Match 'plus' with the corresponding 'minus' functions (#49)

Author: dkhalanskyjb

core/commonMain/src/Instant.kt

@@ -182,6 +182,29 @@ public fun String.toInstant(): Instant = Instant.parse(this)
 public expect fun Instant.plus(period: DateTimePeriod, timeZone: TimeZone): Instant
 
 /**
+ * Returns an instant that is the result of subtracting components of [DateTimePeriod] from this instant. The components
+ * are subtracted in the order from the largest units to the smallest, i.e. from years to nanoseconds.
+ *
+ * @throws DateTimeArithmeticException if this value or the results of intermediate computations are too large to fit in
+ * [LocalDateTime].
+ */
+public fun Instant.minus(period: DateTimePeriod, timeZone: TimeZone): Instant =
+    /* An overflow can happen for any component, but we are only worried about nanoseconds, as having an overflow in
+    any other component means that `plus` will throw due to the minimum value of the numeric type overflowing the
+    platform-specific limits. */
+    if (period.nanoseconds != Long.MIN_VALUE) {
+        val negatedPeriod = with(period) {
+            DateTimePeriod(-years, -months, -days, -hours, -minutes, -seconds, -nanoseconds)
+        }
+        plus(negatedPeriod, timeZone)
+    } else {
+        val negatedPeriod = with(period) {
+            DateTimePeriod(-years, -months, -days, -hours, -minutes, -seconds, -(nanoseconds+1))
+        }
+        plus(negatedPeriod, timeZone).plus(DateTimeUnit.NANOSECOND)
+    }
+
+    /**
  * Returns a [DateTimePeriod] representing the difference between `this` and [other] instants.
  *
  * The components of [DateTimePeriod] are calculated so that adding it to `this` instant results in the [other] instant.
@@ -290,6 +313,17 @@ public fun Instant.minus(other: Instant, timeZone: TimeZone): DateTimePeriod =
  */
 public expect fun Instant.plus(unit: DateTimeUnit, timeZone: TimeZone): Instant
 
+/**
+ * Returns an instant that is the result of subtracting one [unit] from this instant
+ * in the specified [timeZone].
+ *
+ * The returned instant is earlier than this instant.
+ *
+ * @throws DateTimeArithmeticException if this value or the result is too large to fit in [LocalDateTime].
+ */
+public fun Instant.minus(unit: DateTimeUnit, timeZone: TimeZone): Instant =
+    plus(-1, unit, timeZone)
+
 /**
  * Returns an instant that is the result of adding one [unit] to this instant.
  *
@@ -300,6 +334,16 @@ public expect fun Instant.plus(unit: DateTimeUnit, timeZone: TimeZone): Instant
 public fun Instant.plus(unit: DateTimeUnit.TimeBased): Instant =
     plus(1L, unit)
 
+/**
+ * Returns an instant that is the result of subtracting one [unit] from this instant.
+ *
+ * The returned instant is earlier than this instant.
+ *
+ * The return value is clamped to the platform-specific boundaries for [Instant] if the result exceeds them.
+ */
+public fun Instant.minus(unit: DateTimeUnit.TimeBased): Instant =
+    plus(-1L, unit)
+
 /**
  * Returns an instant that is the result of adding the [value] number of the specified [unit] to this instant
  * in the specified [timeZone].
@@ -311,6 +355,17 @@ public fun Instant.plus(unit: DateTimeUnit.TimeBased): Instant =
  */
 public expect fun Instant.plus(value: Int, unit: DateTimeUnit, timeZone: TimeZone): Instant
 
+/**
+ * Returns an instant that is the result of subtracting the [value] number of the specified [unit] from this instant
+ * in the specified [timeZone].
+ *
+ * If the [value] is positive, the returned instant is earlier than this instant.
+ * If the [value] is negative, the returned instant is later than this instant.
+ *
+ * @throws DateTimeArithmeticException if this value or the result is too large to fit in [LocalDateTime].
+ */
+public expect fun Instant.minus(value: Int, unit: DateTimeUnit, timeZone: TimeZone): Instant
+
 /**
  * Returns an instant that is the result of adding the [value] number of the specified [unit] to this instant.
  *
@@ -322,6 +377,17 @@ public expect fun Instant.plus(value: Int, unit: DateTimeUnit, timeZone: TimeZon
 public fun Instant.plus(value: Int, unit: DateTimeUnit.TimeBased): Instant =
     plus(value.toLong(), unit)
 
+/**
+ * Returns an instant that is the result of subtracting the [value] number of the specified [unit] from this instant.
+ *
+ * If the [value] is positive, the returned instant is earlier than this instant.
+ * If the [value] is negative, the returned instant is later than this instant.
+ *
+ * The return value is clamped to the platform-specific boundaries for [Instant] if the result exceeds them.
+ */
+public fun Instant.minus(value: Int, unit: DateTimeUnit.TimeBased): Instant =
+    minus(value.toLong(), unit)
+
 /**
  * Returns an instant that is the result of adding the [value] number of the specified [unit] to this instant
  * in the specified [timeZone].
@@ -333,6 +399,22 @@ public fun Instant.plus(value: Int, unit: DateTimeUnit.TimeBased): Instant =
  */
 public expect fun Instant.plus(value: Long, unit: DateTimeUnit, timeZone: TimeZone): Instant
 
+/**
+ * Returns an instant that is the result of subtracting the [value] number of the specified [unit] from this instant
+ * in the specified [timeZone].
+ *
+ * If the [value] is positive, the returned instant is earlier than this instant.
+ * If the [value] is negative, the returned instant is later than this instant.
+ *
+ * @throws DateTimeArithmeticException if this value or the result is too large to fit in [LocalDateTime].
+ */
+public fun Instant.minus(value: Long, unit: DateTimeUnit, timeZone: TimeZone) =
+    if (value != Long.MIN_VALUE) {
+        plus(-value, unit, timeZone)
+    } else {
+        plus(-(value + 1), unit, timeZone).plus(unit, timeZone)
+    }
+
 /**
  * Returns an instant that is the result of adding the [value] number of the specified [unit] to this instant.
  *
@@ -343,6 +425,21 @@ public expect fun Instant.plus(value: Long, unit: DateTimeUnit, timeZone: TimeZo
  */
 public expect fun Instant.plus(value: Long, unit: DateTimeUnit.TimeBased): Instant
 
+/**
+ * Returns an instant that is the result of subtracting the [value] number of the specified [unit] from this instant.
+ *
+ * If the [value] is positive, the returned instant is earlier than this instant.
+ * If the [value] is negative, the returned instant is later than this instant.
+ *
+ * The return value is clamped to the platform-specific boundaries for [Instant] if the result exceeds them.
+ */
+public fun Instant.minus(value: Long, unit: DateTimeUnit.TimeBased): Instant =
+    if (value != Long.MIN_VALUE) {
+        plus(-value, unit)
+    } else {
+        plus(-(value + 1), unit).plus(unit)
+    }
+
 /**
  * Returns the whole number of the specified date or time [units][unit] between [other] and `this` instants
  * in the specified [timeZone].

core/commonMain/src/LocalDate.kt

@@ -110,6 +110,23 @@ public fun LocalDate.atTime(hour: Int, minute: Int, second: Int = 0, nanosecond:
  */
 expect operator fun LocalDate.plus(period: DatePeriod): LocalDate
 
+/**
+ * Returns a date that is the result of subtracting components of [DatePeriod] from this date. The components are
+ * subtracted in the order from the largest units to the smallest, i.e. from years to days.
+ *
+ * @see LocalDate.periodUntil
+ * @throws DateTimeArithmeticException if this value or the results of intermediate computations are too large to fit in
+ * [LocalDate].
+ */
+public operator fun LocalDate.minus(period: DatePeriod): LocalDate =
+    if (period.days != Int.MIN_VALUE && period.months != Int.MIN_VALUE) {
+        plus(with(period) { DatePeriod(-years, -months, -days) })
+    } else {
+        minus(period.years, DateTimeUnit.YEAR).
+        minus(period.months, DateTimeUnit.MONTH).
+        minus(period.days, DateTimeUnit.DAY)
+    }
+
 /**
  * Returns a [DatePeriod] representing the difference between `this` and [other] dates.
  *
@@ -186,6 +203,15 @@ public expect fun LocalDate.yearsUntil(other: LocalDate): Int
  */
 public expect fun LocalDate.plus(unit: DateTimeUnit.DateBased): LocalDate
 
+/**
+ * Returns a [LocalDate] that is the result of subtracting one [unit] from this date.
+ *
+ * The returned date is earlier than this date.
+ *
+ * @throws DateTimeArithmeticException if the result exceeds the boundaries of [LocalDate].
+ */
+public fun LocalDate.minus(unit: DateTimeUnit.DateBased): LocalDate = plus(-1, unit)
+
 /**
  * Returns a [LocalDate] that is the result of adding the [value] number of the specified [unit] to this date.
  *
@@ -196,6 +222,16 @@ public expect fun LocalDate.plus(unit: DateTimeUnit.DateBased): LocalDate
  */
 public expect fun LocalDate.plus(value: Int, unit: DateTimeUnit.DateBased): LocalDate
 
+/**
+ * Returns a [LocalDate] that is the result of subtracting the [value] number of the specified [unit] from this date.
+ *
+ * If the [value] is positive, the returned date is earlier than this date.
+ * If the [value] is negative, the returned date is later than this date.
+ *
+ * @throws DateTimeArithmeticException if the result exceeds the boundaries of [LocalDate].
+ */
+public expect fun LocalDate.minus(value: Int, unit: DateTimeUnit.DateBased): LocalDate
+
 /**
  * Returns a [LocalDate] that is the result of adding the [value] number of the specified [unit] to this date.
  *
@@ -205,3 +241,13 @@ public expect fun LocalDate.plus(value: Int, unit: DateTimeUnit.DateBased): Loca
  * @throws DateTimeArithmeticException if the result exceeds the boundaries of [LocalDate].
  */
 public expect fun LocalDate.plus(value: Long, unit: DateTimeUnit.DateBased): LocalDate
+
+/**
+ * Returns a [LocalDate] that is the result of subtracting the [value] number of the specified [unit] from this date.
+ *
+ * If the [value] is positive, the returned date is earlier than this date.
+ * If the [value] is negative, the returned date is later than this date.
+ *
+ * @throws DateTimeArithmeticException if the result exceeds the boundaries of [LocalDate].
+ */
+public fun LocalDate.minus(value: Long, unit: DateTimeUnit.DateBased): LocalDate = plus(-value, unit)

core/commonTest/src/InstantTest.kt

@@ -100,6 +100,9 @@ class InstantTest {
                 val diff = instant2.minus(instant1, timeUnit, zone)
                 assertEquals(instant2 - instant1, timeUnit.duration * diff.toDouble())
                 assertEquals(instant2, instant1.plus(diff, timeUnit, zone))
+                assertEquals(instant1, instant2.minus(diff, timeUnit, zone))
+                assertEquals(instant2, instant1.plus(diff, timeUnit))
+                assertEquals(instant1, instant2.minus(diff, timeUnit))
             }
         }
 
@@ -109,12 +112,14 @@ class InstantTest {
         val instant2 = instant1.plus(DateTimePeriod(hours = 24), zone)
         checkComponents(instant2.toLocalDateTime(zone), 2019, 10, 28, 1, 59)
         expectBetween(instant1, instant2, 24, DateTimeUnit.HOUR)
+        assertEquals(instant1, instant2.minus(DateTimePeriod(hours = 24), zone))
 
         val instant3 = instant1.plus(DateTimeUnit.DAY, zone)
         checkComponents(instant3.toLocalDateTime(zone), 2019, 10, 28, 2, 59)
         expectBetween(instant1, instant3, 25, DateTimeUnit.HOUR)
         expectBetween(instant1, instant3, 1, DateTimeUnit.DAY)
         assertEquals(1, instant1.daysUntil(instant3, zone))
+        assertEquals(instant1.minus(DateTimeUnit.HOUR), instant2.minus(DateTimeUnit.DAY, zone))
 
         val instant4 = instant1.plus(14, DateTimeUnit.MONTH, zone)
         checkComponents(instant4.toLocalDateTime(zone), 2020, 12, 27, 2, 59)
@@ -124,19 +129,21 @@ class InstantTest {
         expectBetween(instant1, instant4, 61, DateTimeUnit.WEEK)
         expectBetween(instant1, instant4, 366 + 31 + 30, DateTimeUnit.DAY)
         expectBetween(instant1, instant4, (366 + 31 + 30) * 24 + 1, DateTimeUnit.HOUR)
-
+        assertEquals(instant1.plus(DateTimeUnit.HOUR), instant4.minus(14, DateTimeUnit.MONTH, zone))
 
         val period = DateTimePeriod(days = 1, hours = 1)
         val instant5 = instant1.plus(period, zone)
         checkComponents(instant5.toLocalDateTime(zone), 2019, 10, 28, 3, 59)
         assertEquals(period, instant1.periodUntil(instant5, zone))
         assertEquals(period, instant5.minus(instant1, zone))
         assertEquals(26.hours, instant5.minus(instant1))
+        assertEquals(instant1.plus(DateTimeUnit.HOUR), instant5.minus(period, zone))
 
         val instant6 = instant1.plus(23, DateTimeUnit.HOUR, zone)
         checkComponents(instant6.toLocalDateTime(zone), 2019, 10, 28, 0, 59)
         expectBetween(instant1, instant6, 23, DateTimeUnit.HOUR)
         expectBetween(instant1, instant6, 0, DateTimeUnit.DAY)
+        assertEquals(instant1, instant6.minus(23, DateTimeUnit.HOUR, zone))
     }
 
     @Test
@@ -465,6 +472,19 @@ class InstantRangeTest {
             assertArithmeticFails("$instant") { instant.plus(DateTimePeriod(seconds = Long.MAX_VALUE), UTC) }
             assertArithmeticFails("$instant") { instant.plus(DateTimePeriod(seconds = Long.MIN_VALUE), UTC) }
         }
+        // Arithmetic overflow in an Int
+        for (instant in smallInstants + listOf(maxValidInstant)) {
+            assertEquals(instant.epochSeconds + Int.MIN_VALUE,
+                instant.plus(Int.MIN_VALUE, DateTimeUnit.SECOND, UTC).epochSeconds)
+            assertEquals(instant.epochSeconds - Int.MAX_VALUE,
+                instant.minus(Int.MAX_VALUE, DateTimeUnit.SECOND, UTC).epochSeconds)
+        }
+        for (instant in smallInstants + listOf(minValidInstant)) {
+            assertEquals(instant.epochSeconds + Int.MAX_VALUE,
+                instant.plus(Int.MAX_VALUE, DateTimeUnit.SECOND, UTC).epochSeconds)
+            assertEquals(instant.epochSeconds - Int.MIN_VALUE,
+                instant.minus(Int.MIN_VALUE, DateTimeUnit.SECOND, UTC).epochSeconds)
+        }
         // Overflowing a LocalDateTime in input
         maxValidInstant.plus(DateTimePeriod(nanoseconds = -1), UTC)
         minValidInstant.plus(DateTimePeriod(nanoseconds = 1), UTC)

core/commonTest/src/LocalDateTest.kt

@@ -91,6 +91,9 @@ class LocalDateTest {
         checkComponents(startDate.plus(1, DateTimeUnit.DAY), 2016, 3, 1)
         checkComponents(startDate.plus(DateTimeUnit.YEAR), 2017, 2, 28)
         checkComponents(startDate + DatePeriod(years = 4), 2020, 2, 29)
+        assertEquals(startDate, startDate.plus(DateTimeUnit.DAY).minus(DateTimeUnit.DAY))
+        assertEquals(startDate, startDate.plus(3, DateTimeUnit.DAY).minus(3, DateTimeUnit.DAY))
+        assertEquals(startDate, startDate + DatePeriod(years = 4) - DatePeriod(years = 4))
 
         checkComponents(LocalDate.parse("2016-01-31") + DatePeriod(months = 1), 2016, 2, 29)
 

core/jsMain/src/Instant.kt

@@ -163,6 +163,12 @@ public actual fun Instant.plus(value: Int, unit: DateTimeUnit, timeZone: TimeZon
             throw e
         }
 
+public actual fun Instant.minus(value: Int, unit: DateTimeUnit, timeZone: TimeZone): Instant =
+    if (value == Int.MIN_VALUE)
+        plus(-value.toLong(), unit, timeZone)
+    else
+        plus(-value, unit, timeZone)
+
 actual fun Instant.plus(value: Long, unit: DateTimeUnit.TimeBased): Instant =
     try {
         multiplyAndDivide(value, unit.nanoseconds, NANOS_PER_ONE.toLong()).let { (d, r) ->

core/jsMain/src/LocalDate.kt

@@ -50,6 +50,7 @@ public actual class LocalDate internal constructor(internal val value: jtLocalDa
 
 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.minus(value: Int, unit: DateTimeUnit.DateBased): LocalDate = plusNumber(-value, unit)
 public actual fun LocalDate.plus(value: Long, unit: DateTimeUnit.DateBased): LocalDate = plusNumber(value, unit)
 
 private fun LocalDate.plusNumber(value: Number, unit: DateTimeUnit.DateBased): LocalDate =

core/jvmMain/src/Instant.kt

@@ -113,6 +113,9 @@ public actual fun Instant.plus(unit: DateTimeUnit, timeZone: TimeZone): Instant
 public actual fun Instant.plus(value: Int, unit: DateTimeUnit, timeZone: TimeZone): Instant =
         plus(value.toLong(), unit, timeZone)
 
+public actual fun Instant.minus(value: Int, unit: DateTimeUnit, timeZone: TimeZone): Instant =
+        plus(-value.toLong(), unit, timeZone)
+
 public actual fun Instant.plus(value: Long, unit: DateTimeUnit, timeZone: TimeZone): Instant =
         try {
             val thisZdt = atZone(timeZone)

core/jvmMain/src/LocalDate.kt

@@ -55,6 +55,9 @@ public actual fun LocalDate.plus(unit: DateTimeUnit.DateBased): LocalDate =
 public actual fun LocalDate.plus(value: Int, unit: DateTimeUnit.DateBased): LocalDate =
         plus(value.toLong(), unit)
 
+public actual fun LocalDate.minus(value: Int, unit: DateTimeUnit.DateBased): LocalDate =
+        plus(-value.toLong(), unit)
+
 public actual fun LocalDate.plus(value: Long, unit: DateTimeUnit.DateBased): LocalDate =
         try {
             when (unit) {

core/nativeMain/src/Instant.kt

@@ -300,6 +300,8 @@ public actual fun Instant.plus(unit: DateTimeUnit, timeZone: TimeZone): Instant
     plus(1L, unit, timeZone)
 public actual fun Instant.plus(value: Int, unit: DateTimeUnit, timeZone: TimeZone): Instant =
     plus(value.toLong(), unit, timeZone)
+public actual fun Instant.minus(value: Int, unit: DateTimeUnit, timeZone: TimeZone): Instant =
+    plus(-value.toLong(), unit, timeZone)
 public actual fun Instant.plus(value: Long, unit: DateTimeUnit, timeZone: TimeZone): Instant = try {
     when (unit) {
         is DateTimeUnit.DateBased -> {

core/nativeMain/src/LocalDate.kt

@@ -259,6 +259,8 @@ public actual fun LocalDate.plus(value: Int, unit: DateTimeUnit.DateBased): Loca
         throw DateTimeArithmeticException("Boundaries of LocalDate exceeded when adding a value", e)
     }
 
+public actual fun LocalDate.minus(value: Int, unit: DateTimeUnit.DateBased): LocalDate = plus(-value, unit)
+
 public actual fun LocalDate.plus(value: Long, unit: DateTimeUnit.DateBased): LocalDate =
         if (value > Int.MAX_VALUE || value < Int.MIN_VALUE)
             throw DateTimeArithmeticException("Can't add a Long to a LocalDate") // TODO: less specific message

core/nativeMain/src/ZonedDateTime.kt

@@ -16,7 +16,16 @@ internal class ZonedDateTime(val dateTime: LocalDateTime, private val zone: Time
     internal fun plus(value: Int, unit: DateTimeUnit.DateBased): ZonedDateTime = dateTime.plus(value, unit).resolve()
 
     // Never throws in practice
-    private fun LocalDateTime.resolve(): ZonedDateTime = with(zone) { atZone(offset) }
+    private fun LocalDateTime.resolve(): ZonedDateTime =
+        // workaround for https://github.com/Kotlin/kotlinx-datetime/issues/51
+        if (toInstant(offset).toLocalDateTime(zone) == this@resolve) {
+            // this LocalDateTime is valid in these timezone and offset.
+            ZonedDateTime(this, zone, offset)
+        } else {
+            // this LDT does need proper resolving, as the instant that it would map to given the preferred offset
+            // is is mapped to another LDT.
+            with(zone) { atZone(offset) }
+        }
 
     override fun equals(other: Any?): Boolean =
         this === other || other is ZonedDateTime &&