Add frontend UsersCache class

app/assets/javascripts/lib/utils/users_cache.js

+import Api from '../../api';
+import Cache from './cache';
+
+class UsersCache extends Cache {
+  retrieve(username) {
+    if (this.hasData(username)) {
+      return Promise.resolve(this.get(username));
+    }
+
+    return Api.users('', { username })
+      .then((users) => {
+        if (!users.length) {
+          throw new Error(`User "${username}" could not be found!`);
+        }
+
+        if (users.length > 1) {
+          throw new Error(`Expected username "${username}" to be unique!`);
+        }
+
+        this.internalStorage[username] = users[0];
+      })
+      .then(() => this.get(username));
+  }
+}
+
+export default new UsersCache();

spec/javascripts/lib/utils/users_cache_spec.js

+import Api from '~/api';
+import UsersCache from '~/lib/utils/users_cache';
+
+describe('UsersCache', () => {
+  const dummyUsername = 'win';
+  const dummyUser = 'has a farm';
+
+  beforeEach(() => {
+    UsersCache.internalStorage = { };
+  });
+
+  describe('get', () => {
+    it('returns undefined for empty cache', () => {
+      expect(UsersCache.internalStorage).toEqual({ });
+
+      const user = UsersCache.get(dummyUsername);
+
+      expect(user).toBe(undefined);
+    });
+
+    it('returns undefined for missing user', () => {
+      UsersCache.internalStorage['no body'] = 'no data';
+
+      const user = UsersCache.get(dummyUsername);
+
+      expect(user).toBe(undefined);
+    });
+
+    it('returns matching user', () => {
+      UsersCache.internalStorage[dummyUsername] = dummyUser;
+
+      const user = UsersCache.get(dummyUsername);
+
+      expect(user).toBe(dummyUser);
+    });
+  });
+
+  describe('hasData', () => {
+    it('returns false for empty cache', () => {
+      expect(UsersCache.internalStorage).toEqual({ });
+
+      expect(UsersCache.hasData(dummyUsername)).toBe(false);
+    });
+
+    it('returns false for missing user', () => {
+      UsersCache.internalStorage['no body'] = 'no data';
+
+      expect(UsersCache.hasData(dummyUsername)).toBe(false);
+    });
+
+    it('returns true for matching user', () => {
+      UsersCache.internalStorage[dummyUsername] = dummyUser;
+
+      expect(UsersCache.hasData(dummyUsername)).toBe(true);
+    });
+  });
+
+  describe('remove', () => {
+    it('does nothing if cache is empty', () => {
+      expect(UsersCache.internalStorage).toEqual({ });
+
+      UsersCache.remove(dummyUsername);
+
+      expect(UsersCache.internalStorage).toEqual({ });
+    });
+
+    it('does nothing if cache contains no matching data', () => {
+      UsersCache.internalStorage['no body'] = 'no data';
+
+      UsersCache.remove(dummyUsername);
+
+      expect(UsersCache.internalStorage['no body']).toBe('no data');
+    });
+
+    it('removes matching data', () => {
+      UsersCache.internalStorage[dummyUsername] = dummyUser;
+
+      UsersCache.remove(dummyUsername);
+
+      expect(UsersCache.internalStorage).toEqual({ });
+    });
+  });
+
+  describe('retrieve', () => {
+    let apiSpy;
+
+    beforeEach(() => {
+      spyOn(Api, 'users').and.callFake((query, options) => apiSpy(query, options));
+    });
+
+    it('stores and returns data from API call if cache is empty', (done) => {
+      apiSpy = (query, options) => {
+        expect(query).toBe('');
+        expect(options).toEqual({ username: dummyUsername });
+        return Promise.resolve([dummyUser]);
+      };
+
+      UsersCache.retrieve(dummyUsername)
+      .then((user) => {
+        expect(user).toBe(dummyUser);
+        expect(UsersCache.internalStorage[dummyUsername]).toBe(dummyUser);
+      })
+      .then(done)
+      .catch(done.fail);
+    });
+
+    it('returns undefined if Ajax call fails and cache is empty', (done) => {
+      const dummyError = new Error('server exploded');
+      apiSpy = (query, options) => {
+        expect(query).toBe('');
+        expect(options).toEqual({ username: dummyUsername });
+        return Promise.reject(dummyError);
+      };
+
+      UsersCache.retrieve(dummyUsername)
+      .then(user => fail(`Received unexpected user: ${JSON.stringify(user)}`))
+      .catch((error) => {
+        expect(error).toBe(dummyError);
+      })
+      .then(done)
+      .catch(done.fail);
+    });
+
+    it('makes no Ajax call if matching data exists', (done) => {
+      UsersCache.internalStorage[dummyUsername] = dummyUser;
+      apiSpy = () => fail(new Error('expected no Ajax call!'));
+
+      UsersCache.retrieve(dummyUsername)
+      .then((user) => {
+        expect(user).toBe(dummyUser);
+      })
+      .then(done)
+      .catch(done.fail);
+    });
+  });
+});