import { Emitter } from "@segment/analytics-generic-utils";

type ChangeData = {
  current: URL;
  previous: URL;
};
export interface URLChangeObservableSettings {
  pollInterval?: number;
}

// This seems hacky, but if using react router (or other SPAs), popstate will not always fire on navigation
// Otherwise, we could use popstate / hashchange events
export class URLChangeObservable {
  private emitter = new Emitter<{ change: [ChangeData] }>();
  private pollInterval: number;
  private urlChanged?: (data: ChangeData) => void;
  constructor(settings: URLChangeObservableSettings = {}) {
    this.pollInterval = settings.pollInterval ?? 500;
    this.pollURLChange();
  }

  private pollURLChange() {
    let prevUrl = window.location.href;
    setInterval(() => {
      const currentUrl = window.location.href;
      if (currentUrl != prevUrl) {
        const current = new URL(currentUrl);
        const prev = new URL(prevUrl);
        this.emitter.emit("change", {
          current,
          previous: prev,
        });
        prevUrl = currentUrl;
      }
    }, this.pollInterval);
  }

  subscribe(urlChanged: (data: ChangeData) => void) {
    this.urlChanged = urlChanged;
    this.emitter.on("change", this.urlChanged);
  }

  unsubscribe() {
    this.emitter.off("change", this.urlChanged!);
  }
}