Fix many syncing issues (#952)

src/element/index.ts

@@ -1,3 +1,6 @@
+import { ExcalidrawElement } from "./types";
+import { isInvisiblySmallElement } from "./sizeHelpers";
+
 export { newElement, newTextElement, duplicateElement } from "./newElement";
 export {
   getElementAbsoluteCoords,
@@ -24,3 +27,28 @@ export {
   normalizeDimensions,
 } from "./sizeHelpers";
 export { showSelectedShapeActions } from "./showSelectedShapeActions";
+
+export function getSyncableElements(elements: readonly ExcalidrawElement[]) {
+  // There are places in Excalidraw where synthetic invisibly small elements are added and removed.
+  // It's probably best to keep those local otherwise there might be a race condition that
+  // gets the app into an invalid state. I've never seen it happen but I'm worried about it :)
+  return elements.filter(el => !isInvisiblySmallElement(el));
+}
+
+export function getElementMap(elements: readonly ExcalidrawElement[]) {
+  return getSyncableElements(elements).reduce(
+    (acc: { [key: string]: ExcalidrawElement }, element: ExcalidrawElement) => {
+      acc[element.id] = element;
+      return acc;
+    },
+    {},
+  );
+}
+
+export function getDrawingVersion(elements: readonly ExcalidrawElement[]) {
+  return elements.reduce((acc, el) => acc + el.version, 0);
+}
+
+export function hasNonDeletedElements(elements: readonly ExcalidrawElement[]) {
+  return elements.some(element => !element.isDeleted);
+}