regex_parser.h

#pragma once
#include <iostream>
#include <string>
#include <vector>
using namespace std;

enum TokenType
{
    CHAR,
    ALTERNATION,
    STAR,
    LPAREN,
    RPAREN,
    END
};

struct Token
{
    TokenType type;
    char value;

    explicit Token(TokenType t, char v = '\0') : type(t), value(v) {};
};

struct RegexNode
{
    char type;
    char value;
    RegexNode *left;
    RegexNode *right;

    explicit RegexNode(char t, char v = '\0', RegexNode *l = nullptr, RegexNode *r = nullptr) : type(t), value(v), left(l), right(r) {};
};

class RegexParser
{
private:
    vector<Token> tokens;
    int pos;

    RegexNode *parseAlternation();
    RegexNode *parseConcatenation();
    RegexNode *parseKleene();
    RegexNode *parsePrimary();

    Token currentToken();
    void advance();
    void error(string message);
    vector<Token> tokenize(string regex);

public:
    RegexParser();
    RegexNode *parse(string regex);
};