/** Thin wrapper over the Web Audio API for playing pre-rendered sample buffers. */

let ctx: AudioContext | null = null
const active = new Set<AudioBufferSourceNode>()
let currentFinish: (() => void) | null = null

export function getAudioContext(): AudioContext {
  if (!ctx) ctx = new AudioContext()
  if (ctx.state === 'suspended') void ctx.resume()
  return ctx
}

export function getSampleRate(): number {
  return getAudioContext().sampleRate
}

/** Stop anything currently playing and resolve its promise. */
export function stopAll(): void {
  for (const s of active) {
    try {
      s.stop()
    } catch {
      // already stopped
    }
  }
  active.clear()
  const f = currentFinish
  currentFinish = null
  f?.()
}

/**
 * Play the buffers one after another with a silent gap between them.
 * Resolves when the last buffer ends (or when stopAll() is called).
 */
export function playSequence(buffers: Float32Array[], gapSec = 0.4): Promise<void> {
  const ac = getAudioContext()
  stopAll()
  let t = ac.currentTime + 0.05
  const sources: AudioBufferSourceNode[] = []
  for (const samples of buffers) {
    const buf = ac.createBuffer(1, samples.length, ac.sampleRate)
    buf.getChannelData(0).set(samples)
    const src = ac.createBufferSource()
    src.buffer = buf
    src.connect(ac.destination)
    src.start(t)
    active.add(src)
    sources.push(src)
    t += buf.duration + gapSec
  }
  return new Promise<void>((resolve) => {
    const last = sources[sources.length - 1]
    if (!last) {
      resolve()
      return
    }
    let done = false
    const finish = () => {
      if (done) return
      done = true
      for (const s of sources) active.delete(s)
      if (currentFinish === finish) currentFinish = null
      resolve()
    }
    currentFinish = finish
    last.onended = finish
  })
}