Provide common LocalDate.atStartOfDateIn

Author: ilya-g

core/commonMain/src/LocalDate.kt

@@ -40,6 +40,7 @@ public fun String.toLocalDate(): LocalDate = LocalDate.parse(this)
 public fun LocalDate.atTime(hour: Int, minute: Int, second: Int = 0, nanosecond: Int = 0): LocalDateTime =
     LocalDateTime(year, monthNumber, dayOfMonth, hour, minute, second, nanosecond)
 
+public expect fun LocalDate.atStartOfDayIn(timeZone: TimeZone): Instant
 
 /**
  * @throws DateTimeArithmeticException if arithmetic overflow occurs or the boundaries of [LocalDate] are exceeded at

core/commonTest/src/LocalDateTest.kt

@@ -66,6 +66,25 @@ class LocalDateTest {
         checkLocalDateTimePart(date, datetime)
     }
 
+    @Test
+    fun atStartOfDay() {
+        val paris = TimeZone.of("Europe/Paris")
+        val parisDate = LocalDate(2008, 6, 30)
+        assertEquals(parisDate.atTime(0, 0).toInstant(paris),
+                parisDate.atStartOfDayIn(paris), "paris")
+
+        // TODO: Find another TZ transition that works in Windows
+//        val gaza = TimeZone.of("Asia/Gaza")
+//        val gazaDate = LocalDate(2007, 4, 1)
+//        assertEquals(gazaDate.atTime(1, 0).toInstant(gaza),
+//                gazaDate.atStartOfDayIn(gaza), "gaza")
+
+        val fixed = TimeZone.of("UTC+14")
+        val fixedDate = LocalDate(2007, 4, 1)
+        assertEquals(fixedDate.atTime(0, 0).toInstant(fixed),
+                fixedDate.atStartOfDayIn(fixed), "fixed")
+    }
+
     @Test
     fun addComponents() {
         val startDate = LocalDate(2016, 2, 29)

core/jsMain/src/LocalDate.kt

@@ -46,6 +46,9 @@ public actual class LocalDate internal constructor(internal val value: jtLocalDa
     actual override fun compareTo(other: LocalDate): Int = this.value.compareTo(other.value).toInt()
 }
 
+public actual fun LocalDate.atStartOfDayIn(timeZone: TimeZone): Instant =
+        this.value.atStartOfDay(timeZone.zoneId).toInstant().let(::Instant)
+
 public actual fun LocalDate.plus(unit: DateTimeUnit.DateBased): LocalDate = plusNumber(1, unit)
 public actual fun LocalDate.plus(value: Int, unit: DateTimeUnit.DateBased): LocalDate = plusNumber(value, unit)
 public actual fun LocalDate.plus(value: Long, unit: DateTimeUnit.DateBased): LocalDate = plusNumber(value, unit)

core/jvmMain/src/LocalDate.kt

@@ -47,6 +47,8 @@ public actual class LocalDate internal constructor(internal val value: jtLocalDa
     actual override fun compareTo(other: LocalDate): Int = this.value.compareTo(other.value)
 }
 
+public actual fun LocalDate.atStartOfDayIn(timeZone: TimeZone): Instant =
+        this.value.atStartOfDay(timeZone.zoneId).toInstant().let(::Instant)
 
 public actual fun LocalDate.plus(unit: DateTimeUnit.DateBased): LocalDate =
         plus(1L, unit)

core/nativeMain/src/LocalDate.kt

@@ -242,6 +242,9 @@ public actual class LocalDate actual constructor(actual val year: Int, actual va
     }
 }
 
+public actual fun LocalDate.atStartOfDayIn(timeZone: TimeZone): Instant =
+        timeZone.atStartOfDay(this)
+
 public actual fun LocalDate.plus(unit: DateTimeUnit.DateBased): LocalDate =
         plus(1, unit)
 

core/nativeTest/src/ThreeTenBpTimeZoneTest.kt

@@ -137,17 +137,4 @@ class ThreeTenBpTimeZoneTest {
             zone, ZoneOffset.ofSeconds(2 * 3600)), with(zone) { t.atZone() })
     }
 
-    @Test
-    fun atStartOfDay() {
-        val paris = TimeZone.of("Europe/Paris")
-        assertEquals(LocalDateTime(2008, 6, 30, 0, 0, 0, 0).toInstant(paris),
-            paris.atStartOfDay(LocalDate(2008, 6, 30)), "paris")
-        val gaza = TimeZone.of("Asia/Gaza")
-        assertEquals(LocalDateTime(2007, 4, 1, 1, 0, 0, 0).toInstant(gaza),
-            gaza.atStartOfDay(LocalDate(2007, 4, 1)), "gaza")
-        val fixed = TimeZone.of("UTC+14")
-        assertEquals(LocalDateTime(2007, 4, 1, 0, 0, 0, 0).toInstant(fixed),
-            fixed.atStartOfDay(LocalDate(2007, 4, 1)), "fixed")
-    }
-
 }