#pragma once
#include "error.hpp"
#include <cmath>
#include <exception>
#include <functional>
#include <limits>
#include <optional>
#include <regex>
#include <string>
#include <string_view>
#include <unordered_map>
#include <vector>
namespace math::server {
namespace lexer {
class Error : public server::Error {
public:
explicit Error(const std::string &what)
: server::Error{"lexer error: " + what}
{ }
};
class Token {
public:
enum class Type {
LEFT_PAREN,
RIGHT_PAREN,
PLUS,
MINUS,
ASTERISK,
SLASH,
NUMBER,
};
explicit Token(Type type)
: m_type{type}, m_number_value{nan()}
{ }
explicit Token(double number_value)
: m_type{Type::NUMBER}, m_number_value{number_value}
{ }
bool operator==(const Token& other) const {
return m_type == other.m_type
&& ((is_nan(m_number_value) && is_nan(other.m_number_value))
|| m_number_value == other.m_number_value);
}
bool operator!=(const Token& other) const { return !(*this == other); }
Type get_type() const { return m_type; }
double get_number_value() const {
if (get_type() != Type::NUMBER) {
throw Error{"token must be a number to query its value"};
}
return m_number_value;
}
private:
static constexpr double nan() { return std::numeric_limits<double>::quiet_NaN(); }
static bool is_nan(double x) { return std::isnan(x); }
Type m_type;
double m_number_value;
};
namespace details {
inline std::string_view match_number(const std::string_view& input) {
static constexpr std::regex::flag_type flags =
std::regex_constants::ECMAScript |
std::regex_constants::icase;
// This is a hacky attempt to describe a C-like grammar for floating-point
// numbers using a regex (the tests seem to pass though).
// A proper NFA would be better, I guess.
static const std::regex number_regex{R"REGEX(^(?:\d+(?:\.\d*)?|\.\d+)(e[+-]?(\d*))?)REGEX", flags};
std::cmatch match;
if (!std::regex_search(input.cbegin(), input.cend(), match, number_regex)) {
return {};
}
// If we have the numeric part of a number followed by 'e' and no digits,
// 1) that 'e' definitely belongs to this number token,
// 2) the user forgot to type in the required digits.
const auto& exponent = match[1];
const auto& abs_power = match[2];
if (exponent.matched && abs_power.matched && abs_power.length() == 0) {
throw lexer::Error{"exponent has no digits: " + match[0].str()};
}
return {match[0].first, match[0].length()};
}
inline std::optional<double> parse_number(const std::string_view& input, std::string_view& token) {
const auto view = match_number(input);
if (!view.data()) {
return {};
}
try {
const auto result = std::stod(std::string{view});
token = view;
return result;
} catch (const std::exception& e) {
throw lexer::Error{"couldn't parse number from: " + std::string{view}};
}
return {};
}
inline std::optional<double> parse_number(const std::string_view& input) {
std::string_view token;
return parse_number(input, token);
}
inline bool starts_with(const std::string_view& a, const std::string_view& b) noexcept {
return a.length() >= b.length()
&& a.compare(0, b.length(), b) == 0;
}
inline std::optional<Token::Type> parse_const_token(const std::string_view& input, std::string_view& token) {
// FIXME: Potentially error-prone if there's const token A which is a
// prefix of token B (if the map is not sorted, we'd parse token A, when it
// could've been token B).
// Can be solved by sorting the keys accordingly.
static const std::unordered_map<std::string_view, Token::Type> const_tokens{
{"(", Token::Type::LEFT_PAREN},
{")", Token::Type::RIGHT_PAREN},
{"+", Token::Type::PLUS},
{"-", Token::Type::MINUS},
{"*", Token::Type::ASTERISK},
{"/", Token::Type::SLASH},
};
for (const auto& it : const_tokens) {
const auto& str = it.first;
const auto& type = it.second;
if (starts_with(input, str)) {
token = input.substr(0, str.length());
return type;
}
}
return {};
}
inline std::optional<Token::Type> parse_const_token(const std::string_view& input) {
std::string_view token;
return parse_const_token(input, token);
}
inline std::string_view parse_whitespace(const std::string_view& input) {
static const std::regex ws_regex{R"(\s*)"};
std::cmatch match;
if (std::regex_search(input.cbegin(), input.cend(), match, ws_regex)) {
return {match[0].first, match[0].length()};
}
return {};
}
}
}
class Lexer {
public:
explicit Lexer(const std::string_view& input)
: m_input{input} {
}
using TokenProcessor = std::function<bool (const lexer::Token&)>;
bool for_each_token(const TokenProcessor& process) {
parse_token();
for (auto token = peek_token(); token.has_value(); drop_token(), token = peek_token()) {
if (!process(*token)) {
return false;
}
}
return true;
}
std::vector<lexer::Token> get_tokens() {
std::vector<lexer::Token> tokens;
for_each_token([&tokens] (const lexer::Token& token) {
tokens.emplace_back(token);
return true;
});
return tokens;
}
void parse_token() {
if (m_input.length() == 0) {
return;
}
std::string_view token_view;
m_token_buffer = parse_token(token_view);
if (m_token_buffer.has_value()) {
m_input.remove_prefix(token_view.length());
}
}
bool has_token() const {
return peek_token().has_value();
}
std::optional<lexer::Token> peek_token() const {
return m_token_buffer;
}
void drop_token() {
if (!has_token()) {
throw lexer::Error{"internal: no tokens to drop"};
}
m_token_buffer = {};
parse_token();
}
std::optional<lexer::Token> drop_token_if(lexer::Token::Type type) {
if (!has_token()) {
throw lexer::Error{"internal: no tokens to drop"};
}
if (m_token_buffer.value().get_type() != type) {
return {};
}
const auto result = m_token_buffer;
drop_token();
return result;
}
private:
void consume_whitespace() {
const auto ws = lexer::details::parse_whitespace(m_input);
m_input.remove_prefix(ws.length());
}
std::optional<lexer::Token> parse_token(std::string_view& token_view) {
consume_whitespace();
if (m_input.length() == 0) {
return {};
}
if (const auto const_token = lexer::details::parse_const_token(m_input, token_view); const_token.has_value()) {
return lexer::Token{*const_token};
}
if (const auto number = lexer::details::parse_number(m_input, token_view); number.has_value()) {
return lexer::Token{*number};
}
throw lexer::Error{"invalid input at: " + std::string{m_input}};
}
std::string_view m_input;
std::optional<lexer::Token> m_token_buffer;
};
}
