fix: Fix long running jobs getting executed multiple times (#14)

---------
Signed-off-by: starry-shivam <[email protected]>

Author: starry-shivam

src/main/kotlin/dev/starry/ktscheduler/scheduler/KtScheduler.kt

@@ -277,6 +277,11 @@ class KtScheduler(
 
         dueJobs.forEach { job ->
             logger.info("Processing due jobs...")
+            // Set the next run time for the job or remove it if it has no next run time.
+            // We do this before executing the job to ensure that the job is not executed again
+            // if its task is long-running and the next run time is already due.
+            setNextRunTimeOrRemoveJob(job, now)
+            // Execute the job.
             executor.execute(
                 job = job,
                 onSuccess = { handleJobCompletion(job, now) },
@@ -287,14 +292,13 @@ class KtScheduler(
 
     // Handles the completion of a job by updating the next run time or removing the job.
     private fun handleJobCompletion(job: Job, now: ZonedDateTime) {
-        setNextRunTimeOrRemoveJob(job, now)
+        logger.info("Job ${job.jobId} completed successfully")
         notifyJobComplete(job.jobId)
     }
 
     // Handles an error encountered while executing a job.
     private fun handleJobError(job: Job, now: ZonedDateTime, exception: Exception) {
         logger.severe("Error executing job ${job.jobId}: $exception")
-        setNextRunTimeOrRemoveJob(job, now)
         notifyJobError(job.jobId, exception)
     }
 

src/test/kotlin/dev/starry/ktscheduler/KtSchedulerTest.kt

@@ -26,6 +26,7 @@ import dev.starry.ktscheduler.triggers.OneTimeTrigger
 import junit.framework.TestCase.assertFalse
 import junit.framework.TestCase.assertTrue
 import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.delay
 import kotlinx.coroutines.test.runTest
 import org.junit.Test
 import java.time.ZonedDateTime
@@ -289,6 +290,33 @@ class KtSchedulerTest {
         scheduler.shutdown()
     }
 
+    @Test
+    fun `scheduler should not execute job multiple times if it is still running`(): Unit = runTest {
+        val scheduler = KtScheduler()
+
+        // Create a job that takes 2 seconds to execute
+        val job = Job(
+            jobId = "longRunningJob",
+            trigger = IntervalTrigger(intervalSeconds = 1),
+            nextRunTime = ZonedDateTime.now().plusSeconds(1),
+            callback = { delay(2000) }
+        )
+        val eventListener = TestJobEventListener()
+
+        scheduler.addJob(job)
+        scheduler.addEventListener(eventListener)
+        scheduler.start()
+        Thread.sleep(200)
+        // Job should not be completed yet
+        assertEquals(0, eventListener.completedJobs.size)
+        // Wait for enough time to ensure job has run
+        Thread.sleep(3000)
+        scheduler.shutdown()
+        // Assert that the job was only executed once
+        assertEquals(1, eventListener.completedJobs.size)
+        assertEquals("longRunningJob", eventListener.completedJobs[0])
+    }
+
     private fun createTestJob(
         jobId: String,
         runAt: ZonedDateTime = ZonedDateTime.now().plusSeconds(1),