Refactor PatchSet to be contained in a separate package for reusability.

Author: mtrqq

cluster-autoscaler/simulator/common/patch.go

@@ -0,0 +1,87 @@
+/*
+Copyright 2025 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package common
+
+// Patch represents a single layer of modifications (additions/updates)
+// and deletions for a set of key-value pairs. It's used as a building
+// block for the patchSet.
+type Patch[K comparable, V any] struct {
+	modified map[K]V
+	deleted  map[K]bool
+}
+
+// Set marks a key-value pair as modified in the current patch.
+// If the key was previously marked as deleted, the deletion mark is removed.
+func (p *Patch[K, V]) Set(key K, value V) {
+	p.modified[key] = value
+	delete(p.deleted, key)
+}
+
+// Delete marks a key as deleted in the current patch.
+// If the key was previously marked as modified, the modification is removed.
+func (p *Patch[K, V]) Delete(key K) {
+	delete(p.modified, key)
+	p.deleted[key] = true
+}
+
+// Get retrieves the modified value for a key within this specific patch.
+// It returns the value and true if the key was found in this patch
+// or zero value and false otherwise.
+func (p *Patch[K, V]) Get(key K) (value V, found bool) {
+	value, found = p.modified[key]
+	return value, found
+}
+
+// IsDeleted checks if the key is marked as deleted within this specific patch.
+func (p *Patch[K, V]) IsDeleted(key K) bool {
+	return p.deleted[key]
+}
+
+// NewPatch creates a new, empty patch with no modifications or deletions.
+func NewPatch[K comparable, V any]() *Patch[K, V] {
+	return &Patch[K, V]{
+		modified: make(map[K]V),
+		deleted:  make(map[K]bool),
+	}
+}
+
+// NewPatchFromMap creates a new patch initialized with the data from the provided map
+// the data supplied is recorded as modified in the patch.
+func NewPatchFromMap[M ~map[K]V, K comparable, V any](source M) *Patch[K, V] {
+	if source == nil {
+		source = make(M)
+	}
+
+	return &Patch[K, V]{
+		modified: source,
+		deleted:  make(map[K]bool),
+	}
+}
+
+// mergePatchesInPlace merges two patches into one, while modifying patch a
+// inplace taking records in b as a priority when overwrites are required
+func mergePatchesInPlace[K comparable, V any](a *Patch[K, V], b *Patch[K, V]) *Patch[K, V] {
+	for key, value := range b.modified {
+		a.Set(key, value)
+	}
+
+	for key := range b.deleted {
+		a.Delete(key)
+	}
+
+	return a
+}