async function* readNdjson(response, signal) {
  if (!response.ok || !response.body) {
    throw new Error(`HTTP ${response.status}`)
  }

  const reader = response.body.getReader()
  const decoder = new TextDecoder()
  let buffer = ''

  try {
    while (true) {
      if (signal?.aborted) throw signal.reason
      const { value, done } = await reader.read()
      buffer += decoder.decode(value, { stream: !done })

      const lines = buffer.split('\n')
      buffer = lines.pop() ?? ''
      for (const line of lines) {
        if (line.trim()) yield JSON.parse(line)
      }

      if (done) break
    }
    if (buffer.trim()) yield JSON.parse(buffer)
  } finally {
    reader.releaseLock()
  }
}

const controller = new AbortController()
const response = await fetch('/api/chat', {
  method: 'POST',
  signal: controller.signal,
  headers: { 'content-type': 'application/json' },
  body: JSON.stringify({ prompt: '解释事件循环' })
})

let answer = ''
for await (const event of readNdjson(response, controller.signal)) {
  if (event.type === 'delta') answer += event.text
  if (event.type === 'error') throw new Error(event.message)
  if (event.type === 'done') break
}