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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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