/// <summary>
/// Parses the regex and converts it into an NFA.
/// </summary>
/// <param name="regex"></param>
private NFA RegexToNFA(string regex, ref int index)
{
bool bracket = false;
if (index >= 0 && index < regex.Length)
{
bracket = (regex[index] == '(');
}
if (bracket || (index < 0))
{
index++;
}
NFA result = null;
while (index < regex.Length && regex[index] != ')')
{
NFA newNFA = null;
int combineMode = -1; //0 = concat, 1 = alternate
switch (regex[index])
{
case '(':
newNFA = RegexToNFA(regex, ref index);
combineMode = 0;
break;
case '|':
index++;
newNFA = RegexToNFA(regex, ref index);
combineMode = 1;
break;
case '*':
index++;
combineMode = -1;
break;
case '[':
byte[] transitionBytes = GetTransitionSet(regex, ref index);
newNFA = NFA.ByteTransitionNFA(transitionBytes);
combineMode = 0;
break;
case '.':
transitionBytes = new byte[256];
for (int b = byte.MinValue; b <= byte.MaxValue; b++)
{
transitionBytes[b] = (byte)b;
}
newNFA = NFA.ByteTransitionNFA(transitionBytes);
combineMode = 0;
index++;
break;
case ']':
throw new ParseException("Error at position " + index + "! No ']' expected. Escape it!");
case '\\':
index++;
transitionBytes = new byte[] { Convert.ToByte(regex[index++]) };
newNFA = NFA.ByteTransitionNFA(transitionBytes);
combineMode = 0;
break;
default:
transitionBytes = new byte[] { Convert.ToByte(regex[index++]) };
newNFA = NFA.ByteTransitionNFA(transitionBytes);
combineMode = 0;
break;
}
if (index < regex.Length && regex[index] == '*')
{
newNFA.KleeneStar();
index++;
}
if (combineMode == 0)
{
result = NFA.ConcatNFAs(result, newNFA);
}
else if (combineMode == 1)
{
result = NFA.AlternateNFAs(result, newNFA);
}
}
if (bracket && (index < regex.Length) && regex[index] == ')')
{
index++;
}
else if (bracket && ((index >= regex.Length) || regex[index] != ')'))
{
throw new ParseException("Error at position " + index + "! Closing bracket expected!");
}
return(result);
}