randomize APNS query (#38222)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #36644 

Randomizes the query so we get a new set of 500 every time, and also
improves the index by adding a priority where clause.

It should fine handle up towards 10.000 filtered entries before becoming
slow, and at most we have seen 2k with a customer.

# Checklist for submitter

If some of the following don't apply, delete the relevant line.

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.

## Testing

- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually

changes/36644-randomize-apns-query

@@ -0,0 +1 @@
+- Randomized APNS query to ensure all pending Apple hosts gets a push notification

server/datastore/mysql/apple_mdm.go

@@ -6248,12 +6248,20 @@ GROUP BY h.id`
 
 func (ds *Datastore) GetEnrollmentIDsWithPendingMDMAppleCommands(ctx context.Context) (uuids []string, err error) {
 	const stmt = `
-SELECT DISTINCT neq.id
-FROM nano_enrollment_queue neq
-INNER JOIN nano_enrollments ne ON ne.id = neq.id
-LEFT JOIN nano_command_results ncr ON ncr.command_uuid = neq.command_uuid AND ncr.id = neq.id
-WHERE neq.active = 1 AND ne.enabled=1 AND ncr.status IS NULL
-AND neq.created_at >= NOW() - INTERVAL 7 DAY
+SELECT DISTINCT
+    neq.id
+FROM
+    nano_enrollment_queue neq
+    INNER JOIN nano_enrollments ne ON ne.id = neq.id
+    LEFT JOIN nano_command_results ncr ON ncr.command_uuid = neq.command_uuid
+    AND ncr.id = neq.id
+WHERE
+    neq.active = 1
+    AND ne.enabled = 1
+    AND ncr.status IS NULL
+    AND neq.created_at >= NOW() - INTERVAL 7 DAY
+    AND neq.priority IN (0, 1)
+ORDER BY RAND()
 LIMIT 500
 `
 
@@ -7090,7 +7098,6 @@ func (ds *Datastore) InsertHostLocationData(ctx context.Context, locData fleet.H
 }
 
 func (ds *Datastore) GetHostLocationData(ctx context.Context, hostID uint) (*fleet.HostLocationData, error) {
-
 	var ret fleet.HostLocationData
 
 	err := sqlx.GetContext(ctx, ds.reader(ctx), &ret, "SELECT host_id, latitude, longitude FROM host_last_known_locations WHERE host_id = ?", hostID)

server/datastore/mysql/apple_mdm_test.go

@@ -7155,9 +7155,23 @@ func testGetEnrollmentIDsWithPendingMDMAppleCommands(t *testing.T, ds *Datastore
 	err = commander.EnqueueCommand(ctx, []string{hostUUIDToUserEnrollmentID[hosts[3].UUID], hostUUIDToUserEnrollmentID[hosts[4].UUID], hostUUIDToUserEnrollmentID[hosts[5].UUID]}, rawCmd2)
 	require.NoError(t, err)
 
-	ids, err = ds.GetEnrollmentIDsWithPendingMDMAppleCommands(ctx)
+	firstIds, err := ds.GetEnrollmentIDsWithPendingMDMAppleCommands(ctx)
 	require.NoError(t, err)
-	require.ElementsMatch(t, []string{hosts[1].UUID, hosts[2].UUID, hostUUIDToUserEnrollmentID[hosts[3].UUID], hostUUIDToUserEnrollmentID[hosts[4].UUID], hostUUIDToUserEnrollmentID[hosts[5].UUID]}, ids)
+	require.ElementsMatch(t, []string{hosts[1].UUID, hosts[2].UUID, hostUUIDToUserEnrollmentID[hosts[3].UUID], hostUUIDToUserEnrollmentID[hosts[4].UUID], hostUUIDToUserEnrollmentID[hosts[5].UUID]}, firstIds)
+
+	// Get a list of pending ID's 3 times and match against the first list, to avoid test flakiness.
+	// In a real world scenario it's okay for it to be the same as we will fetch it again later.
+	allAttemptsWereEqual := true
+	for range 3 {
+		secondIds, err := ds.GetEnrollmentIDsWithPendingMDMAppleCommands(ctx)
+		require.NoError(t, err)
+		isIdsEqual := assert.ObjectsAreEqualValues(firstIds, secondIds)
+		if !isIdsEqual {
+			allAttemptsWereEqual = false
+			break
+		}
+	}
+	require.False(t, allAttemptsWereEqual, "GetEnrollmentIDsWithPendingMDMAppleCommands returned the same result 3 times in a row")
 
 	err = storage.StoreCommandReport(&mdm.Request{
 		EnrollID: &mdm.EnrollID{ID: hostUUIDToUserEnrollmentID[hosts[3].UUID]},
@@ -9627,5 +9641,4 @@ func testDeviceLocation(t *testing.T, ds *Datastore) {
 
 	_, err = ds.GetHostLocationData(ctx, iOSHost.ID)
 	require.True(t, fleet.IsNotFound(err))
-
 }