// updateReplicaCount attempts to update the Status.Replicas of the given ReplicaSet, with a single GET/PUT retry.
func updateReplicaCount(rsClient unversionedextensions.ReplicaSetInterface, rs extensions.ReplicaSet, numReplicas, numFullyLabeledReplicas, numReadyReplicas, numAvailableReplicas int) (updateErr error) {
	// This is the steady state. It happens when the ReplicaSet doesn't have any expectations, since
	// we do a periodic relist every 30s. If the generations differ but the replicas are
	// the same, a caller might've resized to the same replica count.
	if int(rs.Status.Replicas) == numReplicas &&
		int(rs.Status.FullyLabeledReplicas) == numFullyLabeledReplicas &&
		int(rs.Status.ReadyReplicas) == numReadyReplicas &&
		int(rs.Status.AvailableReplicas) == numAvailableReplicas &&
		rs.Generation == rs.Status.ObservedGeneration {
		return nil
	}

	// deep copy to avoid mutation now.
	// TODO this method need some work.  Retry on conflict probably, though I suspect this is stomping status to something it probably shouldn't
	copyObj, err := api.Scheme.DeepCopy(rs)
	if err != nil {
		return err
	}
	rs = copyObj.(extensions.ReplicaSet)

	// Save the generation number we acted on, otherwise we might wrongfully indicate
	// that we've seen a spec update when we retry.
	// TODO: This can clobber an update if we allow multiple agents to write to the
	// same status.
	generation := rs.Generation

	var getErr error
	for i, rs := 0, &rs; ; i++ {
		glog.V(4).Infof(fmt.Sprintf("Updating replica count for ReplicaSet: %s/%s, ", rs.Namespace, rs.Name) +
			fmt.Sprintf("replicas %d->%d (need %d), ", rs.Status.Replicas, numReplicas, rs.Spec.Replicas) +
			fmt.Sprintf("fullyLabeledReplicas %d->%d, ", rs.Status.FullyLabeledReplicas, numFullyLabeledReplicas) +
			fmt.Sprintf("readyReplicas %d->%d, ", rs.Status.ReadyReplicas, numReadyReplicas) +
			fmt.Sprintf("availableReplicas %d->%d, ", rs.Status.AvailableReplicas, numAvailableReplicas) +
			fmt.Sprintf("sequence No: %v->%v", rs.Status.ObservedGeneration, generation))

		rs.Status = extensions.ReplicaSetStatus{
			Replicas:             int32(numReplicas),
			FullyLabeledReplicas: int32(numFullyLabeledReplicas),
			ReadyReplicas:        int32(numReadyReplicas),
			AvailableReplicas:    int32(numAvailableReplicas),
			ObservedGeneration:   generation,
		}
		_, updateErr = rsClient.UpdateStatus(rs)
		if updateErr == nil || i >= statusUpdateRetries {
			return updateErr
		}
		// Update the ReplicaSet with the latest resource version for the next poll
		if rs, getErr = rsClient.Get(rs.Name); getErr != nil {
			// If the GET fails we can't trust status.Replicas anymore. This error
			// is bound to be more interesting than the update failure.
			return getErr
		}
	}
}

// UpdateRSWithRetries updates a RS with given applyUpdate function. Note that RS not found error is ignored.
// The returned bool value can be used to tell if the RS is actually updated.
func UpdateRSWithRetries(rsClient unversionedextensions.ReplicaSetInterface, rs *extensions.ReplicaSet, applyUpdate updateRSFunc) (*extensions.ReplicaSet, bool, error) {
	var err error
	var rsUpdated bool
	oldRs := rs
	if err = wait.Poll(10*time.Millisecond, 1*time.Minute, func() (bool, error) {
		rs, err = rsClient.Get(oldRs.Name)
		if err != nil {
			return false, err
		}
		// Apply the update, then attempt to push it to the apiserver.
		if err = applyUpdate(rs); err != nil {
			return false, err
		}
		if rs, err = rsClient.Update(rs); err == nil {
			// Update successful.
			return true, nil
		}
		// TODO: don't retry on perm-failed errors and handle them gracefully
		// Update could have failed due to conflict error. Try again.
		return false, nil
	}); err == nil {
		// When there's no error, we've updated this RS.
		rsUpdated = true
	}

	// Handle returned error from wait poll
	if err == wait.ErrWaitTimeout {
		err = fmt.Errorf("timed out trying to update RS: %+v", oldRs)
	}
	// Ignore the RS not found error, but the RS isn't updated.
	if errors.IsNotFound(err) {
		glog.V(4).Infof("%s %s/%s is not found, skip updating it.", oldRs.Kind, oldRs.Namespace, oldRs.Name)
		err = nil
	}
	// Ignore the precondition violated error, but the RS isn't updated.
	if err == errorsutil.ErrPreconditionViolated {
		glog.V(4).Infof("%s %s/%s precondition doesn't hold, skip updating it.", oldRs.Kind, oldRs.Namespace, oldRs.Name)
		err = nil
	}

	// If the error is non-nil the returned RS cannot be trusted; if rsUpdated is false, the contoller isn't updated;
	// if the error is nil and rsUpdated is true, the returned RS contains the applied update.
	return rs, rsUpdated, err
}