import * as Y from "yjs";
import { Atom, createAtom } from "../observableProvider";

const xmlsObserved = new WeakSet<Y.XmlFragment>();

export function observeXml(value: Y.XmlFragment) {
  if (xmlsObserved.has(value)) {
    // already patched
    return value;
  }
  xmlsObserved.add(value);

  let atom: Atom | undefined;

  const handler = (event: Y.YXmlEvent) => {
    if (
      event.changes.added.size ||
      event.changes.deleted.size ||
      event.changes.keys.size ||
      event.changes.delta.length
    ) {
      atom!.reportChanged();
    }
  };

  atom = createAtom(
    "xml",
    () => {
      value.observe(handler);
    },
    () => {
      value.unobserve(handler);
    }
  );

  function patch(method: string) {
    const originalFunction = value[method];
    value[method] = function () {
      atom!.reportObserved(this._implicitObserver);
      const ret = Reflect.apply(originalFunction, this, arguments);
      return ret;
    };
  }

  function patchGetter(method: string) {
    let target = value;
    let descriptor = Object.getOwnPropertyDescriptor(target, method)!;

    // properties might be defined down the prototype chain (e.g., properties on XmlFragment when working on an XmlElement)
    if (!descriptor) {
      target = Object.getPrototypeOf(target);
      descriptor = Object.getOwnPropertyDescriptor(target, method)!;
    }

    if (!descriptor) {
      target = Object.getPrototypeOf(target);
      descriptor = Object.getOwnPropertyDescriptor(target, method)!;
    }

    if (!descriptor) {
      throw new Error("property not found");
    }

    const originalFunction = descriptor.get!;
    descriptor.get = function () {
      atom!.reportObserved(this._implicitObserver);
      const ret = Reflect.apply(originalFunction, this, arguments);
      return ret;
    };
    Object.defineProperty(value, method, descriptor);
  }

  patch("toString");
  patch("toDOM");
  patch("toArray");
  patch("getAttribute");
  patchGetter("firstChild");

  return value;
}