import { setTimeout as sleep } from 'node:timers/promises'

/**
 * Passes a byte stream on at most `bytesPerSecond` on average: a worker on a
 * line it shares (`edge:node --max-mbit`) reads its range slower, and TCP
 * holds the sender back. The first second's worth goes at once.
 */
export async function* throttle<T extends Uint8Array>(stream: AsyncIterable<T> | Iterable<T>, bytesPerSecond: number): AsyncGenerator<T> {
  const started = Date.now()
  let bytes = 0
  for await (const piece of stream) {
    yield piece
    bytes += piece.byteLength
    const due = started + ((bytes - bytesPerSecond) / bytesPerSecond) * 1000
    const wait = due - Date.now()
    if (wait > 0) await sleep(wait)
  }
}