#nullable enable

​

using System;

using Humanizer;

​

public class Program

{

    /// <summary>

    /// Unit Test Tag!

    ///

    /// Output a currency amount in english words.

    /// 

    /// Press "Run" above, then check the output in the pane below to see if all the tests pass and

    /// the program is correct. 

    /// </summary>

    public static void Main()

    {

        // Unit tests. Add new tests to this list to check for new cases not covered by existing code.

        Test(2, Currency.NZD, "Two dollars.");

        Test(5, Currency.NZD, "Five dollars.");

        Test(5.20m, Currency.NZD, "Five dollars and twenty cents.");

        Test(10.01m, Currency.NZD, "Ten dollars and one cent.");

        Test(8m, Currency.GBP, "Eight pounds.");

        Test(100, Currency.NZD, "One hundred dollars.");

        Test(10.5m, Currency.GBP, "Ten pounds and fifty pence.");

        Test(1, Currency.NZD, "One dollar.");

        Test(57m, Currency.JPY, "Fifty-seven yen.");

        Test(57.6m, Currency.JPY, "Fifty-seven yen.");

        Test(0.10m, Currency.NZD, "Ten cents.");

        Test(0, Currency.NZD, "Zero dollars.");

        Test(0.9999999999m, Currency.NZD, "One dollar.");

        Test(-10.99m, Currency.NZD, "Minus ten dollars and ninety-nine cents.");

        Test(-0.95m, Currency.NZD, "Minus ninety-five cents.");

        Test(0.10m, Currency.NZD, "Ten cents.");

        Test(-0.01m, Currency.NZD, "Minus one cent.");

        Test(0.01m, Currency.NZD, "One cent.");

        Test(10500500001.55m, Currency.NZD, "One billion five hundred million five hundred thousand and one dollars and fifty-five cents.");

        Results();

    }

​

    /// <summary>

    /// Implementation. Make code changes here to make the tests pass.

    /// </summary>

    static string CurrencyInWords(decimal amount, Currency currency)

    {

        amount = Math.Round(amount, 2);

        var wholeAmount = (int)amount;

        var fractionAmount = (int)((amount - (int)amount) * 100m);

        var words = (wholeAmount, fractionAmount) switch {

            (_, 0) => WholeAmountWords(wholeAmount, currency),

            (0, _) => FractionalAmountWords(fractionAmount, currency),

            _ when !currency.SupportsFractionalAmounts() => WholeAmountWords(wholeAmount, currency),

            _ => $"{WholeAmountWords(wholeAmount, currency)} and {FractionalAmountWords(Math.Abs(fractionAmount), currency)}",

        };

​

        return $"{words.Transform(To.SentenceCase)}.";

    }

​

    static string WholeAmountWords(int wholeAmount, Currency currency)

    {

        var currencyWord = wholeAmount != 1 ? currency.PluralisedWord() : currency.Word;

        return $"{wholeAmount.ToWords()} {currencyWord}";

    }

​

    static string FractionalAmountWords(int fractionAmount, Currency currency)

    {

        if (!currency.SupportsFractionalAmounts())

            return string.Empty;

​

        if (fractionAmount == 0)

            return string.Empty;

        var currencyWord = Math.Abs(fractionAmount) > 1 && currency != Currency.GBP ?

            currency.SmallerWord.ToString().Pluralize() :

            currency.SmallerWord.ToString();

        return $"{fractionAmount.ToWords()} {currencyWord}";

    }

​

    class Currency

    {

        public static readonly Currency NZD = new Currency("NZD", "dollar", "cent");

        public static readonly Currency GBP = new Currency("GBP", "pound", "pence");

        public static readonly Currency JPY = new Currency("JPY", "yen", "");

        public string Symbol { get; }

        public string Word { get; }     

        public string SmallerWord { get; }

        public bool SupportsFractionalAmounts() {

            return SmallerWord != "";

        }

        public string PluralisedWord() {

            return Symbol == "JPY" ? Word : Word.Pluralize();

        }

        Currency(string symbol, string word, string smallerWord)

        {

            Symbol = symbol;

            Word = word;

            SmallerWord = smallerWord;

        }

    }

    /*

     * What follows is a very short testing framework. You can ignore everything below here

     * if you want to, or add to it if you want better output from the tests above.

     */

    static int pass, fail;

​

    static void Test(decimal amount, Currency currency, string expected)

    {

        Console.WriteLine($"Test: {amount}, {currency.Symbol}, {expected}");

        string actual;

        try {

            actual = CurrencyInWords(amount, currency);

            if (actual == expected)

            {

                pass++;

                Console.WriteLine("PASS.\n");

                return;

            }

        } catch(Exception e) {

            actual = "Exception: " + e.Message;

        }

        fail++;

        Console.WriteLine("FAIL:");

        Console.WriteLine("    Expected: " + expected);

        Console.WriteLine("    Actual  : " + actual);

        Console.WriteLine();

    }

    static void Results()

    {

        Console.WriteLine($"{pass} / {pass + fail} tests passed.\n");

        Console.WriteLine(fail == 0 ? "SUCCESS!" : "FAILURE!");

    }

}

​