/*
    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.wiki.filters;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
import java.util.Iterator;
import java.util.Properties;
import java.util.Random;
import java.util.StringTokenizer;
import java.util.Vector;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.jsp.PageContext;

import org.apache.commons.lang.time.StopWatch;
import org.apache.log4j.Logger;
import org.apache.oro.text.regex.MalformedPatternException;
import org.apache.oro.text.regex.MatchResult;
import org.apache.oro.text.regex.Pattern;
import org.apache.oro.text.regex.PatternCompiler;
import org.apache.oro.text.regex.PatternMatcher;
import org.apache.oro.text.regex.Perl5Compiler;
import org.apache.oro.text.regex.Perl5Matcher;
import org.apache.wiki.InternalWikiException;
import org.apache.wiki.WikiContext;
import org.apache.wiki.WikiEngine;
import org.apache.wiki.WikiPage;
import org.apache.wiki.WikiProvider;
import org.apache.wiki.api.exceptions.ProviderException;
import org.apache.wiki.api.exceptions.RedirectException;
import org.apache.wiki.api.filters.BasicPageFilter;
import org.apache.wiki.attachment.Attachment;
import org.apache.wiki.auth.user.UserProfile;
import org.apache.wiki.ui.EditorManager;
import org.apache.wiki.util.FileUtil;
import org.apache.wiki.util.HttpUtil;
import org.apache.wiki.util.TextUtil;
import org.suigeneris.jrcs.diff.Diff;
import org.suigeneris.jrcs.diff.DifferentiationFailedException;
import org.suigeneris.jrcs.diff.Revision;
import org.suigeneris.jrcs.diff.delta.AddDelta;
import org.suigeneris.jrcs.diff.delta.ChangeDelta;
import org.suigeneris.jrcs.diff.delta.DeleteDelta;
import org.suigeneris.jrcs.diff.delta.Delta;
import org.suigeneris.jrcs.diff.myers.MyersDiff;

import net.sf.akismet.Akismet;


/**
 *  This is Herb, the JSPWiki spamfilter that can also do choke modifications.
 *
 *  Parameters:
 *  <ul>
 *    <li>wordlist - Page name where the spamword regexps are found.  Use [{SET spamwords='regexp list separated with spaces'}] on
 *     that page.  Default is "SpamFilterWordList".
 *    <li>IPlist - Page name where the IP regexps are found.  Use [{SET ips='regexp list separated with spaces'}] on
 *     that page.  Default is "SpamFilterIPList".
 *    <li>blacklist - The name of an attachment containing the list of spam patterns, one per line. Default is
 *        "SpamFilterWordList/blacklist.txt"</li>
 *    <li>errorpage - The page to which the user is redirected.  Has a special variable $msg which states the reason. Default is "RejectedMessage".
 *    <li>pagechangesinminute - How many page changes are allowed/minute.  Default is 5.</li>
 *    <li>similarchanges - How many similar page changes are allowed before the host is banned.  Default is 2.  (since 2.4.72)</li>
 *    <li>bantime - How long an IP address stays on the temporary ban list (default is 60 for 60 minutes).</li>
 *    <li>maxurls - How many URLs can be added to the page before it is considered spam (default is 5)</li>
 *    <li>akismet-apikey - The Akismet API key (see akismet.org)</li>
 *    <li>ignoreauthenticated - If set to "true", all authenticated users are ignored and never caught in SpamFilter</li>
 *    <li>captcha - Sets the captcha technology to use.  Current allowed values are "none" and "asirra".</li>
 *    <li>strategy - Sets the filtering strategy to use.  If set to "eager", will stop at the first probable
 *        match, and won't consider any other tests.  This is the default, as it's considerably lighter. If set to "score", will go through all of the tests
 *        and calculates a score for the spam, which is then compared to a filter level value.
 *  </ul>
 *
 *  <p>Please see the default editors/plain.jsp for examples on how the SpamFilter integrates
 *  with the editor system.</p>
 *  
 *  <p>Changes by admin users are ignored in any case.</p>
 *
 *  @since 2.1.112
 */
public class SpamFilter extends BasicPageFilter {
    
    private static final String ATTR_SPAMFILTER_SCORE = "spamfilter.score";
    private static final String REASON_REGEXP = "Regexp";
    private static final String REASON_IP_BANNED_TEMPORARILY = "IPBannedTemporarily";
    private static final String REASON_IP_BANNED_PERMANENTLY = "IPBannedPermanently";
    private static final String REASON_BOT_TRAP = "BotTrap";
    private static final String REASON_AKISMET = "Akismet";
    private static final String REASON_TOO_MANY_URLS = "TooManyUrls";
    private static final String REASON_SIMILAR_MODIFICATIONS = "SimilarModifications";
    private static final String REASON_TOO_MANY_MODIFICATIONS = "TooManyModifications";
    private static final String REASON_UTF8_TRAP = "UTF8Trap";

    private static final String LISTVAR = "spamwords";
    private static final String LISTIPVAR = "ips";

    /** The filter property name for specifying the page which contains the list of spamwords.
     *  Value is <tt>{@value}</tt>. */
    public static final String  PROP_WORDLIST              = "wordlist";

    /** The filter property name for specifying the page which contains the list of IPs to ban.
     *  Value is <tt>{@value}</tt>. */
    public static final String  PROP_IPLIST              = "IPlist";

    /** The filter property name for the page to which you are directed if Herb rejects your
     *  edit.  Value is <tt>{@value}</tt>. */
    public static final String  PROP_ERRORPAGE             = "errorpage";
    
    /** The filter property name for specifying how many changes is any given IP address
     *  allowed to do per minute.  Value is <tt>{@value}</tt>.
     */
    public static final String  PROP_PAGECHANGES           = "pagechangesinminute";
    
    /** The filter property name for specifying how many similar changes are allowed
     *  before a host is banned.  Value is <tt>{@value}</tt>.
     */
    public static final String  PROP_SIMILARCHANGES        = "similarchanges";
    
    /** The filter property name for specifying how long a host is banned.  Value is <tt>{@value}</tt>.*/
    public static final String  PROP_BANTIME               = "bantime";
    
    /** The filter property name for the attachment containing the blacklist.  Value is <tt>{@value}</tt>.*/
    public static final String  PROP_BLACKLIST             = "blacklist";
    
    /** The filter property name for specifying how many URLs can any given edit contain.  
     *  Value is <tt>{@value}</tt> */
    public static final String  PROP_MAXURLS               = "maxurls";
    
    /** The filter property name for specifying the Akismet API-key.  Value is <tt>{@value}</tt>. */
    public static final String  PROP_AKISMET_API_KEY       = "akismet-apikey";
    
    /** The filter property name for specifying whether authenticated users should be ignored. Value is <tt>{@value}</tt>. */
    public static final String  PROP_IGNORE_AUTHENTICATED  = "ignoreauthenticated";
    
    /** The filter property name for specifying which captcha technology should be used. Value is <tt>{@value}</tt>. */
    public static final String  PROP_CAPTCHA               = "captcha";
    
    /** The filter property name for specifying which filter strategy should be used.  Value is <tt>{@value}</tt>. */
    public static final String  PROP_FILTERSTRATEGY        = "strategy";

    /** The string specifying the "eager" strategy. Value is <tt>{@value}</tt>. */
    public static final String  STRATEGY_EAGER             = "eager";
    
    /** The string specifying the "score" strategy. Value is <tt>{@value}</tt>. */
    public static final String  STRATEGY_SCORE             = "score";

    private static final String URL_REGEXP = "(http://|https://|mailto:)([A-Za-z0-9_/\\.\\+\\?\\#\\-\\@=&;]+)";

    private String          m_forbiddenWordsPage = "SpamFilterWordList";
    private String          m_forbiddenIPsPage   = "SpamFilterIPList";
    private String          m_errorPage          = "RejectedMessage";
    private String          m_blacklist          = "SpamFilterWordList/blacklist.txt";

    private PatternMatcher  m_matcher = new Perl5Matcher();
    private PatternCompiler m_compiler = new Perl5Compiler();

    private Collection<Pattern> m_spamPatterns = null;
    private Collection<Pattern> m_IPPatterns = null;

    private Date            m_lastRebuild = new Date( 0L );

    private static  Logger  c_spamlog = Logger.getLogger( "SpamLog" );
    private static  Logger  log = Logger.getLogger( SpamFilter.class );


    private Vector<Host>    m_temporaryBanList = new Vector<Host>();

    private int             m_banTime = 60; // minutes

    private Vector<Host>    m_lastModifications = new Vector<Host>();

    /**
     *  How many times a single IP address can change a page per minute?
     */
    private int             m_limitSinglePageChanges = 5;

    /**
     *  How many times can you add the exact same string to a page?
     */
    private int             m_limitSimilarChanges = 2;

    /**
     *  How many URLs can be added at maximum.
     */
    private int             m_maxUrls = 10;

    private Pattern         m_urlPattern;
    private Akismet         m_akismet;

    private String          m_akismetAPIKey = null;

    private boolean         m_useCaptcha = false;

    /** The limit at which we consider something to be spam. */
    private int             m_scoreLimit = 1;

    /**
     * If set to true, will ignore anyone who is in Authenticated role.
     */
    private boolean         m_ignoreAuthenticated = false;

    private boolean         m_stopAtFirstMatch = true;

    private static String   c_hashName;
    private static long     c_lastUpdate;

    /** The HASH_DELAY value is a maximum amount of time that an user can keep
     *  a session open, because after the value has expired, we will invent a new
     *  hash field name.  By default this is {@value} hours, which should be ample
     *  time for someone.
     */
    private static final long HASH_DELAY = 24;


    /**
     *  {@inheritDoc}
     */
    @Override
    public void initialize( WikiEngine engine, Properties properties ) {
        m_forbiddenWordsPage = properties.getProperty( PROP_WORDLIST, m_forbiddenWordsPage );
        m_forbiddenIPsPage = properties.getProperty( PROP_IPLIST, m_forbiddenIPsPage);
        m_errorPage = properties.getProperty( PROP_ERRORPAGE, m_errorPage );
        m_limitSinglePageChanges = TextUtil.getIntegerProperty( properties,
                                                                PROP_PAGECHANGES,
                                                                m_limitSinglePageChanges );
        
        m_limitSimilarChanges = TextUtil.getIntegerProperty( properties,
                                                             PROP_SIMILARCHANGES,
                                                             m_limitSimilarChanges );

        m_maxUrls = TextUtil.getIntegerProperty( properties, PROP_MAXURLS, m_maxUrls );
        m_banTime = TextUtil.getIntegerProperty( properties, PROP_BANTIME, m_banTime );
        m_blacklist = properties.getProperty( PROP_BLACKLIST, m_blacklist );

        m_ignoreAuthenticated = TextUtil.getBooleanProperty( properties,
                                                             PROP_IGNORE_AUTHENTICATED,
                                                             m_ignoreAuthenticated );

        m_useCaptcha = properties.getProperty( PROP_CAPTCHA, "" ).equals("asirra");

        try {
            m_urlPattern = m_compiler.compile( URL_REGEXP );
        } catch( MalformedPatternException e ) {
            log.fatal( "Internal error: Someone put in a faulty pattern.", e );
            throw new InternalWikiException( "Faulty pattern." );
        }

        m_akismetAPIKey = TextUtil.getStringProperty( properties,
                                                      PROP_AKISMET_API_KEY,
                                                      m_akismetAPIKey );

        m_stopAtFirstMatch = TextUtil.getStringProperty( properties,
                                                         PROP_FILTERSTRATEGY,
                                                         STRATEGY_EAGER ).equals( STRATEGY_EAGER );

        log.info( "# Spam filter initialized.  Temporary ban time " + m_banTime +
                  " mins, max page changes/minute: " + m_limitSinglePageChanges );


    }

    private static final int REJECT = 0;
    private static final int ACCEPT = 1;
    private static final int NOTE   = 2;

    private static String log( WikiContext ctx, int type, String source, String message ) {
        message = TextUtil.replaceString( message, "\r\n", "\\r\\n" );
        message = TextUtil.replaceString( message, "\"", "\\\"" );

        String uid = getUniqueID();

        String page   = ctx.getPage().getName();
        String reason = "UNKNOWN";
        String addr   = ctx.getHttpRequest() != null ? HttpUtil.getRemoteAddress( ctx.getHttpRequest() ) : "-";

        switch( type ) {
            case REJECT:
                reason = "REJECTED";
                break;
            case ACCEPT:
                reason = "ACCEPTED";
                break;
            case NOTE:
                reason = "NOTE";
                break;
            default:
                throw new InternalWikiException( "Illegal type " + type );
        }
        c_spamlog.info( reason + " " + source + " " + uid + " " + addr + " \"" + page + "\" " + message );

        return uid;
    }

    /** {@inheritDoc} */
    public String preSave( WikiContext context, String content ) throws RedirectException {
        cleanBanList();
        refreshBlacklists( context );
        Change change = getChange( context, content );

        if( !ignoreThisUser( context ) ) {
            checkBanList( context, change );
            checkSinglePageChange( context, content, change );
            checkIPList( context );
            checkPatternList( context, content, change );
        }

        if( !m_stopAtFirstMatch ) {
            Integer score = ( Integer )context.getVariable( ATTR_SPAMFILTER_SCORE );

            if( score != null && score.intValue() >= m_scoreLimit ) {
                throw new RedirectException( "Herb says you got too many points", getRedirectPage( context ) );
            }
        }

        log( context, ACCEPT, "-", change.toString() );
        return content;
    }

    private void checkStrategy( WikiContext context, String error, String message ) throws RedirectException {
        if( m_stopAtFirstMatch ) {
            throw new RedirectException( message, getRedirectPage( context ) );
        }

        Integer score = ( Integer )context.getVariable( ATTR_SPAMFILTER_SCORE );
        if( score != null ) {
            score = score + 1;
        } else {
            score = 1;
        }

        context.setVariable( ATTR_SPAMFILTER_SCORE, score );
    }
    
    /**
     *  Parses a list of patterns and returns a Collection of compiled Pattern
     *  objects.
     *
     * @param source
     * @param list
     * @return A Collection of the Patterns that were found from the lists.
     */
    private Collection< Pattern > parseWordList( WikiPage source, String list ) {
        ArrayList< Pattern > compiledpatterns = new ArrayList< Pattern >();

        if( list != null ) {
            StringTokenizer tok = new StringTokenizer( list, " \t\n" );

            while( tok.hasMoreTokens() ) {
                String pattern = tok.nextToken();

                try {
                    compiledpatterns.add( m_compiler.compile( pattern ) );
                } catch( MalformedPatternException e ) {
                    log.debug( "Malformed spam filter pattern " + pattern );
                    source.setAttribute("error", "Malformed spam filter pattern " + pattern);
                }
            }
        }

        return compiledpatterns;
    }

    /**
     *  Takes a MT-Blacklist -formatted blacklist and returns a list of compiled Pattern objects.
     *
     *  @param list
     *  @return The parsed blacklist patterns.
     */
    private Collection< Pattern > parseBlacklist( String list ) {
        ArrayList< Pattern > compiledpatterns = new ArrayList< Pattern >();

        if( list != null ) {
            try {
                BufferedReader in = new BufferedReader( new StringReader(list) );
                String line;
                while( (line = in.readLine() ) != null ) {
                    line = line.trim();
                    if( line.length() == 0 ) continue; // Empty line
                    if( line.startsWith("#") ) continue; // It's a comment

                    int ws = line.indexOf( ' ' );
                    if( ws == -1 ) ws = line.indexOf( '\t' );
                    if( ws != -1 ) line = line.substring( 0, ws );

                    try {
                        compiledpatterns.add( m_compiler.compile( line ) );
                    } catch( MalformedPatternException e ) {
                        log.debug( "Malformed spam filter pattern " + line );
                    }
                }
            } catch( IOException e ) {
                log.info( "Could not read patterns; returning what I got" , e );
            }
        }

        return compiledpatterns;
    }

    /**
     *  Takes a single page change and performs a load of tests on the content change.
     *  An admin can modify anything.
     *
     *  @param context
     *  @param content
     *  @throws RedirectException
     */
    private synchronized void checkSinglePageChange( WikiContext context, String content, Change change ) 
            throws RedirectException {
        HttpServletRequest req = context.getHttpRequest();

        if( req != null ) {
            String addr = HttpUtil.getRemoteAddress( req );
            int hostCounter = 0;
            int changeCounter = 0;

            log.debug( "Change is " + change.m_change );

            long time = System.currentTimeMillis() - 60*1000L; // 1 minute

            for( Iterator< Host > i = m_lastModifications.iterator(); i.hasNext(); ) {
                Host host = i.next();

                //
                //  Check if this item is invalid
                //
                if( host.getAddedTime() < time ) {
                    log.debug( "Removed host " + host.getAddress() + " from modification queue (expired)" );
                    i.remove();
                    continue;
                }

                //
                // Check if this IP address has been seen before
                //

                if( host.getAddress().equals( addr ) ) {
                    hostCounter++;
                }

                //
                //  Check, if this change has been seen before
                //

                if( host.getChange() != null && host.getChange().equals( change ) ) {
                    changeCounter++;
                }
            }

            //
            //  Now, let's check against the limits.
            //
            if( hostCounter >= m_limitSinglePageChanges ) {
                Host host = new Host( addr, null );
                m_temporaryBanList.add( host );

                String uid = log( context, REJECT, REASON_TOO_MANY_MODIFICATIONS, change.m_change );
                log.info( "SPAM:TooManyModifications (" + uid + "). Added host " + addr + " to temporary ban list for doing too many modifications/minute" );
                checkStrategy( context, REASON_TOO_MANY_MODIFICATIONS, "Herb says you look like a spammer, and I trust Herb! (Incident code " + uid + ")" );
            }

            if( changeCounter >= m_limitSimilarChanges ) {
                Host host = new Host( addr, null );
                m_temporaryBanList.add( host );

                String uid = log( context, REJECT, REASON_SIMILAR_MODIFICATIONS, change.m_change );
                log.info( "SPAM:SimilarModifications (" + uid + "). Added host " + addr + " to temporary ban list for doing too many similar modifications" );
                checkStrategy( context, REASON_SIMILAR_MODIFICATIONS, "Herb says you look like a spammer, and I trust Herb! (Incident code "+uid+")");
            }

            //
            //  Calculate the number of links in the addition.
            //
            String tstChange  = change.toString();
            int    urlCounter = 0;
            while( m_matcher.contains( tstChange,m_urlPattern ) ) {
                MatchResult m = m_matcher.getMatch();
                tstChange = tstChange.substring( m.endOffset(0) );
                urlCounter++;
            }

            if( urlCounter > m_maxUrls ) {
                Host host = new Host( addr, null );
                m_temporaryBanList.add( host );

                String uid = log( context, REJECT, REASON_TOO_MANY_URLS, change.toString() );
                log.info( "SPAM:TooManyUrls (" + uid + "). Added host " + addr + " to temporary ban list for adding too many URLs" );
                checkStrategy( context, REASON_TOO_MANY_URLS, "Herb says you look like a spammer, and I trust Herb! (Incident code " + uid + ")" );
            }

            //
            //  Check bot trap
            //
            checkBotTrap( context, change );

            //
            //  Check UTF-8 mangling
            //
            checkUTF8( context, change );

            //
            //  Do Akismet check.  This is good to be the last, because this is the most
            //  expensive operation.
            //
            checkAkismet( context, change );

            m_lastModifications.add( new Host( addr, change ) );
        }
    }


    /**
     *  Checks against the akismet system.
     *
     * @param context
     * @param change
     * @throws RedirectException
     */
    private void checkAkismet( WikiContext context, Change change ) throws RedirectException {
        if( m_akismetAPIKey != null ) {
            if( m_akismet == null ) {
                log.info( "Initializing Akismet spam protection." );
                m_akismet = new Akismet( m_akismetAPIKey, context.getEngine().getBaseURL() );

                if( !m_akismet.verifyAPIKey() ) {
                    log.error( "Akismet API key cannot be verified.  Please check your config." );
                    m_akismetAPIKey = null;
                    m_akismet = null;
                }
            }

            HttpServletRequest req = context.getHttpRequest();

            //
            //  Akismet will mark all empty statements as spam, so we'll just
            //  ignore them.
            //
            if( change.m_adds == 0 && change.m_removals > 0 ) {
                return;
            }
            
            if( req != null && m_akismet != null ) {
                log.debug( "Calling Akismet to check for spam..." );

                StopWatch sw = new StopWatch();
                sw.start();

                String ipAddress     = HttpUtil.getRemoteAddress( req );
                String userAgent     = req.getHeader( "User-Agent" );
                String referrer      = req.getHeader( "Referer");
                String permalink     = context.getViewURL( context.getPage().getName() );
                String commentType   = context.getRequestContext().equals( WikiContext.COMMENT ) ? "comment" : "edit";
                String commentAuthor = context.getCurrentUser().getName();
                String commentAuthorEmail = null;
                String commentAuthorURL   = null;

                boolean isSpam = m_akismet.commentCheck( ipAddress,
                                                         userAgent,
                                                         referrer,
                                                         permalink,
                                                         commentType,
                                                         commentAuthor,
                                                         commentAuthorEmail,
                                                         commentAuthorURL,
                                                         change.toString(),
                                                         null );

                sw.stop();
                log.debug( "Akismet request done in: " + sw );

                if( isSpam ) {
                    // Host host = new Host( ipAddress, null );
                    // m_temporaryBanList.add( host );

                    String uid = log( context, REJECT, REASON_AKISMET, change.toString() );
                    log.info( "SPAM:Akismet (" + uid + "). Akismet thinks this change is spam; added host to temporary ban list." );
                    checkStrategy( context, REASON_AKISMET, "Akismet tells Herb you're a spammer, Herb trusts Akismet, and I trust Herb! (Incident code " + uid + ")" );
                }
            }
        }
    }

    /**
     * Returns a static string which can be used to detect spambots which just wildly fill in all the fields.
     *
     * @return A string
     */
    public static String getBotFieldName() {
        return "submit_auth";
    }

    /**
     * This checks whether an invisible field is available in the request, and whether it's contents are suspected spam.
     *
     * @param context
     * @param change
     * @throws RedirectException
     */
    private void checkBotTrap( WikiContext context, Change change ) throws RedirectException {
        HttpServletRequest request = context.getHttpRequest();

        if( request != null ) {
            String unspam = request.getParameter( getBotFieldName() );
            if( unspam != null && unspam.length() > 0 ) {
                String uid = log( context, REJECT, REASON_BOT_TRAP, change.toString() );

                log.info( "SPAM:BotTrap (" + uid + ").  Wildly behaving bot detected." );
                checkStrategy( context, REASON_BOT_TRAP, "Spamming attempt detected. (Incident code " + uid + ")" );
            }
        }
    }

    private void checkUTF8( WikiContext context, Change change ) throws RedirectException {
        HttpServletRequest request = context.getHttpRequest();

        if( request != null ) {
            String utf8field = request.getParameter( "encodingcheck" );

            if( utf8field != null && !utf8field.equals( "\u3041" ) ) {
                String uid = log( context, REJECT, REASON_UTF8_TRAP, change.toString() );

                log.info( "SPAM:UTF8Trap (" + uid + ").  Wildly posting dumb bot detected." );
                checkStrategy( context, REASON_UTF8_TRAP, "Spamming attempt detected. (Incident code " + uid + ")" );
            }
        }
    }

    /** Goes through the ban list and cleans away any host which has expired from it. */
    private synchronized void cleanBanList() {
        long now = System.currentTimeMillis();

        for( Iterator< Host > i = m_temporaryBanList.iterator(); i.hasNext(); ) {
            Host host = i.next();

            if( host.getReleaseTime() < now ) {
                log.debug( "Removed host " + host.getAddress() + " from temporary ban list (expired)" );
                i.remove();
            }
        }
    }

    /**
     *  Checks the ban list if the IP address of the changer is already on it.
     *
     *  @param context
     *  @throws RedirectException
     */
    private void checkBanList( WikiContext context, Change change ) throws RedirectException {
        HttpServletRequest req = context.getHttpRequest();

        if( req != null ) {
            String remote = HttpUtil.getRemoteAddress(req);
            long now = System.currentTimeMillis();

            for( Iterator< Host > i = m_temporaryBanList.iterator(); i.hasNext(); ) {
                Host host = i.next();

                if( host.getAddress().equals( remote ) ) {
                    long timeleft = ( host.getReleaseTime() - now ) / 1000L;

                    log( context, REJECT, REASON_IP_BANNED_TEMPORARILY, change.m_change );
                    checkStrategy( context, REASON_IP_BANNED_TEMPORARILY, "You have been temporarily banned from modifying this wiki. (" + timeleft + " seconds of ban left)" );
                }
            }
        }
    }

    /**
     *  If the spam filter notices changes in the black list page, it will refresh them automatically.
     *
     *  @param context
     */
    private void refreshBlacklists( WikiContext context ) {
        try {

            boolean rebuild = false;

            //
            //  Rebuild, if the spam words page, the attachment or the IP ban page has changed since.
            //
            WikiPage sourceSpam = context.getEngine().getPage( m_forbiddenWordsPage );
            if( sourceSpam != null ) {
                if( m_spamPatterns == null || m_spamPatterns.isEmpty() || sourceSpam.getLastModified().after( m_lastRebuild ) ) {
                    rebuild = true;
                }
            }

            Attachment att = context.getEngine().getAttachmentManager().getAttachmentInfo( context, m_blacklist );
            if( att != null ) {
                if( m_spamPatterns == null || m_spamPatterns.isEmpty() || att.getLastModified().after( m_lastRebuild ) ) {
                    rebuild = true;
                }
            }

            WikiPage sourceIPs = context.getEngine().getPage( m_forbiddenIPsPage );
            if( sourceIPs != null ) {
                if( m_IPPatterns == null || m_IPPatterns.isEmpty() || sourceIPs.getLastModified().after( m_lastRebuild ) ) {
                    rebuild = true;
                }
            }

            //
            //  Do the actual rebuilding.  For simplicity's sake, we always rebuild the complete
            //  filter list regardless of what changed.
            //
            if( rebuild ) {
                m_lastRebuild = new Date();
                m_spamPatterns = parseWordList( sourceSpam,
                                                ( sourceSpam != null ) ? ( String )sourceSpam.getAttribute( LISTVAR ) : null );

                log.info( "Spam filter reloaded - recognizing " + m_spamPatterns.size() + " patterns from page " + m_forbiddenWordsPage );

                m_IPPatterns = parseWordList( sourceIPs,
                        ( sourceIPs != null ) ? ( String )sourceIPs.getAttribute( LISTIPVAR ) : null );
                log.info( "IP filter reloaded - recognizing " + m_IPPatterns.size() + " patterns from page " + m_forbiddenIPsPage );

                if( att != null ) {
                    InputStream in = context.getEngine().getAttachmentManager().getAttachmentStream(att);
                    StringWriter out = new StringWriter();
                    FileUtil.copyContents( new InputStreamReader( in,"UTF-8" ), out );
                    Collection< Pattern > blackList = parseBlacklist( out.toString() );
                    log.info( "...recognizing additional " + blackList.size() + " patterns from blacklist " + m_blacklist );
                    m_spamPatterns.addAll( blackList );
                }
            }
        } catch( IOException ex ) {
            log.info( "Unable to read attachment data, continuing...", ex );
        } catch( ProviderException ex ) {
            log.info( "Failed to read spam filter attachment, continuing...", ex );
        }
    }

    /**
     *  Does a check against a known pattern list.
     *
     *  @param context
     *  @param content
     *  @param change
     *  @throws RedirectException
     */
    private void checkPatternList( WikiContext context, String content, Change change ) throws RedirectException {
        //
        //  If we have no spam patterns defined, or we're trying to save
        //  the page containing the patterns, just return.
        //
        if( m_spamPatterns == null || context.getPage().getName().equals( m_forbiddenWordsPage ) ) {
            return;
        }

        String ch = change.toString();
        if( context.getHttpRequest() != null ) {
            ch += HttpUtil.getRemoteAddress( context.getHttpRequest() );
        }

        for( Pattern p : m_spamPatterns ) {
            // log.debug("Attempting to match page contents with "+p.getPattern());

            if( m_matcher.contains( ch, p ) ) {
                //
                //  Spam filter has a match.
                //
                String uid = log( context, REJECT, REASON_REGEXP + "(" + p.getPattern() + ")", ch );

                log.info( "SPAM:Regexp (" + uid + "). Content matches the spam filter '" + p.getPattern() + "'" );
                checkStrategy( context, REASON_REGEXP, "Herb says '" + p.getPattern() + "' is a bad spam word and I trust Herb! (Incident code " + uid + ")" );
            }
        }
    }


    /**
     *  Does a check against a pattern list of IPs.
     *
     *  @param context
     *  @throws RedirectException
     */
    private void checkIPList( WikiContext context ) throws RedirectException {
        //
        //  If we have no IP patterns defined, or we're trying to save
        //  the page containing the IP patterns, just return.
        //
        if( m_IPPatterns == null || context.getPage().getName().equals( m_forbiddenIPsPage ) ) {
            return;
        }

        String remoteIP = HttpUtil.getRemoteAddress( context.getHttpRequest() );
        log.info("Attempting to match remoteIP " + remoteIP + " against " + m_IPPatterns.size() + " patterns");

        for( Pattern p : m_IPPatterns ) {
             log.debug("Attempting to match remoteIP with " + p.getPattern());

            if( m_matcher.contains( remoteIP, p ) ) {

                //  IP filter has a match.
                //
                String uid = log( context, REJECT, REASON_IP_BANNED_PERMANENTLY + "(" + p.getPattern() + ")", remoteIP );

                log.info( "SPAM:Regexp (" + uid + "). remoteIP matches the IP filter '" + p.getPattern() + "'" );
                checkStrategy( context, REASON_IP_BANNED_PERMANENTLY, "Herb says '" + p.getPattern() + "' is a banned IP and I trust Herb! (Incident code " + uid + ")" );
            }
        }
    }

    private void checkPatternList( WikiContext context, String content, String change ) throws RedirectException {
        Change c = new Change();
        c.m_change = change;
        checkPatternList( context, content, c );
    }
 
    /**
     *  Creates a simple text string describing the added content.
     *
     *  @param context
     *  @param newText
     *  @return Empty string, if there is no change.
     */
    private static Change getChange( WikiContext context, String newText ) {
        WikiPage page = context.getPage();
        StringBuffer change = new StringBuffer();
        WikiEngine engine = context.getEngine();
        // Get current page version

        Change ch = new Change();
        
        try {
            String oldText = engine.getPureText( page.getName(), WikiProvider.LATEST_VERSION );

            String[] first  = Diff.stringToArray( oldText );
            String[] second = Diff.stringToArray( newText );
            Revision rev = Diff.diff( first, second, new MyersDiff() );

            if( rev == null || rev.size() == 0 ) {
                return ch;
            }
            
            for( int i = 0; i < rev.size(); i++ ) {
                Delta d = rev.getDelta( i );

                if( d instanceof AddDelta ) {
                    d.getRevised().toString( change, "", "\r\n" );
                    ch.m_adds++;
                    
                } else if( d instanceof ChangeDelta ) {
                    d.getRevised().toString( change, "", "\r\n" );
                    ch.m_adds++;
                    
                } else if( d instanceof DeleteDelta ) {
                    ch.m_removals++;
                }
            }
        } catch( DifferentiationFailedException e ) {
            log.error( "Diff failed", e );
        }

        //
        //  Don't forget to include the change note, too
        //
        String changeNote = ( String )page.getAttribute( WikiPage.CHANGENOTE );

        if( changeNote != null ) {
            change.append( "\r\n" );
            change.append( changeNote );
        }

        //
        //  And author as well
        //
        if( page.getAuthor() != null ) {
            change.append( "\r\n" + page.getAuthor() );
        }

        ch.m_change = change.toString();
        return ch;
    }

    /**
     *  Returns true, if this user should be ignored.  For example, admin users.
     *
     * @param context
     * @return True, if this users should be ignored.
     */
    private boolean ignoreThisUser( WikiContext context ) {
        if( context.hasAdminPermissions() ) {
            return true;
        }

        if( m_ignoreAuthenticated && context.getWikiSession().isAuthenticated() ) {
            return true;
        }

        if( context.getVariable( "captcha" ) != null ) {
            return true;
        }

        return false;
    }

    /**
     *  Returns a random string of six uppercase characters.
     *
     *  @return A random string
     */
    private static String getUniqueID() {
        StringBuilder sb = new StringBuilder();
        Random rand = new Random();

        for( int i = 0; i < 6; i++ ) {
            char x = ( char )( 'A' + rand.nextInt( 26 ) );
            sb.append( x );
        }

        return sb.toString();
    }

    /**
     *  Returns a page to which we shall redirect, based on the current value of the "captcha" parameter.
     *
     *  @param ctx WikiContext
     *  @return An URL to redirect to
     */
    private String getRedirectPage( WikiContext ctx ) {
        if( m_useCaptcha ) {
            return ctx.getURL( WikiContext.NONE, "Captcha.jsp", "page="+ctx.getEngine().encodeName( ctx.getPage().getName() ) );
        }

        return ctx.getURL( WikiContext.VIEW, m_errorPage );
    }

    /**
     *  Checks whether the UserProfile matches certain checks.
     *
     *  @param profile The profile to check
     *  @param context The WikiContext
     *  @return False, if this userprofile is suspect and should not be allowed to be added.
     *  @since 2.6.1
     */
    public boolean isValidUserProfile( WikiContext context, UserProfile profile ) {
        try {
            checkPatternList( context, profile.getEmail(), profile.getEmail() );
            checkPatternList( context, profile.getFullname(), profile.getFullname() );
            checkPatternList( context, profile.getLoginName(), profile.getLoginName() );
        } catch( RedirectException e ) {
            log.info("Detected attempt to create a spammer user account (see above for rejection reason)");
            return false;
        }

        return true;
    }

    /**
     *  This method is used to calculate an unique code when submitting the page to detect edit conflicts.  
     *  It currently incorporates the last-modified date of the page, and the IP address of the submitter.
     *
     *  @param page The WikiPage under edit
     *  @param request The HTTP Request
     *  @since 2.6
     *  @return A hash value for this page and session
     */
    public static final String getSpamHash( WikiPage page, HttpServletRequest request ) {
        long lastModified = 0;

        if( page.getLastModified() != null ) {
            lastModified = page.getLastModified().getTime();
        }
        long remote = HttpUtil.getRemoteAddress( request ).hashCode();

        return Long.toString( lastModified ^ remote );
    }

    /**
     *  Returns the name of the hash field to be used in this request. The value is unique per session, and once 
     *  the session has expired, you cannot edit anymore.
     *
     *  @param request The page request
     *  @return The name to be used in the hash field
     *  @since  2.6
     */
    public static final String getHashFieldName( HttpServletRequest request ) {
        String hash = null;

        if( request.getSession() != null ) {
            hash = ( String )request.getSession().getAttribute( "_hash" );

            if( hash == null ) {
                hash = c_hashName;
                request.getSession().setAttribute( "_hash", hash );
            }
        }

        if( c_hashName == null || c_lastUpdate < ( System.currentTimeMillis() - HASH_DELAY * 60 * 60 * 1000 ) ) {
            c_hashName = getUniqueID().toLowerCase();
            c_lastUpdate = System.currentTimeMillis();
        }

        return hash != null ? hash : c_hashName;
    }


    /**
     *  This method checks if the hash value is still valid, i.e. if it exists at all. This can occur in two cases: 
     *  either this is a spam bot which is not adaptive, or it is someone who has been editing one page for too long, 
     *  and their session has expired.
     *  <p>
     *  This method puts a redirect to the http response field to page "SessionExpired" and logs the incident in 
     *  the spam log (it may or may not be spam, but it's rather likely that it is).
     *
     *  @param context The WikiContext
     *  @param pageContext The JSP PageContext.
     *  @return True, if hash is okay.  False, if hash is not okay, and you need to redirect.
     *  @throws IOException If redirection fails
     *  @since 2.6
     */
    public static final boolean checkHash( WikiContext context, PageContext pageContext ) throws IOException {
        String hashName = getHashFieldName( (HttpServletRequest)pageContext.getRequest() );

        if( pageContext.getRequest().getParameter(hashName) == null ) {
            if( pageContext.getAttribute( hashName ) == null ) {
                Change change = getChange( context, EditorManager.getEditedText( pageContext ) );
                log( context, REJECT, "MissingHash", change.m_change );

                String redirect = context.getURL( WikiContext.VIEW,"SessionExpired" );
                ( ( HttpServletResponse )pageContext.getResponse() ).sendRedirect( redirect );
                return false;
            }
        }

        return true;
    }

    /**
     * This helper method adds all the input fields to your editor that the SpamFilter requires
     * to check for spam.  This <i>must</i> be in your editor form if you intend to use the SpamFilter.
     *  
     * @param pageContext The PageContext
     * @return A HTML string which contains input fields for the SpamFilter.
     */
    public static final String insertInputFields( PageContext pageContext ) {
        WikiContext ctx = WikiContext.findContext( pageContext );
        WikiEngine engine = ctx.getEngine();

        StringBuilder sb = new StringBuilder();
        if( engine.getContentEncoding().equals( "UTF-8" ) ) {
            sb.append( "<input name='encodingcheck' type='hidden' value='\u3041' />\n" );
        }

        return sb.toString();
    }
    
    /**
     *  A local class for storing host information.
     *
     *  @since
     */
    private class Host {
        
        private long   m_addedTime = System.currentTimeMillis();
        private long   m_releaseTime;
        private String m_address;
        private Change m_change;

        public String getAddress() {
            return m_address;
        }

        public long getReleaseTime() {
            return m_releaseTime;
        }

        public long getAddedTime() {
            return m_addedTime;
        }

        public Change getChange() {
            return m_change;
        }

        public Host( String ipaddress, Change change ) {
            m_address = ipaddress;
            m_change  = change;
            m_releaseTime = System.currentTimeMillis() + m_banTime * 60 * 1000L;
        }
        
    }
    
    private static class Change {
        
        public String m_change;
        public int    m_adds;
        public int    m_removals;
        
        public String toString() {
            return m_change;
        }
        
        public boolean equals( Object o ) {
            if( o instanceof Change ) {
                return m_change.equals( ( ( Change )o ).m_change );
            }
            return false;
        }
        
        public int hashCode() {
            return m_change.hashCode() + 17;
        }
        
    }

}