✨ Add cache helper (#1995)

Author: KATO-Hiro

src/lib/clients/cache_strategy.ts

@@ -0,0 +1,47 @@
+import { Cache } from '$lib/clients/cache';
+
+/**
+ * Utility class for managing cached data for contest tasks.
+ * Provides a mechanism to either retrieve data from cache if available
+ * or fetch it using the provided function.
+ */
+export class ContestTaskCache {
+  /**
+   * Retrieves data from cache if available, otherwise fetches it using the provided function.
+   *
+   * @template T - The type of data being cached and returned
+   * @param {string} key - The unique identifier for the cached data
+   * @param {() => Promise<T>} fetchFunction - Function that returns a Promise resolving to data of type T
+   * @param {Cache<T>} cache - Cache object with get and set methods for type T
+   * @returns {Promise<T>} - The cached data or newly fetched data
+   *
+   * @example
+   * const result = await cacheInstance.getCachedOrFetch(
+   *   'contests-123',
+   *   () => api.fetchContests(),
+   *   contestCache
+   * );
+   */
+  async getCachedOrFetch<T>(
+    key: string,
+    fetchFunction: () => Promise<T>,
+    cache: Cache<T>,
+  ): Promise<T> {
+    const cachedData = cache.get(key);
+
+    if (cachedData) {
+      console.log(`Using cached data for ${key}`);
+      return cachedData;
+    }
+
+    try {
+      const contestTasks = await fetchFunction();
+      cache.set(key, contestTasks);
+
+      return contestTasks;
+    } catch (error) {
+      console.error(`Failed to fetch contests and/or tasks for ${key}:`, error);
+      return [] as unknown as T;
+    }
+  }
+}