/*

 * Copyright (c) 2018-2023, Andreas Kling <kling@serenityos.org>

 * Copyright (c) 2022, Adam Hodgen <ant1441@gmail.com>

 * Copyright (c) 2022, Andrew Kaster <akaster@serenityos.org>

 * Copyright (c) 2023, Shannon Booth <shannon@serenityos.org>

 * Copyright (c) 2023, stelar7 <dudedbz@gmail.com>

 *

 * SPDX-License-Identifier: BSD-2-Clause

 */

#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#parse-a-date-string

WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::Date>> parse_date_string(JS::Realm& realm, StringView value)

{

    // FIXME: Implement spec compliant date string parsing

    auto parts = value.split_view('-', SplitBehavior::KeepEmpty);

    if (parts.size() >= 3) {

        if (auto year = parts.at(0).to_number<u32>(); year.has_value()) {

            if (auto month = parts.at(1).to_number<u32>(); month.has_value()) {

                if (auto day_of_month = parts.at(2).to_number<u32>(); day_of_month.has_value())

                    return JS::Date::create(realm, JS::make_date(JS::make_day(*year, *month - 1, *day_of_month), 0));

            }

        }

    }

    return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Can't parse date string"sv };

}

// 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<JS::NonnullGCPtr<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 };

}

}