/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you 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.apache.logging.log4j.core.util;

import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import java.io.File;
import java.net.InetAddress;
import java.net.MalformedURLException;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.List;
import java.util.function.Function;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.status.StatusLogger;

/**
 * Networking-related convenience methods.
 */
public final class NetUtils {

    private static final Logger LOGGER = StatusLogger.getLogger();
    private static final String UNKNOWN_LOCALHOST = "UNKNOWN_LOCALHOST";

    private NetUtils() {
        // empty
    }

    /**
     * This method gets the network name of the machine we are running on. Returns "UNKNOWN_LOCALHOST" in the unlikely
     * case where the host name cannot be found.
     *
     * @return String the name of the local host
     */
    public static String getLocalHostname() {
        return getHostname(InetAddress::getHostName);
    }

    /**
     * This method gets the FQDN of the machine we are running on.
     * It returns {@value UNKNOWN_LOCALHOST} if the host name cannot be found.
     *
     * @return The canonical name of the local host; or {@value UNKNOWN_LOCALHOST}, if cannot be found.
     */
    public static String getCanonicalLocalHostname() {
        return getHostname(InetAddress::getCanonicalHostName);
    }

    private static String getHostname(final Function<? super InetAddress, ? extends String> callback) {
        try {
            final InetAddress address = InetAddress.getLocalHost();
            return address == null ? UNKNOWN_LOCALHOST : callback.apply(address);
        } catch (final UnknownHostException uhe) {
            try {
                final Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
                while (interfaces.hasMoreElements()) {
                    final NetworkInterface nic = interfaces.nextElement();
                    final Enumeration<InetAddress> addresses = nic.getInetAddresses();
                    while (addresses.hasMoreElements()) {
                        final InetAddress address = addresses.nextElement();
                        if (!address.isLoopbackAddress()) {
                            final String hostname = callback.apply(address);
                            if (hostname != null) {
                                return hostname;
                            }
                        }
                    }
                }
            } catch (final SocketException se) {
                // ignore and log below.
            }
            LOGGER.error("Could not determine local host name", uhe);
            return UNKNOWN_LOCALHOST;
        }
    }

    /**
     *  Returns the local network interface's MAC address if possible. The local network interface is defined here as
     *  the {@link java.net.NetworkInterface} that is both up and not a loopback interface.
     *
     * @return the MAC address of the local network interface or {@code null} if no MAC address could be determined.
     */
    public static byte[] getMacAddress() {
        byte[] mac = null;
        try {
            final InetAddress localHost = InetAddress.getLocalHost();
            try {
                final NetworkInterface localInterface = NetworkInterface.getByInetAddress(localHost);
                if (isUpAndNotLoopback(localInterface)) {
                    mac = localInterface.getHardwareAddress();
                }
                if (mac == null) {
                    final Enumeration<NetworkInterface> networkInterfaces = NetworkInterface.getNetworkInterfaces();
                    if (networkInterfaces != null) {
                        while (networkInterfaces.hasMoreElements() && mac == null) {
                            final NetworkInterface nic = networkInterfaces.nextElement();
                            if (isUpAndNotLoopback(nic)) {
                                mac = nic.getHardwareAddress();
                            }
                        }
                    }
                }
            } catch (final SocketException e) {
                LOGGER.catching(e);
            }
            if (ArrayUtils.isEmpty(mac) && localHost != null) {
                // Emulate a MAC address with an IP v4 or v6
                final byte[] address = localHost.getAddress();
                // Take only 6 bytes if the address is an IPv6 otherwise will pad with two zero bytes
                mac = Arrays.copyOf(address, 6);
            }
        } catch (final UnknownHostException ignored) {
            // ignored
        }
        return mac;
    }

    /**
     * Returns the mac address, if it is available, as a string with each byte separated by a ":" character.
     * @return the mac address String or null.
     */
    public static String getMacAddressString() {
        final byte[] macAddr = getMacAddress();
        if (!ArrayUtils.isEmpty(macAddr)) {
            final StringBuilder sb = new StringBuilder(String.format("%02x", macAddr[0]));
            for (int i = 1; i < macAddr.length; ++i) {
                sb.append(":").append(String.format("%02x", macAddr[i]));
            }
            return sb.toString();
        }
        return null;
    }

    private static boolean isUpAndNotLoopback(final NetworkInterface ni) throws SocketException {
        return ni != null && !ni.isLoopback() && ni.isUp();
    }

    /**
     * Converts a URI string or file path to a URI object.
     *
     * @param path the URI string or path
     * @return the URI object
     */
    @SuppressFBWarnings(
            value = "PATH_TRAVERSAL_IN",
            justification = "Currently `path` comes from a configuration file.")
    public static URI toURI(final String path) {
        try {
            // Resolves absolute URI
            return new URI(path);
        } catch (final URISyntaxException e) {
            // A file path or a Apache Commons VFS URL might contain blanks.
            // A file path may start with a driver letter
            try {
                final URL url = new URL(path);
                return new URI(url.getProtocol(), url.getHost(), url.getPath(), null);
            } catch (MalformedURLException | URISyntaxException nestedEx) {
                return new File(path).toURI();
            }
        }
    }

    public static List<URI> toURIs(final String path) {
        final String[] parts = path.split(",");
        String scheme = null;
        final List<URI> uris = new ArrayList<>(parts.length);
        for (final String part : parts) {
            final URI uri = NetUtils.toURI(scheme != null ? scheme + ":" + part.trim() : part.trim());
            if (scheme == null && uri.getScheme() != null) {
                scheme = uri.getScheme();
            }
            uris.add(uri);
        }
        return uris;
    }
}
