package cache

import (
	"context"
	"sort"
	"sync"
	"time"

	"github.com/containerd/containerd/content"
	"github.com/containerd/containerd/diff"
	"github.com/containerd/containerd/errdefs"
	"github.com/containerd/containerd/filters"
	"github.com/containerd/containerd/gc"
	"github.com/containerd/containerd/leases"
	"github.com/docker/docker/pkg/idtools"
	"github.com/moby/buildkit/cache/metadata"
	"github.com/moby/buildkit/client"
	"github.com/moby/buildkit/identity"
	"github.com/moby/buildkit/snapshot"
	"github.com/moby/buildkit/util/flightcontrol"
	digest "github.com/opencontainers/go-digest"
	imagespecidentity "github.com/opencontainers/image-spec/identity"
	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
	"golang.org/x/sync/errgroup"
)

var (
	ErrLocked   = errors.New("locked")
	errNotFound = errors.New("not found")
	errInvalid  = errors.New("invalid")
)

type ManagerOpt struct {
	Snapshotter     snapshot.Snapshotter
	MetadataStore   *metadata.Store
	ContentStore    content.Store
	LeaseManager    leases.Manager
	PruneRefChecker ExternalRefCheckerFunc
	GarbageCollect  func(ctx context.Context) (gc.Stats, error)
	Applier         diff.Applier
	Differ          diff.Comparer
}

type Accessor interface {
	GetByBlob(ctx context.Context, desc ocispec.Descriptor, parent ImmutableRef, opts ...RefOption) (ImmutableRef, error)
	Get(ctx context.Context, id string, opts ...RefOption) (ImmutableRef, error)

	New(ctx context.Context, parent ImmutableRef, opts ...RefOption) (MutableRef, error)
	GetMutable(ctx context.Context, id string, opts ...RefOption) (MutableRef, error) // Rebase?
	IdentityMapping() *idtools.IdentityMapping
	Metadata(string) *metadata.StorageItem
}

type Controller interface {
	DiskUsage(ctx context.Context, info client.DiskUsageInfo) ([]*client.UsageInfo, error)
	Prune(ctx context.Context, ch chan client.UsageInfo, info ...client.PruneInfo) error
}

type Manager interface {
	Accessor
	Controller
	Close() error
}

type ExternalRefCheckerFunc func() (ExternalRefChecker, error)

type ExternalRefChecker interface {
	Exists(string, []digest.Digest) bool
}

type cacheManager struct {
	records map[string]*cacheRecord
	mu      sync.Mutex
	ManagerOpt
	md *metadata.Store

	muPrune sync.Mutex // make sure parallel prune is not allowed so there will not be inconsistent results
	unlazyG flightcontrol.Group
}

func NewManager(opt ManagerOpt) (Manager, error) {
	cm := &cacheManager{
		ManagerOpt: opt,
		md:         opt.MetadataStore,
		records:    make(map[string]*cacheRecord),
	}

	if err := cm.init(context.TODO()); err != nil {
		return nil, err
	}

	// cm.scheduleGC(5 * time.Minute)

	return cm, nil
}

func (cm *cacheManager) GetByBlob(ctx context.Context, desc ocispec.Descriptor, parent ImmutableRef, opts ...RefOption) (ir ImmutableRef, rerr error) {
	diffID, err := diffIDFromDescriptor(desc)
	if err != nil {
		return nil, err
	}
	chainID := diffID
	blobChainID := imagespecidentity.ChainID([]digest.Digest{desc.Digest, diffID})

	descHandlers := descHandlersOf(opts...)
	if descHandlers == nil || descHandlers[desc.Digest] == nil {
		if _, err := cm.ContentStore.Info(ctx, desc.Digest); errors.Is(err, errdefs.ErrNotFound) {
			return nil, NeedsRemoteProvidersError([]digest.Digest{desc.Digest})
		} else if err != nil {
			return nil, err
		}
	}

	var p *immutableRef
	var parentID string
	if parent != nil {
		pInfo := parent.Info()
		if pInfo.ChainID == "" || pInfo.BlobChainID == "" {
			return nil, errors.Errorf("failed to get ref by blob on non-addressable parent")
		}
		chainID = imagespecidentity.ChainID([]digest.Digest{pInfo.ChainID, chainID})
		blobChainID = imagespecidentity.ChainID([]digest.Digest{pInfo.BlobChainID, blobChainID})

		p2, err := cm.Get(ctx, parent.ID(), NoUpdateLastUsed, descHandlers)
		if err != nil {
			return nil, err
		}
		if err := p2.Finalize(ctx, true); err != nil {
			return nil, err
		}
		parentID = p2.ID()
		p = p2.(*immutableRef)
	}

	releaseParent := false
	defer func() {
		if releaseParent || rerr != nil && p != nil {
			p.Release(context.TODO())
		}
	}()

	cm.mu.Lock()
	defer cm.mu.Unlock()

	sis, err := cm.MetadataStore.Search("blobchainid:" + blobChainID.String())
	if err != nil {
		return nil, err
	}

	if len(sis) > 0 {
		ref, err := cm.get(ctx, sis[0].ID(), opts...)
		if err != nil && !IsNotFound(err) {
			return nil, errors.Wrapf(err, "failed to get record %s by blobchainid", sis[0].ID())
		}
		if p != nil {
			releaseParent = true
		}
		return ref, nil
	}

	sis, err = cm.MetadataStore.Search("chainid:" + chainID.String())
	if err != nil {
		return nil, err
	}

	var link ImmutableRef
	if len(sis) > 0 {
		ref, err := cm.get(ctx, sis[0].ID(), opts...)
		if err != nil && !IsNotFound(err) {
			return nil, errors.Wrapf(err, "failed to get record %s by chainid", sis[0].ID())
		}
		link = ref
	}

	id := identity.NewID()
	snapshotID := chainID.String()
	blobOnly := true
	if link != nil {
		snapshotID = getSnapshotID(link.Metadata())
		blobOnly = getBlobOnly(link.Metadata())
		go link.Release(context.TODO())
	}

	l, err := cm.ManagerOpt.LeaseManager.Create(ctx, func(l *leases.Lease) error {
		l.ID = id
		l.Labels = map[string]string{
			"containerd.io/gc.flat": time.Now().UTC().Format(time.RFC3339Nano),
		}
		return nil
	})
	if err != nil {
		return nil, errors.Wrap(err, "failed to create lease")
	}

	defer func() {
		if rerr != nil {
			if err := cm.ManagerOpt.LeaseManager.Delete(context.TODO(), leases.Lease{
				ID: l.ID,
			}); err != nil {
				logrus.Errorf("failed to remove lease: %+v", err)
			}
		}
	}()

	if err := cm.ManagerOpt.LeaseManager.AddResource(ctx, l, leases.Resource{
		ID:   snapshotID,
		Type: "snapshots/" + cm.ManagerOpt.Snapshotter.Name(),
	}); err != nil {
		return nil, errors.Wrapf(err, "failed to add snapshot %s to lease", id)
	}

	if desc.Digest != "" {
		if err := cm.ManagerOpt.LeaseManager.AddResource(ctx, leases.Lease{ID: id}, leases.Resource{
			ID:   desc.Digest.String(),
			Type: "content",
		}); err != nil {
			return nil, errors.Wrapf(err, "failed to add blob %s to lease", id)
		}
	}

	md, _ := cm.md.Get(id)

	rec := &cacheRecord{
		mu:     &sync.Mutex{},
		cm:     cm,
		refs:   make(map[ref]struct{}),
		parent: p,
		md:     md,
	}

	if err := initializeMetadata(rec, parentID, opts...); err != nil {
		return nil, err
	}

	queueDiffID(rec.md, diffID.String())
	queueBlob(rec.md, desc.Digest.String())
	queueChainID(rec.md, chainID.String())
	queueBlobChainID(rec.md, blobChainID.String())
	queueSnapshotID(rec.md, snapshotID)
	queueBlobOnly(rec.md, blobOnly)
	queueMediaType(rec.md, desc.MediaType)
	queueBlobSize(rec.md, desc.Size)
	queueCommitted(rec.md)

	if err := rec.md.Commit(); err != nil {
		return nil, err
	}

	cm.records[id] = rec

	return rec.ref(true, descHandlers), nil
}

// init loads all snapshots from metadata state and tries to load the records
// from the snapshotter. If snaphot can't be found, metadata is deleted as well.
func (cm *cacheManager) init(ctx context.Context) error {
	items, err := cm.md.All()
	if err != nil {
		return err
	}

	for _, si := range items {
		if _, err := cm.getRecord(ctx, si.ID()); err != nil {
			logrus.Debugf("could not load snapshot %s: %+v", si.ID(), err)
			cm.md.Clear(si.ID())
			cm.LeaseManager.Delete(ctx, leases.Lease{ID: si.ID()})
		}
	}
	return nil
}

// IdentityMapping returns the userns remapping used for refs
func (cm *cacheManager) IdentityMapping() *idtools.IdentityMapping {
	return cm.Snapshotter.IdentityMapping()
}

// Close closes the manager and releases the metadata database lock. No other
// method should be called after Close.
func (cm *cacheManager) Close() error {
	// TODO: allocate internal context and cancel it here
	return cm.md.Close()
}

// Get returns an immutable snapshot reference for ID
func (cm *cacheManager) Get(ctx context.Context, id string, opts ...RefOption) (ImmutableRef, error) {
	cm.mu.Lock()
	defer cm.mu.Unlock()
	return cm.get(ctx, id, opts...)
}

func (cm *cacheManager) Metadata(id string) *metadata.StorageItem {
	cm.mu.Lock()
	defer cm.mu.Unlock()
	r, ok := cm.records[id]
	if !ok {
		return nil
	}
	return r.Metadata()
}

// get requires manager lock to be taken
func (cm *cacheManager) get(ctx context.Context, id string, opts ...RefOption) (*immutableRef, error) {
	rec, err := cm.getRecord(ctx, id, opts...)
	if err != nil {
		return nil, err
	}
	rec.mu.Lock()
	defer rec.mu.Unlock()

	triggerUpdate := true
	for _, o := range opts {
		if o == NoUpdateLastUsed {
			triggerUpdate = false
		}
	}

	descHandlers := descHandlersOf(opts...)

	if rec.mutable {
		if len(rec.refs) != 0 {
			return nil, errors.Wrapf(ErrLocked, "%s is locked", id)
		}
		if rec.equalImmutable != nil {
			return rec.equalImmutable.ref(triggerUpdate, descHandlers), nil
		}
		return rec.mref(triggerUpdate, descHandlers).commit(ctx)
	}

	return rec.ref(triggerUpdate, descHandlers), nil
}

// getRecord returns record for id. Requires manager lock.
func (cm *cacheManager) getRecord(ctx context.Context, id string, opts ...RefOption) (cr *cacheRecord, retErr error) {
	checkLazyProviders := func(rec *cacheRecord) error {
		missing := NeedsRemoteProvidersError(nil)
		dhs := descHandlersOf(opts...)
		for {
			blob := digest.Digest(getBlob(rec.md))
			if isLazy, err := rec.isLazy(ctx); err != nil {
				return err
			} else if isLazy && dhs[blob] == nil {
				missing = append(missing, blob)
			}

			if rec.parent == nil {
				break
			}
			rec = rec.parent.cacheRecord
		}
		if len(missing) > 0 {
			return missing
		}
		return nil
	}

	if rec, ok := cm.records[id]; ok {
		if rec.isDead() {
			return nil, errors.Wrapf(errNotFound, "failed to get dead record %s", id)
		}
		if err := checkLazyProviders(rec); err != nil {
			return nil, err
		}
		return rec, nil
	}

	md, ok := cm.md.Get(id)
	if !ok {
		return nil, errors.Wrapf(errNotFound, "%s not found", id)
	}
	if mutableID := getEqualMutable(md); mutableID != "" {
		mutable, err := cm.getRecord(ctx, mutableID)
		if err != nil {
			// check loading mutable deleted record from disk
			if IsNotFound(err) {
				cm.md.Clear(id)
			}
			return nil, err
		}
		rec := &cacheRecord{
			mu:   &sync.Mutex{},
			cm:   cm,
			refs: make(map[ref]struct{}),
			// mutable refs are always non-lazy, so we can set parent desc handlers to nil
			parent:       mutable.parentRef(false, nil),
			md:           md,
			equalMutable: &mutableRef{cacheRecord: mutable},
		}
		mutable.equalImmutable = &immutableRef{cacheRecord: rec}
		cm.records[id] = rec
		return rec, nil
	}

	var parent *immutableRef
	if parentID := getParent(md); parentID != "" {
		var err error
		parent, err = cm.get(ctx, parentID, append(opts, NoUpdateLastUsed)...)
		if err != nil {
			return nil, err
		}
		defer func() {
			if retErr != nil {
				parent.mu.Lock()
				parent.release(context.TODO())
				parent.mu.Unlock()
			}
		}()
	}

	rec := &cacheRecord{
		mu:      &sync.Mutex{},
		mutable: !getCommitted(md),
		cm:      cm,
		refs:    make(map[ref]struct{}),
		parent:  parent,
		md:      md,
	}

	// the record was deleted but we crashed before data on disk was removed
	if getDeleted(md) {
		if err := rec.remove(ctx, true); err != nil {
			return nil, err
		}
		return nil, errors.Wrapf(errNotFound, "failed to get deleted record %s", id)
	}

	if err := initializeMetadata(rec, getParent(md), opts...); err != nil {
		return nil, err
	}

	cm.records[id] = rec
	if err := checkLazyProviders(rec); err != nil {
		return nil, err
	}
	return rec, nil
}

func (cm *cacheManager) New(ctx context.Context, s ImmutableRef, opts ...RefOption) (mr MutableRef, err error) {
	id := identity.NewID()

	var parent *immutableRef
	var parentID string
	var parentSnapshotID string
	if s != nil {
		if _, ok := s.(*immutableRef); ok {
			parent = s.Clone().(*immutableRef)
		} else {
			p, err := cm.Get(ctx, s.ID(), append(opts, NoUpdateLastUsed)...)
			if err != nil {
				return nil, err
			}
			parent = p.(*immutableRef)
		}
		if err := parent.Finalize(ctx, true); err != nil {
			return nil, err
		}
		if err := parent.Extract(ctx); err != nil {
			return nil, err
		}
		parentSnapshotID = getSnapshotID(parent.md)
		parentID = parent.ID()
	}

	defer func() {
		if err != nil && parent != nil {
			parent.Release(context.TODO())
		}
	}()

	l, err := cm.ManagerOpt.LeaseManager.Create(ctx, func(l *leases.Lease) error {
		l.ID = id
		l.Labels = map[string]string{
			"containerd.io/gc.flat": time.Now().UTC().Format(time.RFC3339Nano),
		}
		return nil
	})
	if err != nil {
		return nil, errors.Wrap(err, "failed to create lease")
	}

	defer func() {
		if err != nil {
			if err := cm.ManagerOpt.LeaseManager.Delete(context.TODO(), leases.Lease{
				ID: l.ID,
			}); err != nil {
				logrus.Errorf("failed to remove lease: %+v", err)
			}
		}
	}()

	if err := cm.ManagerOpt.LeaseManager.AddResource(ctx, l, leases.Resource{
		ID:   id,
		Type: "snapshots/" + cm.ManagerOpt.Snapshotter.Name(),
	}); err != nil {
		return nil, errors.Wrapf(err, "failed to add snapshot %s to lease", id)
	}

	if err := cm.Snapshotter.Prepare(ctx, id, parentSnapshotID); err != nil {
		return nil, errors.Wrapf(err, "failed to prepare %s", id)
	}

	md, _ := cm.md.Get(id)

	rec := &cacheRecord{
		mu:      &sync.Mutex{},
		mutable: true,
		cm:      cm,
		refs:    make(map[ref]struct{}),
		parent:  parent,
		md:      md,
	}

	if err := initializeMetadata(rec, parentID, opts...); err != nil {
		return nil, err
	}

	cm.mu.Lock()
	defer cm.mu.Unlock()

	cm.records[id] = rec // TODO: save to db

	return rec.mref(true, nil), nil
}

func (cm *cacheManager) GetMutable(ctx context.Context, id string, opts ...RefOption) (MutableRef, error) {
	cm.mu.Lock()
	defer cm.mu.Unlock()

	rec, err := cm.getRecord(ctx, id, opts...)
	if err != nil {
		return nil, err
	}

	rec.mu.Lock()
	defer rec.mu.Unlock()
	if !rec.mutable {
		return nil, errors.Wrapf(errInvalid, "%s is not mutable", id)
	}

	if len(rec.refs) != 0 {
		return nil, errors.Wrapf(ErrLocked, "%s is locked", id)
	}

	if rec.equalImmutable != nil {
		if len(rec.equalImmutable.refs) != 0 {
			return nil, errors.Wrapf(ErrLocked, "%s is locked", id)
		}
		delete(cm.records, rec.equalImmutable.ID())
		if err := rec.equalImmutable.remove(ctx, false); err != nil {
			return nil, err
		}
		rec.equalImmutable = nil
	}

	return rec.mref(true, descHandlersOf(opts...)), nil
}

func (cm *cacheManager) Prune(ctx context.Context, ch chan client.UsageInfo, opts ...client.PruneInfo) error {
	cm.muPrune.Lock()

	for _, opt := range opts {
		if err := cm.pruneOnce(ctx, ch, opt); err != nil {
			cm.muPrune.Unlock()
			return err
		}
	}

	cm.muPrune.Unlock()

	if cm.GarbageCollect != nil {
		if _, err := cm.GarbageCollect(ctx); err != nil {
			return err
		}
	}

	return nil
}

func (cm *cacheManager) pruneOnce(ctx context.Context, ch chan client.UsageInfo, opt client.PruneInfo) error {
	filter, err := filters.ParseAll(opt.Filter...)
	if err != nil {
		return errors.Wrapf(err, "failed to parse prune filters %v", opt.Filter)
	}

	var check ExternalRefChecker
	if f := cm.PruneRefChecker; f != nil && (!opt.All || len(opt.Filter) > 0) {
		c, err := f()
		if err != nil {
			return errors.WithStack(err)
		}
		check = c
	}

	totalSize := int64(0)
	if opt.KeepBytes != 0 {
		du, err := cm.DiskUsage(ctx, client.DiskUsageInfo{})
		if err != nil {
			return err
		}
		for _, ui := range du {
			if ui.Shared {
				continue
			}
			totalSize += ui.Size
		}
	}

	return cm.prune(ctx, ch, pruneOpt{
		filter:       filter,
		all:          opt.All,
		checkShared:  check,
		keepDuration: opt.KeepDuration,
		keepBytes:    opt.KeepBytes,
		totalSize:    totalSize,
	})
}

func (cm *cacheManager) prune(ctx context.Context, ch chan client.UsageInfo, opt pruneOpt) error {
	var toDelete []*deleteRecord

	if opt.keepBytes != 0 && opt.totalSize < opt.keepBytes {
		return nil
	}

	cm.mu.Lock()

	gcMode := opt.keepBytes != 0
	cutOff := time.Now().Add(-opt.keepDuration)

	locked := map[*sync.Mutex]struct{}{}

	for _, cr := range cm.records {
		if _, ok := locked[cr.mu]; ok {
			continue
		}
		cr.mu.Lock()

		// ignore duplicates that share data
		if cr.equalImmutable != nil && len(cr.equalImmutable.refs) > 0 || cr.equalMutable != nil && len(cr.refs) == 0 {
			cr.mu.Unlock()
			continue
		}

		if cr.isDead() {
			cr.mu.Unlock()
			continue
		}

		if len(cr.refs) == 0 {
			recordType := GetRecordType(cr)
			if recordType == "" {
				recordType = client.UsageRecordTypeRegular
			}

			shared := false
			if opt.checkShared != nil {
				shared = opt.checkShared.Exists(cr.ID(), cr.parentChain())
			}

			if !opt.all {
				if recordType == client.UsageRecordTypeInternal || recordType == client.UsageRecordTypeFrontend || shared {
					cr.mu.Unlock()
					continue
				}
			}

			c := &client.UsageInfo{
				ID:         cr.ID(),
				Mutable:    cr.mutable,
				RecordType: recordType,
				Shared:     shared,
			}

			usageCount, lastUsedAt := getLastUsed(cr.md)
			c.LastUsedAt = lastUsedAt
			c.UsageCount = usageCount

			if opt.keepDuration != 0 {
				if lastUsedAt != nil && lastUsedAt.After(cutOff) {
					cr.mu.Unlock()
					continue
				}
			}

			if opt.filter.Match(adaptUsageInfo(c)) {
				toDelete = append(toDelete, &deleteRecord{
					cacheRecord: cr,
					lastUsedAt:  c.LastUsedAt,
					usageCount:  c.UsageCount,
				})
				if !gcMode {
					cr.dead = true

					// mark metadata as deleted in case we crash before cleanup finished
					if err := setDeleted(cr.md); err != nil {
						cr.mu.Unlock()
						cm.mu.Unlock()
						return err
					}
				} else {
					locked[cr.mu] = struct{}{}
					continue // leave the record locked
				}
			}
		}
		cr.mu.Unlock()
	}

	if gcMode && len(toDelete) > 0 {
		sortDeleteRecords(toDelete)
		var err error
		for i, cr := range toDelete {
			// only remove single record at a time
			if i == 0 {
				cr.dead = true
				err = setDeleted(cr.md)
			}
			cr.mu.Unlock()
		}
		if err != nil {
			return err
		}
		toDelete = toDelete[:1]
	}

	cm.mu.Unlock()

	if len(toDelete) == 0 {
		return nil
	}

	var err error
	for _, cr := range toDelete {
		cr.mu.Lock()

		usageCount, lastUsedAt := getLastUsed(cr.md)

		c := client.UsageInfo{
			ID:          cr.ID(),
			Mutable:     cr.mutable,
			InUse:       len(cr.refs) > 0,
			Size:        getSize(cr.md),
			CreatedAt:   GetCreatedAt(cr.md),
			Description: GetDescription(cr.md),
			LastUsedAt:  lastUsedAt,
			UsageCount:  usageCount,
		}

		if cr.parent != nil {
			c.Parent = cr.parent.ID()
		}
		if c.Size == sizeUnknown && cr.equalImmutable != nil {
			c.Size = getSize(cr.equalImmutable.md) // benefit from DiskUsage calc
		}
		if c.Size == sizeUnknown {
			cr.mu.Unlock() // all the non-prune modifications already protected by cr.dead
			s, err := cr.Size(ctx)
			if err != nil {
				return err
			}
			c.Size = s
			cr.mu.Lock()
		}

		opt.totalSize -= c.Size

		if cr.equalImmutable != nil {
			if err1 := cr.equalImmutable.remove(ctx, false); err == nil {
				err = err1
			}
		}
		if err1 := cr.remove(ctx, true); err == nil {
			err = err1
		}

		if err == nil && ch != nil {
			ch <- c
		}
		cr.mu.Unlock()
	}
	if err != nil {
		return err
	}

	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
		return cm.prune(ctx, ch, opt)
	}
}

func (cm *cacheManager) markShared(m map[string]*cacheUsageInfo) error {
	if cm.PruneRefChecker == nil {
		return nil
	}
	c, err := cm.PruneRefChecker()
	if err != nil {
		return errors.WithStack(err)
	}

	var markAllParentsShared func(string)
	markAllParentsShared = func(id string) {
		if v, ok := m[id]; ok {
			v.shared = true
			if v.parent != "" {
				markAllParentsShared(v.parent)
			}
		}
	}

	for id := range m {
		if m[id].shared {
			continue
		}
		if b := c.Exists(id, m[id].parentChain); b {
			markAllParentsShared(id)
		}
	}
	return nil
}

type cacheUsageInfo struct {
	refs        int
	parent      string
	size        int64
	mutable     bool
	createdAt   time.Time
	usageCount  int
	lastUsedAt  *time.Time
	description string
	doubleRef   bool
	recordType  client.UsageRecordType
	shared      bool
	parentChain []digest.Digest
}

func (cm *cacheManager) DiskUsage(ctx context.Context, opt client.DiskUsageInfo) ([]*client.UsageInfo, error) {
	filter, err := filters.ParseAll(opt.Filter...)
	if err != nil {
		return nil, errors.Wrapf(err, "failed to parse diskusage filters %v", opt.Filter)
	}

	cm.mu.Lock()

	m := make(map[string]*cacheUsageInfo, len(cm.records))
	rescan := make(map[string]struct{}, len(cm.records))

	for id, cr := range cm.records {
		cr.mu.Lock()
		// ignore duplicates that share data
		if cr.equalImmutable != nil && len(cr.equalImmutable.refs) > 0 || cr.equalMutable != nil && len(cr.refs) == 0 {
			cr.mu.Unlock()
			continue
		}

		usageCount, lastUsedAt := getLastUsed(cr.md)
		c := &cacheUsageInfo{
			refs:        len(cr.refs),
			mutable:     cr.mutable,
			size:        getSize(cr.md),
			createdAt:   GetCreatedAt(cr.md),
			usageCount:  usageCount,
			lastUsedAt:  lastUsedAt,
			description: GetDescription(cr.md),
			doubleRef:   cr.equalImmutable != nil,
			recordType:  GetRecordType(cr),
			parentChain: cr.parentChain(),
		}
		if c.recordType == "" {
			c.recordType = client.UsageRecordTypeRegular
		}
		if cr.parent != nil {
			c.parent = cr.parent.ID()
		}
		if cr.mutable && c.refs > 0 {
			c.size = 0 // size can not be determined because it is changing
		}
		m[id] = c
		rescan[id] = struct{}{}
		cr.mu.Unlock()
	}
	cm.mu.Unlock()

	for {
		if len(rescan) == 0 {
			break
		}
		for id := range rescan {
			v := m[id]
			if v.refs == 0 && v.parent != "" {
				m[v.parent].refs--
				if v.doubleRef {
					m[v.parent].refs--
				}
				rescan[v.parent] = struct{}{}
			}
			delete(rescan, id)
		}
	}

	if err := cm.markShared(m); err != nil {
		return nil, err
	}

	var du []*client.UsageInfo
	for id, cr := range m {
		c := &client.UsageInfo{
			ID:          id,
			Mutable:     cr.mutable,
			InUse:       cr.refs > 0,
			Size:        cr.size,
			Parent:      cr.parent,
			CreatedAt:   cr.createdAt,
			Description: cr.description,
			LastUsedAt:  cr.lastUsedAt,
			UsageCount:  cr.usageCount,
			RecordType:  cr.recordType,
			Shared:      cr.shared,
		}
		if filter.Match(adaptUsageInfo(c)) {
			du = append(du, c)
		}
	}

	eg, ctx := errgroup.WithContext(ctx)

	for _, d := range du {
		if d.Size == sizeUnknown {
			func(d *client.UsageInfo) {
				eg.Go(func() error {
					ref, err := cm.Get(ctx, d.ID, NoUpdateLastUsed)
					if err != nil {
						d.Size = 0
						return nil
					}
					s, err := ref.Size(ctx)
					if err != nil {
						return err
					}
					d.Size = s
					return ref.Release(context.TODO())
				})
			}(d)
		}
	}

	if err := eg.Wait(); err != nil {
		return du, err
	}

	return du, nil
}

func IsNotFound(err error) bool {
	return errors.Is(err, errNotFound)
}

type RefOption interface{}

type cachePolicy int

const (
	cachePolicyDefault cachePolicy = iota
	cachePolicyRetain
)

type withMetadata interface {
	Metadata() *metadata.StorageItem
}

type noUpdateLastUsed struct{}

var NoUpdateLastUsed noUpdateLastUsed

func HasCachePolicyRetain(m withMetadata) bool {
	return getCachePolicy(m.Metadata()) == cachePolicyRetain
}

func CachePolicyRetain(m withMetadata) error {
	return queueCachePolicy(m.Metadata(), cachePolicyRetain)
}

func CachePolicyDefault(m withMetadata) error {
	return queueCachePolicy(m.Metadata(), cachePolicyDefault)
}

func WithDescription(descr string) RefOption {
	return func(m withMetadata) error {
		return queueDescription(m.Metadata(), descr)
	}
}

func WithRecordType(t client.UsageRecordType) RefOption {
	return func(m withMetadata) error {
		return queueRecordType(m.Metadata(), t)
	}
}

func WithCreationTime(tm time.Time) RefOption {
	return func(m withMetadata) error {
		return queueCreatedAt(m.Metadata(), tm)
	}
}

func initializeMetadata(m withMetadata, parent string, opts ...RefOption) error {
	md := m.Metadata()
	if tm := GetCreatedAt(md); !tm.IsZero() {
		return nil
	}

	if err := queueParent(md, parent); err != nil {
		return err
	}

	if err := queueCreatedAt(md, time.Now()); err != nil {
		return err
	}

	for _, opt := range opts {
		if fn, ok := opt.(func(withMetadata) error); ok {
			if err := fn(m); err != nil {
				return err
			}
		}
	}

	return md.Commit()
}

func adaptUsageInfo(info *client.UsageInfo) filters.Adaptor {
	return filters.AdapterFunc(func(fieldpath []string) (string, bool) {
		if len(fieldpath) == 0 {
			return "", false
		}

		switch fieldpath[0] {
		case "id":
			return info.ID, info.ID != ""
		case "parent":
			return info.Parent, info.Parent != ""
		case "description":
			return info.Description, info.Description != ""
		case "inuse":
			return "", info.InUse
		case "mutable":
			return "", info.Mutable
		case "immutable":
			return "", !info.Mutable
		case "type":
			return string(info.RecordType), info.RecordType != ""
		case "shared":
			return "", info.Shared
		case "private":
			return "", !info.Shared
		}

		// TODO: add int/datetime/bytes support for more fields

		return "", false
	})
}

type pruneOpt struct {
	filter       filters.Filter
	all          bool
	checkShared  ExternalRefChecker
	keepDuration time.Duration
	keepBytes    int64
	totalSize    int64
}

type deleteRecord struct {
	*cacheRecord
	lastUsedAt      *time.Time
	usageCount      int
	lastUsedAtIndex int
	usageCountIndex int
}

func sortDeleteRecords(toDelete []*deleteRecord) {
	sort.Slice(toDelete, func(i, j int) bool {
		if toDelete[i].lastUsedAt == nil {
			return true
		}
		if toDelete[j].lastUsedAt == nil {
			return false
		}
		return toDelete[i].lastUsedAt.Before(*toDelete[j].lastUsedAt)
	})

	maxLastUsedIndex := 0
	var val time.Time
	for _, v := range toDelete {
		if v.lastUsedAt != nil && v.lastUsedAt.After(val) {
			val = *v.lastUsedAt
			maxLastUsedIndex++
		}
		v.lastUsedAtIndex = maxLastUsedIndex
	}

	sort.Slice(toDelete, func(i, j int) bool {
		return toDelete[i].usageCount < toDelete[j].usageCount
	})

	maxUsageCountIndex := 0
	var count int
	for _, v := range toDelete {
		if v.usageCount != count {
			count = v.usageCount
			maxUsageCountIndex++
		}
		v.usageCountIndex = maxUsageCountIndex
	}

	sort.Slice(toDelete, func(i, j int) bool {
		return float64(toDelete[i].lastUsedAtIndex)/float64(maxLastUsedIndex)+
			float64(toDelete[i].usageCountIndex)/float64(maxUsageCountIndex) <
			float64(toDelete[j].lastUsedAtIndex)/float64(maxLastUsedIndex)+
				float64(toDelete[j].usageCountIndex)/float64(maxUsageCountIndex)
	})
}

func diffIDFromDescriptor(desc ocispec.Descriptor) (digest.Digest, error) {
	diffIDStr, ok := desc.Annotations["containerd.io/uncompressed"]
	if !ok {
		return "", errors.Errorf("missing uncompressed annotation for %s", desc.Digest)
	}
	diffID, err := digest.Parse(diffIDStr)
	if err != nil {
		return "", errors.Wrapf(err, "failed to parse diffID %q for %s", diffIDStr, desc.Digest)
	}
	return diffID, nil
}