| 1 | export interface AvatarCache { |
| 2 | match(key: string): Promise<Response | undefined>; |
| 3 | put(key: string, response: Response): Promise<void>; |
| 4 | } |
| 5 | |
| 6 | export function createAvatarLoader( |
| 7 | cache: () => Promise<AvatarCache>, |
| 8 | load: (query: string) => Promise<Response> |
| 9 | ): (key: string, query: string) => Promise<Response> { |
| 10 | const pending = new Map<string, Promise<Response>>(); |
| 11 | |
| 12 | return async (key, query) => { |
| 13 | const active = pending.get(key); |
| 14 | if (active) return (await active).clone(); |
| 15 | |
| 16 | const request = (async () => { |
| 17 | let store: AvatarCache | null = null; |
| 18 | try { |
| 19 | store = await cache(); |
| 20 | const cached = await store.match(key); |
| 21 | if (cached) return cached; |
| 22 | } catch { |
| 23 | store = null; |
| 24 | } |
| 25 | |
| 26 | const response = await load(query); |
| 27 | if (response.ok && store) { |
| 28 | try { |
| 29 | await store.put(key, response.clone()); |
| 30 | } catch { |
| 31 | return response; |
| 32 | } |
| 33 | } |
| 34 | return response; |
| 35 | })(); |
| 36 | pending.set(key, request); |
| 37 | try { |
| 38 | return (await request).clone(); |
| 39 | } finally { |
| 40 | if (pending.get(key) === request) pending.delete(key); |
| 41 | } |
| 42 | }; |
| 43 | } |