History.swift

class History<T> {
    
    // MARK: Properties
    
    private var _undoStack: [T] = []
    private var _redoStack: [T] = []
    private var _current: T
    
    // MARK: Getter, Setter
    
    var current: T {
        get {
            return _current
        }
        set {
            _undoStack.append(current)
            _current = newValue
            _redoStack = []
        }
    }
    
    var canUndo: Bool {
        return !_undoStack.isEmpty
    }
    
    var canRedo: Bool {
        return !_redoStack.isEmpty
    }
    
    // MARK: Initializers
    
    init(state: T) {
        self._current = state
    }
    
    // MARK: Functions
    
    func undo() {
        guard let nextState = _undoStack.popLast() else {
            return
        }
        _redoStack.append(_current)
        _current = nextState
    }
    
    func redo() {
        guard let nextState = _redoStack.popLast() else {
            return
        }
        _undoStack.append(_current)
        _current = nextState
    }
}