core-api: add internal attachNodeData and getComponentData helpers

Co-authored-by: Fredrik Adelöw <freben@gmail.com>
Co-authored-by: blam <ben@blam.sh>

packages/core-api/src/lib/componentData.test.tsx

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2020 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 React from 'react';
+import { attachComponentData, getComponentData } from './componentData';
+
+describe('elementData', () => {
+  it('should attach a single piece of data', () => {
+    const data = { foo: 'bar' };
+    const Component = () => null;
+    attachComponentData(Component, 'my-data', data);
+
+    const element = <Component />;
+    expect(getComponentData(element, 'my-data')).toBe(data);
+  });
+
+  it('should attach several distinct pieces of data', () => {
+    const data1 = { foo: 'bar' };
+    const data2 = { test: 'value' };
+    const Component = () => null;
+    attachComponentData(Component, 'my-data', data1);
+    attachComponentData(Component, 'second', data2);
+
+    const element = <Component />;
+    expect(getComponentData(element, 'my-data')).toBe(data1);
+    expect(getComponentData(element, 'second')).toBe(data2);
+  });
+
+  it('returns undefined for missing data', () => {
+    const data = { foo: 'bar' };
+    const Component1 = () => null;
+    const Component2 = () => null;
+    attachComponentData(Component2, 'my-data', data);
+
+    const element1 = <Component1 />;
+    const element2 = <Component2 />;
+    expect(getComponentData(element1, 'missing')).toBeUndefined();
+    expect(getComponentData(element2, 'missing')).toBeUndefined();
+  });
+
+  it('should throw when attempting to overwrite data', () => {
+    const data = { foo: 'bar' };
+    const MyComponent = () => null;
+    attachComponentData(MyComponent, 'my-data', data);
+    expect(() => attachComponentData(MyComponent, 'my-data', data)).toThrow(
+      'Attempted to attach duplicate data "my-data" to component "MyComponent"',
+    );
+  });
+});

packages/core-api/src/lib/componentData.tsx

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2020 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 { ComponentType, ReactNode } from 'react';
+
+const DATA_KEY = Symbol('backstage-component-data');
+
+type DataContainer = {
+  map: Map<string, unknown>;
+};
+
+type ComponentWithData<P> = ComponentType<P> & {
+  [DATA_KEY]?: DataContainer;
+};
+
+type ReactNodeWithData = ReactNode & {
+  type?: { [DATA_KEY]?: DataContainer };
+};
+
+export function attachComponentData<P>(
+  component: ComponentType<P>,
+  type: string,
+  data: unknown,
+) {
+  const dataComponent = component as ComponentWithData<P>;
+
+  let container = dataComponent[DATA_KEY];
+  if (!container) {
+    container = dataComponent[DATA_KEY] = { map: new Map() };
+  }
+
+  if (container.map.has(type)) {
+    const name = component.displayName || component.name;
+    throw new Error(
+      `Attempted to attach duplicate data "${type}" to component "${name}"`,
+    );
+  }
+
+  container.map.set(type, data);
+}
+
+export function getComponentData<T>(
+  node: ReactNode,
+  type: string,
+): T | undefined {
+  if (!node) {
+    return undefined;
+  }
+
+  const container = (node as ReactNodeWithData).type?.[DATA_KEY];
+  if (!container) {
+    return undefined;
+  }
+
+  return container.map.get(type) as T | undefined;
+}