NumbersToText

// -----------------------------------------------------------------------
// <copyright file="NumbersToText.cs" company="Morten T. Pedersen">
// Copyright © Morten T. Pedersen ® All rights reserved
// </copyright>
// -----------------------------------------------------------------------

namespace Morten.Helpers
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;

    internal static class NumbersToText
    {
        #region Private Fields
        private static string[] onesMapping = new string[] { "Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen" };
        private static string[] tensMapping = new string[] { "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety" };
        private static string[] groupMapping = new string[] { "Hundred", "Thousand", "Million", "Billion", "Trillion" };
        #endregion

        #region Methods
        internal static string[] EnglishArrayFromNumber(string number)
        {
            return EnglishArrayFromNumber(Convert.ToInt64(number));
        }

        internal static string[] EnglishArrayFromNumber(double number)
        {
            string[] array = EnglishFromNumber(number).Split(' ');
            return array;
        }

        internal static string[] EnglishArrayFromNumber(int number)
        {
            return EnglishArrayFromNumber((long)number);
        }

        internal static string[] EnglishArrayFromNumber(long number)
        {
            string[] array = EnglishFromNumber(number).Split(' ');
            return array;
        }

        internal static string EnglishFromNumber(string number)
        {
            return EnglishFromNumber(Convert.ToInt64(number));
        }

        internal static string EnglishFromNumber(int number)
        {
            return EnglishFromNumber((long)number);
        }

        internal static string EnglishFromNumber(double number)
        {
            string numberString = number.ToString();
            string[] numberChunks = numberString.Split('.');
            if (numberChunks.Length < 2)
            {
                return EnglishFromNumber(Convert.ToInt64(number));
            }

            string realNumber = EnglishFromNumber(numberChunks[0]);
            List<string> pointDigits = new List<string>();
            for (int i = 0; i < numberChunks[1].Length; ++i)
            {
                string digit = numberChunks[1].Substring(i, 1);
                pointDigits.Add(NumbersToText.onesMapping[Convert.ToInt16(digit)]);
            }

            string finalNumber = realNumber + " Point";
            foreach (string pointDigit in pointDigits)
            {
                finalNumber += " " + pointDigit;
            }

            return finalNumber;
        }

        internal static string EnglishFromNumber(long number)
        {
            if (number == 0)
            {
                return NumbersToText.onesMapping[number];
            }

            string sign = "Positive";
            if (number < 0)
            {
                sign = "Negative";
                number = System.Math.Abs(number);
            }

            string retVal = null;
            int group = 0;
            while (number > 0)
            {
                int numberToProcess = (int)(number % 1000);
                number = number / 1000;

                string groupDescription = ProcessGroup(numberToProcess);
                if (groupDescription != null)
                {
                    if (group > 0)
                    {
                        retVal = NumbersToText.groupMapping[group] + " " + retVal;
                    }

                    retVal = groupDescription + " " + retVal;
                }

                ++group;
            }

            return sign + " " + retVal.Trim();
        }

        private static string ProcessGroup(int number)
        {
            int tens = number % 100;
            int hundreds = number / 100;

            string retVal = null;

            if (hundreds > 0)
            {
                retVal = NumbersToText.onesMapping[hundreds] + " " + NumbersToText.groupMapping[0];
            }

            if (tens > 0)
            {
                if (tens < 20)
                {
                    retVal += ((retVal != null) ? " " : string.Empty) + NumbersToText.onesMapping[tens];
                }
                else
                {
                    int ones = tens % 10;
                    tens = (tens / 10) - 2; // 20's offset

                    retVal += ((retVal != null) ? " " : string.Empty) + NumbersToText.tensMapping[tens];

                    if (ones > 0)
                    {
                        retVal += ((retVal != null) ? " " : string.Empty) + NumbersToText.onesMapping[ones];
                    }
                }
            }

            return retVal;
        }
        #endregion
    }
}