FrontOffice/src/FrontOffice.Main/Utilities/CartService.cs

namespace FrontOffice.Main.Utilities;

public record CartItem(long ProductId, string Title, string ImageUrl, long UnitPrice, int Quantity)
{
    public long LineTotal => UnitPrice * Quantity;
}

public class CartService
{
    private readonly List<CartItem> _items = new();
    public event Action? OnChange;

    public IReadOnlyList<CartItem> Items => _items.AsReadOnly();
    public long Total => _items.Sum(i => i.LineTotal);
    public int Count => _items.Sum(i => i.Quantity);

    public void Add(Product product, int quantity = 1)
    {
        if (quantity <= 0) return;
        var existing = _items.FirstOrDefault(i => i.ProductId == product.Id);
        if (existing is null)
        {
            _items.Add(new CartItem(product.Id, product.Title, product.ImageUrl, product.Price, quantity));
        }
        else
        {
            var idx = _items.IndexOf(existing);
            _items[idx] = existing with { Quantity = existing.Quantity + quantity };
        }
        Notify();
    }

    public void UpdateQuantity(long productId, int quantity)
    {
        var existing = _items.FirstOrDefault(i => i.ProductId == productId);
        if (existing is null) return;
        if (quantity <= 0)
        {
            Remove(productId);
            return;
        }
        var idx = _items.IndexOf(existing);
        _items[idx] = existing with { Quantity = quantity };
        Notify();
    }

    public void Remove(long productId)
    {
        _items.RemoveAll(i => i.ProductId == productId);
        Notify();
    }

    public void Clear()
    {
        _items.Clear();
        Notify();
    }

    private void Notify() => OnChange?.Invoke();
}