#485: Implement TimeZoneRules interface and update TimeZoneRulesCommon to conform

Author: DmitryNekrasov

core/commonKotlin/src/internal/TimeZoneRules.kt

@@ -0,0 +1,17 @@
+/*
+ * Copyright 2019-2025 JetBrains s.r.o. and contributors.
+ * Use of this source code is governed by the Apache 2.0 License that can be found in the LICENSE.txt file.
+ */
+
+package kotlinx.datetime.internal
+
+import kotlinx.datetime.Instant
+import kotlinx.datetime.LocalDateTime
+import kotlinx.datetime.UtcOffset
+
+internal interface TimeZoneRules {
+
+    fun infoAtInstant(instant: Instant): UtcOffset
+
+    fun infoAtDatetime(localDateTime: LocalDateTime): OffsetInfo
+}

core/commonKotlin/src/internal/TimeZoneRulesCommon.kt

@@ -28,7 +28,7 @@ internal class TimeZoneRulesCommon(
      * [recurringZoneRules].
      */
     val recurringZoneRules: RecurringZoneRules?,
-) {
+) : TimeZoneRules {
     init {
         require(offsets.size == transitionEpochSeconds.size + 1) {
             "offsets.size must be one more than transitionEpochSeconds.size"
@@ -65,7 +65,7 @@ internal class TimeZoneRulesCommon(
         }
     }
 
-    fun infoAtInstant(instant: Instant): UtcOffset {
+    override fun infoAtInstant(instant: Instant): UtcOffset {
         val epochSeconds = instant.epochSeconds
         // good: no transitions, or instant is after the last transition
         if (recurringZoneRules != null && transitionEpochSeconds.lastOrNull()?.let { epochSeconds >= it } != false) {
@@ -81,7 +81,7 @@ internal class TimeZoneRulesCommon(
         return offsets[index]
     }
 
-    fun infoAtDatetime(localDateTime: LocalDateTime): OffsetInfo {
+    override fun infoAtDatetime(localDateTime: LocalDateTime): OffsetInfo {
         if (recurringZoneRules != null && transitionLocalDateTimes.lastOrNull()?.let { localDateTime > it } != false) {
             return recurringZoneRules.infoAtLocalDateTime(localDateTime, offsets.last())
         }