De-duplicate loading logic in TreehouseAppContent#preload and `Tree…

…houseAppContent#bind` (#1714)

redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/Content.kt

@@ -19,6 +19,7 @@ import app.cash.redwood.ui.OnBackPressedDispatcher
 import app.cash.redwood.ui.UiConfiguration
 import kotlin.native.ObjCName
 import kotlinx.coroutines.CancellationException
+import kotlinx.coroutines.flow.StateFlow
 
 /**
  * A UI built as an interactive widget tree, that may or may not be actively running, or bound to an
@@ -43,7 +44,7 @@ public interface Content {
    */
   public fun preload(
     onBackPressedDispatcher: OnBackPressedDispatcher,
-    uiConfiguration: UiConfiguration,
+    uiConfiguration: StateFlow<UiConfiguration>,
   )
 
   /**

redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/TreehouseAppContent.kt

@@ -51,10 +51,10 @@ private sealed interface ViewState {
 
   data class Preloading(
     val onBackPressedDispatcher: OnBackPressedDispatcher,
-    val uiConfiguration: UiConfiguration,
+    val uiConfiguration: StateFlow<UiConfiguration>,
   ) : ViewState
 
-  class Bound(
+  data class Bound(
     val view: TreehouseView<*>,
   ) : ViewState
 }
@@ -82,7 +82,7 @@ internal class TreehouseAppContent<A : AppService>(
 
   override fun preload(
     onBackPressedDispatcher: OnBackPressedDispatcher,
-    uiConfiguration: UiConfiguration,
+    uiConfiguration: StateFlow<UiConfiguration>,
   ) {
     dispatchers.checkUi()
     val previousState = stateFlow.value
@@ -101,7 +101,7 @@ internal class TreehouseAppContent<A : AppService>(
             codeSession = codeSession,
             isInitialLaunch = true,
             onBackPressedDispatcher = onBackPressedDispatcher,
-            firstUiConfiguration = MutableStateFlow(nextViewState.uiConfiguration),
+            firstUiConfiguration = uiConfiguration,
           ),
         )
       }
@@ -116,34 +116,18 @@ internal class TreehouseAppContent<A : AppService>(
 
   override fun bind(view: TreehouseView<*>) {
     dispatchers.checkUi()
+
+    if (stateFlow.value.viewState == ViewState.Bound(view)) return // Idempotent.
+
+    preload(view.onBackPressedDispatcher, view.uiConfiguration)
+
     val previousState = stateFlow.value
     val previousViewState = previousState.viewState
 
-    if (previousViewState is ViewState.Bound && previousViewState.view == view) return // Idempotent.
-    check(previousViewState is ViewState.None || previousViewState is ViewState.Preloading)
+    check(previousViewState is ViewState.Preloading)
 
     val nextViewState = ViewState.Bound(view)
-
-    // Start the code if necessary.
-    val codeSession = codeHost.codeSession
-    val nextCodeState = when {
-      previousState.codeState is CodeState.Idle && codeSession != null -> {
-        CodeState.Running(
-          startViewCodeContentBinding(
-            codeSession = codeSession,
-            isInitialLaunch = true,
-            onBackPressedDispatcher = nextViewState.view.onBackPressedDispatcher,
-            firstUiConfiguration = nextViewState.view.uiConfiguration,
-          ),
-        )
-      }
-      else -> previousState.codeState
-    }
-
-    // Ask to get notified when code is ready.
-    if (previousViewState is ViewState.None) {
-      codeHost.addListener(this)
-    }
+    val nextCodeState = previousState.codeState
 
     // Make sure we're showing something in the view; either loaded code or a spinner to show that
     // code is coming.
@@ -201,7 +185,7 @@ internal class TreehouseAppContent<A : AppService>(
     }
 
     val uiConfiguration = when (viewState) {
-      is ViewState.Preloading -> MutableStateFlow(viewState.uiConfiguration)
+      is ViewState.Preloading -> viewState.uiConfiguration
       is ViewState.Bound -> viewState.view.uiConfiguration
       else -> error("unexpected receiveCodeSession with no view bound and no preload")
     }

redwood-treehouse-host/src/commonTest/kotlin/app/cash/redwood/treehouse/CodeHostTest.kt

@@ -294,6 +294,6 @@ class CodeHostTest {
   }
 
   private fun treehouseView(name: String): FakeTreehouseView {
-    return FakeTreehouseView(onBackPressedDispatcher, name)
+    return FakeTreehouseView(name, onBackPressedDispatcher)
   }
 }

redwood-treehouse-host/src/commonTest/kotlin/app/cash/redwood/treehouse/FakeTreehouseView.kt

@@ -20,10 +20,12 @@ import app.cash.redwood.ui.UiConfiguration
 import app.cash.redwood.widget.MutableListChildren
 import app.cash.redwood.widget.SavedStateRegistry
 import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
 
 internal class FakeTreehouseView(
-  override val onBackPressedDispatcher: FakeOnBackPressedDispatcher,
   private val name: String,
+  override val onBackPressedDispatcher: FakeOnBackPressedDispatcher,
+  override val uiConfiguration: StateFlow<UiConfiguration> = MutableStateFlow(UiConfiguration()),
 ) : TreehouseView<FakeWidget> {
   override val widgetSystem = FakeWidgetSystem()
 
@@ -41,8 +43,6 @@ internal class FakeTreehouseView(
 
   override val children = MutableListChildren<FakeWidget>()
 
-  override val uiConfiguration = MutableStateFlow(UiConfiguration())
-
   override val savedStateRegistry: SavedStateRegistry? = null
 
   override fun reset() {

redwood-treehouse-host/src/commonTest/kotlin/app/cash/redwood/treehouse/TreehouseAppContentTest.kt

@@ -27,6 +27,7 @@ import kotlin.test.Test
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.cancel
+import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.runBlocking
 import kotlinx.coroutines.test.UnconfinedTestDispatcher
 import kotlinx.coroutines.test.runTest
@@ -52,7 +53,7 @@ class TreehouseAppContentTest {
     frameClockFactory = FakeFrameClock.Factory,
   )
   private val codeEventPublisher = FakeCodeEventPublisher(eventLog)
-  private val uiConfiguration = UiConfiguration()
+  private val uiConfiguration = MutableStateFlow(UiConfiguration())
 
   @BeforeTest
   fun setUp() {
@@ -487,6 +488,6 @@ class TreehouseAppContentTest {
   }
 
   private fun treehouseView(name: String): FakeTreehouseView {
-    return FakeTreehouseView(onBackPressedDispatcher, name)
+    return FakeTreehouseView(name, onBackPressedDispatcher, uiConfiguration)
   }
 }