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

namespace TaxLibrarySample001
{
    public class TaxHelper
    {
        public static decimal GetTaxResult(decimal income)
        {
            decimal result = 0;

            foreach (var Item in GetTaxTable().OrderBy(r => r.Tax))
            {
                if (Item.ParentTax == null)
                {
                    if (income > 0 && income <= Item.To)
                        result += (income - Item.from) * Item.Tax;
                    else
                        result += (Item.To - Item.from) * Item.Tax;
                    continue;
                }

                if (income > Item.ParentTax.To && income <= Item.To)
                    result += (income - Item.ParentTax.To) * Item.Tax;

                if (income > Item.To)
                    result += (Item.To - Item.ParentTax.To) * Item.Tax;
            }

            return result;
        }

        internal static IEnumerable<TaxTable> GetTaxTable(Func<TaxTable, bool> filter = null)
        {
            List<TaxTable> taxes = new List<TaxTable>();

            taxes.Add(new TaxTable { from = 0, To = 540000, Tax = 0.05m, ParentTax = null });
            taxes.Add(new TaxTable { from = 540001, To = 1210000, Tax = 0.12m, ParentTax = new TaxTable { from = 0, To = 540000, Tax = 0.05m } });
            taxes.Add(new TaxTable { from = 1210001, To = 2420000, Tax = 0.2m, ParentTax = new TaxTable { from = 540001, To = 1210000, Tax = 0.12m } });
            taxes.Add(new TaxTable { from = 2420001, To = 4530000, Tax = 0.3m, ParentTax = new TaxTable { from = 1210001, To = 2420000, Tax = 0.2m } });
            taxes.Add(new TaxTable { from = 4530001, To = 10310000, Tax = 0.4m, ParentTax = new TaxTable { from = 2420001, To = 4530000, Tax = 0.3m } });
            taxes.Add(new TaxTable { from = 10310001, To = 999999999999999, Tax = 0.5m, ParentTax = new TaxTable { from = 4530001, To = 10310000, Tax = 0.4m } });
            if (filter == null)
                return taxes;
            return taxes.Where(filter);
        }
    }

    internal class TaxTable
    {
        public decimal from { get; set; }
        public decimal To { get; set; }
        public decimal Tax { get; set; }
        public TaxTable ParentTax { get; set; }
    }
}