Add findCanonicalTimeZoneId method.

Returns replacements for deprecated time zones. For example,
America/Godthab was replaced with America/Nuuk.

Bug: 172934905
Test: atest CtsIcuTestCases:com.android.i18n.test.timezone
Change-Id: I5c5b5e28f7d41af4bc7d2fc7a547a283132190d4

3 files changed, 74 insertions, 14 deletions

diff --git a/android_icu4j/api/legacy_platform/current.txt b/android_icu4j/api/legacy_platform/current.txt
index a81a0c650..692b2b1bf 100644
--- a/android_icu4j/api/legacy_platform/current.txt
+++ b/android_icu4j/api/legacy_platform/current.txt
@@ -81,6 +81,7 @@ package com.android.i18n.timezone {
   }
 
   public final class CountryZonesFinder {
+    method @Nullable public String findCanonicalTimeZoneId(String);
     method public java.util.List<java.lang.String> lookupAllCountryIsoCodes();
     method public com.android.i18n.timezone.CountryTimeZones lookupCountryTimeZones(String);
     method public java.util.List<com.android.i18n.timezone.CountryTimeZones> lookupCountryTimeZonesForZoneId(String);
diff --git a/android_icu4j/libcore_bridge/src/java/com/android/i18n/timezone/CountryZonesFinder.java b/android_icu4j/libcore_bridge/src/java/com/android/i18n/timezone/CountryZonesFinder.java
index 80a316e1f..61d9a1895 100644
--- a/android_icu4j/libcore_bridge/src/java/com/android/i18n/timezone/CountryZonesFinder.java
+++ b/android_icu4j/libcore_bridge/src/java/com/android/i18n/timezone/CountryZonesFinder.java
@@ -19,6 +19,7 @@ package com.android.i18n.timezone;
 import static com.android.i18n.timezone.XmlUtils.normalizeCountryIso;
 
 import com.android.i18n.timezone.CountryTimeZones.TimeZoneMapping;
+import libcore.util.Nullable;
 
 import java.util.ArrayList;
 import java.util.Collections;
@@ -57,10 +58,11 @@ public final class CountryZonesFinder {
 
     /**
      * Returns an immutable list of {@link CountryTimeZones} for countries that use the specified
-     * time zone. An exact, case-sensitive match is performed on the zone ID. If the match  but the method also
-     * checks for alternative zone IDs. This method never returns null and will usually return a
-     * list containing a single element. It can return an empty list if the zone ID is
-     * not recognized or it is not associated with a country.
+     * time zone. An exact, case-sensitive match is performed on the zone ID. Search is done
+     * over currently used time zone IDs and also over no longer used deprecated(alternative) IDs.
+     * This method never returns null and will usually return a list containing a single element.
+     * It can return an empty list if the zone ID is not recognized or it is not associated with a
+     * country.
      */
     @libcore.api.CorePlatformApi
     public List<CountryTimeZones> lookupCountryTimeZonesForZoneId(String zoneId) {
@@ -104,4 +106,37 @@ public final class CountryZonesFinder {
         }
         return null;
     }
+
+    /**
+     * Returns a canonical time zone ID for the {@code timeZoneId} specified. It is intended for use
+     * when behavioral equivalence of time zones needs to be determined.
+     *
+     * <p>When a time zone ID is returned, it is guaranteed to have the same offset / daylight
+     * savings behavior as the argument, but it might be used in a different country and could
+     * have different I18N properties like display name. The original {@code timeZoneId} will
+     * often be returned.
+     *
+     * <p>If {@code timeZoneId} is unknown or not associated with a country, {@code null} is
+     * returned. e.g. time zones such as Etc/GMT+-XX.
+     *
+     * This method behavior is based on tzlookup.xml file and works with Olson IDs attached to
+     * countries, unlike {@link android.icu.util.TimeZone} which works with wider set of arguments.
+     */
+    @libcore.api.CorePlatformApi
+    @Nullable
+    public String findCanonicalTimeZoneId(String timeZoneId) {
+        for (CountryTimeZones countryTimeZones : countryTimeZonesList) {
+
+            // notafter is ignored as timeZoneId might be deprecated a while ago
+            List<TimeZoneMapping> countryTimeZoneMappings = countryTimeZones.getTimeZoneMappings();
+            for (TimeZoneMapping timeZoneMapping : countryTimeZoneMappings) {
+                if (timeZoneMapping.getTimeZoneId().equals(timeZoneId)
+                        || timeZoneMapping.getAlternativeIds().contains(timeZoneId)) {
+                    return timeZoneMapping.getTimeZoneId();
+                }
+            }
+        }
+
+        return null;
+    }
 }
diff --git a/android_icu4j/testing/src/com/android/i18n/test/timezone/CountryZonesFinderTest.java b/android_icu4j/testing/src/com/android/i18n/test/timezone/CountryZonesFinderTest.java
index 64ec0fd0d..549c8899f 100644
--- a/android_icu4j/testing/src/com/android/i18n/test/timezone/CountryZonesFinderTest.java
+++ b/android_icu4j/testing/src/com/android/i18n/test/timezone/CountryZonesFinderTest.java
@@ -16,22 +16,26 @@
 
 package com.android.i18n.test.timezone;
 
-import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import android.icu.testsharding.MainTestShard;
 
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.List;
-import java.util.stream.Collectors;
 import com.android.i18n.timezone.CountryTimeZones;
 import com.android.i18n.timezone.CountryTimeZones.TimeZoneMapping;
 import com.android.i18n.timezone.CountryZonesFinder;
 
-import android.icu.testsharding.MainTestShard;
+import org.junit.Test;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertSame;
-import static org.junit.Assert.fail;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Collectors;
 
 @MainTestShard
 public class CountryZonesFinderTest {
@@ -119,6 +123,26 @@ public class CountryZonesFinderTest {
         assertNull(countryZonesFinder.lookupCountryTimeZones("DOES_NOT_EXIST"));
     }
 
+    @Test
+    public void findCanonicalTimeZoneId() {
+        TimeZoneMapping usesNewZoneId = timeZoneMappingWithAlts("America/Detroit",
+                list("US/Michigan"));
+        TimeZoneMapping usesOldZoneId = timeZoneMappingWithAlts("US/Central",
+                list("America/Chicago"));
+        CountryTimeZones countryWithAlternativeZones = CountryTimeZones.createValidated(
+                "us", "America/Detroit" /* defaultTimeZoneId */, false /* defaultTimeZoneBoost */,
+                false /* everUsesUtc */,
+                list(usesNewZoneId, usesOldZoneId),
+                "debug info");
+        CountryZonesFinder countryZonesFinder =
+                CountryZonesFinder.createForTests(list(countryWithAlternativeZones));
+
+        assertEquals(countryZonesFinder.findCanonicalTimeZoneId("America/Chicago"), "US/Central");
+        assertEquals(countryZonesFinder.findCanonicalTimeZoneId("US/Michigan"), "America/Detroit");
+        assertEquals(countryZonesFinder.findCanonicalTimeZoneId("America/Detroit"), "America/Detroit");
+        assertNull(countryZonesFinder.findCanonicalTimeZoneId("Mars/Base"));
+    }
+
     private static <X> void assertEqualsAndImmutable(List<X> expected, List<X> actual) {
         assertEquals(expected, actual);
         assertImmutableList(actual);