/*
 * 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;

import java.util.Hashtable;
import org.apache.log4j.helpers.ThreadLocalMap;

/**
 * The MDC class is similar to the {@link NDC} class except that it is based on
 * a map instead of a stack. It provides <em>mapped diagnostic contexts</em>. A
 * <em>Mapped Diagnostic Context</em>, or MDC in short, is an instrument for
 * distinguishing interleaved log output from different sources. Log output is
 * typically interleaved when a server handles multiple clients
 * near-simultaneously.
 * 
 * <p>
 * <b><em>The MDC is managed on a per thread basis</em></b>. A child thread
 * automatically inherits a <em>copy</em> of the mapped diagnostic context of
 * its parent.
 * 
 * <p>
 * The MDC class requires JDK 1.2 or above. Under JDK 1.1 the MDC will always
 * return empty values but otherwise will not affect or harm your application.
 * 
 * @since 1.2
 * 
 * @author Ceki G&uuml;lc&uuml;
 */
public class MDC {

    final static MDC mdc = new MDC();

    static final int HT_SIZE = 7;

    // boolean java1;

    Object tlm;

    private MDC() {
	tlm = new ThreadLocalMap();
    }

    /**
     * Put a context value (the <code>o</code> parameter) as identified with the
     * <code>key</code> parameter into the current thread's context map.
     * 
     * <p>
     * If the current thread does not have a context map it is created as a side
     * effect.
     * 
     */
    static public void put(String key, Object o) {
	if (mdc != null) {
	    mdc.put0(key, o);
	}
    }

    /**
     * Get the context identified by the <code>key</code> parameter.
     * 
     * <p>
     * This method has no side effects.
     */
    static public Object get(String key) {
	if (mdc != null) {
	    return mdc.get0(key);
	}
	return null;
    }

    /**
     * Remove the the context identified by the <code>key</code> parameter.
     * 
     */
    static public void remove(String key) {
	if (mdc != null) {
	    mdc.remove0(key);
	}
    }

    /**
     * Get the current thread's MDC as a hashtable. This method is intended to be
     * used internally.
     */
    public static Hashtable getContext() {
	if (mdc != null) {
	    return mdc.getContext0();
	} else {
	    return null;
	}
    }

    /**
     * Remove all values from the MDC.
     * 
     * @since 1.2.16
     */
    public static void clear() {
	if (mdc != null) {
	    mdc.clear0();
	}
    }

    private void put0(String key, Object o) {
	if (tlm == null) {
	    return;
	} else {
	    Hashtable ht = (Hashtable) ((ThreadLocalMap) tlm).get();
	    if (ht == null) {
		ht = new Hashtable(HT_SIZE);
		((ThreadLocalMap) tlm).set(ht);
	    }
	    ht.put(key, o);
	}
    }

    private Object get0(String key) {
	if (tlm == null) {
	    return null;
	} else {
	    Hashtable ht = (Hashtable) ((ThreadLocalMap) tlm).get();
	    if (ht != null && key != null) {
		return ht.get(key);
	    } else {
		return null;
	    }
	}
    }

    private void remove0(String key) {
	if (tlm != null) {
	    Hashtable ht = (Hashtable) ((ThreadLocalMap) tlm).get();
	    if (ht != null) {
		ht.remove(key);
		// clean up if this was the last key
		if (ht.isEmpty()) {
		    clear0();
		}
	    }
	}
    }

    private Hashtable getContext0() {
	if (tlm == null) {
	    return null;
	} else {
	    return (Hashtable) ((ThreadLocalMap) tlm).get();
	}
    }

    private void clear0() {
	if (tlm != null) {
	    Hashtable ht = (Hashtable) ((ThreadLocalMap) tlm).get();
	    if (ht != null) {
		ht.clear();
	    }

		((ThreadLocalMap) tlm).remove();
	}
    }

}
