61 lines
1.9 KiB
TypeScript
61 lines
1.9 KiB
TypeScript
/**
|
|
* Keeps what the server fetched from another site for a while, by key, so a
|
|
* page or a feed asking again doesn't refetch it: Bandcamp tracklists, YouTube
|
|
* playlists, and link previews. Each holder sets how long an entry lives and
|
|
* how many are kept; past that count, the oldest written goes first.
|
|
*
|
|
* @module
|
|
*/
|
|
|
|
/**
|
|
* A map whose entries expire `ttlMs` after they are written, holding
|
|
* `maxEntries` at most.
|
|
*
|
|
* @example
|
|
* const playlists = new TtlCache<YouTubePlaylist>(6 * 3_600_000, 200);
|
|
* const hit = playlists.get(listId) ?? playlists.set(listId, await fetch());
|
|
*/
|
|
export class TtlCache<V> {
|
|
#entries = new Map<string, { value: V; at: number }>();
|
|
|
|
constructor(readonly ttlMs: number, readonly maxEntries: number) {}
|
|
|
|
/** Returns the value under `key` unless it is missing or expired. */
|
|
get(key: string): V | undefined {
|
|
const hit = this.#entries.get(key);
|
|
if (!hit) return undefined;
|
|
if (Date.now() - hit.at >= this.ttlMs) {
|
|
this.#entries.delete(key);
|
|
return undefined;
|
|
}
|
|
return hit.value;
|
|
}
|
|
|
|
/** Stores `value` under `key` from now on, and returns it. */
|
|
set(key: string, value: V): V {
|
|
this.#entries.delete(key);
|
|
// A Map keeps insertion order, so the first key is the oldest write.
|
|
if (this.#entries.size >= this.maxEntries) {
|
|
const oldest = this.#entries.keys().next().value;
|
|
if (oldest !== undefined) this.#entries.delete(oldest);
|
|
}
|
|
this.#entries.set(key, { value, at: Date.now() });
|
|
return value;
|
|
}
|
|
|
|
/**
|
|
* Removes `key`, or only when `value` is still what it holds, so a late
|
|
* failure can't remove the entry that replaced its own.
|
|
*/
|
|
delete(key: string, value?: V): void {
|
|
if (value === undefined || this.#entries.get(key)?.value === value) {
|
|
this.#entries.delete(key);
|
|
}
|
|
}
|
|
|
|
/** Empties the cache, for the tests' reset between cases. */
|
|
clear(): void {
|
|
this.#entries.clear();
|
|
}
|
|
}
|