From 3fc5e2d6dbbb3a19f7e1d817e74d455679d36e6d Mon Sep 17 00:00:00 2001
From: Roc Wu <rocwind@gmail.com>
Date: Sun, 11 Apr 2021 22:04:03 +0800
Subject: [PATCH] feat: add waitFor() for polling check ready status

---
 src/wait.ts         |  4 ++--
 src/waitFor.spec.ts | 35 +++++++++++++++++++++++++++++++++
 src/waitFor.ts      | 48 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 85 insertions(+), 2 deletions(-)
 create mode 100644 src/waitFor.spec.ts
 create mode 100644 src/waitFor.ts

diff --git a/src/wait.ts b/src/wait.ts
index 6b393af..bc49d8d 100644
--- a/src/wait.ts
+++ b/src/wait.ts
@@ -52,7 +52,7 @@ export type WaitReturn<T, Name extends string> = {
         [P in `reset${Name}`]: ReadyStatusSetter<T>;
     };
 
-export const wait = <T, Name extends string = ''>(name?: Name): WaitReturn<T, Name> => {
+export function wait<T, Name extends string = ''>(name?: Name): WaitReturn<T, Name> {
     let readyStatus: ReadyStatusEnum = ReadyStatusEnum.Pending;
     let resultValue: T;
     let waitPromise: Promise<T>;
@@ -127,4 +127,4 @@ export const wait = <T, Name extends string = ''>(name?: Name): WaitReturn<T, Na
             setResult(ReadyStatusEnum.Pending, value);
         },
     } as WaitReturn<T, Name>;
-};
+}
diff --git a/src/waitFor.spec.ts b/src/waitFor.spec.ts
new file mode 100644
index 0000000..395ae58
--- /dev/null
+++ b/src/waitFor.spec.ts
@@ -0,0 +1,35 @@
+import { waitFor } from './waitFor';
+
+describe('waitFor()', () => {
+    beforeEach(() => {
+        jest.useFakeTimers();
+    });
+
+    it('resolves after second check', () => {
+        const check = jest.fn();
+        check.mockReturnValueOnce(false);
+        check.mockReturnValueOnce(true);
+
+        const result = waitFor(check);
+        jest.runAllTimers();
+
+        expect(check).toHaveBeenCalledTimes(2);
+        expect(setTimeout).toHaveBeenCalledTimes(1);
+        return expect(result).resolves.toEqual(true);
+    });
+
+    it('rejects when check throws error', () => {
+        const check = jest.fn();
+        check.mockReturnValueOnce(false);
+        check.mockImplementationOnce(() => {
+            throw new Error('check error');
+        });
+
+        const result = waitFor(check);
+        jest.runAllTimers();
+
+        expect(check).toHaveBeenCalledTimes(2);
+        expect(setTimeout).toHaveBeenCalledTimes(1);
+        return expect(result).rejects.toEqual(new Error('check error'));
+    });
+});
diff --git a/src/waitFor.ts b/src/waitFor.ts
new file mode 100644
index 0000000..74f7ae7
--- /dev/null
+++ b/src/waitFor.ts
@@ -0,0 +1,48 @@
+import { wait } from './wait';
+
+/**
+ * check function that returns check result
+ * falsy values means not ready, truthy values will be used to resolve the promise
+ */
+type WaitForCheckFun<T> = () => T;
+
+interface WaitForOptions {
+    /**
+     * the interval(ms) for each check, default to 200ms
+     */
+    checkInterval?: number;
+    /**
+     * throw a timeout error and reject the promise after given timeout(ms),
+     * default is no timeout
+     */
+    timeout?: number;
+}
+
+export function waitFor<T>(check: WaitForCheckFun<T>, options?: WaitForOptions): Promise<T> {
+    const { checkInterval = 200, timeout } = options ?? {};
+
+    const { afterReady, setReady, setFailed } = wait<T>();
+
+    const startTimestamp = Date.now();
+    const doCheck = () => {
+        try {
+            const result = check();
+            if (result) {
+                setReady(result);
+                return;
+            }
+
+            if (timeout && Date.now() - startTimestamp > timeout) {
+                setFailed((new Error('timeout') as unknown) as T);
+                return;
+            }
+
+            setTimeout(doCheck, checkInterval);
+        } catch (err) {
+            setFailed(err);
+        }
+    };
+    doCheck();
+
+    return afterReady();
+}