Implement DateTimeUnit.toString and add tests

Author: ilya-g

core/commonMain/src/DateTimeUnit.kt

@@ -9,7 +9,6 @@ import kotlin.time.Duration
 import kotlin.time.ExperimentalTime
 import kotlin.time.nanoseconds
 
-// TODO: toString
 sealed class DateTimeUnit {
 
     abstract operator fun times(scalar: Int): DateTimeUnit
@@ -60,6 +59,8 @@ sealed class DateTimeUnit {
                 this === other || (other is TimeBased && this.nanoseconds == other.nanoseconds)
 
         override fun hashCode(): Int = nanoseconds.toInt() xor (nanoseconds shr Int.SIZE_BITS).toInt()
+
+        override fun toString(): String = formatToString(calendarScale, calendarUnit.toString())
     }
 
     sealed class DateBased : DateTimeUnit() {
@@ -78,6 +79,11 @@ sealed class DateTimeUnit {
                     this === other || (other is DayBased && this.days == other.days)
 
             override fun hashCode(): Int = days xor 0x10000
+
+            override fun toString(): String = if (days % 7 == 0)
+                formatToString(days / 7, "WEEK")
+            else
+                formatToString(days, "DAY")
         }
         class MonthBased(val months: Int) : DateBased() {
             init {
@@ -93,9 +99,18 @@ sealed class DateTimeUnit {
                     this === other || (other is MonthBased && this.months == other.months)
 
             override fun hashCode(): Int = months xor 0x20000
+
+            override fun toString(): String = when {
+                months % 12_00 == 0 -> formatToString(months / 12_00, "CENTURY")
+                months % 12 == 0 -> formatToString(months / 12, "YEAR")
+                months % 3 == 0 -> formatToString(months / 3, "QUARTER")
+                else -> formatToString(months, "MONTH")
+            }
         }
     }
 
+    protected fun formatToString(value: Int, unit: String): String = if (value == 1) unit else "$value-$unit"
+    protected fun formatToString(value: Long, unit: String): String = if (value == 1L) unit else "$value-$unit"
 
     companion object {
         val NANOSECOND = TimeBased(nanoseconds = 1)

core/commonTest/src/DateTimeUnitTest.kt

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2019-2020 JetBrains s.r.o.
+ * 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.test
+
+import kotlinx.datetime.*
+import kotlin.test.*
+
+class DateTimeUnitTest {
+    val U = DateTimeUnit // alias
+
+    @Test
+    fun baseUnits() {
+        val baseUnitProps = listOf(
+                U::NANOSECOND, U::MICROSECOND, U::MILLISECOND, U::SECOND, U::MINUTE, U::HOUR,
+                U::DAY, U::WEEK, U::MONTH, U::QUARTER, U::YEAR, U::CENTURY
+        )
+        for (unit in baseUnitProps) {
+            assertEquals(unit.name, unit.get().toString())
+        }
+
+        val allUnits = baseUnitProps.map { it.get() }
+
+        assertEquals(allUnits.size, allUnits.map { it.hashCode() }.distinct().size)
+
+        for (unit in allUnits) {
+            assertSame(unit, allUnits.singleOrNull { it == unit }) // should be no not same, but equal
+        }
+    }
+
+    @Test
+    fun productUnits() {
+        ensureEquality(U.MICROSECOND, U.NANOSECOND * 1000, "MICROSECOND")
+        ensureEquality(U.MICROSECOND * 2000, U.NANOSECOND * 2000_000, "2-MILLISECOND")
+
+        val twoDays = U.DAY * 2
+        assertEquals("2-DAY", twoDays.toString())
+
+        val twoWeeks = U.WEEK * 2
+        assertEquals("2-WEEK", twoWeeks.toString())
+        assertNotEquals(twoDays, twoWeeks)
+
+        val fortnight = U.DAY * 14
+        ensureEquality(twoWeeks, fortnight, "2-WEEK")
+
+        val fourQuarters = U.QUARTER * 4
+        ensureEquality(U.YEAR, fourQuarters, "YEAR")
+
+        val twoFourMonths = U.MONTH * 24
+        val twoYears = U.YEAR * 2
+        ensureEquality(twoYears, twoFourMonths, "2-YEAR")
+    }
+
+    private fun ensureEquality(v1: Any, v2: Any, expectToString: String) {
+        assertEquals(v1, v2)
+        assertEquals(v1.hashCode(), v2.hashCode())
+        assertEquals(v1.toString(), v2.toString())
+        assertEquals(expectToString, v2.toString())
+    }
+
+}