feat: InMemoryCache implementation

api-server/server/utils/in-memory-cache.js

@@ -0,0 +1,34 @@
+function isPromiseLike(thing) {
+  return !!thing && typeof thing.then === 'function';
+}
+
+function InMemoryCache(initialValue) {
+  const cacheKey = Symbol('cacheKey');
+  const cache = new Map();
+
+  if (typeof initialValue !== 'undefined') {
+    cache.set(cacheKey, initialValue);
+  }
+
+  return {
+    get() {
+      const value = cache.get(cacheKey);
+      return typeof value !== 'undefined' ? value : null;
+    },
+    async update(fn) {
+      const maybePromisedValue = fn();
+      if (isPromiseLike(maybePromisedValue)) {
+        return maybePromisedValue.then(value => cache.set(cacheKey, value));
+      } else {
+        const value = maybePromisedValue;
+        cache.set(cacheKey, value);
+        return null;
+      }
+    },
+    clear() {
+      return cache.delete(cacheKey);
+    }
+  };
+}
+
+export default InMemoryCache;

api-server/server/utils/in-memory-cache.test.js

@@ -0,0 +1,49 @@
+/* global describe expect it beforeEach */
+import inMemoryCache from './in-memory-cache';
+
+describe('InMemoryCache', () => {
+  const theAnswer = 42;
+  const before = 'before';
+  const after = 'after';
+  const emptyCacheValue = null;
+
+  describe('get', () => {
+    it('returns null for an empty cache', () => {
+      const cache = inMemoryCache();
+      expect(cache.get()).toBe(emptyCacheValue);
+    });
+
+    it('returns an initial value', () => {
+      const cache = inMemoryCache(theAnswer);
+      expect(cache.get()).toBe(theAnswer);
+    });
+  });
+
+  describe('update', () => {
+    it('updates the cached value', () => {
+      const cache = inMemoryCache(before);
+      cache.update(() => after);
+      expect(cache.get()).toBe(after);
+    });
+
+    it('can handle promises correctly', done => {
+      const cache = inMemoryCache(before);
+      cache.update(() => new Promise(resolve => resolve(after)));
+      // because async
+      setImmediate(() => {
+        expect(cache.get()).toBe(after);
+        done();
+      });
+    });
+  });
+
+  describe('clear', () => {
+    it('clears the  cache', () => {
+      expect.assertions(2);
+      const cache = inMemoryCache(theAnswer);
+      expect(cache.get()).toBe(theAnswer);
+      cache.clear();
+      expect(cache.get()).toBe(emptyCacheValue);
+    });
+  });
+});