GameSession.cs

using Engine.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Engine.Factories;
using System.ComponentModel;
using Engine.EventArgs;

namespace Engine.ViewModels
{
   public class GameSession : BaseNotificationClass

    {
        public EventHandler<GameMessageEventArgs> OnMessageRaised; 
        
        private Location _currentLocation;
        private Monster _currentMonster;        

        public World CurrentWorld { get; set; }
        public Player CurrentPlayer { get; set; }
        public Location CurrentLocation
        {
            get { return _currentLocation; }
            set
            {
                _currentLocation = value;
                OnPropertyChanged(nameof(CurrentLocation));
                OnPropertyChanged(nameof(HasLocationToNorth));
                OnPropertyChanged(nameof(HasLocationToEast));
                OnPropertyChanged(nameof(HasLocationToWest));
                OnPropertyChanged(nameof(HasLocationToSouth));

                GivePlayerQuestAtLocation();
                GetMonsterAtLocation();
            }
        }       

        public Monster CurrentMonster
        {
            get { return _currentMonster; }
            set
            {
                _currentMonster = value;
                OnPropertyChanged(nameof(CurrentMonster));
                OnPropertyChanged(nameof(HasMonster));
                 
                if(CurrentMonster !=null)
                {
                    RaiseMessage("");
                    RaiseMessage($"You see a {CurrentMonster.Name} here!");
                }
            }
        }

        public Weapon CurrentWeapon { get; set; }

        public bool HasLocationToNorth =>
                    CurrentWorld.LocationAt(CurrentLocation.XCoordinate, CurrentLocation.YCoordinate + 1) != null;

        public bool HasLocationToEast =>
                    CurrentWorld.LocationAt(CurrentLocation.XCoordinate + 1, CurrentLocation.YCoordinate) != null;
            
        public bool HasLocationToSouth =>
                     CurrentWorld.LocationAt(CurrentLocation.XCoordinate, CurrentLocation.YCoordinate -1) != null;
            
        public bool HasLocationToWest =>
                    CurrentWorld.LocationAt(CurrentLocation.XCoordinate -1, CurrentLocation.YCoordinate) != null;
      
        public bool HasMonster => CurrentMonster != null;

        public GameSession()
        {
            CurrentPlayer = new Player
            {
                Name = "Scott",
                CharacterClass = "Fighter",
                HitPoints = 10,
                Gold = 1000000,
                ExperiencePoints = 0,
                Level = 1
            };
                      
                if (!CurrentPlayer.Weapons.Any())
                {
                    CurrentPlayer.AddItemToInventory(ItemFactory.CreateGameItem(1001));
                }
           
            CurrentWorld = WorldFactory.CreateWorld();

            CurrentLocation = CurrentWorld.LocationAt(0, 0);
                       
        }

        public void MoveNorth()
        {
            if(HasLocationToNorth)
            {
                CurrentLocation = CurrentWorld.LocationAt(CurrentLocation.XCoordinate, CurrentLocation.YCoordinate + 1);
            }
        }
        public void MoveEast()
        {
            if (HasLocationToEast)
            {
                CurrentLocation = CurrentWorld.LocationAt(CurrentLocation.XCoordinate + 1, CurrentLocation.YCoordinate);
            }
        }
        public void MoveSouth()
        {
            if (HasLocationToSouth)
            {
                CurrentLocation = CurrentWorld.LocationAt(CurrentLocation.XCoordinate, CurrentLocation.YCoordinate - 1);
            }
        }
        public void MoveWest()
        {
            if (HasLocationToWest)
            {
                CurrentLocation = CurrentWorld.LocationAt(CurrentLocation.XCoordinate - 1, CurrentLocation.YCoordinate);
            }
        }

        private void GivePlayerQuestAtLocation()
        {
            foreach(Quest quest in CurrentLocation.QuestsAvailableHere)
            {
                if (!CurrentPlayer.Quests.Any(q => q.PlayerQuest.ID == quest.ID))
                {
                    CurrentPlayer.Quests.Add(new QuestStatus(quest));
                }
            }
        }

        private void GetMonsterAtLocation()
        {
            CurrentMonster = CurrentLocation.GetMonster();
        }

        public void AttackCurrentMonster()
        {
            if(CurrentWeapon == null)
            {
                RaiseMessage("You must select a weapon to attack.");
                return;
            }
            //determine damage to monster
            int damageToMonster = RandomNumberGenerator.NumberBetween(CurrentWeapon.MinimunDamage, CurrentWeapon.MaximumDamage);

            if(damageToMonster == 0)
            {
                RaiseMessage($"You missed the {CurrentMonster.Name}.");
            }
            else
            {
                CurrentMonster.HitPoints -= damageToMonster;
                RaiseMessage($"You hit the {CurrentMonster.Name} for {damageToMonster} points.");
            }

            //if monster is killed, collect rewards and loot
            if(CurrentMonster.HitPoints<=0)
            {
                RaiseMessage("");
                RaiseMessage($"You defeated the {CurrentMonster.Name}!");

                CurrentPlayer.ExperiencePoints += CurrentMonster.RewardExperiencePoints;
                RaiseMessage($"You receive {CurrentMonster.RewardExperiencePoints} experience points!");

                CurrentPlayer.Gold += CurrentMonster.RewardGold;
                RaiseMessage($"You receive {CurrentMonster.RewardGold} gold.");

                foreach(ItemQuantity itemQuantity in CurrentMonster.Inventory)
                {
                    GameItem item = ItemFactory.CreateGameItem(itemQuantity.ItemID);
                    CurrentPlayer.AddItemToInventory(item);
                    RaiseMessage($"You receive {itemQuantity.Quantity} {item.Name}.");
                }

                //get another monster to fight
                GetMonsterAtLocation();
              }
            else
            {
                //if monster is still alive, let monster attack
                int damageToPlayer = RandomNumberGenerator.NumberBetween(CurrentMonster.MinimumDamage, CurrentMonster.MaximumHitPoints);

                if (damageToPlayer == 0)
                {
                    RaiseMessage($"The monster attacks, but misses you.");
                }
                else
                {
                    CurrentPlayer.HitPoints -= damageToPlayer;
                    RaiseMessage($"The {CurrentMonster.Name} attacks and hit you for {damageToPlayer} points.");
                }
                //if player is killed, move player back to home location
                if (CurrentPlayer.HitPoints <= 0)
                {
                    RaiseMessage("");
                    RaiseMessage($"The {CurrentMonster.Name} killed you.");

                    CurrentLocation = CurrentWorld.LocationAt(0, -1); 
                    CurrentPlayer.HitPoints = CurrentPlayer.Level * 10; 

                }
            }
        }

        private void RaiseMessage(string message)
        {
            OnMessageRaised?.Invoke(this, new GameMessageEventArgs(message));          
        }
               

    }
}

ItemFactory.cs

using Engine.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Engine.Factories
{
    public static class ItemFactory
    {
        private static readonly List<GameItem> _standardGameItems = new List<GameItem>();

        static ItemFactory()
        {

            _standardGameItems.Add(new Weapon(1001, "Pointy Stick", 1, 1, 2));
            _standardGameItems.Add(new Weapon(1002, "Rusty Sword", 5, 1, 3));
            _standardGameItems.Add(new GameItem(9001, "Snake Fang", 1));
            _standardGameItems.Add(new GameItem(9002, "Snakeskin", 2));
            _standardGameItems.Add(new GameItem(9003, "Rat tail", 1));
            _standardGameItems.Add(new GameItem(9004, "Rat fur", 2));
            _standardGameItems.Add(new GameItem(9005, "Spdier fang", 1));
            _standardGameItems.Add(new GameItem(9006, "Spider silk", 2));

        }

        public static GameItem CreateGameItem(int itemTypeID)
        {
            GameItem standardItem = _standardGameItems.FirstOrDefault(item => item.ItemTypeID == itemTypeID);

            if (standardItem != null)
            {
                if (standardItem is Weapon)
                {
                    return (standardItem as Weapon).Clone();
                }
                return standardItem.Clone();
            }
            return null;         
            
        }

    }
}

Player.cs

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

namespace Engine.Models
{
    public class Player: BaseNotificationClass
    {
        private string _name;
        private string _characterClass;
        private int _hitPoints;
        private int _experiencePoints;
        private int _level;
        private int _gold;

        public string Name
        {
            get { return _name; }
            set { _name = value;
                OnPropertyChanged(nameof(Name));}                
        }

        public string CharacterClass
        {
            get { return _characterClass; }
            set { _characterClass = value;
                OnPropertyChanged(nameof(CharacterClass));
                }
        }

        public int HitPoints
        {
            get { return _hitPoints; }
            set { _hitPoints = value;
                OnPropertyChanged(nameof(HitPoints));
                }            
        }

        public int ExperiencePoints
        {
            get { return _experiencePoints; }
            set { _experiencePoints = value;
                OnPropertyChanged(nameof(ExperiencePoints));
                }
        }

        public int Level
        {
            get { return _level; }
            set { _level = value;
                OnPropertyChanged(nameof(Level));
                }
        }

        public int Gold
        {
            get { return _gold; }
            set {   _gold = value;
                OnPropertyChanged(nameof(Gold));
                }
        }

        public ObservableCollection<GameItem> Inventory { get; set; }

        public List<GameItem> Weapons =>
            Inventory.Where(i => i is Weapon).ToList();

        public ObservableCollection<QuestStatus> Quests { get; set; }

        public Player()
        {
            Inventory = new ObservableCollection<GameItem>();
            Quests = new ObservableCollection<QuestStatus>();
        }   

        public void AddItemToInventory(GameItem item)
        {
            Inventory.Add(item);

            OnPropertyChanged(nameof(Weapons));
        }
        
           
    }
}