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/*
 * 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 fun.mike.validation;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * InetAddress validation and conversion routines (java.net.InetAddress).
 *
 * This class provides methods to validate a candidate IP address.
 *
 * 

 * This class is a Singleton; you can retrieve the instance via the {@link #getInstance()} method.
 * 
 *
 * @version $Revision$
 * @since Validator 1.4
 */
public class InetAddressValidator implements Serializable {

    private static final int IPV4_MAX_OCTET_VALUE = 255;

    private static final int MAX_UNSIGNED_SHORT = 0xffff;

    private static final int BASE_16 = 16;

    private static final long serialVersionUID = -919201640201914789L;

    private static final String IPV4_REGEX =
            "^(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})$";

    // Max number of hex groups (separated by :) in an IPV6 address
    private static final int IPV6_MAX_HEX_GROUPS = 8;

    // Max hex digits in each IPv6 group
    private static final int IPV6_MAX_HEX_DIGITS_PER_GROUP = 4;

    /**
     * Singleton instance of this class.
     */
    private static final InetAddressValidator VALIDATOR = new InetAddressValidator();

    /** IPv4 RegexValidator */
    private final RegexValidator ipv4Validator = new RegexValidator(IPV4_REGEX);

    /**
     * Returns the singleton instance of this validator.
     * @return the singleton instance of this validator
     */
    public static InetAddressValidator getInstance() {
        return VALIDATOR;
    }

    /**
     * Checks if the specified string is a valid IP address.
     * @param inetAddress the string to validate
     * @return true if the string validates as an IP address
     */
    public boolean isValid(String inetAddress) {
        return isValidInet4Address(inetAddress) || isValidInet6Address(inetAddress);
    }

    /**
     * Validates an IPv4 address. Returns true if valid.
     * @param inet4Address the IPv4 address to validate
     * @return true if the argument contains a valid IPv4 address
     */
    public boolean isValidInet4Address(String inet4Address) {
        // verify that address conforms to generic IPv4 format
        String[] groups = ipv4Validator.match(inet4Address);

        if (groups == null) {
            return false;
        }

        // verify that address subgroups are legal
        for (String ipSegment : groups) {
            if (ipSegment == null || ipSegment.length() == 0) {
                return false;
            }

            int iIpSegment = 0;

            try {
                iIpSegment = Integer.parseInt(ipSegment);
            } catch(NumberFormatException e) {
                return false;
            }

            if (iIpSegment > IPV4_MAX_OCTET_VALUE) {
                return false;
            }

            if (ipSegment.length() > 1 && ipSegment.startsWith("0")) {
                return false;
            }

        }

        return true;
    }

    /**
     * Validates an IPv6 address. Returns true if valid.
     * @param inet6Address the IPv6 address to validate
     * @return true if the argument contains a valid IPv6 address
     * 
     * @since 1.4.1
     */
    public boolean isValidInet6Address(String inet6Address) {
        boolean containsCompressedZeroes = inet6Address.contains("::");
        if (containsCompressedZeroes && (inet6Address.indexOf("::") != inet6Address.lastIndexOf("::"))) {
            return false;
        }
        if ((inet6Address.startsWith(":") && !inet6Address.startsWith("::"))
                || (inet6Address.endsWith(":") && !inet6Address.endsWith("::"))) {
            return false;
        }
        String[] octets = inet6Address.split(":");
        if (containsCompressedZeroes) {
            List octetList = new ArrayList(Arrays.asList(octets));
            if (inet6Address.endsWith("::")) {
                // String.split() drops ending empty segments
                octetList.add("");
            } else if (inet6Address.startsWith("::") && !octetList.isEmpty()) {
                octetList.remove(0);
            }
            octets = octetList.toArray(new String[octetList.size()]);
        }
        if (octets.length > IPV6_MAX_HEX_GROUPS) {
            return false;
        }
        int validOctets = 0;
        int emptyOctets = 0; // consecutive empty chunks
        for (int index = 0; index < octets.length; index++) {
            String octet = octets[index];
            if (octet.length() == 0) {
                emptyOctets++;
                if (emptyOctets > 1) {
                    return false;
                }
            } else {
                emptyOctets = 0;
                // Is last chunk an IPv4 address?
                if (index == octets.length - 1 && octet.contains(".")) {
                    if (!isValidInet4Address(octet)) {
                        return false;
                    }
                    validOctets += 2;
                    continue;
                }
                if (octet.length() > IPV6_MAX_HEX_DIGITS_PER_GROUP) {
                    return false;
                }
                int octetInt = 0;
                try {
                    octetInt = Integer.parseInt(octet, BASE_16);
                } catch (NumberFormatException e) {
                    return false;
                }
                if (octetInt < 0 || octetInt > MAX_UNSIGNED_SHORT) {
                    return false;
                }
            }
            validOctets++;
        }
        if (validOctets > IPV6_MAX_HEX_GROUPS || (validOctets < IPV6_MAX_HEX_GROUPS && !containsCompressedZeroes)) {
            return false;
        }
        return true;
    }
}