import { isWorkerMessageEnvelope } from './workerMessage'

export function isWebWorkerAvailable(): boolean {
  return typeof window !== 'undefined' && Boolean(window.Worker)
}

export function createWriteWorkerInitPromise(params: { setWorker: (worker: Worker | null) => void }): Promise<void> {
  return new Promise((resolve) => {
    if (!isWebWorkerAvailable()) {
      console.warn('[WriteService] Web Workers not available, using direct writes')
      resolve()
      return
    }

    try {
      const worker = new Worker('/writeWorker.js', { type: 'classic' })
      params.setWorker(worker)
      registerWorkerListeners({ worker, resolve, setWorker: params.setWorker })
    } catch (error) {
      console.warn('[WriteService] Failed to create worker, using direct writes:', error)
      resolve()
    }
  })
}

function registerWorkerListeners(params: {
  worker: Worker
  resolve: () => void
  setWorker: (worker: Worker | null) => void
}): void {
  params.worker.addEventListener('message', (event: MessageEvent<unknown>) => {
    if (!isWorkerMessageEnvelope(event.data)) {
      console.error('[WriteService] Received invalid worker message envelope', { data: event.data })
      return
    }
    if (event.data.type === 'ERROR') {
      console.error('[WriteService] Worker error:', event.data.data)
    }
  })

  params.worker.addEventListener('error', (error) => {
    console.error('[WriteService] Worker error:', error)
    console.warn('[WriteService] Falling back to direct writes')
    params.setWorker(null)
    params.resolve()
  })

  const readyTimeout = setTimeout(() => {
    console.warn('[WriteService] Worker ready timeout, using direct writes')
    params.worker.terminate()
    params.setWorker(null)
    params.resolve()
  }, 2000)

  const readyHandler = (event: MessageEvent<unknown>): void => {
    if (isWorkerMessageEnvelope(event.data) && event.data.type === 'WORKER_READY') {
      clearTimeout(readyTimeout)
      params.worker.removeEventListener('message', readyHandler)
      params.resolve()
    }
  }
  params.worker.addEventListener('message', readyHandler)
}