// WatchControllers begins watching for new, changed, or deleted controllers.
func (r *Registry) WatchControllers(ctx api.Context, label labels.Selector, field fields.Selector, resourceVersion string) (watch.Interface, error) {
	if !field.Empty() {
		return nil, fmt.Errorf("field selectors are not supported on replication controllers")
	}
	version, err := tools.ParseWatchResourceVersion(resourceVersion, "replicationControllers")
	if err != nil {
		return nil, err
	}
	key := makeControllerListKey(ctx)
	return r.WatchList(key, version, func(obj runtime.Object) bool {
		controller, ok := obj.(*api.ReplicationController)
		if !ok {
			// Must be an error: return true to propagate to upper level.
			return true
		}
		match := label.Matches(labels.Set(controller.Labels))
		if match {
			pods, err := r.pods.ListPods(ctx, labels.Set(controller.Spec.Selector).AsSelector())
			if err != nil {
				glog.Warningf("Error listing pods: %v", err)
				// No object that's useable so drop it on the floor
				return false
			}
			if pods == nil {
				glog.Warningf("Pods list is nil.  This should never happen...")
				// No object that's useable so drop it on the floor
				return false
			}
			controller.Status.Replicas = len(pods.Items)
		}
		return match
	})
}

// Matcher returns a generic matcher for a given label and field selector.
func Matcher(label labels.Selector, field fields.Selector) generic.Matcher {
	return generic.MatcherFunc(func(obj runtime.Object) (bool, error) {
		sa, ok := obj.(*api.Secret)
		if !ok {
			return false, fmt.Errorf("not a secret")
		}
		fields := SelectableFields(sa)
		return label.Matches(labels.Set(sa.Labels)) && field.Matches(fields), nil
	})
}

// MatchPersistentVolume returns a generic matcher for a given label and field selector.
func MatchPersistentVolumes(label labels.Selector, field fields.Selector) generic.Matcher {
	return generic.MatcherFunc(func(obj runtime.Object) (bool, error) {
		persistentvolumeObj, ok := obj.(*api.PersistentVolume)
		if !ok {
			return false, fmt.Errorf("not a persistentvolume")
		}
		fields := PersistentVolumeToSelectableFields(persistentvolumeObj)
		return label.Matches(labels.Set(persistentvolumeObj.Labels)) && field.Matches(fields), nil
	})
}

// List obtains a list of ReplicationControllers that match selector.
func (s *storage) ListControllers(ctx api.Context, label labels.Selector, field fields.Selector) (*api.ReplicationControllerList, error) {
	if !field.Empty() {
		return nil, fmt.Errorf("field selector not supported yet")
	}
	obj, err := s.List(ctx, label, field)
	if err != nil {
		return nil, err
	}
	return obj.(*api.ReplicationControllerList), err
}

// MatchNamespace returns a generic matcher for a given label and field selector.
func MatchNamespace(label labels.Selector, field fields.Selector) generic.Matcher {
	return generic.MatcherFunc(func(obj runtime.Object) (bool, error) {
		namespaceObj, ok := obj.(*api.Namespace)
		if !ok {
			return false, fmt.Errorf("not a namespace")
		}
		fields := NamespaceToSelectableFields(namespaceObj)
		return label.Matches(labels.Set(namespaceObj.Labels)) && field.Matches(fields), nil
	})
}

// MatchResourceQuota returns a generic matcher for a given label and field selector.
func MatchResourceQuota(label labels.Selector, field fields.Selector) generic.Matcher {
	return generic.MatcherFunc(func(obj runtime.Object) (bool, error) {
		resourcequotaObj, ok := obj.(*api.ResourceQuota)
		if !ok {
			return false, fmt.Errorf("not a resourcequota")
		}
		fields := ResourceQuotaToSelectableFields(resourcequotaObj)
		return label.Matches(labels.Set(resourcequotaObj.Labels)) && field.Matches(fields), nil
	})
}

// FieldsSelectorParam adds the given selector as a query parameter with the name paramName.
func (r *Request) FieldsSelectorParam(s fields.Selector) *Request {
	if r.err != nil {
		return r
	}
	if s == nil {
		return r
	}
	if s.Empty() {
		return r
	}
	s2, err := s.Transform(func(field, value string) (newField, newValue string, err error) {
		return fieldMappings.filterField(r.apiVersion, r.resource, field, value)
	})
	if err != nil {
		r.err = err
		return r
	}
	return r.setParam(api.FieldSelectorQueryParam(r.apiVersion), s2.String())
}

// WatchServices begins watching for new, changed, or deleted service configurations.
func (r *Registry) WatchServices(ctx api.Context, label labels.Selector, field fields.Selector, resourceVersion string) (watch.Interface, error) {
	version, err := tools.ParseWatchResourceVersion(resourceVersion, "service")
	if err != nil {
		return nil, err
	}
	if !label.Empty() {
		return nil, fmt.Errorf("label selectors are not supported on services")
	}
	if value, found := field.RequiresExactMatch("name"); found {
		key, err := makeServiceKey(ctx, value)
		if err != nil {
			return nil, err
		}
		// TODO: use generic.SelectionPredicate
		return r.Watch(key, version, tools.Everything)
	}
	if field.Empty() {
		return r.WatchList(makeServiceListKey(ctx), version, tools.Everything)
	}
	return nil, fmt.Errorf("only the 'name' and default (everything) field selectors are supported")
}