Limit inheritance policy work to the relevant scope

internal/engine/inheritance_policy_index.go

@@ -0,0 +1,123 @@
+package engine
+
+// inheritancePolicyIndex borrows immutable policy entries. Semantic path
+// segments keep mapping keys distinct from sequence indexes. Record-owned
+// scopes have their own indexes, just as they have their own policy tables.
+type inheritancePolicyIndex struct {
+	entry    *collectionPolicyEntry
+	children map[pathSegment]*inheritancePolicyIndex
+	records  map[int]*inheritancePolicyIndex
+}
+
+func newInheritancePolicyIndex(scope collectionPolicyScope) *inheritancePolicyIndex {
+	index := &inheritancePolicyIndex{}
+	for _, entry := range scope.collections {
+		index.set(entry)
+	}
+	return index
+}
+
+func (index *inheritancePolicyIndex) set(entry collectionPolicyEntry) {
+	node := index
+	for _, segment := range entry.destination.segments {
+		if node.children == nil {
+			node.children = make(map[pathSegment]*inheritancePolicyIndex)
+		}
+		if node.children[segment] == nil {
+			node.children[segment] = &inheritancePolicyIndex{}
+		}
+		node = node.children[segment]
+	}
+	node.entry = &entry
+	node.records = nil
+	for position, owner := range entry.policy.recordOrder {
+		scope := entry.policy.recordPolicies[owner]
+		if len(scope.collections) == 0 {
+			continue
+		}
+		if node.records == nil {
+			node.records = make(map[int]*inheritancePolicyIndex)
+		}
+		node.records[position] = newInheritancePolicyIndex(scope)
+	}
+}
+
+// localize copies only policies in the requested scope. Earlier record-owned
+// policies are considered before direct entries added by destination expansion.
+func (index *inheritancePolicyIndex) localize(prefix Path) collectionPolicyScope {
+	localized := collectionPolicyScope{}
+	node := index
+	for offset, segment := range prefix.segments {
+		if node == nil {
+			return localized
+		}
+		if segment.kind == pathSegmentIndex {
+			if record := node.records[segment.index]; record != nil {
+				remainder := Path{segments: prefix.segments[offset+1:]}
+				for _, entry := range record.localize(remainder).collections {
+					localized.set(entry.destination, entry.policy)
+				}
+			}
+		}
+		node = node.children[segment]
+	}
+	var collect func(*inheritancePolicyIndex)
+	collect = func(node *inheritancePolicyIndex) {
+		if node == nil {
+			return
+		}
+		if node.entry != nil {
+			relative, _ := relativeHistoryPath(prefix, node.entry.destination)
+			localized.set(relative, cloneCollectionPolicyForInheritance(node.entry.policy))
+		}
+		for _, child := range node.children {
+			collect(child)
+		}
+	}
+	collect(node)
+	return localized
+}
+
+func (index *inheritancePolicyIndex) absoluteScope(prefix Path) collectionPolicyScope {
+	scope := collectionPolicyScope{}
+	for _, entry := range index.localize(prefix).collections {
+		scope.set(appendDestination(prefix, entry.destination), entry.policy)
+	}
+	return scope
+}
+
+// replace updates the walker's owned table and its borrowed index together.
+// Retirement visits only direct entries below the changed destination.
+func (index *inheritancePolicyIndex) replace(scope *collectionPolicyScope, prefix Path, replacement collectionPolicyScope) {
+	node := index
+	var parent *inheritancePolicyIndex
+	var last pathSegment
+	for _, segment := range prefix.segments {
+		if node == nil {
+			break
+		}
+		parent, last, node = node, segment, node.children[segment]
+	}
+	var remove func(*inheritancePolicyIndex)
+	remove = func(node *inheritancePolicyIndex) {
+		if node == nil {
+			return
+		}
+		if node.entry != nil {
+			delete(scope.collections, node.entry.destination.String())
+		}
+		for _, child := range node.children {
+			remove(child)
+		}
+	}
+	remove(node)
+	if parent == nil {
+		*index = inheritancePolicyIndex{}
+	} else {
+		delete(parent.children, last)
+	}
+	for _, entry := range replacement.collections {
+		scope.set(entry.destination, entry.policy)
+		index.set(scope.collections[entry.destination.String()])
+	}
+}