/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed 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 io.airlift.slice;

import javax.annotation.Nullable;

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

/**
 * An {@link java.io.InputStream} that counts the number of bytes read.
 *
 * @author Chris Nokleberg
 */
final class CountingInputStream
        extends FilterInputStream
{
    private long count;
    private long mark = -1;

    /**
     * Wraps another input stream, counting the number of bytes read.
     *
     * @param in the input stream to be wrapped
     */
    public CountingInputStream(@Nullable InputStream in)
    {
        super(in);
    }

    /**
     * Returns the number of bytes read.
     */
    public long getCount()
    {
        return count;
    }

    @Override
    public int read()
            throws IOException
    {
        int result = in.read();
        if (result != -1) {
            count++;
        }
        return result;
    }

    @Override
    public int read(byte[] b, int off, int len)
            throws IOException
    {
        int result = in.read(b, off, len);
        if (result != -1) {
            count += result;
        }
        return result;
    }

    @Override
    public long skip(long n)
            throws IOException
    {
        long result = in.skip(n);
        count += result;
        return result;
    }

    @Override
    public synchronized void mark(int readlimit)
    {
        in.mark(readlimit);
        mark = count;
        // it's okay to mark even if mark isn't supported, as reset won't work
    }

    @Override
    public synchronized void reset()
            throws IOException
    {
        if (!in.markSupported()) {
            throw new IOException("Mark not supported");
        }
        if (mark == -1) {
            throw new IOException("Mark not set");
        }

        in.reset();
        count = mark;
    }
}
