Add MultiMap util

utils/multi-map.ts

@@ -0,0 +1,28 @@
+export class MultiMap<V, K extends unknown[]> extends Map<K[0], any> {
+  multiGet(...keys: K): V | undefined {
+    const firstKey = keys[0];
+    const otherKeys = keys.slice(1);
+    if (!this.has(firstKey)) {
+      return undefined;
+    }
+
+    if (otherKeys.length > 0) {
+      return (this.get(firstKey)! as MultiMap<any, any>).multiGet(...otherKeys);
+    }
+    return this.get(firstKey) as V;
+  }
+
+  multiSet(value: V, ...keys: K) {
+    const firstKey = keys[0];
+    const otherKeys = keys.slice(1);
+
+    if (otherKeys.length > 0) {
+      if (!this.has(firstKey)) {
+        this.set(firstKey, new MultiMap());
+      }
+      (this.get(firstKey) as MultiMap<any, any>)!.multiSet(value, ...otherKeys);
+    } else {
+      this.set(firstKey, value);
+    }
+  }
+}