Add private canonical path prefix index

internal/engine/path_prefix.go

@@ -0,0 +1,138 @@
+package engine
+
+type pathPrefixIndex struct {
+	root pathPrefixNode
+}
+
+type pathPrefixNode struct {
+	children   map[string]*pathPrefixNode
+	ids        []int
+	minimumID  int
+	hasMinimum bool
+}
+
+func (node *pathPrefixNode) includeID(id int) {
+	if !node.hasMinimum || id < node.minimumID {
+		node.minimumID = id
+		node.hasMinimum = true
+	}
+}
+
+func (index *pathPrefixIndex) insert(pointer string, id int) {
+	node := &index.root
+	node.includeID(id)
+	visitCanonicalPointerTokens(pointer, func(token string) bool {
+		if node.children == nil {
+			node.children = make(map[string]*pathPrefixNode)
+		}
+		child := node.children[token]
+		if child == nil {
+			child = &pathPrefixNode{}
+			node.children[token] = child
+		}
+		node = child
+		node.includeID(id)
+		return true
+	})
+	node.ids = append(node.ids, id)
+}
+
+func (index *pathPrefixIndex) visitAncestors(pointer string, visit func(int)) {
+	node := &index.root
+	for _, id := range node.ids {
+		visit(id)
+	}
+	visitCanonicalPointerTokens(pointer, func(token string) bool {
+		child := node.children[token]
+		if child == nil {
+			return false
+		}
+		node = child
+		for _, id := range node.ids {
+			visit(id)
+		}
+		return true
+	})
+}
+
+func (index *pathPrefixIndex) visitDescendants(pointer string, visit func(int)) {
+	root := index.nodeAt(pointer)
+	if root == nil {
+		return
+	}
+	var walk func(*pathPrefixNode)
+	walk = func(node *pathPrefixNode) {
+		for _, id := range node.ids {
+			visit(id)
+		}
+		for _, child := range node.children {
+			walk(child)
+		}
+	}
+	walk(root)
+}
+
+func (index *pathPrefixIndex) earliestIntersectingID(pointer string) (int, bool) {
+	bestID, found := 0, false
+	consider := func(id int) {
+		if !found || id < bestID {
+			bestID = id
+			found = true
+		}
+	}
+	node := &index.root
+	for _, id := range node.ids {
+		consider(id)
+	}
+	complete := visitCanonicalPointerTokens(pointer, func(token string) bool {
+		child := node.children[token]
+		if child == nil {
+			return false
+		}
+		node = child
+		for _, id := range node.ids {
+			consider(id)
+		}
+		return true
+	})
+	if complete && node.hasMinimum {
+		consider(node.minimumID)
+	}
+	return bestID, found
+}
+
+func (index *pathPrefixIndex) nodeAt(pointer string) *pathPrefixNode {
+	node := &index.root
+	complete := visitCanonicalPointerTokens(pointer, func(token string) bool {
+		child := node.children[token]
+		if child == nil {
+			return false
+		}
+		node = child
+		return true
+	})
+	if !complete {
+		return nil
+	}
+	return node
+}
+
+func visitCanonicalPointerTokens(pointer string, visit func(string) bool) bool {
+	if pointer == "" {
+		return true
+	}
+	start := 1
+	for {
+		end := start
+		for end < len(pointer) && pointer[end] != '/' {
+			end++
+		}
+		if !visit(pointer[start:end]) {
+			return false
+		}
+		if end == len(pointer) {
+			return true
+		}
+		start = end + 1
+	}
+}