. It also counts the
 * number of exceptions thrown by these invocations. The class uses dynamic proxies to implement
 * this feature.
 *
 * <p>This class is thread safe.
 */
public class InvocationCounter {
    private class InvocationHandlerImpl implements InvocationHandler {
        private final Object target;

        public InvocationHandlerImpl(Object target) {
            this.target = target;
        }

        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            invocationCount.incrementAndGet();
            try {
                return method.invoke(target, args);
            } catch (InvocationTargetException ex) {
                exceptionCount.incrementAndGet();
                throw ex.getCause();
            }
        }
    }

    final AtomicInteger invocationCount = new AtomicInteger();
    final AtomicInteger exceptionCount = new AtomicInteger();

    /**
     * Create a new proxy. Every invocation of a method on this proxy increases the invocation count
     * by one unit. If the invocation results in an exception, then the exception counter is also
     * incremented. The returned proxy implements all interfaces of the target instance.
     *
     * @param target the target instance
     * @return the proxy instance
     */
    public Object createProxy(Object target) {
        Set<Class<?>> ifaces = new HashSet<>();
        Class<?> clazz = target.getClass();
        do {
            ifaces.addAll(Arrays.asList(clazz.getInterfaces()));
            clazz = clazz.getSuperclass();
        } while (clazz != null);
        return Proxy.newProxyInstance(
                InvocationCounter.class.getClassLoader(),
                ifaces.toArray(new Class<?>[ifaces.size()]),
                new InvocationHandlerImpl(target));
    }

    /**
     * Get the number of invocations counted by this instance.
     *
     * @return the number of invocations
     */
    public int getInvocationCount() {
        return invocationCount.get();
    }

    /**
     * Get the number of exceptions counted by this instance.
     *
     * @return the number of exceptions
     */
    public int getExceptionCount() {
        return exceptionCount.get();
    }

    /** Reset all counters to zero. */
    public void reset() {
        invocationCount.set(0);
        exceptionCount.set(0);
    }
}