keyedCapacity.ts

import { withCapacity } from 'radashi'

export function keyedCapacity<TKey, TResult>(capacity: number) {
  const queue = withCapacity(capacity)
  const jobs = new Map<TKey, Promise<TResult>>()

  return {
    keys: (): IterableIterator<TKey> => jobs.keys(),
    get: (key: TKey): Promise<TResult> | undefined => jobs.get(key),
    run(key: TKey, job: () => Promise<TResult>): Promise<TResult> {
      const promise = queue(job).finally(() => jobs.delete(key))
      jobs.set(key, promise)
      return promise
    },
  }
}