Break circular dependency between core and util (#379)

* Break circular dependency between core and util

Created a new :common project and moved a minimum
number of classes to break the circular dependency
between the two projects. This gets rid of the
gradle lint dependency warnings.

Also separated api classes and testing helpers into
separate source sets in :common so that testing
classes may be restricted to test configurations.

common/src/main/java/google/registry/util/DateTimeUtils.java

@@ -0,0 +1,111 @@
+// Copyright 2017 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.util;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+import com.google.common.collect.Iterables;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Ordering;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.util.TimeZone;
+import org.joda.time.DateTime;
+import org.joda.time.DateTimeZone;
+
+/** Utilities methods and constants related to Joda {@link DateTime} objects. */
+public class DateTimeUtils {
+
+  /** The start of the epoch, in a convenient constant. */
+  public static final DateTime START_OF_TIME = new DateTime(0, DateTimeZone.UTC);
+
+  /**
+   * A date in the far future that we can treat as infinity.
+   *
+   * <p>This value is (2^63-1)/1000 rounded down. AppEngine stores dates as 64 bit microseconds, but
+   * Java uses milliseconds, so this is the largest representable date that will survive a
+   * round-trip through Datastore.
+   */
+  public static final DateTime END_OF_TIME = new DateTime(Long.MAX_VALUE / 1000, DateTimeZone.UTC);
+
+  /** Returns the earliest of a number of given {@link DateTime} instances. */
+  public static DateTime earliestOf(DateTime first, DateTime... rest) {
+    return earliestOf(Lists.asList(first, rest));
+  }
+
+  /** Returns the earliest element in a {@link DateTime} iterable. */
+  public static DateTime earliestOf(Iterable<DateTime> dates) {
+    checkArgument(!Iterables.isEmpty(dates));
+    return Ordering.<DateTime>natural().min(dates);
+  }
+
+  /** Returns the latest of a number of given {@link DateTime} instances. */
+  public static DateTime latestOf(DateTime first, DateTime... rest) {
+    return latestOf(Lists.asList(first, rest));
+  }
+
+  /** Returns the latest element in a {@link DateTime} iterable. */
+  public static DateTime latestOf(Iterable<DateTime> dates) {
+    checkArgument(!Iterables.isEmpty(dates));
+    return Ordering.<DateTime>natural().max(dates);
+  }
+
+  /** Returns whether the first {@link DateTime} is equal to or earlier than the second. */
+  public static boolean isBeforeOrAt(DateTime timeToCheck, DateTime timeToCompareTo) {
+    return !timeToCheck.isAfter(timeToCompareTo);
+  }
+
+  /** Returns whether the first {@link DateTime} is equal to or later than the second. */
+  public static boolean isAtOrAfter(DateTime timeToCheck, DateTime timeToCompareTo) {
+    return !timeToCheck.isBefore(timeToCompareTo);
+  }
+
+  /**
+   * Adds years to a date, in the {@code Duration} sense of semantic years. Use this instead of
+   * {@link DateTime#plusYears} to ensure that we never end up on February 29.
+   */
+  public static DateTime leapSafeAddYears(DateTime now, int years) {
+    checkArgument(years >= 0);
+    return years == 0 ? now : now.plusYears(1).plusYears(years - 1);
+  }
+
+  /**
+   * Subtracts years from a date, in the {@code Duration} sense of semantic years. Use this instead
+   * of {@link DateTime#minusYears} to ensure that we never end up on February 29.
+   */
+  public static DateTime leapSafeSubtractYears(DateTime now, int years) {
+    checkArgument(years >= 0);
+    return years == 0 ? now : now.minusYears(1).minusYears(years - 1);
+  }
+
+  /**
+   * Converts a Joda {@link DateTime} object to an equivalent java.time {@link ZonedDateTime}
+   * object.
+   */
+  public static ZonedDateTime toZonedDateTime(DateTime dateTime) {
+    java.time.Instant instant = java.time.Instant.ofEpochMilli(dateTime.getMillis());
+    return ZonedDateTime.ofInstant(instant, ZoneId.of(dateTime.getZone().getID()).normalized());
+  }
+
+  /**
+   * Converts a java.time {@link ZonedDateTime} object to an equivalent Joda {@link DateTime}
+   * object.
+   */
+  public static DateTime toJodaDateTime(ZonedDateTime zonedDateTime) {
+    return new DateTime(
+        zonedDateTime.toInstant().toEpochMilli(),
+        DateTimeZone.forTimeZone(TimeZone.getTimeZone(zonedDateTime.getZone())));
+  }
+}