Agency.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;

namespace RegularExamOOP
{
    internal class Agency
    {
        private string name;
        private List<RealEstate> realEstates;

        public Agency(string name)
        {
            Name = name;
            realEstates = new List<RealEstate>();
        }

        public string Name
        {
            get { return name; }
            set
            {
                if (value.Length < 6)
                {
                    throw new ArgumentException("Invalid agency name!");
                }
                name = value;
            }
        }

        public void AddRealEstate(RealEstate realEstate)
        {
            realEstates.Add(realEstate);
        }

        public bool SellRealEstate(RealEstate realEstate)
        {
            foreach (RealEstate checkRealEstate in realEstates)
            {
                if (checkRealEstate.Address == realEstate.Address && checkRealEstate.Price == realEstate.Price)
                {
                    realEstates.Remove(checkRealEstate);
                    return true;
                }
            }
            return false;
        }

        public double CalculateTotalPrice()
        {
            return realEstates.Select(e => e.Price).Sum();
        }

        public RealEstate GetRealEstateWithHighestPrice()
        {
            return realEstates.OrderByDescending(e => e.Price).First();
        }

        public RealEstate GetRealEstateWithLowestPrice()
        {
            return realEstates.OrderBy(e => e.Price).First();
        }

        public void RenameAgency(string newName)
        {
            Name = newName;
        }

        public void SellAllRealEstates()
        {
            realEstates.Clear();
        }

        public override string ToString()
        {
            var sb = new StringBuilder();

            if (realEstates.Count() > 0)
            {
                sb.Append($"Agency {name} has {realEstates.Count} real estate/s:\n");
                sb.Append(string.Join("\n", realEstates));
            }
            else
            {
                sb.Append($"Agency {name} has no available real estates.");

            }
            return sb.ToString();
        }
    }
}