/// <summary>
/// Parses the next <see cref="BNumber"/> from the stream.
/// </summary>
/// <param name="stream">The stream to parse from.</param>
/// <returns>The parsed <see cref="BNumber"/>.</returns>
/// <exception cref="InvalidBencodeException{BNumber}">Invalid bencode</exception>
/// <exception cref="UnsupportedBencodeException{BNumber}">The bencode is unsupported by this library</exception>
public override BNumber Parse(BencodeStream stream)
{
if (stream == null)
{
throw new ArgumentNullException(nameof(stream));
}
if (stream.Length < MinimumLength)
{
throw InvalidBencodeException <BNumber> .BelowMinimumLength(MinimumLength, stream.Length, stream.Position);
}
var startPosition = stream.Position;
// Numbers must start with 'i'
if (stream.ReadChar() != 'i')
{
throw InvalidBencodeException <BNumber> .UnexpectedChar('i', stream.ReadPreviousChar(), stream.Position);
}
var digits = new StringBuilder();
char c;
for (c = stream.ReadChar(); c != 'e' && c != default(char); c = stream.ReadChar())
{
digits.Append(c);
}
// Last read character should be 'e'
if (c != 'e')
{
throw InvalidBencodeException <BNumber> .InvalidEndChar(c, stream.Position);
}
var isNegative = digits[0] == '-';
var numberOfDigits = isNegative ? digits.Length - 1 : digits.Length;
// We do not support numbers that cannot be stored as a long (Int64)
if (numberOfDigits > BNumber.MaxDigits)
{
throw UnsupportedException(
$"The number '{digits}' has more than 19 digits and cannot be stored as a long (Int64) and therefore is not supported.",
startPosition);
}
// We need at least one digit
if (numberOfDigits < 1)
{
throw InvalidException("It contains no digits.", startPosition);
}
var firstDigit = isNegative ? digits[1] : digits[0];
// Leading zeros are not valid
if (firstDigit == '0' && numberOfDigits > 1)
{
throw InvalidException($"Leading '0's are not valid. Found value '{digits}'.", startPosition);
}
// '-0' is not valid either
if (firstDigit == '0' && numberOfDigits == 1 && isNegative)
{
throw InvalidException("'-0' is not a valid number.", startPosition);
}
long number;
if (!ParseUtil.TryParseLongFast(digits.ToString(), out number))
{
var nonSignChars = isNegative ? digits.ToString(1, digits.Length - 1) : digits.ToString();
if (nonSignChars.Any(x => !x.IsDigit()))
{
throw InvalidException($"The value '{digits}' is not a valid number.", startPosition);
}
throw UnsupportedException(
$"The value '{digits}' is not a valid long (Int64). Supported values range from '{long.MinValue:N0}' to '{long.MaxValue:N0}'.",
startPosition);
}
return(new BNumber(number));
}
