/*
Copyright the Velero contributors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package backup

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"sort"
	"strings"

	"github.com/cockroachdb/errors"
	"github.com/sirupsen/logrus"
	corev1api "k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/api/meta"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
	"k8s.io/apimachinery/pkg/labels"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/client-go/tools/pager"

	"github.com/vmware-tanzu/velero/pkg/client"
	"github.com/vmware-tanzu/velero/pkg/discovery"
	"github.com/vmware-tanzu/velero/pkg/kuberesource"
	"github.com/vmware-tanzu/velero/pkg/plugin/velero"
	"github.com/vmware-tanzu/velero/pkg/util/collections"
)

// itemCollector collects items from the Kubernetes API according to
// the backup spec and writes them to files inside dir.
type itemCollector struct {
	log                   logrus.FieldLogger
	backupRequest         *Request
	discoveryHelper       discovery.Helper
	dynamicFactory        client.DynamicFactory
	cohabitatingResources map[string]*cohabitatingResource
	dir                   string
	pageSize              int
	nsTracker             nsTracker
}

// nsTracker is used to integrate several namespace filters together.
//  1. Backup's namespace Include/Exclude filters;
//  2. Backup's (Or)LabelSelector selected namespace;
//  3. Backup's (Or)LabelSelector selected resources' namespaces.
//
// Rules:
//
//	a. When backup namespace Include/Exclude filters get everything,
//	The namespaces, which do not have backup including resources,
//	are not collected.
//
//	b. If the namespace I/E filters and the (Or)LabelSelectors selected
//	namespaces are different. The tracker takes the union of them.
type nsTracker struct {
	singleLabelSelector labels.Selector
	orLabelSelector     []labels.Selector
	namespaceFilter     *collections.NamespaceIncludesExcludes
	logger              logrus.FieldLogger

	namespaceMap map[string]bool
}

// track add the namespace into the namespaceMap.
func (nt *nsTracker) track(ns string) {
	if nt.namespaceMap == nil {
		nt.namespaceMap = make(map[string]bool)
	}

	if _, ok := nt.namespaceMap[ns]; !ok {
		nt.namespaceMap[ns] = true
	}
}

// isTracked check whether the namespace's name exists in
// namespaceMap.
func (nt *nsTracker) isTracked(ns string) bool {
	if nt.namespaceMap != nil {
		return nt.namespaceMap[ns]
	}
	return false
}

// init initialize the namespaceMap, and add elements according to
// namespace include/exclude filters and the backup label selectors.
func (nt *nsTracker) init(
	unstructuredNSs []unstructured.Unstructured,
	singleLabelSelector labels.Selector,
	orLabelSelector []labels.Selector,
	namespaceFilter *collections.NamespaceIncludesExcludes,
	logger logrus.FieldLogger,
) {
	if nt.namespaceMap == nil {
		nt.namespaceMap = make(map[string]bool)
	}
	nt.singleLabelSelector = singleLabelSelector
	nt.orLabelSelector = orLabelSelector
	nt.namespaceFilter = namespaceFilter
	nt.logger = logger

	for _, namespace := range unstructuredNSs {
		ns := new(corev1api.Namespace)
		if err := runtime.DefaultUnstructuredConverter.FromUnstructured(namespace.UnstructuredContent(), ns); err != nil {
			nt.logger.WithError(err).Errorf("Fail to convert unstructured into namespace %s", namespace.GetName())
			continue
		}
		if ns.Status.Phase != corev1api.NamespaceActive {
			nt.logger.Infof("Skip namespace %s because it's not in Active phase.", namespace.GetName())
			continue
		}

		if nt.singleLabelSelector != nil &&
			nt.singleLabelSelector.Matches(labels.Set(namespace.GetLabels())) {
			nt.logger.Debugf("Track namespace %s, because its labels match backup LabelSelector.",
				namespace.GetName(),
			)

			nt.track(namespace.GetName())
			continue
		}

		if len(nt.orLabelSelector) > 0 {
			for _, selector := range nt.orLabelSelector {
				if selector.Matches(labels.Set(namespace.GetLabels())) {
					nt.logger.Debugf("Track namespace %s, because its labels match the backup OrLabelSelector.",
						namespace.GetName(),
					)
					nt.track(namespace.GetName())
					continue
				}
			}
		}

		// Skip the backup when the backup's namespace filter has
		// default value, and the namespace doesn't match backup
		// LabelSelector and OrLabelSelector.
		// https://github.com/vmware-tanzu/velero/issues/7105
		if nt.namespaceFilter.IncludeEverything() &&
			(nt.singleLabelSelector != nil || len(nt.orLabelSelector) > 0) {
			continue
		}

		if nt.namespaceFilter.ShouldInclude(namespace.GetName()) {
			nt.logger.Debugf("Track namespace %s, because its name match the backup namespace filter.",
				namespace.GetName(),
			)
			nt.track(namespace.GetName())
		}
	}
}

// filterNamespaces filters the input resource list to remove the
// namespaces not tracked by the nsTracker.
func (nt *nsTracker) filterNamespaces(
	resources []*kubernetesResource,
) []*kubernetesResource {
	result := make([]*kubernetesResource, 0)

	for _, resource := range resources {
		if resource.groupResource != kuberesource.Namespaces ||
			nt.isTracked(resource.name) {
			result = append(result, resource)
		}
	}

	return result
}

type kubernetesResource struct {
	groupResource         schema.GroupResource
	preferredGVR          schema.GroupVersionResource
	namespace, name, path string
	orderedResource       bool
	// set to true during backup processing when added to an ItemBlock
	// or if the item is excluded from backup.
	inItemBlockOrExcluded bool
	// Kind is added to facilitate creating an itemKey for progress tracking
	kind string
}

// getItemsFromResourceIdentifiers get the kubernetesResources
// specified by the input parameter resourceIDs.
func (r *itemCollector) getItemsFromResourceIdentifiers(
	resourceIDs []velero.ResourceIdentifier,
) []*kubernetesResource {
	grResourceIDsMap := make(map[schema.GroupResource][]velero.ResourceIdentifier)
	for _, resourceID := range resourceIDs {
		grResourceIDsMap[resourceID.GroupResource] = append(
			grResourceIDsMap[resourceID.GroupResource], resourceID)
	}
	return r.getItems(grResourceIDsMap)
}

// getAllItems gets all backup-relevant items from all API groups.
func (r *itemCollector) getAllItems() []*kubernetesResource {
	resources := r.getItems(nil)

	return r.nsTracker.filterNamespaces(resources)
}

// getItems gets all backup-relevant items from all API groups,
//
// If resourceIDsMap is nil, then all items from the cluster are
// pulled for each API group, subject to include/exclude rules,
// except the namespace, because the namespace filtering depends on
// all namespaced-scoped resources.
//
// If resourceIDsMap is supplied, then only those resources are
// returned, with the appropriate APIGroup information filled in. In
// this case, include/exclude rules are not invoked, since we already
// have the list of items, we just need the item collector/discovery
// helper to fill in the missing GVR, etc. context.
func (r *itemCollector) getItems(
	resourceIDsMap map[schema.GroupResource][]velero.ResourceIdentifier,
) []*kubernetesResource {
	var resources []*kubernetesResource
	for _, group := range r.discoveryHelper.Resources() {
		groupItems, err := r.getGroupItems(r.log, group, resourceIDsMap)
		if err != nil {
			r.log.WithError(err).WithField("apiGroup", group.String()).
				Error("Error collecting resources from API group")
			continue
		}

		resources = append(resources, groupItems...)
	}

	return resources
}

// getGroupItems collects all relevant items from a single API group.
// If resourceIDsMap is supplied, then only those items are returned,
// with GVR/APIResource metadata supplied.
func (r *itemCollector) getGroupItems(
	log logrus.FieldLogger,
	group *metav1.APIResourceList,
	resourceIDsMap map[schema.GroupResource][]velero.ResourceIdentifier,
) ([]*kubernetesResource, error) {
	log = log.WithField("group", group.GroupVersion)

	log.Infof("Getting items for group")

	// Parse so we can check if this is the core group
	gv, err := schema.ParseGroupVersion(group.GroupVersion)
	if err != nil {
		return nil, errors.Wrapf(err, "error parsing GroupVersion %q",
			group.GroupVersion)
	}
	if gv.Group == "" {
		// This is the core group, so make sure we process in the following order:
		// pods, pvcs, pvs, everything else.
		sortCoreGroup(group)
	}

	var items []*kubernetesResource
	for _, resource := range group.APIResources {
		resourceItems, err := r.getResourceItems(log, gv, resource, resourceIDsMap)
		if err != nil {
			log.WithError(err).WithField("resource", resource.String()).
				Error("Error getting items for resource")
			continue
		}

		items = append(items, resourceItems...)
	}

	return items, nil
}

// sortResourcesByOrder sorts items by the names specified in "order".
// Items are not in order will be put at the end in original order.
func sortResourcesByOrder(
	log logrus.FieldLogger,
	items []*kubernetesResource,
	order []string,
) []*kubernetesResource {
	if len(order) == 0 {
		return items
	}
	log.Debugf("Sorting resources using the following order %v...", order)
	itemMap := make(map[string]*kubernetesResource)
	for _, item := range items {
		var fullname string
		if item.namespace != "" {
			fullname = fmt.Sprintf("%s/%s", item.namespace, item.name)
		} else {
			fullname = item.name
		}
		itemMap[fullname] = item
	}
	var sortedItems []*kubernetesResource
	// First select items from the order
	for _, name := range order {
		if item, ok := itemMap[name]; ok {
			item.orderedResource = true
			sortedItems = append(sortedItems, item)
			log.Debugf("%s added to sorted resource list.", item.name)
			delete(itemMap, name)
		} else {
			log.Warnf("Cannot find resource '%s'.", name)
		}
	}
	// Now append the rest in sortedGroupItems, maintain the original order
	for _, item := range items {
		var fullname string
		if item.namespace != "" {
			fullname = fmt.Sprintf("%s/%s", item.namespace, item.name)
		} else {
			fullname = item.name
		}
		if _, ok := itemMap[fullname]; !ok {
			//This item has been inserted in the result
			continue
		}
		sortedItems = append(sortedItems, item)
		log.Debugf("%s added to sorted resource list.", item.name)
	}
	return sortedItems
}

// getOrderedResourcesForType gets order of resourceType from orderResources.
func getOrderedResourcesForType(
	orderedResources map[string]string,
	resourceType string,
) []string {
	if orderedResources == nil {
		return nil
	}
	orderStr, ok := orderedResources[resourceType]
	if !ok || len(orderStr) == 0 {
		return nil
	}
	parts := strings.Split(orderStr, ",")
	orders := make([]string, 0, len(parts))
	for _, part := range parts {
		name := strings.TrimSpace(part)
		if name == "" {
			continue
		}
		orders = append(orders, name)
	}
	return orders
}

// getResourceItems collects all relevant items for a given group-version-resource.
// If resourceIDsMap is supplied, the items will be pulled from here
// rather than from the cluster and applying include/exclude rules.
func (r *itemCollector) getResourceItems(
	log logrus.FieldLogger,
	gv schema.GroupVersion,
	resource metav1.APIResource,
	resourceIDsMap map[schema.GroupResource][]velero.ResourceIdentifier,
) ([]*kubernetesResource, error) {
	log = log.WithField("resource", resource.Name)

	log.Info("Getting items for resource")

	var (
		gvr = gv.WithResource(resource.Name)
		gr  = gvr.GroupResource()
	)

	orders := getOrderedResourcesForType(
		r.backupRequest.Backup.Spec.OrderedResources,
		resource.Name,
	)
	// Getting the preferred group version of this resource
	preferredGVR, _, err := r.discoveryHelper.ResourceFor(gr.WithVersion(""))
	if err != nil {
		return nil, errors.WithStack(err)
	}

	// If we have a resourceIDs map, then only return items listed in it
	if resourceIDsMap != nil {
		resourceIDs, ok := resourceIDsMap[gr]
		if !ok {
			log.Info("Skipping resource because no items found in supplied ResourceIdentifier list")
			return nil, nil
		}
		var items []*kubernetesResource
		for _, resourceID := range resourceIDs {
			log.WithFields(
				logrus.Fields{
					"namespace": resourceID.Namespace,
					"name":      resourceID.Name,
				},
			).Infof("Getting item")
			resourceClient, err := r.dynamicFactory.ClientForGroupVersionResource(
				gv,
				resource,
				resourceID.Namespace,
			)
			if err != nil {
				log.WithError(errors.WithStack(err)).Error("Error getting client for resource")
				continue
			}
			unstructured, err := resourceClient.Get(resourceID.Name, metav1.GetOptions{})
			if err != nil {
				log.WithError(errors.WithStack(err)).Error("Error getting item")
				continue
			}

			path, err := r.writeToFile(unstructured)
			if err != nil {
				log.WithError(err).Error("Error writing item to file")
				continue
			}

			items = append(items, &kubernetesResource{
				groupResource: gr,
				preferredGVR:  preferredGVR,
				namespace:     resourceID.Namespace,
				name:          resourceID.Name,
				path:          path,
				kind:          resource.Kind,
			})
		}

		return items, nil
	}

	if !r.backupRequest.ResourceIncludesExcludes.ShouldInclude(gr.String()) {
		log.Infof("Skipping resource because it's excluded")
		return nil, nil
	}

	if cohabitator, found := r.cohabitatingResources[resource.Name]; found {
		if gv.Group == cohabitator.groupResource1.Group ||
			gv.Group == cohabitator.groupResource2.Group {
			if cohabitator.seen {
				log.WithFields(
					logrus.Fields{
						"cohabitatingResource1": cohabitator.groupResource1.String(),
						"cohabitatingResource2": cohabitator.groupResource2.String(),
					},
				).Infof("Skipping resource because it cohabitates and we've already processed it")
				return nil, nil
			}
			cohabitator.seen = true
		}
	}

	// Handle namespace resource here.
	// Namespace are filtered by namespace include/exclude filters,
	// backup LabelSelectors and OrLabelSelectors are checked too.
	if gr == kuberesource.Namespaces {
		return r.collectNamespaces(
			resource,
			gv,
			gr,
			preferredGVR,
			log,
		)
	}

	clusterScoped := !resource.Namespaced

	namespacesToList := getNamespacesToList(r.backupRequest.NamespaceIncludesExcludes)

	// If we get here, we're backing up something other than namespaces
	if clusterScoped {
		namespacesToList = []string{""}
	}

	grString := gr.String()
	hasNamespacedPolicies := len(r.backupRequest.NamespacedFilterMap) > 0

	var items []*kubernetesResource

	for _, namespace := range namespacesToList {
		// Check per-namespace resource type filter from ResourcePolicy
		if nsFilter := r.backupRequest.GetNamespaceFilter(namespace); nsFilter != nil {
			_, hasSpecific := nsFilter.ResourceFilterMap[grString]
			if !hasSpecific && nsFilter.CatchAllFilter == nil {
				log.Debugf("Skipping resource %s in namespace %s: not in resourceFilters",
					gr, namespace)
				continue
			}
		}

		unstructuredItems, err := r.listResourceByLabelsPerNamespace(
			namespace, gr, gv, resource, log)
		if err != nil {
			continue
		}

		var lastNS string
		var lastNSFilter *ResolvedNamespaceFilter

		// Collect items in included Namespaces
		for i := range unstructuredItems {
			item := &unstructuredItems[i]
			itemNS := item.GetNamespace()

			// Apply namespace inclusion/exclusion and fine-grained filter policies in-memory for cluster-wide queries.
			if itemNS != "" && namespace == "" {
				if r.backupRequest.NamespaceIncludesExcludes != nil &&
					!r.backupRequest.NamespaceIncludesExcludes.ShouldInclude(itemNS) {
					log.Debugf("Skipping resource %s in namespace %s: namespace excluded",
						gr, itemNS)
					continue
				}

				if hasNamespacedPolicies {
					if itemNS != lastNS {
						lastNS = itemNS
						lastNSFilter = r.backupRequest.GetNamespaceFilter(itemNS)
					}

					if lastNSFilter != nil {
						rf := lastNSFilter.ResourceFilterMap[grString]
						if rf == nil {
							rf = lastNSFilter.CatchAllFilter
						}
						if rf == nil {
							log.Debugf("Skipping resource %s in namespace %s: not in resourceFilters",
								gr, itemNS)
							continue
						}

						// In-memory label selector checks for fine-grained filters
						if rf.LabelSelector != nil || len(rf.OrLabelSelectors) > 0 {
							itemLabels := labels.Set(item.GetLabels())
							if rf.LabelSelector != nil && !rf.LabelSelector.Matches(itemLabels) {
								log.Debugf("Skipping resource %s in namespace %s: does not match labelSelector",
									gr, itemNS)
								continue
							}
							if len(rf.OrLabelSelectors) > 0 {
								matched := false
								for _, s := range rf.OrLabelSelectors {
									if s.Matches(itemLabels) {
										matched = true
										break
									}
								}
								if !matched {
									log.Debugf("Skipping resource %s in namespace %s: does not match orLabelSelectors",
										gr, itemNS)
									continue
								}
							}
						}
					}
				}
			}

			path, err := r.writeToFile(item)
			if err != nil {
				log.WithError(err).Error("Error writing item to file")
				continue
			}

			items = append(items, &kubernetesResource{
				groupResource: gr,
				preferredGVR:  preferredGVR,
				namespace:     item.GetNamespace(),
				name:          item.GetName(),
				path:          path,
				kind:          resource.Kind,
			})

			if item.GetNamespace() != "" &&
				r.backupRequest.NamespaceIncludesExcludes.ShouldInclude(item.GetNamespace()) {
				log.Debugf("Track namespace %s in nsTracker", item.GetNamespace())
				r.nsTracker.track(item.GetNamespace())
			}
		}
	}

	if len(orders) > 0 {
		items = sortResourcesByOrder(r.log, items, orders)
	}

	return items, nil
}

func (r *itemCollector) listResourceByLabelsPerNamespace(
	namespace string,
	gr schema.GroupResource,
	gv schema.GroupVersion,
	resource metav1.APIResource,
	logger logrus.FieldLogger,
) ([]unstructured.Unstructured, error) {
	// List items from Kubernetes API
	logger = logger.WithField("namespace", namespace)

	resourceClient, err := r.dynamicFactory.ClientForGroupVersionResource(gv, resource, namespace)
	if err != nil {
		logger.WithError(err).Error("Error getting dynamic client")
		return nil, err
	}

	// 1. Start with global selectors (existing default behavior)
	var orLabelSelectors []string
	var labelSelector string

	if r.backupRequest.Spec.OrLabelSelectors != nil {
		for _, s := range r.backupRequest.Spec.OrLabelSelectors {
			orLabelSelectors = append(orLabelSelectors, metav1.FormatLabelSelector(s))
		}
	}
	if selector := r.backupRequest.Spec.LabelSelector; selector != nil {
		labelSelector = metav1.FormatLabelSelector(selector)
	}

	// 2. Apply fine-grained filter overrides if applicable
	if !resource.Namespaced && r.backupRequest.ClusterScopedFilterMap != nil {
		if rf := r.backupRequest.ClusterScopedFilterMap[gr.String()]; rf != nil {
			// Overwrite global selectors with specific filter
			orLabelSelectors = nil
			labelSelector = ""
			if rf.LabelSelector != nil {
				labelSelector = rf.LabelSelector.String()
			}
			for _, s := range rf.OrLabelSelectors {
				orLabelSelectors = append(orLabelSelectors, s.String())
			}
		}
		// ClusterScopedFilterPolicy: If rf == nil, it intentionally falls back to the global selectors initialized above
	} else if nsFilter := r.backupRequest.GetNamespaceFilter(namespace); nsFilter != nil {
		rf := nsFilter.ResourceFilterMap[gr.String()]
		if rf == nil {
			rf = nsFilter.CatchAllFilter
		}

		if rf != nil {
			// Overwrite global selectors with specific filter
			orLabelSelectors = nil
			labelSelector = ""
			if rf.LabelSelector != nil {
				labelSelector = rf.LabelSelector.String()
			}
			for _, s := range rf.OrLabelSelectors {
				orLabelSelectors = append(orLabelSelectors, s.String())
			}
		} else {
			// NamespacedFilterPolicies: namespacedFilterPolicies acts as an exclusive allowlist.
			// If neither a kind-specific entry nor a catch-all entry exists, skip the kind.
			logger.Debug("Skipping resource kind for namespace as it is not present in the namespace filter policy")
			return nil, nil
		}
	}

	logger.Info("Listing items")
	unstructuredItems := make([]unstructured.Unstructured, 0)

	// Listing items for orLabelSelectors
	errListingForNS := false
	for _, label := range orLabelSelectors {
		unstructuredItems, err = r.listItemsForLabel(unstructuredItems, gr, label, resourceClient)
		if err != nil {
			errListingForNS = true
		}
	}

	if errListingForNS {
		logger.WithError(err).Error("Error listing items")
		return nil, err
	}

	// Listing items for labelSelector (singular)
	if len(orLabelSelectors) == 0 {
		unstructuredItems, err = r.listItemsForLabel(
			unstructuredItems,
			gr,
			labelSelector,
			resourceClient,
		)
		if err != nil {
			logger.WithError(err).Error("Error listing items")
			return nil, err
		}
	}

	logger.Infof("Retrieved %d items", len(unstructuredItems))
	return unstructuredItems, nil
}

func (r *itemCollector) writeToFile(item *unstructured.Unstructured) (string, error) {
	f, err := os.CreateTemp(r.dir, "")
	if err != nil {
		return "", errors.Wrap(err, "error creating temp file")
	}
	defer f.Close()

	jsonBytes, err := json.Marshal(item)
	if err != nil {
		return "", errors.Wrap(err, "error converting item to JSON")
	}

	if _, err := f.Write(jsonBytes); err != nil {
		return "", errors.Wrap(err, "error writing JSON to file")
	}

	if err := f.Close(); err != nil {
		return "", errors.Wrap(err, "error closing file")
	}

	return f.Name(), nil
}

// sortCoreGroup sorts the core API group.
func sortCoreGroup(group *metav1.APIResourceList) {
	sort.SliceStable(group.APIResources, func(i, j int) bool {
		return coreGroupResourcePriority(group.APIResources[i].Name) < coreGroupResourcePriority(group.APIResources[j].Name)
	})
}

// These constants represent the relative priorities for resources in the core API group. We want to
// ensure that we process pods, then pvcs, then pvs, then anything else. This ensures that when a
// pod is backed up, we can perform a pre hook, then process pvcs and pvs (including taking a
// snapshot), then perform a post hook on the pod.
const (
	pod = iota
	pvc
	pv
	other
)

// coreGroupResourcePriority returns the relative priority of the resource, in the following order:
// pods, pvcs, pvs, everything else.
func coreGroupResourcePriority(resource string) int {
	switch strings.ToLower(resource) {
	case "pods":
		return pod
	case "persistentvolumeclaims":
		return pvc
	case "persistentvolumes":
		return pv
	}

	return other
}

// getNamespacesToList examines ie and resolves the includes and excludes to a full list of
// namespaces to list. If ie is nil or it includes *, the result is just "" (list across all
// namespaces). Otherwise, the result is a list of every included namespace minus all excluded ones.
func getNamespacesToList(ie *collections.NamespaceIncludesExcludes) []string {
	if ie == nil {
		return []string{""}
	}

	if ie.ShouldInclude("*") {
		// "" means all namespaces
		return []string{""}
	}

	var list []string
	for _, i := range ie.GetIncludes() {
		if ie.ShouldInclude(i) {
			list = append(list, i)
		}
	}

	return list
}

type cohabitatingResource struct {
	resource       string
	groupResource1 schema.GroupResource
	groupResource2 schema.GroupResource
	seen           bool
}

func newCohabitatingResource(resource, group1, group2 string) *cohabitatingResource {
	return &cohabitatingResource{
		resource:       resource,
		groupResource1: schema.GroupResource{Group: group1, Resource: resource},
		groupResource2: schema.GroupResource{Group: group2, Resource: resource},
		seen:           false,
	}
}

// function to process pager client calls when the pageSize is specified
func (r *itemCollector) processPagerClientCalls(
	gr schema.GroupResource,
	label string,
	resourceClient client.Dynamic,
) (runtime.Object, error) {
	// If limit is positive, use a pager to split list over multiple requests
	// Use Velero's dynamic list function instead of the default
	listPager := pager.New(pager.SimplePageFunc(func(opts metav1.ListOptions) (runtime.Object, error) {
		return resourceClient.List(opts)
	}))
	// Use the page size defined in the server config
	// TODO allow configuration of page buffer size
	listPager.PageSize = int64(r.pageSize)
	// Add each item to temporary slice
	list, paginated, err := listPager.List(context.Background(), metav1.ListOptions{LabelSelector: label})

	if err != nil {
		r.log.WithError(errors.WithStack(err)).Error("Error listing resources")
		return list, err
	}

	if !paginated {
		r.log.Infof("list for groupResource %s was not paginated", gr)
	}

	return list, nil
}

func (r *itemCollector) listItemsForLabel(
	unstructuredItems []unstructured.Unstructured,
	gr schema.GroupResource,
	label string,
	resourceClient client.Dynamic,
) ([]unstructured.Unstructured, error) {
	if r.pageSize > 0 {
		// process pager client calls
		list, err := r.processPagerClientCalls(gr, label, resourceClient)
		if err != nil {
			return unstructuredItems, err
		}

		err = meta.EachListItem(list, func(object runtime.Object) error {
			u, ok := object.(*unstructured.Unstructured)
			if !ok {
				r.log.WithError(errors.WithStack(fmt.Errorf("expected *unstructured.Unstructured but got %T", u))).
					Error("unable to understand entry in the list")
				return fmt.Errorf("expected *unstructured.Unstructured but got %T", u)
			}
			unstructuredItems = append(unstructuredItems, *u)
			return nil
		})
		if err != nil {
			r.log.WithError(errors.WithStack(err)).Error("unable to understand paginated list")
			return unstructuredItems, err
		}
	} else {
		unstructuredList, err := resourceClient.List(metav1.ListOptions{LabelSelector: label})
		if err != nil {
			r.log.WithError(errors.WithStack(err)).Error("Error listing items")
			return unstructuredItems, err
		}
		unstructuredItems = append(unstructuredItems, unstructuredList.Items...)
	}
	return unstructuredItems, nil
}

// collectNamespaces process namespace resource according to namespace filters.
func (r *itemCollector) collectNamespaces(
	resource metav1.APIResource,
	gv schema.GroupVersion,
	gr schema.GroupResource,
	preferredGVR schema.GroupVersionResource,
	log logrus.FieldLogger,
) ([]*kubernetesResource, error) {
	resourceClient, err := r.dynamicFactory.ClientForGroupVersionResource(gv, resource, "")
	if err != nil {
		log.WithError(err).Error("Error getting dynamic client")
		return nil, errors.WithStack(err)
	}

	unstructuredList, err := resourceClient.List(metav1.ListOptions{})

	activeNamespacesHashSet := make(map[string]bool)
	for _, namespace := range unstructuredList.Items {
		activeNamespacesHashSet[namespace.GetName()] = true
	}

	if err != nil {
		log.WithError(errors.WithStack(err)).Error("error list namespaces")
		return nil, errors.WithStack(err)
	}

	// Change to look at the struct includes/excludes
	// In case wildcards are expanded, we need to look at the struct includes/excludes
	for _, includedNSName := range r.backupRequest.NamespaceIncludesExcludes.GetIncludes() {
		nsExists := false
		// Skip checking the namespace existing when it's "*".
		if includedNSName == "*" {
			continue
		}

		if _, ok := activeNamespacesHashSet[includedNSName]; ok {
			nsExists = true
		}

		if !nsExists {
			log.Errorf("fail to get the namespace %s specified in backup.Spec.IncludedNamespaces", includedNSName)
		}
	}

	var singleSelector labels.Selector
	var orSelectors []labels.Selector

	if r.backupRequest.Backup.Spec.LabelSelector != nil {
		var err error
		singleSelector, err = metav1.LabelSelectorAsSelector(
			r.backupRequest.Backup.Spec.LabelSelector)
		if err != nil {
			log.WithError(err).Errorf("Fail to convert backup LabelSelector %s into selector.",
				metav1.FormatLabelSelector(r.backupRequest.Backup.Spec.LabelSelector))
		}
	}
	if r.backupRequest.Backup.Spec.OrLabelSelectors != nil {
		for _, ls := range r.backupRequest.Backup.Spec.OrLabelSelectors {
			orSelector, err := metav1.LabelSelectorAsSelector(ls)
			if err != nil {
				log.WithError(err).Errorf("Fail to convert backup OrLabelSelector %s into selector.",
					metav1.FormatLabelSelector(ls))
			}
			orSelectors = append(orSelectors, orSelector)
		}
	}

	r.nsTracker.init(
		unstructuredList.Items,
		singleSelector,
		orSelectors,
		r.backupRequest.NamespaceIncludesExcludes,
		log,
	)

	var items []*kubernetesResource

	for index := range unstructuredList.Items {
		nsName := unstructuredList.Items[index].GetName()

		path, err := r.writeToFile(&unstructuredList.Items[index])
		if err != nil {
			log.WithError(err).Errorf("Error writing item %s to file", nsName)
			continue
		}

		items = append(items, &kubernetesResource{
			groupResource: gr,
			preferredGVR:  preferredGVR,
			name:          nsName,
			path:          path,
			kind:          resource.Kind,
		})
	}

	return items, nil
}