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/**
 *  Copyright (c) 1997-2013, www.tinygroup.org ([email protected]).
 *
 *  Licensed under the GPL, Version 3.0 (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.gnu.org/licenses/gpl.html
 *
 *  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.tinygroup.commons.tools;

import org.tinygroup.commons.io.ByteArrayOutputStream;

import java.io.DataOutputStream;
import java.lang.reflect.Method;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.security.SecureRandom;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 生成唯一ID。
 * 
 * 唯一ID由以下元素构成：machineId-jvmId-timestamp-counter。
 * 
 * 
 * 默认情况下，UUID由数字和大写字母构成。如果在构造函数时，指定noCase=false
 * ，那么所生成的ID将包含小写字母，这样ID的长度会较短。
 * 
 *
 * @author Michael Zhou
 */
public class UUID {
    private boolean       noCase;
    private String        instanceId;
    private AtomicInteger counter;

    public UUID() {
        this(true);
    }

    public UUID(boolean noCase) {
        // 1. Machine ID - 根据IP/MAC区分
        byte[] machineId = getLocalHostAddress();

        // 2. JVM ID - 根据启动时间区分 + 随机数
        byte[] jvmId = getRandomizedTime();

        this.instanceId = StringUtil.bytesToString(machineId, noCase) + "-" + StringUtil.bytesToString(jvmId, noCase);

        // counter
        this.counter = new AtomicInteger();

        this.noCase = noCase;
    }

    /** 取得local host的地址，如果有可能，取得物理MAC地址。 */
    private static byte[] getLocalHostAddress() {
        Method getHardwareAddress;

        try {
            getHardwareAddress = NetworkInterface.class.getMethod("getHardwareAddress");
        } catch (Exception e) {
            getHardwareAddress = null;
        }

        byte[] addr;

        try {
            InetAddress localHost = InetAddress.getLocalHost();

            if (getHardwareAddress != null) {
                addr = (byte[]) getHardwareAddress.invoke(NetworkInterface.getByInetAddress(localHost)); // maybe null
            } else {
                addr = localHost.getAddress();
            }
        } catch (Exception e) {
            addr = null;
        }

        if (addr == null) {
            addr = new byte[] { 127, 0, 0, 1 };
        }

        return addr;
    }

    /** 取得当前时间，加上随机数。 */
    private byte[] getRandomizedTime() {
        long jvmId = System.currentTimeMillis();
        long random = new SecureRandom().nextLong();

        // 取得上述ID的bytes，并转化成字符串
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        DataOutputStream dos = new DataOutputStream(baos);

        try {
            dos.writeLong(jvmId);
            dos.writeLong(random);
        } catch (Exception e) {
        }

        return baos.toByteArray().toByteArray();
    }

    public String nextID() {
        // MACHINE_ID + JVM_ID + 当前时间 + counter
        return instanceId + "-" + StringUtil.longToString(System.currentTimeMillis(), noCase) + "-"
               + StringUtil.longToString(counter.getAndIncrement(), noCase);
    }
}