packages/core: added ApiAggregator class

packages/core/src/api/apis/ApiAggregator.test.ts

@@ -0,0 +1,46 @@
+/*
+ * 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 { ApiAggregator } from './ApiAggregator';
+import { ApiRef } from './ApiRef';
+import { ApiRegistry } from './ApiRegistry';
+
+describe('ApiAggregator', () => {
+  const apiARef = new ApiRef<number>({ id: 'a', description: '' });
+  const apiBRef = new ApiRef<number>({ id: 'b', description: '' });
+
+  it('should forward implementations', () => {
+    const agg = new ApiAggregator(
+      ApiRegistry.from([
+        [apiARef, 5],
+        [apiBRef, 10],
+      ]),
+    );
+    expect(agg.get(apiARef)).toBe(5);
+    expect(agg.get(apiBRef)).toBe(10);
+  });
+
+  it('should return the first implementation', () => {
+    const agg = new ApiAggregator(
+      ApiRegistry.from([
+        [apiARef, 1],
+        [apiARef, 2],
+      ]),
+    );
+    expect(agg.get(apiARef)).toBe(2);
+    expect(agg.get(apiBRef)).toBe(undefined);
+  });
+});

packages/core/src/api/apis/ApiAggregator.ts

@@ -0,0 +1,40 @@
+/*
+ * 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 { ApiRef } from './ApiRef';
+import { ApiHolder } from './types';
+
+/**
+ * An ApiHolder that queries multiple other holders from for
+ * an Api implementation, returning the first one encountered..
+ */
+export class ApiAggregator implements ApiHolder {
+  private readonly holders: ApiHolder[];
+
+  constructor(...holders: ApiHolder[]) {
+    this.holders = holders;
+  }
+
+  get<T>(apiRef: ApiRef<T>): T | undefined {
+    for (const holder of this.holders) {
+      const api = holder.get(apiRef);
+      if (api) {
+        return api;
+      }
+    }
+    return undefined;
+  }
+}