/*
 * 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.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.commons.net.util.NetConstants;

/**
 * This class wraps an input stream, replacing all singly occurring &lt;LF&gt; (linefeed) characters with &lt;CR&gt;&lt;LF&gt; (carriage return followed by
 * linefeed), which is the NETASCII standard for representing a newline. You would use this class to implement ASCII file transfers requiring conversion to
 * NETASCII.
 *
 *
 */

public final class ToNetASCIIInputStream extends FilterInputStream {
    private static final int NOTHING_SPECIAL = 0;
    private static final int LAST_WAS_CR = 1;
    private static final int LAST_WAS_NL = 2;
    private int status;

    /**
     * Creates a ToNetASCIIInputStream instance that wraps an existing InputStream.
     *
     * @param input The InputStream to wrap.
     */
    public ToNetASCIIInputStream(final InputStream input) {
        super(input);
        status = NOTHING_SPECIAL;
    }

    @Override
    public int available() throws IOException {
        final int result;

        result = in.available();

        if (status == LAST_WAS_NL) {
            return result + 1;
        }

        return result;
    }

    /** Returns false. Mark is not supported. */
    @Override
    public boolean markSupported() {
        return false;
    }

    /**
     * Reads and returns the next byte in the stream. If the end of the message has been reached, returns -1.
     *
     * @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 {
        final int ch;

        if (status == LAST_WAS_NL) {
            status = NOTHING_SPECIAL;
            return '\n';
        }

        ch = in.read();

        switch (ch) {
        case '\r':
            status = LAST_WAS_CR;
            return '\r';
        case '\n':
            if (status != LAST_WAS_CR) {
                status = LAST_WAS_NL;
                return '\r';
            }
            //$FALL-THROUGH$
        default:
            status = NOTHING_SPECIAL;
            return ch;
        }
        // statement not reached
        // return ch;
    }

    /**
     * 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, int length) throws IOException {
        int ch;
        final int off;

        if (length < 1) {
            return 0;
        }

        ch = available();

        if (length > ch) {
            length = ch;
        }

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

        if ((ch = read()) == NetConstants.EOS) {
            return NetConstants.EOS;
        }

        off = offset;

        do {
            buffer[offset++] = (byte) ch;
        } while (--length > 0 && (ch = read()) != NetConstants.EOS);

        return offset - off;
    }
}
