From c2d6668aaac5ee1a5862821f902fbe58d58888e7 Mon Sep 17 00:00:00 2001
From: Alejandro Celaya <alejandrocelaya@gmail.com>
Date: Wed, 18 Sep 2024 10:44:20 +0200
Subject: [PATCH] Add usePolledAPIFetch hook to do API polling (#6683)

---
 lms/static/scripts/frontend_apps/utils/api.ts |  71 ++++++++++++
 .../frontend_apps/utils/test/api-test.js      | 101 +++++++++++++++++-
 2 files changed, 171 insertions(+), 1 deletion(-)

diff --git a/lms/static/scripts/frontend_apps/utils/api.ts b/lms/static/scripts/frontend_apps/utils/api.ts
index ad34793992..8a7a75577d 100644
--- a/lms/static/scripts/frontend_apps/utils/api.ts
+++ b/lms/static/scripts/frontend_apps/utils/api.ts
@@ -1,3 +1,4 @@
+import { useStableCallback } from '@hypothesis/frontend-shared';
 import { useCallback, useEffect, useRef, useState } from 'preact/hooks';
 
 import type { Pagination } from '../api-types';
@@ -214,6 +215,76 @@ export function useAPIFetch<T = unknown>(
   return useFetch(path ? `${path}${paramStr}` : null, fetcher);
 }
 
+export type PolledAPIFetchOptions<T> = {
+  /** Path for API call */
+  path: string;
+  /** Query params for API call */
+  params?: QueryParams;
+  /** Determines if, based on the result, the API should be called again */
+  shouldRefresh: (result: FetchResult<T>) => boolean;
+
+  /**
+   * Amount of ms after which a refresh should happen, if shouldRefresh()
+   * returns true.
+   * Defaults to 500ms.
+   */
+  refreshAfter?: number;
+
+  /** Test seam */
+  _setTimeout?: typeof setTimeout;
+  /** Test seam */
+  _clearTimeout?: typeof clearTimeout;
+};
+
+/**
+ * Hook that fetches data using authenticated API requests.
+ *
+ * This is a variant of {@link useAPIFetch} that supports automatically
+ * refreshing results at an interval until some condition is met.
+ * This is useful for example when calling an API that reports the status of a
+ * long-running operation.
+ */
+export function usePolledAPIFetch<T = unknown>({
+  path,
+  params,
+  shouldRefresh: unstableShouldRefresh,
+  refreshAfter = 500,
+  /* istanbul ignore next - test seam */
+  _setTimeout = setTimeout,
+  /* istanbul ignore next - test seam */
+  _clearTimeout = clearTimeout,
+}: PolledAPIFetchOptions<T>): FetchResult<T> {
+  const result = useAPIFetch<T>(path, params);
+  const shouldRefresh = useStableCallback(unstableShouldRefresh);
+
+  const timeout = useRef<ReturnType<typeof _setTimeout> | null>(null);
+  const resetTimeout = useCallback(() => {
+    if (timeout.current) {
+      _clearTimeout(timeout.current);
+    }
+    timeout.current = null;
+  }, [_clearTimeout]);
+
+  useEffect(() => {
+    if (result.isLoading) {
+      return () => {};
+    }
+
+    // Once we finish loading, schedule a retry if the request should be
+    // refreshed
+    if (shouldRefresh(result)) {
+      timeout.current = _setTimeout(() => {
+        result.retry();
+        timeout.current = null;
+      }, refreshAfter);
+    }
+
+    return resetTimeout;
+  }, [_setTimeout, refreshAfter, resetTimeout, result, shouldRefresh]);
+
+  return result;
+}
+
 export type PaginatedFetchResult<T> = Omit<FetchResult<T>, 'mutate'> & {
   /** Determines if currently loading the first page */
   isLoadingFirstPage: boolean;
diff --git a/lms/static/scripts/frontend_apps/utils/test/api-test.js b/lms/static/scripts/frontend_apps/utils/test/api-test.js
index e1971d9136..a7c998f8b7 100644
--- a/lms/static/scripts/frontend_apps/utils/test/api-test.js
+++ b/lms/static/scripts/frontend_apps/utils/test/api-test.js
@@ -1,4 +1,4 @@
-import { waitFor } from '@hypothesis/frontend-testing';
+import { delay, waitFor } from '@hypothesis/frontend-testing';
 import { mount } from 'enzyme';
 
 import { Config } from '../../config';
@@ -9,6 +9,7 @@ import {
   useAPIFetch,
   $imports,
   usePaginatedAPIFetch,
+  usePolledAPIFetch,
 } from '../api';
 
 function createResponse(status, body) {
@@ -651,3 +652,101 @@ describe('usePaginatedAPIFetch', () => {
     assert.equal(getMainContent(wrapper), 'No content');
   });
 });
+
+describe('usePolledAPIFetch', () => {
+  let fakeUseFetch;
+  let fakeRetry;
+  let fakeClearTimeout;
+
+  function mockFetchFinished() {
+    fakeUseFetch.returns({
+      data: {},
+      isLoading: false,
+      retry: fakeRetry,
+    });
+  }
+
+  function mockLoadingState() {
+    fakeUseFetch.returns({
+      data: null,
+      isLoading: true,
+    });
+  }
+
+  beforeEach(() => {
+    fakeUseFetch = sinon.stub();
+    mockLoadingState();
+
+    fakeRetry = sinon.stub();
+    fakeClearTimeout = sinon.stub();
+
+    const fakeUseConfig = sinon.stub();
+    fakeUseConfig.returns({
+      api: { authToken: 'some-token' },
+    });
+
+    $imports.$mock({
+      '../config': { useConfig: fakeUseConfig },
+      './fetch': { useFetch: fakeUseFetch },
+    });
+  });
+
+  afterEach(() => {
+    $imports.$restore();
+  });
+
+  function TestWidget({ shouldRefresh }) {
+    const result = usePolledAPIFetch({
+      path: '/api/some/path',
+      shouldRefresh,
+
+      // Keep asynchronous nature of mocked setTimeout, but with a virtually
+      // immediate execution of the callback
+      _setTimeout: callback => setTimeout(callback),
+      _clearTimeout: fakeClearTimeout,
+    });
+
+    return (
+      <div data-testid="main-content">
+        {result.isLoading && 'Loading'}
+        {result.data && 'Loaded'}
+      </div>
+    );
+  }
+
+  function createComponent(shouldRefresh) {
+    return mount(<TestWidget shouldRefresh={shouldRefresh} />);
+  }
+
+  it('does not refresh while loading is in progress', async () => {
+    const shouldRefresh = sinon.stub().returns(true);
+    createComponent(shouldRefresh);
+
+    assert.notCalled(shouldRefresh);
+  });
+
+  it('refreshes requests until shouldRefresh returns false', async () => {
+    mockFetchFinished();
+
+    const shouldRefresh = sinon.stub().returns(true);
+    createComponent(shouldRefresh);
+
+    assert.called(shouldRefresh);
+
+    // Retry should be called once timeout ends
+    assert.notCalled(fakeRetry);
+    await delay(1);
+    assert.calledOnce(fakeRetry);
+  });
+
+  it('clears pending timeout when component is unmounted', () => {
+    mockFetchFinished();
+
+    const shouldRefresh = sinon.stub().returns(true);
+    const wrapper = createComponent(shouldRefresh);
+
+    wrapper.unmount();
+
+    assert.called(fakeClearTimeout);
+  });
+});