import UndoStack from '../src/undo-stack';

describe('UndoStack', function UndoStackSpecs() {
  beforeEach(() => {
    this.undoManager = new UndoStack();
  });

  afterEach(() => {
    advanceClock(500);
  });

  describe('undo', () => {
    it('can restore history items, and returns null when none are available', () => {
      this.undoManager.save('A');
      this.undoManager.save('B');
      this.undoManager.save('C');
      expect(this.undoManager.current()).toBe('C');
      expect(this.undoManager.undo()).toBe('B');
      expect(this.undoManager.current()).toBe('B');
      expect(this.undoManager.undo()).toBe('A');
      expect(this.undoManager.current()).toBe('A');
      expect(this.undoManager.undo()).toBe(null);
      expect(this.undoManager.current()).toBe('A');
    });

    it('limits the undo stack to the MAX_HISTORY_SIZE', () => {
      this.undoManager._MAX_STACK_SIZE = 3;
      this.undoManager.save('A');
      this.undoManager.save('B');
      this.undoManager.save('C');
      this.undoManager.save('D');
      expect(this.undoManager.current()).toBe('D');
      expect(this.undoManager.undo()).toBe('C');
      expect(this.undoManager.undo()).toBe('B');
      expect(this.undoManager.undo()).toBe(null);
      expect(this.undoManager.current()).toBe('B');
    });
  });

  describe('undo followed by redo', () => {
    it('can restore previously undone history items', () => {
      this.undoManager.save('A');
      this.undoManager.save('B');
      this.undoManager.save('C');
      expect(this.undoManager.current()).toBe('C');
      expect(this.undoManager.undo()).toBe('B');
      expect(this.undoManager.current()).toBe('B');
      expect(this.undoManager.redo()).toBe('C');
      expect(this.undoManager.current()).toBe('C');
    });

    it('cannot be used after pushing additional items', () => {
      this.undoManager.save('A');
      this.undoManager.save('B');
      this.undoManager.save('C');
      expect(this.undoManager.current()).toBe('C');
      expect(this.undoManager.undo()).toBe('B');
      this.undoManager.save('D');
      expect(this.undoManager.redo()).toBe(null);
      expect(this.undoManager.current()).toBe('D');
    });
  });
});