ladybird/AK/GenericLexer.cpp

/*
 * Copyright (c) 2020, Benoit Lormeau <blormeau@outlook.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Assertions.h>
#include <AK/GenericLexer.h>
#include <AK/String.h>
#include <AK/StringBuilder.h>

namespace AK {

GenericLexer::GenericLexer(const StringView& input)
    : m_input(input)
{
}

GenericLexer::~GenericLexer()
{
}

// Tells whether the parser's index has reached input's end
bool GenericLexer::is_eof() const
{
    return m_index >= m_input.length();
}

// Returns the current character at the parser index, plus `offset` if specified
char GenericLexer::peek(size_t offset) const
{
    return (m_index + offset < m_input.length()) ? m_input[m_index + offset] : '\0';
}

// Tests the next character in the input
bool GenericLexer::next_is(char expected) const
{
    return peek() == expected;
}

// Tests if the `expected` string comes next in the input
bool GenericLexer::next_is(StringView expected) const
{
    for (size_t i = 0; i < expected.length(); ++i)
        if (peek(i) != expected[i])
            return false;
    return true;
}

// Tests if the `expected` string comes next in the input
bool GenericLexer::next_is(const char* expected) const
{
    for (size_t i = 0; expected[i] != '\0'; ++i)
        if (peek(i) != expected[i])
            return false;
    return true;
}

// Go back to the previous character
void GenericLexer::retreat()
{
    VERIFY(m_index > 0);
    m_index--;
}

// Consume a character and advance the parser index
char GenericLexer::consume()
{
    VERIFY(!is_eof());
    return m_input[m_index++];
}

// Consume the given character if it is next in the input
bool GenericLexer::consume_specific(char specific)
{
    if (peek() != specific)
        return false;

    ignore();
    return true;
}

// Consume the given string if it is next in the input
bool GenericLexer::consume_specific(StringView str)
{
    if (!next_is(str))
        return false;

    ignore(str.length());
    return true;
}

// Consume the given string if it is next in the input
bool GenericLexer::consume_specific(const char* str)
{
    return consume_specific(StringView(str));
}

// Consume a number of characters
StringView GenericLexer::consume(size_t count)
{
    if (count == 0)
        return {};

    size_t start = m_index;
    size_t length = min(count, m_input.length() - m_index);
    m_index += length;

    return m_input.substring_view(start, length);
}

// Consume the rest of the input
StringView GenericLexer::consume_all()
{
    if (is_eof())
        return {};

    auto rest = m_input.substring_view(m_index, m_input.length() - m_index);
    m_index = m_input.length();
    return rest;
}

// Consume until a new line is found
StringView GenericLexer::consume_line()
{
    size_t start = m_index;
    while (!is_eof() && peek() != '\r' && peek() != '\n')
        m_index++;
    size_t length = m_index - start;

    consume_specific('\r');
    consume_specific('\n');

    if (length == 0)
        return {};
    return m_input.substring_view(start, length);
}

// Consume and return characters until `stop` is peek'd
// The `stop` character is ignored, as it is user-defined
StringView GenericLexer::consume_until(char stop)
{
    size_t start = m_index;
    while (!is_eof() && peek() != stop)
        m_index++;
    size_t length = m_index - start;

    ignore();

    if (length == 0)
        return {};
    return m_input.substring_view(start, length);
}

// Consume and return characters until the string `stop` is found
// The `stop` string is ignored, as it is user-defined
StringView GenericLexer::consume_until(const char* stop)
{
    size_t start = m_index;
    while (!is_eof() && !next_is(stop))
        m_index++;
    size_t length = m_index - start;

    ignore(__builtin_strlen(stop));

    if (length == 0)
        return {};
    return m_input.substring_view(start, length);
}

/*
 * Consume a string surrounded by single or double quotes. The returned
 * StringView does not include the quotes. An escape character can be provided
 * to capture the enclosing quotes. Please note that the escape character will
 * still be in the resulting StringView
 */
StringView GenericLexer::consume_quoted_string(char escape_char)
{
    if (!next_is(is_quote))
        return {};

    char quote_char = consume();
    size_t start = m_index;
    while (!is_eof()) {
        if (next_is(escape_char))
            m_index++;
        else if (next_is(quote_char))
            break;
        m_index++;
    }
    size_t length = m_index - start;

    if (peek() != quote_char) {
        // Restore the index in case the string is unterminated
        m_index = start - 1;
        return {};
    }

    // Ignore closing quote
    ignore();

    return m_input.substring_view(start, length);
}

String GenericLexer::consume_and_unescape_string(char escape_char)
{
    auto view = consume_quoted_string(escape_char);
    if (view.is_null())
        return {};

    StringBuilder builder;
    for (size_t i = 0; i < view.length(); ++i)
        builder.append(consume_escaped_character(escape_char));
    return builder.to_string();
}

char GenericLexer::consume_escaped_character(char escape_char, const StringView& escape_map)
{
    if (!consume_specific(escape_char))
        return consume();

    auto c = consume();

    for (size_t i = 0; i < escape_map.length(); i += 2) {
        if (c == escape_map[i])
            return escape_map[i + 1];
    }

    return c;
}

// Ignore a number of characters (1 by default)
void GenericLexer::ignore(size_t count)
{
    count = min(count, m_input.length() - m_index);
    m_index += count;
}

// Ignore characters until `stop` is peek'd
// The `stop` character is ignored as it is user-defined
void GenericLexer::ignore_until(char stop)
{
    while (!is_eof() && peek() != stop)
        m_index++;

    ignore();
}

// Ignore characters until the string `stop` is found
// The `stop` string is ignored, as it is user-defined
void GenericLexer::ignore_until(const char* stop)
{
    while (!is_eof() && !next_is(stop))
        m_index++;

    ignore(__builtin_strlen(stop));
}

}