core-api: add versioned value types and helpers

Co-authored-by: Juan Lulkin <jmaiz@spotify.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/core-api/src/lib/versionedValues.test.ts

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+/*
+ * 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 { createVersionedValueMap } from './versionedValues';
+
+describe('createVersionedValueMap', () => {
+  it('should be empty', () => {
+    const map = createVersionedValueMap({});
+
+    // @ts-expect-error
+    expect(map.atVersion(1 as any)).toBe(undefined);
+  });
+
+  it('should access values by version', () => {
+    const map = createVersionedValueMap({ 1: 'v1', 2: 'v2' });
+
+    expect(map.atVersion(1)).toBe('v1');
+    expect(map.atVersion(2)).toBe('v2');
+
+    // @ts-expect-error
+    expect(map.atVersion(0)).toBe(undefined);
+    // @ts-expect-error
+    expect(map.atVersion(NaN)).toBe(undefined);
+    // @ts-expect-error
+    expect(map.atVersion(Infinity)).toBe(undefined);
+  });
+});

packages/core-api/src/lib/versionedValues.ts

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+/*
+ * 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.
+ */
+
+/**
+ * The versioned value interface is a container for a set of values that
+ * can be looked up by version. It is intended to be used as a container
+ * for values that can be versioned independently of package versions.
+ */
+export type VersionedValue<Versions extends { [version: number]: any }> = {
+  atVersion<Version extends keyof Versions>(
+    version: Version,
+  ): Versions[Version] | undefined;
+};
+
+/**
+ * Creates a container for a map of versioned values that implements VersionedValue.
+ */
+export function createVersionedValueMap<
+  Versions extends { [version: number]: any }
+>(versions: Versions): VersionedValue<Versions> {
+  Object.freeze(versions);
+  return {
+    atVersion(version) {
+      return versions[version];
+    },
+  };
+}