Duration Comparison (#262)

Author: red-avtovo

arrow-libs/fx/arrow-fx-test/src/main/kotlin/arrow/fx/test/generators/Generators.kt

@@ -9,6 +9,7 @@ import arrow.fx.DecisionPartialOf
 import arrow.fx.ForIO
 import arrow.fx.IO
 import arrow.fx.Schedule
+import arrow.fx.typeclasses.Duration
 import arrow.fx.typeclasses.Fiber
 import arrow.fx.typeclasses.FiberPartialOf
 import arrow.fx.typeclasses.nanoseconds
@@ -22,6 +23,9 @@ fun <F, A, E> Gen<E>.raiseError(AP: ApplicativeError<F, E>): Gen<Kind<F, A>> =
 
 fun Gen.Companion.timeUnit(): Gen<TimeUnit> = Gen.from(TimeUnit.values())
 
+fun duration(): Gen<Duration> =
+  Gen.bind(Gen.long(), Gen.timeUnit(), ::Duration)
+
 fun IO.Companion.genK() = object : GenK<ForIO> {
   override fun <A> genK(gen: Gen<A>): Gen<Kind<ForIO, A>> = Gen.oneOf(
     gen.map(IO.Companion::just),

arrow-libs/fx/arrow-fx/src/main/kotlin/arrow/fx/typeclasses/Duration.kt

@@ -20,6 +20,15 @@ data class Duration(val amount: Long, val timeUnit: TimeUnit) {
       else -> d + this // Swap this and d to add to the smaller unit
     }
   }
+
+  operator fun compareTo(d: Duration): Int = run {
+    val comp = timeUnit.compareTo(d.timeUnit)
+    when {
+      comp == 0 -> amount.compareTo(d.amount)
+      comp < 0 -> amount.compareTo(timeUnit.convert(d.amount, d.timeUnit))
+      else -> -d.compareTo(this)
+    }
+  }
 }
 
 operator fun Int.times(d: Duration) = d * this

arrow-libs/fx/arrow-fx/src/test/kotlin/arrow/fx/data/DurationTest.kt

@@ -1,21 +1,22 @@
 package arrow.fx.data
 
 import arrow.core.test.UnitSpec
-import arrow.core.test.generators.intSmall
-import arrow.fx.typeclasses.Duration
-import arrow.fx.test.generators.timeUnit
-import io.kotlintest.properties.Gen
 import io.kotlintest.properties.forAll
+import arrow.fx.test.generators.duration
 
 class DurationTest : UnitSpec() {
 
   init {
     "plus should be commutative" {
-      forAll(Gen.intSmall(), Gen.timeUnit(), Gen.intSmall(), Gen.timeUnit()) { i, u, j, v ->
-        val a = Duration(i.toLong(), u)
-        val b = Duration(j.toLong(), v)
+      forAll(duration(), duration()) { a, b ->
         a + b == b + a
       }
     }
+
+    "comparison should correct in both directions" {
+      forAll(duration(), duration()) { a, b ->
+        a < b == b > a
+      }
+    }
   }
 }