1 files changed, 80 insertions, 0 deletions
diff --git a/packages/frontend/src/scripts/cache.ts b/packages/frontend/src/scripts/cache.ts
new file mode 100644
index 0000000000..858e5f03bf
--- /dev/null
+++ b/packages/frontend/src/scripts/cache.ts
@@ -0,0 +1,80 @@
+
+export class Cache<T> {
+	private cachedAt: number | null = null;
+	private value: T | undefined;
+	private lifetime: number;
+
+	constructor(lifetime: Cache<never>['lifetime']) {
+		this.lifetime = lifetime;
+	}
+
+	public set(value: T): void {
+		this.cachedAt = Date.now();
+		this.value = value;
+	}
+
+	public get(): T | undefined {
+		if (this.cachedAt == null) return undefined;
+		if ((Date.now() - this.cachedAt) > this.lifetime) {
+			this.value = undefined;
+			this.cachedAt = null;
+			return undefined;
+		}
+		return this.value;
+	}
+
+	public delete() {
+		this.value = undefined;
+		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
+	 * optional: キャッシュが存在してもvalidatorでfalseを返すとキャッシュ無効扱いにします
+	 */
+	public async fetch(fetcher: () => Promise<T>, validator?: (cachedValue: T) => boolean): Promise<T> {
+		const cachedValue = this.get();
+		if (cachedValue !== undefined) {
+			if (validator) {
+				if (validator(cachedValue)) {
+					// Cache HIT
+					return cachedValue;
+				}
+			} else {
+				// Cache HIT
+				return cachedValue;
+			}
+		}
+
+		// Cache MISS
+		const value = await fetcher();
+		this.set(value);
+		return value;
+	}
+
+	/**
+	 * 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
+	 * optional: キャッシュが存在してもvalidatorでfalseを返すとキャッシュ無効扱いにします
+	 */
+	public async fetchMaybe(fetcher: () => Promise<T | undefined>, validator?: (cachedValue: T) => boolean): Promise<T | undefined> {
+		const cachedValue = this.get();
+		if (cachedValue !== undefined) {
+			if (validator) {
+				if (validator(cachedValue)) {
+					// Cache HIT
+					return cachedValue;
+				}
+			} else {
+				// Cache HIT
+				return cachedValue;
+			}
+		}
+
+		// Cache MISS
+		const value = await fetcher();
+		if (value !== undefined) {
+			this.set(value);
+		}
+		return value;
+	}
+}