text: /*
   * Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #include <LibJS/Runtime/AbstractOperations.h>
  #include <LibJS/Runtime/Array.h>
  #include <LibJS/Runtime/GlobalObject.h>
  #include <LibJS/Runtime/Temporal/AbstractOperations.h>
  #include <LibJS/Runtime/Temporal/Calendar.h>
  #include <LibJS/Runtime/Temporal/CalendarConstructor.h>
  #include <LibJS/Runtime/Temporal/PlainDate.h>
  #include <LibJS/Runtime/Temporal/PlainDateTime.h>
  #include <LibJS/Runtime/Temporal/PlainTime.h>
  #include <LibJS/Runtime/Temporal/ZonedDateTime.h>
  #include <LibJS/Runtime/Value.h>
  
  namespace JS::Temporal {
  
  // 12 Temporal.Calendar Objects, https://tc39.es/proposal-temporal/#sec-temporal-calendar-objects
  Calendar::Calendar(String identifier, Object& prototype)
      : Object(prototype)
      , m_identifier(move(identifier))
  {
  }
  
  // 12.1.1 CreateTemporalCalendar ( identifier [ , newTarget ] ), https://tc39.es/proposal-temporal/#sec-temporal-createtemporalcalendar
  Calendar* create_temporal_calendar(GlobalObject& global_object, String const& identifier, FunctionObject* new_target)
  {
      auto& vm = global_object.vm();
  
      // 1. Assert: ! IsBuiltinCalendar(identifier) is true.
      VERIFY(is_builtin_calendar(identifier));
  
      // 2. If newTarget is not provided, set newTarget to %Temporal.Calendar%.
      if (!new_target)
          new_target = global_object.temporal_calendar_constructor();
  
      // 3. Let object be ? OrdinaryCreateFromConstructor(newTarget, "%Temporal.Calendar.prototype%", « [[InitializedTemporalCalendar]], [[Identifier]] »).
      // 4. Set object.[[Identifier]] to identifier.
      auto* object = ordinary_create_from_constructor<Calendar>(global_object, *new_target, &GlobalObject::temporal_calendar_prototype, identifier);
      if (vm.exception())
          return {};
  
      // 5. Return object.
      return object;
  }
  
  // 12.1.2 IsBuiltinCalendar ( id ), https://tc39.es/proposal-temporal/#sec-temporal-isbuiltincalendar
  // NOTE: This is the minimum IsBuiltinCalendar implementation for engines without ECMA-402.
  bool is_builtin_calendar(String const& identifier)
  {
      // 1. If id is not "iso8601", return false.
      if (identifier != "iso8601"sv)
          return false;
  
      // 2. Return true.
      return true;
  }
  
  // 12.1.3 GetBuiltinCalendar ( id )
  Calendar* get_builtin_calendar(GlobalObject& global_object, String const& identifier)
  {
      auto& vm = global_object.vm();
  
      // 1. If ! IsBuiltinCalendar(id) is false, throw a RangeError exception.
      if (!is_builtin_calendar(identifier)) {
          vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidCalendarIdentifier, identifier);
          return {};
      }
  
      // 2. Return ? Construct(%Temporal.Calendar%, « id »).
      MarkedValueList arguments(vm.heap());
      arguments.append(js_string(vm, identifier));
      auto calendar = vm.construct(*global_object.temporal_calendar_constructor(), *global_object.temporal_calendar_constructor(), move(arguments));
      if (vm.exception())
          return {};
      return static_cast<Calendar*>(&calendar.as_object());
  }
  
  // 12.1.4 GetISO8601Calendar ( )
  Calendar* get_iso8601_calendar(GlobalObject& global_object)
  {
      // 1. Return ! GetBuiltinCalendar("iso8601").
      return get_builtin_calendar(global_object, "iso8601");
  }
  
  // 12.1.5 CalendarFields ( calendar, fieldNames ), https://tc39.es/proposal-temporal/#sec-temporal-calendarfields
  Vector<String> calendar_fields(GlobalObject& global_object, Object& calendar, Vector<StringView> const& field_names)
  {
      auto& vm = global_object.vm();
  
      // 1. Let fields be ? GetMethod(calendar, "fields").
      auto fields = Value(&calendar).get_method(global_object, vm.names.fields);
      if (vm.exception())
          return {};
  
      // 2. Let fieldsArray be ! CreateArrayFromList(fieldNames).
      Vector<Value> field_names_values;
      for (auto& field_name : field_names)
          field_names_values.append(js_string(vm, field_name));
      Value fields_array = Array::create_from(global_object, field_names_values);
  
      // 3. If fields is not undefined, then
      if (fields) {
          // a. Set fieldsArray to ? Call(fields, calendar, « fieldsArray »).
          fields_array = vm.call(*fields, &calendar, fields_array);
          if (vm.exception())
              return {};
      }
  
      // 4. Return ? IterableToListOfType(fieldsArray, « String »).
      auto list = iterable_to_list_of_type(global_object, fields_array, { OptionType::String });
      if (vm.exception())
          return {};
  
      Vector<String> result;
      for (auto& value : list)
          result.append(value.as_string().string());
      return result;
  }
  
  // 12.1.9 CalendarYear ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendaryear
  double calendar_year(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Let result be ? Invoke(calendar, "year", « dateLike »).
      auto result = calendar.invoke(vm.names.year, &date_like);
      if (vm.exception())
          return {};
  
      // 3. If result is undefined, throw a RangeError exception.
      if (result.is_undefined()) {
          vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidCalendarFunctionResult, vm.names.year.as_string());
          return {};
      }
  
      // 4. Return ? ToIntegerOrInfinity(result).
      return result.to_integer_or_infinity(global_object);
  }
  
  // 12.1.10 CalendarMonth ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendarmonth
  double calendar_month(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Let result be ? Invoke(calendar, "month", « dateLike »).
      auto result = calendar.invoke(vm.names.month, &date_like);
      if (vm.exception())
          return {};
  
      // 3. If result is undefined, throw a RangeError exception.
      if (result.is_undefined()) {
          vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidCalendarFunctionResult, vm.names.month.as_string());
          return {};
      }
  
      // 4. Return ? ToPositiveIntegerOrInfinity(result).
      return to_positive_integer_or_infinity(global_object, result);
  }
  
  // 12.1.11 CalendarMonthCode ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendarmonthcode
  String calendar_month_code(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Let result be ? Invoke(calendar, "monthCode", « dateLike »).
      auto result = calendar.invoke(vm.names.monthCode, &date_like);
      if (vm.exception())
          return {};
  
      // 3. If result is undefined, throw a RangeError exception.
      if (result.is_undefined()) {
          vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidCalendarFunctionResult, vm.names.monthCode.as_string());
          return {};
      }
  
      // 4. Return ? ToString(result).
      return result.to_string(global_object);
  }
  
  // 12.1.12 CalendarDay ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendarday
  double calendar_day(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Let result be ? Invoke(calendar, "day", « dateLike »).
      auto result = calendar.invoke(vm.names.day, &date_like);
      if (vm.exception())
          return {};
  
      // 3. If result is undefined, throw a RangeError exception.
      if (result.is_undefined()) {
          vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidCalendarFunctionResult, vm.names.day.as_string());
          return {};
      }
  
      // 4. Return ? ToPositiveIntegerOrInfinity(result).
      return to_positive_integer_or_infinity(global_object, result);
  }
  
  // 12.1.13 CalendarDayOfWeek ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendardayofweek
  Value calendar_day_of_week(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Return ? Invoke(calendar, "dayOfWeek", « dateLike »).
      return calendar.invoke(vm.names.dayOfWeek, &date_like);
  }
  
  // 12.1.14 CalendarDayOfYear ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendardayofyear
  Value calendar_day_of_year(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Return ? Invoke(calendar, "dayOfYear", « dateLike »).
      return calendar.invoke(vm.names.dayOfYear, &date_like);
  }
  
  // 12.1.15 CalendarWeekOfYear ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendarweekofyear
  Value calendar_week_of_year(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Return ? Invoke(calendar, "weekOfYear", « dateLike »).
      return calendar.invoke(vm.names.weekOfYear, &date_like);
  }
  
  // 12.1.16 CalendarDaysInWeek ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendardaysinweek
  Value calendar_days_in_week(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Return ? Invoke(calendar, "daysInWeek", « dateLike »).
      return calendar.invoke(vm.names.daysInWeek, &date_like);
  }
  
  // 12.1.17 CalendarDaysInMonth ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendardaysinmonth
  Value calendar_days_in_month(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Return ? Invoke(calendar, "daysInMonth", « dateLike »).
      return calendar.invoke(vm.names.daysInMonth, &date_like);
  }
  
  // 12.1.18 CalendarDaysInYear ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendardaysinyear
  Value calendar_days_in_year(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Return ? Invoke(calendar, "daysInYear", « dateLike »).
      return calendar.invoke(vm.names.daysInYear, &date_like);
  }
  
  // 12.1.19 CalendarMonthsInYear ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendarmonthsinyear
  Value calendar_months_in_year(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Return ? Invoke(calendar, "monthsInYear", « dateLike »).
      return calendar.invoke(vm.names.monthsInYear, &date_like);
  }
  
  // 12.1.20 CalendarInLeapYear ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendarinleapyear
  Value calendar_in_leap_year(GlobalObject& global_object, Object& calendar, Object& date_like)
  {
      auto& vm = global_object.vm();
      // 1. Assert: Type(calendar) is Object.
  
      // 2. Return ? Invoke(calendar, "inLeapYear", « dateLike »).
      return calendar.invoke(vm.names.inLeapYear, &date_like);
  }
  
  // 12.1.21 ToTemporalCalendar ( temporalCalendarLike ), https://tc39.es/proposal-temporal/#sec-temporal-totemporalcalendar
  Object* to_temporal_calendar(GlobalObject& global_object, Value temporal_calendar_like)
  {
      auto& vm = global_object.vm();
  
      // 1. If Type(temporalCalendarLike) is Object, then
      if (temporal_calendar_like.is_object()) {
          auto& temporal_calendar_like_object = temporal_calendar_like.as_object();
          // a. If temporalCalendarLike has an [[InitializedTemporalDate]], [[InitializedTemporalDateTime]], [[InitializedTemporalMonthDay]], [[InitializedTemporalTime]], [[InitializedTemporalYearMonth]], or [[InitializedTemporalZonedDateTime]] internal slot, then
          // i. Return temporalCalendarLike.[[Calendar]].
          if (is<PlainDate>(temporal_calendar_like_object))
              return &static_cast<PlainDate&>(temporal_calendar_like_object).calendar();
          if (is<PlainDateTime>(temporal_calendar_like_object))
              return &static_cast<PlainDateTime&>(temporal_calendar_like_object).calendar();
          if (is<PlainTime>(temporal_calendar_like_object))
              return &static_cast<PlainTime&>(temporal_calendar_like_object).calendar();
          if (is<ZonedDateTime>(temporal_calendar_like_object))
              return &static_cast<ZonedDateTime&>(temporal_calendar_like_object).calendar();
          // TODO: The rest of the Temporal built-ins (PlainMonthDay, PlainYearMonth)
  
          // b. If ? HasProperty(temporalCalendarLike, "calendar") is false, return temporalCalendarLike.
          auto has_property = temporal_calendar_like_object.has_property(vm.names.calendar);
          if (vm.exception())
              return {};
          if (!has_property)
              return &temporal_calendar_like_object;
  
          // c. Set temporalCalendarLike to ? Get(temporalCalendarLike, "calendar").
          temporal_calendar_like = temporal_calendar_like_object.get(vm.names.calendar);
          if (vm.exception())
              return {};
          // d. If Type(temporalCalendarLike) is Object and ? HasProperty(temporalCalendarLike, "calendar") is false, return temporalCalendarLike.
          if (temporal_calendar_like.is_object()) {
              has_property = temporal_calendar_like.as_object().has_property(vm.names.calendar);
              if (vm.exception())
                  return {};
              if (!has_property)
                  return &temporal_calendar_like.as_object();
          }
      }
  
      // 2. Let identifier be ? ToString(temporalCalendarLike).
      auto identifier = temporal_calendar_like.to_string(global_object);
      if (vm.exception())
          return {};
  
      // 3. If ! IsBuiltinCalendar(identifier) is false, then
      if (!is_builtin_calendar(identifier)) {
          // a. Let identifier be ? ParseTemporalCalendarString(identifier).
          auto parsed_identifier = parse_temporal_calendar_string(global_object, identifier);
          if (vm.exception())
              return {};
          identifier = move(*parsed_identifier);
      }
  
      // 4. Return ! CreateTemporalCalendar(identifier).
      return create_temporal_calendar(global_object, identifier);
  }
  
  // 12.1.22 ToTemporalCalendarWithISODefault ( temporalCalendarLike ), https://tc39.es/proposal-temporal/#sec-temporal-totemporalcalendarwithisodefault
  Object* to_temporal_calendar_with_iso_default(GlobalObject& global_object, Value temporal_calendar_like)
  {
      // 1. If temporalCalendarLike is undefined, then
      if (temporal_calendar_like.is_undefined()) {
          // a. Return ! GetISO8601Calendar().
          return get_iso8601_calendar(global_object);
      }
      // 2. Return ? ToTemporalCalendar(temporalCalendarLike).
      return to_temporal_calendar(global_object, temporal_calendar_like);
  }
  
  // 12.1.23 GetTemporalCalendarWithISODefault ( item ), https://tc39.es/proposal-temporal/#sec-temporal-gettemporalcalendarwithisodefault
  Object* get_temporal_calendar_with_iso_default(GlobalObject& global_object, Object& item)
  {
      auto& vm = global_object.vm();
  
      // 1. If item has an [[InitializedTemporalDate]], [[InitializedTemporalDateTime]], [[InitializedTemporalMonthDay]], [[InitializedTemporalTime]], [[InitializedTemporalYearMonth]], or [[InitializedTemporalZonedDateTime]] internal slot, then
      // a. Return item.[[Calendar]].
      if (is<PlainDate>(item))
          return &static_cast<PlainDate&>(item).calendar();
      if (is<PlainDateTime>(item))
          return &static_cast<PlainDateTime&>(item).calendar();
      if (is<PlainTime>(item))
          return &static_cast<PlainTime&>(item).calendar();
      if (is<ZonedDateTime>(item))
          return &static_cast<ZonedDateTime&>(item).calendar();
      // TODO: The rest of the Temporal built-ins (PlainMonthDay, PlainYearMonth)
  
      // 2. Let calendar be ? Get(item, "calendar").
      auto calendar = item.get(vm.names.calendar);
      if (vm.exception())
          return {};
  
      // 3. Return ? ToTemporalCalendarWithISODefault(calendar).
      return to_temporal_calendar_with_iso_default(global_object, calendar);
  }
  
  // 12.1.24 DateFromFields ( calendar, fields, options ), https://tc39.es/proposal-temporal/#sec-temporal-datefromfields
  PlainDate* date_from_fields(GlobalObject& global_object, Object& calendar, Object& fields, Object& options)
  {
      auto& vm = global_object.vm();
  
      // 1. Assert: Type(calendar) is Object.
      // 2. Assert: Type(fields) is Object.
  
      // 3. Let date be ? Invoke(calendar, "dateFromFields", « fields, options »).
      auto date = calendar.invoke(vm.names.dateFromFields, &fields, &options);
      if (vm.exception())
          return {};
  
      // 4. Perform ? RequireInternalSlot(date, [[InitializedTemporalDate]]).
      auto* date_object = date.to_object(global_object);
      if (!date_object)
          return {};
      if (!is<PlainDate>(date_object)) {
          vm.throw_exception<TypeError>(global_object, ErrorType::NotA, "Temporal.PlainDate");
          return {};
      }
  
      // 5. Return date.
      return static_cast<PlainDate*>(date_object);
  }
  
  // 12.1.28 CalendarEquals ( one, two ), https://tc39.es/proposal-temporal/#sec-temporal-calendarequals
  bool calendar_equals(GlobalObject& global_object, Object& one, Object& two)
  {
      auto& vm = global_object.vm();
  
      // 1. If one and two are the same Object value, return true.
      if (&one == &two)
          return true;
  
      // 2. Let calendarOne be ? ToString(one).
      auto calendar_one = Value(&one).to_string(global_object);
      if (vm.exception())
          return {};
      // 3. Let calendarTwo be ? ToString(two).
      auto calendar_two = Value(&two).to_string(global_object);
      if (vm.exception())
          return {};
  
      // 4. If calendarOne is calendarTwo, return true.
      if (calendar_one == calendar_two)
          return true;
      // 5. Return false.
      return false;
  }
  
  // 12.1.29 ConsolidateCalendars ( one, two ), https://tc39.es/proposal-temporal/#sec-temporal-consolidatecalendars
  Object* consolidate_calendars(GlobalObject& global_object, Object& one, Object& two)
  {
      auto& vm = global_object.vm();
      // 1. If one and two are the same Object value, return two.
      if (&one == &two)
          return &two;
  
      // 2. Let calendarOne be ? ToString(one).
      auto calendar_one = Value(&one).to_string(global_object);
      if (vm.exception())
          return {};
  
      // 3. Let calendarTwo be ? ToString(two).
      auto calendar_two = Value(&two).to_string(global_object);
      if (vm.exception())
          return {};
  
      // 4. If calendarOne is calendarTwo, return two.
      if (calendar_one == calendar_two)
          return &two;
  
      // 5. If calendarOne is "iso8601", return two.
      if (calendar_one == "iso8601"sv)
          return &two;
  
      // 6. If calendarTwo is "iso8601", return one.
      if (calendar_two == "iso8601"sv)
          return &one;
  
      // 7. Throw a RangeError exception.
      vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidCalendar);
      return {};
  }
  
  // 12.1.30 IsISOLeapYear ( year ), https://tc39.es/proposal-temporal/#sec-temporal-isisoleapyear
  bool is_iso_leap_year(i32 year)
  {
      // 1. Assert: year is an integer.
  
      // 2. If year modulo 4 ≠ 0, return false.
      if (year % 4 != 0)
          return false;
  
      // 3. If year modulo 400 = 0, return true.
      if (year % 400 == 0)
          return true;
  
      // 4. If year modulo 100 = 0, return false.
      if (year % 100 == 0)
          return false;
  
      // 5. Return true.
      return true;
  }
  
  // 12.1.31 ISODaysInYear ( year ), https://tc39.es/proposal-temporal/#sec-temporal-isodaysinyear
  u16 iso_days_in_year(i32 year)
  {
      // 1. Assert: year is an integer.
  
      // 2. If ! IsISOLeapYear(year) is true, then
      if (is_iso_leap_year(year)) {
          // a. Return 366.
          return 366;
      }
  
      // 3. Return 365.
      return 365;
  }
  
  // 12.1.32 ISODaysInMonth ( year, month ), https://tc39.es/proposal-temporal/#sec-temporal-isodaysinmonth
  u8 iso_days_in_month(i32 year, u8 month)
  {
      // 1. Assert: year is an integer.
  
      // 2. Assert: month is an integer, month ≥ 1, and month ≤ 12.
      VERIFY(month >= 1 && month <= 12);
  
      // 3. If month is 1, 3, 5, 7, 8, 10, or 12, return 31.
      if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12)
          return 31;
  
      // 4. If month is 4, 6, 9, or 11, return 30.
      if (month == 4 || month == 6 || month == 9 || month == 11)
          return 30;
  
      // 5. If ! IsISOLeapYear(year) is true, return 29.
      if (is_iso_leap_year(year))
          return 29;
  
      // 6. Return 28.
      return 28;
  }
  
  // 12.1.33 ToISODayOfWeek ( year, month, day ), https://tc39.es/proposal-temporal/#sec-temporal-toisodayofweek
  u8 to_iso_day_of_week(i32 year, u8 month, u8 day)
  {
      // 1. Assert: year is an integer.
      // 2. Assert: month is an integer.
      // 3. Assert: day is an integer.
  
      // 4. Let date be the date given by year, month, and day.
      // 5. Return date's day of the week according to ISO-8601.
      // NOTE: Implemented based on https://cs.uwaterloo.ca/~alopez-o/math-faq/node73.html
      auto normalized_month = month + (month < 3 ? 10 : -2);
      auto normalized_year = year - (month < 3 ? 1 : 0);
      auto century = normalized_year / 100;
      auto truncated_year = normalized_year - (century * 100);
      auto result = (day + static_cast<u8>((2.6 * normalized_month) - 0.2) - (2 * century) + truncated_year + (truncated_year / 4) + (century / 4)) % 7;
      if (result <= 0) // Mathematical modulo
          result += 7;
      return result;
  }
  
  // 12.1.34 ToISODayOfYear ( year, month, day ), https://tc39.es/proposal-temporal/#sec-temporal-toisodayofyear
  u16 to_iso_day_of_year(i32 year, u8 month, u8 day)
  {
      // 1. Assert: year is an integer.
      // 2. Assert: month is an integer.
      // 3. Assert: day is an integer.
  
      // 4. Let date be the date given by year, month, and day.
      // 5. Return date's ordinal date in the year according to ISO-8601.
      u16 days = day;
      for (u8 i = month - 1; i > 0; --i)
          days += iso_days_in_month(year, i);
      return days;
  }
  
  // 12.1.35 ToISOWeekOfYear ( year, month, day ), https://tc39.es/proposal-temporal/#sec-temporal-toisoweekofyear
  u8 to_iso_week_of_year(i32 year, u8 month, u8 day)
  {
      // 1. Assert: year is an integer.
      // 2. Assert: month is an integer.
      // 3. Assert: day is an integer.
  
      // 4. Let date be the date given by year, month, and day.
      // 5. Return date's week number according to ISO-8601.
      auto day_of_year = to_iso_day_of_year(year, month, day);
      auto day_of_week = to_iso_day_of_week(year, month, day);
      auto week = (day_of_year - day_of_week + 10) / 7;
  
      if (week < 1) {
          auto day_of_jump = to_iso_day_of_week(year, 1, 1);
          if (day_of_jump == 5 || (is_iso_leap_year(year) && day_of_jump == 6))
              return 53;
          else
              return 52;
      } else if (week == 53) {
          auto days_in_year = iso_days_in_year(year);
          if (days_in_year - day_of_year < 4 - day_of_week)
              return 1;
      }
  
      return week;
  }
  
  // 12.1.36 BuildISOMonthCode ( month ), https://tc39.es/proposal-temporal/#sec-buildisomonthcode
  String build_iso_month_code(u8 month)
  {
      return String::formatted("M{:02}", month);
  }
  
  // 12.1.37 ResolveISOMonth ( fields ), https://tc39.es/proposal-temporal/#sec-temporal-resolveisomonth
  double resolve_iso_month(GlobalObject& global_object, Object& fields)
  {
      auto& vm = global_object.vm();
  
      // 1. Let month be ? Get(fields, "month").
      auto month = fields.get(vm.names.month);
      if (vm.exception())
          return {};
  
      // 2. Let monthCode be ? Get(fields, "monthCode").
      auto month_code = fields.get(vm.names.monthCode);
      if (vm.exception())
          return {};
  
      // 3. If monthCode is undefined, then
      if (month_code.is_undefined()) {
          // a. If month is undefined, throw a TypeError exception.
          if (month.is_undefined()) {
              vm.throw_exception<TypeError>(global_object, ErrorType::TemporalMissingRequiredProperty, vm.names.month.as_string());
              return {};
          }
          // b. Return month.
          return month.as_double();
      }
  
      // 4. Assert: Type(monthCode) is String.
      VERIFY(month_code.is_string());
      auto& month_code_string = month_code.as_string().string();
      // 5. Let monthLength be the length of monthCode.
      auto month_length = month_code_string.length();
      // 6. If monthLength is not 3, throw a RangeError exception.
      if (month_length != 3) {
          vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidMonthCode);
          return {};
      }
      // 7. Let numberPart be the substring of monthCode from 1.
      auto number_part = month_code_string.substring(1);
      // 8. Set numberPart to ! ToIntegerOrInfinity(numberPart).
      auto number_part_integer = Value(js_string(vm, move(number_part))).to_integer_or_infinity(global_object);
      // 9. If numberPart < 1 or numberPart > 12, throw a RangeError exception.
      if (number_part_integer < 1 || number_part_integer > 12) {
          vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidMonthCode);
          return {};
      }
      // 10. If month is not undefined, and month ≠ numberPart, then
      if (!month.is_undefined() && month.as_double() != number_part_integer) {
          // a. Throw a RangeError exception.
          vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidMonthCode);
          return {};
      }
      // 11. If ! SameValueNonNumeric(monthCode, ! BuildISOMonthCode(numberPart)) is false, then
      if (month_code_string != build_iso_month_code(number_part_integer)) {
          // a. Throw a RangeError exception.
          vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidMonthCode);
          return {};
      }
      // 12. Return numberPart.
      return number_part_integer;
  }
  
  // 12.1.38 ISODateFromFields ( fields, options ), https://tc39.es/proposal-temporal/#sec-temporal-isodatefromfields
  Optional<TemporalDate> iso_date_from_fields(GlobalObject& global_object, Object& fields, Object& options)
  {
      auto& vm = global_object.vm();
  
      // 1. Assert: Type(fields) is Object.
  
      // 2. Let overflow be ? ToTemporalOverflow(options).
      auto overflow = to_temporal_overflow(global_object, options);
      if (vm.exception())
          return {};
  
      // 3. Set fields to ? PrepareTemporalFields(fields, « "day", "month", "monthCode", "year" », «»).
      auto* prepared_fields = prepare_temporal_fields(global_object, fields, { "day", "month", "monthCode", "year" }, {});
      if (vm.exception())
          return {};
  
      // 4. Let year be ? Get(fields, "year").
      auto year = prepared_fields->get(vm.names.year);
      if (vm.exception())
          return {};
  
      // 5. If year is undefined, throw a TypeError exception.
      if (year.is_undefined()) {
          vm.throw_exception<TypeError>(global_object, ErrorType::TemporalMissingRequiredProperty, vm.names.year.as_string());
          return {};
      }
  
      // 6. Let month be ? ResolveISOMonth(fields).
      auto month = resolve_iso_month(global_object, *prepared_fields);
      if (vm.exception())
          return {};
  
      // 7. Let day be ? Get(fields, "day").
      auto day = prepared_fields->get(vm.names.day);
      if (vm.exception())
          return {};
  
      // 8. If day is undefined, throw a TypeError exception.
      if (day.is_undefined()) {
          vm.throw_exception<TypeError>(global_object, ErrorType::TemporalMissingRequiredProperty, vm.names.day.as_string());
          return {};
      }
  
      // 9. Return ? RegulateISODate(year, month, day, overflow).
      return regulate_iso_date(global_object, year.as_double(), month, day.as_double(), *overflow);
  }
  
  // 12.1.41 ISOYear ( temporalObject ), https://tc39.es/proposal-temporal/#sec-temporal-isoyear
  i32 iso_year(Object& temporal_object)
  {
      // 1. Assert: temporalObject has an [[ISOYear]] internal slot.
      // NOTE: Asserted by the VERIFY_NOT_REACHED at the end
  
      // 2. Return 𝔽(temporalObject.[[ISOYear]]).
      // TODO: add the rest of the builtins with a [[ISOYear]] slot (PlainYearMonth, PlainMonthDay)
      if (is<PlainDate>(temporal_object))
          return static_cast<PlainDate&>(temporal_object).iso_year();
      if (is<PlainDateTime>(temporal_object))
          return static_cast<PlainDateTime&>(temporal_object).iso_year();
      VERIFY_NOT_REACHED();
  }
  
  // 12.1.42 ISOMonth ( temporalObject ), https://tc39.es/proposal-temporal/#sec-temporal-isomonth
  u8 iso_month(Object& temporal_object)
  {
      // 1. Assert: temporalObject has an [[ISOMonth]] internal slot.
      // NOTE: Asserted by the VERIFY_NOT_REACHED at the end
  
      // 2. Return 𝔽(temporalObject.[[ISOMonth]]).
      // TODO: add the rest of the builtins with a [[ISOMonth]] slot (PlainYearMonth, PlainMonthDay)
      if (is<PlainDate>(temporal_object))
          return static_cast<PlainDate&>(temporal_object).iso_month();
      if (is<PlainDateTime>(temporal_object))
          return static_cast<PlainDateTime&>(temporal_object).iso_month();
      VERIFY_NOT_REACHED();
  }
  
  // 12.1.43 ISOMonthCode ( temporalObject ), https://tc39.es/proposal-temporal/#sec-temporal-isomonthcode
  String iso_month_code(Object& temporal_object)
  {
      // 1. Assert: temporalObject has an [[ISOMonth]] internal slot.
      // NOTE: Asserted by the VERIFY_NOT_REACHED at the end
  
      // 2. Return ! BuildISOMonthCode(temporalObject.[[ISOMonth]]).
      // TODO: add the rest of the builtins with a [[ISOMonth]] slot (PlainYearMonth, PlainMonthDay)
      if (is<PlainDate>(temporal_object))
          return build_iso_month_code(static_cast<PlainDate&>(temporal_object).iso_month());
      if (is<PlainDateTime>(temporal_object))
          return build_iso_month_code(static_cast<PlainDateTime&>(temporal_object).iso_month());
      VERIFY_NOT_REACHED();
  }
  
  // 12.1.44 ISODay ( temporalObject ), https://tc39.es/proposal-temporal/#sec-temporal-isomonthcode
  u8 iso_day(Object& temporal_object)
  {
      // 1. Assert: temporalObject has an [[ISODay]] internal slot.
      // NOTE: Asserted by the VERIFY_NOT_REACHED at the end
  
      // 2. Return 𝔽(temporalObject.[[ISODay]]).
      // TODO: add the rest of the builtins with a [[ISODay]] slot (PlainYearMonth, PlainMonthDay)
      if (is<PlainDate>(temporal_object))
          return static_cast<PlainDate&>(temporal_object).iso_day();
      if (is<PlainDateTime>(temporal_object))
          return static_cast<PlainDateTime&>(temporal_object).iso_day();
      VERIFY_NOT_REACHED();
  }
  
  }
  