/*
    * 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.logging.log4j.core.layout;
  
  import java.nio.ByteBuffer;
  import java.nio.CharBuffer;
  import java.nio.charset.Charset;
  import java.nio.charset.CharsetEncoder;
  import java.nio.charset.CodingErrorAction;
  import java.util.Objects;
  
  import org.apache.logging.log4j.core.util.Constants;
  import org.apache.logging.log4j.status.StatusLogger;
  
  /**
   * Encoder for StringBuilders that uses ThreadLocals to avoid locking as much as possible.
   */
  public class StringBuilderEncoder implements Encoder<StringBuilder> {
  
      private static final int DEFAULT_BYTE_BUFFER_SIZE = 8 * 1024;
      /**
       * This ThreadLocal uses raw and inconvenient Object[] to store three heterogeneous objects (CharEncoder, CharBuffer
       * and ByteBuffer) instead of a custom class, because it needs to contain JDK classes, no custom (Log4j) classes.
       * Where possible putting only JDK classes in ThreadLocals is preferable to avoid memory leaks in web containers:
       * the Log4j classes may be loaded by a separate class loader which cannot be garbage collected if a thread pool
       * threadlocal still has a reference to it.
       *
       * Using just one ThreadLocal instead of three separate ones is an optimization: {@link ThreadLocal.ThreadLocalMap}
       * is polluted less, {@link ThreadLocal.ThreadLocalMap#get()} is called only once on each call to {@link #encode}
       * instead of three times.
       */
      private final ThreadLocal<Object[]> threadLocal = new ThreadLocal<>();
      private final Charset charset;
      private final int charBufferSize;
      private final int byteBufferSize;
  
      public StringBuilderEncoder(final Charset charset) {
          this(charset, Constants.ENCODER_CHAR_BUFFER_SIZE, DEFAULT_BYTE_BUFFER_SIZE);
      }
  
      public StringBuilderEncoder(final Charset charset, final int charBufferSize, final int byteBufferSize) {
          this.charBufferSize = charBufferSize;
          this.byteBufferSize = byteBufferSize;
          this.charset = Objects.requireNonNull(charset, "charset");
      }
  
      @Override
      public void encode(final StringBuilder source, final ByteBufferDestination destination) {
          try {
              final Object[] threadLocalState = getThreadLocalState();
              final CharsetEncoder charsetEncoder = (CharsetEncoder) threadLocalState[0];
              final CharBuffer charBuffer = (CharBuffer) threadLocalState[1];
              final ByteBuffer byteBuffer = (ByteBuffer) threadLocalState[2];
              TextEncoderHelper.encodeText(charsetEncoder, charBuffer, byteBuffer, source, destination);
          } catch (final Exception ex) {
              logEncodeTextException(ex, source, destination);
              TextEncoderHelper.encodeTextFallBack(charset, source, destination);
          }
      }
  
      private Object[] getThreadLocalState() {
          Object[] threadLocalState = threadLocal.get();
          if (threadLocalState == null) {
              threadLocalState = new Object[] {
                      charset.newEncoder().onMalformedInput(CodingErrorAction.REPLACE)
                              .onUnmappableCharacter(CodingErrorAction.REPLACE),
                      CharBuffer.allocate(charBufferSize),
                      ByteBuffer.allocate(byteBufferSize)
              };
              threadLocal.set(threadLocalState);
          } else {
              ((CharsetEncoder) threadLocalState[0]).reset();
              ((CharBuffer) threadLocalState[1]).clear();
              ((ByteBuffer) threadLocalState[2]).clear();
          }
          return threadLocalState;
      }
  
      private void logEncodeTextException(final Exception ex, final StringBuilder text,
              final ByteBufferDestination destination) {
          StatusLogger.getLogger().error("Recovering from StringBuilderEncoder.encode('{}') error: {}", text, ex, ex);
      }
  }