feat(keys): enable accurate retrieval of all valid cache keys

src/cache.test.ts

@@ -51,4 +51,32 @@ describe('cache', () => {
     const iceCreamStateAfter5Sec = get('ice cream state');
     expect(iceCreamStateAfter5Sec).toEqual(undefined); // no longer defined, since the item level seconds until expiration was 5
   });
+  it('should accurately get keys', () => {
+    // create the cache
+    const { set, keys } = createCache();
+
+    // check key is added when value is set
+    set('meaning-of-life', '42');
+    const keys1 = keys();
+    expect(keys1.length).toEqual(1);
+    expect(keys1[0]).toEqual('meaning-of-life');
+
+    // check that there are no duplicates when key value is updated
+    set('meaning-of-life', '42.0');
+    const keys2 = keys();
+    expect(keys2.length).toEqual(1);
+    expect(keys2[0]).toEqual('meaning-of-life');
+
+    // check that multiple keys can be set
+    set('purpose-of-life', 'propagation');
+    const keys3 = keys();
+    expect(keys3.length).toEqual(2);
+    expect(keys3[1]).toEqual('purpose-of-life');
+
+    // check that invalidation removes the key
+    set('meaning-of-life', undefined);
+    const keys4 = keys();
+    expect(keys4.length).toEqual(1);
+    expect(keys4[0]).toEqual('purpose-of-life');
+  });
 });

src/cache.ts

@@ -1,6 +1,7 @@
 export interface SimpleInMemoryCache<T> {
   get: (key: string) => T | undefined;
   set: (key: string, value: T, options?: { secondsUntilExpiration?: number }) => void;
+  keys: () => string[];
 }
 
 export interface SimpleInMemoryCacheState<T> {
@@ -16,7 +17,18 @@ export const createCache = <T>({ defaultSecondsUntilExpiration = 5 * 60 }: { def
   const cache: SimpleInMemoryCacheState<T> = {};
 
   // define how to set an item into the cache
-  const set = (key: string, value: T, { secondsUntilExpiration = defaultSecondsUntilExpiration }: { secondsUntilExpiration?: number } = {}) => {
+  const set = (
+    key: string,
+    value: T | undefined,
+    { secondsUntilExpiration = defaultSecondsUntilExpiration }: { secondsUntilExpiration?: number } = {},
+  ) => {
+    // handle cache invalidation
+    if (value === undefined) {
+      delete cache[key];
+      return;
+    }
+
+    // handle setting
     const expiresAtMse = getMseNow() + secondsUntilExpiration * 1000;
     cache[key] = { value, expiresAtMse };
   };
@@ -29,6 +41,12 @@ export const createCache = <T>({ defaultSecondsUntilExpiration = 5 * 60 }: { def
     return cacheContent.value; // otherwise, its in the cache and not expired, so return the value
   };
 
+  // define how to grab all valid keys
+  const keys = () =>
+    Object.entries(cache)
+      .filter(([_, value]) => value.expiresAtMse > getMseNow())
+      .map(([key]) => key);
+
   // return the api
-  return { set, get };
+  return { set, get, keys };
 };