Teso_API/Teso API/Models/CouponRateCalculator.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Teso_API.Models
{
    public class CouponRateCalculator
    {
       public static int GetRate(double discount)
        {
            if (discount < 100)
            {
                string discounted = $"{discount:F1}";
                string first = discounted.Substring(0, discounted.IndexOf("."));
                string last = discounted.Substring(discounted.IndexOf(".") + 1);

                int firstNumber = int.Parse(first);
                int lastNumber = int.Parse(last);
                if (discount < 0.51)
                {
                    return 0;
                }
                else if (discount < 2)
                {
                    return 1;
                }
                else if (firstNumber < lastNumber)
                {
                    return lastNumber;
                }
                else if (firstNumber > lastNumber)
                {
                    return firstNumber;
                }
                else
                {
                    return firstNumber;
                }
            }
            else if (discount < 1000)
            {
                double result = discount % 100;
                if (result == 0)
                {
                    return 100;
                }
                else
                {
                    return (int)Math.Ceiling(result);
                }
            }
            else
            {
                return 100;
            }
        }
    }

}