/// <summary>Gets the new anchor position as a consequence of this document change</summary>
public int NewOffset(int offset, AnchorMapping.EMove move_type)
{
if (offset > Offset)
{
offset -= Math.Min(offset - Offset, TextRemoved.Length - Offset);
}
if (offset >= Offset)
{
offset += move_type switch
{
AnchorMapping.EMove.Default => offset > Offset ? TextInserted.Length : 0,
AnchorMapping.EMove.BeforeInsertion => offset > Offset ? TextInserted.Length : 0,
AnchorMapping.EMove.AfterInsertion => TextInserted.Length,
_ => throw new Exception("Unknown anchor movement type")
};
}
return(offset);
}
}
// Notes:
// - TextAnchor references an offset (a position between two characters). It automatically updates
// when text is inserted/removed in the document.
// - TextAnchor only adds a weak reference to document.Change so unsubscribing isn't needed and
// anchors wont keep a Document from being collected.
// - To track a segment, use AnchorSegment which implements ISegment using two text anchors.
// - Use TextDocument.CreateAnchor to create an anchor from an offset.
// - Anchor movement is ambiguous if text is inserted exactly at the anchor's location. Does the anchor
// stay before the inserted text, or does it move after it? The property MovementType is used to determine
// which of these options the anchor will choose.
//
// Example:
// auto anchor = document.CreateAnchor(offset);
// ChangeMyDocument();
// int newOffset = anchor.Offset;
internal TextAnchor(TextDocument document, int offset, AnchorMapping.EMove move)
{
Offset = offset;
Movement = move;
document.ChangeInternal += WeakRef.MakeWeak <DocumentChangeEventArgs>(HandleDocChanged, h => document.ChangeInternal -= h);
void HandleDocChanged(object?sender, DocumentChangeEventArgs e)
{
if (!(sender is TextDocument doc))
{
throw new Exception("sender should be a TextDocument");
}
if (e.After && !IsDeleted)
{
// If the anchor is before the change, ignore
if (Offset < e.Offset)
{
}
// If the anchor is after the removed text, adjust by the difference in inserted - removed
else if (Offset >= e.Offset + e.TextRemoved.Length)
{
Offset += e.TextInserted.Length - e.TextRemoved.Length;
}
// Otherwise, the anchor is within the removed text
else
{
switch (Movement)
{
case AnchorMapping.EMove.Default:
{
// If the anchor is at the insertion offset, move to after the inserted text
if (Offset == e.Offset)
{
Offset += e.TextInserted.Length - e.TextRemoved.Length;
}
// Otherwise, delete the anchor
else
{
Delete();
}
break;
}
case AnchorMapping.EMove.BeforeInsertion:
{
// Move the anchor to the insertion offset
Offset += e.Offset;
break;
}
case AnchorMapping.EMove.AfterInsertion:
{
// Move the anchor to after the insertion
Offset += e.TextInserted.Length - e.TextRemoved.Length;
break;
}
default:
{
throw new Exception("Unknown anchor movement type");
}
}
}
}
}
}