private IExpression ParseOctalEscapeOrNumberedBackreference()
{
int endIndex = GetNumberEndIndex();
string numberString = regex.Substring(index, endIndex - index);
index = endIndex; // swallow number
int number = Int32.Parse(numberString);
if (number >= 1 && number <= 9)
{
return(Backreference.For(number));
}
else if (numberString[0] == '8' || numberString[0] == '9')
{
return(CharacterEscapes.Octal(numberString));
}
else if (number >= 10)
{
if (number < groupNames.Count)
{
return(Backreference.For(number));
}
else
{
return(CharacterEscapes.Octal(numberString));
}
}
// The Regex constructor to prevent backreferences to \0 and invalid octal codes
throw new InvalidOperationException();
}
private IExpression ParseControlCharacterEscape()
{
++index; // swallow 'c'
char controlCharacter = regex[index];
++index; // swallow control character
return(CharacterEscapes.ControlCharacter(controlCharacter));
}
private IExpression ParseUnicodeCharacterEscape()
{
++index; // swallow 'u'
int endIndex = GetHexidecimalNumberEndIndex(Math.Min(index + 4, regex.Length));
string numberString = regex.Substring(index, endIndex - index);
index = endIndex; // swallow code
return(CharacterEscapes.Unicode(numberString));
}
private IExpression ParseHexidecimalEscape()
{
++index; // swallow 'x'
int endIndex = GetHexidecimalNumberEndIndex(Math.Min(index + 2, regex.Length));
string numberString = regex.Substring(index, endIndex - index);
index = endIndex; // swallow hex number
return(CharacterEscapes.Hexidecimal(numberString));
}
private IExpression ParseUnicodeCategory(bool isPositive)
{
++index; // swallow 'p' or 'P'
if (regex[index] != '{')
{
return(CharacterEscapes.For('p'));
}
++index; // swallow {
int endIndex = regex.IndexOf('}', index);
if (endIndex == -1)
{
// The Regex constructor should prevent this from happening.
throw new InvalidOperationException();
}
string category = regex.Substring(index, endIndex - index);
index = endIndex + 1; // swallow category and '}'
return(new UnicodeCategory($@"\{(isPositive ? 'p' : 'P')}{{{category}}}"));
}
private IExpression ParseEscapeSequenceInternal(ExpressionContext context)
{
++index;
char nextChar = regex[index];
switch (nextChar)
{
case 'A': return(ParseAnchor(Anchors.A));
case 'Z': return(ParseAnchor(Anchors.Z));
case 'z': return(ParseAnchor(Anchors.z));
case 'G': return(ParseAnchor(Anchors.G));
case 'b':
return((context == ExpressionContext.CharacterGroup)
? ParseCharacterEscape(CharacterEscapes.Backspace)
: ParseAnchor(Anchors.b));
case 'B': return(ParseAnchor(Anchors.B));
case 'k': return(ParseNamedBackreference());
case 'w': return(ParseCharacterClass(CharacterClasses.Word));
case 'W': return(ParseCharacterClass(CharacterClasses.NonWord));
case 's': return(ParseCharacterClass(CharacterClasses.Whitespace));
case 'S': return(ParseCharacterClass(CharacterClasses.NonWhitespace));
case 'd': return(ParseCharacterClass(CharacterClasses.Digit));
case 'D': return(ParseCharacterClass(CharacterClasses.NonDigit));
case 'p': return(ParseUnicodeCategory(isPositive: true));
case 'P': return(ParseUnicodeCategory(isPositive: false));
case 'a': return(ParseCharacterEscape(CharacterEscapes.Bell));
case 't': return(ParseCharacterEscape(CharacterEscapes.Tab));
case 'r': return(ParseCharacterEscape(CharacterEscapes.CarriageReturn));
case 'v': return(ParseCharacterEscape(CharacterEscapes.VerticalTab));
case 'f': return(ParseCharacterEscape(CharacterEscapes.FormFeed));
case 'n': return(ParseCharacterEscape(CharacterEscapes.NewLine));
case 'e': return(ParseCharacterEscape(CharacterEscapes.Escape));
case '.': return(ParseCharacterEscape(CharacterEscapes.Period));
case '$': return(ParseCharacterEscape(CharacterEscapes.Dollar));
case '^': return(ParseCharacterEscape(CharacterEscapes.Carot));
case '{': return(ParseCharacterEscape(CharacterEscapes.LeftCurlyBrace));
case '[': return(ParseCharacterEscape(CharacterEscapes.LeftSquareBracket));
case '(': return(ParseCharacterEscape(CharacterEscapes.LeftParenthesis));
case '|': return(ParseCharacterEscape(CharacterEscapes.Pipe));
case ')': return(ParseCharacterEscape(CharacterEscapes.RightParenthesis));
case '*': return(ParseCharacterEscape(CharacterEscapes.Asterisk));
case '+': return(ParseCharacterEscape(CharacterEscapes.Plus));
case '?': return(ParseCharacterEscape(CharacterEscapes.QuestionMark));
case '\\': return(ParseCharacterEscape(CharacterEscapes.Backslash));
case 'x': return(ParseHexidecimalEscape());
case 'c': return(ParseControlCharacterEscape());
case 'u': return(ParseUnicodeCharacterEscape());
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
return(ParseOctalEscapeOrNumberedBackreference());
default: return(ParseCharacterEscape(CharacterEscapes.For(nextChar)));
}
}
