/**
  This mixin allows a class to return a singleton, as well as a method to quickly
  read/write attributes on the singleton.


  Example usage:

  ```javascript

    // Define your class and apply the Mixin
    User = EmberObject.extend({});
    User.reopenClass(Singleton);

    // Retrieve the current instance:
    var instance = User.current();

  ```

  Commonly you want to read or write a property on the singleton. There's a
  helper method which is a little nicer than `.current().get()`:

  ```javascript

    // Sets the age to 34
    User.currentProp('age', 34);

    console.log(User.currentProp('age')); // 34

  ```

  If you want to customize how the singleton is created, redefine the `createCurrent`
  method:

  ```javascript

    // Define your class and apply the Mixin
    Foot = EmberObject.extend({});
    Foot.reopenClass(Singleton, {
      createCurrent: function() {
        return Foot.create({toes: 5});
      }
    });

    console.log(Foot.currentProp('toes')); // 5

  ```
**/
import Mixin from "@ember/object/mixin";

const Singleton = Mixin.create({
  current() {
    if (!this._current) {
      this._current = this.createCurrent();
    }
    return this._current;
  },

  /**
    How the singleton instance is created. This can be overridden
    with logic for creating (or even returning null) your instance.

    By default it just calls `create` with an empty object.
  **/
  createCurrent() {
    return this.create({});
  },

  // Returns OR sets a property on the singleton instance.
  currentProp(property, value) {
    var instance = this.current();
    if (!instance) {
      return;
    }

    if (typeof value !== "undefined") {
      instance.set(property, value);
      return value;
    } else {
      return instance.get(property);
    }
  },

  resetCurrent(val) {
    this._current = val;
  }
});

export default Singleton;
