internal HighFidelityTrackingPoint(ITextVersion version, int position, PointTrackingMode trackingMode, TrackingFidelityMode fidelity)
: base(version, position, trackingMode)
{
if (fidelity != TrackingFidelityMode.UndoRedo && fidelity != TrackingFidelityMode.Backward)
{
throw new ArgumentOutOfRangeException(nameof(fidelity));
}
List <VersionNumberPosition> initialHistory = null;
if (fidelity == TrackingFidelityMode.UndoRedo && version.VersionNumber > 0)
{
// The system may perform undo operations that reach prior to the initial version; if any of
// those transitions are noninvertible, then redoing back to the initial version will give the
// wrong answer. Thus we save the state of the point for the initial version, unless the
// initial version happens to be version zero (in which case we could not undo past it).
initialHistory = new List <VersionNumberPosition>();
if (version.VersionNumber != version.ReiteratedVersionNumber)
{
Debug.Assert(version.ReiteratedVersionNumber < version.VersionNumber);
// If the current version and reiterated version differ, also remember the position
// using the reiterated version number, since when undoing back to this point it
// will be the key that is used.
initialHistory.Add(new VersionNumberPosition(version.ReiteratedVersionNumber, position));
}
initialHistory.Add(new VersionNumberPosition(version.VersionNumber, position));
}
this.cachedPosition = new VersionPositionHistory(version, position, initialHistory);
this.fidelity = fidelity;
}
protected override int TrackPosition(ITextVersion targetVersion)
{
// Compute the new position on the requested snapshot.
// This object caches the most recently requested version and the position in that version.
//
// We are relying on the atomicity of pointer copies (this.cachedPosition might change after we've
// fetched it below but we will always get a self-consistent VersionPosition). This ensures we
// have proper behavior when called from multiple threads (multiple threads may all track and update the
// cached value if called at inconvenient times, but they will return consistent results).
//
// In most cases, one can track backwards from the cached version to a previously computed
// version and get the same result, but this is not always the case: in particular, when the
// position lies in a deleted region, simulating reinsertion of that region will not cause
// the previous value of the position to be recovered. Such transitions are called noninvertible.
// This class explicitly tracks the positions of the point for versions for which the subsequent
// transition is noninvertible; this allows the value to be computed properly when tracking backwards
// or in undo/redo situations.
VersionPositionHistory cached = this.cachedPosition; // must fetch just once
if (targetVersion == cached.Version)
{
// easy!
return(cached.Position);
}
List <VersionNumberPosition> noninvertibleHistory = cached.NoninvertibleHistory;
int targetPosition;
if (targetVersion.VersionNumber > cached.Version.VersionNumber)
{
// Roll the cached version forward to the requested version.
targetPosition = TrackPositionForwardInTime
(this.trackingMode,
this.fidelity,
ref noninvertibleHistory,
cached.Position,
cached.Version,
targetVersion);
// Cache new position
this.cachedPosition = new VersionPositionHistory(targetVersion, targetPosition, noninvertibleHistory);
}
else
{
// roll backwards from the cached version
targetPosition = TrackPositionBackwardInTime
(this.trackingMode,
this.fidelity == TrackingFidelityMode.Backward ? noninvertibleHistory : null,
cached.Position,
cached.Version,
targetVersion);
}
return(targetPosition);
}
public override string ToString()
{
VersionPositionHistory c = this.cachedPosition;
System.Text.StringBuilder sb = new System.Text.StringBuilder("*");
sb.Append(ToString(c.Version, c.Position, this.trackingMode));
if (c.NoninvertibleHistory != null)
{
sb.Append("[");
foreach (VersionNumberPosition vp in c.NoninvertibleHistory)
{
sb.Append(string.Format(System.Globalization.CultureInfo.CurrentCulture, "V{0}@{1}", vp.VersionNumber, vp.Position));
}
sb.Append("]");
}
return(sb.ToString());
}
