export class ReconnectingEventSource {
  constructor(url, { retryDelayMs = 2000, maxRetryDelayMs = 15000 } = {}) {
    this.url = url;
    this.retryDelayMs = retryDelayMs;
    this.maxRetryDelayMs = maxRetryDelayMs;
    this.onmessage = null;
    this.onerror = null;
    this._closed = false;
    this._es = null;
    this._currentDelay = retryDelayMs;
    this._connect();
  }

  _connect() {
    if (this._closed) return;
    this._es = new EventSource(this.url);
    this._es.onmessage = (event) => {
      this._currentDelay = this.retryDelayMs;
      if (this.onmessage) this.onmessage(event);
    };
    this._es.onerror = (event) => {
      if (this.onerror) this.onerror(event);
      this._scheduleReconnect();
    };
  }

  _scheduleReconnect() {
    if (this._closed) return;
    if (this._es) this._es.close();
    const delay = this._currentDelay;
    this._currentDelay = Math.min(this._currentDelay * 2, this.maxRetryDelayMs);
    setTimeout(() => this._connect(), delay);
  }

  close() {
    this._closed = true;
    if (this._es) this._es.close();
    this._es = null;
  }
}