/*
    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.diff;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.StringTokenizer;

import org.apache.log4j.Logger;
import org.apache.wiki.WikiContext;
import org.apache.wiki.WikiEngine;
import org.apache.wiki.api.exceptions.NoRequiredPropertyException;
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.RevisionVisitor;
import org.suigeneris.jrcs.diff.delta.AddDelta;
import org.suigeneris.jrcs.diff.delta.ChangeDelta;
import org.suigeneris.jrcs.diff.delta.Chunk;
import org.suigeneris.jrcs.diff.delta.DeleteDelta;
import org.suigeneris.jrcs.diff.delta.Delta;
import org.suigeneris.jrcs.diff.myers.MyersDiff;


/**
 * A seriously better diff provider, which highlights changes word-by-word using
 * CSS.
 *
 * Suggested by John Volkar.
 *
 */
public class ContextualDiffProvider implements DiffProvider {

    private static final Logger log = Logger.getLogger( ContextualDiffProvider.class );

    /**
     *  A jspwiki.properties value to define how many characters are shown around the change context.
     *  The current value is <tt>{@value}</tt>.
     */
    public static final String PROP_UNCHANGED_CONTEXT_LIMIT = "jspwiki.contextualDiffProvider.unchangedContextLimit";

    //TODO all of these publics can become jspwiki.properties entries...
    //TODO span title= can be used to get hover info...

    public boolean m_emitChangeNextPreviousHyperlinks = true;

    //Don't use spans here the deletion and insertions are nested in this...
    public String m_changeStartHtml    = ""; //This could be a image '>' for a start marker
    public String m_changeEndHtml      = ""; //and an image for an end '<' marker
    public String m_diffStart          = "<div class=\"diff-wikitext\">";
    public String m_diffEnd            = "</div>";

    // Unfortunately we need to do dumb HTML here for RSS feeds.

    public String m_insertionStartHtml = "<font color=\"#8000FF\"><span class=\"diff-insertion\">";
    public String m_insertionEndHtml   = "</span></font>";
    public String m_deletionStartHtml  = "<strike><font color=\"red\"><span class=\"diff-deletion\">";
    public String m_deletionEndHtml    = "</span></font></strike>";
    private String m_anchorPreIndex    = "<a name=\"change-";
    private String m_anchorPostIndex   = "\" />";
    private String m_backPreIndex      = "<a class=\"diff-nextprev\" title=\"Go to previous change\" href=\"#change-";
    private String m_backPostIndex     = "\">&lt;&lt;</a>";
    private String m_forwardPreIndex   = "<a class=\"diff-nextprev\" title=\"Go to next change\" href=\"#change-";
    private String m_forwardPostIndex  = "\">&gt;&gt;</a>";
    public String m_elidedHeadIndicatorHtml = "<br/><br/><b>...</b>";
    public String m_elidedTailIndicatorHtml = "<b>...</b><br/><br/>";
    public String m_lineBreakHtml = "<br />";
    public String m_alternatingSpaceHtml = "&nbsp;";

    // This one, I will make property file based...
    private static final int LIMIT_MAX_VALUE = (Integer.MAX_VALUE /2) - 1;
    private int m_unchangedContextLimit = LIMIT_MAX_VALUE;


    /**
     *  Constructs this provider.
     */
    public ContextualDiffProvider()
    {}

    /**
     * @see org.apache.wiki.WikiProvider#getProviderInfo()
     * 
     * {@inheritDoc}
     */
    public String getProviderInfo()
    {
        return "ContextualDiffProvider";
    }

    /**
     * @see org.apache.wiki.WikiProvider#initialize(org.apache.wiki.WikiEngine,
     *      java.util.Properties)
     *      
     * {@inheritDoc}
     */
    public void initialize(WikiEngine engine, Properties properties) throws NoRequiredPropertyException, IOException
    {
        String configuredLimit = properties.getProperty(PROP_UNCHANGED_CONTEXT_LIMIT, 
                                                        Integer.toString(LIMIT_MAX_VALUE));
        int limit = LIMIT_MAX_VALUE;
        try
        {
            limit = Integer.parseInt(configuredLimit);
        }
        catch (NumberFormatException e)
        {
            log.warn("Failed to parseInt " + PROP_UNCHANGED_CONTEXT_LIMIT + "=" + configuredLimit
                + "   Will use a huge number as limit.", e);
        }
        m_unchangedContextLimit = limit;
    }



    /**
     * Do a colored diff of the two regions. This. is. serious. fun. ;-)
     *
     * @see org.apache.wiki.diff.DiffProvider#makeDiffHtml(WikiContext, String, String)
     * 
     * {@inheritDoc}
     */
    public synchronized String makeDiffHtml( WikiContext ctx, String wikiOld, String wikiNew )
    {
        //
        // Sequencing handles lineterminator to <br /> and every-other consequtive space to a &nbsp;
        //
        String[] alpha = sequence( TextUtil.replaceEntities( wikiOld ) );
        String[] beta  = sequence( TextUtil.replaceEntities( wikiNew ) );

        Revision rev = null;
        try
        {
            rev = Diff.diff( alpha, beta, new MyersDiff() );
        }
        catch( DifferentiationFailedException dfe )
        {
            log.error( "Diff generation failed", dfe );
            return "Error while creating version diff.";
        }

        int revSize = rev.size();

        StringBuffer sb = new StringBuffer();

        sb.append( m_diffStart );

        //
        // The MyersDiff is a bit dumb by converting a single line multi-word diff into a series
        // of Changes. The ChangeMerger pulls them together again...
        //
        ChangeMerger cm = new ChangeMerger( sb, alpha, revSize );

        rev.accept( cm );

        cm.shutdown();

        sb.append( m_diffEnd );

        return sb.toString();
    }

    /**
     * Take the string and create an array from it, split it first on newlines, making
     * sure to preserve the newlines in the elements, split each resulting element on
     * spaces, preserving the spaces.
     *
     * All this preseving of newlines and spaces is so the wikitext when diffed will have fidelity
     * to it's original form.  As a side affect we see edits of purely whilespace.
     */
    private String[] sequence( String wikiText )
    {
        String[] linesArray = Diff.stringToArray( wikiText );

        List<String> list = new ArrayList<String>();

        for( int i = 0; i < linesArray.length; i++ )
        {
            String line = linesArray[i];

            String lastToken = null;
            String token = null;
            // StringTokenizer might be discouraged but it still is perfect here...
            for (StringTokenizer st = new StringTokenizer( line, " ", true ); st.hasMoreTokens();)
            {
                token = st.nextToken();

                if(" ".equals( lastToken) && " ".equals( token ))
                    token = m_alternatingSpaceHtml;

                list.add(token);
                lastToken = token;
            }

            list.add(m_lineBreakHtml); // Line Break
        }

        return list.toArray( new String[0] );
    }

    /**
     * This helper class does the housekeeping for merging
     * our various changes down and also makes sure that the
     * whole change process is threadsafe by encapsulating
     * all necessary variables.
     */
    private final class ChangeMerger implements RevisionVisitor
    {
        private StringBuffer m_sb = null;

        /** Keeping score of the original lines to process */
        private int m_max = -1;

        private int m_index = 0;

        /** Index of the next element to be copied into the output. */
        private int m_firstElem = 0;

        /** Link Anchor counter */
        private int m_count = 1;

        /** State Machine Mode */
        private int m_mode = -1; /* -1: Unset, 0: Add, 1: Del, 2: Change mode */

        /** Buffer to coalesce the changes together */
        private StringBuffer m_origBuf = null;

        private StringBuffer m_newBuf = null;

        /** Reference to the source string array */
        private String[] m_origStrings = null;

        private ChangeMerger( final StringBuffer sb, final String[] origStrings, final int max )
        {
            m_sb = sb;
            m_origStrings = origStrings != null ? origStrings.clone() : null;
            m_max = max;

            m_origBuf = new StringBuffer();
            m_newBuf = new StringBuffer();
        }

        private void updateState( Delta delta )
        {
            m_index++;

            Chunk orig = delta.getOriginal();

            if (orig.first() > m_firstElem)
            {
                // We "skip" some lines in the output.
                // So flush out the last Change, if one exists.
                flushChanges();

                // Allow us to "skip" large swaths of unchanged text, show a "limited" amound of
                // unchanged context so the changes are shown in
                if ((orig.first() - m_firstElem) > 2 * m_unchangedContextLimit)
                {
                    if (m_firstElem > 0)
                    {
                        int endIndex = Math.min( m_firstElem + m_unchangedContextLimit, m_origStrings.length -1 );

                        for (int j = m_firstElem; j < endIndex; j++)
                            m_sb.append(m_origStrings[j]);

                        m_sb.append(m_elidedTailIndicatorHtml);
                    }

                    m_sb.append(m_elidedHeadIndicatorHtml);

                    int startIndex = Math.max(orig.first() - m_unchangedContextLimit, 0);
                    for (int j = startIndex; j < orig.first(); j++)
                        m_sb.append(m_origStrings[j]);

                }
                else
                {
                    // No need to skip anything, just output the whole range...
                    for (int j = m_firstElem; j < orig.first(); j++)
                    m_sb.append( m_origStrings[j] );
                }
            }
            m_firstElem = orig.last() + 1;
        }

        public void visit( Revision rev )
        {
            // GNDN (Goes nowhere, does nothing)
        }

        public void visit( AddDelta delta )
        {
            updateState( delta );

            // We have run Deletes up to now. Flush them out.
            if( m_mode == 1 )
            {
                flushChanges();
                m_mode = -1;
            }
            // We are in "neutral mode". Start a new Change
            if( m_mode == -1 )
            {
                m_mode = 0;
            }

            // We are in "add mode".
            if( m_mode == 0 || m_mode == 2 )
            {
                addNew( delta.getRevised() );
                m_mode = 1;
            }
        }

        public void visit( ChangeDelta delta )
        {
            updateState( delta );

            // We are in "neutral mode". A Change might be merged with an add or delete.
            if( m_mode == -1 )
            {
                m_mode = 2;
            }

            // Add the Changes to the buffers.
            addOrig( delta.getOriginal() );
            addNew( delta.getRevised() );
        }

        public void visit( DeleteDelta delta )
        {
            updateState( delta );

            // We have run Adds up to now. Flush them out.
            if( m_mode == 0 )
            {
                flushChanges();
                m_mode = -1;
            }
            // We are in "neutral mode". Start a new Change
            if( m_mode == -1 )
            {
                m_mode = 1;
            }

            // We are in "delete mode".
            if( m_mode == 1 || m_mode == 2 )
            {
                addOrig( delta.getOriginal() );
                m_mode = 1;
            }
        }

        public void shutdown()
        {
            m_index = m_max + 1; // Make sure that no hyperlink gets created
            flushChanges();

            if (m_firstElem < m_origStrings.length)
            {
                // If there's more than the limit of the orginal left just emit limit and elided...
                if ((m_origStrings.length - m_firstElem) > m_unchangedContextLimit)
                {
                    int endIndex = Math.min( m_firstElem + m_unchangedContextLimit, m_origStrings.length -1 );

                    for (int j = m_firstElem; j < endIndex; j++)
                    m_sb.append( m_origStrings[j] );

                    m_sb.append(m_elidedTailIndicatorHtml);
                }
                else
                // emit entire tail of original...
                {
                    for (int j = m_firstElem; j < m_origStrings.length; j++)
                        m_sb.append(m_origStrings[j]);
                }
            }
        }

        private void addOrig( Chunk chunk )
        {
            if( chunk != null )
            {
                chunk.toString( m_origBuf );
            }
        }

        private void addNew( Chunk chunk )
        {
            if( chunk != null )
            {
                chunk.toString( m_newBuf );
            }
        }



        private void flushChanges()
        {

            if( m_newBuf.length() + m_origBuf.length() > 0 )
            {
                // This is the span element which encapsulates anchor and the change itself
                m_sb.append( m_changeStartHtml );

                // Do we want to have a "back link"?
                if( m_emitChangeNextPreviousHyperlinks && m_count > 1 )
                {
                    m_sb.append( m_backPreIndex );
                    m_sb.append( m_count - 1 );
                    m_sb.append( m_backPostIndex );
                }

                // An anchor for the change.
                if (m_emitChangeNextPreviousHyperlinks)
                {
                    m_sb.append( m_anchorPreIndex );
                    m_sb.append( m_count++ );
                    m_sb.append( m_anchorPostIndex );
                }

                // ... has been added
                if( m_newBuf.length() > 0 )
                {
                    m_sb.append( m_insertionStartHtml );
                    m_sb.append( m_newBuf );
                    m_sb.append( m_insertionEndHtml );
                }

                // .. has been removed
                if( m_origBuf.length() > 0 )
                {
                    m_sb.append( m_deletionStartHtml );
                    m_sb.append( m_origBuf );
                    m_sb.append( m_deletionEndHtml );
                }

                // Do we want a "forward" link?
                if( m_emitChangeNextPreviousHyperlinks && (m_index < m_max) )
                {
                    m_sb.append( m_forwardPreIndex );
                    m_sb.append( m_count ); // Has already been incremented.
                    m_sb.append( m_forwardPostIndex );
                }

                m_sb.append( m_changeEndHtml );

                // Nuke the buffers.
                m_origBuf = new StringBuffer();
                m_newBuf = new StringBuffer();
            }

            // After a flush, everything is reset.
            m_mode = -1;
        }
    }
}