/*
 * 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.commons.net.pop3;

import java.io.IOException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

import org.apache.commons.net.util.Base64;


/**
 * A POP3 Cilent class with protocol and authentication extensions support
 * (RFC2449 and RFC2195).
 * @see POP3Client
 * @since 3.0
 */
public class ExtendedPOP3Client extends POP3SClient
{
    /**
     * The default ExtendedPOP3Client constructor.
     * Creates a new Extended POP3 Client.
     * @throws NoSuchAlgorithmException on error
     */
    public ExtendedPOP3Client() throws NoSuchAlgorithmException
    {
        super();
    }

    /***
     * Authenticate to the POP3 server by sending the AUTH command with the
     * selected mechanism, using the given username and the given password.
     * <p>
     * @param method the {@link AUTH_METHOD} to use
     * @param username the user name
     * @param password the password
     * @return True if successfully completed, false if not.
     * @exception IOException  If an I/O error occurs while either sending a
     *      command to the server or receiving a reply from the server.
     * @exception NoSuchAlgorithmException If the CRAM hash algorithm
     *      cannot be instantiated by the Java runtime system.
     * @exception InvalidKeyException If the CRAM hash algorithm
     *      failed to use the given password.
     * @exception InvalidKeySpecException If the CRAM hash algorithm
     *      failed to use the given password.
     ***/
    public boolean auth(AUTH_METHOD method,
                        String username, String password)
                        throws IOException, NoSuchAlgorithmException,
                        InvalidKeyException, InvalidKeySpecException
    {
        if (sendCommand(POP3Command.AUTH, method.getAuthName())
        != POP3Reply.OK_INT) {
            return false;
        }

        switch(method) {
            case PLAIN:
                // the server sends an empty response ("+ "), so we don't have to read it.
                return sendCommand(
                    new String(
                        Base64.encodeBase64(("\000" + username + "\000" + password).getBytes(getCharset())),
                        getCharset())
                    ) == POP3Reply.OK;
            case CRAM_MD5:
                // get the CRAM challenge
                byte[] serverChallenge = Base64.decodeBase64(getReplyString().substring(2).trim());
                // get the Mac instance
                Mac hmac_md5 = Mac.getInstance("HmacMD5");
                hmac_md5.init(new SecretKeySpec(password.getBytes(getCharset()), "HmacMD5"));
                // compute the result:
                byte[] hmacResult = _convertToHexString(hmac_md5.doFinal(serverChallenge)).getBytes(getCharset());
                // join the byte arrays to form the reply
                byte[] usernameBytes = username.getBytes(getCharset());
                byte[] toEncode = new byte[usernameBytes.length + 1 /* the space */ + hmacResult.length];
                System.arraycopy(usernameBytes, 0, toEncode, 0, usernameBytes.length);
                toEncode[usernameBytes.length] = ' ';
                System.arraycopy(hmacResult, 0, toEncode, usernameBytes.length + 1, hmacResult.length);
                // send the reply and read the server code:
                return sendCommand(Base64.encodeBase64StringUnChunked(toEncode)) == POP3Reply.OK;
            default:
                return false;
        }
    }

    /**
     * Converts the given byte array to a String containing the hex values of the bytes.
     * For example, the byte 'A' will be converted to '41', because this is the ASCII code
     * (and the byte value) of the capital letter 'A'.
     * @param a The byte array to convert.
     * @return The resulting String of hex codes.
     */
    private String _convertToHexString(byte[] a)
    {
        StringBuilder result = new StringBuilder(a.length*2);
        for (byte element : a)
        {
            if ( (element & 0x0FF) <= 15 ) {
                result.append("0");
            }
            result.append(Integer.toHexString(element & 0x0FF));
        }
        return result.toString();
    }

    /**
     * The enumeration of currently-supported authentication methods.
     */
    public static enum AUTH_METHOD
    {
        /** The standarised (RFC4616) PLAIN method, which sends the password unencrypted (insecure). */
        PLAIN("PLAIN"),

        /** The standarised (RFC2195) CRAM-MD5 method, which doesn't send the password (secure). */
        CRAM_MD5("CRAM-MD5");

        private final String methodName;

        AUTH_METHOD(String methodName){
            this.methodName = methodName;
        }
        /**
         * Gets the name of the given authentication method suitable for the server.
         * @return The name of the given authentication method suitable for the server.
         */
        public final String getAuthName()
        {
            return this.methodName;
        }
    }
}