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

using FrontOffice.BFF.ShopingCart.Protobuf.Protos.ShopingCart;
using Google.Protobuf.WellKnownTypes;

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 ShopingCartContract.ShopingCartContractClient _client;
    private readonly List<CartItem> _items = new();
    public event Action? OnChange;

    public CartService(ShopingCartContract.ShopingCartContractClient client)
    {
        _client = client;
        _ = LoadFromServerAsync();
    }

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

    public async Task 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();

        try
        {
            await _client.AddNewUserCartAsync(new AddNewUserCartRequest
            {
                ProductId = product.Id,
                Count = quantity
            });
        }
        catch
        {
            // Best-effort sync with backend; keep local state on failure
        }
    }

    public async Task 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();

        try
        {
            await _client.UpdateUserCartAsync(new UpdateUserCartRequest
            {
                UserCartId = productId,
                Count = quantity
            });
        }
        catch
        {
            // Best-effort sync with backend; keep local state on failure
        }
    }

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

        try
        {
            // Interpret Count=0 as remove from cart
            await _client.UpdateUserCartAsync(new UpdateUserCartRequest
            {
                UserCartId = productId,
                Count = 0
            });
        }
        catch
        {
            // Best-effort sync with backend; keep local state on failure
        }
    }

    public async Task Clear()
    {
        var productIds = _items.Select(i => i.ProductId).ToList();
        _items.Clear();
        Notify();

        try
        {
            foreach (var id in productIds)
            {
                await _client.UpdateUserCartAsync(new UpdateUserCartRequest
                {
                    UserCartId = id,
                    Count = 0
                });
            }
        }
        catch
        {
            // Best-effort sync with backend; keep local state on failure
        }
    }

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

    private async Task LoadFromServerAsync()
    {
        try
        {
            var response = await _client.GetAllUserCartAsync(new Empty());
            _items.Clear();
            foreach (var m in response.Models)
            {
                var item = new CartItem(
                    ProductId: m.Id,
                    Title: m.Title ?? string.Empty,
                    ImageUrl: string.IsNullOrWhiteSpace(m.ImagePath) ? string.Empty : UrlUtility.DownloadUrl + m.ImagePath,
                    UnitPrice: m.Price,
                    Quantity: m.SaleCount > 0 ? m.SaleCount : 1);
                _items.Add(item);
            }
            Notify();
        }
        catch
        {
            // If backend is unreachable or user is unauthenticated, fall back to local-only cart.
        }
    }
}