MainActivity: Fix piling up of background jobs.

app/src/main/java/de/ccc/events/badge/card10/MainActivity.kt

@@ -31,6 +31,7 @@ import android.os.Bundle
 import androidx.appcompat.app.AppCompatActivity
 import androidx.core.app.ActivityCompat
 import androidx.core.content.ContextCompat
+import androidx.work.ExistingPeriodicWorkPolicy
 import androidx.work.PeriodicWorkRequestBuilder
 import androidx.work.WorkManager
 import de.ccc.events.badge.card10.background.SetClockJob
@@ -41,6 +42,8 @@ import java.util.concurrent.TimeUnit
 private const val REQUEST_CODE_ENABLE_BLUETOOTH = 1
 private const val REQUEST_CODE_PERMISSIONS = 2
 
+private const val WORK_NAME = "update_clock"
+
 class MainActivity : AppCompatActivity() {
 
     val bluetoothAdapter = BluetoothAdapter.getDefaultAdapter()
@@ -104,13 +107,13 @@ class MainActivity : AppCompatActivity() {
         val workManager = WorkManager.getInstance(this)
         if (!bluetoothAdapter.bondedDevices.isEmpty()
         ) {
-            val setClockRequest =
+            val updateClockRequest =
                 PeriodicWorkRequestBuilder<SetClockJob>(1, TimeUnit.MINUTES)
                     .build()
             workManager
-                .enqueue(setClockRequest)
+                .enqueueUniquePeriodicWork(WORK_NAME, ExistingPeriodicWorkPolicy.REPLACE, updateClockRequest)
         } else {
-            // TODO cancel job
+            workManager.cancelUniqueWork(WORK_NAME)
         }
     }
 }