techtest.cs

#define CONTRACTS_FULL

using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using NUnit.Framework;

namespace EnergyQuoteService
{
    class Program
    {
        static void Main(string[] args)
        {
            var quoteService = new QuoteService(new BasicRateCalculator());

            PopulateDemoTariff(quoteService);

            var quoteRequest = GetDemoQuoteRequest();

            var cheapestQuote = quoteService.GetCheapestQuote(quoteRequest);

            Console.WriteLine("Date: {0} Gas usage: {1} Electricity usage: {2} Cheapest tariff: {3} Annual cost: {4}",
                cheapestQuote.QuoteCreationDate, cheapestQuote.GasUsage, cheapestQuote.ElectricityUsage, cheapestQuote.TariffName, 
                cheapestQuote.AnnualCost.ToString("F"));

            Console.Read();
        }

        public static QuoteRequest GetDemoQuoteRequest()
        {
            var quoteRequest = new QuoteRequest
            {
                AnnualElectricityUsage = 4000,
                AnnualGasUsage = 2000,
                Email = "[email protected]",
                ValidFrom = DateTime.Today
            };

            return quoteRequest;
        }

        public static void PopulateDemoTariff(QuoteService quoteService)
        {
            var energySaver = new Tariff()
            {
                Name = "Energy Saver",
                GasInitialRate = 0.25M,
                GasFinalRate = 0.50M,
                ElectricityInitialRate = 0.30M,
                ElectricityFinalRate = 0.60M,
                InitialExpiryDate = new DateTime(2016, 06, 01)
            };

            var discountEnergy = new Tariff()
            {
                Name = "Discount Energy",
                GasInitialRate = 0.20M,
                GasFinalRate = 0.75M,
                ElectricityInitialRate = 0.20M,
                ElectricityFinalRate = 0.90M,
                InitialExpiryDate = new DateTime(2016, 09, 15)
            };

            var standard = new Tariff()
            {
                Name = "Standard",
                GasInitialRate = 0.65M,
                ElectricityInitialRate = 0.80M,
            };

            var saveOnline = new Tariff()
            {
                Name = "Save Online",
                GasInitialRate = 0.25M,
                GasFinalRate = 0.60M,
                ElectricityInitialRate = 0.10M,
                ElectricityFinalRate = 1M,
                InitialExpiryDate = new DateTime(2016, 08, 23)
            };

            quoteService.AddTariff(energySaver);
            quoteService.AddTariff(discountEnergy);
            quoteService.AddTariff(standard);
            quoteService.AddTariff(saveOnline);
        }
    }

    /// <summary>
    /// The QuoteService class is responsible for providing the Cheapest Quote
    /// </summary>
    public class QuoteService
    {
        private readonly IRateCalculator _rateCalculator;
        public List<Tariff> TariffList { get; }

        private QuoteService() { /* this is a little neat trick to block incorrect instantiation :) */ }

        /// <summary>
        /// The default constructor for the QuoteService class
        /// </summary>
        /// <param name="rateCalculator"></param>
        public QuoteService(IRateCalculator rateCalculator)
        {
            _rateCalculator = rateCalculator;
            TariffList = new List<Tariff>();
        }

        /// <summary>
        /// Adds a tariff to the list of known tariffs
        /// </summary>
        /// <param name="newTariff"></param>
        public void AddTariff(Tariff newTariff)
        {
            TariffList.Add(newTariff);
        }

        /// <summary>
        /// Clears the list of registered tariffs
        /// </summary>
        public void ClearTariffList()
        {
            TariffList.Clear();
        }

        /// <summary>
        /// Gets the final cost for a quote based on a tariff
        /// </summary>
        /// <param name="quoteRequest"></param>
        /// <param name="tariff"></param>
        /// <returns></returns>
        public decimal GetFinalCost(QuoteRequest quoteRequest, Tariff tariff)
        {
            var timeOnInitialRate = _rateCalculator.GetTimeOnInitialRate(quoteRequest.ValidFrom, tariff.InitialExpiryDate);
            var initialElectricityRateUnitCost = _rateCalculator.GetRateUnitCost(timeOnInitialRate, quoteRequest.AnnualElectricityUsage, tariff.ElectricityInitialRate);
            var initialGasRateUnitCost = _rateCalculator.GetRateUnitCost(timeOnInitialRate, quoteRequest.AnnualGasUsage, tariff.GasInitialRate);
            var timeOnFinalUnitRate = _rateCalculator.GetTimeOnFinalRate(timeOnInitialRate);
            var finalGasUnitRateCost = _rateCalculator.GetRateUnitCost(timeOnFinalUnitRate, quoteRequest.AnnualGasUsage, tariff.GasFinalRate);
            var finalElectricityRateCost = _rateCalculator.GetRateUnitCost(timeOnFinalUnitRate,quoteRequest.AnnualElectricityUsage, tariff.ElectricityFinalRate);
            var finalCost = initialElectricityRateUnitCost + initialGasRateUnitCost + finalElectricityRateCost + finalGasUnitRateCost;

            return finalCost;
        }

        /// <summary>
        /// Returns the cheapest quote for the desired quote request
        /// </summary>
        /// <param name="quoteRequest"></param>
        /// <returns></returns>
        public CheapestQuote GetCheapestQuote(QuoteRequest quoteRequest)
        {
            #region Contract-Pre-Condition

            if (TariffList.Count == 0)
            {
                throw new ArgumentException("Cannot get cheapest tariff because there are no registered tariffs.");
            }

            #endregion

            var cheapestQuote = new CheapestQuote();

            foreach (var tariff in TariffList)
            {
                var finalCost = GetFinalCost(quoteRequest, tariff);

                if(IsQuoteCheaper(cheapestQuote, finalCost))
                {
                    cheapestQuote.AnnualCost = finalCost;
                    cheapestQuote.TariffName = tariff.Name;
                    cheapestQuote.ElectricityUsage = quoteRequest.AnnualElectricityUsage;
                    cheapestQuote.GasUsage = quoteRequest.AnnualGasUsage;
                    cheapestQuote.CustomerEmail = quoteRequest.Email;
                }
            }

            return cheapestQuote;
        }

        /// <summary>
        /// Returns true if a quote is cheaper
        /// </summary>
        /// <param name="cheapestQuote"></param>
        /// <param name="finalCost"></param>
        /// <returns></returns>
        public bool IsQuoteCheaper(CheapestQuote cheapestQuote, decimal finalCost)
        {
            if (decimal.Compare(cheapestQuote.AnnualCost, finalCost) > 0)
            {
                return true;
            }

            if (cheapestQuote.TariffName == null)
            {
                return true;
            }

            return false;
        }
    }

    /// <summary>
    /// The interface IRateCalculator defines the contract for a Rate Calculator
    /// </summary>
    public interface IRateCalculator
    {
        decimal GetTimeOnInitialRate(DateTime startDate, DateTime endDate);
        decimal GetTimeOnFinalRate(decimal daysInInitialRate);
        decimal GetRateUnitCost(decimal days, decimal consumption, decimal rate);
    }

    /// <summary>
    /// The BasicRateCalculator class is a concrete implementation containing the strategy 
    /// described in the technical exercise for calculating the quote.
    /// </summary>
    public sealed class BasicRateCalculator : IRateCalculator
    {
        /// <summary>
        /// Gets the ammount of running days between the start and end date
        /// </summary>
        /// <param name="startDate"></param>
        /// <param name="endDate"></param>
        public decimal GetTimeOnInitialRate(DateTime startDate, DateTime endDate)
        {
            #region Contract-Post-Condition

            Contract.Ensures(Contract.Result<decimal>() >= 0M);

            #endregion

            decimal timeOnInitialRate = 365;

            if (endDate != DateTime.MinValue)
            {
                var timeSpan = endDate - startDate;
                timeOnInitialRate = Convert.ToDecimal(timeSpan.TotalDays);
            }

            return timeOnInitialRate;
        }

        /// <summary>
        /// Gets the ammount of running days until the end of the year
        /// </summary>
        /// <param name="daysInInitialRate"></param>
        /// <returns></returns>
        public decimal GetTimeOnFinalRate(decimal daysInInitialRate)
        {
            return 365M - daysInInitialRate;
        }

        /// <summary>
        /// Gets the cost of the initial rate the client will pay
        /// </summary>
        /// <param name="days"></param>
        /// <param name="consumption"></param>
        /// <param name="rate"></param>
        /// <returns></returns>
        public decimal GetRateUnitCost(decimal days, decimal consumption, decimal rate)
        {
            return days / 365M * consumption * rate;
        }
    }

    /// <summary>
    /// The QuoteRequest class represents a request of a quote to the system
    /// </summary>
    public class QuoteRequest
    {
        #region Backing-Fields

        private decimal _annualGasUsage;
        private decimal _annualElectricityUsage;
        private string _email;

        #endregion

        /// <summary>
        /// The initial date this quote is valid from
        /// </summary>
        public DateTime ValidFrom { get; set; }

        /// <summary>
        /// The email address of the customer
        /// </summary>
        public string Email
        {
            get { return _email; }
            set
            {
                #region Contract-Invariant

                if (string.IsNullOrEmpty(value))
                {
                    throw new ArgumentException("The email address cannot be null or empty.", nameof(Email));
                }

                #endregion

                _email = value;
            }
        }

        /// <summary>
        /// The annual gas usage of the customer 
        /// </summary>
        public decimal AnnualGasUsage
        {
            get { return _annualGasUsage; }
            set
            {
                #region Contract-Invariant

                if (value < decimal.Zero)
                {
                    throw new ArgumentOutOfRangeException(nameof(AnnualGasUsage), "The customer annual gas usage cannot be a negative value.");
                }

                #endregion

                _annualGasUsage = value;
            }
        }

        /// <summary>
        /// The annual electricity usage of the customer
        /// </summary>
        public decimal AnnualElectricityUsage
        {
            get { return _annualElectricityUsage; }
            set
            {
                #region Contract-Invariant

                if (value < decimal.Zero)
                {
                    throw new ArgumentOutOfRangeException(nameof(AnnualElectricityUsage), "The customer electricity usage cannot be a negative value.");
                }

                #endregion

                _annualElectricityUsage = value;
            }
        }
    }

    /// <summary>
    /// The Tariff class represents
    /// </summary>
    public class Tariff
    {
        /// <summary>
        /// The name of the Tariff (i.e EnergySaver, Standard)
        /// </summary>
        public string Name { get; set; }

        #region Backing-Fields

        private decimal _gasInitialRate;
        private decimal _gasFinalRate;
        private decimal _electricityInitialRate;
        private decimal _electricityFinalRate;

        #endregion

        /// <summary>
        /// The initial gas rate of the tariff
        /// </summary>
        public decimal GasInitialRate
        {
            get { return _gasInitialRate; }
            set
            {
                #region Contract-Invariant

                if (value <= decimal.Zero)
                {
                    throw new ArgumentOutOfRangeException(nameof(GasInitialRate), "The initial gas rate must be positive and higher than zero.");
                }

                #endregion

                _gasInitialRate = value;
            }
        }

        /// <summary>
        /// The final gas rate of the tariff
        /// </summary>
        public decimal GasFinalRate
        {
            get { return _gasFinalRate; }
            set
            {
                #region Contract-Invariant

                if (value <= decimal.Zero)
                {
                    throw new ArgumentOutOfRangeException(nameof(GasFinalRate), "The final gas rate must be positive and higher than zero.");
                }

                #endregion

                _gasFinalRate = value;
            }
        }

        /// <summary>
        /// The initial electricity rate of the tariff
        /// </summary>
        public decimal ElectricityInitialRate
        {
            get { return _electricityInitialRate; }
            set
            {
                #region Contract-Invariant

                if (value <= decimal.Zero)
                {
                    throw new ArgumentOutOfRangeException(nameof(ElectricityInitialRate), "The electricity initial gas rate must be positive and higher than zero.");
                }

                #endregion

                _electricityInitialRate = value;
            }
        }

        /// <summary>
        /// The final electricity rate of the tariff
        /// </summary>
        public decimal ElectricityFinalRate
        {
            get { return _electricityFinalRate; }
            set
            {
                #region Contract-Invariant

                if (value <= decimal.Zero)
                {
                    throw new ArgumentOutOfRangeException(nameof(ElectricityFinalRate), "The electricity final gas rate must be positive and higher than zero.");
                }

                #endregion

                _electricityFinalRate = value;
            }
        }

        /// <summary>
        /// The date when this tariff will initially expire
        /// </summary>
        public DateTime InitialExpiryDate { get; set; }
    }

    /// <summary>
    /// The CheapestQuote class is a simple Value Object for returning the cheapest tariff
    /// </summary>
    public class CheapestQuote
    {
        public CheapestQuote()
        {
            QuoteCreationDate = DateTime.Now;
        }

        /// <summary>
        /// The name of the Cheapest Tariff
        /// </summary>
        public string TariffName { get; set; }

        /// <summary>
        /// The email address of the Customer
        /// </summary>
        public string CustomerEmail { get; set; }

        /// <summary>
        /// The annual cost of the tariff
        /// </summary>
        public decimal AnnualCost { get; set; }

        /// <summary>
        /// The electricity usage of the client
        /// </summary>
        public decimal ElectricityUsage { get; set; }

        /// <summary>
        /// The gas usage of the client
        /// </summary>
        public decimal GasUsage { get; set; }

        /// <summary>
        /// The date when the quote was generated
        /// </summary>
        public DateTime QuoteCreationDate { get; }
    }

    [TestFixture]
    public class TestQuoteService
    {
        private QuoteService _quoteService;
        private QuoteRequest _testQuoteRequest;
        private Tariff _testTariff;

        [OneTimeSetUp]
        public void SetUp()
        {
            _quoteService = new QuoteService(new BasicRateCalculator());

            _testQuoteRequest = new QuoteRequest()
            {
                Email = "[email protected]",
                AnnualGasUsage = 1500M,
                AnnualElectricityUsage = 3000M,
                ValidFrom = new DateTime(2012, 12, 01)
            };

            _testTariff = new Tariff()
            {
                Name = "Example Saver",
                GasInitialRate = 0.25M,
                GasFinalRate = 0.50M,
                ElectricityInitialRate = 0.30M,
                ElectricityFinalRate = 0.60M,
                InitialExpiryDate = new DateTime(2013, 06, 01)
            };
        }

        [Test]
        public void TestGetFinalCost()
        {
            var finalCost = _quoteService.GetFinalCost(_testQuoteRequest, _testTariff);
            Assert.AreEqual("1914.25", finalCost.ToString("F"));
        }

        [Test]
        public void TestExceptionEmptyTariffList()
        {
            _quoteService.ClearTariffList();
            Assert.Throws<ArgumentException>(() => _quoteService.GetCheapestQuote(_testQuoteRequest));
        }

        [Test]
        public void TestGetCheapestRate()
        {
            var quoteRequest = new QuoteRequest()
            {
                Email = "[email protected]",
                AnnualGasUsage = 1500M,
                AnnualElectricityUsage = 3000M,
                ValidFrom = new DateTime(2014, 01, 01)
            };

            var energySaver = new Tariff()
            {
                Name = "Energy Saver",
                GasInitialRate = 0.25M,
                GasFinalRate = 0.50M,
                ElectricityInitialRate = 0.30M,
                ElectricityFinalRate = 0.60M,
                InitialExpiryDate = new DateTime(2014, 06, 01)
            };

            var discountEnergy = new Tariff()
            {
                Name = "Discount Energy",
                GasInitialRate = 0.20M,
                GasFinalRate = 0.75M,
                ElectricityInitialRate = 0.20M,
                ElectricityFinalRate = 0.90M,
                InitialExpiryDate = new DateTime(2014, 09, 15)
            };

            var standard = new Tariff()
            {
                Name = "Standard",
                GasInitialRate = 0.65M,
                ElectricityInitialRate = 0.80M,
            };

            var saveOnline = new Tariff()
            {
                Name = "Save Online",
                GasInitialRate = 0.25M,
                GasFinalRate = 0.60M,
                ElectricityInitialRate = 0.10M,
                ElectricityFinalRate = 1M,
                InitialExpiryDate = new DateTime(2014, 08, 23)
            };

            _quoteService.AddTariff(energySaver);
            _quoteService.AddTariff(discountEnergy);
            _quoteService.AddTariff(standard);
            _quoteService.AddTariff(saveOnline);

            var cheapestQuote = _quoteService.GetCheapestQuote(quoteRequest);

            Assert.AreEqual(cheapestQuote.TariffName, "Discount Energy");
        }

        [Test]
        public void TestIsQuoteCheaperTrue()
        {
            var cheapestQuote = new CheapestQuote();
            cheapestQuote.TariffName = "Test";
            cheapestQuote.AnnualCost = 200M;
            Assert.IsTrue(_quoteService.IsQuoteCheaper(cheapestQuote, 100M));
        }

        [Test]
        public void TestIsQuoteCheaperFalse()
        {
            var cheapestQuote = new CheapestQuote();
            cheapestQuote.TariffName = "Test";
            cheapestQuote.AnnualCost = 200M;
            Assert.IsFalse(_quoteService.IsQuoteCheaper(cheapestQuote, 300M));
        }

        [Test]
        public void TestIsQuoteCheaperThenBlankQuote()
        {
            var cheapestQuote = new CheapestQuote();
            Assert.IsTrue(_quoteService.IsQuoteCheaper(cheapestQuote, 100M));
        }
    }

    [TestFixture]
    public class TestQuoteRequest
    {
        private QuoteRequest _quoteRequest;

        [OneTimeSetUp]
        public void SetUp()
        {
            _quoteRequest = new QuoteRequest();
        }

        [Test]
        public void TestExceptionInvalidEmail()
        {
            Assert.Throws<ArgumentException>(() => _quoteRequest.Email = "");
        }

        [Test]
        public void TestExceptionAnnualGasUsageOutOfRange()
        {
            Assert.Throws<ArgumentOutOfRangeException>(() => _quoteRequest.AnnualGasUsage = -1M);
        }

        [Test]
        public void TestExceptionAnnualElectricityUsageOutOfRange()
        {
            Assert.Throws<ArgumentOutOfRangeException>(() => _quoteRequest.AnnualElectricityUsage = -1M);
        }

        [Test]
        public void TestEmail()
        {
            _quoteRequest.Email = "[email protected]";
            Assert.AreEqual("[email protected]", _quoteRequest.Email);
        }
    }

    [TestFixture]
    public class TestBasicRateCalculator
    {
        private BasicRateCalculator _basicRateCalculator;

        [OneTimeSetUp]
        public void SetUp()
        {
            _basicRateCalculator = new BasicRateCalculator();
        }

        [Test]
        public void TestGetTimeOnInitialRate()
        {
            var startDate = new DateTime(2016, 01, 01);
            var endDate = new DateTime(2016, 09, 05);
            Assert.AreEqual(248M, _basicRateCalculator.GetTimeOnInitialRate(startDate, endDate));
        }

        [Test]
        public void TestGetTimeOnFinalRate()
        {
            Assert.AreEqual(183M, _basicRateCalculator.GetTimeOnFinalRate(182));
        }

        [Test]
        public void TestGetRateUnitCost()
        {
            var rate = _basicRateCalculator.GetRateUnitCost(182M, 1500M, 0.25M);
            var rateFormatted = rate.ToString("F");
            Assert.AreEqual("186.99", rateFormatted);
        }
    }

    [TestFixture]
    public class TestTariff
    {
        private Tariff _tariff;

        [OneTimeSetUp]
        public void SetUp()
        {
            _tariff = new Tariff();
        }

        [Test]
        public void TestExceptionSetGasInitialRateOutOfRange()
        {
            Assert.Throws<ArgumentOutOfRangeException>(() => _tariff.GasInitialRate = 0);
        }

        [Test]
        public void TestExceptionSetGasFinalRateOutOfRange()
        {
            Assert.Throws<ArgumentOutOfRangeException>(() => _tariff.GasFinalRate = 0);
        }

        [Test]
        public void TestExceptionSetElectricityInitialRateOutOfRange()
        {
            Assert.Throws<ArgumentOutOfRangeException>(() => _tariff.ElectricityInitialRate = 0);
        }

        [Test]
        public void TestExceptionSetElectricityFinalRateOutOfRange()
        {
            Assert.Throws<ArgumentOutOfRangeException>(() => _tariff.ElectricityFinalRate = 0);
        }

        [Test]
        public void TestGetGasInitialRate()
        {
            Assert.AreEqual(_tariff.GasInitialRate, default(decimal));
        }

        [Test]
        public void TestGetGasFinalRate()
        {
            Assert.AreEqual(_tariff.GasFinalRate, default(decimal));
        }

        [Test]
        public void TestGetElectricityInitialRate()
        {
            _tariff.ElectricityInitialRate = 1;
            Assert.AreEqual(_tariff.ElectricityInitialRate, 1);
        }

        [Test]
        public void TestGetElectricityFinalRate()
        {
            Assert.AreEqual(_tariff.ElectricityFinalRate, default(decimal));
        }

        [Test]
        public void TestGetSetName()
        {
            _tariff.Name = "TestTariff";
            Assert.AreEqual(_tariff.Name, "TestTariff");
        }
    }
}