From 7124884b493a85d893540ce0e3dee634b97409b4 Mon Sep 17 00:00:00 2001
From: Arkadii Ivanov <arkadii.ivanov@corp.badoo.com>
Date: Fri, 20 Mar 2020 13:02:47 +0000
Subject: [PATCH] Optimize Maybe.switchIfEmpty(Single)

---
 .../com/badoo/reaktive/maybe/SwitchIfEmpty.kt | 22 +++++-
 .../reaktive/maybe/SwitchIfEmptySingleTest.kt | 77 +++++++++++++++++++
 2 files changed, 96 insertions(+), 3 deletions(-)
 create mode 100644 reaktive/src/commonTest/kotlin/com/badoo/reaktive/maybe/SwitchIfEmptySingleTest.kt

diff --git a/reaktive/src/commonMain/kotlin/com/badoo/reaktive/maybe/SwitchIfEmpty.kt b/reaktive/src/commonMain/kotlin/com/badoo/reaktive/maybe/SwitchIfEmpty.kt
index ba6bb2f5d..2d7e87eae 100644
--- a/reaktive/src/commonMain/kotlin/com/badoo/reaktive/maybe/SwitchIfEmpty.kt
+++ b/reaktive/src/commonMain/kotlin/com/badoo/reaktive/maybe/SwitchIfEmpty.kt
@@ -6,7 +6,9 @@ import com.badoo.reaktive.base.SuccessCallback
 import com.badoo.reaktive.base.subscribeSafe
 import com.badoo.reaktive.disposable.Disposable
 import com.badoo.reaktive.single.Single
-import com.badoo.reaktive.single.asMaybe
+import com.badoo.reaktive.single.SingleCallbacks
+import com.badoo.reaktive.single.SingleObserver
+import com.badoo.reaktive.single.single
 
 fun <T> Maybe<T>.switchIfEmpty(other: Maybe<T>): Maybe<T> =
     maybe { emitter ->
@@ -27,5 +29,19 @@ fun <T> Maybe<T>.switchIfEmpty(other: Maybe<T>): Maybe<T> =
     }
 
 fun <T> Maybe<T>.switchIfEmpty(other: Single<T>): Single<T> =
-    switchIfEmpty(other.asMaybe())
-        .asSingleOrError()
+    single { emitter ->
+        subscribe(
+            object : MaybeObserver<T>, SuccessCallback<T> by emitter, ErrorCallback by emitter {
+                override fun onSubscribe(disposable: Disposable) {
+                    emitter.setDisposable(disposable)
+                }
+
+                override fun onComplete() {
+                    other.subscribeSafe(
+                        object : SingleObserver<T>, Observer by this, SingleCallbacks<T> by emitter {
+                        }
+                    )
+                }
+            }
+        )
+    }
diff --git a/reaktive/src/commonTest/kotlin/com/badoo/reaktive/maybe/SwitchIfEmptySingleTest.kt b/reaktive/src/commonTest/kotlin/com/badoo/reaktive/maybe/SwitchIfEmptySingleTest.kt
new file mode 100644
index 000000000..c96d7e3ef
--- /dev/null
+++ b/reaktive/src/commonTest/kotlin/com/badoo/reaktive/maybe/SwitchIfEmptySingleTest.kt
@@ -0,0 +1,77 @@
+package com.badoo.reaktive.maybe
+
+import com.badoo.reaktive.single.singleOf
+import com.badoo.reaktive.test.base.assertError
+import com.badoo.reaktive.test.base.assertSubscribed
+import com.badoo.reaktive.test.base.hasSubscribers
+import com.badoo.reaktive.test.maybe.TestMaybe
+import com.badoo.reaktive.test.single.TestSingle
+import com.badoo.reaktive.test.single.assertSuccess
+import com.badoo.reaktive.test.single.test
+import kotlin.test.Test
+import kotlin.test.assertFalse
+
+class SwitchIfEmptySingleTest : MaybeToSingleTests by MaybeToSingleTestsImpl({ switchIfEmpty(singleOf(0)) }) {
+
+    private val upstream = TestMaybe<Int?>()
+    private val other = TestSingle<Int?>()
+    private val observer = upstream.switchIfEmpty(other).test()
+
+    @Test
+    fun succeeds_WHEN_upstream_succeeded_with_non_null_value() {
+        upstream.onSuccess(0)
+
+        observer.assertSuccess(0)
+    }
+
+    @Test
+    fun succeeds_WHEN_upstream_succeeded_with_null_value() {
+        upstream.onSuccess(null)
+
+        observer.assertSuccess(null)
+    }
+
+    @Test
+    fun does_not_subscribe_to_other_IF_upstream_not_finished() {
+        assertFalse(other.hasSubscribers)
+    }
+
+    @Test
+    fun does_not_subscribe_to_other_WHEN_upstream_succeeded() {
+        upstream.onSuccess(0)
+
+        assertFalse(other.hasSubscribers)
+    }
+
+    @Test
+    fun subscribes_to_other_WHEN_upstream_completed() {
+        upstream.onComplete()
+
+        observer.assertSubscribed()
+    }
+
+    @Test
+    fun succeeds_WHEN_upstream_completed_and_other_succeeded_with_non_null_value() {
+        upstream.onComplete()
+        other.onSuccess(0)
+
+        observer.assertSuccess(0)
+    }
+
+    @Test
+    fun succeeds_WHEN_upstream_completed_and_other_succeeded_with_null_value() {
+        upstream.onComplete()
+        other.onSuccess(null)
+
+        observer.assertSuccess(null)
+    }
+
+    @Test
+    fun produces_error_WHEN_upstream_completed_and_other_produced_error() {
+        val error = Exception()
+        upstream.onComplete()
+        other.onError(error)
+
+        observer.assertError(error)
+    }
+}