Add SuspendAction to create an action from a suspend function

formula-coroutines/src/main/java/com/instacart/formula/coroutines/SuspendAction.kt

@@ -0,0 +1,75 @@
+package com.instacart.formula.coroutines
+
+import com.instacart.formula.Action
+import com.instacart.formula.Cancelable
+import kotlinx.coroutines.CoroutineStart
+import kotlinx.coroutines.DelicateCoroutinesApi
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+
+/**
+ * Adapter which allows creating Formula [Action] from a Kotlin suspend function. Take a
+ * look at [SuspendAction.from] to create an [Action] from [suspend] type.
+ */
+interface SuspendAction<Event> : Action<Event> {
+
+    companion object {
+        /**
+         * Creates an [Action] which will launch a [suspend] created by factory function [create]
+         *
+         * ```
+         * SuspendAction.from { locationManager.currentLocation() }.onEvent { event ->
+         *   transition()
+         * }
+         * ```
+         */
+        fun <Event> from(
+            create: suspend () -> Event
+        ): SuspendAction<Event> {
+            return SuspendActionImpl(null, create)
+        }
+
+        /**
+         * Creates an [Action] which will launch a [suspend] created by factory function [create].
+         *
+         * ```
+         * SuspendAction.from(itemId) { repo.fetchItem(itemId) }.onEvent { event ->
+         *   transition()
+         * }
+         * ```
+         *
+         * @param key Used to distinguish this [Action] from other actions.
+         */
+        fun <Event> from(
+            key: Any?,
+            create: suspend () -> Event
+        ): SuspendAction<Event> {
+            return SuspendActionImpl(key, create)
+        }
+    }
+
+    suspend fun execute(): Event
+
+    @OptIn(DelicateCoroutinesApi::class)
+    override fun start(send: (Event) -> Unit): Cancelable? {
+        val job = GlobalScope.launch(start = CoroutineStart.UNDISPATCHED) {
+            withContext(Dispatchers.Unconfined) {
+                val event = execute()
+                send(event)
+            }
+        }
+        return Cancelable(job::cancel)
+    }
+}
+
+private data class SuspendActionImpl<Event>(
+    private val key: Any?,
+    private val factory: suspend () -> Event
+) : SuspendAction<Event> {
+
+    override suspend fun execute(): Event = factory()
+
+    override fun key(): Any? = key
+}

formula-coroutines/src/test/java/com/instacart/formula/coroutines/SuspendActionTest.kt

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+package com.instacart.formula.coroutines
+
+import com.google.common.truth.Truth.assertThat
+import kotlinx.coroutines.delay
+import org.junit.Test
+
+class SuspendActionTest {
+
+    @Test
+    fun `default key is null`() {
+        val action = SuspendAction.from { delay(100) }
+        assertThat(action.key()).isNull()
+    }
+
+    @Test
+    fun `specified key`() {
+        val action = SuspendAction.from("unique-key") { delay(100) }
+        assertThat(action.key()).isEqualTo("unique-key")
+    }
+}