/*
 * 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.nio.charset.StandardCharsets;

/**
 * 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");
        _lineSeparatorBytes = _lineSeparator.getBytes(StandardCharsets.US_ASCII);
    }

    /**
     * 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 boolean isConversionRequired()
    {
        return !_noConversionRequired;
    }

    private int length;

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


    // 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.
     */
    @Override
    public int available() throws IOException
    {
        if (in == null) {
            throw new IOException("Stream closed");
        }
        return buf.length - pos + in.available();
    }


    /**
     * 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 readInt();
    }


    /**
     * 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(final 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.
     *
     * @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(final byte buffer[], int offset, final int length) throws IOException
    {
        if (_noConversionRequired) {
            return super.read(buffer, offset, length);
        }

        if (length < 1) {
            return 0;
        }

        int ch;
        final int off;

        ch = available();

        this.length = length > ch ? ch : length;

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


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

        off = offset;

        do
        {
            buffer[offset++] = (byte)ch;
        }
        while (--this.length > 0 && (ch = readInt()) != -1);


        return offset - off;
    }


    private int readInt() throws IOException
    {
        int ch;

        ch = super.read();

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

        return ch;
    }

}