From 83681d6236ce67b032ba1192c151b27e566b30a0 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Fri, 23 Feb 2024 16:03:16 +0100
Subject: [PATCH] Support document forking

---
 javascript/src/api.ts       | 44 ++++++++++++++++++++++++++++++++++++-
 javascript/src/ydocument.ts | 27 ++++++++++++++++++++++-
 2 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/javascript/src/api.ts b/javascript/src/api.ts
index 807fd18..bd67a95 100644
--- a/javascript/src/api.ts
+++ b/javascript/src/api.ts
@@ -20,7 +20,7 @@ import type {
   JSONValue,
   PartialJSONValue
 } from '@lumino/coreutils';
-import type { IObservableDisposable } from '@lumino/disposable';
+import type { IDisposable, IObservableDisposable } from '@lumino/disposable';
 import type { ISignal } from '@lumino/signaling';
 
 /**
@@ -80,6 +80,26 @@ export interface ISharedBase extends IObservableDisposable {
   transact(f: () => void, undoable?: boolean): void;
 }
 
+/**
+ * An interface for a document provider.
+ */
+export interface IDocumentProvider extends IDisposable {
+  /**
+   * Returns a Promise that resolves when the document provider is ready.
+   */
+  readonly ready: Promise<void>;
+
+  /**
+   * Request to fork the room in the backend, and connect the shared document to the forked room.
+   */
+  fork(): Promise<void>;
+
+  /**
+   * Connect a shared document to a forked room with forkId and return a document provider.
+   */
+  connectFork(forkId: string, sharedDocument: ISharedDocument): IDocumentProvider;
+}
+
 /**
  * Implement an API for Context information on the shared information.
  * This is used by, for example, docregistry to share the file-path of the edited content.
@@ -114,6 +134,28 @@ export interface ISharedDocument extends ISharedBase {
    * The changed signal.
    */
   readonly changed: ISignal<this, DocumentChange>;
+
+  /**
+   * Get a provider with a given ID
+   *
+   * @param providerId The provider ID
+   */
+  getProvider(providerId: string, sharedModel?: ISharedDocument): IDocumentProvider;
+
+  /**
+   * Set a provider for this document
+   *
+   * @param providerId Provider ID (either 'root' or a UUID)
+   * @param provider The document provider
+   */
+  setProvider(providerId: string, provider: IDocumentProvider): void;
+
+  /**
+   * Add a fork ID to the document's ystate, as a new key 'fork_{forkId}'
+   *
+   * @param forkId The fork ID to add to the document
+   */
+  addFork(forkId: string): void;
 }
 
 /**
diff --git a/javascript/src/ydocument.ts b/javascript/src/ydocument.ts
index c923c12..90e1114 100644
--- a/javascript/src/ydocument.ts
+++ b/javascript/src/ydocument.ts
@@ -7,7 +7,7 @@ import { JSONExt, JSONObject, JSONValue } from '@lumino/coreutils';
 import { ISignal, Signal } from '@lumino/signaling';
 import { Awareness } from 'y-protocols/awareness';
 import * as Y from 'yjs';
-import type { DocumentChange, ISharedDocument, StateChange } from './api.js';
+import type { DocumentChange, IDocumentProvider, ISharedDocument, StateChange } from './api';
 
 /**
  * Generic shareable document.
@@ -28,6 +28,8 @@ export abstract class YDocument<T extends DocumentChange>
     this._awareness = new Awareness(this._ydoc);
 
     this._ystate.observe(this.onStateChanged);
+
+    this._providers = {};
   }
 
   /**
@@ -35,6 +37,28 @@ export abstract class YDocument<T extends DocumentChange>
    */
   abstract readonly version: string;
 
+  addFork(forkId: string) {
+    this.ystate.set(`fork_${forkId}`, 'new');
+  }
+
+  getProvider(providerId: string, sharedModel?: ISharedDocument): IDocumentProvider {
+    if (!(providerId in this._providers)) {
+      if (providerId === 'root') {
+        throw new Error('Cannot get a new provider for root document');
+      }
+      if (sharedModel === undefined) {
+        throw new Error('New provider needs a shared document');
+      }
+      const root_provider = this._providers['root'];
+      this._providers[providerId] = root_provider.connectFork(providerId, sharedModel!);
+    }
+    return this._providers[providerId];
+  }
+
+  setProvider(providerId: string, provider: IDocumentProvider) {
+    this._providers[providerId] = provider;
+  }
+
   /**
    * YJS document.
    */
@@ -200,6 +224,7 @@ export abstract class YDocument<T extends DocumentChange>
   private _awareness: Awareness;
   private _isDisposed = false;
   private _disposed = new Signal<this, void>(this);
+  private _providers: { [key: string]: IDocumentProvider };
 }
 
 /**