misskey/packages/frontend/src/scripts/cache.ts

import { ref } from "vue";

export class Cache<T> {
	private cachedAt: number | null = null;
	public value = ref<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 = value;
	}

	private get(): T | undefined {
		if (this.cachedAt == null) return undefined;
		if ((Date.now() - this.cachedAt) > this.lifetime) {
			this.value.value = undefined;
			this.cachedAt = null;
			return undefined;
		}
		return this.value.value;
	}

	public delete() {
		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;
	}
}