[REF] component: introduce RootFiber.setCounter and update scheduler

The goal is to be able to execute code whenever a root fiber is ready,
and before the next animation frame

src/app/app.ts

@@ -101,6 +101,7 @@ export class App<
 
   destroy() {
     if (this.root) {
+      this.scheduler.flush();
       this.root.destroy();
     }
   }

src/component/component_node.ts

@@ -245,7 +245,8 @@ export class ComponentNode<P extends object = any, E = any> implements VNode<Com
   _render(fiber: Fiber | RootFiber) {
     try {
       fiber.bdom = this.renderFn();
-      fiber.root!.counter--;
+      const root = fiber.root!;
+      root.setCounter(root.counter - 1);
     } catch (e) {
       handleError({ node: this, error: e });
     }

src/component/error_handling.ts

@@ -30,7 +30,8 @@ function _handleError(node: ComponentNode | null, error: any, isFirstRound = fal
 
     if (stopped) {
       if (isFirstRound && fiber && fiber.node.fiber) {
-        fiber.root!.counter--;
+        const root = fiber.root!;
+        root.setCounter(root.counter - 1);
       }
       return true;
     }

src/component/fibers.ts

@@ -16,7 +16,7 @@ export function makeRootFiber(node: ComponentNode): Fiber {
   let current = node.fiber;
   if (current) {
     let root = current.root!;
-    root.counter = root.counter + 1 - cancelFibers(current.children);
+    root.setCounter(root.counter + 1 - cancelFibers(current.children));
     current.children = [];
     current.bdom = null;
     if (fibersInError.has(current)) {
@@ -74,7 +74,7 @@ export class Fiber {
     if (parent) {
       this.deep = parent.deep;
       const root = parent.root!;
-      root.counter++;
+      root.setCounter(root.counter + 1);
       this.root = root;
       parent.children.push(this);
     } else {
@@ -144,6 +144,13 @@ export class RootFiber extends Fiber {
       handleError({ fiber: current || this, error: e });
     }
   }
+
+  setCounter(newValue: number) {
+    this.counter = newValue;
+    if (newValue === 0) {
+      this.node.app.scheduler.flush();
+    }
+  }
 }
 
 type Position = "first-child" | "last-child";

src/component/scheduler.ts

@@ -11,27 +11,15 @@ export class Scheduler {
   // interactions with other code, such as test frameworks that override them
   static requestAnimationFrame = window.requestAnimationFrame.bind(window);
   tasks: Set<RootFiber> = new Set();
-  isRunning: boolean = false;
   requestAnimationFrame: Window["requestAnimationFrame"];
+  frame: number = 0;
 
   constructor() {
     this.requestAnimationFrame = Scheduler.requestAnimationFrame;
   }
 
-  start() {
-    this.isRunning = true;
-    this.scheduleTasks();
-  }
-
-  stop() {
-    this.isRunning = false;
-  }
-
   addFiber(fiber: Fiber) {
     this.tasks.add(fiber.root!);
-    if (!this.isRunning) {
-      this.start();
-    }
   }
 
   /**
@@ -39,39 +27,34 @@ export class Scheduler {
    * Other tasks are left unchanged.
    */
   flush() {
-    this.tasks.forEach((fiber) => {
-      if (fiber.root !== fiber) {
-        this.tasks.delete(fiber);
-        return;
-      }
-      const hasError = fibersInError.has(fiber);
-      if (hasError && fiber.counter !== 0) {
-        this.tasks.delete(fiber);
-        return;
-      }
-      if (fiber.node.status === STATUS.DESTROYED) {
-        this.tasks.delete(fiber);
-        return;
-      }
-
-      if (fiber.counter === 0) {
-        if (!hasError) {
-          fiber.complete();
-        }
-        this.tasks.delete(fiber);
-      }
-    });
-    if (this.tasks.size === 0) {
-      this.stop();
+    if (this.frame === 0) {
+      this.frame = this.requestAnimationFrame(() => {
+        this.frame = 0;
+        this.tasks.forEach((fiber) => this.processFiber(fiber));
+      });
     }
   }
 
-  scheduleTasks() {
-    this.requestAnimationFrame(() => {
-      this.flush();
-      if (this.isRunning) {
-        this.scheduleTasks();
+  processFiber(fiber: RootFiber) {
+    if (fiber.root !== fiber) {
+      this.tasks.delete(fiber);
+      return;
+    }
+    const hasError = fibersInError.has(fiber);
+    if (hasError && fiber.counter !== 0) {
+      this.tasks.delete(fiber);
+      return;
+    }
+    if (fiber.node.status === STATUS.DESTROYED) {
+      this.tasks.delete(fiber);
+      return;
+    }
+
+    if (fiber.counter === 0) {
+      if (!hasError) {
+        fiber.complete();
       }
-    });
+      this.tasks.delete(fiber);
+    }
   }
 }