/*
 * 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 hivemall.utils.io;

import java.io.EOFException;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;

public final class NIOUtils {
    private static final int INT_BYTES = Integer.SIZE / 8;
    private static final int CHAR_BYTES = Character.SIZE / 8;

    private NIOUtils() {}

    public static int requiredBytes(@Nullable final String s) {
        if (s == null) {
            return INT_BYTES;
        }
        int size = s.length();
        return INT_BYTES + CHAR_BYTES * size;
    }

    public static void putString(@Nullable final String s, @Nonnull final ByteBuffer dst) {
        if (s == null) {
            dst.putInt(-1);
            return;
        }
        final char[] array = s.toCharArray();
        final int size = array.length;
        dst.putInt(size);
        for (int i = 0; i < size; i++) {
            dst.putChar(array[i]);
        }
    }

    @Nullable
    public static String getString(@Nonnull final ByteBuffer src) {
        final int size = src.getInt();
        if (size == -1) {
            return null;
        }
        final char[] array = new char[size];
        for (int i = 0; i < size; i++) {
            array[i] = src.getChar();
        }
        return new String(array);
    }

    /**
     * Read until dst buffer is filled or src channel is reached end.
     * 
     * @return The number of bytes read, 0 or more
     */
    public static int read(@Nonnull final FileChannel src, @Nonnull final ByteBuffer dst,
            @Nonnegative final long position) throws IOException {
        int count = 0;
        long offset = position;
        while (dst.remaining() > 0) {
            int n = src.read(dst, offset);
            if (n == -1) {
                break;
            }
            offset += n;
            count += n;
        }
        return count;
    }

    public static void readFully(final FileChannel src, final ByteBuffer dst, final long position)
            throws IOException {
        while (dst.remaining() > 0) {
            if (-1 == src.read(dst, position + dst.position())) {
                throw new EOFException();
            }
        }
    }

    public static int writeFully(@Nonnull final FileChannel dst, @Nonnull final ByteBuffer src,
            @Nonnegative final long position) throws IOException {
        int count = 0;
        while (src.remaining() > 0) {
            count += dst.write(src, position + src.position());
        }
        return count;
    }

    public static int writeFully(@Nonnull final FileChannel dst, @Nonnull final ByteBuffer src)
            throws IOException {
        int count = 0;
        while (src.remaining() > 0) {
            count += dst.write(src);
        }
        return count;
    }

}