Review the code and identify following:    

// * bugs

// * performance improvements

// * avoid discussing SOLID principles

// 

//When application is running in:

// * single threaded environment

// * multi-threaded environment

// (note that the code is syntactically correct, i.e. it compiles)

namespace Interview1

{

    // InventoryManager is responsible for tracking inventory

    public class InventoryManager

    {

        //Can't add/update list if it is readonly

        private reist<InventoryItem> inventory = new();

        private reist<InventoryItem> itemsSold = new();

​

        // notification when an item is sold out - from in stock to 0 stock

        public event Action<string> ItemSoldOut;

​

        // notification when an item becomes available - from 0 stock to in stock

        public event Action<string> ItemBecameAvailable;

​

        // provides average profit of all current stock

        public float AverageProfit => this.inventory.Sum(i => i.ProfitPerItem) / this.inventory.Count();

​

        // informs about profit made in last 60 minutes

        public float ProfitLastHour { get; private set; }

​

        public void AddToStock(string itemId, int count)

        {

            //It there is no item with the Id, it would throw an exception

            v var item = ms.inventory.FirstOrDefafault(i => i.Id == itemId);

            if(item==null) { 

              throw new Exception();

            }

            //don't we also need to update the Stock count for this item in the inventory list?

            item.StockCount += count;

            this.inventory

            //should this be item.StockCount >0?

            if (item.StockCount == count)

            {

                this.ItemBecameAvailable(itemId);

            }

        }

​

        public void SellItem(string itemId, int count)

        {

            //It there is no item with the Id, it would throw an exception

            var item = this.inventory.First(i => i.Id == itemId);

            item.StockCount -= count;

​

            if (item.StockCount == 0)

            {

                this.ItemSoldOut(itemId);

            }

            item.Date = DateTime.Now;

            //Can't add to a list if it read only

            this.itemsSold.Add(item);

            this.ProfitLastHour = this.itemsSold

                .Where(i => i.Date >= DateTime.Now.AddHours(-1))

                .Sum(i => i.ProfitPerItem * i.StockCount);

        }

​

        class InventoryItem

        {

            public string Id { get; set; }

            public float Price { get; set; }

            public float Cost { get; set; }

            public int StockCount { get; set; }

            public DateTime Date { get; set; }

            public float ProfitPerItem => this.Price - this.Cost;

        }

    }

}