ladybird/Libraries/LibRegex/RegexLexer.cpp

/*
 * Copyright (c) 2020, Emanuel Sprung <emanuel.sprung@gmail.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include "RegexLexer.h"
#include <AK/Assertions.h>
#include <AK/Debug.h>
#include <AK/Format.h>

namespace regex {

char const* Token::name(TokenType const type)
{
    switch (type) {
#define __ENUMERATE_REGEX_TOKEN(x) \
    case TokenType::x:             \
        return #x;
        ENUMERATE_REGEX_TOKENS
#undef __ENUMERATE_REGEX_TOKEN
    default:
        VERIFY_NOT_REACHED();
        return "<Unknown>";
    }
}

char const* Token::name() const
{
    return name(m_type);
}

Lexer::Lexer()
    : GenericLexer(StringView {})
{
}

Lexer::Lexer(StringView const source)
    : GenericLexer(source)
{
}

void Lexer::back(size_t offset)
{
    if (offset == m_index + 1)
        offset = m_index; // 'position == 0' occurs twice.

    VERIFY(offset <= m_index);
    if (!offset)
        return;
    m_index -= offset;
    m_previous_position = (m_index > 0) ? m_index - 1 : 0;
}

char Lexer::consume()
{
    m_previous_position = m_index;
    return GenericLexer::consume();
}

void Lexer::reset()
{
    m_index = 0;
    m_current_token = { TokenType::Eof, 0, {} };
    m_previous_position = 0;
}

Token Lexer::next()
{
    size_t token_start_position;

    auto begin_token = [&] {
        token_start_position = m_index;
    };

    auto commit_token = [&](auto type) -> Token& {
        VERIFY(token_start_position + m_previous_position - token_start_position + 1 <= m_input.length());
        auto substring = m_input.substring_view(token_start_position, m_previous_position - token_start_position + 1);
        m_current_token = Token(type, token_start_position, substring);
        return m_current_token;
    };

    auto emit_token = [&](auto type) -> Token& {
        m_current_token = Token(type, m_index, m_input.substring_view(m_index, 1));
        consume();
        return m_current_token;
    };

    auto match_escape_sequence = [&]() -> size_t {
        switch (peek(1)) {
        case '^':
        case '.':
        case '[':
        case ']':
        case '$':
        case '(':
        case ')':
        case '|':
        case '*':
        case '+':
        case '?':
        case '{':
        case '\\':
            return 2;
        default:
            dbgln_if(REGEX_DEBUG, "[LEXER] Found invalid escape sequence: \\{:c} (the parser will have to deal with this!)", peek(1));
            return 0;
        }
    };

    while (m_index < m_input.length()) {
        auto ch = peek();
        if (ch == '(')
            return emit_token(TokenType::LeftParen);

        if (ch == ')')
            return emit_token(TokenType::RightParen);

        if (ch == '{')
            return emit_token(TokenType::LeftCurly);

        if (ch == '}')
            return emit_token(TokenType::RightCurly);

        if (ch == '[')
            return emit_token(TokenType::LeftBracket);

        if (ch == ']')
            return emit_token(TokenType::RightBracket);

        if (ch == '.')
            return emit_token(TokenType::Period);

        if (ch == '*')
            return emit_token(TokenType::Asterisk);

        if (ch == '+')
            return emit_token(TokenType::Plus);

        if (ch == '$')
            return emit_token(TokenType::Dollar);

        if (ch == '^')
            return emit_token(TokenType::Circumflex);

        if (ch == '|')
            return emit_token(TokenType::Pipe);

        if (ch == '?')
            return emit_token(TokenType::Questionmark);

        if (ch == ',')
            return emit_token(TokenType::Comma);

        if (ch == '/')
            return emit_token(TokenType::Slash);

        if (ch == '=')
            return emit_token(TokenType::EqualSign);

        if (ch == ':')
            return emit_token(TokenType::Colon);

        if (ch == '-')
            return emit_token(TokenType::HyphenMinus);

        if (ch == '\\') {
            size_t escape = match_escape_sequence();
            if (escape > 0) {
                begin_token();
                for (size_t i = 0; i < escape; ++i)
                    consume();
                return commit_token(TokenType::EscapeSequence);
            }
        }

        return emit_token(TokenType::Char);
    }

    return Token(TokenType::Eof, m_index, {});
}

}