Add document locks

plugin/src/sync-functions/locks.ts

@@ -0,0 +1,39 @@
+import { DocumentId } from "src/database/document-metadata";
+
+const locked = new Set<DocumentId>();
+const waiters = new Map<DocumentId, Array<() => void>>();
+
+export function tryLockDocument(documentId: DocumentId): boolean {
+	if (locked.has(documentId)) {
+		return false;
+	}
+
+	locked.add(documentId);
+	return true;
+}
+
+export function waitForDocumentLock(documentId: DocumentId): Promise<void> {
+	if (tryLockDocument(documentId)) {
+		return Promise.resolve();
+	}
+
+	return new Promise((resolve) => {
+		if (!waiters.has(documentId)) {
+			waiters.set(documentId, []);
+		}
+
+		waiters.get(documentId)!.push(resolve);
+	});
+}
+
+export function unlockDocument(documentId: DocumentId): void {
+	if (!locked.has(documentId)) {
+		throw new Error(`Document ${documentId} is not locked`);
+	}
+
+	if (waiters.has(documentId)) {
+		waiters.get(documentId)!.shift()?.();
+	} else {
+		locked.delete(documentId);
+	}
+}