text: /*
   * Copyright (c) 2020-2021, Linus Groh <linusg@serenityos.org>
   * Copyright (c) 2022, Tim Flynn <trflynn89@serenityos.org>
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #include <AK/NumericLimits.h>
  #include <AK/StringBuilder.h>
  #include <AK/Time.h>
  #include <LibCore/DateTime.h>
  #include <LibJS/Runtime/AbstractOperations.h>
  #include <LibJS/Runtime/Date.h>
  #include <LibJS/Runtime/GlobalObject.h>
  #include <LibTimeZone/TimeZone.h>
  #include <time.h>
  
  namespace JS {
  
  Date* Date::create(GlobalObject& global_object, double date_value)
  {
      return global_object.heap().allocate<Date>(global_object, date_value, *global_object.date_prototype());
  }
  
  Date::Date(double date_value, Object& prototype)
      : Object(prototype)
      , m_date_value(date_value)
  {
  }
  
  Date::~Date()
  {
  }
  
  String Date::iso_date_string() const
  {
      int year = year_from_time(m_date_value);
  
      StringBuilder builder;
      if (year < 0)
          builder.appendff("-{:06}", -year);
      else if (year > 9999)
          builder.appendff("+{:06}", year);
      else
          builder.appendff("{:04}", year);
      builder.append('-');
      builder.appendff("{:02}", month_from_time(m_date_value) + 1);
      builder.append('-');
      builder.appendff("{:02}", date_from_time(m_date_value));
      builder.append('T');
      builder.appendff("{:02}", hour_from_time(m_date_value));
      builder.append(':');
      builder.appendff("{:02}", min_from_time(m_date_value));
      builder.append(':');
      builder.appendff("{:02}", sec_from_time(m_date_value));
      builder.append('.');
      builder.appendff("{:03}", ms_from_time(m_date_value));
      builder.append('Z');
  
      return builder.build();
  }
  
  // DayWithinYear(t), https://tc39.es/ecma262/#eqn-DayWithinYear
  u16 day_within_year(double t)
  {
      if (!Value(t).is_finite_number())
          return 0;
  
      // Day(t) - DayFromYear(YearFromTime(t))
      return static_cast<u16>(day(t) - day_from_year(year_from_time(t)));
  }
  
  // DateFromTime(t), https://tc39.es/ecma262/#sec-date-number
  u8 date_from_time(double t)
  {
      switch (month_from_time(t)) {
      // DayWithinYear(t) + 1𝔽 if MonthFromTime(t) = +0𝔽
      case 0:
          return day_within_year(t) + 1;
      // DayWithinYear(t) - 30𝔽 if MonthFromTime(t) = 1𝔽
      case 1:
          return day_within_year(t) - 30;
      // DayWithinYear(t) - 58𝔽 - InLeapYear(t) if MonthFromTime(t) = 2𝔽
      case 2:
          return day_within_year(t) - 58 - in_leap_year(t);
      // DayWithinYear(t) - 89𝔽 - InLeapYear(t) if MonthFromTime(t) = 3𝔽
      case 3:
          return day_within_year(t) - 89 - in_leap_year(t);
      // DayWithinYear(t) - 119𝔽 - InLeapYear(t) if MonthFromTime(t) = 4𝔽
      case 4:
          return day_within_year(t) - 119 - in_leap_year(t);
      // DayWithinYear(t) - 150𝔽 - InLeapYear(t) if MonthFromTime(t) = 5𝔽
      case 5:
          return day_within_year(t) - 150 - in_leap_year(t);
      // DayWithinYear(t) - 180𝔽 - InLeapYear(t) if MonthFromTime(t) = 6𝔽
      case 6:
          return day_within_year(t) - 180 - in_leap_year(t);
      // DayWithinYear(t) - 211𝔽 - InLeapYear(t) if MonthFromTime(t) = 7𝔽
      case 7:
          return day_within_year(t) - 211 - in_leap_year(t);
      // DayWithinYear(t) - 242𝔽 - InLeapYear(t) if MonthFromTime(t) = 8𝔽
      case 8:
          return day_within_year(t) - 242 - in_leap_year(t);
      // DayWithinYear(t) - 272𝔽 - InLeapYear(t) if MonthFromTime(t) = 9𝔽
      case 9:
          return day_within_year(t) - 272 - in_leap_year(t);
      // DayWithinYear(t) - 303𝔽 - InLeapYear(t) if MonthFromTime(t) = 10𝔽
      case 10:
          return day_within_year(t) - 303 - in_leap_year(t);
      // DayWithinYear(t) - 333𝔽 - InLeapYear(t) if MonthFromTime(t) = 11𝔽
      case 11:
          return day_within_year(t) - 333 - in_leap_year(t);
      default:
          VERIFY_NOT_REACHED();
      }
  }
  
  // DaysInYear(y), https://tc39.es/ecma262/#eqn-DaysInYear
  u16 days_in_year(i32 y)
  {
      // 365𝔽 if (ℝ(y) modulo 4) ≠ 0
      if (y % 4 != 0)
          return 365;
      // 366𝔽 if (ℝ(y) modulo 4) = 0 and (ℝ(y) modulo 100) ≠ 0
      if (y % 4 == 0 && y % 100 != 0)
          return 366;
      // 365𝔽 if (ℝ(y) modulo 100) = 0 and (ℝ(y) modulo 400) ≠ 0
      if (y % 100 == 0 && y % 400 != 0)
          return 365;
      // 366𝔽 if (ℝ(y) modulo 400) = 0
      if (y % 400 == 0)
          return 366;
      VERIFY_NOT_REACHED();
  }
  
  // DayFromYear(y), https://tc39.es/ecma262/#eqn-DaysFromYear
  double day_from_year(i32 y)
  {
      // 𝔽(365 × (ℝ(y) - 1970) + floor((ℝ(y) - 1969) / 4) - floor((ℝ(y) - 1901) / 100) + floor((ℝ(y) - 1601) / 400))
      return 365.0 * (y - 1970) + floor((y - 1969) / 4.0) - floor((y - 1901) / 100.0) + floor((y - 1601) / 400.0);
  }
  
  // TimeFromYear(y), https://tc39.es/ecma262/#eqn-TimeFromYear
  double time_from_year(i32 y)
  {
      // msPerDay × DayFromYear(y)
      return Date::ms_per_day * day_from_year(y);
  }
  
  // YearFromTime(t), https://tc39.es/ecma262/#eqn-YearFromTime
  i32 year_from_time(double t)
  {
      // the largest integral Number y (closest to +∞) such that TimeFromYear(y) ≤ t
      if (!Value(t).is_finite_number())
          return NumericLimits<i32>::max();
  
      // Approximation using average number of milliseconds per year. We might have to adjust this guess afterwards.
      auto year = static_cast<i32>(t / (365.2425 * Date::ms_per_day) + 1970);
  
      auto year_t = time_from_year(year);
      if (year_t > t)
          year--;
      else if (year_t + days_in_year(year) * Date::ms_per_day <= t)
          year++;
  
      return year;
  }
  
  // InLeapYear(t), https://tc39.es/ecma262/#eqn-InLeapYear
  bool in_leap_year(double t)
  {
      // +0𝔽 if DaysInYear(YearFromTime(t)) = 365𝔽
      // 1𝔽 if DaysInYear(YearFromTime(t)) = 366𝔽
      return days_in_year(year_from_time(t)) == 366;
  }
  
  // MonthFromTime(t), https://tc39.es/ecma262/#eqn-MonthFromTime
  u8 month_from_time(double t)
  {
      auto in_leap_year = JS::in_leap_year(t);
      auto day_within_year = JS::day_within_year(t);
  
      // +0𝔽 if +0𝔽 ≤ DayWithinYear(t) < 31𝔽
      if (day_within_year < 31)
          return 0;
      // 1𝔽 if 31𝔽 ≤ DayWithinYear(t) < 59𝔽 + InLeapYear(t)
      if (31 <= day_within_year && day_within_year < 59 + in_leap_year)
          return 1;
      // 2𝔽 if 59𝔽 + InLeapYear(t) ≤ DayWithinYear(t) < 90𝔽 + InLeapYear(t)
      if (59 + in_leap_year <= day_within_year && day_within_year < 90 + in_leap_year)
          return 2;
      // 3𝔽 if 90𝔽 + InLeapYear(t) ≤ DayWithinYear(t) < 120𝔽 + InLeapYear(t)
      if (90 + in_leap_year <= day_within_year && day_within_year < 120 + in_leap_year)
          return 3;
      // 4𝔽 if 120𝔽 + InLeapYear(t) ≤ DayWithinYear(t) < 151𝔽 + InLeapYear(t)
      if (120 + in_leap_year <= day_within_year && day_within_year < 151 + in_leap_year)
          return 4;
      // 5𝔽 if 151𝔽 + InLeapYear(t) ≤ DayWithinYear(t) < 181𝔽 + InLeapYear(t)
      if (151 + in_leap_year <= day_within_year && day_within_year < 181 + in_leap_year)
          return 5;
      // 6𝔽 if 181𝔽 + InLeapYear(t) ≤ DayWithinYear(t) < 212𝔽 + InLeapYear(t)
      if (181 + in_leap_year <= day_within_year && day_within_year < 212 + in_leap_year)
          return 6;
      // 7𝔽 if 212𝔽 + InLeapYear(t) ≤ DayWithinYear(t) < 243𝔽 + InLeapYear(t)
      if (212 + in_leap_year <= day_within_year && day_within_year < 243 + in_leap_year)
          return 7;
      // 8𝔽 if 243𝔽 + InLeapYear(t) ≤ DayWithinYear(t) < 273𝔽 + InLeapYear(t)
      if (243 + in_leap_year <= day_within_year && day_within_year < 273 + in_leap_year)
          return 8;
      // 9𝔽 if 273𝔽 + InLeapYear(t) ≤ DayWithinYear(t) < 304𝔽 + InLeapYear(t)
      if (273 + in_leap_year <= day_within_year && day_within_year < 304 + in_leap_year)
          return 9;
      // 10𝔽 if 304𝔽 + InLeapYear(t) ≤ DayWithinYear(t) < 334𝔽 + InLeapYear(t)
      if (304 + in_leap_year <= day_within_year && day_within_year < 334 + in_leap_year)
          return 10;
      // 11𝔽 if 334𝔽 + InLeapYear(t) ≤ DayWithinYear(t) < 365𝔽 + InLeapYear(t)
      if (334 + in_leap_year <= day_within_year && day_within_year < 365 + in_leap_year)
          return 11;
      VERIFY_NOT_REACHED();
  }
  
  // HourFromTime(t), https://tc39.es/ecma262/#eqn-HourFromTime
  u8 hour_from_time(double t)
  {
      if (!Value(t).is_finite_number())
          return 0;
  
      // 𝔽(floor(ℝ(t / msPerHour)) modulo HoursPerDay)
      return static_cast<u8>(modulo(floor(t / Date::ms_per_hour), Date::hours_per_day));
  }
  
  // MinFromTime(t), https://tc39.es/ecma262/#eqn-MinFromTime
  u8 min_from_time(double t)
  {
      if (!Value(t).is_finite_number())
          return 0;
  
      // 𝔽(floor(ℝ(t / msPerMinute)) modulo MinutesPerHour)
      return static_cast<u8>(modulo(floor(t / Date::ms_per_minute), Date::minutes_per_hour));
  }
  
  // SecFromTime(t), https://tc39.es/ecma262/#eqn-SecFromTime
  u8 sec_from_time(double t)
  {
      if (!Value(t).is_finite_number())
          return 0;
  
      // 𝔽(floor(ℝ(t / msPerSecond)) modulo SecondsPerMinute)
      return static_cast<u8>(modulo(floor(t / Date::ms_per_second), Date::seconds_per_minute));
  }
  
  // msFromTime(t), https://tc39.es/ecma262/#eqn-msFromTime
  u16 ms_from_time(double t)
  {
      if (!Value(t).is_finite_number())
          return 0;
  
      // 𝔽(ℝ(t) modulo msPerSecond)
      return static_cast<u16>(modulo(t, Date::ms_per_second));
  }
  
  // 21.4.1.6 Week Day, https://tc39.es/ecma262/#sec-week-day
  u8 week_day(double t)
  {
      if (!Value(t).is_finite_number())
          return 0;
  
      // 𝔽(ℝ(Day(t) + 4𝔽) modulo 7)
      return static_cast<u8>(modulo(day(t) + 4, 7));
  }
  
  // 21.4.1.7 LocalTZA ( t, isUTC ), https://tc39.es/ecma262/#sec-local-time-zone-adjustment
  double local_tza(double time, [[maybe_unused]] bool is_utc, Optional<StringView> time_zone_override)
  {
      // The time_zone_override parameter is non-standard, but allows callers to override the system
      // time zone with a specific value without setting environment variables.
      auto time_zone = time_zone_override.value_or(TimeZone::current_time_zone());
  
      // When isUTC is true, LocalTZA( tUTC, true ) should return the offset of the local time zone from
      // UTC measured in milliseconds at time represented by time value tUTC. When the result is added to
      // tUTC, it should yield the corresponding Number tlocal.
  
      // When isUTC is false, LocalTZA( tlocal, false ) should return the offset of the local time zone from
      // UTC measured in milliseconds at local time represented by Number tlocal. When the result is subtracted
      // from tlocal, it should yield the corresponding time value tUTC.
  
      auto time_since_epoch = Value(time).is_finite_number() ? AK::Time::from_milliseconds(time) : AK::Time::max();
      auto maybe_offset = TimeZone::get_time_zone_offset(time_zone, time_since_epoch);
  
      return maybe_offset.has_value() ? static_cast<double>(maybe_offset->seconds) * 1000 : 0;
  }
  
  // 21.4.1.8 LocalTime ( t ), https://tc39.es/ecma262/#sec-localtime
  double local_time(double time)
  {
      // 1. Return t + LocalTZA(t, true).
      return time + local_tza(time, true);
  }
  
  // 21.4.1.9 UTC ( t ), https://tc39.es/ecma262/#sec-utc-t
  double utc_time(double time)
  {
      // 1. Return t - LocalTZA(t, false).
      return time - local_tza(time, false);
  }
  
  // 21.4.1.11 MakeTime ( hour, min, sec, ms ), https://tc39.es/ecma262/#sec-maketime
  Value make_time(GlobalObject& global_object, Value hour, Value min, Value sec, Value ms)
  {
      // 1. If hour is not finite or min is not finite or sec is not finite or ms is not finite, return NaN.
      if (!hour.is_finite_number() || !min.is_finite_number() || !sec.is_finite_number() || !ms.is_finite_number())
          return js_nan();
  
      // 2. Let h be 𝔽(! ToIntegerOrInfinity(hour)).
      auto h = MUST(hour.to_integer_or_infinity(global_object));
      // 3. Let m be 𝔽(! ToIntegerOrInfinity(min)).
      auto m = MUST(min.to_integer_or_infinity(global_object));
      // 4. Let s be 𝔽(! ToIntegerOrInfinity(sec)).
      auto s = MUST(sec.to_integer_or_infinity(global_object));
      // 5. Let milli be 𝔽(! ToIntegerOrInfinity(ms)).
      auto milli = MUST(ms.to_integer_or_infinity(global_object));
      // 6. Let t be ((h * msPerHour + m * msPerMinute) + s * msPerSecond) + milli, performing the arithmetic according to IEEE 754-2019 rules (that is, as if using the ECMAScript operators * and +).
      // NOTE: C++ arithmetic abides by IEEE 754 rules
      auto t = ((h * Date::ms_per_hour + m * Date::ms_per_minute) + s * Date::ms_per_second) + milli;
      // 7. Return t.
      return Value(t);
  }
  
  // Day(t), https://tc39.es/ecma262/#eqn-Day
  double day(double time_value)
  {
      return floor(time_value / Date::ms_per_day);
  }
  
  // TimeWithinDay(t), https://tc39.es/ecma262/#eqn-TimeWithinDay
  double time_within_day(double time)
  {
      // 𝔽(ℝ(t) modulo ℝ(msPerDay))
      return modulo(time, Date::ms_per_day);
  }
  
  // 21.4.1.12 MakeDay ( year, month, date ), https://tc39.es/ecma262/#sec-makeday
  Value make_day(GlobalObject& global_object, Value year, Value month, Value date)
  {
      // 1. If year is not finite or month is not finite or date is not finite, return NaN.
      if (!year.is_finite_number() || !month.is_finite_number() || !date.is_finite_number())
          return js_nan();
  
      // 2. Let y be 𝔽(! ToIntegerOrInfinity(year)).
      auto y = MUST(year.to_integer_or_infinity(global_object));
      // 3. Let m be 𝔽(! ToIntegerOrInfinity(month)).
      auto m = MUST(month.to_integer_or_infinity(global_object));
      // 4. Let dt be 𝔽(! ToIntegerOrInfinity(date)).
      auto dt = MUST(date.to_integer_or_infinity(global_object));
      // 5. Let ym be y + 𝔽(floor(ℝ(m) / 12)).
      auto ym = y + floor(m / 12);
      // 6. If ym is not finite, return NaN.
      if (!Value(ym).is_finite_number())
          return js_nan();
      // 7. Let mn be 𝔽(ℝ(m) modulo 12).
      auto mn = modulo(m, 12);
  
      // 8. Find a finite time value t such that YearFromTime(t) is ym and MonthFromTime(t) is mn and DateFromTime(t) is 1𝔽; but if this is not possible (because some argument is out of range), return NaN.
      if (!AK::is_within_range<int>(ym) || !AK::is_within_range<int>(mn + 1))
          return js_nan();
  
      // FIXME: We are avoiding AK::years_to_days_since_epoch here because it is implemented by looping over
      //        the range [1970, ym), which will spin for any time value with an extremely large year.
      auto t = time_from_year(ym) + (day_of_year(static_cast<int>(ym), static_cast<int>(mn) + 1, 1) * Date::ms_per_day);
  
      // 9. Return Day(t) + dt - 1𝔽.
      return Value(day(static_cast<double>(t)) + dt - 1);
  }
  
  // 21.4.1.13 MakeDate ( day, time ), https://tc39.es/ecma262/#sec-makedate
  Value make_date(Value day, Value time)
  {
      // 1. If day is not finite or time is not finite, return NaN.
      if (!day.is_finite_number() || !time.is_finite_number())
          return js_nan();
  
      // 2. Let tv be day × msPerDay + time.
      auto tv = Value(day.as_double() * Date::ms_per_day + time.as_double());
  
      // 3. If tv is not finite, return NaN.
      if (!tv.is_finite_number())
          return js_nan();
  
      // 4. Return tv.
      return tv;
  }
  
  // 21.4.1.14 TimeClip ( time ), https://tc39.es/ecma262/#sec-timeclip
  Value time_clip(GlobalObject& global_object, Value time)
  {
      // 1. If time is not finite, return NaN.
      if (!time.is_finite_number())
          return js_nan();
  
      // 2. If abs(ℝ(time)) > 8.64 × 10^15, return NaN.
      if (fabs(time.as_double()) > 8.64E15)
          return js_nan();
  
      // 3. Return 𝔽(! ToIntegerOrInfinity(time)).
      return Value(MUST(time.to_integer_or_infinity(global_object)));
  }
  
  }
  