#pragma once

#include <cstdint>
#include <fstream>
#include <string>
#include <unordered_map>
#include <vector>

namespace stela {

struct Pos {
    size_t index;
    int64_t line;
    int64_t col;
};

struct Error {
    Pos pos;
    std::string message;
};

enum class TokenType {
    Error,
    Eof,
    If,
    Else,
    Return,
    Public,
    Private,
    Class,
    Derivable,
    Derives,
    Enumeration,
    Associate,
    Attribute,
    Operation,
    StateMachine,
    Transition,
    Initial,
    Final,
    Entry,
    Exit,
    LParen,
    RParen,
    LBrace,
    RBrace,
    LBracket,
    RBracket,
    Dot,
    Comma,
    Semicolon,
    Colon,
    ColonColon,
    Minus,
    MinusLt,
    Equal,
    Id,
    Int,
};

struct Token {
    TokenType type;
    Pos pos;
    uint64_t id;
};

class Lexer {
public:
    Lexer(std::ifstream& file, std::vector<Error>& errors)
        : file(&file)
        , current_char(file.get())
        , errors(&errors)
    { }

    auto next() -> Token;

private:
    inline auto step()
    {
        if (this->current_char == EOF) {
            this->eof_reached = true;
            return;
        }
        if (this->current_char == '\n') {
            this->line += 1;
            this->col = 1;
        } else {
            this->col += 1;
        }
        this->current_char = this->file->get();
        this->index += 1;
    }

    inline auto single_token(TokenType type, Pos pos) -> Token
    {
        step();
        return token(type, pos);
    }
    inline auto error_token(Pos pos, std::string message) const -> Token
    {
        this->errors->push_back(Error { pos, message });
        return token(TokenType::Error, pos);
    }
    inline auto token(TokenType type, Pos pos) const -> Token
    {
        return Token { type, pos, 0 };
    }
    inline auto pos() const -> Pos
    {
        return Pos {
            .index = this->index,
            .line = this->line,
            .col = this->col,
        };
    }

    inline auto done() const -> bool { return this->eof_reached; }
    inline auto current() const -> char
    {
        return static_cast<char>(this->current_char);
    }

    auto populate_keyword_map();

    bool eof_reached = false;

    size_t index = 0;
    int64_t line = 1;
    int64_t col = 1;

    std::ifstream* file;
    int current_char;

    std::unordered_map<std::string, TokenType> keyword_map {};

    std::vector<std::string> symbol_values {};
    std::vector<int64_t> int_values {};

    std::vector<Error>* errors;
};

}