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/*
 * tksCommons
 * 
 * Author : Thomas Kuhlmann (ThK-Systems, http://www.thk-systems.de) License : LGPL (https://www.gnu.org/licenses/lgpl.html)
 */
package de.thksystems.util.network;

import java.util.Hashtable;
import java.util.List;
import java.util.Vector;

import javax.naming.NamingEnumeration;
import javax.naming.NamingException;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;

public final class DNSUtils {

	private static DirContext dnsDirContext = null;

	private DNSUtils() {
	}

	public enum RecordType {
		A, CNAME, NS, MX, SOA
	}

	private static DirContext getDnsDirContext() throws NamingException {
		if (dnsDirContext == null) {
			Hashtable env = new Hashtable<>();
			env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
			dnsDirContext = new InitialDirContext(env);
		}
		return dnsDirContext;
	}

	/**
	 * Get domain-records for hostname.
	 * 
	 * Adapted from http://mowyourlawn.com/files/RecordType.java.txt.
	 */
	public static List lookup(String hostName, RecordType record) {

		List result = new Vector<>();
		try {
			Attributes attrs = getDnsDirContext().getAttributes(hostName, new String[] { record.name() });
			Attribute attr = attrs.get(record.name());
			if (attr != null) {
				NamingEnumeration attrEnum = attr.getAll();
				while (attrEnum.hasMoreElements()) {
					result.add(attrEnum.next().toString());
				}
			}
		} catch (NamingException e) {
			return new Vector();
		}
		return result;
	}

	/**
	 * Get all domain-records for hostname.
	 */
	public static List lookupAll(String hostName) {

		List result = new Vector<>();
		for (RecordType drt : RecordType.values()) {
			result.addAll(lookup(hostName, drt));
		}
		return result;
	}

	/**
	 * Checks, if the given hostname matches the given IP-address-string.
	 */
	public static boolean isMatchingIpAddress(String hostName, String ipAddr) {
		List allIps = lookupAll(hostName);
		for (String ip : allIps) {
			if (ip.equals(ipAddr)) {
				return true;
			}
		}
		return false;
	}

	/**
	 * Check for existing host-name.
	 */
	public static boolean exists(String hostName) {
		for (RecordType drt : RecordType.values()) {
			List result = lookup(hostName, drt);
			if (result.size() > 0) {
				return true;
			}
		}
		return false;
	}
}