/*
 * 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.log4j.helpers;

import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.pattern.LogEvent;

import java.lang.reflect.Method;
import java.util.Set;
import java.io.ByteArrayOutputStream;
import java.io.ObjectOutputStream;
import java.io.ByteArrayInputStream;
import java.io.ObjectInputStream;

public final class MDCKeySetExtractor {
    private final Method getKeySetMethod;
    public static final MDCKeySetExtractor INSTANCE = new MDCKeySetExtractor();

    private MDCKeySetExtractor() {
	//
	// log4j 1.2.15 and later will have method to get names
	// of all keys in MDC
	//
	Method getMethod = null;

	try {
	    getMethod = LoggingEvent.class.getMethod("getPropertyKeySet", null);
	} catch (Exception ex) {
	    getMethod = null;
	}
	getKeySetMethod = getMethod;

    }

    public Set getPropertyKeySet(final LoggingEvent event) throws Exception {
	//
	// MDC keys are not visible prior to log4j 1.2.15
	//
	Set keySet = null;
	if (getKeySetMethod != null) {
	    keySet = (Set) getKeySetMethod.invoke(event, null);
	} else {
	    //
	    // for 1.2.14 and earlier could serialize and
	    // extract MDC content
	    ByteArrayOutputStream outBytes = new ByteArrayOutputStream();
	    ObjectOutputStream os = new ObjectOutputStream(outBytes);
	    os.writeObject(event);
	    os.close();

	    byte[] raw = outBytes.toByteArray();
	    //
	    // bytes 6 and 7 should be the length of the original classname
	    // should be the same as our substitute class name
	    final String subClassName = LogEvent.class.getName();
	    if (raw[6] == 0 || raw[7] == subClassName.length()) {
		//
		// manipulate stream to use our class name
		//
		for (int i = 0; i < subClassName.length(); i++) {
		    raw[8 + i] = (byte) subClassName.charAt(i);
		}
		ByteArrayInputStream inBytes = new ByteArrayInputStream(raw);
		ObjectInputStream is = new ObjectInputStream(inBytes);
		Object cracked = is.readObject();
		if (cracked instanceof LogEvent) {
		    keySet = ((LogEvent) cracked).getPropertyKeySet();
		}
		is.close();
	    }
	}
	return keySet;
    }
}
