LocalTime#toSecondOfDay & LocalTime#ofSecondOfDay.

core/common/src/LocalTime.kt

@@ -40,6 +40,20 @@ public expect class LocalTime : Comparable<LocalTime> {
          */
         public fun parse(isoString: String): LocalTime
 
+        /**
+         * Returns a LocalTime with the specified [secondOfDay]. The nanosecond field will be set to zero.
+         *
+         * @throws IllegalArgumentException if the boundaries of [secondOfDay] are exceeded.
+         */
+        public fun fromSecondOfDay(secondOfDay: Int): LocalTime
+
+        /**
+         * Returns a LocalTime with the specified [nanosecondOfDay].
+         *
+         * @throws IllegalArgumentException if the boundaries of [nanosecondOfDay] are exceeded.
+         */
+        public fun fromNanosecondOfDay(nanosecondOfDay: Long): LocalTime
+
         internal val MIN: LocalTime
         internal val MAX: LocalTime
     }
@@ -66,6 +80,12 @@ public expect class LocalTime : Comparable<LocalTime> {
     /** Returns the nanosecond-of-second time component of this time value. */
     public val nanosecond: Int
 
+    /** Returns the time as a second of a day, from 0 to 24 * 60 * 60 - 1. */
+    public fun toSecondOfDay(): Int
+
+    /** Returns the time as a nanosecond of a day, from 0 to 24 * 60 * 60 * 1_000_000_000 - 1. */
+    public fun toNanosecondOfDay(): Long
+
     /**
      * Compares `this` time value with the [other] time value.
      * Returns zero if this value is equal to the other, a negative number if this value occurs earlier
@@ -110,4 +130,4 @@ public fun LocalTime.atDate(year: Int, month: Month, dayOfMonth: Int = 0): Local
 /**
  * Combines this time's components with the specified [LocalDate] components into a [LocalDateTime] value.
  */
-public fun LocalTime.atDate(date: LocalDate): LocalDateTime = LocalDateTime(date, this)
+public fun LocalTime.atDate(date: LocalDate): LocalDateTime = LocalDateTime(date, this)

core/common/test/LocalTimeTest.kt

@@ -6,8 +6,6 @@
 package kotlinx.datetime.test
 
 import kotlinx.datetime.*
-import kotlinx.datetime.Clock
-import kotlin.math.min
 import kotlin.test.*
 
 class LocalTimeTest {
@@ -85,6 +83,58 @@ class LocalTimeTest {
         assertFailsWith<IllegalArgumentException> { LocalTime(0, 0, 0, 1_000_000_000) }
     }
 
+    @Test
+    fun fromNanosecondOfDay() {
+        val data = mapOf(
+            0L to LocalTime(0, 0),
+            5000000001L to LocalTime(0, 0, 5, 1),
+            44105123456789L to LocalTime(12, 15, 5, 123456789),
+            86399999999999L to LocalTime(23, 59, 59, 999999999),
+        )
+
+        data.forEach { (nanosecondOfDay, localTime) ->
+            assertEquals(nanosecondOfDay, localTime.toNanosecondOfDay())
+            assertEquals(localTime, LocalTime.fromNanosecondOfDay(nanosecondOfDay))
+        }
+    }
+
+    @Test
+    fun fromNanosecondOfDayInvalid() {
+        assertFailsWith<IllegalArgumentException> { LocalTime.fromNanosecondOfDay(-1) }
+        assertFailsWith<IllegalArgumentException> { LocalTime.fromNanosecondOfDay(86400000000000L) }
+        assertFailsWith<IllegalArgumentException> { LocalTime.fromNanosecondOfDay(Long.MAX_VALUE) }
+    }
+
+    @Test
+    fun fromSecondOfDay() {
+        val data = mapOf(
+            0 to LocalTime(0, 0),
+            5 to LocalTime(0, 0, 5),
+            44105 to LocalTime(12, 15, 5),
+            86399 to LocalTime(23, 59, 59),
+        )
+
+        data.forEach { (secondOfDay, localTime) ->
+            assertEquals(secondOfDay, localTime.toSecondOfDay())
+            assertEquals(localTime, LocalTime.fromSecondOfDay(secondOfDay))
+        }
+    }
+
+    @Test
+    fun fromSecondOfDayInvalid() {
+        assertFailsWith<IllegalArgumentException> { LocalTime.fromSecondOfDay(-1) }
+        assertFailsWith<IllegalArgumentException> { LocalTime.fromSecondOfDay(86400) }
+        assertFailsWith<IllegalArgumentException> { LocalTime.fromSecondOfDay(Int.MAX_VALUE) }
+    }
+
+    @Test
+    fun fromSecondOfDayIgnoresNanosecond() {
+        assertEquals(
+            0,
+            LocalTime(0, 0, 0, 100).toSecondOfDay(),
+        )
+    }
+
     @Test
     fun atDate() {
         val time = LocalTime(12, 1, 59)

core/js/src/LocalTime.kt

@@ -26,6 +26,8 @@ public actual class LocalTime internal constructor(internal val value: jtLocalTi
     public actual val minute: Int get() = value.minute().toInt()
     public actual val second: Int get() = value.second().toInt()
     public actual val nanosecond: Int get() = value.nano().toInt()
+    public actual fun toSecondOfDay(): Int = value.toSecondOfDay().toInt()
+    public actual fun toNanosecondOfDay(): Long = value.toNanoOfDay().toLong()
 
     override fun equals(other: Any?): Boolean =
         (this === other) || (other is LocalTime && this.value == other.value)
@@ -44,7 +46,19 @@ public actual class LocalTime internal constructor(internal val value: jtLocalTi
             throw e
         }
 
+        public actual fun fromSecondOfDay(secondOfDay: Int): LocalTime = try {
+            jtLocalTime.ofSecondOfDay(secondOfDay, 0).let(::LocalTime)
+        } catch (e: Throwable) {
+            throw IllegalArgumentException(e)
+        }
+
+        public actual fun fromNanosecondOfDay(nanosecondOfDay: Long): LocalTime = try {
+            jtLocalTime.ofNanoOfDay(nanosecondOfDay).let(::LocalTime)
+        } catch (e: Throwable) {
+            throw IllegalArgumentException(e)
+        }
+
         internal actual val MIN: LocalTime = LocalTime(jtLocalTime.MIN)
         internal actual val MAX: LocalTime = LocalTime(jtLocalTime.MAX)
     }
-}
+}

core/jvm/src/LocalTime.kt

@@ -29,6 +29,8 @@ public actual class LocalTime internal constructor(internal val value: jtLocalTi
     public actual val minute: Int get() = value.minute
     public actual val second: Int get() = value.second
     public actual val nanosecond: Int get() = value.nano
+    public actual fun toSecondOfDay(): Int = value.toSecondOfDay()
+    public actual fun toNanosecondOfDay(): Long = value.toNanoOfDay()
 
     override fun equals(other: Any?): Boolean =
         (this === other) || (other is LocalTime && this.value == other.value)
@@ -46,7 +48,19 @@ public actual class LocalTime internal constructor(internal val value: jtLocalTi
             throw DateTimeFormatException(e)
         }
 
+        public actual fun fromSecondOfDay(secondOfDay: Int): LocalTime = try {
+            jtLocalTime.ofSecondOfDay(secondOfDay.toLong()).let(::LocalTime)
+        } catch (e: DateTimeException) {
+            throw IllegalArgumentException(e)
+        }
+
+        public actual fun fromNanosecondOfDay(nanosecondOfDay: Long): LocalTime = try {
+            jtLocalTime.ofNanoOfDay(nanosecondOfDay).let(::LocalTime)
+        } catch (e: DateTimeException) {
+            throw IllegalArgumentException(e)
+        }
+
         internal actual val MIN: LocalTime = LocalTime(jtLocalTime.MIN)
         internal actual val MAX: LocalTime = LocalTime(jtLocalTime.MAX)
     }
-}
+}

core/native/src/LocalTime.kt

@@ -62,6 +62,12 @@ public actual class LocalTime actual constructor(
         public actual fun parse(isoString: String): LocalTime =
             localTimeParser.parse(isoString)
 
+        public actual fun fromSecondOfDay(secondOfDay: Int): LocalTime =
+            ofSecondOfDay(secondOfDay, 0)
+
+        public actual fun fromNanosecondOfDay(nanosecondOfDay: Long): LocalTime =
+            ofNanoOfDay(nanosecondOfDay)
+
         // org.threeten.bp.LocalTime#ofSecondOfDay(long, int)
         internal fun ofSecondOfDay(secondOfDay: Int, nanoOfSecond: Int): LocalTime {
             // Unidiomatic code due to https://github.com/Kotlin/kotlinx-datetime/issues/5
@@ -117,6 +123,16 @@ public actual class LocalTime actual constructor(
         return (nod xor (nod ushr 32)).toInt()
     }
 
+    // org.threeten.bp.LocalTime#toSecondOfDay
+    public actual fun toSecondOfDay(): Int {
+        var total: Int = hour * SECONDS_PER_HOUR
+        total += minute * SECONDS_PER_MINUTE
+        total += second
+        return total
+    }
+
+    public actual fun toNanosecondOfDay(): Long = toNanoOfDay()
+
     // org.threeten.bp.LocalTime#toNanoOfDay
     internal fun toNanoOfDay(): Long {
         var total: Long = hour.toLong() * NANOS_PER_ONE * SECONDS_PER_HOUR
@@ -126,14 +142,6 @@ public actual class LocalTime actual constructor(
         return total
     }
 
-    // org.threeten.bp.LocalTime#toSecondOfDay
-    internal fun toSecondOfDay(): Int {
-        var total: Int = hour * SECONDS_PER_HOUR
-        total += minute * SECONDS_PER_MINUTE
-        total += second
-        return total
-    }
-
     // org.threeten.bp.LocalTime#toString
     actual override fun toString(): String {
         val buf = StringBuilder(18)