81 lines
2 KiB
TypeScript
81 lines
2 KiB
TypeScript
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export class Cache<T> {
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private cachedAt: number | null = null;
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private value: T | undefined;
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private lifetime: number;
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constructor(lifetime: Cache<never>['lifetime']) {
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this.lifetime = lifetime;
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}
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public set(value: T): void {
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this.cachedAt = Date.now();
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this.value = value;
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}
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public get(): T | undefined {
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if (this.cachedAt == null) return undefined;
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if ((Date.now() - this.cachedAt) > this.lifetime) {
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this.value = undefined;
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this.cachedAt = null;
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return undefined;
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}
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return this.value;
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}
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public delete() {
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this.value = undefined;
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this.cachedAt = null;
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}
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/**
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* 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
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* 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
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*/
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public async fetch(fetcher: () => Promise<T>, validator?: (cachedValue: T) => boolean): Promise<T> {
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const cachedValue = this.get();
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if (cachedValue !== undefined) {
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if (validator) {
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if (validator(cachedValue)) {
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// Cache HIT
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return cachedValue;
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}
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} else {
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// Cache HIT
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return cachedValue;
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}
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}
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// Cache MISS
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const value = await fetcher();
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this.set(value);
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return value;
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}
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/**
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* 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
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* 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
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*/
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public async fetchMaybe(fetcher: () => Promise<T | undefined>, validator?: (cachedValue: T) => boolean): Promise<T | undefined> {
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const cachedValue = this.get();
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if (cachedValue !== undefined) {
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if (validator) {
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if (validator(cachedValue)) {
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// Cache HIT
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return cachedValue;
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}
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} else {
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// Cache HIT
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return cachedValue;
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}
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}
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// Cache MISS
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const value = await fetcher();
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if (value !== undefined) {
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this.set(value);
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}
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return value;
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}
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}
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