Represent normalizable time zones with FixedOffsetTimeZone

Author: ilya-g

core/common/test/TimeZoneTest.kt

@@ -106,11 +106,16 @@ class TimeZoneTest {
     @Test
     fun utcOffsetNormalization() {
         val sameOffsetTZs = listOf("+04", "+04:00", "UTC+4", "UT+04", "GMT+04:00:00").map { TimeZone.of(it) }
-        val instant = Instant.fromEpochSeconds(0)
-        val offsets = sameOffsetTZs.map { it.offsetAt(instant) }
+        for (tz in sameOffsetTZs) {
+            assertIs<FixedOffsetTimeZone>(tz)
+        }
+        val offsets = sameOffsetTZs.map { (it as FixedOffsetTimeZone).offset }
+        val zoneIds = sameOffsetTZs.map { it.id }
 
         assertTrue(offsets.distinct().size == 1, "Expected all offsets to be equal: $offsets")
         assertTrue(offsets.map { it.toString() }.distinct().size == 1, "Expected all offsets to have the same string representation: $offsets")
+
+        assertTrue(zoneIds.distinct().size > 1, "Expected some fixed offset zones to have different ids: $zoneIds")
     }
 
     // from 310bp

core/js/src/TimeZone.kt

@@ -26,31 +26,38 @@ public actual open class TimeZone internal constructor(internal val zoneId: Zone
     override fun toString(): String = zoneId.toString()
 
     public actual companion object {
-        public actual fun currentSystemDefault(): TimeZone = ZoneId.systemDefault().let(::TimeZone)
+        public actual fun currentSystemDefault(): TimeZone = ofZone(ZoneId.systemDefault())
         public actual val UTC: FixedOffsetTimeZone = UtcOffset(jtZoneOffset.UTC).asTimeZone()
 
         public actual fun of(zoneId: String): TimeZone = try {
-            val zone = ZoneId.of(zoneId)
-            if (zone is jtZoneOffset) {
-                FixedOffsetTimeZone(UtcOffset(zone))
-            } else {
-                TimeZone(zone)
-            }
+            ofZone(ZoneId.of(zoneId))
         } catch (e: Throwable) {
             if (e.isJodaDateTimeException()) throw IllegalTimeZoneException(e)
             throw e
         }
 
+        private fun ofZone(zoneId: ZoneId): TimeZone = when {
+            zoneId is jtZoneOffset ->
+                FixedOffsetTimeZone(UtcOffset(zoneId))
+            zoneId.rules().isFixedOffset() ->
+                FixedOffsetTimeZone(UtcOffset(zoneId.normalized() as jtZoneOffset), zoneId)
+            else ->
+                TimeZone(zoneId)
+        }
+
+
         public actual val availableZoneIds: Set<String> get() = ZoneId.getAvailableZoneIds().toSet()
     }
 }
 
 @Serializable(with = FixedOffsetTimeZoneSerializer::class)
-public actual class FixedOffsetTimeZone actual constructor(public actual val offset: UtcOffset): TimeZone(offset.zoneOffset) {
-    private val zoneOffset get() = zoneId as jtZoneOffset
+public actual class FixedOffsetTimeZone
+internal constructor(public actual val offset: UtcOffset, zoneId: ZoneId): TimeZone(zoneId) {
+
+    public actual constructor(offset: UtcOffset) : this(offset, offset.zoneOffset)
 
     @Deprecated("Use offset.totalSeconds", ReplaceWith("offset.totalSeconds"))
-    public actual val totalSeconds: Int get() = zoneOffset.totalSeconds().toInt()
+    public actual val totalSeconds: Int get() = offset.totalSeconds
 }
 
 

core/jvm/src/Converters.kt

@@ -57,7 +57,7 @@ public fun TimeZone.toJavaZoneId(): java.time.ZoneId = this.zoneId
 /**
  * Converts this [java.time.ZoneId][java.time.ZoneId] value to a [kotlinx.datetime.TimeZone][TimeZone] value.
  */
-public fun java.time.ZoneId.toKotlinTimeZone(): TimeZone = TimeZone(this)
+public fun java.time.ZoneId.toKotlinTimeZone(): TimeZone = TimeZone.ofZone(this)
 
 
 /**

core/jvm/src/TimeZoneJvm.kt

@@ -31,28 +31,35 @@ public actual open class TimeZone internal constructor(internal val zoneId: Zone
     override fun toString(): String = zoneId.toString()
 
     public actual companion object {
-        public actual fun currentSystemDefault(): TimeZone = ZoneId.systemDefault().let(::TimeZone)
+        public actual fun currentSystemDefault(): TimeZone = ofZone(ZoneId.systemDefault())
         public actual val UTC: FixedOffsetTimeZone = UtcOffset(jtZoneOffset.UTC).asTimeZone()
 
         public actual fun of(zoneId: String): TimeZone = try {
-            val zone = ZoneId.of(zoneId)
-            if (zone is jtZoneOffset) {
-                FixedOffsetTimeZone(UtcOffset(zone))
-            } else {
-                TimeZone(zone)
-            }
+            ofZone(ZoneId.of(zoneId))
         } catch (e: Exception) {
             if (e is DateTimeException) throw IllegalTimeZoneException(e)
             throw e
         }
 
+        internal fun ofZone(zoneId: ZoneId): TimeZone = when {
+            zoneId is jtZoneOffset ->
+                FixedOffsetTimeZone(UtcOffset(zoneId))
+            zoneId.rules.isFixedOffset ->
+                FixedOffsetTimeZone(UtcOffset(zoneId.normalized() as jtZoneOffset), zoneId)
+            else ->
+                TimeZone(zoneId)
+        }
+
         public actual val availableZoneIds: Set<String> get() = ZoneId.getAvailableZoneIds()
     }
 }
 
 @Serializable(with = FixedOffsetTimeZoneSerializer::class)
 public actual class FixedOffsetTimeZone
-public actual constructor(public actual val offset: UtcOffset): TimeZone(offset.zoneOffset) {
+internal constructor(public actual val offset: UtcOffset, zoneId: ZoneId): TimeZone(zoneId) {
+
+    public actual constructor(offset: UtcOffset) : this(offset, offset.zoneOffset)
+
     @Deprecated("Use offset.totalSeconds", ReplaceWith("offset.totalSeconds"))
     public actual val totalSeconds: Int get() = offset.totalSeconds
 }

core/jvm/test/ConvertersTest.kt

@@ -126,6 +126,20 @@ class ConvertersTest {
         test("Europe/Berlin")
     }
 
+    @Test
+    fun fixedOffsetTimeZone() {
+        val zone = TimeZone.of("UTC") as FixedOffsetTimeZone
+
+        val jtZone = zone.toJavaZoneId()
+        val jtZoneOffset = zone.toJavaZoneOffset()
+
+        assertEquals(zone.id, jtZone.id)
+        assertNotEquals(jtZone, jtZoneOffset)
+        assertEquals(jtZone.normalized(), jtZoneOffset)
+
+        assertIs<FixedOffsetTimeZone>(jtZone.toKotlinTimeZone())
+    }
+
     @Test
     fun zoneOffset() {
         fun test(offsetString: String) {