import { ChangedProperties } from "@segment/analytics-signals-runtime";
import { URLChangeObservable } from "../../../lib/detect-url-change";
import { createNavigationSignal } from "../../../types/factories";
import { SignalEmitter } from "../../emitter";
import { SignalGenerator } from "../types";

function getChangedProperties(url1: URL, url2: URL): ChangedProperties[] {
  const changed: ChangedProperties[] = [];
  const propertiesToCompare = ["pathname", "search", "hash"] as const;

  for (const property of propertiesToCompare) {
    if (url1[property] !== url2[property]) {
      if (property === "pathname") {
        changed.push("path");
      } else {
        changed.push(property);
      }
    }
  }

  return changed;
}

export class OnNavigationEventGenerator implements SignalGenerator {
  id = "navigation";

  urlChange: URLChangeObservable;
  constructor() {
    this.urlChange = new URLChangeObservable();
  }

  register(emitter: SignalEmitter): () => void {
    emitter.emit(
      createNavigationSignal({
        ...this.createCommonFields(),
      }),
    );

    // emit a navigation signal whenever the URL has changed
    this.urlChange.subscribe(({ previous, current }) =>
      emitter.emit(
        createNavigationSignal({
          previousUrl: previous.href,
          changedProperties: getChangedProperties(current, previous),
          ...this.createCommonFields(),
        }),
      ),
    );

    return () => {
      this.urlChange.unsubscribe();
    };
  }

  private createCommonFields() {
    return {
      // these fields are named after those from the page call, rather than a DOM api.
      currentUrl: location.href,
      path: location.pathname,
      hash: location.hash,
      search: location.search,
      title: document.title,
    };
  }
}