57 lines
1.2 KiB
TypeScript
57 lines
1.2 KiB
TypeScript
export class Cache<T> {
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public cache: Map<string, { date: number; value: T; }>;
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private lifetime: number;
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public fetcher: (key: string) => Promise<T | undefined>;
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constructor(lifetime: number, fetcher: Cache<T>['fetcher']) {
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this.cache = new Map();
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this.lifetime = lifetime;
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this.fetcher = fetcher;
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}
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public set(key: string, value: T): void {
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this.cache.set(key, {
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date: Date.now(),
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value,
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});
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}
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public get(key: string): T | undefined {
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const cached = this.cache.get(key);
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if (cached == null) return undefined;
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// discard if past the cache lifetime
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if ((Date.now() - cached.date) > this.lifetime) {
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this.cache.delete(key);
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return undefined;
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}
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return cached.value;
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}
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public delete(key: string): void {
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this.cache.delete(key);
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}
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/**
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* If the value is cached, it is returned. Otherwise the fetcher is
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* run to get the value. If the fetcher returns undefined, it is
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* returned but not cached.
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*/
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public async fetch(key: string): Promise<T | undefined> {
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const cached = this.get(key);
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if (cached !== undefined) {
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return cached;
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} else {
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const value = await this.fetcher(key);
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// don't cache undefined
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if (value !== undefined) {
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this.set(key, value);
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}
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return value;
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}
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}
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}
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