type State = { count: number; items: string[] };
type Action = { type: string; payload?: string };

export function reducer(state: State, action: Action): State {
  // Usa switch para manejar cada tipo de acción
  // Retorna SIEMPRE un nuevo objeto con spread — nunca modifiques state
  switch(action.type) {
    case 'INCREMENT':
      return { ...state, count: state.count + 1 };
    case 'DECREMENT':
      return { ...state, count: state.count - 1 };
    case 'ADD_ITEM':
      return { ...state, items: [...state.items, action.payload] };
    default: 
      return { ...state };
  }
  
}