test: Add tests for caching

Signed-off-by: Tim Hårek Andreassen <tim@harek.no>

lib/caching.test.ts

@@ -0,0 +1,52 @@
+import { assertEquals } from "$std/assert/mod.ts";
+import { forTestingOnly } from "./caching.ts";
+import { storage } from "./storage.ts";
+import { testUtils } from "./test-utils.ts";
+
+Deno.test("Verify getTimeSinceLastFetch for correct difference", () => {
+  const earlyDate = new Date("2024-04-07T20:24:32Z");
+  const date = new Date("2024-04-07T23:24:32Z");
+  const timeSinceLastFetch = forTestingOnly.getTimeSinceLastFetch(date, earlyDate);
+
+  assertEquals(timeSinceLastFetch, 3);
+});
+
+Deno.test("Verify getTimeSinceLastFetch for bad date", () => {
+  const earlyDate = new Date("2024-04-07T20:24:32Z");
+  const date = new Date("bad date");
+  const timeSinceLastFetch = forTestingOnly.getTimeSinceLastFetch(date, earlyDate);
+
+  assertEquals(timeSinceLastFetch, NaN);
+});
+
+Deno.test("Verify getTimeSinceLastFetch for bad dates (plural)", () => {
+  const earlyDate = new Date("badest date");
+  const date = new Date("bad date");
+  const timeSinceLastFetch = forTestingOnly.getTimeSinceLastFetch(date, earlyDate);
+
+  assertEquals(timeSinceLastFetch, NaN);
+});
+
+Deno.test("Verify seriesFromStorage is old", () => {
+  const earlyDate = new Date("2024-04-07T21:24:32Z");
+  const date = new Date("2024-04-07T23:24:32Z");
+  const timeSinceLastFetch = forTestingOnly.getTimeSinceLastFetch(date, earlyDate);
+
+  const series = testUtils.generateSeries({ lastFetchedAt: date });
+  const syncInterval = 2;
+  const isNew = forTestingOnly.isSeriesFromStorageNew(series, syncInterval, timeSinceLastFetch);
+
+  assertEquals(isNew, true);
+});
+
+Deno.test("Verify seriesFromStorage is new", () => {
+  const earlyDate = new Date("2024-04-07T20:24:32Z");
+  const date = new Date("2024-04-07T23:24:32Z");
+  const timeSinceLastFetch = forTestingOnly.getTimeSinceLastFetch(date, earlyDate);
+
+  const series = testUtils.generateSeries({ lastFetchedAt: date });
+  const syncInterval = 2;
+  const isNew = forTestingOnly.isSeriesFromStorageNew(series, syncInterval, timeSinceLastFetch);
+
+  assertEquals(isNew, false);
+});

lib/caching.ts

@@ -52,6 +52,22 @@ async function updateFetch(existingSeries: Series): Promise<UpdatedSeries | null
   return updated;
 }
 
+function getTimeSinceLastFetch(inputDate: Date, againstDate = new Date()): number | null {
+  return datetime.difference(inputDate, againstDate, { units: ["hours"] }).hours ?? null;
+}
+
+function isSeriesFromStorageNew(
+  seriesFromStorage: Series,
+  syncInterval = SYNC_INTERVAL_HOURS,
+  timeSinceLastFetch = getTimeSinceLastFetch(seriesFromStorage.lastFetchedAt),
+) {
+  return !Number.isNaN(timeSinceLastFetch) &&
+    seriesFromStorage !== null &&
+    timeSinceLastFetch !== null &&
+    timeSinceLastFetch !== undefined &&
+    timeSinceLastFetch <= syncInterval;
+}
+
 async function getSeries(options: { id: string }): Promise<Series | null> {
   const seriesFromStorage = await storage.read(options);
 
@@ -64,16 +80,8 @@ async function getSeries(options: { id: string }): Promise<Series | null> {
     return await initialFetch(options);
   }
 
-  const timeSinceLastFetch =
-    datetime.difference(seriesFromStorage.lastFetchedAt, new Date(), { units: ["hours"] }).hours;
-
   // we have the feed in storage and it's not too old
-  if (
-    seriesFromStorage !== null &&
-    timeSinceLastFetch !== null &&
-    timeSinceLastFetch !== undefined &&
-    timeSinceLastFetch <= SYNC_INTERVAL_HOURS
-  ) {
+  if (isSeriesFromStorageNew(seriesFromStorage)) {
     return seriesFromStorage;
   }
 
@@ -88,3 +96,8 @@ async function getSeries(options: { id: string }): Promise<Series | null> {
 export const caching = {
   getSeries,
 };
+
+export const forTestingOnly = {
+  getTimeSinceLastFetch,
+  isSeriesFromStorageNew,
+};

lib/test-utils.ts

@@ -11,6 +11,7 @@ function generateSeries(overrides: Partial<Series> = {}): Series {
     lastFetchedAt: faker.date.recent(),
     episodes: new Array(faker.number.int({ min: 0, max: 100 }))
       .fill(null).map(() => (generateEpisode(overrides))),
+    ...overrides,
   };
 }