ladybird/Libraries/LibWeb/HTML/Dates.cpp

/*
 * Copyright (c) 2018-2023, Andreas Kling <andreas@ladybird.org>
 * Copyright (c) 2022, Adam Hodgen <ant1441@gmail.com>
 * Copyright (c) 2022, Andrew Kaster <akaster@serenityos.org>
 * Copyright (c) 2023-2025, Shannon Booth <shannon@serenityos.org>
 * Copyright (c) 2023, stelar7 <dudedbz@gmail.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/GenericLexer.h>
#include <AK/Time.h>
#include <LibWeb/HTML/Dates.h>

namespace Web::HTML {

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#week-number-of-the-last-day
u32 week_number_of_the_last_day(u64 year)
{
    // https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#weeks
    // NOTE: A year is considered to have 53 weeks if either of the following conditions are satisfied:
    // - January 1 of that year is a Thursday.
    // - January 1 of that year is a Wednesday and the year is divisible by 400, or divisible by 4, but not 100.

    // Note: Gauss's algorithm for determining the day of the week with D = 1, and M = 0
    // https://en.wikipedia.org/wiki/Determination_of_the_day_of_the_week#Gauss's_algorithm
    u8 day_of_week = (1 + 5 * ((year - 1) % 4) + 4 * ((year - 1) % 100) + 6 * ((year - 1) % 400)) % 7;

    if (day_of_week == 4 || (day_of_week == 3 && (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0))))
        return 53;

    return 52;
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#valid-week-string
bool is_valid_week_string(StringView value)
{
    // A string is a valid week string representing a week-year year and week week if it consists of the following components in the given order:

    // 1. Four or more ASCII digits, representing year, where year > 0
    // 2. A U+002D HYPHEN-MINUS character (-)
    // 3. A U+0057 LATIN CAPITAL LETTER W character (W)
    // 4. Two ASCII digits, representing the week week, in the range 1 ≤ week ≤ maxweek, where maxweek is the week number of the last day of week-year year
    auto parts = value.split_view('-', SplitBehavior::KeepEmpty);
    if (parts.size() != 2)
        return false;
    if (parts[0].length() < 4)
        return false;
    for (auto digit : parts[0])
        if (!is_ascii_digit(digit))
            return false;
    if (parts[1].length() != 3)
        return false;

    if (!parts[1].starts_with('W'))
        return false;
    if (!is_ascii_digit(parts[1][1]))
        return false;
    if (!is_ascii_digit(parts[1][2]))
        return false;

    u64 year = 0;
    for (auto d : parts[0]) {
        year *= 10;
        year += parse_ascii_digit(d);
    }
    auto week = (parse_ascii_digit(parts[1][1]) * 10) + parse_ascii_digit(parts[1][2]);

    return week >= 1 && week <= week_number_of_the_last_day(year);
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#valid-month-string
bool is_valid_month_string(StringView value)
{
    // A string is a valid month string representing a year year and month month if it consists of the following components in the given order:

    // 1. Four or more ASCII digits, representing year, where year > 0
    // 2. A U+002D HYPHEN-MINUS character (-)
    // 3. Two ASCII digits, representing the month month, in the range 1 ≤ month ≤ 12

    auto parts = value.split_view('-', SplitBehavior::KeepEmpty);
    if (parts.size() != 2)
        return false;

    if (parts[0].length() < 4)
        return false;
    for (auto digit : parts[0])
        if (!is_ascii_digit(digit))
            return false;

    if (parts[1].length() != 2)
        return false;

    if (!is_ascii_digit(parts[1][0]))
        return false;
    if (!is_ascii_digit(parts[1][1]))
        return false;

    auto month = (parse_ascii_digit(parts[1][0]) * 10) + parse_ascii_digit(parts[1][1]);
    return month >= 1 && month <= 12;
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#valid-date-string
bool is_valid_date_string(StringView value)
{
    // A string is a valid date string representing a year year, month month, and day day if it consists of the following components in the given order:

    // 1. A valid month string, representing year and month
    // 2. A U+002D HYPHEN-MINUS character (-)
    // 3. Two ASCII digits, representing day, in the range 1 ≤ day ≤ maxday where maxday is the number of days in the month month and year year
    auto parts = value.split_view('-', SplitBehavior::KeepEmpty);
    if (parts.size() != 3)
        return false;

    if (!is_valid_month_string(ByteString::formatted("{}-{}", parts[0], parts[1])))
        return false;

    if (parts[2].length() != 2)
        return false;

    i64 year = 0;
    for (auto d : parts[0]) {
        year *= 10;
        year += parse_ascii_digit(d);
    }
    auto month = (parse_ascii_digit(parts[1][0]) * 10) + parse_ascii_digit(parts[1][1]);
    i64 day = (parse_ascii_digit(parts[2][0]) * 10) + parse_ascii_digit(parts[2][1]);

    return day >= 1 && day <= AK::days_in_month(year, month);
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#valid-local-date-and-time-string
bool is_valid_local_date_and_time_string(StringView value)
{
    auto parts_split_by_T = value.split_view('T', SplitBehavior::KeepEmpty);
    if (parts_split_by_T.size() == 2)
        return is_valid_date_string(parts_split_by_T[0]) && is_valid_time_string(parts_split_by_T[1]);
    auto parts_split_by_space = value.split_view(' ', SplitBehavior::KeepEmpty);
    if (parts_split_by_space.size() == 2)
        return is_valid_date_string(parts_split_by_space[0]) && is_valid_time_string(parts_split_by_space[1]);

    return false;
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#valid-normalised-local-date-and-time-string
String normalize_local_date_and_time_string(String const& value)
{
    if (auto spaces = value.count(" "sv); spaces > 0) {
        VERIFY(spaces == 1);
        return MUST(value.replace(" "sv, "T"sv, ReplaceMode::FirstOnly));
    }

    VERIFY(value.count("T"sv) == 1);
    return value;
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#valid-time-string
bool is_valid_time_string(StringView value)
{
    // A string is a valid time string representing an hour hour, a minute minute, and a second second if it consists of the following components in the given order:

    // 1. Two ASCII digits, representing hour, in the range 0 ≤ hour ≤ 23
    // 2. A U+003A COLON character (:)
    // 3. Two ASCII digits, representing minute, in the range 0 ≤ minute ≤ 59
    // 4. If second is nonzero, or optionally if second is zero:
    // 1. A U+003A COLON character (:)
    // 2. Two ASCII digits, representing the integer part of second, in the range 0 ≤ s ≤ 59
    // 3. If second is not an integer, or optionally if second is an integer:
    // 1. A U+002E FULL STOP character (.)
    // 2. One, two, or three ASCII digits, representing the fractional part of second
    auto parts = value.split_view(':', SplitBehavior::KeepEmpty);
    if (parts.size() != 2 && parts.size() != 3)
        return false;
    if (parts[0].length() != 2)
        return false;
    if (!(is_ascii_digit(parts[0][0]) && is_ascii_digit(parts[0][1])))
        return false;
    auto hour = (parse_ascii_digit(parts[0][0]) * 10) + parse_ascii_digit(parts[0][1]);
    if (hour > 23)
        return false;
    if (parts[1].length() != 2)
        return false;
    if (!(is_ascii_digit(parts[1][0]) && is_ascii_digit(parts[1][1])))
        return false;
    auto minute = (parse_ascii_digit(parts[1][0]) * 10) + parse_ascii_digit(parts[1][1]);
    if (minute > 59)
        return false;
    if (parts.size() == 2)
        return true;

    if (parts[2].length() < 2)
        return false;
    if (!(is_ascii_digit(parts[2][0]) && is_ascii_digit(parts[2][1])))
        return false;
    auto second = (parse_ascii_digit(parts[2][0]) * 10) + parse_ascii_digit(parts[2][1]);
    if (second > 59)
        return false;
    if (parts[2].length() == 2)
        return true;
    auto second_parts = parts[2].split_view('.', SplitBehavior::KeepEmpty);
    if (second_parts.size() != 2)
        return false;
    if (second_parts[1].length() < 1 || second_parts[1].length() > 3)
        return false;
    for (auto digit : second_parts[1])
        if (!is_ascii_digit(digit))
            return false;

    return true;
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-time-string
WebIDL::ExceptionOr<GC::Ref<JS::Date>> parse_time_string(JS::Realm& realm, StringView value)
{
    // FIXME: Implement spec compliant time string parsing
    auto parts = value.split_view(':', SplitBehavior::KeepEmpty);
    if (parts.size() >= 2) {
        if (auto hours = parts.at(0).to_number<u32>(); hours.has_value()) {
            if (auto minutes = parts.at(1).to_number<u32>(); minutes.has_value()) {
                if (parts.size() >= 3) {
                    if (auto seconds = parts.at(2).to_number<u32>(); seconds.has_value())
                        return JS::Date::create(realm, JS::make_time(*hours, *minutes, *seconds, 0));
                }
                return JS::Date::create(realm, JS::make_date(0, JS::make_time(*hours, *minutes, 0, 0)));
            }
        }
    }
    return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Can't parse time string"sv };
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-month-component
static Optional<YearAndMonth> parse_a_month_component(GenericLexer& input)
{
    // 1. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is
    //    not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer.
    //    Let that number be the year.
    auto year_string = input.consume_while(is_ascii_digit);
    if (year_string.length() < 4)
        return {};
    auto maybe_year = year_string.to_number<u32>();
    if (!maybe_year.has_value())
        return {};
    auto year = maybe_year.value();

    // 2. If year is not a number greater than zero, then fail.
    if (year < 1)
        return {};

    // 3. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then
    //    fail. Otherwise, move position forwards one character.
    if (!input.consume_specific('-'))
        return {};

    // 4. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not
    //    exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that
    //    number be the month.
    auto month_string = input.consume_while(is_ascii_digit);
    if (month_string.length() != 2)
        return {};
    auto month = month_string.to_number<u32>().value();

    // 5. If month is not a number in the range 1 ≤ month ≤ 12, then fail.
    if (month < 1 || month > 12)
        return {};

    // 6. Return year and month.
    return YearAndMonth { year, month };
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-month-string
Optional<YearAndMonth> parse_a_month_string(StringView input_view)
{
    // 1. Let input be the string being parsed.
    // 2. Let position be a pointer into input, initially pointing at the start of the string.
    GenericLexer input { input_view };

    // 3. Parse a month component to obtain year and month. If this returns nothing, then fail.
    auto year_and_month = parse_a_month_component(input);
    if (!year_and_month.has_value())
        return {};

    // 4. If position is not beyond the end of input, then fail.
    if (!input.is_eof())
        return {};

    // 5. Return year and month.
    return year_and_month;
}

i32 number_of_months_since_unix_epoch(YearAndMonth year_and_month)
{
    return (year_and_month.year - 1970) * 12 + year_and_month.month - 1;
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-week-string
Optional<WeekYearAndWeek> parse_a_week_string(StringView input_view)
{
    // 1. Let input be the string being parsed.
    // 2. Let position be a pointer into input, initially pointing at the start of the string.
    GenericLexer input { input_view };

    // 3. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is
    //    not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer.
    //    Let that number be the year.
    auto year_string = input.consume_while(is_ascii_digit);
    if (year_string.length() < 4)
        return {};
    auto maybe_year = year_string.to_number<u32>();
    if (!maybe_year.has_value())
        return {};
    auto year = maybe_year.value();

    // 4. If year is not a number greater than zero, then fail.
    if (year < 1)
        return {};

    // 5. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then
    //    fail. Otherwise, move position forwards one character.
    if (!input.consume_specific('-'))
        return {};

    // 6. If position is beyond the end of input or if the character at position is not a U+0057 LATIN CAPITAL LETTER W character
    //    (W), then fail. Otherwise, move position forwards one character.
    if (!input.consume_specific('W'))
        return {};

    // 7. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not
    //    exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that
    //    number be the week.
    auto week_string = input.consume_while(is_ascii_digit);
    if (week_string.length() != 2)
        return {};
    auto week = week_string.to_number<u32>().value();

    // 8. Let maxweek be the week number of the last day of year year.
    auto maxweek = week_number_of_the_last_day(year);

    // 9. If week is not a number in the range 1 ≤ week ≤ maxweek, then fail.
    if (week < 1 || week > maxweek)
        return {};

    // 10. If position is not beyond the end of input, then fail.
    if (!input.is_eof())
        return {};

    // 11. Return the week-year number year and the week number week.
    return WeekYearAndWeek { year, week };
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-date-component
static Optional<YearMonthDay> parse_a_date_component(GenericLexer& input)
{
    // 1. Parse a month component to obtain year and month. If this returns nothing, then fail.
    auto maybe_month_component = parse_a_month_component(input);
    if (!maybe_month_component.has_value())
        return {};
    auto month_component = maybe_month_component.value();

    // 2. Let maxday be the number of days in month month of year year.
    u32 maxday = AK::days_in_month(month_component.year, month_component.month);

    // 3. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail.
    //    Otherwise, move position forwards one character.
    if (!input.consume_specific('-'))
        return {};

    // 4. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not
    //    exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that
    //    number be the day.
    auto day_string = input.consume_while(is_ascii_digit);
    if (day_string.length() != 2)
        return {};
    auto day = day_string.to_number<u32>().value();

    // 5. If day is not a number in the range 1 ≤ day ≤ maxday, then fail.
    if (day < 1 || day > maxday)
        return {};

    // 6. Return year, month, and day.
    return YearMonthDay { month_component.year, month_component.month, day };
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-date-string
Optional<YearMonthDay> parse_a_date_string(StringView input_view)
{
    // 1. Let input be the string being parsed.
    // 2. Let position be a pointer into input, initially pointing at the start of the string.
    GenericLexer input { input_view };

    // 3. Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
    auto year_month_day = parse_a_date_component(input);
    if (!year_month_day.has_value())
        return {};

    // 4. If position is not beyond the end of input, then fail.
    if (!input.is_eof())
        return {};

    // 5. Let date be the date with year year, month month, and day day.
    // 6. Return date.
    return year_month_day.release_value();
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-time-component
static Optional<HourMinuteSecond> parse_a_time_component(GenericLexer& input)
{
    // 1. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence
    //    is not exactly two characters long, then fail.  Otherwise, interpret the resulting sequence as a base-ten
    //    integer. Let that number be the hour.
    auto hour_string = input.consume_while(is_ascii_digit);
    if (hour_string.length() != 2)
        return {};
    auto maybe_hour = hour_string.to_number<i32>();
    if (!maybe_hour.has_value())
        return {};
    auto hour = maybe_hour.value();

    // 2. If hour is not a number in the range 0 ≤ hour ≤ 23, then fail.
    if (hour < 0 || hour > 23)
        return {};

    // 3. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then
    //    fail. Otherwise, move position forwards one character.
    if (!input.consume_specific(':'))
        return {};

    // 4. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence
    //    is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer.
    //    Let that number be the minute.
    auto minute_string = input.consume_while(is_ascii_digit);
    if (minute_string.length() != 2)
        return {};
    auto maybe_minute = minute_string.to_number<i32>();
    if (!maybe_minute.has_value())
        return {};
    auto minute = maybe_minute.value();

    // 5. If minute is not a number in the range 0 ≤ minute ≤ 59, then fail.
    if (minute < 0 || hour > 59)
        return {};

    // 6. Let second be 0.
    i32 second = 0;

    // 7. If position is not beyond the end of input and the character at position is U+003A (:), then:
    if (input.consume_specific(':')) {
        // 1. Advance position to the next character in input.
        // 2. If position is beyond the end of input, or at the last character in input, or if the next two characters in
        //    input starting at position are not both ASCII digits, then fail.
        if (input.is_eof() || input.tell_remaining() == 1 || (!is_ascii_digit(input.peek()) && !is_ascii_digit(input.peek(1))))
            return {};

        // 3. Collect a sequence of code points that are either ASCII digits or U+002E FULL STOP characters from input
        //    given position.
        auto second_string = input.consume_while([](auto ch) { return is_ascii_digit(ch) || ch == '.'; });
        // If the collected sequence is three characters long, or if it is longer than three characters long and the third
        // character is not a U+002E FULL STOP character, or if it has more than one U+002E FULL STOP character, then fail.
        if (second_string.length() == 3)
            return {};
        if (second_string.length() > 3 && second_string[2] != '.')
            return {};
        if (second_string.find_all("."sv).size() > 1)
            return {};
        // Otherwise, interpret the resulting sequence as a base-ten number (possibly with a fractional part). Set second
        // to that number.
        // NB: The spec doesn't state requirements for what we must do with the fractional part of the second(s) string.
        //     The spec neither requires that we separately preserve it nor requires that we completely discard it. If we
        //     did have any reason at all to preserve it, we could parse the string into a float here. But there doesn't
        //     seem to be any point in doing that, because there’s nothing in the corresponding calling algorithm(s) in the
        //     spec that takes a milliseconds field and does anything with it anyway.
        auto maybe_second = second_string.to_number<i32>();
        if (!maybe_second.has_value())
            return {};
        second = maybe_second.value();

        // 4. If second is not a number in the range 0 ≤ second < 60, then fail.
        if (second < 0 || second > 60)
            return {};
    }

    // 8. Return hour, minute, and second.
    return HourMinuteSecond { hour, minute, second };
}

// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-local-date-and-time-string
Optional<DateAndTime> parse_a_local_date_and_time_string(StringView input_view)
{
    // 1. Let input be the string being parsed.
    // 2. Let position be a pointer into input, initially pointing at the start of the string.
    GenericLexer input { input_view };
    // 3. Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
    auto year_month_day = parse_a_date_component(input);
    if (!year_month_day.has_value())
        return {};
    // 4. If position is beyond the end of input or if the character at position is neither a U+0054 LATIN CAPITAL
    //    LETTER T character (T) nor a U+0020 SPACE character, then fail. Otherwise, move position forwards one character.
    if (!input.consume_specific("T") && !input.consume_specific(" "))
        return {};
    // 5. Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
    auto hour_minute_second = parse_a_time_component(input);
    if (!hour_minute_second.has_value())
        return {};
    // 6. If position is not beyond the end of input, then fail.
    if (!input.is_eof())
        return {};
    // 7. Let date be the date with year year, month month, and day day.
    // 8. Let time be the time with hour hour, minute minute, and second second.
    // 9. Return date and time.
    return DateAndTime { year_month_day.release_value(), hour_minute_second.release_value() };
}

}