Introduce a utility class for finding reasonable times to send push notifications

service/src/test/java/org/whispersystems/textsecuregcm/scheduler/SchedulingUtilTest.java

@@ -0,0 +1,68 @@
+package org.whispersystems.textsecuregcm.scheduler;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import com.google.i18n.phonenumbers.PhoneNumberUtil;
+import java.time.Clock;
+import java.time.LocalTime;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import org.junit.jupiter.api.Test;
+import org.whispersystems.textsecuregcm.storage.Account;
+import org.whispersystems.textsecuregcm.storage.Device;
+
+class SchedulingUtilTest {
+
+  @Test
+  void getNextRecommendedNotificationTime() {
+    {
+      final Account account = mock(Account.class);
+
+      // The account has a phone number that can be resolved to a region with known timezones
+      when(account.getNumber()).thenReturn(PhoneNumberUtil.getInstance().format(
+          PhoneNumberUtil.getInstance().getExampleNumber("DE"), PhoneNumberUtil.PhoneNumberFormat.E164));
+
+      final ZoneId berlinZoneId = ZoneId.of("Europe/Berlin");
+      final ZonedDateTime beforeNotificationTime = ZonedDateTime.now(berlinZoneId).with(LocalTime.of(13, 0));
+
+      assertEquals(
+          beforeNotificationTime.with(LocalTime.of(14, 0)).toInstant(),
+          SchedulingUtil.getNextRecommendedNotificationTime(account, LocalTime.of(14, 0),
+              Clock.fixed(beforeNotificationTime.toInstant(), berlinZoneId)));
+
+      final ZonedDateTime afterNotificationTime = ZonedDateTime.now(berlinZoneId).with(LocalTime.of(15, 0));
+
+      assertEquals(
+          afterNotificationTime.with(LocalTime.of(14, 0)).plusDays(1).toInstant(),
+          SchedulingUtil.getNextRecommendedNotificationTime(account, LocalTime.of(14, 0),
+              Clock.fixed(afterNotificationTime.toInstant(), berlinZoneId)));
+    }
+
+    {
+      final Account account = mock(Account.class);
+      final Device primaryDevice = mock(Device.class);
+
+      // The account does not have a phone number that can be connected to a region/time zone
+      when(account.getNumber()).thenReturn("Not a parseable number");
+      when(account.getPrimaryDevice()).thenReturn(primaryDevice);
+      when(primaryDevice.getCreated())
+          .thenReturn(ZonedDateTime.of(2024, 7, 10, 9, 53, 12, 0, ZoneId.systemDefault()).toInstant().toEpochMilli());
+
+      final ZonedDateTime beforeNotificationTime = ZonedDateTime.now(ZoneId.systemDefault()).with(LocalTime.of(9, 0));
+
+      assertEquals(
+          beforeNotificationTime.with(LocalTime.of(9, 53, 12)).toInstant(),
+          SchedulingUtil.getNextRecommendedNotificationTime(account, LocalTime.of(14, 0),
+              Clock.fixed(beforeNotificationTime.toInstant(), ZoneId.systemDefault())));
+
+      final ZonedDateTime afterNotificationTime = ZonedDateTime.now(ZoneId.systemDefault()).with(LocalTime.of(10, 0));
+
+      assertEquals(
+          afterNotificationTime.with(LocalTime.of(9, 53, 12)).plusDays(1).toInstant(),
+          SchedulingUtil.getNextRecommendedNotificationTime(account, LocalTime.of(14, 0),
+              Clock.fixed(afterNotificationTime.toInstant(), ZoneId.systemDefault())));
+    }
+  }
+}