/*
 * Copyright 2015 Netflix, Inc.
 *
 * 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.netflix.discovery.util;

import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.util.Enumeration;

/**
 * @author Tomasz Bak
 */
public final class SystemUtil {

    private SystemUtil() {
    }

    /**
     * Returns server IP address (v4 or v6) bound to local NIC. If multiple NICs are present, choose 'eth0' or 'en0' or
     * any one with name ending with 0. If non found, take first on the list that is not localhost. If no NIC
     * present (relevant only for desktop deployments), return loopback address.
     */
    public static String getServerIPv4() {
        String candidateAddress = null;
        try {
            Enumeration<NetworkInterface> nics = NetworkInterface.getNetworkInterfaces();
            while (nics.hasMoreElements()) {
                NetworkInterface nic = nics.nextElement();
                Enumeration<InetAddress> inetAddresses = nic.getInetAddresses();
                while (inetAddresses.hasMoreElements()) {
                    String address = inetAddresses.nextElement().getHostAddress();
                    String nicName = nic.getName();
                    if (nicName.startsWith("eth0") || nicName.startsWith("en0")) {
                        return address;
                    }
                    if (nicName.endsWith("0") || candidateAddress == null) {
                        candidateAddress = address;
                    }
                }
            }
        } catch (SocketException e) {
            throw new RuntimeException("Cannot resolve local network address", e);
        }
        return candidateAddress == null ? "127.0.0.1" : candidateAddress;
    }

    public static void main(String[] args) {
        System.out.println("Found IP=" + getServerIPv4());
    }
}