homework/Services/CartService.cs

using System.Text.Json;

using TechnoWorld.Data;
using TechnoWorld.Models;

namespace TechnoWorld.Services;

public class CartService
{
    private const string SessionKey = "CartItems";
    private readonly IHttpContextAccessor _http;

    public CartService(IHttpContextAccessor http)
    {
        _http = http;
    }

    public List<CartItem> GetItems()
    {
        var ids = GetIds();
        var items = new List<CartItem>();

        foreach (var (productId, quantity) in ids)
        {
            var product = ProductStore.Products.FirstOrDefault(p => p.Id == productId);
            if (product == null)
            {
                continue;
            }

            items.Add(new CartItem { ProductId = productId, Product = product, Quantity = quantity });
        }

        return items;
    }

    public int GetCount()
    {
        return GetIds().Values.Sum();
    }

    public decimal GetTotal()
    {
        return GetItems().Sum(i => i.Subtotal);
    }

    public void Add(int productId, int quantity = 1)
    {
        var ids = GetIds();
        ids[productId] = ids.GetValueOrDefault(productId) + quantity;
        Save(ids);
    }

    public void SetQuantity(int productId, int quantity)
    {
        var ids = GetIds();
        if (quantity <= 0)
        {
            ids.Remove(productId);
        }
        else
        {
            ids[productId] = quantity;
        }

        Save(ids);
    }

    public void Remove(int productId)
    {
        var ids = GetIds();
        ids.Remove(productId);
        Save(ids);
    }

    public void Clear()
    {
        _http.HttpContext?.Session.Remove(SessionKey);
    }

    private Dictionary<int, int> GetIds()
    {
        var session = _http.HttpContext?.Session;
        if (session == null)
        {
            return new Dictionary<int, int>();
        }

        var json = session.GetString(SessionKey);
        if (string.IsNullOrEmpty(json))
        {
            return new Dictionary<int, int>();
        }

        try
        {
            return JsonSerializer.Deserialize<Dictionary<int, int>>(json) ?? new Dictionary<int, int>();
        }
        catch
        {
            return new Dictionary<int, int>();
        }
    }

    private void Save(Dictionary<int, int> ids)
    {
        var session = _http.HttpContext?.Session;
        if (session == null)
        {
            return;
        }

        session.SetString(SessionKey, JsonSerializer.Serialize(ids));
    }
}