/*
 *  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.harmony.auth.internal.kerberos.v5;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

import org.apache.harmony.auth.internal.nls.Messages;
import org.apache.harmony.javax.security.auth.kerberos.KerberosKey;
import org.apache.harmony.javax.security.auth.kerberos.KerberosPrincipal;
import org.apache.harmony.security.asn1.DerInputStream;

/**
 * @see http://www.ietf.org/rfc/rfc4120.txt
 */
public class KrbClient {

	// default kdc server
	private static final String DEFAULT_KDC = "java.security.krb5.kdc"; //$NON-NLS-1$

	// default realm
	private static final String DEFAULT_REALM = "java.security.krb5.realm"; //$NON-NLS-1$

	private static String kdc;

	private static String realm;

	private static int port = 88;// default

	private static final int BUF_SIZE = 1024;

	private static boolean isInitialized = false;

	/**
	 * Get credentials from Authentication Service.
	 * 
	 * @param address
	 *            - service host
	 * @param port
	 *            - service port
	 * @param cname
	 *            - client's principal identifier
	 * @param realm
	 *            - client's realm
	 * @return - ticket
	 */
	public static KDCReply doAS(PrincipalName cname, char[] password)
			throws KerberosException {

		setEnv();

		final PrincipalName sname = new PrincipalName(
				PrincipalName.NT_SRV_XHST, new String[] { "krbtgt", realm }); //$NON-NLS-1$

		final KDCRequest request = new KDCRequest(KDCRequest.AS_REQ, cname,
				realm, sname);

		try {
			final DatagramSocket socket = request.send(
					InetAddress.getByName(kdc), port);

			final ByteArrayOutputStream out = new ByteArrayOutputStream(
					BUF_SIZE);

			final byte[] buf = new byte[BUF_SIZE];

			final DatagramPacket resp = new DatagramPacket(buf, buf.length);

			int bytesRead = BUF_SIZE;
			while (bytesRead == BUF_SIZE) {
				socket.receive(resp);

				bytesRead = resp.getLength();
				out.write(buf, resp.getOffset(), bytesRead);
			}
			final DerInputStream in = new DerInputStream(out.toByteArray());

			if (in.tag == KDCReply.AS_REP_ASN1.constrId) { // TODO AS reply
				final KDCReply reply = (KDCReply) KDCReply.AS_REP_ASN1
						.decode(in);

				final KerberosKey key = new KerberosKey(new KerberosPrincipal(
						cname.getName()[0] + '@' + realm, cname.getType()),
						password, "DES");

				reply.decrypt(key);

				return reply;
			} else if (in.tag == KerberosErrorMessage.ASN1.constrId) {
				final KerberosErrorMessage errMsg = KerberosErrorMessage
						.decode(in);
				// auth.52=Error code: {0}
				throw new KerberosException(Messages.getString(
						"auth.52", errMsg.getErrorCode())); //$NON-NLS-1$
			} else {
				throw new KerberosException(); // FIXME
			}

		} catch (final IOException e) {
			throw new KerberosException(e.getMessage()); // FIXME
		}
	}

	public static KDCReply doTGS() throws KerberosException {
		setEnv();

		return null;
	}

	public static synchronized String getRealm() throws KerberosException {
		if (!isInitialized) {
			setEnv();
		}
		return realm;
	}

	private static void setEnv() throws KerberosException {
		if (isInitialized) {
			return;
		}

		// TODO put in doPrivileged
		kdc = System.getProperty(DEFAULT_KDC);
		realm = System.getProperty(DEFAULT_REALM);
		if (kdc == null && realm != null || kdc != null && realm == null) {
			// both properties should be set or unset together
			throw new KerberosException();// FIXME message
		} else if (kdc == null && realm == null) {

			// reading config from configuration file 'krb5.conf'
			KrbConfig config = null;
			try {
				config = KrbConfig.getSystemConfig();
			} catch (final IOException e) {
				throw new KerberosException(e.getMessage());
			}

			if (config == null) {
				// no config file was found
				throw new KerberosException();// FIXME err msg
			}
			realm = config.getValue("libdefaults", //$NON-NLS-1$
					"default_realm"); //$NON-NLS-1$

			// TODO set KDC
			return;
		}

		final int pos = kdc.indexOf(':');
		if (pos != -1) {
			port = Integer.parseInt(kdc.substring(pos + 1));
			kdc = kdc.substring(0, pos);
		}

		isInitialized = true;
	}

	private KrbClient() {
		// no objects
	}
}