refactor(frontend): scripts -> utility

packages/frontend/src/utility/cache.ts

@@ -0,0 +1,53 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { ref } from 'vue';
+
+export class Cache<T> {
+	private cachedAt: number | null = null;
+	public value = ref<T | undefined>();
+	private lifetime: number;
+	private fetcher: () => Promise<T>;
+
+	constructor(lifetime: Cache<never>['lifetime'], fetcher: () => Promise<T>) {
+		this.lifetime = lifetime;
+		this.fetcher = fetcher;
+	}
+
+	public set(value: T): void {
+		this.cachedAt = Date.now();
+		this.value.value = value;
+	}
+
+	private get(): T | undefined {
+		if (this.cachedAt == null) return undefined;
+		if ((Date.now() - this.cachedAt) > this.lifetime) {
+			this.value.value = undefined;
+			this.cachedAt = null;
+			return undefined;
+		}
+		return this.value.value;
+	}
+
+	public delete() {
+		this.cachedAt = null;
+	}
+
+	/**
+	 * キャッシュがあればそれを返し、無ければfetcherを呼び出して結果をキャッシュ&返します
+	 */
+	public async fetch(): Promise<T> {
+		const cachedValue = this.get();
+		if (cachedValue !== undefined) {
+			// Cache HIT
+			return cachedValue;
+		}
+
+		// Cache MISS
+		const value = await this.fetcher();
+		this.set(value);
+		return value;
+	}
+}