/*
 * 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.io.Reader;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ListIterator;
import java.util.StringTokenizer;

import org.apache.commons.net.io.DotTerminatedMessageReader;

/**
 * The POP3Client class implements the client side of the Internet POP3
 * Protocol defined in RFC 1939.  All commands are supported, including
 * the APOP command which requires MD5 encryption.  See RFC 1939 for
 * more details on the POP3 protocol.
 * <p>
 * Rather than list it separately for each method, we mention here that
 * every method communicating with the server and throwing an IOException
 * can also throw a
 * {@link org.apache.commons.net.MalformedServerReplyException}
 * , which is a subclass
 * of IOException.  A MalformedServerReplyException will be thrown when
 * the reply received from the server deviates enough from the protocol
 * specification that it cannot be interpreted in a useful manner despite
 * attempts to be as lenient as possible.
 *
 *
 * @see POP3MessageInfo
 * @see org.apache.commons.net.io.DotTerminatedMessageReader
 * @see org.apache.commons.net.MalformedServerReplyException
 */

public class POP3Client extends POP3
{

    private static POP3MessageInfo parseStatus(final String line)
    {
        int num, size;
        final StringTokenizer tokenizer;

        tokenizer = new StringTokenizer(line);

        if (!tokenizer.hasMoreElements()) {
            return null;
        }

        num = size = 0;

        try
        {
            num = Integer.parseInt(tokenizer.nextToken());

            if (!tokenizer.hasMoreElements()) {
                return null;
            }

            size = Integer.parseInt(tokenizer.nextToken());
        }
        catch (final NumberFormatException e)
        {
            return null;
        }

        return new POP3MessageInfo(num, size);
    }

    private static POP3MessageInfo parseUID(String line)
    {
        int num;
        final StringTokenizer tokenizer;

        tokenizer = new StringTokenizer(line);

        if (!tokenizer.hasMoreElements()) {
            return null;
        }

        num = 0;

        try
        {
            num = Integer.parseInt(tokenizer.nextToken());

            if (!tokenizer.hasMoreElements()) {
                return null;
            }

            line = tokenizer.nextToken();
        }
        catch (final NumberFormatException e)
        {
            return null;
        }

        return new POP3MessageInfo(num, line);
    }

    /**
     * Send a CAPA command to the POP3 server.
     * @return True if the command was successful, false if not.
     * @throws IOException If a network I/O error occurs in the process of
     *        sending the CAPA command.
     * @since 3.1 (was previously in ExtendedPOP3Client)
     */
    public boolean capa() throws IOException
    {
        if (sendCommand(POP3Command.CAPA) == POP3Reply.OK) {
            getAdditionalReply();
            return true;
        }
        return false;

    }

    /**
     * Login to the POP3 server with the given username and password.  You
     * must first connect to the server with
     * {@link org.apache.commons.net.SocketClient#connect  connect }
     * before attempting to login.  A login attempt is only valid if
     * the client is in the
     * {@link org.apache.commons.net.pop3.POP3#AUTHORIZATION_STATE AUTHORIZATION_STATE }
     * .  After logging in, the client enters the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * .
     *
     * @param username  The account name being logged in to.
     * @param password  The plain text password of the account.
     * @return True if the login attempt was successful, false if not.
     * @throws IOException If a network I/O error occurs in the process of
     *            logging in.
     */
    public boolean login(final String username, final String password) throws IOException
    {
        if (getState() != AUTHORIZATION_STATE) {
            return false;
        }

        if (sendCommand(POP3Command.USER, username) != POP3Reply.OK) {
            return false;
        }

        if (sendCommand(POP3Command.PASS, password) != POP3Reply.OK) {
            return false;
        }

        setState(TRANSACTION_STATE);

        return true;
    }


    /**
     * Login to the POP3 server with the given username and authentication
     * information.  Use this method when connecting to a server requiring
     * authentication using the APOP command.  Because the timestamp
     * produced in the greeting banner varies from server to server, it is
     * not possible to consistently extract the information.  Therefore,
     * after connecting to the server, you must call
     * {@link org.apache.commons.net.pop3.POP3#getReplyString getReplyString }
     *  and parse out the timestamp information yourself.
     * <p>
     * You must first connect to the server with
     * {@link org.apache.commons.net.SocketClient#connect  connect }
     * before attempting to login.  A login attempt is only valid if
     * the client is in the
     * {@link org.apache.commons.net.pop3.POP3#AUTHORIZATION_STATE AUTHORIZATION_STATE }
     * .  After logging in, the client enters the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * .  After connecting, you must parse out the
     * server specific information to use as a timestamp, and pass that
     * information to this method.  The secret is a shared secret known
     * to you and the server.  See RFC 1939 for more details regarding
     * the APOP command.
     *
     * @param username  The account name being logged in to.
     * @param timestamp  The timestamp string to combine with the secret.
     * @param secret  The shared secret which produces the MD5 digest when
     *        combined with the timestamp.
     * @return True if the login attempt was successful, false if not.
     * @throws IOException If a network I/O error occurs in the process of
     *            logging in.
     * @throws NoSuchAlgorithmException If the MD5 encryption algorithm
     *      cannot be instantiated by the Java runtime system.
     */
    public boolean login(final String username, String timestamp, final String secret)
    throws IOException, NoSuchAlgorithmException
    {
        int i;
        final byte[] digest;
        final StringBuilder buffer;
        final StringBuilder digestBuffer;
        final MessageDigest md5;

        if (getState() != AUTHORIZATION_STATE) {
            return false;
        }

        md5 = MessageDigest.getInstance("MD5");
        timestamp += secret;
        digest = md5.digest(timestamp.getBytes(getCharset()));
        digestBuffer = new StringBuilder(128);

        for (i = 0; i < digest.length; i++) {
            final int digit = digest[i] & 0xff;
            if (digit <= 15) { // Add leading zero if necessary (NET-351)
                digestBuffer.append("0");
            }
            digestBuffer.append(Integer.toHexString(digit));
        }

        buffer = new StringBuilder(256);
        buffer.append(username);
        buffer.append(' ');
        buffer.append(digestBuffer.toString());

        if (sendCommand(POP3Command.APOP, buffer.toString()) != POP3Reply.OK) {
            return false;
        }

        setState(TRANSACTION_STATE);

        return true;
    }


    /**
     * Logout of the POP3 server.  To fully disconnect from the server
     * you must call
     * {@link org.apache.commons.net.pop3.POP3#disconnect  disconnect }.
     * A logout attempt is valid in any state.  If
     * the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * , it enters the
     * {@link org.apache.commons.net.pop3.POP3#UPDATE_STATE UPDATE_STATE }
     *  on a successful logout.
     *
     * @return True if the logout attempt was successful, false if not.
     * @throws IOException If a network I/O error occurs in the process
     *           of logging out.
     */
    public boolean logout() throws IOException
    {
        if (getState() == TRANSACTION_STATE) {
            setState(UPDATE_STATE);
        }
        sendCommand(POP3Command.QUIT);
        return replyCode == POP3Reply.OK;
    }


    /**
     * Send a NOOP command to the POP3 server.  This is useful for keeping
     * a connection alive since most POP3 servers will timeout after 10
     * minutes of inactivity.  A noop attempt will only succeed if
     * the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * .
     *
     * @return True if the noop attempt was successful, false if not.
     * @throws IOException If a network I/O error occurs in the process of
     *        sending the NOOP command.
     */
    public boolean noop() throws IOException
    {
        if (getState() == TRANSACTION_STATE) {
            return sendCommand(POP3Command.NOOP) == POP3Reply.OK;
        }
        return false;
    }


    /**
     * Delete a message from the POP3 server.  The message is only marked
     * for deletion by the server.  If you decide to unmark the message, you
     * must issuse a {@link #reset  reset } command.  Messages marked
     * for deletion are only deleted by the server on
     * {@link #logout  logout }.
     * A delete attempt can only succeed if the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * .
     *
     * @param messageId  The message number to delete.
     * @return True if the deletion attempt was successful, false if not.
     * @throws IOException If a network I/O error occurs in the process of
     *           sending the delete command.
     */
    public boolean deleteMessage(final int messageId) throws IOException
    {
        if (getState() == TRANSACTION_STATE) {
            return sendCommand(POP3Command.DELE, Integer.toString(messageId))
                    == POP3Reply.OK;
        }
        return false;
    }


    /**
     * Reset the POP3 session.  This is useful for undoing any message
     * deletions that may have been performed.  A reset attempt can only
     * succeed if the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * .
     *
     * @return True if the reset attempt was successful, false if not.
     * @throws IOException If a network I/O error occurs in the process of
     *      sending the reset command.
     */
    public boolean reset() throws IOException
    {
        if (getState() == TRANSACTION_STATE) {
            return sendCommand(POP3Command.RSET) == POP3Reply.OK;
        }
        return false;
    }

    /**
     * Get the mailbox status.  A status attempt can only
     * succeed if the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * .  Returns a POP3MessageInfo instance
     * containing the number of messages in the mailbox and the total
     * size of the messages in bytes.  Returns null if the status the
     * attempt fails.
     *
     * @return A POP3MessageInfo instance containing the number of
     *         messages in the mailbox and the total size of the messages
     *         in bytes.  Returns null if the status the attempt fails.
     * @throws IOException If a network I/O error occurs in the process of
     *       sending the status command.
     */
    public POP3MessageInfo status() throws IOException
    {
        if (getState() != TRANSACTION_STATE) {
            return null;
        }
        if (sendCommand(POP3Command.STAT) != POP3Reply.OK) {
            return null;
        }
        return parseStatus(lastReplyLine.substring(3));
    }


    /**
     * List an individual message.  A list attempt can only
     * succeed if the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * .  Returns a POP3MessageInfo instance
     * containing the number of the listed message and the
     * size of the message in bytes.  Returns null if the list
     * attempt fails (e.g., if the specified message number does
     * not exist).
     *
     * @param messageId  The number of the message list.
     * @return A POP3MessageInfo instance containing the number of the
     *         listed message and the size of the message in bytes.  Returns
     *         null if the list attempt fails.
     * @throws IOException If a network I/O error occurs in the process of
     *         sending the list command.
     */
    public POP3MessageInfo listMessage(final int messageId) throws IOException
    {
        if (getState() != TRANSACTION_STATE) {
            return null;
        }
        if (sendCommand(POP3Command.LIST, Integer.toString(messageId))
                != POP3Reply.OK) {
            return null;
        }
        return parseStatus(lastReplyLine.substring(3));
    }


    /**
     * List all messages.  A list attempt can only
     * succeed if the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * .  Returns an array of POP3MessageInfo instances,
     * each containing the number of a message and its size in bytes.
     * If there are no messages, this method returns a zero length array.
     * If the list attempt fails, it returns null.
     *
     * @return An array of POP3MessageInfo instances representing all messages
     * in the order they appear in the mailbox,
     * each containing the number of a message and its size in bytes.
     * If there are no messages, this method returns a zero length array.
     * If the list attempt fails, it returns null.
     * @throws IOException If a network I/O error occurs in the process of
     *     sending the list command.
     */
    public POP3MessageInfo[] listMessages() throws IOException
    {
        if (getState() != TRANSACTION_STATE) {
            return null;
        }
        if (sendCommand(POP3Command.LIST) != POP3Reply.OK) {
            return null;
        }
        getAdditionalReply();

        // This could be a zero length array if no messages present
        final POP3MessageInfo[] messages = new POP3MessageInfo[replyLines.size() - 2]; // skip first and last lines

        final ListIterator<String> en = replyLines.listIterator(1); // Skip first line

        // Fetch lines.
        for (int line = 0; line < messages.length; line++) {
            messages[line] = parseStatus(en.next());
        }

        return messages;
    }

    /**
     * List the unique identifier for a message.  A list attempt can only
     * succeed if the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * .  Returns a POP3MessageInfo instance
     * containing the number of the listed message and the
     * unique identifier for that message.  Returns null if the list
     * attempt fails  (e.g., if the specified message number does
     * not exist).
     *
     * @param messageId  The number of the message list.
     * @return A POP3MessageInfo instance containing the number of the
     *         listed message and the unique identifier for that message.
     *         Returns null if the list attempt fails.
     * @throws IOException If a network I/O error occurs in the process of
     *        sending the list unique identifier command.
     */
    public POP3MessageInfo listUniqueIdentifier(final int messageId)
    throws IOException
    {
        if (getState() != TRANSACTION_STATE) {
            return null;
        }
        if (sendCommand(POP3Command.UIDL, Integer.toString(messageId))
                != POP3Reply.OK) {
            return null;
        }
        return parseUID(lastReplyLine.substring(3));
    }


    /**
     * List the unique identifiers for all messages.  A list attempt can only
     * succeed if the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * .  Returns an array of POP3MessageInfo instances,
     * each containing the number of a message and its unique identifier.
     * If there are no messages, this method returns a zero length array.
     * If the list attempt fails, it returns null.
     *
     * @return An array of POP3MessageInfo instances representing all messages
     * in the order they appear in the mailbox,
     * each containing the number of a message and its unique identifier
     * If there are no messages, this method returns a zero length array.
     * If the list attempt fails, it returns null.
     * @throws IOException If a network I/O error occurs in the process of
     *     sending the list unique identifier command.
     */
    public POP3MessageInfo[] listUniqueIdentifiers() throws IOException
    {
        if (getState() != TRANSACTION_STATE) {
            return null;
        }
        if (sendCommand(POP3Command.UIDL) != POP3Reply.OK) {
            return null;
        }
        getAdditionalReply();

        // This could be a zero length array if no messages present
        final POP3MessageInfo[] messages = new POP3MessageInfo[replyLines.size() - 2]; // skip first and last lines

        final ListIterator<String> en = replyLines.listIterator(1); // skip first line

        // Fetch lines.
        for (int line = 0; line < messages.length; line++) {
            messages[line] = parseUID(en.next());
        }

        return messages;
    }


    /**
     * Retrieve a message from the POP3 server.  A retrieve message attempt
     * can only succeed if the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * <p>
     * You must not issue any commands to the POP3 server (i.e., call any
     * other methods) until you finish reading the message from the
     * returned BufferedReader instance.
     * The POP3 protocol uses the same stream for issuing commands as it does
     * for returning results.  Therefore the returned BufferedReader actually reads
     * directly from the POP3 connection.  After the end of message has been
     * reached, new commands can be executed and their replies read.  If
     * you do not follow these requirements, your program will not work
     * properly.
     *
     * @param messageId  The number of the message to fetch.
     * @return A DotTerminatedMessageReader instance
     * from which the entire message can be read.
     * This can safely be cast to a {@link java.io.BufferedReader BufferedReader} in order to
     * use the {@link java.io.BufferedReader#readLine() BufferedReader#readLine()} method.
     * Returns null if the retrieval attempt fails  (e.g., if the specified
     * message number does not exist).
     * @throws IOException If a network I/O error occurs in the process of
     *        sending the retrieve message command.
     */
    public Reader retrieveMessage(final int messageId) throws IOException
    {
        if (getState() != TRANSACTION_STATE) {
            return null;
        }
        if (sendCommand(POP3Command.RETR, Integer.toString(messageId)) != POP3Reply.OK) {
            return null;
        }

        return new DotTerminatedMessageReader(reader);
    }


    /**
     * Retrieve only the specified top number of lines of a message from the
     * POP3 server.  A retrieve top lines attempt
     * can only succeed if the client is in the
     * {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }
     * <p>
     * You must not issue any commands to the POP3 server (i.e., call any
     * other methods) until you finish reading the message from the returned
     * BufferedReader instance.
     * The POP3 protocol uses the same stream for issuing commands as it does
     * for returning results.  Therefore the returned BufferedReader actually reads
     * directly from the POP3 connection.  After the end of message has been
     * reached, new commands can be executed and their replies read.  If
     * you do not follow these requirements, your program will not work
     * properly.
     *
     * @param messageId  The number of the message to fetch.
     * @param numLines  The top number of lines to fetch. This must be &gt;= 0.
     * @return  A DotTerminatedMessageReader instance
     * from which the specified top number of lines of the message can be
     * read.
     * This can safely be cast to a {@link java.io.BufferedReader BufferedReader} in order to
     * use the {@link java.io.BufferedReader#readLine() BufferedReader#readLine()} method.
     * Returns null if the retrieval attempt fails  (e.g., if the specified
     * message number does not exist).
     * @throws IOException If a network I/O error occurs in the process of
     *       sending the top command.
     */
    public Reader retrieveMessageTop(final int messageId, final int numLines)
    throws IOException
    {
        if (numLines < 0 || getState() != TRANSACTION_STATE) {
            return null;
        }
        if (sendCommand(POP3Command.TOP, Integer.toString(messageId) + " " +
                        Integer.toString(numLines)) != POP3Reply.OK) {
            return null;
        }

        return new DotTerminatedMessageReader(reader);
    }


}