// Copyright 2017 JanusGraph 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 org.janusgraph.diskstorage.util;

import java.nio.ByteBuffer;

/**
 * Utility methods for dealing with ByteBuffers in concurrent access
 * environments, i.e. these methods only use static access to the buffer.
 *
 *
 * @author Matthias Broecheler (me@matthiasb.com)
 */
public class ByteBufferUtil {

    /* ################
     * ByteBuffer Creation Helpers
     * ################
     */

    public static final ByteBuffer zeroByteBuffer(int len) {
        ByteBuffer res = ByteBuffer.allocate(len);
        for (int i = 0; i < len; i++) res.put((byte) 0);
        res.flip();
        return res;
    }

    public static final ByteBuffer oneByteBuffer(int len) {
        ByteBuffer res = ByteBuffer.allocate(len);
        for (int i = 0; i < len; i++) res.put((byte) -1);
        res.flip();
        return res;
    }

    /* ################
     * ByteBuffer Comparison, HashCode and toString
     * ################
     */

    /**
     * Compares two {@link java.nio.ByteBuffer}s and checks whether the first ByteBuffer is smaller than the second.
     *
     * @param a First ByteBuffer
     * @param b Second ByteBuffer
     * @return true if the first ByteBuffer is smaller than the second
     */
    public static final boolean isSmallerThan(ByteBuffer a, ByteBuffer b) {
        return compare(a, b)<0;
    }

    /**
     * Compares two {@link java.nio.ByteBuffer}s and checks whether the first ByteBuffer is smaller than or equal to the second.
     *
     * @param a First ByteBuffer
     * @param b Second ByteBuffer
     * @return true if the first ByteBuffer is smaller than or equal to the second
     */
    public static boolean isSmallerOrEqualThan(ByteBuffer a, ByteBuffer b) {
        return compare(a, b)<=0;
    }

    /**
     * Compares two {@link java.nio.ByteBuffer}s according to their byte order (and not the byte value).
     * <p/>
     *
     * @param b1             First ByteBuffer
     * @param b2             Second ByteBuffer
     * @return a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.
     */
    public static final int compare(ByteBuffer b1, ByteBuffer b2) {
        if (b1 == b2) {
            return 0;
        }
        int p1=b1.position(), p2 = b2.position();
        while (p1<b1.limit() || p2<b2.limit()) {
            if (p1>=b1.limit()) return -1;
            else if (p2>=b2.limit()) return 1;
            else {
                int cmp = compare(b1.get(p1), b2.get(p2));
                if (cmp!=0) return cmp;
            }
            p1++; p2++;
        }
        return 0; //Must be equal
    }

    private static int compare(byte c1, byte c2) {
        int a = c1 & 0xff;
        int b = c2 & 0xff;

        return a - b;
    }

    public static String bytesToHex(ByteBuffer bytes) {
        final int offset = bytes.position();
        final int size = bytes.remaining();
        final char[] c = new char[size * 2];
        for (int i = 0; i < size; i++) {
            final int bint = bytes.get(i + offset);
            c[i * 2] = Hex.byteToChar[(bint & 0xf0) >> 4];
            c[1 + i * 2] = Hex.byteToChar[bint & 0x0f];
        }
        return Hex.wrapCharArray(c);
    }


    public static final String toString(ByteBuffer b, String separator) {
        StringBuilder s = new StringBuilder();
        for (int i=b.position();i<b.limit();i++) {
            if (i>b.position()) s.append(separator);
            byte c = b.get(i);
            if (c>=0) s.append(c);
            else s.append(256+c);
        }
        return s.toString();
    }
}