using System;

using System.Collections.Generic;

using System.Text.Json;

public class Program

{

    public class ContractBalance

    {

        public string DataAreaID {get; set;}

        public string ContractNumber {get; set;}

        public List<ContractBalanceMonth> MonthQuantities {get; set;}

    }

    public class ContractBalanceMonth

    {

        public int Month {get; set;}

        public int Year {get; set;}

        public decimal ScheduledQty {get; set;}

        public decimal OrderedQty {get; set;}

        public decimal ShippedQty {get; set;}

        public decimal InvoicedQty {get; set;}

        public decimal CreditQty {get; set;}

        public decimal AvailableQty => ScheduledQty - Math.Max(OrderedQty, ShippedQty) + CreditQty;

    }

    public static void Main()

    {

        var opt = new JsonSerializerOptions

        {

            AllowTrailingCommas = true,

            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,

            ReadCommentHandling = JsonCommentHandling.Skip,

            PropertyNameCaseInsensitive = true,

            WriteIndented = true

        };

        var obj = new ContractBalance

        {

            DataAreaID = "us01",

            ContractNumber = "1112223",

            MonthQuantities = new List<ContractBalanceMonth>

            {

                new ContractBalanceMonth

                {

                    Month = 10,

                    Year = 2021,

                    ScheduledQty = 1000.5m,

                    OrderedQty = 500.5m,

                    ShippedQty = 500.5m,

                    InvoicedQty = 500.5m,

                    CreditQty = 10.3m

                },

                new ContractBalanceMonth

                {

                    Month = 11,

                    Year = 2021,

                    ScheduledQty = 1000.5m,

                    OrderedQty = 500.5m,

                    ShippedQty = 520.5m,

                    InvoicedQty = 500.5m

                },

                new ContractBalanceMonth

                {

                    Month = 12,

                    Year = 2021,

                    ScheduledQty = 1000.5m,

                    OrderedQty = 500.5m,

                    ShippedQty = 500.5m,

                    InvoicedQty = 500.5m

                },

            }

        };

        Console.WriteLine(JsonSerializer.Serialize(obj, opt));

    }

}