/**
 * @author Martin Karkowski
 * @email m.karkowski@zema.de
 * @create date 2020-08-25 23:01:24
 * @modify date 2020-08-25 23:08:42
 * @desc [description]
 */

/**
 * Function to get a singleton
 * @param identifier 
 * @param create 
 */
export function getSingleton<T>(identifier: string, create: () => T) {
  // 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;
}