cart.state.ts

@State<CartStateModel>({
  name: 'cartItems',
  defaults: {
    cartItems: {},
  },
})
export class CartState {
  @Action(AddToCart)
  addProduct(ctx: StateContext<CartStateModel>, action: AddToCart) {
    const state = ctx.getState();
    ctx.setState({
      ...state,
      cartItems: {
        ...state.cartItems,
        [action.payload.sku]: (state.cartItems[action.payload.sku] || 0) + 1,
      },
    });
  }

  @Action(RemoveFromCart)
  removeProduct(ctx: StateContext<CartStateModel>, action: RemoveFromCart) {
    const state = ctx.getState();
    ctx.patchState({
      cartItems: {
        ...state.cartItems,
        [action.payload.sku]: Math.max((state.cartItems[action.payload.sku] || 0) - 1, 0),
      },
    });
  }

  @Action(EmptyCart)
  emptyCart(ctx: StateContext<CartStateModel>, action: EmptyCart) {
    ctx.setState({ cartItems: {} });
  }
}