/*
 * Copyright 2017 Hippo Seven
 *
 * 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 com.hippo.util;
/*
 * Created by Hippo on 2017/9/4.
 */

public class HashCodeUtils {

    private static final int X = 31;

    /**
     * <pre>{@code
     * args[0].hashCode()*31^(n-1) + args[1].hashCode()*31^(n-2) + ... + args[n-1].hashCode()
     * }</pre>
     * Returns 0 if {@code args == null}.
     */
    public static int hashCode(Object... args) {
        if (args == null) {
            return 0;
        }
        int hash = 0;
        for (Object o : args) {
            hash = X * hash + (o != null ? o.hashCode() : 0);
        }
        return hash;
    }

    /**
     * http://stackoverflow.com/questions/332079
     *
     * @param bytes The bytes to convert.
     * @return A {@link String} converted from the bytes of a hashable key used
     * to store a filename on the disk, to hex digits.
     */
    public static String bytesToHexString(final byte[] bytes) {
        final StringBuilder builder = new StringBuilder();
        for (final byte b : bytes) {
            final String hex = Integer.toHexString(0xFF & b);
            if (hex.length() == 1) {
                builder.append('0');
            }
            builder.append(hex);
        }
        return builder.toString();
    }
}