Create Maps utility comparison functions

src/utils/maps.ts

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+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+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.
+*/
+
+import { arrayDiff, arrayMerge, arrayUnion } from "./arrays";
+
+/**
+ * Determines the keys added, changed, and removed between two Maps.
+ * For changes, simple triple equal comparisons are done, not in-depth
+ * tree checking.
+ * @param a The first object. Must be defined.
+ * @param b The second object. Must be defined.
+ * @returns The difference between the keys of each object.
+ */
+export function mapDiff<K, V>(a: Map<K, V>, b: Map<K, V>): { changed: K[], added: K[], removed: K[] } {
+    const aKeys = [...a.keys()];
+    const bKeys = [...b.keys()];
+    const keyDiff = arrayDiff(aKeys, bKeys);
+    const possibleChanges = arrayUnion(aKeys, bKeys);
+    const changes = possibleChanges.filter(k => a.get(k) !== b.get(k));
+
+    return {changed: changes, added: keyDiff.added, removed: keyDiff.removed};
+}
+
+/**
+ * Gets all the key changes (added, removed, or value difference) between
+ * two Maps. Triple equals is used to compare values, not in-depth tree
+ * checking.
+ * @param a The first object. Must be defined.
+ * @param b The second object. Must be defined.
+ * @returns The keys which have been added, removed, or changed between the
+ * two objects.
+ */
+export function mapKeyChanges<K, V>(a: Map<K, V>, b: Map<K, V>): K[] {
+    const diff = mapDiff(a, b);
+    return arrayMerge(diff.removed, diff.added, diff.changed);
+}