feat: add bases for GitHub API interaction and cache

content/.vuepress/composables/cache.ts

@@ -0,0 +1,46 @@
+import { Observable, of } from 'rxjs';
+
+const cacheAgeLimitInMilliseconds = 1000 * 60 * 60;
+
+export function isDataOutdated(name: string): boolean {
+  const lastUpdated: number = +localStorage.getItem(name + '-timestamp');
+  const now: number = Date.now();
+  const elapsedTime: number = now - lastUpdated;
+  return elapsedTime > cacheAgeLimitInMilliseconds;
+}
+
+export function storeInCache<T>(
+  data: Observable<T>,
+  name: string
+): Observable<T> {
+  data.subscribe({
+    next: (response: T) => {
+      localStorage.setItem(name, JSON.stringify(response));
+      localStorage.setItem(name + '-timestamp', `${Date.now()}`);
+    },
+  });
+  return data;
+}
+
+export function readFromCache<T>(
+  name: string,
+  callback: () => Observable<T>
+): Observable<T> {
+  let data: Observable<T>;
+  if (isDataOutdated(name)) {
+    data = storeInCache<T>(callback(), name);
+  } else {
+    let dataFromCache = localStorage.getItem(name);
+    try {
+      data = of(JSON.parse(dataFromCache));
+    } catch (err) {
+      console.error(
+        `Could not parse ${JSON.stringify(
+          dataFromCache
+        )}: ${err}. Fetching again data from callback function.`
+      );
+      data = storeInCache<T>(callback(), name);
+    }
+  }
+  return data;
+}