//The NumberSpelling class provides static methods to spell integers
//
// SINGLE DIGIT NATURAL INTEGERS
// @param digit: any single-digit integer 0 .. 9
//    String onesWord(int digit) : Zero, One, Two. .. Nine
//    String teenWord(int digit) : Ten, Eleven, Twelve, .. Nineteen
//    String tensWord(int digit) : Zero, Ten, Twenty, Ninety
//
// 2-DIGIT or 3-DIGIT NATURAL INTEGERS
// @param number: any natural number of no more than 2/3 digits
//    String twoDigitSpelling(int number)  : Zero .. Ninety Nine
//    String threeDigitSpelling(int number): Zero .. Nine Hundred Ninety Nine
//
// Any valid Java int
// @param number: any positive or negative Java int
//    String spelling(int number)
//
public class NumberSpelling
{
   //Returns the spelling of a ones word: Zero, One, Two, .. Ten
   // @param digit : a single digit integer 0 .. 9
   public static String onesWord(int digit)
   {
      switch ( digit )
      {
         case 0 : return "Zero";
         case 1 : return "One";
         case 2 : return "Two";
         case 3 : return "Three";
         case 4 : return "Four";
         case 5 : return "Five";
         case 6 : return "Six";
         case 7 : return "Seven";
         case 8 : return "Eight";
         case 9 : return "Nine";
         default: throw new RuntimeException("Invalid digit " + digit);
      }
   }
       
   //Returns the spelling of a teen word: Ten, Eleven, .. Nineteen
   // @param digit : a single digit integer 0 .. 9
   public static String teenWord(int digit)
   {
      switch ( digit )
      {
         case 0 : return "Ten";
         case 1 : return "Eleven";
         case 2 : return "Twelve";
         case 3 : return "Thirteen";
         case 4 : return "Fourteen";
         case 5 : return "Fifteen";
         case 6 : return "Sixteen";
         case 7 : return "Seventeen";
         case 8 : return "Eighteen";
         case 9 : return "Nineteen";
         default: throw new RuntimeException("Invalid digit " + digit);
      }
   }
   
   //Returns the spelling of a tens word: Zero, Ten, Twenty, .. Ninety
   // @param digit : a single digit integer 0 .. 9
   public static String tensWord(int digit)
   {
      switch ( digit )
      {
         case 0 : return "Zero";
         case 1 : return "Ten";
         case 2 : return "Twenty";
         case 3 : return "Thirty";
         case 4 : return "Forty";
         case 5 : return "Fifty";
         case 6 : return "Sixty";
         case 7 : return "Seventy";
         case 8 : return "Eighty";
         case 9 : return "Ninety";
         default: throw new RuntimeException("Invalid digit " + digit);
      }
   } 
   
   //Return the spelling of any 2-digit natural number
   // @param number: an integer in the range 0 .. 99
   public static String twoDigitSpelling(int number)
   {
      if (number < 0 || number > 99)
         throw new RuntimeException(number + " is NOT a 2-Digit Natural Number");
         
      if (number == 0)
         return "Zero";
         
      int tens = number / 10;
      int ones = number % 10;
      
      if (tens == 1)
         return teenWord(ones);
         
      String spelling = "";
      if (tens > 1)
         spelling = spelling + tensWord(tens) + " ";
      if (ones > 0)
         spelling = spelling + onesWord(ones);
         
      return spelling.trim();
   }
   
   //Returns the spelling of any 3-digit natural number
   // @param number: an integer in the range 0 .. 999
   public static String threeDigitSpelling(int number)
   {
      if (number < 0 || number > 999)
         throw new RuntimeException(number + " is NOT a 3-Digit Natural Number");
         
      if (number == 0)
         return "Zero";
      
      String spelling = "";
            
      //Begin with the words of the 100's digit, if any
      int hundreds = number / 100;
      if (hundreds != 0)
         spelling = onesWord(hundreds) + " Hundred ";
      
      //Append the spelling of the 2-digit remainder, if any
      int remainder = number % 100;
      if (remainder != 0)
         spelling = spelling + twoDigitSpelling(remainder);
         
      return spelling.trim();
   }
   
   //Returns the spelling, in words, of any Java int
   public static String spelling(int number)
   {
      if (number == 0)
         return "Zero";
         
      if (number < 0)
         return "Negative " + spelling(-number);
      
      String words = spelling(number / 1000000000, "Billion ") +
                     spelling(number % 1000000000 / 1000000, "Million ") +
                     spelling(number % 1000000 / 1000, "Thousand ") +
                     spelling(number % 1000, "");
      return words.trim();
   }
   
   //Helper Method: Spell a 3-digit part of a number with it's part suffix
   //@param triple: a 3-digit integer
   //@param suffix: "Billion", "Million", "Thousand" or ""
   private static String spelling(int triple, String suffix)
   {
      if (triple == 0)
         return "";
         
      return threeDigitSpelling(triple) + " " + suffix;
   }
}