/*
    * ====================================================================
    * 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  
  package org.apache.http.impl.io;
  
  import java.io.IOException;
  import java.io.OutputStream;
  import java.nio.ByteBuffer;
  import java.nio.CharBuffer;
  import java.nio.charset.CharsetEncoder;
  import java.nio.charset.CoderResult;
  
  import org.apache.http.io.BufferInfo;
  import org.apache.http.io.HttpTransportMetrics;
  import org.apache.http.io.SessionOutputBuffer;
  import org.apache.http.protocol.HTTP;
  import org.apache.http.util.Args;
  import org.apache.http.util.Asserts;
  import org.apache.http.util.ByteArrayBuffer;
  import org.apache.http.util.CharArrayBuffer;
  
  /**
   * Abstract base class for session output buffers that stream data to
   * an arbitrary {@link OutputStream}. This class buffers small chunks of
   * output data in an internal byte array for optimal output performance.
   * <p>
   * {@link #writeLine(CharArrayBuffer)} and {@link #writeLine(String)} methods
   * of this class use CR-LF as a line delimiter.
   *
   * @since 4.3
   */
  public class SessionOutputBufferImpl implements SessionOutputBuffer, BufferInfo {
  
      private static final byte[] CRLF = new byte[] {HTTP.CR, HTTP.LF};
  
      private final HttpTransportMetricsImpl metrics;
      private final ByteArrayBuffer buffer;
      private final int fragementSizeHint;
      private final CharsetEncoder encoder;
  
      private OutputStream outStream;
      private ByteBuffer bbuf;
  
      /**
       * Creates new instance of SessionOutputBufferImpl.
       *
       * @param metrics HTTP transport metrics.
       * @param bufferSize buffer size. Must be a positive number.
       * @param fragementSizeHint fragment size hint defining a minimal size of a fragment
       *   that should be written out directly to the socket bypassing the session buffer.
       *   Value {@code 0} disables fragment buffering.
       * @param charEncoder charEncoder to be used for encoding HTTP protocol elements.
       *   If {@code null} simple type cast will be used for char to byte conversion.
       */
      public SessionOutputBufferImpl(
              final HttpTransportMetricsImpl metrics,
              final int bufferSize,
              final int fragementSizeHint,
              final CharsetEncoder charEncoder) {
          super();
          Args.positive(bufferSize, "Buffer size");
          Args.notNull(metrics, "HTTP transport metrcis");
          this.metrics = metrics;
          this.buffer = new ByteArrayBuffer(bufferSize);
          this.fragementSizeHint = fragementSizeHint >= 0 ? fragementSizeHint : 0;
          this.encoder = charEncoder;
      }
  
      public SessionOutputBufferImpl(
              final HttpTransportMetricsImpl metrics,
              final int bufferSize) {
          this(metrics, bufferSize, bufferSize, null);
      }
  
      public void bind(final OutputStream outStream) {
         this.outStream = outStream;
     }
 
     public boolean isBound() {
         return this.outStream != null;
     }
 
     @Override
     public int capacity() {
         return this.buffer.capacity();
     }
 
     @Override
     public int length() {
         return this.buffer.length();
     }
 
     @Override
     public int available() {
         return capacity() - length();
     }
 
     private void streamWrite(final byte[] b, final int off, final int len) throws IOException {
         Asserts.notNull(outStream, "Output stream");
         this.outStream.write(b, off, len);
     }
 
     private void flushStream() throws IOException {
         if (this.outStream != null) {
             this.outStream.flush();
         }
     }
 
     private void flushBuffer() throws IOException {
         final int len = this.buffer.length();
         if (len > 0) {
             streamWrite(this.buffer.buffer(), 0, len);
             this.buffer.clear();
             this.metrics.incrementBytesTransferred(len);
         }
     }
 
     @Override
     public void flush() throws IOException {
         flushBuffer();
         flushStream();
     }
 
     @Override
     public void write(final byte[] b, final int off, final int len) throws IOException {
         if (b == null) {
             return;
         }
         // Do not want to buffer large-ish chunks
         // if the byte array is larger then MIN_CHUNK_LIMIT
         // write it directly to the output stream
         if (len > this.fragementSizeHint || len > this.buffer.capacity()) {
             // flush the buffer
             flushBuffer();
             // write directly to the out stream
             streamWrite(b, off, len);
             this.metrics.incrementBytesTransferred(len);
         } else {
             // Do not let the buffer grow unnecessarily
             final int freecapacity = this.buffer.capacity() - this.buffer.length();
             if (len > freecapacity) {
                 // flush the buffer
                 flushBuffer();
             }
             // buffer
             this.buffer.append(b, off, len);
         }
     }
 
     @Override
     public void write(final byte[] b) throws IOException {
         if (b == null) {
             return;
         }
         write(b, 0, b.length);
     }
 
     @Override
     public void write(final int b) throws IOException {
         if (this.fragementSizeHint > 0) {
             if (this.buffer.isFull()) {
                 flushBuffer();
             }
             this.buffer.append(b);
         } else {
             flushBuffer();
             this.outStream.write(b);
         }
     }
 
     /**
      * Writes characters from the specified string followed by a line delimiter
      * to this session buffer.
      * <p>
      * This method uses CR-LF as a line delimiter.
      *
      * @param      s   the line.
      * @throws  IOException  if an I/O error occurs.
      */
     @Override
     public void writeLine(final String s) throws IOException {
         if (s == null) {
             return;
         }
         if (s.length() > 0) {
             if (this.encoder == null) {
                 for (int i = 0; i < s.length(); i++) {
                     write(s.charAt(i));
                 }
             } else {
                 final CharBuffer cbuf = CharBuffer.wrap(s);
                 writeEncoded(cbuf);
             }
         }
         write(CRLF);
     }
 
     /**
      * Writes characters from the specified char array followed by a line
      * delimiter to this session buffer.
      * <p>
      * This method uses CR-LF as a line delimiter.
      *
      * @param      charbuffer the buffer containing chars of the line.
      * @throws  IOException  if an I/O error occurs.
      */
     @Override
     public void writeLine(final CharArrayBuffer charbuffer) throws IOException {
         if (charbuffer == null) {
             return;
         }
         if (this.encoder == null) {
             int off = 0;
             int remaining = charbuffer.length();
             while (remaining > 0) {
                 int chunk = this.buffer.capacity() - this.buffer.length();
                 chunk = Math.min(chunk, remaining);
                 if (chunk > 0) {
                     this.buffer.append(charbuffer, off, chunk);
                 }
                 if (this.buffer.isFull()) {
                     flushBuffer();
                 }
                 off += chunk;
                 remaining -= chunk;
             }
         } else {
             final CharBuffer cbuf = CharBuffer.wrap(charbuffer.buffer(), 0, charbuffer.length());
             writeEncoded(cbuf);
         }
         write(CRLF);
     }
 
     private void writeEncoded(final CharBuffer cbuf) throws IOException {
         if (!cbuf.hasRemaining()) {
             return;
         }
         if (this.bbuf == null) {
             this.bbuf = ByteBuffer.allocate(1024);
         }
         this.encoder.reset();
         while (cbuf.hasRemaining()) {
             final CoderResult result = this.encoder.encode(cbuf, this.bbuf, true);
             handleEncodingResult(result);
         }
         final CoderResult result = this.encoder.flush(this.bbuf);
         handleEncodingResult(result);
         this.bbuf.clear();
     }
 
     private void handleEncodingResult(final CoderResult result) throws IOException {
         if (result.isError()) {
             result.throwException();
         }
         this.bbuf.flip();
         while (this.bbuf.hasRemaining()) {
             write(this.bbuf.get());
         }
         this.bbuf.compact();
     }
 
     @Override
     public HttpTransportMetrics getMetrics() {
         return this.metrics;
     }
 
 }