/*
    * ====================================================================
    * 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.hc.core5.http.impl.io;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.nio.ByteBuffer;
  import java.nio.CharBuffer;
  import java.nio.charset.CharsetDecoder;
  import java.nio.charset.CoderResult;
  
  import org.apache.hc.core5.http.Chars;
  import org.apache.hc.core5.http.MessageConstraintException;
  import org.apache.hc.core5.http.impl.BasicHttpTransportMetrics;
  import org.apache.hc.core5.http.io.HttpTransportMetrics;
  import org.apache.hc.core5.http.io.SessionInputBuffer;
  import org.apache.hc.core5.util.Args;
  import org.apache.hc.core5.util.ByteArrayBuffer;
  import org.apache.hc.core5.util.CharArrayBuffer;
  
  /**
   * Abstract base class for session input buffers that stream data from
   * an arbitrary {@link InputStream}. This class buffers input data in
   * an internal byte array for optimal input performance.
   * <p>
   * {@link #readLine(CharArrayBuffer, InputStream)} method of this class treat a lone
   * LF as valid line delimiters in addition to CR-LF required
   * by the HTTP specification.
   *
   * @since 4.3
   */
  public class SessionInputBufferImpl implements SessionInputBuffer {
  
      private final BasicHttpTransportMetrics metrics;
      private final byte[] buffer;
      private final ByteArrayBuffer lineBuffer;
      private final int minChunkLimit;
      private final int maxLineLen;
      private final CharsetDecoder decoder;
  
      private int bufferPos;
      private int bufferLen;
      private CharBuffer cbuf;
  
      /**
       * Creates new instance of SessionInputBufferImpl.
       *
       * @param metrics HTTP transport metrics.
       * @param bufferSize buffer size. Must be a positive number.
       * @param minChunkLimit size limit below which data chunks should be buffered in memory
       *   in order to minimize native method invocations on the underlying network socket.
       *   The optimal value of this parameter can be platform specific and defines a trade-off
       *   between performance of memory copy operations and that of native method invocation.
       *   If negative default chunk limited will be used.
       * @param maxLineLen maximum line length.
       * @param charDecoder charDecoder to be used for decoding HTTP protocol elements.
       *   If {@code null} simple type cast will be used for byte to char conversion.
       */
      public SessionInputBufferImpl(
              final BasicHttpTransportMetrics metrics,
              final int bufferSize,
              final int minChunkLimit,
              final int maxLineLen,
              final CharsetDecoder charDecoder) {
          Args.notNull(metrics, "HTTP transport metrics");
          Args.positive(bufferSize, "Buffer size");
          this.metrics = metrics;
          this.buffer = new byte[bufferSize];
          this.bufferPos = 0;
          this.bufferLen = 0;
          this.minChunkLimit = minChunkLimit >= 0 ? minChunkLimit : 512;
          this.maxLineLen = maxLineLen > 0 ? maxLineLen : 0;
          this.lineBuffer = new ByteArrayBuffer(bufferSize);
          this.decoder = charDecoder;
     }
 
     public SessionInputBufferImpl(
             final BasicHttpTransportMetrics metrics,
             final int bufferSize) {
         this(metrics, bufferSize, bufferSize, 0, null);
     }
 
     public SessionInputBufferImpl(final int bufferSize, final int maxLineLen) {
         this(new BasicHttpTransportMetrics(), bufferSize, bufferSize, maxLineLen, null);
     }
 
     public SessionInputBufferImpl(final int bufferSize, final CharsetDecoder decoder) {
         this(new BasicHttpTransportMetrics(), bufferSize, bufferSize, 0, decoder);
     }
 
     public SessionInputBufferImpl(final int bufferSize) {
         this(new BasicHttpTransportMetrics(), bufferSize, bufferSize, 0, null);
     }
 
     @Override
     public int capacity() {
         return this.buffer.length;
     }
 
     @Override
     public int length() {
         return this.bufferLen - this.bufferPos;
     }
 
     @Override
     public int available() {
         return capacity() - length();
     }
 
     public int fillBuffer(final InputStream inputStream) throws IOException {
         Args.notNull(inputStream, "Input stream");
         // compact the buffer if necessary
         if (this.bufferPos > 0) {
             final int len = this.bufferLen - this.bufferPos;
             if (len > 0) {
                 System.arraycopy(this.buffer, this.bufferPos, this.buffer, 0, len);
             }
             this.bufferPos = 0;
             this.bufferLen = len;
         }
         final int readLen;
         final int off = this.bufferLen;
         final int len = this.buffer.length - off;
         readLen = inputStream.read(this.buffer, off, len);
         if (readLen == -1) {
             return -1;
         }
         this.bufferLen = off + readLen;
         this.metrics.incrementBytesTransferred(readLen);
         return readLen;
     }
 
     public boolean hasBufferedData() {
         return this.bufferPos < this.bufferLen;
     }
 
     public void clear() {
         this.bufferPos = 0;
         this.bufferLen = 0;
     }
 
     @Override
     public int read(final InputStream inputStream) throws IOException {
         Args.notNull(inputStream, "Input stream");
         int readLen;
         while (!hasBufferedData()) {
             readLen = fillBuffer(inputStream);
             if (readLen == -1) {
                 return -1;
             }
         }
         return this.buffer[this.bufferPos++] & 0xff;
     }
 
     @Override
     public int read(final byte[] b, final int off, final int len, final InputStream inputStream) throws IOException {
         Args.notNull(inputStream, "Input stream");
         if (b == null) {
             return 0;
         }
         if (hasBufferedData()) {
             final int chunk = Math.min(len, this.bufferLen - this.bufferPos);
             System.arraycopy(this.buffer, this.bufferPos, b, off, chunk);
             this.bufferPos += chunk;
             return chunk;
         }
         // If the remaining capacity is big enough, read directly from the
         // underlying input stream bypassing the buffer.
         if (len > this.minChunkLimit) {
             final int read = inputStream.read(b, off, len);
             if (read > 0) {
                 this.metrics.incrementBytesTransferred(read);
             }
             return read;
         }
         // otherwise read to the buffer first
         while (!hasBufferedData()) {
             final int readLen = fillBuffer(inputStream);
             if (readLen == -1) {
                 return -1;
             }
         }
         final int chunk = Math.min(len, this.bufferLen - this.bufferPos);
         System.arraycopy(this.buffer, this.bufferPos, b, off, chunk);
         this.bufferPos += chunk;
         return chunk;
     }
 
     @Override
     public int read(final byte[] b, final InputStream inputStream) throws IOException {
         if (b == null) {
             return 0;
         }
         return read(b, 0, b.length, inputStream);
     }
 
     /**
      * Reads a complete line of characters up to a line delimiter from this
      * session buffer into the given line buffer. The number of chars actually
      * read is returned as an integer. The line delimiter itself is discarded.
      * If no char is available because the end of the stream has been reached,
      * the value {@code -1} is returned. This method blocks until input
      * data is available, end of file is detected, or an exception is thrown.
      * <p>
      * This method treats a lone LF as a valid line delimiters in addition
      * to CR-LF required by the HTTP specification.
      *
      * @param     charBuffer   the line buffer, one line of characters upon return
      * @return     the total number of bytes read into the buffer, or
      *             {@code -1} is there is no more data because the end of
      *             the stream has been reached.
      * @throws  IOException  if an I/O error occurs.
      */
     @Override
     public int readLine(final CharArrayBuffer charBuffer, final InputStream inputStream) throws IOException {
         Args.notNull(charBuffer, "Char array buffer");
         Args.notNull(inputStream, "Input stream");
         int readLen = 0;
         boolean retry = true;
         while (retry) {
             // attempt to find end of line (LF)
             int pos = -1;
             for (int i = this.bufferPos; i < this.bufferLen; i++) {
                 if (this.buffer[i] == Chars.LF) {
                     pos = i;
                     break;
                 }
             }
 
             if (this.maxLineLen > 0) {
                 final int currentLen = this.lineBuffer.length()
                         + (pos >= 0 ? pos : this.bufferLen) - this.bufferPos;
                 if (currentLen >= this.maxLineLen) {
                     throw new MessageConstraintException("Maximum line length limit exceeded");
                 }
             }
 
             if (pos != -1) {
                 // end of line found.
                 if (this.lineBuffer.isEmpty()) {
                     // the entire line is preset in the read buffer
                     return lineFromReadBuffer(charBuffer, pos);
                 }
                 retry = false;
                 final int len = pos + 1 - this.bufferPos;
                 this.lineBuffer.append(this.buffer, this.bufferPos, len);
                 this.bufferPos = pos + 1;
             } else {
                 // end of line not found
                 if (hasBufferedData()) {
                     final int len = this.bufferLen - this.bufferPos;
                     this.lineBuffer.append(this.buffer, this.bufferPos, len);
                     this.bufferPos = this.bufferLen;
                 }
                 readLen = fillBuffer(inputStream);
                 if (readLen == -1) {
                     retry = false;
                 }
             }
         }
         if (readLen == -1 && this.lineBuffer.isEmpty()) {
             // indicate the end of stream
             return -1;
         }
         return lineFromLineBuffer(charBuffer);
     }
 
     /**
      * Reads a complete line of characters up to a line delimiter from this
      * session buffer. The line delimiter itself is discarded. If no char is
      * available because the end of the stream has been reached,
      * {@code null} is returned. This method blocks until input data is
      * available, end of file is detected, or an exception is thrown.
      * <p>
      * This method treats a lone LF as a valid line delimiters in addition
      * to CR-LF required by the HTTP specification.
      *
      * @return HTTP line as a string
      * @throws  IOException  if an I/O error occurs.
      */
     private int lineFromLineBuffer(final CharArrayBuffer charBuffer)
             throws IOException {
         // discard LF if found
         int len = this.lineBuffer.length();
         if (len > 0) {
             if (this.lineBuffer.byteAt(len - 1) == Chars.LF) {
                 len--;
             }
             // discard CR if found
             if (len > 0 && this.lineBuffer.byteAt(len - 1) == Chars.CR) {
                 len--;
             }
         }
         if (this.decoder == null) {
             charBuffer.append(this.lineBuffer, 0, len);
         } else {
             final ByteBuffer bbuf =  ByteBuffer.wrap(this.lineBuffer.array(), 0, len);
             len = appendDecoded(charBuffer, bbuf);
         }
         this.lineBuffer.clear();
         return len;
     }
 
     private int lineFromReadBuffer(final CharArrayBuffer charbuffer, final int position)
             throws IOException {
         int pos = position;
         final int off = this.bufferPos;
         int len;
         this.bufferPos = pos + 1;
         if (pos > off && this.buffer[pos - 1] == Chars.CR) {
             // skip CR if found
             pos--;
         }
         len = pos - off;
         if (this.decoder == null) {
             charbuffer.append(this.buffer, off, len);
         } else {
             final ByteBuffer bbuf =  ByteBuffer.wrap(this.buffer, off, len);
             len = appendDecoded(charbuffer, bbuf);
         }
         return len;
     }
 
     private int appendDecoded(
             final CharArrayBuffer charbuffer, final ByteBuffer bbuf) throws IOException {
         if (!bbuf.hasRemaining()) {
             return 0;
         }
         if (this.cbuf == null) {
             this.cbuf = CharBuffer.allocate(1024);
         }
         this.decoder.reset();
         int len = 0;
         while (bbuf.hasRemaining()) {
             final CoderResult result = this.decoder.decode(bbuf, this.cbuf, true);
             len += handleDecodingResult(result, charbuffer);
         }
         final CoderResult result = this.decoder.flush(this.cbuf);
         len += handleDecodingResult(result, charbuffer);
         this.cbuf.clear();
         return len;
     }
 
     private int handleDecodingResult(
             final CoderResult result,
             final CharArrayBuffer charBuffer) throws IOException {
         if (result.isError()) {
             result.throwException();
         }
         this.cbuf.flip();
         final int len = this.cbuf.remaining();
         while (this.cbuf.hasRemaining()) {
             charBuffer.append(this.cbuf.get());
         }
         this.cbuf.compact();
         return len;
     }
 
     @Override
     public HttpTransportMetrics getMetrics() {
         return this.metrics;
     }
 
 }