// *****************************************************************************
// Lexer.h
// ~~~~~~~
// author    : Hung Q. Ngo
// description: a simple lexical analyzer
// *****************************************************************************

#ifndef LEXER_H_
#define LEXER_H_

#include <string>
#include <set>

enum token_types_t { 
    IDENT,  // a sequence of alphanumeric characters and _, starting with alpha
    STRING, // sequence of characters between " ", no escape
    ENDTOK, // end of string/file, no more token
    ERRTOK  // unrecognized token
};

struct Token {
    token_types_t type;
    std::string value;
    // constructor for Token
    Token(token_types_t tt=ENDTOK, std::string val="") : type(tt), value(val) {}
};

/**
 * -----------------------------------------------------------------------------
 * the Lexer class:
 * - take a string to be scanned
 * - scan for tokens and return one at a time
 * -----------------------------------------------------------------------------
 */
class Lexer {
    public:
    // constructor
    Lexer(std::string str="");

    // a couple of modifiers
    void set_input(std::string); // set a new input, 
    void restart();              // move cursor to the beginning, restart

    Token next_token();    // returns the next token
    bool has_more_token(); // are there more token(s)?

    private:
    std::string input_str;     // the input string to be scanned
    size_t      cur_pos;       // current position in the input string
    bool        in_err;        // are we in the error state?
    std::set<char> separators; // in C++11, we could use unordered_set
};

#endif