/*
 * 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.commons.net.io;

import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;
import java.io.UnsupportedEncodingException;

This class wraps an input stream, replacing all occurrences
of <CR><LF> (carriage return followed by a linefeed),
which is the NETASCII standard for representing a newline, with the
local line separator representation.  You would use this class to
implement ASCII file transfers requiring conversion from NETASCII.
/***
 * This class wraps an input stream, replacing all occurrences
 * of &lt;CR&gt;&lt;LF&gt; (carriage return followed by a linefeed),
 * which is the NETASCII standard for representing a newline, with the
 * local line separator representation.  You would use this class to
 * implement ASCII file transfers requiring conversion from NETASCII.
 *
 *
 ***/

public final class FromNetASCIIInputStream extends PushbackInputStream
{
    static final boolean _noConversionRequired;
    static final String _lineSeparator;
    static final byte[] _lineSeparatorBytes;

    static {
        _lineSeparator = System.getProperty("line.separator");
        _noConversionRequired = _lineSeparator.equals("\r\n");
        try {
            _lineSeparatorBytes = _lineSeparator.getBytes("US-ASCII");
        } catch (UnsupportedEncodingException e) {
           throw new RuntimeException("Broken JVM - cannot find US-ASCII charset!",e);
        }
    }

    private int __length = 0;

    
Returns true if the NetASCII line separator differs from the system
line separator, false if they are the same.  This method is useful
to determine whether or not you need to instantiate a
FromNetASCIIInputStream object.
Returns:
True if the NETASCII line separator differs from the local
  system line separator, false if they are the same./***
     * Returns true if the NetASCII line separator differs from the system
     * line separator, false if they are the same.  This method is useful
     * to determine whether or not you need to instantiate a
     * FromNetASCIIInputStream object.
     *
     * @return True if the NETASCII line separator differs from the local
     *   system line separator, false if they are the same.
     ***/
    public static final boolean isConversionRequired()
    {
        return !_noConversionRequired;
    }

    
Creates a FromNetASCIIInputStream instance that wraps an existing
InputStream.
Params:
input – the stream to wrap/***
     * Creates a FromNetASCIIInputStream instance that wraps an existing
     * InputStream.
     * @param input the stream to wrap
     ***/
    public FromNetASCIIInputStream(InputStream input)
    {
        super(input, _lineSeparatorBytes.length + 1);
    }


    private int __read() throws IOException
    {
        int ch;

        ch = super.read();

        if (ch == '\r')
        {
            ch = super.read();
            if (ch == '\n')
            {
                unread(_lineSeparatorBytes);
                ch = super.read();
                // This is a kluge for read(byte[], ...) to read the right amount
                --__length;
            }
            else
            {
                if (ch != -1) {
                    unread(ch);
                }
                return '\r';
            }
        }

        return ch;
    }


    
Reads and returns the next byte in the stream.  If the end of the
message has been reached, returns -1.  Note that a call to this method
may result in multiple reads from the underlying input stream in order
to convert NETASCII line separators to the local line separator format.
This is transparent to the programmer and is only mentioned for
completeness.
Throws:
IOException – If an error occurs while reading the underlying
           stream.
Returns:
The next character in the stream. Returns -1 if the end of the
         stream has been reached./***
     * Reads and returns the next byte in the stream.  If the end of the
     * message has been reached, returns -1.  Note that a call to this method
     * may result in multiple reads from the underlying input stream in order
     * to convert NETASCII line separators to the local line separator format.
     * This is transparent to the programmer and is only mentioned for
     * completeness.
     *
     * @return The next character in the stream. Returns -1 if the end of the
     *          stream has been reached.
     * @throws IOException If an error occurs while reading the underlying
     *            stream.
     ***/
    @Override
    public int read() throws IOException
    {
        if (_noConversionRequired) {
            return super.read();
        }

        return __read();
    }


    
Reads the next number of bytes from the stream into an array and
returns the number of bytes read.  Returns -1 if the end of the
stream has been reached.
Params:
buffer –  The byte array in which to store the data.
Throws:
IOException – If an error occurs in reading the underlying
           stream.
Returns:
The number of bytes read. Returns -1 if the
         end of the message has been reached./***
     * Reads the next number of bytes from the stream into an array and
     * returns the number of bytes read.  Returns -1 if the end of the
     * stream has been reached.
     *
     * @param buffer  The byte array in which to store the data.
     * @return The number of bytes read. Returns -1 if the
     *          end of the message has been reached.
     * @throws IOException If an error occurs in reading the underlying
     *            stream.
     ***/
    @Override
    public int read(byte buffer[]) throws IOException
    {
        return read(buffer, 0, buffer.length);
    }


    
Reads the next number of bytes from the stream into an array and returns
the number of bytes read.  Returns -1 if the end of the
message has been reached.  The characters are stored in the array
starting from the given offset and up to the length specified.
Params:
buffer – The byte array in which to store the data.
offset –  The offset into the array at which to start storing data.
length –   The number of bytes to read.
Throws:
IOException – If an error occurs while reading the underlying
           stream.
Returns:
The number of bytes read. Returns -1 if the
         end of the stream has been reached./***
     * Reads the next number of bytes from the stream into an array and returns
     * the number of bytes read.  Returns -1 if the end of the
     * message has been reached.  The characters are stored in the array
     * starting from the given offset and up to the length specified.
     *
     * @param buffer The byte array in which to store the data.
     * @param offset  The offset into the array at which to start storing data.
     * @param length   The number of bytes to read.
     * @return The number of bytes read. Returns -1 if the
     *          end of the stream has been reached.
     * @throws IOException If an error occurs while reading the underlying
     *            stream.
     ***/
    @Override
    public int read(byte buffer[], int offset, int length) throws IOException
    {
        if (_noConversionRequired) {
            return super.read(buffer, offset, length);
        }

        if (length < 1) {
            return 0;
        }

        int ch, off;

        ch = available();

        __length = (length > ch ? ch : length);

        // If nothing is available, block to read only one character
        if (__length < 1) {
            __length = 1;
        }


        if ((ch = __read()) == -1) {
            return -1;
        }

        off = offset;

        do
        {
            buffer[offset++] = (byte)ch;
        }
        while (--__length > 0 && (ch = __read()) != -1);


        return (offset - off);
    }


    // PushbackInputStream in JDK 1.1.3 returns the wrong thing
    // TODO - can we delete this override now?
    
Returns the number of bytes that can be read without blocking EXCEPT
when newline conversions have to be made somewhere within the
available block of bytes.  In other words, you really should not
rely on the value returned by this method if you are trying to avoid
blocking.
/***
     * Returns the number of bytes that can be read without blocking EXCEPT
     * when newline conversions have to be made somewhere within the
     * available block of bytes.  In other words, you really should not
     * rely on the value returned by this method if you are trying to avoid
     * blocking.
     ***/
    @Override
    public int available() throws IOException
    {
        if (in == null) {
            throw new IOException("Stream closed");
        }
        return (buf.length - pos) + in.available();
    }

}