// Copyright (c) 2019 Egor Tensin <Egor.Tensin@gmail.com>
// This file is part of the "math-server" project.
// For details, see https://github.com/egor-tensin/math-server.
// Distributed under the MIT License.
#include "error.hpp"
#include "lexer.hpp"
#include "token.hpp"
#include "token_type.hpp"
#include <exception>
#include <optional>
#include <regex>
#include <string_view>
#include <string>
#include <vector>
namespace math::server {
namespace lexer {
namespace {
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;
{
const auto begin = input.data();
const auto end = begin + input.length();
if (!std::regex_search(begin, end, 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 LexerError{"exponent has no digits: " + match[0].str()};
}
}
return {match[0].first, static_cast<std::size_t>(match[0].length())};
}
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&) {
throw LexerError{"internal: couldn't parse number from: " + std::string{view}};
}
return {};
}
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;
}
std::optional<token::Type> parse_const_token(const std::string_view& input, std::string_view& token) {
for (const auto type : token::const_tokens()) {
const auto str = token::type_to_string(type);
if (starts_with(input, str)) {
token = std::string_view(input.data(), str.length());
return {type};
}
}
return {};
}
}
namespace details {
std::optional<double> parse_number(const std::string_view& input) {
std::string_view token;
return lexer::parse_number(input, token);
}
std::optional<token::Type> parse_const_token(const std::string_view& input) {
std::string_view token;
return lexer::parse_const_token(input, token);
}
std::string_view parse_whitespace(const std::string_view& input) {
static const std::regex ws_regex{R"(^\s+)"};
std::cmatch match;
{
const auto begin = input.data();
const auto end = begin + input.length();
if (std::regex_search(begin, end, match, ws_regex)) {
return std::string_view(match[0].first, match[0].length());
}
}
return {};
}
}
}
Lexer::Lexer(const std::string_view& input)
: Lexer{lexer::Input{input}} {
}
Lexer::Lexer(const lexer::Input& input)
: m_input{input} {
consume_token();
}
bool Lexer::for_each_token(const TokenProcessor& process) {
for (auto token = peek_token(); token.has_value(); drop_token(), token = peek_token()) {
if (!process(*token)) {
return false;
}
}
return true;
}
std::vector<Lexer::ParsedToken> Lexer::get_tokens() {
std::vector<ParsedToken> tokens;
for_each_token([&tokens] (const ParsedToken& token) {
tokens.emplace_back(token);
return true;
});
return tokens;
}
void Lexer::drop_token() {
if (!has_token()) {
throw LexerError{"internal: no tokens to drop"};
}
m_token_buffer = {};
consume_token();
}
std::optional<Lexer::ParsedToken> Lexer::drop_token_of_type(Type type) {
if (!has_token()) {
throw LexerError{"internal: no tokens to drop"};
}
if (m_token_buffer.value().get_type() != type) {
return {};
}
const auto result = m_token_buffer;
drop_token();
return result;
}
void Lexer::consume_whitespace() {
const auto ws = parse_whitespace();
if (!ws.has_value()) {
return;
}
m_input.consume(ws->get_length());
}
void Lexer::consume_token() {
if (m_input.empty()) {
return;
}
consume_whitespace();
if (m_input.empty()) {
return;
}
auto token{parse_token()};
m_input.consume(token.get_length());
m_token_buffer = std::move(token);
}
std::optional<Lexer::ParsedToken> Lexer::parse_whitespace() const {
const auto token_view = lexer::details::parse_whitespace(m_input.get_input());
if (token_view.empty()) {
return {};
}
return ParsedToken{Token{Token::Type::WHITESPACE}, m_input.get_pos(), token_view};
}
std::optional<Lexer::ParsedToken> Lexer::parse_const_token() const {
std::string_view token_view;
const auto type = lexer::parse_const_token(m_input.get_input(), token_view);
if (!type.has_value()) {
return {};
}
return ParsedToken{Token{*type}, m_input.get_pos(), token_view};
}
std::optional<Lexer::ParsedToken> Lexer::parse_number() const {
std::string_view token_view;
const auto number = lexer::parse_number(m_input.get_input(), token_view);
if (!number.has_value()) {
return {};
}
return ParsedToken{Token{*number}, m_input.get_pos(), token_view};
}
Lexer::ParsedToken Lexer::parse_token() const {
if (const auto const_token = parse_const_token(); const_token.has_value()) {
return *const_token;
}
if (const auto number = parse_number(); number.has_value()) {
return *number;
}
throw LexerError{"invalid input at: " + std::string{m_input.get_input()}};
}
}
