Add minus operator function

src/main/kotlin/io/webcodr/sweetdate/extension/LocalDate.kt

@@ -1,17 +1,29 @@
 package io.webcodr.sweetdate.extension
 
-import io.webcodr.sweetdate.unit.Days
-import io.webcodr.sweetdate.unit.Months
 import io.webcodr.sweetdate.unit.Unit
-import io.webcodr.sweetdate.unit.Weeks
-import io.webcodr.sweetdate.unit.Years
 import java.time.LocalDate
 
-operator fun LocalDate.plus(unit: Unit): LocalDate {
-    return when(unit) {
-        is Days -> this.plusDays(unit.days)
-        is Weeks -> this.plusWeeks(unit.weeks)
-        is Months -> this.plusMonths(unit.months)
-        is Years -> this.plusYears(unit.years)
+enum class Sign {
+    PLUS, MINUS
+}
+
+fun add(
+    date: LocalDate,
+    unit: Unit,
+    sign: Sign
+): LocalDate {
+    val value = when(sign) {
+        Sign.PLUS -> unit.value
+        Sign.MINUS -> -unit.value
     }
+
+    return date.plus(value, unit.chronoUnit)
+}
+
+operator fun LocalDate.plus(unit: Unit): LocalDate {
+    return add(this, unit, Sign.PLUS)
+}
+
+operator fun LocalDate.minus(unit: Unit): LocalDate {
+    return add(this, unit, Sign.MINUS)
 }

src/main/kotlin/io/webcodr/sweetdate/unit/Unit.kt

@@ -1,8 +1,20 @@
 package io.webcodr.sweetdate.unit
 
-sealed class Unit
+import java.time.temporal.ChronoUnit
 
-class Days(val days: Long): Unit()
-class Weeks(val weeks: Long): Unit()
-class Months(val months: Long): Unit()
-class Years(val years: Long): Unit()
+sealed class Unit(val value: Long) {
+    abstract val chronoUnit: ChronoUnit
+}
+
+class Days(value: Long): Unit(value) {
+    override val chronoUnit = ChronoUnit.DAYS
+}
+class Weeks(value: Long): Unit(value) {
+    override val chronoUnit = ChronoUnit.WEEKS
+}
+class Months(value: Long): Unit(value) {
+    override val chronoUnit = ChronoUnit.MONTHS
+}
+class Years(value: Long): Unit(value) {
+    override val chronoUnit = ChronoUnit.YEARS
+}

src/test/kotlin/io/webcodr/sweetdate/extension/LocalDateTest.kt

@@ -10,35 +10,61 @@ import org.junit.jupiter.api.Assertions.*
 import java.time.LocalDate
 
 internal class LocalDateTest {
+    private val baseDate = LocalDate.now()
+
     @Test
     fun testPlusDays() {
-        val baseDate = LocalDate.now()
         val result = baseDate + Days(10)
 
         assertEquals(baseDate.plusDays(10), result)
     }
 
     @Test
     fun testPlusWeeks() {
-        val baseDate = LocalDate.now()
         val result = baseDate + Weeks(10)
 
         assertEquals(baseDate.plusWeeks(10), result)
     }
 
     @Test
     fun testPlusMonths() {
-        val baseDate = LocalDate.now()
         val result = baseDate + Months(10)
 
         assertEquals(baseDate.plusMonths(10), result)
     }
 
     @Test
     fun testPlusYears() {
-        val baseDate = LocalDate.now()
         val result = baseDate + Years(10)
 
         assertEquals(baseDate.plusYears(10), result)
     }
+
+    @Test
+    fun testMinusDays() {
+        val result = baseDate - Days(10)
+
+        assertEquals(baseDate.minusDays(10), result)
+    }
+
+    @Test
+    fun testMinusWeeks() {
+        val result = baseDate - Weeks(10)
+
+        assertEquals(baseDate.minusWeeks(10), result)
+    }
+
+    @Test
+    fun testMinusMonths() {
+        val result = baseDate - Months(10)
+
+        assertEquals(baseDate.minusMonths(10), result)
+    }
+
+    @Test
+    fun testMinusYears() {
+        val result = baseDate - Years(10)
+
+        assertEquals(baseDate.minusYears(10), result)
+    }
 }