Built for performance & creativity

// A signed S3 link: reused for 40 minutes, shared while it's being
// fetched, and never allowed to hang the player
private linkFor(track: BeatTrack, fresh = false): Promise<string> {
  const hit = this.links.get(track.id)
  if (!fresh && hit && Date.now() - hit.at < LINK_TTL) return Promise.resolve(hit.url)
  const inFlight = this.pending.get(track.id)
  if (!fresh && inFlight) return inFlight
  const abort = new AbortController()
  const timer = window.setTimeout(() => abort.abort(), LINK_TIMEOUT)
  const request = getBeatSignedUrl(track.id, abort.signal)
    .then(url => {
      if (!url) throw new Error('No audio link')
      this.links.set(track.id, { url, at: Date.now() })
      return url
    })
    .finally(() => {
      window.clearTimeout(timer)
      if (this.pending.get(track.id) === request) this.pending.delete(track.id)
    })
  this.pending.set(track.id, request)
  return request
}