initial stub and bdo implementation

Author: stephenarosaj

packages/data-connect/src/api/Cache.ts

@@ -0,0 +1,85 @@
+/* eslint-disable @typescript-eslint/no-unused-vars */
+/**
+ * @license
+ * Copyright 2024 Google LLC
+ *
+ * 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.
+ */
+
+type Value = string | number | boolean | null | undefined | object | Value[]; // Value is any FDC scalar value // ! this is just for debugging/testing!!! 
+
+/**
+ * map of [query + variables] --> stubs returned from that query
+ */
+const stubCache = new Map<string, StubDataObject>();
+
+/**
+ * map of [entity primary key] --> data for that entity
+ */
+const bdoCache = new Map<string, BackingDataObject>();
+
+// operation stub result tree
+export interface StubResultTree {
+  [key: string]: StubDataObject | StubDataObjectList;
+}
+
+// StubDataObject contains a reference to its BackingDataObject
+// Generated Data implements this interface
+export interface StubDataObject {
+  readonly typedKey: string;
+  [key: string]: Value | StubDataObject;
+}
+
+// Custom class for holding lists of objects.
+// We will need this for supporting operations like append, delete, paginate
+// not strictly necessary for caching but might be good to get it ready.
+class StubDataObjectList extends Array<StubDataObject> {}
+
+// Class used to hold entity values across all queries
+// public because its referenced from Gen SDK
+export class BackingDataObject {
+  // Stable unique key identifying the entity across types.
+  // TypeName + CompositePrimaryKey
+  private typedKey: string;
+
+  // Represent values received from server
+  private serverValues: Map<string, Value> = new Map(); // Value is any FDC scalar value
+
+  private listeners: StubDataObject[] = [];
+
+  // Updates value for named property
+  updateFromServer(value: Value, key: string): void {
+    this.serverValues.set(key, value);
+    // update listeners
+    for (const listener of this.listeners) {
+      listener[key] = value;
+    }
+  }
+
+  protected value(key: string): Value | undefined {
+    return this.serverValues.get(key);
+
+    // FUTURE - for latency comp
+    // return this.localValues.get(key) ?? this.serverValues.get(key)
+  }
+
+  // ----- FUTURE - for latency comp
+
+  // Values modified locally
+  private localValues: Map<string, Value> = new Map(); // Value is any FDC scalar value
+
+  updateLocal(value: Value, key: string): void {
+    this.localValues.set(key, value);
+    // notify listeners
+  }
+}