/*
 * 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.io.IOException;
import java.io.Writer;
import java.io.OutputStream;
import java.io.OutputStreamWriter;

import org.apache.log4j.spi.ErrorHandler;
import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.helpers.QuietWriter;
import org.apache.log4j.helpers.LogLog;

// Contibutors: Jens Uwe Pipka <jens.pipka@gmx.de>
//              Ben Sandee

/**
   WriterAppender appends log events to a {@link java.io.Writer} or an
   {@link java.io.OutputStream} depending on the user's choice.

   @author Ceki G&uuml;lc&uuml;
   @since 1.1 */
public class WriterAppender extends AppenderSkeleton {


  /**
     Immediate flush means that the underlying writer or output stream
     will be flushed at the end of each append operation. Immediate
     flush is slower but ensures that each append request is actually
     written. If <code>immediateFlush</code> is set to
     <code>false</code>, then there is a good chance that the last few
     logs events are not actually written to persistent media if and
     when the application crashes.

     <p>The <code>immediateFlush</code> variable is set to
     <code>true</code> by default.

  */
  protected boolean immediateFlush = true;

  /**
     The encoding to use when writing.  <p>The
     <code>encoding</code> variable is set to <code>null</null> by
     default which results in the utilization of the system's default
     encoding.  */
  protected String encoding;

  /**
     This is the {@link QuietWriter quietWriter} where we will write
     to.
  */
  protected QuietWriter qw;


  /**
     This default constructor does nothing.  */
  public
  WriterAppender() {
  }

  /**
     Instantiate a WriterAppender and set the output destination to a
     new {@link OutputStreamWriter} initialized with <code>os</code>
     as its {@link OutputStream}.  */
  public
  WriterAppender(Layout layout, OutputStream os) {
    this(layout, new OutputStreamWriter(os));
  }

  /**
     Instantiate a WriterAppender and set the output destination to
     <code>writer</code>.

     <p>The <code>writer</code> must have been previously opened by
     the user.  */
  public
  WriterAppender(Layout layout, Writer writer) {
    this.layout = layout;
    this.setWriter(writer);
  }

  /**
     If the <b>ImmediateFlush</b> option is set to
     <code>true</code>, the appender will flush at the end of each
     write. This is the default behavior. If the option is set to
     <code>false</code>, then the underlying stream can defer writing
     to physical medium to a later time.

     <p>Avoiding the flush operation at the end of each append results in
     a performance gain of 10 to 20 percent. However, there is safety
     tradeoff involved in skipping flushing. Indeed, when flushing is
     skipped, then it is likely that the last few log events will not
     be recorded on disk when the application exits. This is a high
     price to pay even for a 20% performance gain.
   */
  public
  void setImmediateFlush(boolean value) {
    immediateFlush = value;
  }

  /**
     Returns value of the <b>ImmediateFlush</b> option.
   */
  public
  boolean getImmediateFlush() {
    return immediateFlush;
  }

  /**
     Does nothing.
  */
  public
  void activateOptions() {
  }


  /**
     This method is called by the {@link AppenderSkeleton#doAppend}
     method.

     <p>If the output stream exists and is writable then write a log
     statement to the output stream. Otherwise, write a single warning
     message to <code>System.err</code>.

     <p>The format of the output will depend on this appender's
     layout.

  */
  public
  void append(LoggingEvent event) {

    // Reminder: the nesting of calls is:
    //
    //    doAppend()
    //      - check threshold
    //      - filter
    //      - append();
    //        - checkEntryConditions();
    //        - subAppend();

    if(!checkEntryConditions()) {
      return;
    }
    subAppend(event);
   }

  /**
     This method determines if there is a sense in attempting to append.

     <p>It checks whether there is a set output target and also if
     there is a set layout. If these checks fail, then the boolean
     value <code>false</code> is returned. */
  protected
  boolean checkEntryConditions() {
    if(this.closed) {
      LogLog.warn("Not allowed to write to a closed appender.");
      return false;
    }

    if(this.qw == null) {
      errorHandler.error("No output stream or file set for the appender named ["+
			name+"].");
      return false;
    }

    if(this.layout == null) {
      errorHandler.error("No layout set for the appender named ["+ name+"].");
      return false;
    }
    return true;
  }


  /**
     Close this appender instance. The underlying stream or writer is
     also closed.

     <p>Closed appenders cannot be reused.

     @see #setWriter
     @since 0.8.4 */
  public
  synchronized
  void close() {
    if(this.closed)
      return;
    this.closed = true;
    writeFooter();
    reset();
  }

  /**
   * Close the underlying {@link java.io.Writer}.
   * */
  protected void closeWriter() {
    if(qw != null) {
      try {
	qw.close();
      } catch(IOException e) {
	// There is do need to invoke an error handler at this late
	// stage.
	LogLog.error("Could not close " + qw, e);
      }
    }
  }

  /**
     Returns an OutputStreamWriter when passed an OutputStream.  The
     encoding used will depend on the value of the
     <code>encoding</code> property.  If the encoding value is
     specified incorrectly the writer will be opened using the default
     system encoding (an error message will be printed to the loglog.  */
  protected
  OutputStreamWriter createWriter(OutputStream os) {
    OutputStreamWriter retval = null;

    String enc = getEncoding();
    if(enc != null) {
      try {
	retval = new OutputStreamWriter(os, enc);
      } catch(IOException e) {
	LogLog.warn("Error initializing output writer.");
	LogLog.warn("Unsupported encoding?");
      }
    }
    if(retval == null) {
      retval = new OutputStreamWriter(os);
    }
    return retval;
  }

  public String getEncoding() {
    return encoding;
  }

  public void setEncoding(String value) {
    encoding = value;
  }




  /**
     Set the {@link ErrorHandler} for this WriterAppender and also the
     underlying {@link QuietWriter} if any. */
  public synchronized void setErrorHandler(ErrorHandler eh) {
    if(eh == null) {
      LogLog.warn("You have tried to set a null error-handler.");
    } else {
      this.errorHandler = eh;
      if(this.qw != null) {
	this.qw.setErrorHandler(eh);
      }
    }
  }

  /**
    <p>Sets the Writer where the log output will go. The
    specified Writer must be opened by the user and be
    writable.

    <p>The <code>java.io.Writer</code> will be closed when the
    appender instance is closed.


    <p><b>WARNING:</b> Logging to an unopened Writer will fail.
    <p>
    @param writer An already opened Writer.  */
  public synchronized void setWriter(Writer writer) {
    reset();
    this.qw = new QuietWriter(writer, errorHandler);
    //this.tp = new TracerPrintWriter(qw);
    writeHeader();
  }


  /**
     Actual writing occurs here.

     <p>Most subclasses of <code>WriterAppender</code> will need to
     override this method.

     @since 0.9.0 */
  protected
  void subAppend(LoggingEvent event) {
    this.qw.write(this.layout.format(event));

    if(layout.ignoresThrowable()) {
      String[] s = event.getThrowableStrRep();
      if (s != null) {
	int len = s.length;
	for(int i = 0; i < len; i++) {
	  this.qw.write(s[i]);
	  this.qw.write(Layout.LINE_SEP);
	}
      }
    }

    if(this.immediateFlush) {
      this.qw.flush();
    }
  }



  /**
     The WriterAppender requires a layout. Hence, this method returns
     <code>true</code>.
  */
  public
  boolean requiresLayout() {
    return true;
  }

  /**
     Clear internal references to the writer and other variables.

     Subclasses can override this method for an alternate closing
     behavior.  */
  protected
  void reset() {
    closeWriter();
    this.qw = null;
    //this.tp = null;
  }


  /**
     Write a footer as produced by the embedded layout's {@link
     Layout#getFooter} method.  */
  protected
  void writeFooter() {
    if(layout != null) {
      String f = layout.getFooter();
      if(f != null && this.qw != null) {
	this.qw.write(f);
	this.qw.flush();
      }
    }
  }

  /**
     Write a header as produced by the embedded layout's {@link
     Layout#getHeader} method.  */
  protected
  void writeHeader() {
    if(layout != null) {
      String h = layout.getHeader();
      if(h != null && this.qw != null)
	this.qw.write(h);
    }
  }
}