components/LiteCharms.Features.MidrandBooks/Orders/CartService.cs

using LiteCharms.Features.Abstractions;
using LiteCharms.Features.MidrandBooks.Orders.Models;
using LiteCharms.Features.MidrandBooks.Products.Models;

namespace LiteCharms.Features.MidrandBooks.Orders;

public sealed class CartService : IService
{
    private Cart cart = new();

    public Cart GetCart() => cart;

    public void LoadCart(Cart savedCart) => cart = savedCart;

    public void AddItem(ProductPrice productPrice)
    {
        var itemExists = false;

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

                itemExists = true;

                break;
            }
        }

        if (!itemExists)
            cart.Items.Add(new CartItem
            {
                Price = productPrice,
                Amount = productPrice.Amount,
                Quantity = 1,
            });

        CalculateTotalPrice();
    }

    public void UpdateQuantity(long productPriceId, int newQuantity)
    {
        if (newQuantity <= 0)
        {
            RemoveAllSameItem(productPriceId);

            return;
        }

        for (var i = 0; i < cart.Items.Count; i++)
        {
            if (cart.Items[i].Price!.Id == productPriceId)
            {
                var oldQuantity = cart.Items[i].Quantity;
                var pricePerUnit = cart.Items[i].Price!.Amount;

                cart.Items[i].Quantity = newQuantity;
                cart.Items[i].Amount = pricePerUnit * newQuantity;
                break;
            }
        }

        CalculateTotalPrice();
    }

    public void RemoveOneItem(long productPriceId)
    {
        for (var i = 0; i < cart.Items.Count; i++)
        {
            if (cart.Items[i].Price!.Id == productPriceId)
            {
                if (cart.Items[i].Quantity <= 1)
                {
                    cart.Items.RemoveAt(i);
                }
                else
                {
                    cart.Items[i].Quantity--;
                    cart.Items[i].Amount -= cart.Items[i].Price!.Amount;
                }

                break;
            }
        }

        CalculateTotalPrice();
    }

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

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

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

        CalculateTotalPrice();
    }

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

            return;
        }

        cart = new Cart();
    }

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

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

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

        cart.TotalPrice = gross + cart.TotalVat;

        return cart.TotalPrice;
    }
}