Stop using global file locks

frontend/sync-client/src/sync-operations/document-locks.ts

@@ -0,0 +1,50 @@
+import type { RelativePath } from "../persistence/database";
+
+export class DocumentLocks {
+	private readonly locked = new Set<RelativePath>();
+	private readonly waiters = new Map<RelativePath, (() => void)[]>();
+
+	public tryLockDocument(relativePath: RelativePath): boolean {
+		if (this.locked.has(relativePath)) {
+			return false;
+		}
+
+		this.locked.add(relativePath);
+		return true;
+	}
+
+	public async waitForDocumentLock(
+		relativePath: RelativePath
+	): Promise<void> {
+		if (this.tryLockDocument(relativePath)) {
+			return Promise.resolve();
+		}
+
+		return new Promise((resolve) => {
+			let waiting = this.waiters.get(relativePath);
+			if (!waiting) {
+				waiting = [];
+				this.waiters.set(relativePath, waiting);
+			}
+
+			waiting.push(resolve);
+		});
+	}
+
+	public unlockDocument(relativePath: RelativePath): void {
+		if (!this.locked.has(relativePath)) {
+			throw new Error(
+				`Document ${relativePath} is not locked, cannot unlock`
+			);
+		}
+
+		// Remove the first element to ensure FIFO unblocking order
+		const nextWaiting = this.waiters.get(relativePath)?.shift();
+
+		if (nextWaiting) {
+			nextWaiting();
+		} else {
+			this.locked.delete(relativePath);
+		}
+	}
+}