package com.fsck.k9.mail.store;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.security.GeneralSecurityException;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;

import javax.net.ssl.SSLContext;
import javax.net.ssl.TrustManager;
import javax.net.ssl.SSLException;

import android.util.Config;
import android.util.Log;

import com.fsck.k9.k9;
import com.fsck.k9.PeekableInputStream;
import com.fsck.k9.Utility;
import com.fsck.k9.mail.AuthenticationFailedException;
import com.fsck.k9.mail.FetchProfile;
import com.fsck.k9.mail.Flag;
import com.fsck.k9.mail.Folder;
import com.fsck.k9.mail.Message;
import com.fsck.k9.mail.MessageRetrievalListener;
import com.fsck.k9.mail.MessagingException;
import com.fsck.k9.mail.Part;
import com.fsck.k9.mail.Store;
import com.fsck.k9.mail.CertificateValidationException;
import com.fsck.k9.mail.internet.MimeBodyPart;
import com.fsck.k9.mail.internet.MimeHeader;
import com.fsck.k9.mail.internet.MimeMessage;
import com.fsck.k9.mail.internet.MimeMultipart;
import com.fsck.k9.mail.internet.MimeUtility;
import com.fsck.k9.mail.store.ImapResponseParser.ImapList;
import com.fsck.k9.mail.store.ImapResponseParser.ImapResponse;
import com.fsck.k9.mail.transport.CountingOutputStream;
import com.fsck.k9.mail.transport.EOLConvertingOutputStream;
import com.beetstra.jutf7.CharsetProvider;

/**
 * <pre>
 * TODO Need to start keeping track of UIDVALIDITY
 * TODO Need a default response handler for things like folder updates
 * TODO In fetch(), if we need a ImapMessage and were given
 * something else we can try to do a pre-fetch first.
 *
 * ftp://ftp.isi.edu/in-notes/rfc2683.txt When a client asks for
 * certain information in a FETCH command, the server may return the requested
 * information in any order, not necessarily in the order that it was requested.
 * Further, the server may return the information in separate FETCH responses
 * and may also return information that was not explicitly requested (to reflect
 * to the client changes in the state of the subject message).
 * </pre>
 */
public class ImapStore extends Store {
    public static final int CONNECTION_SECURITY_NONE = 0;
    public static final int CONNECTION_SECURITY_TLS_OPTIONAL = 1;
    public static final int CONNECTION_SECURITY_TLS_REQUIRED = 2;
    public static final int CONNECTION_SECURITY_SSL_REQUIRED = 3;
    public static final int CONNECTION_SECURITY_SSL_OPTIONAL = 4;

    private static final Flag[] PERMANENT_FLAGS = { Flag.DELETED, Flag.SEEN };

    private String mHost;
    private int mPort;
    private String mUsername;
    private String mPassword;
    private int mConnectionSecurity;
    private String mPathPrefix;

    private LinkedList<ImapConnection> mConnections =
            new LinkedList<ImapConnection>();

    /**
     * Charset used for converting folder names to and from UTF-7 as defined by RFC 3501.
     */
    private Charset mModifiedUtf7Charset;

    /**
     * Cache of ImapFolder objects. ImapFolders are attached to a given folder on the server
     * and as long as their associated connection remains open they are reusable between
     * requests. This cache lets us make sure we always reuse, if possible, for a given
     * folder name.
     */
    private HashMap<String, ImapFolder> mFolderCache = new HashMap<String, ImapFolder>();

    /**
     * imap://user:password@server:port CONNECTION_SECURITY_NONE
     * imap+tls://user:password@server:port CONNECTION_SECURITY_TLS_OPTIONAL
     * imap+tls+://user:password@server:port CONNECTION_SECURITY_TLS_REQUIRED
     * imap+ssl+://user:password@server:port CONNECTION_SECURITY_SSL_REQUIRED
     * imap+ssl://user:password@server:port CONNECTION_SECURITY_SSL_OPTIONAL
     *
     * @param _uri
     */
    public ImapStore(String _uri) throws MessagingException {
        URI uri;
        try {
            uri = new URI(_uri);
        } catch (URISyntaxException use) {
            throw new MessagingException("Invalid ImapStore URI", use);
        }

        String scheme = uri.getScheme();
        if (scheme.equals("imap")) {
            mConnectionSecurity = CONNECTION_SECURITY_NONE;
            mPort = 143;
        } else if (scheme.equals("imap+tls")) {
            mConnectionSecurity = CONNECTION_SECURITY_TLS_OPTIONAL;
            mPort = 143;
        } else if (scheme.equals("imap+tls+")) {
            mConnectionSecurity = CONNECTION_SECURITY_TLS_REQUIRED;
            mPort = 143;
        } else if (scheme.equals("imap+ssl+")) {
            mConnectionSecurity = CONNECTION_SECURITY_SSL_REQUIRED;
            mPort = 993;
        } else if (scheme.equals("imap+ssl")) {
            mConnectionSecurity = CONNECTION_SECURITY_SSL_OPTIONAL;
            mPort = 993;
        } else {
            throw new MessagingException("Unsupported protocol");
        }

        mHost = uri.getHost();

        if (uri.getPort() != -1) {
            mPort = uri.getPort();
        }

        if (uri.getUserInfo() != null) {
            String[] userInfoParts = uri.getUserInfo().split(":", 2);
            mUsername = userInfoParts[0];
            if (userInfoParts.length > 1) {
                mPassword = userInfoParts[1];
            }
        }

        if ((uri.getPath() != null) && (uri.getPath().length() > 0)) {
            mPathPrefix = uri.getPath().substring(1);
        }

        mModifiedUtf7Charset = new CharsetProvider().charsetForName("X-RFC-3501");
    }

    @Override
    public Folder getFolder(String name) throws MessagingException {
        ImapFolder folder;
        synchronized (mFolderCache) {
            folder = mFolderCache.get(name);
            if (folder == null) {
                folder = new ImapFolder(name);
                mFolderCache.put(name, folder);
            }
        }
        return folder;
    }


    @Override
    public Folder[] getPersonalNamespaces() throws MessagingException {
        ImapConnection connection = getConnection();
        try {
            ArrayList<Folder> folders = new ArrayList<Folder>();
            List<ImapResponse> responses =
                    connection.executeSimpleCommand(String.format("LIST \"\" \"%s*\"",
                        mPathPrefix == null ? "" : mPathPrefix));
            for (ImapResponse response : responses) {
                if (response.get(0).equals("LIST")) {
                    boolean includeFolder = true;
                    String folder = decodeFolderName(response.getString(3));
                    if (folder.equalsIgnoreCase("INBOX")) {
                        continue;
                    }
                    ImapList attributes = response.getList(1);
                    for (int i = 0, count = attributes.size(); i < count; i++) {
                        String attribute = attributes.getString(i);
                        if (attribute.equalsIgnoreCase("\\NoSelect")) {
                            includeFolder = false;
                        }
                    }
                    if (includeFolder) {
                        folders.add(getFolder(folder));
                    }
                }
            }
            folders.add(getFolder("INBOX"));
            return folders.toArray(new Folder[] {});
        } catch (IOException ioe) {
            connection.close();
            throw new MessagingException("Unable to get folder list.", ioe);
        } finally {
            releaseConnection(connection);
        }
    }

    @Override
    public void checkSettings() throws MessagingException {
        try {
            ImapConnection connection = new ImapConnection();
            connection.open();
            connection.close();
        }
        catch (IOException ioe) {
            throw new MessagingException("Unable to connect.", ioe);
        }
    }

    /**
     * Gets a connection if one is available for reuse, or creates a new one if not.
     * @return
     */
    private ImapConnection getConnection() throws MessagingException {
        synchronized (mConnections) {
            ImapConnection connection = null;
            while ((connection = mConnections.poll()) != null) {
                try {
                    connection.executeSimpleCommand("NOOP");
                    break;
                }
                catch (IOException ioe) {
                    connection.close();
                }
            }
            if (connection == null) {
                connection = new ImapConnection();
            }
            return connection;
        }
    }

    private void releaseConnection(ImapConnection connection) {
        mConnections.offer(connection);
    }

    private String encodeFolderName(String name) {
        try {
            ByteBuffer bb = mModifiedUtf7Charset.encode(name);
            byte[] b = new byte[bb.limit()];
            bb.get(b);
            return new String(b, "US-ASCII");
        }
        catch (UnsupportedEncodingException uee) {
            /*
             * The only thing that can throw this is getBytes("US-ASCII") and if US-ASCII doesn't
             * exist we're totally screwed.
             */
            throw new RuntimeException("Unabel to encode folder name: " + name, uee);
        }
    }

    private String decodeFolderName(String name) {
        /*
         * Convert the encoded name to US-ASCII, then pass it through the modified UTF-7
         * decoder and return the Unicode String.
         */
        try {
            byte[] encoded = name.getBytes("US-ASCII");
            CharBuffer cb = mModifiedUtf7Charset.decode(ByteBuffer.wrap(encoded));
            return cb.toString();
        }
        catch (UnsupportedEncodingException uee) {
            /*
             * The only thing that can throw this is getBytes("US-ASCII") and if US-ASCII doesn't
             * exist we're totally screwed.
             */
            throw new RuntimeException("Unable to decode folder name: " + name, uee);
        }
    }

    class ImapFolder extends Folder {
        private String mName;
        private int mMessageCount = -1;
        private ImapConnection mConnection;
        private OpenMode mMode;
        private boolean mExists;

        public ImapFolder(String name) {
            this.mName = name;
        }

        public void open(OpenMode mode) throws MessagingException {
            if (isOpen() && mMode == mode) {
                // Make sure the connection is valid. If it's not we'll close it down and continue
                // on to get a new one.
                try {
                    mConnection.executeSimpleCommand("NOOP");
                    return;
                }
                catch (IOException ioe) {
                    ioExceptionHandler(mConnection, ioe);
                }
            }
            synchronized (this) {
                mConnection = getConnection();
            }
            // * FLAGS (\Answered \Flagged \Deleted \Seen \Draft NonJunk
            // $MDNSent)
            // * OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft
            // NonJunk $MDNSent \*)] Flags permitted.
            // * 23 EXISTS
            // * 0 RECENT
            // * OK [UIDVALIDITY 1125022061] UIDs valid
            // * OK [UIDNEXT 57576] Predicted next UID
            // 2 OK [READ-WRITE] Select completed.
            try {
                List<ImapResponse> responses = mConnection.executeSimpleCommand(
                        String.format("SELECT \"%s\"",
                                encodeFolderName(mName)));
                /*
                 * If the command succeeds we expect the folder has been opened read-write
                 * unless we are notified otherwise in the responses.
                 */
                mMode = OpenMode.READ_WRITE;

                for (ImapResponse response : responses) {
                    if (response.mTag == null && response.get(1).equals("EXISTS")) {
                        mMessageCount = response.getNumber(0);
                    }
                    else if (response.mTag != null && response.size() >= 2) {
                        if ("[READ-ONLY]".equalsIgnoreCase(response.getString(1))) {
                            mMode = OpenMode.READ_ONLY;
                        }
                        else if ("[READ-WRITE]".equalsIgnoreCase(response.getString(1))) {
                            mMode = OpenMode.READ_WRITE;
                        }
                    }
                }

                if (mMessageCount == -1) {
                    throw new MessagingException(
                            "Did not find message count during select");
                }
                mExists = true;

            } catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
        }

        public boolean isOpen() {
            return mConnection != null;
        }

        @Override
        public OpenMode getMode() throws MessagingException {
            return mMode;
        }

        public void close(boolean expunge) {
            if (!isOpen()) {
                return;
            }
            // TODO implement expunge
            mMessageCount = -1;
            synchronized (this) {
                releaseConnection(mConnection);
                mConnection = null;
            }
        }

        public String getName() {
            return mName;
        }

        public boolean exists() throws MessagingException {
            if (mExists) {
                return true;
            }
            /*
             * This method needs to operate in the unselected mode as well as the selected mode
             * so we must get the connection ourselves if it's not there. We are specifically
             * not calling checkOpen() since we don't care if the folder is open.
             */
            ImapConnection connection = null;
            synchronized(this) {
                if (mConnection == null) {
                    connection = getConnection();
                }
                else {
                    connection = mConnection;
                }
            }
            try {
                connection.executeSimpleCommand(String.format("STATUS \"%s\" (UIDVALIDITY)",
                        encodeFolderName(mName)));
                mExists = true;
                return true;
            }
            catch (MessagingException me) {
                return false;
            }
            catch (IOException ioe) {
                throw ioExceptionHandler(connection, ioe);
            }
            finally {
                if (mConnection == null) {
                    releaseConnection(connection);
                }
            }
        }

        public boolean create(FolderType type) throws MessagingException {
            /*
             * This method needs to operate in the unselected mode as well as the selected mode
             * so we must get the connection ourselves if it's not there. We are specifically
             * not calling checkOpen() since we don't care if the folder is open.
             */
            ImapConnection connection = null;
            synchronized(this) {
                if (mConnection == null) {
                    connection = getConnection();
                }
                else {
                    connection = mConnection;
                }
            }
            try {
                connection.executeSimpleCommand(String.format("CREATE \"%s\"",
                        encodeFolderName(mName)));
                return true;
            }
            catch (MessagingException me) {
                return false;
            }
            catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
            finally {
                if (mConnection == null) {
                    releaseConnection(connection);
                }
            }
        }

        @Override
        public void copyMessages(Message[] messages, Folder folder) throws MessagingException {
            checkOpen();
            String[] uids = new String[messages.length];
            for (int i = 0, count = messages.length; i < count; i++) {
                uids[i] = messages[i].getUid();
            }
            try {
                mConnection.executeSimpleCommand(String.format("UID COPY %s \"%s\"",
                        Utility.combine(uids, ','),
                        encodeFolderName(folder.getName())));
            }
            catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
        }

        @Override
        public int getMessageCount() {
            return mMessageCount;
        }

        @Override
        public int getUnreadMessageCount() throws MessagingException {
            checkOpen();
            try {
                int unreadMessageCount = 0;
                List<ImapResponse> responses = mConnection.executeSimpleCommand(
                        String.format("STATUS \"%s\" (UNSEEN)",
                                encodeFolderName(mName)));
                for (ImapResponse response : responses) {
                    if (response.mTag == null && response.get(0).equals("STATUS")) {
                        ImapList status = response.getList(2);
                        unreadMessageCount = status.getKeyedNumber("UNSEEN");
                    }
                }
                return unreadMessageCount;
            }
            catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
        }

        @Override
        public void delete(boolean recurse) throws MessagingException {
            throw new Error("ImapStore.delete() not yet implemented");
        }

        @Override
        public Message getMessage(String uid) throws MessagingException {
            checkOpen();

            try {
                try {
                    List<ImapResponse> responses =
                            mConnection.executeSimpleCommand(String.format("UID SEARCH UID %S", uid));
                    for (ImapResponse response : responses) {
                        if (response.mTag == null && response.get(0).equals("SEARCH")) {
                            for (int i = 1, count = response.size(); i < count; i++) {
                                if (uid.equals(response.get(i))) {
                                    return new ImapMessage(uid, this);
                                }
                            }
                        }
                    }
                }
                catch (MessagingException me) {
                    return null;
                }
            }
            catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
            return null;
        }

        @Override
        public Message[] getMessages(int start, int end, MessageRetrievalListener listener)
                throws MessagingException {
            if (start < 1 || end < 1 || end < start) {
                throw new MessagingException(
                        String.format("Invalid message set %d %d",
                                start, end));
            }
            checkOpen();
            ArrayList<Message> messages = new ArrayList<Message>();
            try {
                ArrayList<String> uids = new ArrayList<String>();
                List<ImapResponse> responses = mConnection
                        .executeSimpleCommand(String.format("UID SEARCH %d:%d NOT DELETED", start, end));
                for (ImapResponse response : responses) {
                    if (response.get(0).equals("SEARCH")) {
                        for (int i = 1, count = response.size(); i < count; i++) {
                            uids.add(response.getString(i));
                        }
                    }
                }
                for (int i = 0, count = uids.size(); i < count; i++) {
                    if (listener != null) {
                        listener.messageStarted(uids.get(i), i, count);
                    }
                    ImapMessage message = new ImapMessage(uids.get(i), this);
                    messages.add(message);
                    if (listener != null) {
                        listener.messageFinished(message, i, count);
                    }
                }
            } catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
            return messages.toArray(new Message[] {});
        }

        public Message[] getMessages(MessageRetrievalListener listener) throws MessagingException {
            return getMessages(null, listener);
        }

        public Message[] getMessages(String[] uids, MessageRetrievalListener listener)
                throws MessagingException {
            checkOpen();
            ArrayList<Message> messages = new ArrayList<Message>();
            try {
                if (uids == null) {
                    List<ImapResponse> responses = mConnection
                            .executeSimpleCommand("UID SEARCH 1:* NOT DELETED");
                    ArrayList<String> tempUids = new ArrayList<String>();
                    for (ImapResponse response : responses) {
                        if (response.get(0).equals("SEARCH")) {
                            for (int i = 1, count = response.size(); i < count; i++) {
                                tempUids.add(response.getString(i));
                            }
                        }
                    }
                    uids = tempUids.toArray(new String[] {});
                }
                for (int i = 0, count = uids.length; i < count; i++) {
                    if (listener != null) {
                        listener.messageStarted(uids[i], i, count);
                    }
                    ImapMessage message = new ImapMessage(uids[i], this);
                    messages.add(message);
                    if (listener != null) {
                        listener.messageFinished(message, i, count);
                    }
                }
            } catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
            return messages.toArray(new Message[] {});
        }

        public void fetch(Message[] messages, FetchProfile fp, MessageRetrievalListener listener)
                throws MessagingException {
            if (messages == null || messages.length == 0) {
                return;
            }
            checkOpen();
            String[] uids = new String[messages.length];
            HashMap<String, Message> messageMap = new HashMap<String, Message>();
            for (int i = 0, count = messages.length; i < count; i++) {
                uids[i] = messages[i].getUid();
                messageMap.put(uids[i], messages[i]);
            }

            /*
             * Figure out what command we are going to run:
             * Flags - UID FETCH (FLAGS)
             * Envelope - UID FETCH ([FLAGS] INTERNALDATE UID RFC822.SIZE FLAGS BODY.PEEK[HEADER.FIELDS (date subject from content-type to cc)])
             *
             */
            LinkedHashSet<String> fetchFields = new LinkedHashSet<String>();
            fetchFields.add("UID");
            if (fp.contains(FetchProfile.Item.FLAGS)) {
                fetchFields.add("FLAGS");
            }
            if (fp.contains(FetchProfile.Item.ENVELOPE)) {
                fetchFields.add("INTERNALDATE");
                fetchFields.add("RFC822.SIZE");
                fetchFields.add("BODY.PEEK[HEADER.FIELDS (date subject from content-type to cc)]");
            }
            if (fp.contains(FetchProfile.Item.STRUCTURE)) {
                fetchFields.add("BODYSTRUCTURE");
            }
            if (fp.contains(FetchProfile.Item.BODY_SANE)) {
                fetchFields.add(String.format("BODY.PEEK[]<0.%d>", FETCH_BODY_SANE_SUGGESTED_SIZE));
            }
            if (fp.contains(FetchProfile.Item.BODY)) {
                fetchFields.add("BODY.PEEK[]");
            }
            for (Object o : fp) {
                if (o instanceof Part) {
                    Part part = (Part) o;
                    String partId = part.getHeader(MimeHeader.HEADER_ANDROID_ATTACHMENT_STORE_DATA)[0];
                    fetchFields.add("BODY.PEEK[" + partId + "]");
                }
            }

            try {
                String tag = mConnection.sendCommand(String.format("UID FETCH %s (%s)",
                        Utility.combine(uids, ','),
                        Utility.combine(fetchFields.toArray(new String[fetchFields.size()]), ' ')
                        ), false);
                ImapResponse response;
                int messageNumber = 0;
                do {
                    response = mConnection.readResponse();

                    if (response.mTag == null && response.get(1).equals("FETCH")) {
                        ImapList fetchList = (ImapList)response.getKeyedValue("FETCH");
                        String uid = fetchList.getKeyedString("UID");

                        Message message = messageMap.get(uid);

                        if (listener != null) {
                            listener.messageStarted(uid, messageNumber++, messageMap.size());
                        }

                        if (fp.contains(FetchProfile.Item.FLAGS)) {
                            ImapList flags = fetchList.getKeyedList("FLAGS");
                            ImapMessage imapMessage = (ImapMessage) message;
                            if (flags != null) {
                                for (int i = 0, count = flags.size(); i < count; i++) {
                                    String flag = flags.getString(i);
                                    if (flag.equals("\\Deleted")) {
                                        imapMessage.setFlagInternal(Flag.DELETED, true);
                                    }
                                    else if (flag.equals("\\Answered")) {
                                        imapMessage.setFlagInternal(Flag.ANSWERED, true);
                                    }
                                    else if (flag.equals("\\Seen")) {
                                        imapMessage.setFlagInternal(Flag.SEEN, true);
                                    }
                                    else if (flag.equals("\\Flagged")) {
                                        imapMessage.setFlagInternal(Flag.FLAGGED, true);
                                    }
                                }
                            }
                        }
                        if (fp.contains(FetchProfile.Item.ENVELOPE)) {
                            Date internalDate = fetchList.getKeyedDate("INTERNALDATE");
                            int size = fetchList.getKeyedNumber("RFC822.SIZE");
                            InputStream headerStream = fetchList.getLiteral(fetchList.size() - 1);

                            ImapMessage imapMessage = (ImapMessage) message;

                            message.setInternalDate(internalDate);
                            imapMessage.setSize(size);
                            imapMessage.parse(headerStream);
                        }
                        if (fp.contains(FetchProfile.Item.STRUCTURE)) {
                            ImapList bs = fetchList.getKeyedList("BODYSTRUCTURE");
                            if (bs != null) {
                                try {
                                    parseBodyStructure(bs, message, "TEXT");
                                }
                                catch (MessagingException e) {
                                    if (Config.LOGV) {
                                        Log.v(k9.LOG_TAG, "Error handling message", e);
                                    }
                                    message.setBody(null);
                                }
                            }
                        }
                        if (fp.contains(FetchProfile.Item.BODY)) {
                            InputStream bodyStream = fetchList.getLiteral(fetchList.size() - 1);
                            ImapMessage imapMessage = (ImapMessage) message;
                            imapMessage.parse(bodyStream);
                        }
                        if (fp.contains(FetchProfile.Item.BODY_SANE)) {
                            InputStream bodyStream = fetchList.getLiteral(fetchList.size() - 1);
                            ImapMessage imapMessage = (ImapMessage) message;
                            imapMessage.parse(bodyStream);
                        }
                        for (Object o : fp) {
                            if (o instanceof Part) {
                                Part part = (Part) o;
                                InputStream bodyStream = fetchList.getLiteral(fetchList.size() - 1);
                                String contentType = part.getContentType();
                                String contentTransferEncoding = part.getHeader(
                                        MimeHeader.HEADER_CONTENT_TRANSFER_ENCODING)[0];
                                part.setBody(MimeUtility.decodeBody(
                                        bodyStream,
                                        contentTransferEncoding));
                            }
                        }

                        if (listener != null) {
                            listener.messageFinished(message, messageNumber, messageMap.size());
                        }
                    }

                    while (response.more());

                } while (response.mTag == null);
            }
            catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
        }

        @Override
        public Flag[] getPermanentFlags() throws MessagingException {
            return PERMANENT_FLAGS;
        }

        /**
         * Handle any untagged responses that the caller doesn't care to handle themselves.
         * @param responses
         */
        private void handleUntaggedResponses(List<ImapResponse> responses) {
            for (ImapResponse response : responses) {
                handleUntaggedResponse(response);
            }
        }

        /**
         * Handle an untagged response that the caller doesn't care to handle themselves.
         * @param response
         */
        private void handleUntaggedResponse(ImapResponse response) {
            if (response.mTag == null && response.get(1).equals("EXISTS")) {
                mMessageCount = response.getNumber(0);
            }
        }

        private void parseBodyStructure(ImapList bs, Part part, String id)
                throws MessagingException {
            if (bs.get(0) instanceof ImapList) {
                /*
                 * This is a multipart/*
                 */
                MimeMultipart mp = new MimeMultipart();
                for (int i = 0, count = bs.size(); i < count; i++) {
                    if (bs.get(i) instanceof ImapList) {
                        /*
                         * For each part in the message we're going to add a new BodyPart and parse
                         * into it.
                         */
                        ImapBodyPart bp = new ImapBodyPart();
                        if (id.equals("TEXT")) {
                            parseBodyStructure(bs.getList(i), bp, Integer.toString(i + 1));
                        }
                        else {
                            parseBodyStructure(bs.getList(i), bp, id + "." + (i + 1));
                        }
                        mp.addBodyPart(bp);
                    }
                    else {
                        /*
                         * We've got to the end of the children of the part, so now we can find out
                         * what type it is and bail out.
                         */
                        String subType = bs.getString(i);
                        mp.setSubType(subType.toLowerCase());
                        break;
                    }
                }
                part.setBody(mp);
            }
            else{
                /*
                 * This is a body. We need to add as much information as we can find out about
                 * it to the Part.
                 */

                /*
                 body type
                 body subtype
                 body parameter parenthesized list
                 body id
                 body description
                 body encoding
                 body size
                 */


                String type = bs.getString(0);
                String subType = bs.getString(1);
                String mimeType = (type + "/" + subType).toLowerCase();

                ImapList bodyParams = null;
                if (bs.get(2) instanceof ImapList) {
                    bodyParams = bs.getList(2);
                }
                String encoding = bs.getString(5);
                int size = bs.getNumber(6);

                if (MimeUtility.mimeTypeMatches(mimeType, "message/rfc822")) {
//                  A body type of type MESSAGE and subtype RFC822
//                  contains, immediately after the basic fields, the
//                  envelope structure, body structure, and size in
//                  text lines of the encapsulated message.
//                    [MESSAGE, RFC822, [NAME, Fwd: [#HTR-517941]:  update plans at 1am Friday - Memory allocation - displayware.eml], NIL, NIL, 7BIT, 5974, NIL, [INLINE, [FILENAME*0, Fwd: [#HTR-517941]:  update plans at 1am Friday - Memory all, FILENAME*1, ocation - displayware.eml]], NIL]
                    /*
                     * This will be caught by fetch and handled appropriately.
                     */
                    throw new MessagingException("BODYSTRUCTURE message/rfc822 not yet supported.");
                }

                /*
                 * Set the content type with as much information as we know right now.
                 */
                String contentType = String.format("%s", mimeType);

                if (bodyParams != null) {
                    /*
                     * If there are body params we might be able to get some more information out
                     * of them.
                     */
                    for (int i = 0, count = bodyParams.size(); i < count; i += 2) {
                        contentType += String.format(";\n %s=\"%s\"",
                                bodyParams.getString(i),
                                bodyParams.getString(i + 1));
                    }
                }

                part.setHeader(MimeHeader.HEADER_CONTENT_TYPE, contentType);

                // Extension items
                ImapList bodyDisposition = null;
                if (("text".equalsIgnoreCase(type))
                        && (bs.size() > 8)
                        && (bs.get(9) instanceof ImapList)) {
                    bodyDisposition = bs.getList(9);
                }
                else if (!("text".equalsIgnoreCase(type))
                        && (bs.size() > 7)
                        && (bs.get(8) instanceof ImapList)) {
                    bodyDisposition = bs.getList(8);
                }

                String contentDisposition = "";

                if (bodyDisposition != null && bodyDisposition.size() > 0) {
                    if (!"NIL".equalsIgnoreCase(bodyDisposition.getString(0))) {
                        contentDisposition = bodyDisposition.getString(0).toLowerCase();
                    }

                    if ((bodyDisposition.size() > 1)
                            && (bodyDisposition.get(1) instanceof ImapList)) {
                        ImapList bodyDispositionParams = bodyDisposition.getList(1);
                        /*
                         * If there is body disposition information we can pull some more information
                         * about the attachment out.
                         */
                        for (int i = 0, count = bodyDispositionParams.size(); i < count; i += 2) {
                            contentDisposition += String.format(";\n %s=\"%s\"",
                                    bodyDispositionParams.getString(i).toLowerCase(),
                                    bodyDispositionParams.getString(i + 1));
                        }
                    }
                }

                if (MimeUtility.getHeaderParameter(contentDisposition, "size") == null) {
                    contentDisposition += String.format(";\n size=%d", size);
                }

                /*
                 * Set the content disposition containing at least the size. Attachment
                 * handling code will use this down the road.
                 */
                part.setHeader(MimeHeader.HEADER_CONTENT_DISPOSITION, contentDisposition);


                /*
                 * Set the Content-Transfer-Encoding header. Attachment code will use this
                 * to parse the body.
                 */
                part.setHeader(MimeHeader.HEADER_CONTENT_TRANSFER_ENCODING, encoding);

                if (part instanceof ImapMessage) {
                    ((ImapMessage) part).setSize(size);
                }
                else if (part instanceof ImapBodyPart) {
                    ((ImapBodyPart) part).setSize(size);
                }
                else {
                    throw new MessagingException("Unknown part type " + part.toString());
                }
                part.setHeader(MimeHeader.HEADER_ANDROID_ATTACHMENT_STORE_DATA, id);
            }

        }

        /**
         * Appends the given messages to the selected folder. This implementation also determines
         * the new UID of the given message on the IMAP server and sets the Message's UID to the
         * new server UID.
         */
        public void appendMessages(Message[] messages) throws MessagingException {
            checkOpen();
            try {
                for (Message message : messages) {
                    CountingOutputStream out = new CountingOutputStream();
                    EOLConvertingOutputStream eolOut = new EOLConvertingOutputStream(out);
                    message.writeTo(eolOut);
                    eolOut.flush();
                    mConnection.sendCommand(
                            String.format("APPEND \"%s\" {%d}",
                                    encodeFolderName(mName),
                                    out.getCount()), false);
                    ImapResponse response;
                    do {
                        response = mConnection.readResponse();
                        if (response.mCommandContinuationRequested) {
                            eolOut = new EOLConvertingOutputStream(mConnection.mOut);
                            message.writeTo(eolOut);
                            eolOut.write('\r');
                            eolOut.write('\n');
                            eolOut.flush();
                        }
                        else if (response.mTag == null) {
                            handleUntaggedResponse(response);
                        }
                        while (response.more());
                    } while(response.mTag == null);

                    /*
                     * Try to find the UID of the message we just appended using the
                     * Message-ID header.
                     */
                    String[] messageIdHeader = message.getHeader("Message-ID");
                    if (messageIdHeader == null || messageIdHeader.length == 0) {
                        continue;
                    }
                    String messageId = messageIdHeader[0];
                    List<ImapResponse> responses =
                        mConnection.executeSimpleCommand(
                                String.format("UID SEARCH (HEADER MESSAGE-ID %s)", messageId));
                    for (ImapResponse response1 : responses) {
                        if (response1.mTag == null && response1.get(0).equals("SEARCH")
                                && response1.size() > 1) {
                            message.setUid(response1.getString(1));
                        }
                    }

                }
            }
            catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
        }

        public Message[] expunge() throws MessagingException {
            checkOpen();
            try {
                handleUntaggedResponses(mConnection.executeSimpleCommand("EXPUNGE"));
            } catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
            return null;
        }

        public void setFlags(Message[] messages, Flag[] flags, boolean value)
                throws MessagingException {
            checkOpen();
            String[] uids = new String[messages.length];
            for (int i = 0, count = messages.length; i < count; i++) {
                uids[i] = messages[i].getUid();
            }
            ArrayList<String> flagNames = new ArrayList<String>();
            for (int i = 0, count = flags.length; i < count; i++) {
                Flag flag = flags[i];
                if (flag == Flag.SEEN) {
                    flagNames.add("\\Seen");
                }
                else if (flag == Flag.DELETED) {
                    flagNames.add("\\Deleted");
                }
            }
            try {
                mConnection.executeSimpleCommand(String.format("UID STORE %s %sFLAGS.SILENT (%s)",
                        Utility.combine(uids, ','),
                        value ? "+" : "-",
                        Utility.combine(flagNames.toArray(new String[flagNames.size()]), ' ')));
            }
            catch (IOException ioe) {
                throw ioExceptionHandler(mConnection, ioe);
            }
        }

        private void checkOpen() throws MessagingException {
            if (!isOpen()) {
                throw new MessagingException("Folder " + mName + " is not open.");
            }
        }

        private MessagingException ioExceptionHandler(ImapConnection connection, IOException ioe)
                throws MessagingException {
            connection.close();
            close(false);
            return new MessagingException("IO Error", ioe);
        }

        @Override
        public boolean equals(Object o) {
            if (o instanceof ImapFolder) {
                return ((ImapFolder)o).mName.equals(mName);
            }
            return super.equals(o);
        }
    }

    /**
     * A cacheable class that stores the details for a single IMAP connection.
     */
    class ImapConnection {
        private Socket mSocket;
        private PeekableInputStream mIn;
        private OutputStream mOut;
        private ImapResponseParser mParser;
        private int mNextCommandTag;

        public void open() throws IOException, MessagingException {
            if (isOpen()) {
                return;
            }

            mNextCommandTag = 1;

            try {
                SocketAddress socketAddress = new InetSocketAddress(mHost, mPort);
                if (mConnectionSecurity == CONNECTION_SECURITY_SSL_REQUIRED ||
                        mConnectionSecurity == CONNECTION_SECURITY_SSL_OPTIONAL) {
                    SSLContext sslContext = SSLContext.getInstance("TLS");
                    final boolean secure = mConnectionSecurity == CONNECTION_SECURITY_SSL_REQUIRED;
                    sslContext.init(null, new TrustManager[] {
                            TrustManagerFactory.get(mHost, secure)
                    }, new SecureRandom());
                    mSocket = sslContext.getSocketFactory().createSocket();
                    mSocket.connect(socketAddress, SOCKET_CONNECT_TIMEOUT);
                } else {
                    mSocket = new Socket();
                    mSocket.connect(socketAddress, SOCKET_CONNECT_TIMEOUT);
                }

                mSocket.setSoTimeout(Store.SOCKET_READ_TIMEOUT);

                mIn = new PeekableInputStream(new BufferedInputStream(mSocket.getInputStream(),
                        1024));
                mParser = new ImapResponseParser(mIn);
                mOut = mSocket.getOutputStream();

                // BANNER
                mParser.readResponse();

                if (mConnectionSecurity == CONNECTION_SECURITY_TLS_OPTIONAL
                        || mConnectionSecurity == CONNECTION_SECURITY_TLS_REQUIRED) {
                    // CAPABILITY
                    List<ImapResponse> responses = executeSimpleCommand("CAPABILITY");
                    if (responses.size() != 2) {
                        throw new MessagingException("Invalid CAPABILITY response received");
                    }
                    if (responses.get(0).contains("STARTTLS")) {
                        // STARTTLS
                        executeSimpleCommand("STARTTLS");

                        SSLContext sslContext = SSLContext.getInstance("TLS");
                        boolean secure = mConnectionSecurity == CONNECTION_SECURITY_TLS_REQUIRED;
                        sslContext.init(null, new TrustManager[] {
                                TrustManagerFactory.get(mHost, secure)
                        }, new SecureRandom());
                        mSocket = sslContext.getSocketFactory().createSocket(mSocket, mHost, mPort,
                                true);
                        mSocket.setSoTimeout(Store.SOCKET_READ_TIMEOUT);
                        mIn = new PeekableInputStream(new BufferedInputStream(mSocket
                                .getInputStream(), 1024));
                        mParser = new ImapResponseParser(mIn);
                        mOut = mSocket.getOutputStream();
                    } else if (mConnectionSecurity == CONNECTION_SECURITY_TLS_REQUIRED) {
                        throw new MessagingException("TLS not supported but required");
                    }
                }

                mOut = new BufferedOutputStream(mOut);

                try {
                    // TODO eventually we need to add additional authentication
                    // options such as SASL
                    executeSimpleCommand("LOGIN " + mUsername + " " + mPassword, true);
                } catch (ImapException ie) {
                    throw new AuthenticationFailedException(ie.getAlertText(), ie);

                } catch (MessagingException me) {
                    throw new AuthenticationFailedException(null, me);
                }
            } catch (SSLException e) {
                throw new CertificateValidationException(e.getMessage(), e);
            } catch (GeneralSecurityException gse) {
                throw new MessagingException(
                        "Unable to open connection to IMAP server due to security error.", gse);
            }
        }

        public boolean isOpen() {
            return (mIn != null && mOut != null && mSocket != null && mSocket.isConnected() && !mSocket
                    .isClosed());
        }

        public void close() {
//            if (isOpen()) {
//                try {
//                    executeSimpleCommand("LOGOUT");
//                } catch (Exception e) {
//
//                }
//            }
            try {
                mIn.close();
            } catch (Exception e) {

            }
            try {
                mOut.close();
            } catch (Exception e) {

            }
            try {
                mSocket.close();
            } catch (Exception e) {

            }
            mIn = null;
            mOut = null;
            mSocket = null;
        }

        public ImapResponse readResponse() throws IOException, MessagingException {
            return mParser.readResponse();
        }

        public String sendCommand(String command, boolean sensitive)
            throws MessagingException, IOException {
            open();
            String tag = Integer.toString(mNextCommandTag++);
            String commandToSend = tag + " " + command;
            mOut.write(commandToSend.getBytes());
            mOut.write('\r');
            mOut.write('\n');
            mOut.flush();
            if (Config.LOGD) {
                if (k9.DEBUG) {
                    if (sensitive && !k9.DEBUG_SENSITIVE) {
                        Log.d(k9.LOG_TAG, ">>> "
                                + "[Command Hidden, Enable Sensitive Debug Logging To Show]");
                    } else {
                        Log.d(k9.LOG_TAG, ">>> " + commandToSend);
                    }
                }
            }
            return tag;
        }

        public List<ImapResponse> executeSimpleCommand(String command) throws IOException,
                ImapException, MessagingException {
            return executeSimpleCommand(command, false);
        }

        public List<ImapResponse> executeSimpleCommand(String command, boolean sensitive)
                throws IOException, ImapException, MessagingException {
            String tag = sendCommand(command, sensitive);
            ArrayList<ImapResponse> responses = new ArrayList<ImapResponse>();
            ImapResponse response;
            do {
                response = mParser.readResponse();
                responses.add(response);
            } while (response.mTag == null);
            if (response.size() < 1 || !response.get(0).equals("OK")) {
                throw new ImapException(response.toString(), response.getAlertText());
            }
            return responses;
        }
    }

    class ImapMessage extends MimeMessage {
        ImapMessage(String uid, Folder folder) throws MessagingException {
            this.mUid = uid;
            this.mFolder = folder;
        }

        public void setSize(int size) {
            this.mSize = size;
        }

        public void parse(InputStream in) throws IOException, MessagingException {
            super.parse(in);
        }

        public void setFlagInternal(Flag flag, boolean set) throws MessagingException {
            super.setFlag(flag, set);
        }

        @Override
        public void setFlag(Flag flag, boolean set) throws MessagingException {
            super.setFlag(flag, set);
            mFolder.setFlags(new Message[] { this }, new Flag[] { flag }, set);
        }
    }

    class ImapBodyPart extends MimeBodyPart {
        public ImapBodyPart() throws MessagingException {
            super();
        }

        public void setSize(int size) {
            this.mSize = size;
        }
    }

    class ImapException extends MessagingException {
        String mAlertText;

        public ImapException(String message, String alertText, Throwable throwable) {
            super(message, throwable);
            this.mAlertText = alertText;
        }

        public ImapException(String message, String alertText) {
            super(message);
            this.mAlertText = alertText;
        }

        public String getAlertText() {
            return mAlertText;
        }

        public void setAlertText(String alertText) {
            mAlertText = alertText;
        }
    }
}