Software/Visual_Studio/Scripting/Tango.Scripting.Editors/Utils/Constants.cs


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// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
// This code is distributed under the GNU LGPL (for details please see \doc\license.txt)

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq;
using System.Globalization;
using System.Linq.Expressions;
using System.Threading;
using Tango.Scripting.Editors.Utils;

namespace Tango.Scripting.Editors.Document
{
    /// <summary>
    /// This class is the main class of the text model. Basically, it is a <see cref="System.Text.StringBuilder"/> with events.
    /// </summary>
    /// <remarks>
    /// <b>Thread safety:</b>
    /// <inheritdoc cref="VerifyAccess"/>
    /// <para>However, there is a single method that is thread-safe: <see cref="CreateSnapshot()"/> (and its overloads).</para>
    /// </remarks>
    public sealed class TextDocument : ITextSource, INotifyPropertyChanged
    {
        #region Thread ownership
        readonly object lockObject = new object();
        Thread owner = Thread.CurrentThread;

        /// <summary>
        /// Verifies that the current thread is the documents owner thread.
        /// Throws an <see cref="InvalidOperationException"/> if the wrong thread accesses the TextDocument.
        /// </summary>
        /// <remarks>
        /// <para>The TextDocument class is not thread-safe. A document instance expects to have a single owner thread
        /// and will throw an <see cref="InvalidOperationException"/> when accessed from another thread.
        /// It is possible to change the owner thread using the <see cref="SetOwnerThread"/> method.</para>
        /// </remarks>
        public void VerifyAccess()
        {
            if (Thread.CurrentThread != owner)
                throw new InvalidOperationException("TextDocument can be accessed only from the thread that owns it.");
        }

        /// <summary>
        /// Transfers ownership of the document to another thread. This method can be used to load
        /// a file into a TextDocument on a background thread and then transfer ownership to the UI thread
        /// for displaying the document.
        /// </summary>
        /// <remarks>
        /// <inheritdoc cref="VerifyAccess"/>
        /// <para>
        /// The owner can be set to null, which means that no thread can access the document. But, if the document
        /// has no owner thread, any thread may take ownership by calling <see cref="SetOwnerThread"/>.
        /// </para>
        /// </remarks>
        public void SetOwnerThread(Thread newOwner)
        {
            // We need to lock here to ensure that in the null owner case,
            // only one thread succeeds in taking ownership.
            lock (lockObject)
            {
                if (owner != null)
                {
                    VerifyAccess();
                }
                owner = newOwner;
            }
        }
        #endregion

        #region Fields + Constructor
        readonly Rope<char> rope;
        readonly DocumentLineTree lineTree;
        readonly LineManager lineManager;
        readonly TextAnchorTree anchorTree;
        ChangeTrackingCheckpoint currentCheckpoint;

        /// <summary>
        /// Create an empty text document.
        /// </summary>
        public TextDocument()
            : this(string.Empty)
        {
        }

        /// <summary>
        /// Create a new text document with the specified initial text.
        /// </summary>
        public TextDocument(IEnumerable<char> initialText)
        {
            if (initialText == null)
                throw new ArgumentNullException("initialText");
            rope = new Rope<char>(initialText);
            lineTree = new DocumentLineTree(this);
            lineManager = new LineManager(lineTree, this);
            lineTrackers.CollectionChanged += delegate
            {
                lineManager.UpdateListOfLineTrackers();
            };

            anchorTree = new TextAnchorTree(this);
            undoStack = new UndoStack();
            FireChangeEvents();
        }

        /// <summary>
        /// Create a new text document with the specified initial text.
        /// </summary>
        public TextDocument(ITextSource initialText)
            : this(GetTextFromTextSource(initialText))
        {
        }

        // gets the text from a text source, directly retrieving the underlying rope where possible
        static IEnumerable<char> GetTextFromTextSource(ITextSource textSource)
        {
            if (textSource == null)
                throw new ArgumentNullException("textSource");

            RopeTextSource rts = textSource as RopeTextSource;
            if (rts != null)
                return rts.GetRope();

            TextDocument doc = textSource as TextDocument;
            if (doc != null)
                return doc.rope;

            return textSource.Text;
        }
        #endregion

        #region Text
        void ThrowIfRangeInvalid(int offset, int length)
        {
            if (offset < 0 || offset > rope.Length)
            {
                throw new ArgumentOutOfRangeException("offset", offset, "0 <= offset <= " + rope.Length.ToString(CultureInfo.InvariantCulture));
            }
            if (length < 0 || offset + length > rope.Length)
            {
                throw new ArgumentOutOfRangeException("length", length, "0 <= length, offset(" + offset + ")+length <= " + rope.Length.ToString(CultureInfo.InvariantCulture));
            }
        }

        /// <inheritdoc/>
        public string GetText(int offset, int length)
        {
            VerifyAccess();
            return rope.ToString(Math.Max(offset, 0), length);
        }

        /// <summary>
        /// Retrieves the text for a portion of the document.
        /// </summary>
        public string GetText(ISegment segment)
        {
            if (segment == null)
                throw new ArgumentNullException("segment");
            return GetText(segment.Offset, segment.Length);
        }

        int ITextSource.IndexOfAny(char[] anyOf, int startIndex, int count)
        {
            DebugVerifyAccess(); // frequently called (NewLineFinder), so must be fast in release builds
            return rope.IndexOfAny(anyOf, startIndex, count);
        }

        /// <inheritdoc/>
        public char GetCharAt(int offset)
        {
            DebugVerifyAccess(); // frequently called, so must be fast in release builds
            return rope[offset];
        }

        WeakReference cachedText;

        /// <summary>
        /// Gets/Sets the text of the whole document.
        /// </summary>
        public string Text
        {
            get
            {
                VerifyAccess();
                string completeText = cachedText != null ? (cachedText.Target as string) : null;
                if (completeText == null)
                {
                    completeText = rope.ToString();
                    cachedText = new WeakReference(completeText);
                }
                return completeText;
            }
            set
            {
                VerifyAccess();
                if (value == null)
                    throw new ArgumentNullException("value");
                Replace(0, rope.Length, value);
            }
        }

        /// <inheritdoc/>
        /// <remarks><inheritdoc cref="Changing"/></remarks>
        public event EventHandler TextChanged;

        /// <inheritdoc/>
        public int TextLength
        {
            get
            {
                VerifyAccess();
                return rope.Length;
            }
        }

        /// <summary>
        /// Is raised when the TextLength property changes.
        /// </summary>
        /// <remarks><inheritdoc cref="Changing"/></remarks>
        [Obsolete("This event will be removed in a future version; use the PropertyChanged event instead")]
        public event EventHandler TextLengthChanged;

        /// <summary>
        /// Is raised when one of the properties <see cref="Text"/>, <see cref="TextLength"/>, <see cref="LineCount"/>,
        /// <see cref="UndoStack"/> changes.
        /// </summary>
        /// <remarks><inheritdoc cref="Changing"/></remarks>
        public event PropertyChangedEventHandler PropertyChanged;

        /// <summary>
        /// Is raised before the document changes.
        /// </summary>
        /// <remarks>
        /// <para>Here is the order in which events are raised during a document update:</para>
        /// <list type="bullet">
        /// <item><description><b><see cref="BeginUpdate">BeginUpdate()</see></b></description>
        ///   <list type="bullet">
        ///   <item><description>Start of change group (on undo stack)</description></item>
        ///   <item><description><see cref="UpdateStarted"/> event is raised</description></item>
        ///   </list></item>
        /// <item><description><b><see cref="Insert(int,string)">Insert()</see> / <see cref="Remove(int,int)">Remove()</see> / <see cref="Replace(int,int,string)">Replace()</see></b></description>
        ///   <list type="bullet">
        ///   <item><description><see cref="Changing"/> event is raised</description></item>
        ///   <item><description>The document is changed</description></item>
        ///   <item><description><see cref="TextAnchor.Deleted">TextAnchor.Deleted</see> event is raised if anchors were
        ///     in the deleted text portion</description></item>
        ///   <item><description><see cref="Changed"/> event is raised</description></item>
        ///   </list></item>
        /// <item><description><b><see cref="EndUpdate">EndUpdate()</see></b></description>
        ///   <list type="bullet">
        ///   <item><description><see cref="TextChanged"/> event is raised</description></item>
        ///   <item><description><see cref="PropertyChanged"/> event is raised (for the Text, TextLength, LineCount properties, in that order)</description></item>
        ///   <item><description>End of change group (on undo stack)</description></item>
        ///   <item><description><see cref="UpdateFinished"/> event is raised</description></item>
        ///   </list></item>
        /// </list>
        /// <para>
        /// If the insert/remove/replace methods are called without a call to <c>BeginUpdate()</c>,
        /// they will call <c>BeginUpdate()</c> and <c>EndUpdate()</c> to ensure no change happens outside of <c>UpdateStarted</c>/<c>UpdateFinished</c>.
        /// </para><para>
        /// There can be multiple document changes between the <c>BeginUpdate()</c> and <c>EndUpdate()</c> calls.
        /// In this case, the events associated with EndUpdate will be raised only once after the whole document update is done.
        /// </para><para>
        /// The <see cref="UndoStack"/> listens to the <c>UpdateStarted</c> and <c>UpdateFinished</c> events to group all changes into a single undo step.
        /// </para>
        /// </remarks>
        public event EventHandler<DocumentChangeEventArgs> Changing;

        /// <summary>
        /// Is raised after the document has changed.
        /// </summary>
        /// <remarks><inheritdoc cref="Changing"/></remarks>
        public event EventHandler<DocumentChangeEventArgs> Changed;

        /// <summary>
        /// Creates a snapshot of the current text.
        /// </summary>
        /// <remarks>
        /// <para>This method returns an immutable snapshot of the document, and may be safely called even when
        /// the document's owner thread is concurrently modifying the document.
        /// </para><para>
        /// This special thread-safety guarantee is valid only for TextDocument.CreateSnapshot(), not necessarily for other
        /// classes implementing ITextSource.CreateSnapshot().
        /// </para><para>
        /// </para>
        /// </remarks>
        public ITextSource CreateSnapshot()
        {
            lock (lockObject)
            {
                return new RopeTextSource(rope.Clone());
            }
        }

        /// <summary>
        /// Creates a snapshot of the current text.
        /// Additionally, creates a checkpoint that allows tracking document changes.
        /// </summary>
        /// <remarks><inheritdoc cref="CreateSnapshot()"/><inheritdoc cref="ChangeTrackingCheckpoint"/></remarks>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1021:AvoidOutParameters", Justification = "Need to return snapshot and checkpoint together to ensure thread-safety")]
        public ITextSource CreateSnapshot(out ChangeTrackingCheckpoint checkpoint)
        {
            lock (lockObject)
            {
                if (currentCheckpoint == null)
                    currentCheckpoint = new ChangeTrackingCheckpoint(lockObject);
                checkpoint = currentCheckpoint;
                return new RopeTextSource(rope.Clone());
            }
        }

        internal ChangeTrackingCheckpoint CreateChangeTrackingCheckpoint()
        {
            lock (lockObject)
            {
                if (currentCheckpoint == null)
                    currentCheckpoint = new ChangeTrackingCheckpoint(lockObject);
                return currentCheckpoint;
            }
        }

        /// <summary>
        /// Creates a snapshot of a part of the current text.
        /// </summary>
        /// <remarks><inheritdoc cref="CreateSnapshot()"/></remarks>
        public ITextSource CreateSnapshot(int offset, int length)
        {
            lock (lockObject)
            {
                return new RopeTextSource(rope.GetRange(offset, length));
            }
        }

        /// <inheritdoc/>
        public System.IO.TextReader CreateReader()
        {
            lock (lockObject)
            {
                return new RopeTextReader(rope);
            }
        }
        #endregion

        #region BeginUpdate / EndUpdate
        int beginUpdateCount;

        /// <summary>
        /// Gets if an update is running.
        /// </summary>
        /// <remarks><inheritdoc cref="BeginUpdate"/></remarks>
        public bool IsInUpdate
        {
            get
            {
                VerifyAccess();
                return beginUpdateCount > 0;
            }
        }

        /// <summary>
        /// Immediately calls <see cref="BeginUpdate()"/>,
        /// and returns an IDisposable that calls <see cref="EndUpdate()"/>.
        /// </summary>
        /// <remarks><inheritdoc cref="BeginUpdate"/></remarks>
        public IDisposable RunUpdate()
        {
            BeginUpdate();
            return new CallbackOnDispose(EndUpdate);
        }

        /// <summary>
        /// <para>Begins a group of document changes.</para>
        /// <para>Some events are suspended until EndUpdate is called, and the <see cref="UndoStack"/> will
        /// group all changes into a single action.</para>
        /// <para>Calling BeginUpdate several times increments a counter, only after the appropriate number
        /// of EndUpdate calls the events resume their work.</para>
        /// </summary>
        /// <remarks><inheritdoc cref="Changing"/></remarks>
        public void BeginUpdate()
        {
            VerifyAccess();
            if (inDocumentChanging)
                throw new InvalidOperationException("Cannot change document within another document change.");
            beginUpdateCount++;
            if (beginUpdateCount == 1)
            {
                undoStack.StartUndoGroup();
                if (UpdateStarted != null)
                    UpdateStarted(this, EventArgs.Empty);
            }
        }

        /// <summary>
        /// Ends a group of document changes.
        /// </summary>
        /// <remarks><inheritdoc cref="Changing"/></remarks>
        public void EndUpdate()
        {
            VerifyAccess();
            if (inDocumentChanging)
                throw new InvalidOperationException("Cannot end update within document change.");
            if (beginUpdateCount == 0)
                throw new InvalidOperationException("No update is active.");
            if (beginUpdateCount == 1)
            {
                // fire change events inside the change group - event handlers might add additional
                // document changes to the change group
                FireChangeEvents();
                undoStack.EndUndoGroup();
                beginUpdateCount = 0;
                if (UpdateFinished != null)
                    UpdateFinished(this, EventArgs.Empty);
            }
            else
            {
                beginUpdateCount -= 1;
            }
        }

        /// <summary>
        /// Occurs when a document change starts.
        /// </summary>
        /// <remarks><inheritdoc cref="Changing"/></remarks>
        public event EventHandler UpdateStarted;

        /// <summary>
        /// Occurs when a document change is finished.
        /// </summary>
        /// <remarks><inheritdoc cref="Changing"/></remarks>
        public event EventHandler UpdateFinished;
        #endregion

        #region Fire events after update
        int oldTextLength;
        int oldLineCount;
        bool fireTextChanged;

        /// <summary>
        /// Fires TextChanged, TextLengthChanged, LineCountChanged if required.
        /// </summary>
        internal void FireChangeEvents()
        {
            // it may be necessary to fire the event multiple times if the document is changed
            // from inside the event handlers
            while (fireTextChanged)
            {
                fireTextChanged = false;
                if (TextChanged != null)
                    TextChanged(this, EventArgs.Empty);
                OnPropertyChanged("Text");

                int textLength = rope.Length;
                if (textLength != oldTextLength)
                {
                    oldTextLength = textLength;
                    if (TextLengthChanged != null)
                        TextLengthChanged(this, EventArgs.Empty);
                    OnPropertyChanged("TextLength");
                }
                int lineCount = lineTree.LineCount;
                if (lineCount != oldLineCount)
                {
                    oldLineCount = lineCount;
                    if (LineCountChanged != null)
                        LineCountChanged(this, EventArgs.Empty);
                    OnPropertyChanged("LineCount");
                }
            }
        }

        void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
        #endregion

        #region Insert / Remove  / Replace
        /// <summary>
        /// Inserts text.
        /// </summary>
        public void Insert(int offset, string text)
        {
            Replace(offset, 0, text);
        }

        /// <summary>
        /// Removes text.
        /// </summary>
        public void Remove(ISegment segment)
        {
            Replace(segment, string.Empty);
        }

        /// <summary>
        /// Removes text.
        /// </summary>
        public void Remove(int offset, int length)
        {
            Replace(offset, length, string.Empty);
        }

        internal bool inDocumentChanging;

        /// <summary>
        /// Replaces text.
        /// </summary>
        public void Replace(ISegment segment, string text)
        {
            if (segment == null)
                throw new ArgumentNullException("segment");
            Replace(segment.Offset, segment.Length, text, null);
        }

        /// <summary>
        /// Replaces text.
        /// </summary>
        public void Replace(int offset, int length, string text)
        {
            Replace(offset, length, text, null);
        }

        /// <summary>
        /// Replaces text.
        /// </summary>
        /// <param name="offset">The starting offset of the text to be replaced.</param>
        /// <param name="length">The length of the text to be replaced.</param>
        /// <param name="text">The new text.</param>
        /// <param name="offsetChangeMappingType">The offsetChangeMappingType determines how offsets inside the old text are mapped to the new text.
        /// This affects how the anchors and segments inside the replaced region behave.</param>
        public void Replace(int offset, int length, string text, OffsetChangeMappingType offsetChangeMappingType)
        {
            if (text == null)
                throw new ArgumentNullException("text");
            // Please see OffsetChangeMappingType XML comments for details on how these modes work.
            switch (offsetChangeMappingType)
            {
                case OffsetChangeMappingType.Normal:
                    Replace(offset, length, text, null);
                    break;
                case OffsetChangeMappingType.KeepAnchorBeforeInsertion:
                    Replace(offset, length, text, OffsetChangeMap.FromSingleElement(
                        new OffsetChangeMapEntry(offset, length, text.Length, false, true)));
                    break;
                case OffsetChangeMappingType.RemoveAndInsert:
                    if (length == 0 || text.Length == 0)
                    {
                        // only insertion or only removal?
                        // OffsetChangeMappingType doesn't matter, just use Normal.
                        Replace(offset, length, text, null);
                    }
                    else
                    {
                        OffsetChangeMap map = new OffsetChangeMap(2);
                        map.Add(new OffsetChangeMapEntry(offset, length, 0));
                        map.Add(new OffsetChangeMapEntry(offset, 0, text.Length));
                        map.Freeze();
                        Replace(offset, length, text, map);
                    }
                    break;
                case OffsetChangeMappingType.CharacterReplace:
                    if (length == 0 || text.Length == 0)
                    {
                        // only insertion or only removal?
                        // OffsetChangeMappingType doesn't matter, just use Normal.
                        Replace(offset, length, text, null);
                    }
                    else if (text.Length > length)
                    {
                        // look at OffsetChangeMappingType.CharacterReplace XML comments on why we need to replace
                        // the last character
                        OffsetChangeMapEntry entry = new OffsetChangeMapEntry(offset + length - 1, 1, 1 + text.Length - length);
                        Replace(offset, length, text, OffsetChangeMap.FromSingleElement(entry));
                    }
                    else if (text.Length < length)
                    {
                        OffsetChangeMapEntry entry = new OffsetChangeMapEntry(offset + text.Length, length - text.Length, 0, true, false);
                        Replace(offset, length, text, OffsetChangeMap.FromSingleElement(entry));
                    }
                    else
                    {
                        Replace(offset, length, text, OffsetChangeMap.Empty);
                    }
                    break;
                default:
                    throw new ArgumentOutOfRangeException("offsetChangeMappingType", offsetChangeMappingType, "Invalid enum value");
            }
        }

        /// <summary>
        /// Replaces text.
        /// </summary>
        /// <param name="offset">The starting offset of the text to be replaced.</param>
        /// <param name="length">The length of the text to be replaced.</param>
        /// <param name="text">The new text.</param>
        /// <param name="offsetChangeMap">The offsetChangeMap determines how offsets inside the old text are mapped to the new text.
        /// This affects how the anchors and segments inside the replaced region behave.
        /// If you pass null (the default when using one of the other overloads), the offsets are changed as
        /// in OffsetChangeMappingType.Normal mode.
        /// If you pass OffsetChangeMap.Empty, then everything will stay in its old place (OffsetChangeMappingType.CharacterReplace mode).
        /// The offsetChangeMap must be a valid 'explanation' for the document change. See <see cref="OffsetChangeMap.IsValidForDocumentChange"/>.
        /// Passing an OffsetChangeMap to the Replace method will automatically freeze it to ensure the thread safety of the resulting
        /// DocumentChangeEventArgs instance.
        /// </param>
        public void Replace(int offset, int length, string text, OffsetChangeMap offsetChangeMap)
        {
            if (text == null)
                throw new ArgumentNullException("text");

            if (offsetChangeMap != null)
                offsetChangeMap.Freeze();

            // Ensure that all changes take place inside an update group.
            // Will also take care of throwing an exception if inDocumentChanging is set.
            BeginUpdate();
            try
            {
                // protect document change against corruption by other changes inside the event handlers
                inDocumentChanging = true;
                try
                {
                    // The range verification must wait until after the BeginUpdate() call because the document
                    // might be modified inside the UpdateStarted event.
                    ThrowIfRangeInvalid(offset, length);

                    DoReplace(offset, length, text, offsetChangeMap);
                }
                finally
                {
                    inDocumentChanging = false;
                }
            }
            finally
            {
                EndUpdate();
            }
        }

        void DoReplace(int offset, int length, string newText, OffsetChangeMap offsetChangeMap)
        {
            if (length == 0 && newText.Length == 0)
                return;

            // trying to replace a single character in 'Normal' mode?
            // for single characters, 'CharacterReplace' mode is equivalent, but more performant
            // (we don't have to touch the anchorTree at all in 'CharacterReplace' mode)
            if (length == 1 && newText.Length == 1 && offsetChangeMap == null)
                offsetChangeMap = OffsetChangeMap.Empty;

            string removedText = rope.ToString(offset, length);
            DocumentChangeEventArgs args = new DocumentChangeEventArgs(offset, removedText, newText, offsetChangeMap);

            // fire DocumentChanging event
            if (Changing != null)
                Changing(this, args);

            undoStack.Push(this, args);

            cachedText = null; // reset cache of complete document text
            fireTextChanged = true;
            DelayedEvents delayedEvents = new DelayedEvents();

            lock (lockObject)
            {
                // create linked list of checkpoints, if required
                if (currentCheckpoint != null)
                {
                    currentCheckpoint = currentCheckpoint.Append(args);
                }

                // now update the textBuffer and lineTree
                if (offset == 0 && length == rope.Length)
                {
                    // optimize replacing the whole document
                    rope.Clear();
                    rope.InsertText(0, newText);
                    lineManager.Rebuild();
                }
                else
                {
                    rope.RemoveRange(offset, length);
                    lineManager.Remove(offset, length);
#if DEBUG
                    lineTree.CheckProperties();
#endif
                    rope.InsertText(offset, newText);
                    lineManager.Insert(offset, newText);
#if DEBUG
                    lineTree.CheckProperties();
#endif
                }
            }

            // update text anchors
            if (offsetChangeMap == null)
            {
                anchorTree.HandleTextChange(args.CreateSingleChangeMapEntry(), delayedEvents);
            }
            else
            {
                foreach (OffsetChangeMapEntry entry in offsetChangeMap)
                {
                    anchorTree.HandleTextChange(entry, delayedEvents);
                }
            }

            // raise delayed events after our data structures are consistent again
            delayedEvents.RaiseEvents();

            // fire DocumentChanged event
            if (Changed != null)
                Changed(this, args);
        }
        #endregion

        #region GetLineBy...
        /// <summary>
        /// Gets a read-only list of lines.
        /// </summary>
        /// <remarks><inheritdoc cref="DocumentLine"/></remarks>
        public IList<DocumentLine> Lines
        {
            get { return lineTree; }
        }

        /// <summary>
        /// Gets a line by the line number: O(log n)
        /// </summary>
        public DocumentLine GetLineByNumber(int number)
        {
            VerifyAccess();
            if (number < 1 || number > lineTree.LineCount)
                throw new ArgumentOutOfRangeException("number", number, "Value must be between 1 and " + lineTree.LineCount);
            return lineTree.GetByNumber(number);
        }

        /// <summary>
        /// Gets a document lines by offset.
        /// Runtime: O(log n)
        /// </summary>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Globalization", "CA1305:SpecifyIFormatProvider", MessageId = "System.Int32.ToString")]
        public DocumentLine GetLineByOffset(int offset)
        {
            VerifyAccess();
            if (offset < 0 || offset > rope.Length)
            {
                throw new ArgumentOutOfRangeException("offset", offset, "0 <= offset <= " + rope.Length.ToString());
            }
            return lineTree.GetByOffset(offset);
        }
        #endregion

        /// <summary>
        /// Gets the offset from a text location.
        /// </summary>
        /// <seealso cref="GetLocation"/>
        public int GetOffset(TextLocation location)
        {
            return GetOffset(location.Line, location.Column);
        }

        /// <summary>
        /// Gets the offset from a text location.
        /// </summary>
        /// <seealso cref="GetLocation"/>
        public int GetOffset(int line, int column)
        {
            DocumentLine docLine = GetLineByNumber(line);
            if (column <= 0)
                return docLine.Offset;
            if (column > docLine.Length)
                return docLine.EndOffset;
            return docLine.Offset + column - 1;
        }

        /// <summary>
        /// Gets the location from an offset.
        /// </summary>
        /// <seealso cref="GetOffset(TextLocation)"/>
        public TextLocation GetLocation(int offset)
        {
            DocumentLine line = GetLineByOffset(offset);
            return new TextLocation(line.LineNumber, offset - line.Offset + 1);
        }

        readonly ObservableCollection<ILineTracker> lineTrackers = new ObservableCollection<ILineTracker>();

        /// <summary>
        /// Gets the list of <see cref="ILineTracker"/>s attached to this document.
        /// You can add custom line trackers to this list.
        /// </summary>
        public IList<ILineTracker> LineTrackers
        {
            get
            {
                VerifyAccess();
                return lineTrackers;
            }
        }

        UndoStack undoStack;

        /// <summary>
        /// Gets the <see cref="UndoStack"/> of the document.
        /// </summary>
        /// <remarks>This property can also be used to set the undo stack, e.g. for sharing a common undo stack between multiple documents.</remarks>
        public UndoStack UndoStack
        {
            get { return undoStack; }
            set
            {
                if (value == null)
                    throw new ArgumentNullException();
                if (value != undoStack)
                {
                    undoStack.ClearAll(); // first clear old undo stack, so that it can't be used to perform unexpected changes on this document
                                          // ClearAll() will also throw an exception when it's not safe to replace the undo stack (e.g. update is currently in progress)
                    undoStack = value;
                    OnPropertyChanged("UndoStack");
                }
            }
        }

        /// <summary>
        /// Creates a new <see cref="TextAnchor"/> at the specified offset.
        /// </summary>
        /// <inheritdoc cref="TextAnchor" select="remarks|example"/>
        public TextAnchor CreateAnchor(int offset)
        {
            VerifyAccess();
            if (offset < 0 || offset > rope.Length)
            {
                throw new ArgumentOutOfRangeException("offset", offset, "0 <= offset <= " + rope.Length.ToString(CultureInfo.InvariantCulture));
            }
            return anchorTree.CreateAnchor(offset);
        }

        #region LineCount
        /// <summary>
        /// Gets the total number of lines in the document.
        /// Runtime: O(1).
        /// </summary>
        public int LineCount
        {
            get
            {
                VerifyAccess();
                return lineTree.LineCount;
            }
        }

        /// <summary>
        /// Is raised when the LineCount property changes.
        /// </summary>
        [Obsolete("This event will be removed in a future version; use the PropertyChanged event instead")]
        public event EventHandler LineCountChanged;
        #endregion

        #region Debugging
        [Conditional("DEBUG")]
        internal void DebugVerifyAccess()
        {
            VerifyAccess();
        }

        /// <summary>
        /// Gets the document lines tree in string form.
        /// </summary>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1024:UsePropertiesWhereAppropriate")]
        internal string GetLineTreeAsString()
        {
#if DEBUG
            return lineTree.GetTreeAsString();
#else
			return "Not available in release build.";
#endif
        }

        /// <summary>
        /// Gets the text anchor tree in string form.
        /// </summary>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1024:UsePropertiesWhereAppropriate")]
        internal string GetTextAnchorTreeAsString()
        {
#if DEBUG
            return anchorTree.GetTreeAsString();
#else
			return "Not available in release build.";
#endif
        }
        #endregion
    }
}