Retail_manager/RMWPFUserInterface/ViewModels/SalesViewModel.cs

using Caliburn.Micro;
using RMWPFInterfaceLibrary.Api;
using RMWPFInterfaceLibrary.Models;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace RMWPFUserInterface.ViewModels
{
    public class SalesViewModel : Screen
    {
        IProductEndPoint _productEndPoint;
        public SalesViewModel(IProductEndPoint productEndPoint)
        {
            _productEndPoint = productEndPoint;
        }

        protected override async void OnViewLoaded(object view)
        {
            base.OnViewLoaded(view);
            await LoadProducts();
        }

        private async Task LoadProducts()
        {
            var prods = await _productEndPoint.GetAll();
            Products = new BindingList<ProductModel>(prods);
        }

        private BindingList<ProductModel> _products;

        public BindingList<ProductModel> Products
        {
            get { return _products; }
            set 
            { 
                _products = value; 
                NotifyOfPropertyChange(() => Products);
            }
        }

        private ProductModel _selectedProduct;

        public ProductModel SelectedProduct
        {
            get { return _selectedProduct; }
            set 
            { 
                _selectedProduct = value;
                NotifyOfPropertyChange(() => SelectedProduct);
                NotifyOfPropertyChange(() => CanAddToCart);
            }
        }


        private BindingList<CartItemModel> _cart = new BindingList<CartItemModel>();

        public BindingList<CartItemModel> Cart
        {
            get { return _cart; }
            set 
            {
                _cart = value;
                NotifyOfPropertyChange(() => Cart);
            }
        }

        private int _itemQuantity = 1;

        public int ItemQuantity
        {
            get { return _itemQuantity; }
            set 
            {
                _itemQuantity = value; 
                NotifyOfPropertyChange(() => ItemQuantity);
                NotifyOfPropertyChange(() => CanAddToCart);
            }
        }

        public string SubTotal 
        { 
            get
            {
                decimal subTotal = 0;

                foreach (var item in Cart)
                {
                    subTotal += item.Product.RetailPrice * item.QuantityInCart;
                }

                return subTotal.ToString("C");
            }
        }

        public string Tax
        {
            get
            {
                // replace with calulation;
                return "$0.00";
            }
        }

        public string Total
        {
            get
            {
                // replace with calulation;
                return "$0.00";
            }
        }

        public bool CanAddToCart
        {
            get
            {
                bool output = false;

                if (ItemQuantity > 0 && SelectedProduct?.QuantityInStock >= ItemQuantity)
                {
                    output = true;
                }

                return output;
            }
        }
        public void AddToCart()
        {
            CartItemModel existingItem = Cart.FirstOrDefault(x => x.Product == SelectedProduct);

            if (existingItem != null)
            {
                existingItem.QuantityInCart += ItemQuantity;
            }
            else
            {
                CartItemModel item = new CartItemModel
                {
                    Product = SelectedProduct,
                    QuantityInCart = ItemQuantity
                };

                Cart.Add(item);
            }
            SelectedProduct.QuantityInStock -= ItemQuantity;
            ItemQuantity = 1;
            NotifyOfPropertyChange(() => SubTotal);
            Cart.ResetBindings();
        }

        public bool CanRemoveFromCart
        {
            get
            {
                bool output = false;

                // Make sure something is selected

                return output;
            }
        }
        public void RemoveFromCart()
        {
            NotifyOfPropertyChange(() => SubTotal);
        }

        public bool CanCheckOut
        {
            get
            {
                bool output = false;

                // Make sure there is something in the cart

                return output;
            }
        }
        public void CheckOut()
        {

        }
    }
}