/// <summary>
/// This method implements both multiplication and addition (determined via the 'o' operand).
/// It takes StringNumbers a and b and adds/multiplies them and returns a new StringNumber
/// with the result. It implements the contract defined in StringNumber class comment.
///
/// It basically works by calculating the numeric result and then stepping (a char at a time) through
/// the result, a and b simultaneously, checking for non-digits. If one is found for the
/// current 'column', a.NonDigitReplacement is appended to a string result. Else the digit
/// in the numeric result is appended.
/// Finally the string result is converted into a new StringNumber (StringNumber's are
/// immutable, remember) and returned.
/// </summary>
/// <param name="a">the first StringNumber to add/multiply</param>
/// <param name="b">the second StringNumber to add/multiply</param>
/// <param name="o">which operation to apply to a and b: Multiply or Add</param>
/// <returns></returns>
internal static StringNumber OperatorImplementation(StringNumber a, StringNumber b, Operation o)
{
if (a == null || b == null)
{
return(null);
}
var aNum = (BigInteger)a;
var bNum = (BigInteger)b;
var result = (o == Operation.ADDITION) ? aNum + bNum : aNum * bNum;
int aLen = a.InitialValue.Length;
int bLen = b.InitialValue.Length;
int maxLen = Math.Max(result.ToString().Length, Math.Max(aLen, bLen));
string resultStr = result.ToString("D" + maxLen);
var sb = new StringBuilder(maxLen);
int aOffset = maxLen - aLen;
int bOffset = maxLen - bLen;
for (int i = 0; i < maxLen; i++)
{
int index = maxLen - i - 1;
if ((aLen > index) && !Char.IsDigit(a.InitialValue[i - aOffset]))
{
sb.Append(a.NonDigitReplacement);
}
else if ((bLen > index) && !Char.IsDigit(b.InitialValue[i - bOffset]))
{
sb.Append(a.NonDigitReplacement);
}
else
{
sb.Append(resultStr[i]);
}
}
return(new StringNumber(sb.ToString(), a.NonDigitReplacement));
}
internal static string AsString(StringNumber s)
{
if (s == null)
{
return(null);
}
int sLen = s.InitialValue.Length;
var sb = new StringBuilder(sLen);
for (int i = 0; i < sLen; i++)
{
if (IsNonDigit(s.InitialValue, sLen, i))
{
sb.Append(s.NonDigitReplacement);
}
else
{
sb.Append(s.InitialValue[i]);
}
}
return(sb.ToString());
}
internal static StringNumber AdditionOperator(StringNumber a, StringNumber b)
{
return(OperatorImplementation(a, b, Operation.ADDITION));
}
internal static StringNumber MultiplicationOperator(StringNumber a, StringNumber b)
{
return(OperatorImplementation(a, b, Operation.MULTIPLICATION));
}
internal StringNumberImplementation(StringNumber s)
{
this.StringNumber = s;
}