From 0863ff948210b92bd0b68064247a0e5f520066f9 Mon Sep 17 00:00:00 2001
From: Patrik Oldsberg <poldsberg@gmail.com>
Date: Sat, 27 Feb 2021 16:18:08 +0100
Subject: [PATCH] core-api: new internal utility for accessing global
 singletons

---
 .../core-api/src/extensions/componentData.tsx | 20 ++-------
 .../core-api/src/lib/globalObject.test.ts     | 42 +++++++++++++++++++
 packages/core-api/src/lib/globalObject.ts     | 17 +++++++-
 3 files changed, 61 insertions(+), 18 deletions(-)
 create mode 100644 packages/core-api/src/lib/globalObject.test.ts

diff --git a/packages/core-api/src/extensions/componentData.tsx b/packages/core-api/src/extensions/componentData.tsx
index 3d2558276d..d18379d25f 100644
--- a/packages/core-api/src/extensions/componentData.tsx
+++ b/packages/core-api/src/extensions/componentData.tsx
@@ -15,7 +15,7 @@
  */
 
 import { ComponentType, ReactNode } from 'react';
-import { globalObject } from '../lib/globalObject';
+import { getGlobalSingleton } from '../lib/globalObject';
 
 // TODO(Rugvip): Access via symbol is deprecated, remove once on 0.3.x
 const DATA_KEY = Symbol('backstage-component-data');
@@ -32,22 +32,10 @@ type MaybeComponentNode = ReactNode & {
   type?: ComponentType<any> & { [DATA_KEY]?: DataContainer };
 };
 
-const GLOBAL_KEY = '__@backstage/component-data-store__';
-
 // The store is bridged across versions using the global object
-function getStore() {
-  let storeObj = globalObject[GLOBAL_KEY] as
-    | { store: WeakMap<ComponentType<any>, DataContainer> }
-    | undefined;
-  if (!storeObj) {
-    const store = new WeakMap<ComponentType<any>, DataContainer>();
-    storeObj = { store };
-    globalObject[GLOBAL_KEY] = storeObj;
-  }
-  return storeObj.store;
-}
-
-const store = getStore();
+const { store } = getGlobalSingleton('component-data-store', () => ({
+  store: new WeakMap<ComponentType<any>, DataContainer>(),
+}));
 
 export function attachComponentData<P>(
   component: ComponentType<P>,
diff --git a/packages/core-api/src/lib/globalObject.test.ts b/packages/core-api/src/lib/globalObject.test.ts
new file mode 100644
index 0000000000..f539483a83
--- /dev/null
+++ b/packages/core-api/src/lib/globalObject.test.ts
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2021 Spotify AB
+ *
+ * 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 { getGlobalSingleton } from './globalObject';
+
+const anyGlobal = global as any;
+
+describe('getGlobalSingleton', () => {
+  beforeEach(() => {
+    delete anyGlobal['__@backstage/my-thing__'];
+  });
+
+  it('should return an existing value', () => {
+    const myThing = {};
+    anyGlobal['__@backstage/my-thing__'] = myThing;
+
+    expect(getGlobalSingleton('my-thing', () => ({}))).toBe(myThing);
+    expect(getGlobalSingleton('my-thing', () => ({}))).toBe(myThing);
+  });
+
+  it('should should create a new value', () => {
+    const myNewThing = {};
+
+    expect(anyGlobal['__@backstage/my-thing__']).toBe(undefined);
+    expect(getGlobalSingleton('my-thing', () => myNewThing)).toBe(myNewThing);
+    expect(anyGlobal['__@backstage/my-thing__']).toBe(myNewThing);
+    expect(getGlobalSingleton('my-thing', () => ({}))).toBe(myNewThing);
+  });
+});
diff --git a/packages/core-api/src/lib/globalObject.ts b/packages/core-api/src/lib/globalObject.ts
index 85f16212fe..c7f9f98882 100644
--- a/packages/core-api/src/lib/globalObject.ts
+++ b/packages/core-api/src/lib/globalObject.ts
@@ -15,7 +15,7 @@
  */
 
 // https://github.com/zloirock/core-js/issues/86#issuecomment-115759028
-function getGlobal() {
+function getGlobalObject() {
   if (typeof window !== 'undefined' && window.Math === Math) {
     return window;
   }
@@ -26,4 +26,17 @@ function getGlobal() {
   return Function('return this')();
 }
 
-export const globalObject = getGlobal();
+export const globalObject = getGlobalObject();
+
+export function getGlobalSingleton<T>(id: string, supplier: () => T): T {
+  const key = `__@backstage/${id}__`;
+
+  let value = globalObject[key];
+  if (value) {
+    return value;
+  }
+
+  value = supplier();
+  globalObject[key] = value;
+  return value;
+}