/*-
 * ============LICENSE_START=======================================================
 * SDC
 * ================================================================================
 * Copyright (C) 2017 AT&T Intellectual Property. All rights reserved.
 * ================================================================================
 * Licensed 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.
 * ============LICENSE_END=========================================================
 */

package org.openecomp.core.logging.context;

import org.openecomp.core.logging.api.context.ContextPropagationService;
import org.slf4j.MDC;

import java.util.Map;

/**
 * Propagates the <a href="http://www.slf4j.org/manual.html#mdc">SLF4J Mapped Diagnostic Context
 * (MDC)</a> of a thread onto a runnable created by that thread, so that the context is available
 * when the runnable is executed in a new thread.
 */
public class MdcPropagationService implements ContextPropagationService {

  public Runnable create(Runnable task) {
    return new MdcCopyingWrapper(task);
  }

  private static class MdcCopyingWrapper implements Runnable {

    private final Runnable task;
    private final Map<String, String> context;

    private MdcCopyingWrapper(Runnable task) {
      this.task = task;
      this.context = MDC.getCopyOfContextMap();
    }

    private static void replaceMdc(Map<String, String> context) {

      if (context == null) {
        MDC.clear();
      } else {
        MDC.setContextMap(context);
      }
    }

    @Override
    public void run() {

      Map<String, String> oldContext = MDC.getCopyOfContextMap();
      replaceMdc(this.context);

      try {
        task.run();
      } finally {
        replaceMdc(oldContext);
      }
    }
  }
}