From 0e4a111f81cceed275d9bec2695f6e401fb654d8 Mon Sep 17 00:00:00 2001
From: syuilo <Syuilotan@yahoo.co.jp>
Date: Fri, 12 Nov 2021 02:02:25 +0900
Subject: refactoring

Resolve #7779
---
 packages/backend/src/misc/cache.ts | 43 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 packages/backend/src/misc/cache.ts

(limited to 'packages/backend/src/misc/cache.ts')

diff --git a/packages/backend/src/misc/cache.ts b/packages/backend/src/misc/cache.ts
new file mode 100644
index 0000000000..71fbbd8a4c
--- /dev/null
+++ b/packages/backend/src/misc/cache.ts
@@ -0,0 +1,43 @@
+export class Cache<T> {
+	private cache: Map<string | null, { date: number; value: T; }>;
+	private lifetime: number;
+
+	constructor(lifetime: Cache<never>['lifetime']) {
+		this.cache = new Map();
+		this.lifetime = lifetime;
+	}
+
+	public set(key: string | null, value: T): void {
+		this.cache.set(key, {
+			date: Date.now(),
+			value
+		});
+	}
+
+	public get(key: string | null): T | undefined {
+		const cached = this.cache.get(key);
+		if (cached == null) return undefined;
+		if ((Date.now() - cached.date) > this.lifetime) {
+			this.cache.delete(key);
+			return undefined;
+		}
+		return cached.value;
+	}
+
+	public delete(key: string | null) {
+		this.cache.delete(key);
+	}
+
+	public async fetch(key: string | null, fetcher: () => Promise<T>): Promise<T> {
+		const cachedValue = this.get(key);
+		if (cachedValue !== undefined) {
+			// Cache HIT
+			return cachedValue;
+		}
+
+		// Cache MISS
+		const value = await fetcher();
+		this.set(key, value);
+		return value;
+	}
+}
-- 
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