/*
 * Copyright (C) The Apache Software Foundation. All rights reserved.
 *
 * This software is published under the terms of the Apache Software
 * License version 1.1, a copy of which has been included with this
 * distribution in the LICENSE.txt file.  */

package org.apache.log4j;

import org.apache.log4j.Layout;
import org.apache.log4j.spi.Filter;
import org.apache.log4j.spi.ErrorHandler;
import org.apache.log4j.spi.OptionHandler;
import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.helpers.OnlyOnceErrorHandler;
import org.apache.log4j.helpers.LogLog;


/** 
 * Abstract superclass of the other appenders in the package.
 *  
 *  This class provides the code for common functionality, such as
 *  support for threshold filtering and support for general filters.
 *
 * @since 0.8.1
 * @author Ceki Gülcü 
 * */
public abstract class AppenderSkeleton implements Appender, OptionHandler {

  /** The layout variable does not need to be set if the appender
      implementation has its own layout. */
  protected Layout layout;

  /** Appenders are named. */
  protected String name;

  /**
     There is no level threshold filtering by default.  */
  protected Priority threshold;

  /** 
      It is assumed and enforced that errorHandler is never null.
  */
  protected ErrorHandler errorHandler = new OnlyOnceErrorHandler();

  /** The first filter in the filter chain. Set to null
      initially. */
  protected Filter headFilter;
  /** The last filter in the filter chain. */
  protected Filter tailFilter;

  /**
     Is this appender closed? 
   */
  protected boolean closed = false;


  /**
     Derived appenders should override this method if option structure
     requires it.  */
  public
  void activateOptions() {
  }


  /**
     Add a filter to end of the filter list.

     @since 0.9.0
   */
  public
  void addFilter(Filter newFilter) {
    if(headFilter == null) {
      headFilter = tailFilter = newFilter;
    } else {
      tailFilter.next = newFilter;
      tailFilter = newFilter;    
    }
  }

  /**
     Subclasses of AppenderSkeleton should implement this
     method to perform actual logging. See also {@link #doAppend
     AppenderSkeleton.doAppend} method.

     @since 0.9.0
  */
  abstract
  protected
  void append(LoggingEvent event);


  /**
     Clear the filters chain.
     
     @since 0.9.0 */
  public
  void clearFilters() {
    headFilter = tailFilter = null;
  }

  /**
     Finalize this appender by calling the derived class'
     close method.

     @since 0.8.4 */
  public
  void finalize() {
    // An appender might be closed then garbage collected. There is no
    // point in closing twice.
    if(this.closed) 
      return;

    LogLog.debug("Finalizing appender named ["+name+"].");
    close();
  }


  /** 
      Return the currently set {@link ErrorHandler} for this
      Appender.  

      @since 0.9.0 */
  public
  ErrorHandler getErrorHandler() {
    return this.errorHandler;
  }


  /**
     Returns the head Filter.
     
     @since 1.1
  */
  public
  Filter getFilter() {
    return headFilter;
  }

  /** 
      Return the first filter in the filter chain for this
      Appender. The return value may be null if no is
      filter is set.
      
  */
  public
  final
  Filter getFirstFilter() {
    return headFilter;
  }

  /**
     Returns the layout of this appender. The value may be null.
  */
  public
  Layout getLayout() {
    return layout;
  }


  /**
     Returns the name of this FileAppender.
   */
  public
  final
  String getName() {
    return this.name;
  }

  /**
     Returns this appenders threshold level. See the {@link
     #setThreshold} method for the meaning of this option.
     
     @since 1.1 */
  public
  Priority getThreshold() {
    return threshold;
  }


  /**
     Check whether the message level is below the appender's
     threshold. If there is no threshold set, then the return value is
     always true.

  */
  public
  boolean isAsSevereAsThreshold(Priority priority) {
    return ((threshold == null) || priority.isGreaterOrEqual(threshold));
  }


  /**
    * This method performs threshold checks and invokes filters before
    * delegating actual logging to the subclasses specific {@link
    * AppenderSkeleton#append} method.
    * */
  public
  synchronized 
  void doAppend(LoggingEvent event) {
    if(closed) {
      LogLog.error("Attempted to append to closed appender named ["+name+"].");
      return;
    }
    
    if(!isAsSevereAsThreshold(event.getLevel())) {
      return;
    }

    Filter f = this.headFilter;
    
    FILTER_LOOP:
    while(f != null) {
      switch(f.decide(event)) {
      case Filter.DENY: return;
      case Filter.ACCEPT: break FILTER_LOOP;
      case Filter.NEUTRAL: f = f.next;
      }
    }
    
    this.append(event);    
  }

  /** 
      Set the {@link ErrorHandler} for this Appender.
      @since 0.9.0
  */
  public
  synchronized
  void setErrorHandler(ErrorHandler eh) {
    if(eh == null) {
      // We do not throw exception here since the cause is probably a
      // bad config file.
      LogLog.warn("You have tried to set a null error-handler.");
    } else {
      this.errorHandler = eh;
    }
  }

  /**
     Set the layout for this appender. Note that some appenders have
     their own (fixed) layouts or do not use one. For example, the
     {@link org.apache.log4j.net.SocketAppender} ignores the layout set
     here. 
  */
  public
  void setLayout(Layout layout) {
    this.layout = layout;
  }

  
  /**
     Set the name of this Appender.
   */
  public
  void setName(String name) {
    this.name = name;
  }


  /**
     Set the threshold level. All log events with lower level
     than the threshold level are ignored by the appender.
     
     
In configuration files this option is specified by setting the
     value of the Threshold option to a level
     string, such as "DEBUG", "INFO" and so on.
     
     @since 0.8.3 */
  public
  void setThreshold(Priority threshold) {
    this.threshold = threshold;
  }  
}