midrandbooks/MidrandBookshop/Services/ShoppingCart/CartService.cs

using LiteCharms.Features.Browser;
using LiteCharms.Features.Hasher;
using LiteCharms.Features.MidrandBooks.Authors.Models;
using LiteCharms.Features.MidrandBooks.Products.Models;
using MidrandBookshop.Services.ShoppingCart.Models;

namespace MidrandBookshop.Services.ShoppingCart;

public sealed class CartService(LocalStorageService localStorage)
{
    private readonly string CartStorageKey = HashService.ToMd5Hash(nameof(Cart)).Value;

    public Cart ShoppingCart { get; private set; } = new();

    public event Action? OnCartChanged;

    public static Func<Cart, long, int> GetCartItemQuantity = (shoppingCart, productPriceId) =>
        shoppingCart.Items.FirstOrDefault(p => p.Price!.Id == productPriceId)?.Quantity ?? 1;

    public Cart GetCart() => ShoppingCart;

    public void NotifyStateChanged() => OnCartChanged?.Invoke();

    public async Task LoadCartFromStorageAsync()
    {
        var loadResult = await localStorage.GetAsync<Cart>(CartStorageKey);

        if (loadResult.IsFailed) await localStorage.SaveAsync(CartStorageKey, ShoppingCart);

        if (loadResult.IsSuccess) ShoppingCart = loadResult.Value;

        NotifyStateChanged();
    }

    public async Task SaveCartToStorageAsync() => await localStorage.SaveAsync(CartStorageKey, ShoppingCart);

    public void AddItem(ProductPrice productPrice, Product product, Author author)
    {
        var itemExists = false;

        for (var i = 0; i < ShoppingCart.Items.Count; i++)
        {
            if (ShoppingCart.Items[i].Price!.Id == productPrice.Id)
            {
                ShoppingCart.Items[i].Quantity++;
                ShoppingCart.Items[i].Amount += productPrice.Amount;

                itemExists = true;

                break;
            }
        }

        if (!itemExists)
            ShoppingCart.Items.Add(new CartItem
            {
                Product = product,
                Author = author,
                Price = productPrice,
                Amount = productPrice.Amount,
                Quantity = 1,
            });

        CalculateTotalPrice();
        NotifyStateChanged();
    }

    public void UpdateQuantity(long productPriceId, int delta)
    {
        for (var i = 0; i < ShoppingCart.Items.Count; i++)
        {
            if (ShoppingCart.Items[i].Price!.Id == productPriceId)
            {
                var oldQuantity = ShoppingCart.Items[i].Quantity;
                var pricePerUnit = ShoppingCart.Items[i].Price!.Amount;

                ShoppingCart.Items[i].Quantity += delta;
                ShoppingCart.Items[i].Amount = pricePerUnit * ShoppingCart.Items[i].Quantity;
                break;
            }
        }

        CalculateTotalPrice();
        NotifyStateChanged();
    }

    public void RemoveOneItem(long productPriceId)
    {
        for (var i = 0; i < ShoppingCart.Items.Count; i++)
        {
            if (ShoppingCart.Items[i].Price!.Id == productPriceId)
            {
                if (ShoppingCart.Items[i].Quantity <= 1)
                {
                    ShoppingCart.Items.Remove(ShoppingCart.Items[i]);

                    break;
                }
                else
                {
                    ShoppingCart.Items[i].Quantity--;
                    ShoppingCart.Items[i].Amount -= ShoppingCart.Items[i].Price!.Amount;
                }

                break;
            }
        }

        CalculateTotalPrice();
        NotifyStateChanged();
    }

    public void RemoveAllSameItem(long productPriceId)
    {
        if (ShoppingCart.Items.Count == 0) return;

        var item = ShoppingCart.Items.FirstOrDefault(i => i.Price?.Id == productPriceId);

        if (item is not null) ShoppingCart.Items.Remove(item);

        CalculateTotalPrice();
        NotifyStateChanged();
    }

    public void Clear()
    {
        if(ShoppingCart.CustomerId is not null || ShoppingCart.OrderId is not null)
        {
            ShoppingCart.TotalAmount = 0;
            ShoppingCart.TotalVat = 0;
            ShoppingCart.Items.Clear();

            return;
        }

        ShoppingCart = new Cart();

        NotifyStateChanged();
    }

    public decimal CalculateTotalPrice()
    {
        if (ShoppingCart.Items.Count == 0) return 0;

        var gross = ShoppingCart.Items.Sum(i => i.Amount);

        if (!ShoppingCart.IsVatInclusive) ShoppingCart.TotalVat = gross * ShoppingCart.VatRate;

        ShoppingCart.TotalAmount = gross + ShoppingCart.TotalVat;

        return ShoppingCart.TotalAmount;
    }
}