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/*
* SPDX-FileCopyrightText: syuilo and misskey-project
* SPDX-License-Identifier: AGPL-3.0-only
*/
export type FetchFunction<K, V> = (key: K) => Promise<V>;
type ResolveReject<V> = Parameters<ConstructorParameters<typeof Promise<V>>[0]>;
type ResolverPair<V> = {
resolve: ResolveReject<V>[0];
reject: ResolveReject<V>[1];
};
export class DebounceLoader<K, V> {
private resolverMap = new Map<K, ResolverPair<V>>();
private promiseMap = new Map<K, Promise<V>>();
private resolvedPromise = Promise.resolve();
constructor(private loadFn: FetchFunction<K, V>) {}
public load(key: K): Promise<V> {
const promise = this.promiseMap.get(key);
if (typeof promise !== 'undefined') {
return promise;
}
const isFirst = this.promiseMap.size === 0;
const newPromise = new Promise<V>((resolve, reject) => {
this.resolverMap.set(key, { resolve, reject });
});
this.promiseMap.set(key, newPromise);
if (isFirst) {
this.enqueueDebouncedLoadJob();
}
return newPromise;
}
private runDebouncedLoad(): void {
const resolvers = [...this.resolverMap];
this.resolverMap.clear();
this.promiseMap.clear();
for (const [key, { resolve, reject }] of resolvers) {
this.loadFn(key).then(resolve, reject);
}
}
private enqueueDebouncedLoadJob(): void {
this.resolvedPromise.then(() => {
process.nextTick(() => {
this.runDebouncedLoad();
});
});
}
}
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