Add helper to convert a kotlin flow to a Condition

This extension function makes it easier to convert a kotlin flow to a
Condition for interoperability between the repository pattern which
utilizes flows and the Monitor framework.

Bug: 277762120
Test: atest ConditionExtensionsTest
Change-Id: I1e0b137ff87f489eaaa94799df48fcb86e882358

packages/SystemUI/shared/src/com/android/systemui/shared/condition/ConditionExtensions.kt

@@ -0,0 +1,23 @@
+package com.android.systemui.shared.condition
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.launch
+
+/** Converts a boolean flow to a [Condition] object which can be used with a [Monitor] */
+@JvmOverloads
+fun Flow<Boolean>.toCondition(scope: CoroutineScope, initialValue: Boolean? = null): Condition {
+    return object : Condition(initialValue, false) {
+        var job: Job? = null
+
+        override fun start() {
+            job = scope.launch { collect { updateCondition(it) } }
+        }
+
+        override fun stop() {
+            job?.cancel()
+            job = null
+        }
+    }
+}

packages/SystemUI/tests/src/com/android/systemui/shared/condition/ConditionExtensionsTest.kt

@@ -0,0 +1,135 @@
+package com.android.systemui.shared.condition
+
+import android.testing.AndroidTestingRunner
+import androidx.test.filters.SmallTest
+import com.android.systemui.SysuiTestCase
+import com.google.common.truth.Truth.assertThat
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.MutableSharedFlow
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.emptyFlow
+import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.TestScope
+import kotlinx.coroutines.test.runCurrent
+import kotlinx.coroutines.test.runTest
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@OptIn(ExperimentalCoroutinesApi::class)
+@SmallTest
+@RunWith(AndroidTestingRunner::class)
+class ConditionExtensionsTest : SysuiTestCase() {
+    private lateinit var testScope: TestScope
+
+    @Before
+    fun setUp() {
+        testScope = TestScope(StandardTestDispatcher())
+    }
+
+    @Test
+    fun flowInitiallyTrue() =
+        testScope.runTest {
+            val flow = flowOf(true)
+            val condition = flow.toCondition(this)
+
+            runCurrent()
+            assertThat(condition.isConditionSet).isFalse()
+
+            condition.start()
+            runCurrent()
+            assertThat(condition.isConditionSet).isTrue()
+            assertThat(condition.isConditionMet).isTrue()
+        }
+
+    @Test
+    fun flowInitiallyFalse() =
+        testScope.runTest {
+            val flow = flowOf(false)
+            val condition = flow.toCondition(this)
+
+            runCurrent()
+            assertThat(condition.isConditionSet).isFalse()
+
+            condition.start()
+            runCurrent()
+            assertThat(condition.isConditionSet).isTrue()
+            assertThat(condition.isConditionMet).isFalse()
+        }
+
+    @Test
+    fun emptyFlowWithNoInitialValue() =
+        testScope.runTest {
+            val flow = emptyFlow<Boolean>()
+            val condition = flow.toCondition(this)
+            condition.start()
+
+            runCurrent()
+            assertThat(condition.isConditionSet).isFalse()
+            assertThat(condition.isConditionMet).isFalse()
+        }
+
+    @Test
+    fun emptyFlowWithInitialValueOfTrue() =
+        testScope.runTest {
+            val flow = emptyFlow<Boolean>()
+            val condition = flow.toCondition(scope = this, initialValue = true)
+            condition.start()
+
+            runCurrent()
+            assertThat(condition.isConditionSet).isTrue()
+            assertThat(condition.isConditionMet).isTrue()
+        }
+
+    @Test
+    fun emptyFlowWithInitialValueOfFalse() =
+        testScope.runTest {
+            val flow = emptyFlow<Boolean>()
+            val condition = flow.toCondition(scope = this, initialValue = false)
+            condition.start()
+
+            runCurrent()
+            assertThat(condition.isConditionSet).isTrue()
+            assertThat(condition.isConditionMet).isFalse()
+        }
+
+    @Test
+    fun conditionUpdatesWhenFlowEmitsNewValue() =
+        testScope.runTest {
+            val flow = MutableStateFlow(false)
+            val condition = flow.toCondition(this)
+            condition.start()
+
+            runCurrent()
+            assertThat(condition.isConditionSet).isTrue()
+            assertThat(condition.isConditionMet).isFalse()
+
+            flow.value = true
+            runCurrent()
+            assertThat(condition.isConditionMet).isTrue()
+
+            flow.value = false
+            runCurrent()
+            assertThat(condition.isConditionMet).isFalse()
+
+            condition.stop()
+        }
+
+    @Test
+    fun stoppingConditionUnsubscribesFromFlow() =
+        testScope.runTest {
+            val flow = MutableSharedFlow<Boolean>()
+            val condition = flow.toCondition(this)
+            runCurrent()
+            assertThat(flow.subscriptionCount.value).isEqualTo(0)
+
+            condition.start()
+            runCurrent()
+            assertThat(flow.subscriptionCount.value).isEqualTo(1)
+
+            condition.stop()
+            runCurrent()
+            assertThat(flow.subscriptionCount.value).isEqualTo(0)
+        }
+}