import { EventSourcePolyfill } from "event-source-polyfill";

class SseSource {
  private readonly accessId: number
  private readonly url: URL
  private eventSource: EventSource | null = null

  constructor(mercureBaseUrl: string, accessId: number) {
    this.accessId = accessId
    this.url = new URL(mercureBaseUrl)
    this.url.searchParams.append('topic', "access/" + this.accessId)
  }

  getUrl () {
    return this.url
  }

  isOpen () {
    return this.eventSource !== null && this.eventSource.readyState === EventSource.OPEN
  }

  public subscribe () {
    if (this.isOpen()) {
      throw new Error('SSE - Already subscribed to this event source')
    }
    if (process.server) {
      throw new Error('SSE - Cannot subscribe on server side')
    }

    this.eventSource = new EventSourcePolyfill(
      this.url.toString(),
      { withCredentials: true }
    );

    this.eventSource.onerror = (event) => {
      console.error('SSE - An error happened : ' + JSON.stringify(event))
      this.eventSource?.close()
    }
    this.eventSource.onopen = () => {
      console.log('SSE - Listening for events...')
    }
    this.eventSource.onmessage = event => {
      const data = JSON.parse(event.data)
      console.log(data)
    }
  }

  public unsubscribe () {
    if (this.eventSource === null || this.eventSource.readyState === EventSource.CLOSED) {
      return
    }
    this.eventSource.close()
    console.log('SSE - Subscription closed')
  }
}

export default SseSource