put sync stuff in bemo worker (#4060)

this PR puts sync stuff in the bemo worker, and sets up a temporary
dev-only page in dotcom for testing bemo stuff


### Change type

- [ ] `bugfix`
- [ ] `improvement`
- [x] `feature`
- [ ] `api`
- [ ] `other`

### Test plan

1. Create a shape...
2.

- [ ] Unit tests
- [ ] End to end tests

### Release notes

- Fixed a bug with...

packages/sync-react/src/useRemoteSyncClient.ts

@@ -0,0 +1,144 @@
+import {
+	ClientWebSocketAdapter,
+	TLCloseEventCode,
+	TLIncompatibilityReason,
+	TLPersistentClientSocketStatus,
+	TLRemoteSyncError,
+	TLSyncClient,
+	schema,
+} from '@tldraw/sync'
+import { useEffect, useState } from 'react'
+import {
+	Signal,
+	TAB_ID,
+	TLRecord,
+	TLStore,
+	TLStoreSnapshot,
+	TLStoreWithStatus,
+	TLUserPreferences,
+	computed,
+	createPresenceStateDerivation,
+	defaultUserPreferences,
+	getUserPreferences,
+	useTLStore,
+	useValue,
+} from 'tldraw'
+
+const MULTIPLAYER_EVENT_NAME = 'multiplayer.client'
+
+/** @public */
+export type RemoteTLStoreWithStatus = Exclude<
+	TLStoreWithStatus,
+	{ status: 'synced-local' } | { status: 'not-synced' }
+>
+
+/** @public */
+export function useRemoteSyncClient(opts: UseSyncClientConfig): RemoteTLStoreWithStatus {
+	const [state, setState] = useState<{
+		readyClient?: TLSyncClient<TLRecord, TLStore>
+		error?: Error
+	} | null>(null)
+	const { uri, roomId = 'default', userPreferences: prefs } = opts
+
+	const store = useTLStore({ schema })
+
+	const error: NonNullable<typeof state>['error'] = state?.error ?? undefined
+	const track = opts.trackAnalyticsEvent
+
+	useEffect(() => {
+		if (error) return
+
+		const userPreferences = computed<{ id: string; color: string; name: string }>(
+			'userPreferences',
+			() => {
+				const user = prefs?.get() ?? getUserPreferences()
+				return {
+					id: user.id,
+					color: user.color ?? defaultUserPreferences.color,
+					name: user.name ?? defaultUserPreferences.name,
+				}
+			}
+		)
+
+		const socket = new ClientWebSocketAdapter(async () => {
+			// set sessionKey as a query param on the uri
+			const withParams = new URL(uri)
+			withParams.searchParams.set('sessionKey', TAB_ID)
+			withParams.searchParams.set('storeId', store.id)
+			return withParams.toString()
+		})
+
+		socket.onStatusChange((val: TLPersistentClientSocketStatus, closeCode?: number) => {
+			if (val === 'error' && closeCode === TLCloseEventCode.NOT_FOUND) {
+				track?.(MULTIPLAYER_EVENT_NAME, { name: 'room-not-found', roomId })
+				setState({ error: new TLRemoteSyncError(TLIncompatibilityReason.RoomNotFound) })
+				client.close()
+				socket.close()
+				return
+			}
+		})
+
+		let didCancel = false
+
+		const client = new TLSyncClient({
+			store,
+			socket,
+			didCancel: () => didCancel,
+			onLoad(client) {
+				track?.(MULTIPLAYER_EVENT_NAME, { name: 'load', roomId })
+				setState({ readyClient: client })
+			},
+			onLoadError(err) {
+				track?.(MULTIPLAYER_EVENT_NAME, { name: 'load-error', roomId })
+				console.error(err)
+				setState({ error: err })
+			},
+			onSyncError(reason) {
+				track?.(MULTIPLAYER_EVENT_NAME, { name: 'sync-error', roomId, reason })
+				setState({ error: new TLRemoteSyncError(reason) })
+			},
+			onAfterConnect() {
+				// if the server crashes and loses all data it can return an empty document
+				// when it comes back up. This is a safety check to make sure that if something like
+				// that happens, it won't render the app broken and require a restart. The user will
+				// most likely lose all their changes though since they'll have been working with pages
+				// that won't exist. There's certainly something we can do to make this better.
+				// but the likelihood of this happening is very low and maybe not worth caring about beyond this.
+				store.ensureStoreIsUsable()
+			},
+			presence: createPresenceStateDerivation(userPreferences)(store),
+		})
+
+		return () => {
+			didCancel = true
+			client.close()
+			socket.close()
+		}
+	}, [prefs, roomId, store, uri, error, track])
+
+	return useValue<RemoteTLStoreWithStatus>(
+		'remote synced store',
+		() => {
+			if (!state) return { status: 'loading' }
+			if (state.error) return { status: 'error', error: state.error }
+			if (!state.readyClient) return { status: 'loading' }
+			const connectionStatus = state.readyClient.socket.connectionStatus
+			return {
+				status: 'synced-remote',
+				connectionStatus: connectionStatus === 'error' ? 'offline' : connectionStatus,
+				store: state.readyClient.store,
+			}
+		},
+		[state]
+	)
+}
+
+/** @public */
+export interface UseSyncClientConfig {
+	uri: string
+	roomId?: string
+	userPreferences?: Signal<TLUserPreferences>
+	snapshotForNewRoomRef?: { current: null | TLStoreSnapshot }
+	/* @internal */
+	trackAnalyticsEvent?(name: string, data: { [key: string]: any }): void
+}