/*******************************************************************************
 * Copyright (c) 2000, 2008 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 * Port to the D programming language:
 *     Frank Benoit <benoit@tionex.de>
 *******************************************************************************/
module dwtx.jface.text.projection.ProjectionDocument;

import dwtx.jface.text.projection.ProjectionMapping; // packageimport
import dwtx.jface.text.projection.ChildDocumentManager; // packageimport
import dwtx.jface.text.projection.SegmentUpdater; // packageimport
import dwtx.jface.text.projection.Segment; // packageimport
import dwtx.jface.text.projection.FragmentUpdater; // packageimport
import dwtx.jface.text.projection.ProjectionDocumentEvent; // packageimport
import dwtx.jface.text.projection.ChildDocument; // packageimport
import dwtx.jface.text.projection.IMinimalMapping; // packageimport
import dwtx.jface.text.projection.Fragment; // packageimport
import dwtx.jface.text.projection.ProjectionTextStore; // packageimport
import dwtx.jface.text.projection.ProjectionDocumentManager; // packageimport


import dwt.dwthelper.utils;

import dwtx.dwtxhelper.Collection;


import dwtx.jface.text.AbstractDocument;
import dwtx.jface.text.BadLocationException;
import dwtx.jface.text.BadPositionCategoryException;
import dwtx.jface.text.DefaultLineTracker;
import dwtx.jface.text.DocumentEvent;
import dwtx.jface.text.IDocument;
import dwtx.jface.text.IDocumentExtension;
import dwtx.jface.text.IDocumentInformationMapping;
import dwtx.jface.text.IDocumentListener;
import dwtx.jface.text.ILineTracker;
import dwtx.jface.text.IRegion;
import dwtx.jface.text.ITextStore;
import dwtx.jface.text.Position;
import dwtx.jface.text.Region;
import dwtx.jface.text.TextUtilities;


/**
 * A <code>ProjectionDocument</code> represents a projection of its master
 * document. The contents of a projection document is a sequence of fragments of
 * the master document, i.e. the projection document can be thought as being
 * constructed from the master document by not copying the whole master document
 * but omitting several ranges of the master document.
 * <p>
 * The projection document indirectly utilizes its master document as
 * <code>ITextStore</code> by means of a <code>ProjectionTextStore</code>.
 * <p>
 * The content of a projection document can be changed in two ways. Either by a
 * text replace applied to the master document or the projection document. Or by
 * changing the projection between the master document and the projection
 * document. For the latter the two methods <code>addMasterDocumentRange</code>
 * and <code>removeMasterDocumentRange</code> are provided. For any
 * manipulation, the projection document sends out a
 * {@link dwtx.jface.text.projection.ProjectionDocumentEvent} describing
 * the change.
 * <p>
 * Clients are not supposed to directly instantiate this class. In order to
 * obtain a projection document, a
 * {@link dwtx.jface.text.projection.ProjectionDocumentManager}should be
 * used. This class is not intended to be subclassed outside of its origin
 * package.</p>
 *
 * @since 3.0
 * @noinstantiate This class is not intended to be instantiated by clients.
 * @noextend This class is not intended to be subclassed by clients.
 */
public class ProjectionDocument : AbstractDocument {


    /**
     * Prefix of the name of the position category used to keep track of the master
     * document's fragments that correspond to the segments of the projection
     * document.
     */
    private const static String FRAGMENTS_CATEGORY_PREFIX= "__fragmentsCategory"; //$NON-NLS-1$

    /**
     * Name of the position category used to keep track of the project
     * document's segments that correspond to the fragments of the master
     * document.
     */
    private const static String SEGMENTS_CATEGORY= "__segmentsCategory"; //$NON-NLS-1$


    /** The master document */
    private IDocument fMasterDocument;
    /** The master document as document extension */
    private IDocumentExtension fMasterDocumentExtension;
    /** The fragments' position category */
    private String fFragmentsCategory;
    /** The segment's position category */
    private String fSegmentsCategory;
    /** The document event issued by the master document */
    private DocumentEvent fMasterEvent;
    /** The document event to be issued by the projection document */
    private ProjectionDocumentEvent fSlaveEvent;
    /** The original document event generated by a direct manipulation of this projection document */
    private DocumentEvent fOriginalEvent;
    /** Indicates whether the projection document initiated a master document update or not */
    private bool fIsUpdating= false;
    /** Indicated whether the projection document is in auto expand mode nor not */
    private bool fIsAutoExpanding= false;
    /** The position updater for the segments */
    private SegmentUpdater fSegmentUpdater;
    /** The position updater for the fragments */
    private FragmentUpdater fFragmentsUpdater;
    /** The projection mapping */
    private ProjectionMapping fMapping;

    /**
     * Creates a projection document for the given master document.
     *
     * @param masterDocument the master document
     */
    public this(IDocument masterDocument) {
        super();

        fMasterDocument= masterDocument;
        if ( cast(IDocumentExtension)fMasterDocument )
            fMasterDocumentExtension= cast(IDocumentExtension) fMasterDocument;

        fSegmentsCategory= SEGMENTS_CATEGORY;
        fFragmentsCategory= FRAGMENTS_CATEGORY_PREFIX + hashCode();
        fMasterDocument.addPositionCategory(fFragmentsCategory);
        fFragmentsUpdater= new FragmentUpdater(fFragmentsCategory);
        fMasterDocument.addPositionUpdater(fFragmentsUpdater);

        fMapping= new ProjectionMapping(masterDocument, fFragmentsCategory, this, fSegmentsCategory);

        ITextStore s= new ProjectionTextStore(masterDocument, fMapping);
        ILineTracker tracker= new DefaultLineTracker();

        setTextStore(s);
        setLineTracker(tracker);

        completeInitialization();

        initializeProjection();
        tracker.set(s.get(0, s.getLength()));
    }

    /**
     * Disposes this projection document.
     */
    public void dispose() {
        fMasterDocument.removePositionUpdater(fFragmentsUpdater);
        try {
            fMasterDocument.removePositionCategory(fFragmentsCategory);
        } catch (BadPositionCategoryException x) {
            // allow multiple dispose calls
        }
    }

    private void internalError() {
        throw new IllegalStateException();
    }

    /**
     * Returns the fragments of the master documents.
     *
     * @return the fragment of the master document
     */
    protected final Position[] getFragments() {
        try {
            return fMasterDocument.getPositions(fFragmentsCategory);
        } catch (BadPositionCategoryException e) {
            internalError();
        }
        // unreachable
        return null;
    }

    /**
     * Returns the segments of this projection document.
     *
     * @return the segments of this projection document
     */
    protected final Position[] getSegments() {
        try {
            return getPositions(fSegmentsCategory);
        } catch (BadPositionCategoryException e) {
            internalError();
        }
        // unreachable
        return null;
    }

    /**
     * Returns the projection mapping used by this document.
     *
     * @return the projection mapping used by this document
     * @deprecated As of 3.4, replaced by {@link #getDocumentInformationMapping()}
     */
    public ProjectionMapping getProjectionMapping(){
        return fMapping;
    }

    /**
     * Returns the projection mapping used by this document.
     *
     * @return the projection mapping used by this document
     * @since 3.4
     */
    public IDocumentInformationMapping getDocumentInformationMapping() {
        return fMapping;
    }

    /**
     * Returns the master document of this projection document.
     *
     * @return the master document of this projection document
     */
    public IDocument getMasterDocument() {
        return fMasterDocument;
    }

    /*
     * @see dwtx.jface.text.IDocumentExtension4#getDefaultLineDelimiter()
     * @since 3.1
     */
    public String getDefaultLineDelimiter() {
        return TextUtilities.getDefaultLineDelimiter(fMasterDocument);
    }

    /**
     * Initializes the projection document from the master document based on
     * the master's fragments.
     */
    private void initializeProjection() {

        try {

            addPositionCategory(fSegmentsCategory);
            fSegmentUpdater= new SegmentUpdater(fSegmentsCategory);
            addPositionUpdater(fSegmentUpdater);

            int offset= 0;
            Position[] fragments= getFragments();
            for (int i= 0; i < fragments.length; i++) {
                Fragment fragment= cast(Fragment) fragments[i];
                Segment segment= new Segment(offset, fragment.getLength());
                segment.fragment= fragment;
                addPosition(fSegmentsCategory, segment);
                offset += fragment.length;
            }

        } catch (BadPositionCategoryException x) {
            internalError();
        } catch (BadLocationException x) {
            internalError();
        }
    }

    /**
     * Creates a segment for the given fragment at the given position inside the list of segments.
     *
     * @param fragment the corresponding fragment
     * @param index the index in the list of segments
     * @return the created segment
     * @throws BadLocationException in case the fragment is invalid
     * @throws BadPositionCategoryException in case the segment category is invalid
     */
    private Segment createSegmentFor(Fragment fragment, int index)  {

        int offset= 0;
        if (index > 0) {
            Position[] segments= getSegments();
            Segment segment= cast(Segment) segments[index - 1];
            offset= segment.getOffset() + segment.getLength();
        }

        Segment segment= new Segment(offset, 0);
        segment.fragment= fragment;
        fragment.segment= segment;
        addPosition(fSegmentsCategory, segment);
        return segment;
    }

    /**
     * Adds the given range of the master document to this projection document.
     *
     * @param offsetInMaster offset of the master document range
     * @param lengthInMaster length of the master document range
     * @param masterDocumentEvent the master document event that causes this
     *            projection change or <code>null</code> if none
     * @throws BadLocationException if the given range is invalid in the master
     *             document
     */
    private void internalAddMasterDocumentRange(int offsetInMaster, int lengthInMaster, DocumentEvent masterDocumentEvent)  {
        if (lengthInMaster is 0)
            return;

        try {

            Position[] fragments= getFragments();
            int index= fMasterDocument.computeIndexInCategory(fFragmentsCategory, offsetInMaster);

            Fragment left= null;
            Fragment right= null;

            if (index < fragments.length) {
                Fragment fragment= cast(Fragment) fragments[index];
                if (offsetInMaster is fragment.offset)
                    if (fragment.length is 0) // the fragment does not overlap - it is a zero-length fragment at the same offset
                        left= fragment;
                    else
                        throw new IllegalArgumentException("overlaps with existing fragment"); //$NON-NLS-1$
                if (offsetInMaster + lengthInMaster is fragment.offset)
                    right= fragment;
            }

            if (0 < index && index <= fragments.length) {
                Fragment fragment= cast(Fragment) fragments[index - 1];
                if (fragment.includes(offsetInMaster))
                    throw new IllegalArgumentException("overlaps with existing fragment"); //$NON-NLS-1$
                if (fragment.getOffset() + fragment.getLength() is offsetInMaster)
                    left= fragment;
            }

            int offsetInSlave= 0;
            if (index > 0) {
                Fragment fragment= cast(Fragment) fragments[index - 1];
                Segment segment= fragment.segment;
                offsetInSlave= segment.getOffset() + segment.getLength();
            }

            ProjectionDocumentEvent event= new ProjectionDocumentEvent(this, offsetInSlave, 0, fMasterDocument.get(offsetInMaster, lengthInMaster), offsetInMaster, lengthInMaster, masterDocumentEvent);
            super.fireDocumentAboutToBeChanged(event);

            // check for neighboring fragment
            if (left !is null && right !is null) {

                int endOffset= right.getOffset() + right.getLength();
                left.setLength(endOffset - left.getOffset());
                left.segment.setLength(left.segment.getLength() + right.segment.getLength());

                removePosition(fSegmentsCategory, right.segment);
                fMasterDocument.removePosition(fFragmentsCategory, right);

            } else if (left !is null) {
                int endOffset= offsetInMaster +lengthInMaster;
                left.setLength(endOffset - left.getOffset());
                left.segment.markForStretch();

            } else if (right !is null) {
                right.setOffset(right.getOffset() - lengthInMaster);
                right.setLength(right.getLength() + lengthInMaster);
                right.segment.markForStretch();

            } else {
                // create a new segment
                Fragment fragment= new Fragment(offsetInMaster, lengthInMaster);
                fMasterDocument.addPosition(fFragmentsCategory, fragment);
                Segment segment= createSegmentFor(fragment, index);
                segment.markForStretch();
            }

            getTracker().replace(event.getOffset(), event.getLength(), event.getText());
            super.fireDocumentChanged(event);

        } catch (BadPositionCategoryException x) {
            internalError();
        }
    }

    /**
     * Finds the fragment of the master document that represents the given range.
     *
     * @param offsetInMaster the offset of the range in the master document
     * @param lengthInMaster the length of the range in the master document
     * @return the fragment representing the given master document range
     */
    private Fragment findFragment(int offsetInMaster, int lengthInMaster) {
        Position[] fragments= getFragments();
        for (int i= 0; i < fragments.length; i++) {
            Fragment f= cast(Fragment) fragments[i];
            if (f.getOffset() <= offsetInMaster && offsetInMaster + lengthInMaster <= f.getOffset() + f.getLength())
                return f;
        }
        return null;
    }

    /**
     * Removes the given range of the master document from this projection
     * document.
     *
     * @param offsetInMaster the offset of the range in the master document
     * @param lengthInMaster the length of the range in the master document
     *
     * @throws BadLocationException if the given range is not valid in the
     *             master document
     * @throws IllegalArgumentException if the given range is not projected in
     *             this projection document or is not completely comprised by
     *             an existing fragment
     */
    private void internalRemoveMasterDocumentRange(int offsetInMaster, int lengthInMaster)  {
        try {

            IRegion imageRegion= fMapping.toExactImageRegion(new Region(offsetInMaster, lengthInMaster));
            if (imageRegion is null)
                throw new IllegalArgumentException();

            Fragment fragment= findFragment(offsetInMaster, lengthInMaster);
            if (fragment is null)
                throw new IllegalArgumentException();

            ProjectionDocumentEvent event= new ProjectionDocumentEvent(this, imageRegion.getOffset(), imageRegion.getLength(), "", offsetInMaster, lengthInMaster); //$NON-NLS-1$
            super.fireDocumentAboutToBeChanged(event);

            if (fragment.getOffset() is offsetInMaster) {
                fragment.setOffset(offsetInMaster + lengthInMaster);
                fragment.setLength(fragment.getLength() - lengthInMaster);
            } else if (fragment.getOffset() + fragment.getLength() is offsetInMaster + lengthInMaster) {
                fragment.setLength(fragment.getLength() - lengthInMaster);
            } else {
                // split fragment into three fragments, let position updater remove it

                // add fragment for the region to be removed
                Fragment newFragment= new Fragment(offsetInMaster, lengthInMaster);
                Segment segment= new Segment(imageRegion.getOffset(), imageRegion.getLength());
                newFragment.segment= segment;
                segment.fragment= newFragment;
                fMasterDocument.addPosition(fFragmentsCategory, newFragment);
                addPosition(fSegmentsCategory, segment);

                // add fragment for the remainder right of the deleted range in the original fragment
                int offset= offsetInMaster + lengthInMaster;
                newFragment= new Fragment(offset, fragment.getOffset() + fragment.getLength() - offset);
                offset= imageRegion.getOffset() + imageRegion.getLength();
                segment= new Segment(offset, fragment.segment.getOffset() + fragment.segment.getLength() - offset);
                newFragment.segment= segment;
                segment.fragment= newFragment;
                fMasterDocument.addPosition(fFragmentsCategory, newFragment);
                addPosition(fSegmentsCategory, segment);

                // adjust length of initial fragment (the left one)
                fragment.setLength(offsetInMaster - fragment.getOffset());
                fragment.segment.setLength(imageRegion.getOffset() - fragment.segment.getOffset());
            }

            getTracker().replace(event.getOffset(), event.getLength(), event.getText());
            super.fireDocumentChanged(event);

        } catch (BadPositionCategoryException x) {
            internalError();
        }
    }

    /**
     * Returns the sequence of all master document regions which are contained
     * in the given master document range and which are not yet part of this
     * projection document.
     *
     * @param offsetInMaster the range offset in the master document
     * @param lengthInMaster the range length in the master document
     * @return the sequence of regions which are not yet part of the projection
     *         document
     * @throws BadLocationException in case the given range is invalid in the
     *         master document
     */
    public final IRegion[] computeUnprojectedMasterRegions(int offsetInMaster, int lengthInMaster)  {

        IRegion[] fragments= null;
        IRegion imageRegion= fMapping.toImageRegion(new Region(offsetInMaster, lengthInMaster));
        if (imageRegion !is null)
            fragments= fMapping.toExactOriginRegions(imageRegion);

        if (fragments is null || fragments.length is 0)
            return [ new Region(offsetInMaster, lengthInMaster) ];

        List gaps= new ArrayList();

        IRegion region= fragments[0];
        if (offsetInMaster < region.getOffset())
            gaps.add(new Region(offsetInMaster, region.getOffset() - offsetInMaster));

        for (int i= 0; i < fragments.length - 1; i++) {
            IRegion left= fragments[i];
            IRegion right= fragments[i + 1];
            int leftEnd= left.getOffset() + left.getLength();
            if (leftEnd < right.getOffset())
                gaps.add(new Region(leftEnd, right.getOffset() - leftEnd));
        }

        region= fragments[fragments.length - 1];
        int leftEnd= region.getOffset() + region.getLength();
        int rightEnd= offsetInMaster + lengthInMaster;
        if (leftEnd < rightEnd)
            gaps.add(new Region(leftEnd, rightEnd - leftEnd));

        IRegion[] result= new IRegion[gaps.size()];
        gaps.toArray(result);
        return result;
    }

    /**
     * Returns the first master document region which is contained in the given
     * master document range and which is not yet part of this projection
     * document.
     *
     * @param offsetInMaster the range offset in the master document
     * @param lengthInMaster the range length in the master document
     * @return the first region that is not yet part of the projection document
     * @throws BadLocationException in case the given range is invalid in the
     *         master document
     * @since 3.1
     */
    private IRegion computeFirstUnprojectedMasterRegion(int offsetInMaster, int lengthInMaster)  {

        IRegion[] fragments= null;
        IRegion imageRegion= fMapping.toImageRegion(new Region(offsetInMaster, lengthInMaster));
        if (imageRegion !is null)
            fragments= fMapping.toExactOriginRegions(imageRegion);

        if (fragments is null || fragments.length is 0)
            return new Region(offsetInMaster, lengthInMaster);

        IRegion region= fragments[0];
        if (offsetInMaster < region.getOffset())
            return new Region(offsetInMaster, region.getOffset() - offsetInMaster);

        for (int i= 0; i < fragments.length - 1; i++) {
            IRegion left= fragments[i];
            IRegion right= fragments[i + 1];
            int leftEnd= left.getOffset() + left.getLength();
            if (leftEnd < right.getOffset())
                return new Region(leftEnd, right.getOffset() - leftEnd);
        }

        region= fragments[fragments.length - 1];
        int leftEnd= region.getOffset() + region.getLength();
        int rightEnd= offsetInMaster + lengthInMaster;
        if (leftEnd < rightEnd)
            return new Region(leftEnd, rightEnd - leftEnd);

        return null;
    }

    /**
     * Ensures that the given range of the master document is part of this
     * projection document.
     *
     * @param offsetInMaster the offset of the master document range
     * @param lengthInMaster the length of the master document range
     * @throws BadLocationException in case the master event is not valid
     */
    public void addMasterDocumentRange(int offsetInMaster, int lengthInMaster)  {
        addMasterDocumentRange(offsetInMaster, lengthInMaster, null);
    }

    /**
     * Ensures that the given range of the master document is part of this
     * projection document.
     *
     * @param offsetInMaster the offset of the master document range
     * @param lengthInMaster the length of the master document range
     * @param masterDocumentEvent the master document event which causes this
     *            projection change, or <code>null</code> if none
     * @throws BadLocationException in case the master event is not valid
     */
    private void addMasterDocumentRange(int offsetInMaster, int lengthInMaster, DocumentEvent masterDocumentEvent)  {
        /*
         * Calling internalAddMasterDocumentRange may cause other master ranges
         * to become unfolded, resulting in re-entrant calls to this method. In
         * order to not add a region twice, we have to compute the next region
         * to add in every iteration.
         *
         * To place an upper bound on the number of iterations, we use the number
         * of fragments * 2 as the limit.
         */
        int limit= Math.max(getFragments().length * 2, 20);
        while (true) {
            if (limit-- < 0)
                throw new IllegalArgumentException("safety loop termination"); //$NON-NLS-1$

            IRegion gap= computeFirstUnprojectedMasterRegion(offsetInMaster, lengthInMaster);
            if (gap is null)
                return;

            internalAddMasterDocumentRange(gap.getOffset(), gap.getLength(), masterDocumentEvent);
        }
    }

    /**
     * Ensures that the given range of the master document is not part of this
     * projection document.
     *
     * @param offsetInMaster the offset of the master document range
     * @param lengthInMaster the length of the master document range
     * @throws BadLocationException in case the master event is not valid
     */
    public void removeMasterDocumentRange(int offsetInMaster, int lengthInMaster)  {
        IRegion[] fragments= computeProjectedMasterRegions(offsetInMaster, lengthInMaster);
        if (fragments is null || fragments.length is 0)
            return;

        for (int i= 0; i < fragments.length; i++) {
            IRegion fragment= fragments[i];
            internalRemoveMasterDocumentRange(fragment.getOffset(), fragment.getLength());
        }
    }

    /**
     * Returns the sequence of all master document regions with are contained in the given master document
     * range and which are part of this projection document. May return <code>null</code> if no such
     * regions exist.
     *
     * @param offsetInMaster the range offset in the master document
     * @param lengthInMaster the range length in the master document
     * @return the sequence of regions which are part of the projection document or <code>null</code>
     * @throws BadLocationException in case the given range is invalid in the master document
     */
    public final IRegion[] computeProjectedMasterRegions(int offsetInMaster, int lengthInMaster)  {
        IRegion imageRegion= fMapping.toImageRegion(new Region(offsetInMaster, lengthInMaster));
        return imageRegion !is null ? fMapping.toExactOriginRegions(imageRegion) : null;
    }

    /**
     * Returns whether this projection is being updated.
     *
     * @return <code>true</code> if the document is updating
     */
    protected bool isUpdating() {
        return fIsUpdating;
    }

    /*
     * @see dwtx.jface.text.IDocument#replace(int, int, java.lang.String)
     */
    public void replace(int offset, int length, String text)  {
        try {
            fIsUpdating= true;
            if (fMasterDocumentExtension !is null)
                fMasterDocumentExtension.stopPostNotificationProcessing();

            super.replace(offset, length, text);

        } finally {
            fIsUpdating= false;
            if (fMasterDocumentExtension !is null)
                fMasterDocumentExtension.resumePostNotificationProcessing();
        }
    }

    /*
     * @see dwtx.jface.text.IDocument#set(java.lang.String)
     */
    public void set(String text) {
        try {
            fIsUpdating= true;
            if (fMasterDocumentExtension !is null)
                fMasterDocumentExtension.stopPostNotificationProcessing();

            super.set(text);

        } finally {
            fIsUpdating= false;
            if (fMasterDocumentExtension !is null)
                fMasterDocumentExtension.resumePostNotificationProcessing();
        }
    }

    /**
     * Transforms a document event of the master document into a projection
     * document based document event.
     *
     * @param masterEvent the master document event
     * @return the slave document event
     * @throws BadLocationException in case the master event is not valid
     */
    private ProjectionDocumentEvent normalize(DocumentEvent masterEvent)  {
        if (!isUpdating()) {
            IRegion imageRegion= fMapping.toExactImageRegion(new Region(masterEvent.getOffset(), masterEvent.getLength()));
            if (imageRegion !is null)
                return new ProjectionDocumentEvent(this, imageRegion.getOffset(), imageRegion.getLength(), masterEvent.getText(), masterEvent);
            return null;
        }

        ProjectionDocumentEvent event= new ProjectionDocumentEvent(this, fOriginalEvent.getOffset(), fOriginalEvent.getLength(), fOriginalEvent.getText(), masterEvent);
        fOriginalEvent= null;
        return event;
    }

    /**
     * Ensures that when the master event affects this projection document, that the whole region described by the
     * event is part of this projection document.
     *
     * @param masterEvent the master document event
     * @return <code>true</code> if masterEvent affects this projection document
     * @throws BadLocationException in case the master event is not valid
     */
    protected final bool adaptProjectionToMasterChange(DocumentEvent masterEvent)  {
        if (!isUpdating() && fFragmentsUpdater.affectsPositions(masterEvent) || fIsAutoExpanding && masterEvent.getLength() > 0) {

            addMasterDocumentRange(masterEvent.getOffset(), masterEvent.getLength(), masterEvent);
            return true;

        } else if (fMapping.getImageLength() is 0 && masterEvent.getLength() is 0) {

            Position[] fragments= getFragments();
            if (fragments.length is 0) {
                // there is no segment in this projection document, thus one must be created
                // need to bypass the usual infrastructure as the new segment/fragment would be of length 0 and thus the segmentation be not well formed
                try {
                    Fragment fragment= new Fragment(0, 0);
                    fMasterDocument.addPosition(fFragmentsCategory, fragment);
                    createSegmentFor(fragment, 0);
                } catch (BadPositionCategoryException x) {
                    internalError();
                }
            }
        }

        return isUpdating();
    }

    /**
     * When called, this projection document is informed about a forthcoming
     * change of its master document. This projection document checks whether
     * the master document change affects it and if so informs all document
     * listeners.
     *
     * @param masterEvent the master document event
     */
    public void masterDocumentAboutToBeChanged(DocumentEvent masterEvent) {
        try {

            bool assertNotNull= adaptProjectionToMasterChange(masterEvent);
            fSlaveEvent= normalize(masterEvent);
            if (assertNotNull && fSlaveEvent is null)
                internalError();

            fMasterEvent= masterEvent;
            if (fSlaveEvent !is null)
                delayedFireDocumentAboutToBeChanged();

        } catch (BadLocationException e) {
            internalError();
        }
    }

    /**
     * When called, this projection document is informed about a change of its
     * master document. If this projection document is affected it informs all
     * of its document listeners.
     *
     * @param masterEvent the master document event
     */
    public void masterDocumentChanged(DocumentEvent masterEvent) {
        if ( !isUpdating() && masterEvent is fMasterEvent) {
            if (fSlaveEvent !is null) {
                try {
                    getTracker().replace(fSlaveEvent.getOffset(), fSlaveEvent.getLength(), fSlaveEvent.getText());
                    fireDocumentChanged(fSlaveEvent);
                } catch (BadLocationException e) {
                    internalError();
                }
            } else if (ensureWellFormedSegmentation(masterEvent.getOffset()))
                fMapping.projectionChanged();
        }
    }

    /*
     * @see dwtx.jface.text.AbstractDocument#fireDocumentAboutToBeChanged(dwtx.jface.text.DocumentEvent)
     */
    protected void fireDocumentAboutToBeChanged(DocumentEvent event) {
        fOriginalEvent= event;
        // delay it until there is a notification from the master document
        // at this point, it is expensive to construct the master document information
    }

    /**
     * Fires the slave document event as about-to-be-changed event to all registered listeners.
     */
    private void delayedFireDocumentAboutToBeChanged() {
        super.fireDocumentAboutToBeChanged(fSlaveEvent);
    }

    /**
     * Ignores the given event and sends the semantically equal slave document event instead.
     *
     * @param event the event to be ignored
     */
    protected void fireDocumentChanged(DocumentEvent event) {
        super.fireDocumentChanged(fSlaveEvent);
    }

    /*
     * @see dwtx.jface.text.AbstractDocument#updateDocumentStructures(dwtx.jface.text.DocumentEvent)
     */
    protected void updateDocumentStructures(DocumentEvent event) {
        super.updateDocumentStructures(event);
        ensureWellFormedSegmentation(computeAnchor(event));
        fMapping.projectionChanged();
    }

    private int computeAnchor(DocumentEvent event) {
        if ( cast(ProjectionDocumentEvent)event ) {
            ProjectionDocumentEvent slave= cast(ProjectionDocumentEvent) event;
            Object changeType= slave.getChangeType();
            if (ProjectionDocumentEvent.CONTENT_CHANGE is changeType) {
                DocumentEvent master= slave.getMasterEvent();
                if (master !is null)
                    return master.getOffset();
            } else if (ProjectionDocumentEvent.PROJECTION_CHANGE is changeType) {
                return slave.getMasterOffset();
            }
        }
        return -1;
    }

    private bool ensureWellFormedSegmentation(int anchorOffset) {
        bool changed= false;
        Position[] segments= getSegments();
        for (int i= 0; i < segments.length; i++) {
            Segment segment= cast(Segment) segments[i];
            if (segment.isDeleted() || segment.getLength() is 0) {
                try {
                    removePosition(fSegmentsCategory, segment);
                    fMasterDocument.removePosition(fFragmentsCategory, segment.fragment);
                    changed= true;
                } catch (BadPositionCategoryException e) {
                    internalError();
                }
            } else if (i < segments.length - 1) {
                Segment next= cast(Segment) segments[i + 1];
                if (next.isDeleted() || next.getLength() is 0)
                    continue;
                Fragment fragment= segment.fragment;
                if (fragment.getOffset() + fragment.getLength() is next.fragment.getOffset()) {
                    // join fragments and their corresponding segments
                    segment.setLength(segment.getLength() + next.getLength());
                    fragment.setLength(fragment.getLength() + next.fragment.getLength());
                    next.delete_();
                }
            }
        }

        if (changed && anchorOffset !is -1) {
            Position[] changedSegments= getSegments();
            if (changedSegments is null || changedSegments.length is 0) {
                Fragment fragment= new Fragment(anchorOffset, 0);
                try {
                    fMasterDocument.addPosition(fFragmentsCategory, fragment);
                    createSegmentFor(fragment, 0);
                } catch (BadLocationException e) {
                    internalError();
                } catch (BadPositionCategoryException e) {
                    internalError();
                }
            }
        }

        return changed;
    }

    /*
     * @see IDocumentExtension#registerPostNotificationReplace(IDocumentListener, IDocumentExtension.IReplace)
     */
    public void registerPostNotificationReplace(IDocumentListener owner, IDocumentExtension.IReplace replace) {
        if (!isUpdating())
            throw new UnsupportedOperationException();
        super.registerPostNotificationReplace(owner, replace);
    }

    /**
     * Sets the auto expand mode for this document.
     *
     * @param autoExpandMode <code>true</code> if auto-expanding
     */
    public void setAutoExpandMode(bool autoExpandMode) {
        fIsAutoExpanding= autoExpandMode;
    }

    /**
     * Replaces all master document ranges with the given master document range.
     *
     * @param offsetInMaster the offset in the master document
     * @param lengthInMaster the length in the master document
     * @throws BadLocationException if the given range of the master document is not valid
     */
    public void replaceMasterDocumentRanges(int offsetInMaster, int lengthInMaster)  {
        try {

            ProjectionDocumentEvent event= new ProjectionDocumentEvent(this, 0, fMapping.getImageLength(), fMasterDocument.get(offsetInMaster, lengthInMaster), offsetInMaster, lengthInMaster);
            super.fireDocumentAboutToBeChanged(event);

            Position[] fragments= getFragments();
            for (int i= 0; i < fragments.length; i++) {
                Fragment fragment= cast(Fragment) fragments[i];
                fMasterDocument.removePosition(fFragmentsCategory, fragment);
                removePosition(fSegmentsCategory, fragment.segment);
            }

            Fragment fragment= new Fragment(offsetInMaster, lengthInMaster);
            Segment segment= new Segment(0, 0);
            segment.fragment= fragment;
            fragment.segment= segment;
            fMasterDocument.addPosition(fFragmentsCategory, fragment);
            addPosition(fSegmentsCategory, segment);

            getTracker().set(fMasterDocument.get(offsetInMaster, lengthInMaster));
            super.fireDocumentChanged(event);

        } catch (BadPositionCategoryException x) {
            internalError();
        }
    }
}