feat: multiplayer undo / redo (excalidraw#7348)

dev-docs/docs/@excalidraw/excalidraw/api/props/excalidraw-api.mdx

@@ -22,7 +22,7 @@ You can use this prop when you want to access some [Excalidraw APIs](https://git
 | API | Signature | Usage |
 | --- | --- | --- |
 | [updateScene](#updatescene) | `function` | updates the scene with the sceneData |
-| [updateLibrary](#updatelibrary) | `function` | updates the scene with the sceneData |
+| [updateLibrary](#updatelibrary) | `function` | updates the library |
 | [addFiles](#addfiles) | `function` | add files data to the appState |
 | [resetScene](#resetscene) | `function` | Resets the scene. If `resetLoadingState` is passed as true then it will also force set the loading state to false. |
 | [getSceneElementsIncludingDeleted](#getsceneelementsincludingdeleted) | `function` | Returns all the elements including the deleted in the scene |
@@ -65,7 +65,7 @@ You can use this function to update the scene with the sceneData. It accepts the
 | `elements` | [`ImportedDataState["elements"]`](https://github.com/excalidraw/excalidraw/blob/master/packages/excalidraw/data/types.ts#L38) | The `elements` to be updated in the scene |
 | `appState` | [`ImportedDataState["appState"]`](https://github.com/excalidraw/excalidraw/blob/master/packages/excalidraw/data/types.ts#L39) | The `appState` to be updated in the scene. |
 | `collaborators` | <code>Map<string, <a href="https://github.com/excalidraw/excalidraw/blob/master/packages/excalidraw/types.ts#L37">Collaborator></a></code> | The list of collaborators to be updated in the scene. |
-| `commitToHistory` | `boolean` | Implies if the `history (undo/redo)` should be recorded. Defaults to `false`. |
+| `commitToStore` | `boolean` | Implies if the change should be captured and commited to the `store`. Commited changes are emmitted and listened to by other components, such as `History` for undo / redo purposes. Defaults to `false`. |
 
 ```jsx live
 function App() {

excalidraw-app/App.tsx

@@ -438,7 +438,7 @@ const ExcalidrawWrapper = () => {
             excalidrawAPI.updateScene({
               ...data.scene,
               ...restore(data.scene, null, null, { repairBindings: true }),
-              commitToHistory: true,
+              commitToStore: true,
             });
           }
         });

excalidraw-app/collab/Collab.tsx

@@ -356,7 +356,6 @@ class Collab extends PureComponent<CollabProps, CollabState> {
 
       this.excalidrawAPI.updateScene({
         elements,
-        commitToHistory: false,
       });
     }
   };
@@ -501,14 +500,12 @@ class Collab extends PureComponent<CollabProps, CollabState> {
         }
         return element;
       });
-      // remove deleted elements from elements array & history to ensure we don't
+      // remove deleted elements from elements array to ensure we don't
       // expose potentially sensitive user data in case user manually deletes
       // existing elements (or clears scene), which would otherwise be persisted
       // to database even if deleted before creating the room.
-      this.excalidrawAPI.history.clear();
       this.excalidrawAPI.updateScene({
         elements,
-        commitToHistory: true,
       });
 
       this.saveCollabRoomToFirebase(getSyncableElements(elements));
@@ -544,9 +541,7 @@ class Collab extends PureComponent<CollabProps, CollabState> {
               const remoteElements = decryptedData.payload.elements;
               const reconciledElements =
                 this._reconcileElements(remoteElements);
-              this.handleRemoteSceneUpdate(reconciledElements, {
-                init: true,
-              });
+              this.handleRemoteSceneUpdate(reconciledElements);
               // noop if already resolved via init from firebase
               scenePromise.resolve({
                 elements: reconciledElements,
@@ -745,19 +740,11 @@ class Collab extends PureComponent<CollabProps, CollabState> {
 
   private handleRemoteSceneUpdate = (
     elements: ReconciledExcalidrawElement[],
-    { init = false }: { init?: boolean } = {},
   ) => {
     this.excalidrawAPI.updateScene({
       elements,
-      commitToHistory: !!init,
     });
 
-    // We haven't yet implemented multiplayer undo functionality, so we clear the undo stack
-    // when we receive any messages from another peer. This UX can be pretty rough -- if you
-    // undo, a user makes a change, and then try to redo, your element(s) will be lost. However,
-    // right now we think this is the right tradeoff.
-    this.excalidrawAPI.history.clear();
-
     this.loadImageFiles();
   };
 

excalidraw-app/data/index.ts

@@ -269,7 +269,7 @@ export const loadScene = async (
     // in the scene database/localStorage, and instead fetch them async
     // from a different database
     files: data.files,
-    commitToHistory: false,
+    commitToStore: false,
   };
 };
 

excalidraw-app/tests/collab.test.tsx

@@ -1,13 +1,18 @@
 import { vi } from "vitest";
 import {
+  act,
   render,
   updateSceneData,
   waitFor,
 } from "../../packages/excalidraw/tests/test-utils";
 import ExcalidrawApp from "../App";
 import { API } from "../../packages/excalidraw/tests/helpers/api";
-import { createUndoAction } from "../../packages/excalidraw/actions/actionHistory";
 import { syncInvalidIndices } from "../../packages/excalidraw/fractionalIndex";
+import {
+  createRedoAction,
+  createUndoAction,
+} from "../../packages/excalidraw/actions/actionHistory";
+import { newElementWith } from "../../packages/excalidraw";
 
 const { h } = window;
 
@@ -58,39 +63,188 @@ vi.mock("socket.io-client", () => {
   };
 });
 
+/**
+ * These test would deserve to be extended by testing collab with (at least) two clients simultanouesly,
+ * while having access to both scenes, appstates stores, histories and etc.
+ * i.e. multiplayer history tests could be a good first candidate, as we could test both history stacks simultaneously.
+ */
 describe("collaboration", () => {
-  it("creating room should reset deleted elements", async () => {
+  it("should allow to undo / redo even on force-deleted elements", async () => {
     await render(<ExcalidrawApp />);
-    // To update the scene with deleted elements before starting collab
+    const rect1Props = {
+      type: "rectangle",
+      id: "A",
+      height: 200,
+      width: 100,
+    } as const;
+
+    const rect2Props = {
+      type: "rectangle",
+      id: "B",
+      width: 100,
+      height: 200,
+    } as const;
+
+    const rect1 = API.createElement({ ...rect1Props });
+    const rect2 = API.createElement({ ...rect2Props });
+
+    updateSceneData({
+      elements: syncInvalidIndices([rect1, rect2]),
+      commitToStore: true,
+    });
+
     updateSceneData({
       elements: syncInvalidIndices([
-        API.createElement({ type: "rectangle", id: "A" }),
-        API.createElement({
-          type: "rectangle",
-          id: "B",
-          isDeleted: true,
-        }),
+        rect1,
+        newElementWith(h.elements[1], { isDeleted: true }),
       ]),
+      commitToStore: true,
     });
+
     await waitFor(() => {
+      expect(API.getUndoStack().length).toBe(2);
+      expect(API.getSnapshot()).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: true }),
+      ]);
       expect(h.elements).toEqual([
-        expect.objectContaining({ id: "A" }),
-        expect.objectContaining({ id: "B", isDeleted: true }),
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: true }),
       ]);
-      expect(API.getStateHistory().length).toBe(1);
     });
+
+    // one form of force deletion happens when starting the collab, not to sync potentially sensitive data into the server
     window.collab.startCollaboration(null);
+
+    await waitFor(() => {
+      expect(API.getUndoStack().length).toBe(2);
+      // we never delete from the local snapshot as it is used for correct diff calculation
+      expect(API.getSnapshot()).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: true }),
+      ]);
+      expect(h.elements).toEqual([expect.objectContaining(rect1Props)]);
+    });
+
+    const undoAction = createUndoAction(h.history, h.store);
+    act(() => h.app.actionManager.executeAction(undoAction));
+
+    // with explicit undo (as addition) we expect our item to be restored from the snapshot!
     await waitFor(() => {
-      expect(h.elements).toEqual([expect.objectContaining({ id: "A" })]);
-      expect(API.getStateHistory().length).toBe(1);
+      expect(API.getUndoStack().length).toBe(1);
+      expect(API.getSnapshot()).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: false }),
+      ]);
+      expect(h.elements).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: false }),
+      ]);
+    });
+
+    // simulate force deleting the element remotely
+    updateSceneData({
+      elements: syncInvalidIndices([rect1]),
+    });
+
+    await waitFor(() => {
+      expect(API.getUndoStack().length).toBe(1);
+      expect(API.getRedoStack().length).toBe(1);
+      expect(API.getSnapshot()).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: true }),
+      ]);
+      expect(h.elements).toEqual([expect.objectContaining(rect1Props)]);
     });
 
-    const undoAction = createUndoAction(h.history);
-    // noop
-    h.app.actionManager.executeAction(undoAction);
+    const redoAction = createRedoAction(h.history, h.store);
+    act(() => h.app.actionManager.executeAction(redoAction));
+
+    // with explicit redo (as removal) we again restore the element from the snapshot!
     await waitFor(() => {
-      expect(h.elements).toEqual([expect.objectContaining({ id: "A" })]);
-      expect(API.getStateHistory().length).toBe(1);
+      expect(API.getUndoStack().length).toBe(2);
+      expect(API.getRedoStack().length).toBe(0);
+      expect(API.getSnapshot()).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: true }),
+      ]);
+      expect(h.elements).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: true }),
+      ]);
+    });
+
+    act(() => h.app.actionManager.executeAction(undoAction));
+
+    // simulate local update
+    updateSceneData({
+      elements: syncInvalidIndices([
+        h.elements[0],
+        newElementWith(h.elements[1], { x: 100 }),
+      ]),
+      commitToStore: true,
+    });
+
+    await waitFor(() => {
+      expect(API.getUndoStack().length).toBe(2);
+      expect(API.getRedoStack().length).toBe(0);
+      expect(API.getSnapshot()).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: false, x: 100 }),
+      ]);
+      expect(h.elements).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: false, x: 100 }),
+      ]);
+    });
+
+    act(() => h.app.actionManager.executeAction(undoAction));
+
+    // we expect to iterate the stack to the first visible change
+    await waitFor(() => {
+      expect(API.getUndoStack().length).toBe(1);
+      expect(API.getRedoStack().length).toBe(1);
+      expect(API.getSnapshot()).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: false, x: 0 }),
+      ]);
+      expect(h.elements).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: false, x: 0 }),
+      ]);
+    });
+
+    // simulate force deleting the element remotely
+    updateSceneData({
+      elements: syncInvalidIndices([rect1]),
+    });
+
+    // snapshot was correctly updated and marked the element as deleted
+    await waitFor(() => {
+      expect(API.getUndoStack().length).toBe(1);
+      expect(API.getRedoStack().length).toBe(1);
+      expect(API.getSnapshot()).toEqual([
+        expect.objectContaining(rect1Props),
+        expect.objectContaining({ ...rect2Props, isDeleted: true, x: 0 }),
+      ]);
+      expect(h.elements).toEqual([expect.objectContaining(rect1Props)]);
+    });
+
+    act(() => h.app.actionManager.executeAction(redoAction));
+
+    // with explicit redo (as update) we again restored the element from the snapshot!
+    await waitFor(() => {
+      expect(API.getUndoStack().length).toBe(2);
+      expect(API.getRedoStack().length).toBe(0);
+      expect(API.getSnapshot()).toEqual([
+        expect.objectContaining({ id: "A", isDeleted: false }),
+        expect.objectContaining({ id: "B", isDeleted: true, x: 100 }),
+      ]);
+      expect(h.history.isRedoStackEmpty).toBeTruthy();
+      expect(h.elements).toEqual([
+        expect.objectContaining({ id: "A", isDeleted: false }),
+        expect.objectContaining({ id: "B", isDeleted: true, x: 100 }),
+      ]);
     });
   });
 });

packages/excalidraw/CHANGELOG.md

@@ -15,9 +15,14 @@ Please add the latest change on the top under the correct section.
 
 ### Features
 
+- Added support for multiplayer undo/redo, by calculating invertible increments and storing them inside the local-only undo/redo stacks. [#7348](https://github.com/excalidraw/excalidraw/pull/7348)
+
 - `MainMenu.DefaultItems.ToggleTheme` now supports `onSelect(theme: string)` callback, and optionally `allowSystemTheme: boolean` alongside `theme: string` to indicate you want to allow users to set to system theme (you need to handle this yourself). [#7853](https://github.com/excalidraw/excalidraw/pull/7853)
+
 - Add `useHandleLibrary`'s `opts.adapter` as the new recommended pattern to handle library initialization and persistence on library updates. [#7655](https://github.com/excalidraw/excalidraw/pull/7655)
+
 - Add `useHandleLibrary`'s `opts.migrationAdapter` adapter to handle library migration during init, when migrating from one data store to another (e.g. from LocalStorage to IndexedDB). [#7655](https://github.com/excalidraw/excalidraw/pull/7655)
+
 - Soft-deprecate `useHandleLibrary`'s `opts.getInitialLibraryItems` in favor of `opts.adapter`. [#7655](https://github.com/excalidraw/excalidraw/pull/7655)
 
 - Add `onPointerUp` prop [#7638](https://github.com/excalidraw/excalidraw/pull/7638).
@@ -30,6 +35,10 @@ Please add the latest change on the top under the correct section.
 
 ### Breaking Changes
 
+- Renamed required `updatedScene` parameter from `commitToHistory` into `commitToStore` [#7348](https://github.com/excalidraw/excalidraw/pull/7348).
+
+### Breaking Changes
+
 - `ExcalidrawEmbeddableElement.validated` was removed and moved to private editor state. This should largely not affect your apps unless you were reading from this attribute. We keep validating embeddable urls internally, and the public [`props.validateEmbeddable`](https://docs.excalidraw.com/docs/@excalidraw/excalidraw/api/props#validateembeddable) still applies. [#7539](https://github.com/excalidraw/excalidraw/pull/7539)
 
 - `ExcalidrawTextElement.baseline` was removed and replaced with a vertical offset computation based on font metrics, performed on each text element re-render. In case of custom font usage, extend the `FONT_METRICS` object with the related properties.
@@ -92,8 +101,6 @@ define: {
 
 - Disable caching bounds for arrow labels [#7343](https://github.com/excalidraw/excalidraw/pull/7343)
 
----
-
 ## 0.17.0 (2023-11-14)
 
 ### Features

packages/excalidraw/actions/actionAddToLibrary.ts

@@ -3,6 +3,7 @@ import { deepCopyElement } from "../element/newElement";
 import { randomId } from "../random";
 import { t } from "../i18n";
 import { LIBRARY_DISABLED_TYPES } from "../constants";
+import { StoreAction } from "../store";
 
 export const actionAddToLibrary = register({
   name: "addToLibrary",
@@ -17,7 +18,7 @@ export const actionAddToLibrary = register({
     for (const type of LIBRARY_DISABLED_TYPES) {
       if (selectedElements.some((element) => element.type === type)) {
         return {
-          commitToHistory: false,
+          storeAction: StoreAction.NONE,
           appState: {
             ...appState,
             errorMessage: t(`errors.libraryElementTypeError.${type}`),
@@ -41,7 +42,7 @@ export const actionAddToLibrary = register({
       })
       .then(() => {
         return {
-          commitToHistory: false,
+          storeAction: StoreAction.NONE,
           appState: {
             ...appState,
             toast: { message: t("toast.addedToLibrary") },
@@ -50,7 +51,7 @@ export const actionAddToLibrary = register({
       })
       .catch((error) => {
         return {
-          commitToHistory: false,
+          storeAction: StoreAction.NONE,
           appState: {
             ...appState,
             errorMessage: error.message,