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Who cares about Domain Rules?

, 20 Nov 2006 MIT
With this article, I am evolving a domain problem towards the best possible solution.
domainrules_src.zip
BusinessRules
0 - Procedural_Way
0 - Procedural_Way.smp
ProceduralWay.cd
Tests
1 - Evolution One
1 - Evolution One.smp
EvolutionOne.cd
Tests
2 - Evolution Two
2 - Evolution Two.smp
EvolutionTwo.cd
Tests
3 - Evolution Three
3 - Evolution Three.smp
EvolutionThree.cd
IncomeTaxEngine.cd
Tests
4 - Evolution Four
4 - Evolution Four.smp
EvolutionFour.cd
Tests
5 - Evolution Five
5 - Evolution Five.smp
EvolutionFive.cd
TaxBandGenerator.cd
Tests
bin
Debug
BusinessRules.dll
BusinessRules.dll.lastcodeanalysissucceeded
NMock2.dll
BusinessRules.csproj.user
obj
Debug
BusinessRules.dll
TempPE
Properties
Tools
NMock2.dll
nunit.framework.dll
using System.Collections.Generic;

namespace BusinessRules.Evolution_Five
{
    /// <summary>
    /// Income Tax Engine domain object that encapsulate the tax related concepts.
    /// </summary>
    public class IncomeTaxEngine : IIncomeTaxEngine
    {
        #region Constants

        private const double ZeroValue = 0.0;

        #endregion

        #region Fields

        private List<TaxBand> taxBands;
        private ITaxBandGenerator generator;

        #endregion

        #region C'tors

        /// <summary>
        /// Initializes a new instance of the <see cref="IncomeTaxEngine"/> class.
        /// </summary>
        public IncomeTaxEngine()
        {
            // Use the tax band generator to construct 
            // the tax band collection.
            generator = TaxBandGenerator.CreateInstance();
            taxBands = generator.CreateTaxBands();
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="IncomeTaxEngine"/> class.
        /// </summary>
        /// <param name="cultureInfo">An instance of the current culture info.</param>
        public IncomeTaxEngine(ICurrentCultureInfo cultureInfo)
        {
            // Use the tax band generator to construct 
            // the tax band collection.
            generator = TaxBandGenerator.CreateInstance(cultureInfo);
            taxBands = generator.CreateTaxBands();
        }

        #endregion

        #region Methods

        /// <summary>
        /// Calculates the tax liability for an investor.
        /// </summary>
        /// <param name="income">The investor's income.</param>
        /// <returns>
        /// Returns a double representing the tax rate for the investor.
        /// </returns>
        public double CalculateTaxLiability(double income)
        {
            double taxLiability = ZeroValue;

            taxBands.ForEach(delegate(TaxBand taxBand)
             {
                taxLiability += taxBand.CalculateTaxPortion(income);
             });

            return taxLiability;
        }

        /// <summary>
        /// Calculates the tax rate for an investor.
        /// </summary>
        /// <param name="income">The investor's income.</param>
        /// <returns>
        /// Returns a double representing the tax liability for the investor.
        /// </returns>
        public double CalculateTaxRate(double income)
        {
            TaxBand selectedBand = taxBands.Find(delegate(TaxBand taxBand)
             {
                 bool incomeWithinBands = (income >= taxBand.LowerLimitAmount && 
                                           income <= taxBand.UpperLimitAmount);
                 return incomeWithinBands;
             });

            return selectedBand.TaxRate;
        }

        #endregion
    }
}

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This article, along with any associated source code and files, is licensed under The MIT License

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About the Author

Maruis Marais
Web Developer
New Zealand New Zealand
No Biography provided

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