optimising previous salt calculation function

Author: sophia-chen-ttd

src/main/java/com/uid2/admin/secret/SaltRotation.java

@@ -19,6 +19,7 @@
 public class SaltRotation {
     private final IKeyGenerator keyGenerator;
     private final long THIRTY_DAYS_IN_MS = Duration.ofDays(30).toMillis();
+    private final long DAY_IN_MS = Duration.ofDays(1).toMillis();
 
     public SaltRotation(IKeyGenerator keyGenerator) {
         this.keyGenerator = keyGenerator;
@@ -83,12 +84,13 @@ private long calculateRefreshFrom(long lastUpdated, long nextEffective) {
         return lastUpdated + (multiplier * THIRTY_DAYS_IN_MS);
     }
 
-    private String calculatePreviousSalt(SaltEntry oldSalt, boolean shouldRotate, long nextEffective) throws Exception {
+    private String calculatePreviousSalt(SaltEntry salt, boolean shouldRotate, long nextEffective) throws Exception {
         if (shouldRotate) {
-            return oldSalt.currentSalt();
+            return salt.currentSalt();
         }
-        if (ChronoUnit.DAYS.between(Instant.ofEpochMilli(oldSalt.lastUpdated()), Instant.ofEpochMilli(nextEffective)) < 90) {
-            return oldSalt.previousSalt();
+        long age = nextEffective - salt.lastUpdated();
+        if ( age / DAY_IN_MS < 90) {
+            return salt.previousSalt();
         }
         return null;
     }

src/test/java/com/uid2/admin/secret/SaltRotationTest.java

@@ -280,8 +280,8 @@ void rotateSaltsRemovePreviousSaltIfOver90DaysOld() throws Exception {
         final long over90Days = daysEarlier(100).toEpochMilli();
         final RotatingSaltProvider.SaltSnapshot lastSnapshot = SnapshotBuilder.start()
                 .withEntries(
-                    new SaltEntry(1, "1", lessThan90Days, "currentSalt", null, "lessThan90Days", null, null),
-                    new SaltEntry(2, "2", lessThan90Days, "currentSalt", null, "lessThan90Days", null, null),
+                    new SaltEntry(1, "1", lessThan90Days, "currentSalt", null, "lessThan90DaysOld", null, null),
+                    new SaltEntry(2, "2", lessThan90Days, "currentSalt", null, "lessThan90DaysOld", null, null),
                     new SaltEntry(3, "3", is90DaysOld, "currentSalt", null, "90DaysOld", null, null),
                     new SaltEntry(4, "4", is90DaysOld, "currentSalt", null, "90DaysOld", null, null),
                     new SaltEntry(5, "5", over90Days, "currentSalt", null, null, null, null),
@@ -291,7 +291,7 @@ void rotateSaltsRemovePreviousSaltIfOver90DaysOld() throws Exception {
 
         final SaltRotation.Result result = saltRotation.rotateSalts(lastSnapshot, minAges, 0.5, targetDate);
         assertTrue(result.hasSnapshot());
-        assertEquals(2, Arrays.stream(result.getSnapshot().getAllRotatingSalts()).filter(s -> "lessThan90Days".equals(s.previousSalt())).count());
+        assertEquals(2, Arrays.stream(result.getSnapshot().getAllRotatingSalts()).filter(s -> "lessThan90DaysOld".equals(s.previousSalt())).count());
         assertEquals(1, Arrays.stream(result.getSnapshot().getAllRotatingSalts()).filter(s -> s.previousSalt() == null).count());
         assertEquals(3, Arrays.stream(result.getSnapshot().getAllRotatingSalts()).filter(s -> "currentSalt".equals(s.previousSalt())).count());