/**
 * @author Martin Karkowski
 * @email m.karkowski@zema.de
 * @create date 2020-08-25 23:01:24
 * @modify date 2020-11-07 00:35:49
 * @desc [description]
 */

/**
 * Function to get a singleton. To create the singleton, the parameter *create* is used. This will be called once.
 * The singleton will be stored as *global* variable and can be accessed by the identifier
 *
 * @author M.Karkowski
 * @export
 * @template T The Type of the singleton
 * @param {string} identifier Identifier to access the singleton
 * @param {() => T} create The Callback which is used to create the instance.
 * @return An object, containing the key **instances**, where you'll find the instance and an helper function **setInstance** to redefine the instance
 */
export function getSingleton<T>(
  identifier: string,
  create: () => T
): {
  instance: T;
  setInstance: (value: T) => void;
} {
  // Extract all
  const globalSymbols = Object.getOwnPropertySymbols(global);

  // create a unique, global symbol name
  // -----------------------------------
  const IDENTIFIER_DISPATCHER_CONTAINER = Symbol.for(identifier);

  // check if the global object has this symbol
  // add it if it does not have the symbol, yet
  // ------------------------------------------
  const hasContainer =
    globalSymbols.indexOf(IDENTIFIER_DISPATCHER_CONTAINER) > -1;

  if (!hasContainer) {
    global[IDENTIFIER_DISPATCHER_CONTAINER] = create();
  }

  const ret: {
    instance: T;
    setInstance: (value: T) => void;
  } = {
    instance: global[IDENTIFIER_DISPATCHER_CONTAINER],
    setInstance: (value: T) => {
      global[IDENTIFIER_DISPATCHER_CONTAINER] = value;
    },
  };

  // define the singleton API
  // ------------------------
  Object.defineProperty(ret, "instance", {
    get: function () {
      return global[IDENTIFIER_DISPATCHER_CONTAINER];
    },
  });

  // ensure the API is never changed
  // -------------------------------
  Object.freeze(ret);

  return ret;
}