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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;
}
}
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