package fi.iki.elonen;

/*
 * ====================================================================
 * 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/>.
 *
 */

import java.io.IOException;
import java.io.InputStream;

/**
 * Implements chunked transfer coding. The content is received in small chunks.
 * Entities transferred using this input stream can be of unlimited length.
 * After the stream is read to the end, it provides access to the trailers,
 * if any.
 * <p>
 * Note that this class NEVER closes the underlying stream, even when
 * {@link #close()} gets called. Instead, it will read until the "end" of its
 * chunking on close, which allows for the seamless execution of subsequent
 * HTTP 1.1 requests, while not requiring the client to remember to read the
 * entire contents of the response.
 *
 *
 * @since 4.0
 *
 */
public class ChunkedInputStream extends InputStream
{

	private enum State
	{
		CHUNK_LEN, CHUNK_DATA, CHUNK_CRLF, CHUNK_INVALID
	}

	private static final int BUFFER_SIZE = 2048;

	/** The session input buffer */
	private final InputStream inputStream;

	private State state;

	/** The chunk size */
	private long chunkSize;

	/** The current position within the current chunk */
	private long pos;

	/** True if we've reached the end of stream */
	private boolean eof;

	/** True if this stream is closed */
	private boolean closed;

	/**
	 * Default constructor.
	 *
	 * @param buffer Session input buffer
	 * @param inputStream Input stream
	 * @param http1Config Message http1Config. If {@code null} {@link Http1Config#DEFAULT} will be
	 *           used.
	 *
	 * @since 4.4
	 */
	public ChunkedInputStream( final InputStream inputStream )
	{
		super();
		this.inputStream = inputStream;
		this.pos = 0L;
		this.state = State.CHUNK_LEN;
	}

	@Override
	public int available() throws IOException
	{
		final int len = this.inputStream.available();
		return (int)Math.min( len, this.chunkSize - this.pos );
	}

	/**
	 * <p>
	 * Returns all the data in a chunked stream in coalesced form. A chunk
	 * is followed by a CRLF. The method returns -1 as soon as a chunksize of 0
	 * is detected.
	 * </p>
	 *
	 * <p>
	 * Trailer headers are read automatically at the end of the stream and
	 * can be obtained with the getResponseFooters() method.
	 * </p>
	 *
	 * @return -1 of the end of the stream has been reached or the next data
	 *         byte
	 * @throws IOException in case of an I/O error
	 */
	@Override
	public int read() throws IOException
	{
		if ( this.closed ) {
			throw new StreamClosedException( "Already closed" );
		}
		if ( this.eof ) {
			return -1;
		}
		if ( state != State.CHUNK_DATA ) {
			nextChunk();
			if ( this.eof ) {
				return -1;
			}
		}
		final int b = inputStream.read();
		if ( b != -1 ) {
			pos++;
			if ( pos >= chunkSize ) {
				state = State.CHUNK_CRLF;
			}
			return b;
		}
		throw new MalformedChunkCodingException( "Truncated chunk (expected size: " + chunkSize + "; actual size: " + pos + ")" );
	}

	/**
	 * Read some bytes from the stream.
	 * 
	 * @param b The byte array that will hold the contents from the stream.
	 * @param off The offset into the byte array at which bytes will start to be
	 *           placed.
	 * @param len the maximum number of bytes that can be returned.
	 * @return The number of bytes returned or -1 if the end of stream has been
	 *         reached.
	 * @throws IOException in case of an I/O error
	 */
	@Override
	public int read( final byte[] b, final int off, final int len ) throws IOException
	{
		if ( closed ) {
			throw new StreamClosedException( "Already closed" );
		}

		if ( eof ) {
			return -1;
		}
		if ( state != State.CHUNK_DATA ) {
			nextChunk();
			if ( eof ) {
				return -1;
			}
		}
		int bytesRead = inputStream.read( b, off, (int)Math.min( len, chunkSize - pos ) );
		if ( bytesRead != -1 ) {
			pos += bytesRead;
			if ( pos >= chunkSize ) {
				state = State.CHUNK_CRLF;
			}
			return bytesRead;
		}
		eof = true;
		throw new MalformedChunkCodingException( "Truncated chunk (expected size: " + chunkSize + "; actual size: " + pos + ")" );
	}

	/**
	 * Read some bytes from the stream.
	 * 
	 * @param b The byte array that will hold the contents from the stream.
	 * @return The number of bytes returned or -1 if the end of stream has been
	 *         reached.
	 * @throws IOException in case of an I/O error
	 */
	@Override
	public int read( final byte[] b ) throws IOException
	{
		return read( b, 0, b.length );
	}

	/**
	 * Read the next chunk.
	 * 
	 * @throws IOException in case of an I/O error
	 */
	private void nextChunk() throws IOException
	{
		if ( state == State.CHUNK_INVALID ) {
			throw new MalformedChunkCodingException( "Corrupt data stream" );
		}
		try {
			chunkSize = getChunkSize();
			if ( chunkSize < 0L ) {
				throw new MalformedChunkCodingException( "Negative chunk size" );
			}
			state = State.CHUNK_DATA;
			pos = 0L;
			if ( chunkSize == 0L ) {
				eof = true;
				try {
					inputStream.read();
					inputStream.read();
				} catch ( IOException e ) {
					throw new MalformedChunkCodingException( "No CRLF after final zero chunk" );
				}
			}
		} catch ( final MalformedChunkCodingException ex ) {
			state = State.CHUNK_INVALID;
			throw ex;
		}
	}

	/**
	 * Expects the stream to start with a chunksize in hex with optional
	 * comments after a semicolon. The line must end with a CRLF: "a3; some
	 * comment\r\n" Positions the stream at the start of the next line.
	 */
	private long getChunkSize() throws IOException
	{
		int ch;
		int prevCh;
		boolean hadSemi;
		final State st = this.state;
		switch ( st ) {
		case CHUNK_CRLF:
			ch = inputStream.read();
			ch = ( ch << 8 ) | inputStream.read();
			if ( ch < 0 ) {
				throw new MalformedChunkCodingException(
						"CRLF expected at end of chunk" );
			}
			if ( ch != 3338 ) {
				throw new MalformedChunkCodingException(
						"Unexpected content at the end of chunk" );
			}
			state = State.CHUNK_LEN;
			//$FALL-THROUGH$
		case CHUNK_LEN:
			prevCh = -1;
			hadSemi = false;
			StringBuilder sb = new StringBuilder( 8 );
			for ( ;; ) {
				ch = inputStream.read();
				if ( ch == -1 )
					break;
				if ( prevCh == 13 && ch == 10 ) {
					break;
				}
				prevCh = ch;
				if ( ch == 13 )
					continue;
				if ( ch == ';' ) {
					hadSemi = true;
				}
				if ( hadSemi )
					continue;
				sb.append( (char)ch );
			}
			if ( prevCh != 13 || ch != 10 ) {
				throw new StreamClosedException( "Premature end of chunk coded message body" );
			}
			final String s = sb.toString();
			try {
				return Long.parseLong( s, 16 );
			} catch ( final NumberFormatException e ) {
				throw new MalformedChunkCodingException( "Invalid hex-length in chunk header: " + s );
			}
		default:
			throw new IllegalStateException( "Inconsistent codec state" );
		}
	}

	/**
	 * Reads the remainder of the chunked message, leaving the underlying
	 * stream at a position to start reading the next response without
	 * scanning. But does NOT close the underlying stream.
	 * 
	 * @throws IOException in case of an I/O error
	 */
	@Override
	public void close() throws IOException
	{
		if ( !closed ) {
			try {
				if ( !eof && state != State.CHUNK_INVALID ) {
					// Optimistically check if the content has been fully read
					// when there's no data remaining in the current chunk.
					// This is common when self-terminating content (e.g. JSON)
					// is parsed from response streams.
					if ( chunkSize == pos && chunkSize > 0 && read() == -1 ) {
						return;
					}
					// read and discard the remainder of the message
					final byte[] buff = new byte[ BUFFER_SIZE ];
					while ( read( buff ) >= 0 ) {
					}
				}
			} finally {
				eof = true;
				closed = true;
			}
		}
	}

	public static class MalformedChunkCodingException extends IOException
	{
		private static final long serialVersionUID = 7092137465179737109L;

		public MalformedChunkCodingException( String msg )
		{
			super( msg );
		}
	}

	public static class StreamClosedException extends IOException
	{
		private static final long serialVersionUID = -5871567871867283867L;

		public StreamClosedException( String msg )
		{
			super( msg );
		}
	}

}