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Topp Standard Core addressing basics of Java SE.
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/*
 * Project: Topp Standard
 * GitHub: https://github.com/sabroe/Topp-Standard
 *
 * Copyright 2024 Morten Sabroe Mortensen
 *
 * 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.yelstream.topp.standard.net;

import com.yelstream.topp.standard.util.function.ex.SupplierWithException;
import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.ToString;
import lombok.experimental.UtilityClass;

import java.io.IOException;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.List;

/**
 * Utility addressing instances of {@link Inet4Addresses}.
 * Provides standard IPv4 addresses and related utilities.
 *
 * @author Morten Sabroe Mortensen
 * @version 1.0
 * @since 2024-07-11
 */
@UtilityClass
public class Inet4Addresses {  //TO-DO: Let tests take care of this: System.setProperty("java.net.preferIPv6Addresses", "true");
    /**
     * The "unspecified" IP address.
     */
    public static final String UNSPECIFIED_ADDRESS_NAME="0.0.0.0";

    /**
     * The loopback address.
     */
    public static final String LOOPBACK_ADDRESS_NAME="127.0.0.1";

    /**
     * The localhost address name.
     */
    public static final String LOCALHOST_ADDRESS_NAME="localhost";

    /**
     * Standard addresses in the sense that they are special or often referenced.
     */
    @Getter
    @SuppressWarnings("java:S115")
    @AllArgsConstructor
    @ToString
    enum StandardAddress {
        /**
         * The loopback address.
         */
        LoopBack(Inet4Addresses::getIPv4LoopbackAddress),

        /**
         * The localhost address.
         */
        LocalHost(Inet4Addresses::getIPv4LocalHost),

        /**
         * The localhost address by name.
         */
        LocalHostByName(()->getIPv4AddressByName(LOCALHOST_ADDRESS_NAME)),

        /**
         * The loopback address by name.
         */
        LoopBackByName(()->getIPv4AddressByName(LOOPBACK_ADDRESS_NAME)),

        /**
         * The "unspecified" address by name.
         */
        Unspecified(()->getIPv4AddressByName(UNSPECIFIED_ADDRESS_NAME));

        /**
         * Address supplier.
         */
        private final SupplierWithException addressSupplier;

        /**
         * Gets the address.
         * @return Address.
         * @throws IOException Thrown in case of I/O error.
         */
        public InetAddress getAddress() throws IOException {
            return addressSupplier.get();
        }

        /**
         * Gets all enumeration values.
         * @return All enumeration values.
         */
        public static List getAll() {
            return Arrays.asList(values());
        }

        /**
         * Converts enumeration values to a list.
         * @param addresses Values.
         * @return Created list of values.
         */
        public static List toList(StandardAddress... addresses) {
            return Arrays.asList(addresses);
        }

        /**
         * Gets all address suppliers
         * @return Address suppliers.
         */
        public static List> getAllSuppliers() {
            return toSupplierList(getAll());
        }

        /**
         * Converts values to a list of suppliers of values.
         * @param addresses Values.
         * @return Address suppliers.
         */
        public static List> toSupplierList(StandardAddress... addresses) {
            return Arrays.stream(addresses).map(StandardAddress::getAddressSupplier).toList();
        }

        /**
         * Converts values to a list of suppliers of values.
         * @param addresses Values.
         * @return Address suppliers.
         */
        public static List> toSupplierList(List addresses) {
            return addresses.stream().map(StandardAddress::getAddressSupplier).toList();
        }
    }


    /**
     * Resolves the IPv4 address by name.
     * @param name The address name.
     * @return The IPv4 address.
     * @throws IOException Thrown in case of I/O error.
     */
    private static Inet4Address getIPv4AddressByName(String name) throws IOException {
        InetAddress[] addresses = InetAddress.getAllByName(name);
        for (InetAddress address : addresses) {
            if (address instanceof Inet4Address) {
                return (Inet4Address) address;
            }
        }
        throw new IOException("No IPv4 address found for " + name);
    }

    /**
     * Gets the IPv4 loopback address.
     * @return The IPv4 loopback address.
     * @throws IOException Thrown in case of I/O error.
     */
    private static Inet4Address getIPv4LoopbackAddress() throws IOException {
        return getIPv4AddressByName(LOOPBACK_ADDRESS_NAME);
    }

    /**
     * Gets the IPv4 local host address.
     * @return The IPv4 local host address.
     * @throws IOException Thrown in case of I/O error.
     */
    private static InetAddress getIPv4LocalHost() throws IOException {
        return InetAddress.getLocalHost();

/*
        InetAddress[] addresses = InetAddress.getAllByName("localhost");
        for (InetAddress address : addresses) {
            if (address instanceof Inet4Address inet4Address) {
                return inet4Address;
            }
        }
        return null;
*/
/*
        // If no IPv4 address found, return any InetAddress (preferably IPv6)
        return addresses[0];
*/
    }

    /**
     * Gets the external local host address (IPv4).
     *
     * @return The external local host IPv4 address.
     * @throws IOException Thrown in case of I/O error.
     */
    private static Inet4Address getExternalLocalHost() throws IOException {
        Enumeration networkInterfaces = NetworkInterface.getNetworkInterfaces();
        while (networkInterfaces.hasMoreElements()) {
            NetworkInterface networkInterface = networkInterfaces.nextElement();
            Enumeration addresses = networkInterface.getInetAddresses();
            while (addresses.hasMoreElements()) {
                InetAddress addr = addresses.nextElement();
                if (addr instanceof Inet4Address && !addr.isLoopbackAddress() && !addr.isLinkLocalAddress()) {
                    return (Inet4Address) addr;
                }
            }
        }
        throw new IOException("External local host address (IPv4) not found.");
    }
}