littleshop/TeleBot/TeleBot/Models/ShoppingCart.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace TeleBot.Models
{
    public class ShoppingCart
    {
        public string Id { get; set; } = Guid.NewGuid().ToString();
        public List<CartItem> Items { get; set; } = new();
        public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
        public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
        
        public void AddItem(Guid productId, string productName, decimal price, int quantity = 1, Guid? multiBuyId = null, string? selectedVariant = null)
        {
            var existingItem = Items.FirstOrDefault(i =>
                i.ProductId == productId && i.MultiBuyId == multiBuyId && i.SelectedVariant == selectedVariant);

            if (existingItem != null)
            {
                // For multi-buys, we don't add quantities - each multi-buy is a separate bundle
                // For regular items, we add the quantities together
                if (!multiBuyId.HasValue)
                {
                    existingItem.Quantity += quantity;
                    existingItem.UpdateTotalPrice();
                }
                // If it's a multi-buy and already exists, we don't add it again
                // (user should explicitly add another multi-buy bundle if they want more)
            }
            else
            {
                var newItem = new CartItem
                {
                    ProductId = productId,
                    MultiBuyId = multiBuyId,
                    SelectedVariant = selectedVariant,
                    ProductName = productName,
                    UnitPrice = price,
                    Quantity = quantity
                };
                newItem.UpdateTotalPrice(); // Ensure total is calculated after all properties are set
                Items.Add(newItem);
            }

            UpdatedAt = DateTime.UtcNow;
        }
        
        public void RemoveItem(Guid productId)
        {
            Items.RemoveAll(i => i.ProductId == productId);
            UpdatedAt = DateTime.UtcNow;
        }
        
        public void UpdateQuantity(Guid productId, int quantity)
        {
            var item = Items.FirstOrDefault(i => i.ProductId == productId);
            if (item != null)
            {
                if (quantity <= 0)
                {
                    RemoveItem(productId);
                }
                else
                {
                    item.Quantity = quantity;
                    item.UpdateTotalPrice();
                    UpdatedAt = DateTime.UtcNow;
                }
            }
        }
        
        public void Clear()
        {
            Items.Clear();
            UpdatedAt = DateTime.UtcNow;
        }
        
        public decimal GetTotalAmount()
        {
            return Items.Sum(i => i.TotalPrice);
        }
        
        public int GetTotalItems()
        {
            return Items.Sum(i => i.Quantity);
        }
        
        public bool IsEmpty()
        {
            return !Items.Any();
        }
    }
    
    public class CartItem
    {
        public Guid ProductId { get; set; }
        public Guid? MultiBuyId { get; set; }  // For quantity pricing (e.g., 3 for £25)
        public string? SelectedVariant { get; set; }  // For color/flavor selection
        public string ProductName { get; set; } = string.Empty;
        public int Quantity { get; set; }
        public decimal UnitPrice { get; set; }  // For multi-buys, this is the bundle price; for regular items, it's per-unit
        public decimal TotalPrice { get; set; }

        public CartItem()
        {
            // Don't calculate total in constructor - wait for properties to be set
        }

        public void UpdateTotalPrice()
        {
            // For multi-buys, UnitPrice is already the total bundle price
            // For regular items, we need to multiply by quantity
            if (MultiBuyId.HasValue)
            {
                TotalPrice = UnitPrice; // Bundle price, not multiplied
            }
            else
            {
                TotalPrice = UnitPrice * Quantity; // Regular per-unit pricing
            }
        }
    }
}