public RegExToken NextToken()
{
// These keeps track of classes
var classState = new CharacterClassState();
var numberedRepetitionState = new NumberedRepetitionState();
state = State.Normal;
while (input.Peek() != -1)
{
var c = (char)input.Read();
switch (state)
{
case State.Normal:
switch (c)
{
case '\\':
state = State.NormalEscaped;
break;
case '[':
state = State.BeginCharacterClass;
break;
case '{':
state = State.NumberedRepetition;
break;
case '(': return new RegExToken { Type = RegExToken.TokenType.OperatorOpenParanthesis };
case ')': return new RegExToken { Type = RegExToken.TokenType.OperatorCloseParanthesis };
case '|': return new RegExToken { Type = RegExToken.TokenType.OperatorOr };
case '+': return new RegExToken { Type = RegExToken.TokenType.OperatorPlus };
case '*': return new RegExToken { Type = RegExToken.TokenType.OperatorMul };
case '?': return new RegExToken { Type = RegExToken.TokenType.OperatorQuestion };
case '.': return new RegExToken { Type = RegExToken.TokenType.Accept, Characters = AllCharactersExceptNull };
default: return new RegExToken { Type = RegExToken.TokenType.Accept, Characters = SingleChar(c)};
}
break;
case State.NormalEscaped:
{
var characters = EscapedCharToAcceptCharRange(c);
if (!characters.Any())
{
throw new LexerConstructionException(string.Format("Unknown escaped character '{0}'", c));
}
return new RegExToken {Characters = characters, Type = RegExToken.TokenType.Accept};
}
case State.BeginCharacterClass:
switch (c)
{
case '^':
if (classState.Negated)
{
// If the classstate is ALREADY negated
// Readd the ^ to the expression
classState.LastChar = '^';
state = State.InsideCharacterClass;
}
classState.Negated = true;
break;
case '[':
case ']':
case '-':
// This does not break the character class TODO: I THINK!!!
classState.LastChar = c;
break;
case '\\':
state = State.InsideCharacterClassEscaped;
break;
default:
classState.LastChar = c;
state = State.InsideCharacterClass;
break;
}
break;
case State.InsideCharacterClass:
switch (c)
{
case '-':
state = State.RangeEnd;
break;
case '[':
throw new LexerConstructionException("Opening new character class inside an already open one");
case ']':
if (classState.LastChar != (char)0)
classState.CharsSet.Add(classState.LastChar);
// Ending class
return new RegExToken
{
Type = RegExToken.TokenType.Accept,
Characters = classState.Negated
? AllCharactersExceptNull.Except(classState.CharsSet)
: classState.CharsSet
};
case '\\':
state = State.InsideCharacterClassEscaped;
break;
default:
if (classState.LastChar != 0)
classState.CharsSet.Add(classState.LastChar);
classState.LastChar = c;
break;
}
break;
case State.InsideCharacterClassEscaped:
{
var characters = EscapedCharToAcceptCharsInClass(c);
if (!characters.Any())
{
throw new LexerConstructionException(string.Format("Unknown escaped character '{0}' in character class", c));
}
if (classState.LastChar != 0)
classState.CharsSet.Add(classState.LastChar);
classState.CharsSet.UnionWith(characters);
classState.LastChar = (char)0;
state = State.InsideCharacterClass;
}
break;
case State.RangeEnd:
switch (c)
{
case ']':
// We found the - at the position BEFORE the end of the class
// which means we should handle it as a litteral and end the class
classState.CharsSet.Add(classState.LastChar);
classState.CharsSet.Add('-');
return new RegExToken
{
Type = RegExToken.TokenType.Accept,
Characters = classState.Negated
? AllCharactersExceptNull.Except(classState.CharsSet)
: classState.CharsSet
};
default:
char lastClassChar = classState.LastChar;
char from = lastClassChar < c ? lastClassChar : c;
char to = lastClassChar < c ? c : lastClassChar;
classState.CharsSet.AddRange(from, to);
classState.LastChar = (char) 0;
state = State.InsideCharacterClass;
break;
}
break;
case State.NumberedRepetition:
switch (c)
{
case '0': // Is it really OK to start with a 0. It is now.
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
numberedRepetitionState.Chars.Add(c);
break;
case '}':
case ':':
case ',':
// Parse whatever is in Chars
int reps;
// Number is required in FIRST part but OPTIONAL in the second
if (numberedRepetitionState.Chars.Any() || numberedRepetitionState.CurrentPart == 0)
{
if (!int.TryParse(new string(numberedRepetitionState.Chars.ToArray()), out reps))
{
throw new LexerConstructionException("Numbered repetition operator contains operand that is not a number");
}
}
else
{
// End up here when nothing specified in the last part.
// Use the max value to say that it can be infinite numbers.
reps = int.MaxValue;
}
numberedRepetitionState.Chars.Clear();
// Set the right value
if (numberedRepetitionState.CurrentPart == 0)
{
numberedRepetitionState.MinRepetitions = reps;
}
else
{
numberedRepetitionState.MaxRepetitions = reps;
}
if (c == ':' || c == ',')
{
++numberedRepetitionState.CurrentPart;
if (numberedRepetitionState.CurrentPart > 1)
throw new LexerConstructionException("More than one , in numbered repetition.");
}
else
{
return new RegExToken
{
Type = RegExToken.TokenType.NumberedRepeat,
MinRepetitions = numberedRepetitionState.MinRepetitions,
MaxRepetitions = numberedRepetitionState.MaxRepetitions
};
}
break;
default:
throw new LexerConstructionException(
string.Format("Illegal character {0} in numbered repetition", c));
}
break;
}
}
// We get here if we try to lex when the expression has ended.
return null;
}
