iOS-specific LayoutAnimation integration

Summary:
Turn on Fabric LayoutAnimations on iOS.

I will gate this change behind a QE before landing.

Changelog: [Internal]

Reviewed By: shergin

Differential Revision: D21583932

fbshipit-source-id: 0e0f988b44af37eb6fb22cccb48b0c7aa5020ca7

React/Fabric/RCTScheduler.h

@@ -64,6 +64,12 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (facebook::react::MountingCoordinator::Shared)mountingCoordinatorWithSurfaceId:(facebook::react::SurfaceId)surfaceId;
 
+- (void)onAnimationStarted;
+
+- (void)onAllAnimationsComplete;
+
+- (void)animationTick;
+
 @end
 
 NS_ASSUME_NONNULL_END

React/Fabric/RCTScheduler.mm

@@ -7,10 +7,12 @@
 
 #import "RCTScheduler.h"
 
+#import <react/animations/LayoutAnimationDriver.h>
 #import <react/componentregistry/ComponentDescriptorFactory.h>
 #import <react/debug/SystraceSection.h>
 #import <react/scheduler/Scheduler.h>
 #import <react/scheduler/SchedulerDelegate.h>
+#include <react/utils/RunLoopObserver.h>
 
 #import <React/RCTFollyConvert.h>
 
@@ -61,23 +63,82 @@ class SchedulerDelegateProxy : public SchedulerDelegate {
   void *scheduler_;
 };
 
+class LayoutAnimationDelegateProxy : public LayoutAnimationStatusDelegate, public RunLoopObserver::Delegate {
+ public:
+  LayoutAnimationDelegateProxy(void *scheduler) : scheduler_(scheduler) {}
+  virtual ~LayoutAnimationDelegateProxy() {}
+
+  void onAnimationStarted() override
+  {
+    RCTScheduler *scheduler = (__bridge RCTScheduler *)scheduler_;
+    [scheduler onAnimationStarted];
+  }
+
+  /**
+   * Called when the LayoutAnimation engine completes all pending animations.
+   */
+  void onAllAnimationsComplete() override
+  {
+    RCTScheduler *scheduler = (__bridge RCTScheduler *)scheduler_;
+    [scheduler onAllAnimationsComplete];
+  }
+
+  void activityDidChange(RunLoopObserver::Delegate const *delegate, RunLoopObserver::Activity activity) const
+      noexcept override
+  {
+    RCTScheduler *scheduler = (__bridge RCTScheduler *)scheduler_;
+    [scheduler animationTick];
+  }
+
+ private:
+  void *scheduler_;
+};
+
 @implementation RCTScheduler {
   std::shared_ptr<Scheduler> _scheduler;
+  std::shared_ptr<LayoutAnimationDriver> _animationDriver;
   std::shared_ptr<SchedulerDelegateProxy> _delegateProxy;
+  std::shared_ptr<LayoutAnimationDelegateProxy> _layoutAnimationDelegateProxy;
+  RunLoopObserver::Unique _uiRunLoopObserver;
+  BOOL _layoutAnimationsEnabled;
 }
 
 - (instancetype)initWithToolbox:(facebook::react::SchedulerToolbox)toolbox
 {
   if (self = [super init]) {
+    auto reactNativeConfig =
+        toolbox.contextContainer->at<std::shared_ptr<const ReactNativeConfig>>("ReactNativeConfig");
+    _layoutAnimationsEnabled = reactNativeConfig->getBool("react_fabric:enabled_layout_animations_ios");
+
     _delegateProxy = std::make_shared<SchedulerDelegateProxy>((__bridge void *)self);
-    _scheduler = std::make_shared<Scheduler>(toolbox, nullptr, _delegateProxy.get());
+
+    if (_layoutAnimationsEnabled) {
+      _layoutAnimationDelegateProxy = std::make_shared<LayoutAnimationDelegateProxy>((__bridge void *)self);
+      _animationDriver = std::make_unique<LayoutAnimationDriver>(_layoutAnimationDelegateProxy.get());
+      _uiRunLoopObserver =
+          toolbox.mainRunLoopObserverFactory(RunLoopObserver::Activity::BeforeWaiting, _layoutAnimationDelegateProxy);
+      _uiRunLoopObserver->setDelegate(_layoutAnimationDelegateProxy.get());
+    }
+
+    _scheduler = std::make_shared<Scheduler>(
+        toolbox, (_animationDriver ? _animationDriver.get() : nullptr), _delegateProxy.get());
   }
 
   return self;
 }
 
+- (void)animationTick
+{
+  _scheduler->animationTick();
+}
+
 - (void)dealloc
 {
+  if (_animationDriver) {
+    _animationDriver->setLayoutAnimationStatusDelegate(nullptr);
+  }
+  _animationDriver = nullptr;
+
   _scheduler->setDelegate(nullptr);
 }
 
@@ -90,7 +151,13 @@ class SchedulerDelegateProxy : public SchedulerDelegate {
   SystraceSection s("-[RCTScheduler startSurfaceWithSurfaceId:...]");
 
   auto props = convertIdToFollyDynamic(initialProps);
-  _scheduler->startSurface(surfaceId, RCTStringFromNSString(moduleName), props, layoutConstraints, layoutContext);
+  _scheduler->startSurface(
+      surfaceId,
+      RCTStringFromNSString(moduleName),
+      props,
+      layoutConstraints,
+      layoutContext,
+      (_animationDriver ? _animationDriver.get() : nullptr));
   _scheduler->renderTemplateToSurface(
       surfaceId, props.getDefault("navigationConfig").getDefault("initialUITemplate", "").getString());
 }
@@ -127,4 +194,18 @@ class SchedulerDelegateProxy : public SchedulerDelegate {
   return _scheduler->findMountingCoordinator(surfaceId);
 }
 
+- (void)onAnimationStarted
+{
+  if (_uiRunLoopObserver) {
+    _uiRunLoopObserver->enable();
+  }
+}
+
+- (void)onAllAnimationsComplete
+{
+  if (_uiRunLoopObserver) {
+    _uiRunLoopObserver->disable();
+  }
+}
+
 @end