feat: support async handling and add CronJob status tracking (#894)

## Description
This PR improves async handling in the CronJob class and adds status
tracking functionality.

- Modified the `fireOnTick()` method to return a Promise for better
async callback handling
- Added an `isCallbackRunning` flag to track the running state of
CronJob instances
- Updated the test suite to use the new async behavior and track the
job's running state
- Added `waitForCompletion` functionality to the `job.stop()` method
- waits for running jobs to complete before executing the `onComplete`
callback

During test case writing, I encountered a type error with sinon.
To resolve this, added `sinon.restore()` to the `afterEach` block.

Reference:
https://stackoverflow.com/questions/73232999/sinon-cant-install-fake-timers-twice-on-the-same-global-object

<img width="811" alt="스크린샷 2024-09-03 오후 7 10 58"
src="https://github.com/user-attachments/assets/b87deee7-14b2-4407-8fea-a1cb469ef44b">

## Related Issue
Closes #713
Closes #556

## Motivation and Context
These changes allow the CronJob class to handle asynchronous callbacks
more effectively and provide a way to track the running state of jobs.

## How Has This Been Tested?
- Updated existing test suite to verify the new async behavior
- Adjusted test timeouts to use the `tickAsync` method
- Added new test cases to check for proper waiting of running callbacks
before stopping

## Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)

## Checklist:
- [x] My code follows the code style of this project.
- [x] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.
- [x] I have added tests to cover my changes.
- [x] All new and existing tests passed.
- [ ] If my change introduces a breaking change, I have added a `!`
after the type/scope in the title (see the Conventional Commits
standard).

---------

Co-authored-by: Brandon der Blätter <intcreator@users.noreply.github.com>

Author: Zamoca42

README.md

@@ -194,6 +194,8 @@ day of week    0-7 (0 or 7 is Sunday, or use names)
 
 - `unrefTimeout`: [OPTIONAL] - Useful for controlling event loop behavior. More details [here](https://nodejs.org/api/timers.html#timers_timeout_unref).
 
+- `waitForCompletion`: [OPTIONAL] - If `true`, no additional instances of the `onTick` callback function will run until the current onTick callback has completed. Any new scheduled executions that occur while the current callback is running will be skipped entirely. Default is `false`.
+
 #### Methods
 
 - `from` (static): Create a new CronJob object providing arguments as an object. See argument names and descriptions above.
@@ -214,6 +216,23 @@ day of week    0-7 (0 or 7 is Sunday, or use names)
 
 - `addCallback`: Permits addition of `onTick` callbacks.
 
+#### Properties
+
+- `isCallbackRunning`: [READ-ONLY] Indicates if a callback is currently executing.
+
+  ```javascript
+  const job = new CronJob('* * * * * *', async () => {
+  	console.log(job.isCallbackRunning); // true during callback execution
+  	await someAsyncTask();
+  	console.log(job.isCallbackRunning); // still true until callback completes
+  });
+
+  console.log(job.isCallbackRunning); // false
+  job.start();
+  console.log(job.running); // true (schedule is active)
+  console.log(job.isCallbackRunning); // false (no callback executing)
+  ```
+
 ### CronTime Class
 
 #### Constructor

src/job.ts

@@ -21,10 +21,16 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 	onComplete?: WithOnComplete<OC> extends true
 		? CronOnCompleteCallback
 		: undefined;
+	waitForCompletion = false;
 
+	private _isCallbackRunning = false;
 	private _timeout?: NodeJS.Timeout;
 	private _callbacks: CronCallback<C, WithOnComplete<OC>>[] = [];
 
+	get isCallbackRunning() {
+		return this._isCallbackRunning;
+	}
+
 	constructor(
 		cronTime: CronJobParams<OC, C>['cronTime'],
 		onTick: CronJobParams<OC, C>['onTick'],
@@ -34,7 +40,8 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 		context?: CronJobParams<OC, C>['context'],
 		runOnInit?: CronJobParams<OC, C>['runOnInit'],
 		utcOffset?: null,
-		unrefTimeout?: CronJobParams<OC, C>['unrefTimeout']
+		unrefTimeout?: CronJobParams<OC, C>['unrefTimeout'],
+		waitForCompletion?: CronJobParams<OC, C>['waitForCompletion']
 	);
 	constructor(
 		cronTime: CronJobParams<OC, C>['cronTime'],
@@ -45,7 +52,8 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 		context?: CronJobParams<OC, C>['context'],
 		runOnInit?: CronJobParams<OC, C>['runOnInit'],
 		utcOffset?: CronJobParams<OC, C>['utcOffset'],
-		unrefTimeout?: CronJobParams<OC, C>['unrefTimeout']
+		unrefTimeout?: CronJobParams<OC, C>['unrefTimeout'],
+		waitForCompletion?: CronJobParams<OC, C>['waitForCompletion']
 	);
 	constructor(
 		cronTime: CronJobParams<OC, C>['cronTime'],
@@ -56,9 +64,11 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 		context?: CronJobParams<OC, C>['context'],
 		runOnInit?: CronJobParams<OC, C>['runOnInit'],
 		utcOffset?: CronJobParams<OC, C>['utcOffset'],
-		unrefTimeout?: CronJobParams<OC, C>['unrefTimeout']
+		unrefTimeout?: CronJobParams<OC, C>['unrefTimeout'],
+		waitForCompletion?: CronJobParams<OC, C>['waitForCompletion']
 	) {
 		this.context = (context ?? this) as CronContext<C>;
+		this.waitForCompletion = Boolean(waitForCompletion);
 
 		// runtime check for JS users
 		if (timeZone != null && utcOffset != null) {
@@ -92,7 +102,7 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 
 		if (runOnInit) {
 			this.lastExecution = new Date();
-			this.fireOnTick();
+			void this.fireOnTick();
 		}
 
 		if (start) this.start();
@@ -117,7 +127,8 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 				params.context,
 				params.runOnInit,
 				params.utcOffset,
-				params.unrefTimeout
+				params.unrefTimeout,
+				params.waitForCompletion
 			);
 		} else if (params.utcOffset != null) {
 			return new CronJob<OC, C>(
@@ -129,7 +140,8 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 				params.context,
 				params.runOnInit,
 				params.utcOffset,
-				params.unrefTimeout
+				params.unrefTimeout,
+				params.waitForCompletion
 			);
 		} else {
 			return new CronJob<OC, C>(
@@ -141,7 +153,8 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 				params.context,
 				params.runOnInit,
 				params.utcOffset,
-				params.unrefTimeout
+				params.unrefTimeout,
+				params.waitForCompletion
 			);
 		}
 	}
@@ -193,14 +206,26 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 		return this.cronTime.sendAt();
 	}
 
-	fireOnTick() {
-		for (const callback of this._callbacks) {
-			void callback.call(
-				this.context,
-				this.onComplete as WithOnComplete<OC> extends true
-					? CronOnCompleteCallback
-					: never
-			);
+	async fireOnTick() {
+		if (!this.waitForCompletion && this._isCallbackRunning) return;
+
+		this._isCallbackRunning = true;
+
+		try {
+			for (const callback of this._callbacks) {
+				const result = callback.call(
+					this.context,
+					this.onComplete as WithOnComplete<OC> extends true
+						? CronOnCompleteCallback
+						: never
+				);
+
+				if (this.waitForCompletion) await result;
+			}
+		} catch (error) {
+			console.error('[Cron] error in callback', error);
+		} finally {
+			this._isCallbackRunning = false;
 		}
 	}
 
@@ -209,9 +234,7 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 	}
 
 	start() {
-		if (this.running) {
-			return;
-		}
+		if (this.running) return;
 
 		const MAXDELAY = 2147483647; // The maximum number of milliseconds setTimeout will wait.
 		let timeout = this.cronTime.getTimeout();
@@ -262,11 +285,9 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 				this.running = false;
 
 				// start before calling back so the callbacks have the ability to stop the cron job
-				if (!this.runOnce) {
-					this.start();
-				}
+				if (!this.runOnce) this.start();
 
-				this.fireOnTick();
+				void this.fireOnTick();
 			}
 		};
 
@@ -290,14 +311,37 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 		return this.lastExecution;
 	}
 
+	private async _executeOnComplete() {
+		if (typeof this.onComplete !== 'function') return;
+
+		try {
+			await this.onComplete.call(this.context);
+		} catch (error) {
+			console.error('[Cron] error in onComplete callback:', error);
+		}
+	}
+
+	private async _waitForJobCompletion() {
+		while (this._isCallbackRunning) {
+			await new Promise(resolve => setTimeout(resolve, 100));
+		}
+	}
+
 	/**
 	 * Stop the cronjob.
 	 */
 	stop() {
 		if (this._timeout) clearTimeout(this._timeout);
 		this.running = false;
-		if (typeof this.onComplete === 'function') {
-			void this.onComplete.call(this.context);
+
+		if (!this.waitForCompletion) {
+			void this._executeOnComplete();
+			return;
 		}
+
+		void Promise.resolve().then(async () => {
+			await this._waitForJobCompletion();
+			await this._executeOnComplete();
+		});
 	}
 }

src/types/cron.types.ts

@@ -15,6 +15,7 @@ interface BaseCronJobParams<
 	context?: C;
 	runOnInit?: boolean | null;
 	unrefTimeout?: boolean | null;
+	waitForCompletion?: boolean | null;
 }
 
 export type CronJobParams<