LibJS: Begin implementing the relativeTo option of Duration.round

Author: https://github.com/trflynn89
Commit: 70ad66d3c0
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2513
Reviewed-by: https://github.com/shannonbooth ✅

Libraries/LibJS/Runtime/Temporal/PlainDateTime.cpp

@@ -6,8 +6,8 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <LibJS/Runtime/Temporal/AbstractOperations.h>
 #include <LibJS/Runtime/Temporal/Calendar.h>
+#include <LibJS/Runtime/Temporal/Duration.h>
 #include <LibJS/Runtime/Temporal/Instant.h>
 #include <LibJS/Runtime/Temporal/PlainDate.h>
 #include <LibJS/Runtime/Temporal/PlainDateTime.h>
@@ -81,4 +81,90 @@ ISODateTime balance_iso_date_time(double year, double month, double day, double
     return combine_iso_date_and_time_record(balanced_date, balanced_time);
 }
 
+// 5.5.10 CompareISODateTime ( isoDateTime1, isoDateTime2 ), https://tc39.es/proposal-temporal/#sec-temporal-compareisodatetime
+i8 compare_iso_date_time(ISODateTime const& iso_date_time1, ISODateTime const& iso_date_time2)
+{
+    // 1. Let dateResult be CompareISODate(isoDateTime1.[[ISODate]], isoDateTime2.[[ISODate]]).
+    auto date_result = compare_iso_date(iso_date_time1.iso_date, iso_date_time2.iso_date);
+
+    // 2. If dateResult ≠ 0, return dateResult.
+    if (date_result != 0)
+        return date_result;
+
+    // 3. Return CompareTimeRecord(isoDateTime1.[[Time]], isoDateTime2.[[Time]]).
+    return compare_time_record(iso_date_time1.time, iso_date_time2.time);
+}
+
+// 5.5.12 DifferenceISODateTime ( isoDateTime1, isoDateTime2, calendar, largestUnit ), https://tc39.es/proposal-temporal/#sec-temporal-differenceisodatetime
+ThrowCompletionOr<InternalDuration> difference_iso_date_time(VM& vm, ISODateTime const& iso_date_time1, ISODateTime const& iso_date_time2, StringView calendar, Unit largest_unit)
+{
+    // 1. Assert: ISODateTimeWithinLimits(isoDateTime1) is true.
+    VERIFY(iso_date_time_within_limits(iso_date_time1));
+
+    // 2. Assert: ISODateTimeWithinLimits(isoDateTime2) is true.
+    VERIFY(iso_date_time_within_limits(iso_date_time2));
+
+    // 3. Let timeDuration be DifferenceTime(isoDateTime1.[[Time]], isoDateTime2.[[Time]]).
+    auto time_duration = difference_time(iso_date_time1.time, iso_date_time2.time);
+
+    // 4. Let timeSign be TimeDurationSign(timeDuration).
+    auto time_sign = time_duration_sign(time_duration);
+
+    // 5. Let dateSign be CompareISODate(isoDateTime2.[[ISODate]], isoDateTime1.[[ISODate]]).
+    auto date_sign = compare_iso_date(iso_date_time2.iso_date, iso_date_time1.iso_date);
+
+    // 6. Let adjustedDate be isoDateTime2.[[ISODate]].
+    auto adjusted_date = iso_date_time2.iso_date;
+
+    // 7. If timeSign = -dateSign, then
+    if (time_sign == -date_sign) {
+        // a. Set adjustedDate to BalanceISODate(adjustedDate.[[Year]], adjustedDate.[[Month]], adjustedDate.[[Day]] + timeSign).
+        adjusted_date = balance_iso_date(adjusted_date.year, adjusted_date.month, static_cast<double>(adjusted_date.day) + time_sign);
+
+        // b. Set timeDuration to ? Add24HourDaysToTimeDuration(timeDuration, -timeSign).
+        time_duration = TRY(add_24_hour_days_to_time_duration(vm, time_duration, -time_sign));
+    }
+
+    // 8. Let dateLargestUnit be LargerOfTwoTemporalUnits(DAY, largestUnit).
+    auto date_largest_unit = larger_of_two_temporal_units(Unit::Day, largest_unit);
+
+    // 9. Let dateDifference be CalendarDateUntil(calendar, isoDateTime1.[[ISODate]], adjustedDate, dateLargestUnit).
+    auto date_difference = calendar_date_until(vm, calendar, iso_date_time1.iso_date, adjusted_date, date_largest_unit);
+
+    // 10. If largestUnit is not dateLargestUnit, then
+    if (largest_unit != date_largest_unit) {
+        // a. Set timeDuration to ? Add24HourDaysToTimeDuration(timeDuration, dateDifference.[[Days]]).
+        time_duration = TRY(add_24_hour_days_to_time_duration(vm, time_duration, date_difference.days));
+
+        // b. Set dateDifference.[[Days]] to 0.
+        date_difference.days = 0;
+    }
+
+    // 11. Return ? CombineDateAndTimeDuration(dateDifference, timeDuration).
+    return TRY(combine_date_and_time_duration(vm, date_difference, move(time_duration)));
+}
+
+// 5.5.13 DifferencePlainDateTimeWithRounding ( isoDateTime1, isoDateTime2, calendar, largestUnit, roundingIncrement, smallestUnit, roundingMode ), https://tc39.es/proposal-temporal/#sec-temporal-differenceplaindatetimewithrounding
+ThrowCompletionOr<InternalDuration> difference_plain_date_time_with_rounding(VM& vm, ISODateTime const& iso_date_time1, ISODateTime const& iso_date_time2, StringView calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode rounding_mode)
+{
+    // 1. If CompareISODateTime(isoDateTime1, isoDateTime2) = 0, then
+    if (compare_iso_date_time(iso_date_time1, iso_date_time2) == 0) {
+        // a. Return ! CombineDateAndTimeDuration(ZeroDateDuration(), 0).
+        return MUST(combine_date_and_time_duration(vm, zero_date_duration(vm), TimeDuration { 0 }));
+    }
+
+    // 2. Let diff be ? DifferenceISODateTime(isoDateTime1, isoDateTime2, calendar, largestUnit).
+    auto diff = TRY(difference_iso_date_time(vm, iso_date_time1, iso_date_time2, calendar, largest_unit));
+
+    // 3. If smallestUnit is NANOSECOND and roundingIncrement = 1, return diff.
+    if (smallest_unit == Unit::Nanosecond && rounding_increment == 1)
+        return diff;
+
+    // 4. Let destEpochNs be GetUTCEpochNanoseconds(isoDateTime2).
+    auto dest_epoch_ns = get_utc_epoch_nanoseconds(iso_date_time2);
+
+    // 5. Return ? RoundRelativeDuration(diff, destEpochNs, isoDateTime1, UNSET, calendar, largestUnit, roundingIncrement, smallestUnit, roundingMode).
+    return TRY(round_relative_duration(vm, diff, dest_epoch_ns, iso_date_time1, {}, calendar, largest_unit, rounding_increment, smallest_unit, rounding_mode));
+}
+
 }