private static boolean isIPv6Address()

in src/main/java/org/apache/commons/io/FilenameUtils.java [1138:1196]
57 lines of code
22 McCabe index (conditional complexity)

    private static boolean isIPv6Address(final String inet6Address) {
        final 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) {
            final List<String> 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(EMPTY_STRING_ARRAY);
        }
        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++) {
            final String octet = octets[index];
            if (octet.isEmpty()) {
                emptyOctets++;
                if (emptyOctets > 1) {
                    return false;
                }
            } else {
                emptyOctets = 0;
                // Is last chunk an IPv4 address?
                if (index == octets.length - 1 && octet.contains(".")) {
                    if (!isIPv4Address(octet)) {
                        return false;
                    }
                    validOctets += 2;
                    continue;
                }
                if (octet.length() > IPV6_MAX_HEX_DIGITS_PER_GROUP) {
                    return false;
                }
                final int octetInt;
                try {
                    octetInt = Integer.parseInt(octet, BASE_16);
                } catch (final NumberFormatException e) {
                    return false;
                }
                if (octetInt < 0 || octetInt > MAX_UNSIGNED_SHORT) {
                    return false;
                }
            }
            validOctets++;
        }
        return validOctets <= IPV6_MAX_HEX_GROUPS && (validOctets >= IPV6_MAX_HEX_GROUPS || containsCompressedZeroes);
    }