public List <Token> Convert(string regexString)
{
var result = new List <Token>();
var currentCharIndex = 0;
var length = regexString.Length;
while (currentCharIndex != length)
{
var currentChar = regexString[currentCharIndex];
Token toAdd;
switch (currentChar)
{
case '(':
toAdd = new LeftBracketToken();
break;
case ')':
toAdd = new RightBracketToken();
break;
case '*':
toAdd = new StarToken();
break;
case '|':
toAdd = new SumToken();
break;
case '\\':
currentCharIndex++;
if (currentCharIndex == length)
{
throw new RegexParseException($"Backslash at the end of input escaping nothing.");
}
toAdd = new CharacterClassToken($"\\{regexString[currentCharIndex]}");
break;
case '[':
currentCharIndex++;
var startingIndex = currentCharIndex;
while (currentCharIndex != length && regexString[currentCharIndex] != ']')
{
// Escape inside character class
if ('\\'.Equals(regexString[currentCharIndex]))
{
currentCharIndex++;
}
currentCharIndex++;
}
if (currentCharIndex == length)
{
throw new RegexParseException($"Character class not properly closed in {regexString}");
}
var value = regexString.Substring(startingIndex, currentCharIndex - startingIndex);
toAdd = new CharacterClassToken(value);
break;
default:
toAdd = new CharacterClassToken($"\\{currentChar}");
break;
}
result.Add(toAdd);
currentCharIndex++;
}
return(result);
}
private Regex CreateRegexFromCharacterClassToken(CharacterClassToken token)
{
var chars = token.Value;
var regexes = new List <Regex>();
for (var index = 0; index < chars.Length; index++)
{
var currentChar = chars[index];
switch (currentChar)
{
case '\\':
index++;
if (index == chars.Length)
{
throw new RegexParserInternalException("Character class: escape (\\) at the end of body.");
}
regexes.Add(chars[index].ToRegex());
break;
case '-':
var previousIndex = index - 1;
var nextIndex = index + 1;
if (nextIndex == chars.Length)
{
throw new RegexParserInternalException(
$"Character class: unescaped minus at the end of body: {chars}");
}
if ('\\'.Equals(chars[nextIndex]))
{
nextIndex++;
}
if (nextIndex == chars.Length)
{
throw new RegexParserInternalException(
$"Character class: backslash after minus at the end of body: {chars}");
}
if (previousIndex < 0)
{
throw new RegexParserInternalException(
$"Character class: unescaped minus at the beginning of body: {chars}");
}
regexes.RemoveAt(regexes.Count - 1);
var startCharacter = chars[previousIndex];
var endCharacter = chars[nextIndex];
if (startCharacter > endCharacter)
{
throw new RegexParserInternalException(
$"Character class: start character > end character: {startCharacter} > {endCharacter}");
}
for (var charToAdd = startCharacter; charToAdd <= endCharacter; charToAdd++)
{
regexes.Add(charToAdd.ToRegex());
}
index = nextIndex;
break;
default:
regexes.Add(currentChar.ToRegex());
break;
}
}
return(RegexUtils.Sum(regexes.ToArray()));
}
