// Finds a node/edge pair matching a given symbol offset in the tree.
// If the pair matches a character within a text node, the text node is split.
internal void GetNodeAndEdgeAtOffset(int offset, bool splitNode, out SplayTreeNode node, out ElementEdge edge)
{
int nodeOffset;
int siblingTreeOffset;
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(offset >= 1 && offset <= this.InternalSymbolCount - 1, "Bogus symbol offset!");
// 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;
nodeOffset = 0;
// Each iteration walks through one tree.
while (true)
{
// While we're at it, fix up the node's SymbolOffsetCache,
// since we're doing the work already.
Invariant.Assert(node.Generation != _rootNode.Generation ||
node.SymbolOffsetCache == -1 ||
node.SymbolOffsetCache == nodeOffset, "Bad node offset cache!");
node.Generation = _rootNode.Generation;
node.SymbolOffsetCache = nodeOffset;
if (offset == nodeOffset)
{
edge = ElementEdge.BeforeStart;
checkZeroWidthNode = true;
break;
}
if (node is TextTreeRootNode || node is TextTreeTextElementNode)
{
if (offset == nodeOffset + 1)
{
edge = ElementEdge.AfterStart;
break;
}
if (offset == nodeOffset + node.SymbolCount - 1)
{
edge = ElementEdge.BeforeEnd;
break;
}
}
if (offset == nodeOffset + node.SymbolCount)
{
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....
if (splitNode)
{
node = ((TextTreeTextNode)node).Split(offset - nodeOffset, ElementEdge.AfterEnd);
}
edge = ElementEdge.BeforeStart;
break;
}
// Need to look into one of the child nodes.
node = node.ContainedNode;
nodeOffset += 1; // Skip over the parent element start edge.
// Walk down the sibling tree.
node = node.GetSiblingAtOffset(offset - nodeOffset, out siblingTreeOffset);
nodeOffset += siblingTreeOffset;
}
// If we're on a zero-width TextTreeTextNode we need some special handling.
if (checkZeroWidthNode)
{
node = AdjustForZeroWidthNode(node, edge);
}
}
