Rate-limit DB writes

frontend/sync-client/src/utils/rate-limit.test.ts

@@ -0,0 +1,66 @@
+import { rateLimit } from "./rate-limit";
+import { jest } from "@jest/globals";
+
+describe("rateLimit", () => {
+	beforeEach(() => {
+		jest.useFakeTimers();
+	});
+
+	afterEach(() => {
+		jest.useRealTimers();
+	});
+
+	it("should call the function immediately on first invocation", async () => {
+		const mockFn = jest
+			.fn<() => Promise<string>>()
+			.mockResolvedValue("result");
+		const rateLimited = rateLimit(mockFn, 100);
+
+		const promise = rateLimited();
+		expect(mockFn).toHaveBeenCalledTimes(1);
+
+		await promise;
+	});
+
+	it("should call the function again after the interval has passed", async () => {
+		const mockFn = jest
+			.fn<(value: number) => Promise<string>>()
+			.mockResolvedValue("result");
+
+		const rateLimited = rateLimit(mockFn, 100);
+
+		const promise1 = rateLimited(1);
+		await promise1;
+
+		jest.advanceTimersByTime(200);
+
+		const promise2 = rateLimited(2);
+		await promise2;
+
+		expect(mockFn).toHaveBeenCalledTimes(2);
+		expect(mockFn).toHaveBeenCalledWith(2);
+	});
+
+	it("should use the most recent arguments if multiple calls are made within interval", async () => {
+		const mockFn = jest
+			.fn<(value: string) => Promise<string>>()
+			.mockImplementation(async (val) => `${val}-result`);
+		const rateLimited = rateLimit(mockFn, 100);
+
+		const promise1 = rateLimited("first");
+		jest.advanceTimersByTime(10);
+		const promise2 = rateLimited("second");
+		jest.advanceTimersByTime(10);
+		const promise3 = rateLimited("third");
+
+		jest.advanceTimersByTime(1000);
+
+		expect(await promise1).toEqual("first-result");
+		expect(await promise2).toEqual("third-result");
+		expect(await promise3).toBeUndefined();
+
+		expect(mockFn).toHaveBeenCalledTimes(2);
+		expect(mockFn).toHaveBeenNthCalledWith(1, "first");
+		expect(mockFn).toHaveBeenNthCalledWith(2, "third");
+	});
+});