// Finds a node/edge pair matching a given char offset in the tree.
// If the pair matches a character within a text node, the text node is split.
internal void GetNodeAndEdgeAtCharOffset(int charOffset, out TextTreeNode node, out ElementEdge edge)
{
int nodeCharOffset;
int siblingTreeCharOffset;
bool checkZeroWidthNode;
// Offset zero/SymbolCount-1 are before/after the root node, which
// is an illegal position -- you can't add or remove content there
// and it's never exposed publicly.
Invariant.Assert(charOffset >= 0 && charOffset <= this.IMECharCount, "Bogus char offset!");
if (this.IMECharCount == 0)
{
node = null;
edge = ElementEdge.BeforeStart;
return;
}
// If this flag is set true on exit, we need to consider the case
// where we've found a "zero-width" (SymbolCount == 0) text node.
// Zero width nodes needs special handling, since they are logically
// part of a following or preceding node.
checkZeroWidthNode = false;
// Find the node.
node = _rootNode;
nodeCharOffset = 0;
// Each iteration walks through one tree.
while (true)
{
int leftEdgeCharCount = 0;
TextTreeTextElementNode textElementNode = node as TextTreeTextElementNode;
if (textElementNode != null)
{
leftEdgeCharCount = textElementNode.IMELeftEdgeCharCount;
if (leftEdgeCharCount > 0)
{
if (charOffset == nodeCharOffset)
{
edge = ElementEdge.BeforeStart;
break;
}
if (charOffset == nodeCharOffset + leftEdgeCharCount)
{
edge = ElementEdge.AfterStart;
break;
}
}
}
else if (node is TextTreeTextNode || node is TextTreeObjectNode)
{
if (charOffset == nodeCharOffset)
{
edge = ElementEdge.BeforeStart;
checkZeroWidthNode = true;
break;
}
if (charOffset == nodeCharOffset + node.IMECharCount)
{
edge = ElementEdge.AfterEnd;
checkZeroWidthNode = true;
break;
}
}
// No child node? That means we're inside a TextTreeTextNode.
if (node.ContainedNode == null)
{
Invariant.Assert(node is TextTreeTextNode);
// Need to split the TextTreeTextNode.
// Here we want a character buried inside a single node, split
// the node open....
node = ((TextTreeTextNode)node).Split(charOffset - nodeCharOffset, ElementEdge.AfterEnd);
edge = ElementEdge.BeforeStart;
break;
}
// Need to look into one of the child nodes.
node = (TextTreeNode)node.ContainedNode;
nodeCharOffset += leftEdgeCharCount; // Skip over the parent element start edge.
// Walk down the sibling tree.
node = (TextTreeNode)node.GetSiblingAtCharOffset(charOffset - nodeCharOffset, out siblingTreeCharOffset);
nodeCharOffset += siblingTreeCharOffset;
}
// If we're on a zero-width TextTreeTextNode we need some special handling.
if (checkZeroWidthNode)
{
node = (TextTreeNode)AdjustForZeroWidthNode(node, edge);
}
}