/*
   Copyright The containerd Authors.

   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 metadata

import (
	"context"
	"fmt"
	"strings"
	"sync"
	"time"

	"github.com/containerd/containerd/errdefs"
	"github.com/containerd/containerd/labels"
	"github.com/containerd/containerd/log"
	"github.com/containerd/containerd/metadata/boltutil"
	"github.com/containerd/containerd/mount"
	"github.com/containerd/containerd/namespaces"
	"github.com/containerd/containerd/snapshots"
	"github.com/pkg/errors"
	bolt "go.etcd.io/bbolt"
)

type snapshotter struct {
	snapshots.Snapshotter
	name string
	db   *DB
	l    sync.RWMutex
}

// newSnapshotter returns a new Snapshotter which namespaces the given snapshot
// using the provided name and database.
func newSnapshotter(db *DB, name string, sn snapshots.Snapshotter) *snapshotter {
	return &snapshotter{
		Snapshotter: sn,
		name:        name,
		db:          db,
	}
}

func createKey(id uint64, namespace, key string) string {
	return fmt.Sprintf("%s/%d/%s", namespace, id, key)
}

func getKey(tx *bolt.Tx, ns, name, key string) string {
	bkt := getSnapshotterBucket(tx, ns, name)
	if bkt == nil {
		return ""
	}
	bkt = bkt.Bucket([]byte(key))
	if bkt == nil {
		return ""
	}
	v := bkt.Get(bucketKeyName)
	if len(v) == 0 {
		return ""
	}
	return string(v)
}

func (s *snapshotter) resolveKey(ctx context.Context, key string) (string, error) {
	ns, err := namespaces.NamespaceRequired(ctx)
	if err != nil {
		return "", err
	}

	var id string
	if err := view(ctx, s.db, func(tx *bolt.Tx) error {
		id = getKey(tx, ns, s.name, key)
		if id == "" {
			return errors.Wrapf(errdefs.ErrNotFound, "snapshot %v does not exist", key)
		}
		return nil
	}); err != nil {
		return "", err
	}

	return id, nil
}

func (s *snapshotter) Stat(ctx context.Context, key string) (snapshots.Info, error) {
	ns, err := namespaces.NamespaceRequired(ctx)
	if err != nil {
		return snapshots.Info{}, err
	}

	var (
		bkey  string
		local = snapshots.Info{
			Name: key,
		}
	)
	if err := view(ctx, s.db, func(tx *bolt.Tx) error {
		bkt := getSnapshotterBucket(tx, ns, s.name)
		if bkt == nil {
			return errors.Wrapf(errdefs.ErrNotFound, "snapshot %v does not exist", key)
		}
		sbkt := bkt.Bucket([]byte(key))
		if sbkt == nil {
			return errors.Wrapf(errdefs.ErrNotFound, "snapshot %v does not exist", key)
		}
		local.Labels, err = boltutil.ReadLabels(sbkt)
		if err != nil {
			return errors.Wrap(err, "failed to read labels")
		}
		if err := boltutil.ReadTimestamps(sbkt, &local.Created, &local.Updated); err != nil {
			return errors.Wrap(err, "failed to read timestamps")
		}
		bkey = string(sbkt.Get(bucketKeyName))
		local.Parent = string(sbkt.Get(bucketKeyParent))

		return nil
	}); err != nil {
		return snapshots.Info{}, err
	}

	info, err := s.Snapshotter.Stat(ctx, bkey)
	if err != nil {
		return snapshots.Info{}, err
	}

	return overlayInfo(info, local), nil
}

func (s *snapshotter) Update(ctx context.Context, info snapshots.Info, fieldpaths ...string) (snapshots.Info, error) {
	s.l.RLock()
	defer s.l.RUnlock()

	ns, err := namespaces.NamespaceRequired(ctx)
	if err != nil {
		return snapshots.Info{}, err
	}

	if info.Name == "" {
		return snapshots.Info{}, errors.Wrap(errdefs.ErrInvalidArgument, "")
	}

	var (
		bkey  string
		local = snapshots.Info{
			Name: info.Name,
		}
	)
	if err := update(ctx, s.db, func(tx *bolt.Tx) error {
		bkt := getSnapshotterBucket(tx, ns, s.name)
		if bkt == nil {
			return errors.Wrapf(errdefs.ErrNotFound, "snapshot %v does not exist", info.Name)
		}
		sbkt := bkt.Bucket([]byte(info.Name))
		if sbkt == nil {
			return errors.Wrapf(errdefs.ErrNotFound, "snapshot %v does not exist", info.Name)
		}

		local.Labels, err = boltutil.ReadLabels(sbkt)
		if err != nil {
			return errors.Wrap(err, "failed to read labels")
		}
		if err := boltutil.ReadTimestamps(sbkt, &local.Created, &local.Updated); err != nil {
			return errors.Wrap(err, "failed to read timestamps")
		}

		// Handle field updates
		if len(fieldpaths) > 0 {
			for _, path := range fieldpaths {
				if strings.HasPrefix(path, "labels.") {
					if local.Labels == nil {
						local.Labels = map[string]string{}
					}

					key := strings.TrimPrefix(path, "labels.")
					local.Labels[key] = info.Labels[key]
					continue
				}

				switch path {
				case "labels":
					local.Labels = info.Labels
				default:
					return errors.Wrapf(errdefs.ErrInvalidArgument, "cannot update %q field on snapshot %q", path, info.Name)
				}
			}
		} else {
			local.Labels = info.Labels
		}
		if err := validateSnapshot(&local); err != nil {
			return err
		}
		local.Updated = time.Now().UTC()

		if err := boltutil.WriteTimestamps(sbkt, local.Created, local.Updated); err != nil {
			return errors.Wrap(err, "failed to read timestamps")
		}
		if err := boltutil.WriteLabels(sbkt, local.Labels); err != nil {
			return errors.Wrap(err, "failed to read labels")
		}
		bkey = string(sbkt.Get(bucketKeyName))
		local.Parent = string(sbkt.Get(bucketKeyParent))

		return nil
	}); err != nil {
		return snapshots.Info{}, err
	}

	info, err = s.Snapshotter.Stat(ctx, bkey)
	if err != nil {
		return snapshots.Info{}, err
	}

	return overlayInfo(info, local), nil
}

func overlayInfo(info, overlay snapshots.Info) snapshots.Info {
	// Merge info
	info.Name = overlay.Name
	info.Created = overlay.Created
	info.Updated = overlay.Updated
	info.Parent = overlay.Parent
	if info.Labels == nil {
		info.Labels = overlay.Labels
	} else {
		for k, v := range overlay.Labels {
			overlay.Labels[k] = v
		}
	}
	return info
}

func (s *snapshotter) Usage(ctx context.Context, key string) (snapshots.Usage, error) {
	bkey, err := s.resolveKey(ctx, key)
	if err != nil {
		return snapshots.Usage{}, err
	}
	return s.Snapshotter.Usage(ctx, bkey)
}

func (s *snapshotter) Mounts(ctx context.Context, key string) ([]mount.Mount, error) {
	bkey, err := s.resolveKey(ctx, key)
	if err != nil {
		return nil, err
	}
	return s.Snapshotter.Mounts(ctx, bkey)
}

func (s *snapshotter) Prepare(ctx context.Context, key, parent string, opts ...snapshots.Opt) ([]mount.Mount, error) {
	return s.createSnapshot(ctx, key, parent, false, opts)
}

func (s *snapshotter) View(ctx context.Context, key, parent string, opts ...snapshots.Opt) ([]mount.Mount, error) {
	return s.createSnapshot(ctx, key, parent, true, opts)
}

func (s *snapshotter) createSnapshot(ctx context.Context, key, parent string, readonly bool, opts []snapshots.Opt) ([]mount.Mount, error) {
	s.l.RLock()
	defer s.l.RUnlock()

	ns, err := namespaces.NamespaceRequired(ctx)
	if err != nil {
		return nil, err
	}

	var base snapshots.Info
	for _, opt := range opts {
		if err := opt(&base); err != nil {
			return nil, err
		}
	}

	if err := validateSnapshot(&base); err != nil {
		return nil, err
	}

	var m []mount.Mount
	if err := update(ctx, s.db, func(tx *bolt.Tx) error {
		bkt, err := createSnapshotterBucket(tx, ns, s.name)
		if err != nil {
			return err
		}

		bbkt, err := bkt.CreateBucket([]byte(key))
		if err != nil {
			if err == bolt.ErrBucketExists {
				err = errors.Wrapf(errdefs.ErrAlreadyExists, "snapshot %q", key)
			}
			return err
		}
		if err := addSnapshotLease(ctx, tx, s.name, key); err != nil {
			return err
		}

		var bparent string
		if parent != "" {
			pbkt := bkt.Bucket([]byte(parent))
			if pbkt == nil {
				return errors.Wrapf(errdefs.ErrNotFound, "parent snapshot %v does not exist", parent)
			}
			bparent = string(pbkt.Get(bucketKeyName))

			cbkt, err := pbkt.CreateBucketIfNotExists(bucketKeyChildren)
			if err != nil {
				return err
			}
			if err := cbkt.Put([]byte(key), nil); err != nil {
				return err
			}

			if err := bbkt.Put(bucketKeyParent, []byte(parent)); err != nil {
				return err
			}
		}

		sid, err := bkt.NextSequence()
		if err != nil {
			return err
		}
		bkey := createKey(sid, ns, key)
		if err := bbkt.Put(bucketKeyName, []byte(bkey)); err != nil {
			return err
		}

		ts := time.Now().UTC()
		if err := boltutil.WriteTimestamps(bbkt, ts, ts); err != nil {
			return err
		}
		if err := boltutil.WriteLabels(bbkt, base.Labels); err != nil {
			return err
		}

		// TODO: Consider doing this outside of transaction to lessen
		// metadata lock time
		if readonly {
			m, err = s.Snapshotter.View(ctx, bkey, bparent)
		} else {
			m, err = s.Snapshotter.Prepare(ctx, bkey, bparent)
		}
		return err
	}); err != nil {
		return nil, err
	}
	return m, nil
}

func (s *snapshotter) Commit(ctx context.Context, name, key string, opts ...snapshots.Opt) error {
	s.l.RLock()
	defer s.l.RUnlock()

	ns, err := namespaces.NamespaceRequired(ctx)
	if err != nil {
		return err
	}

	var base snapshots.Info
	for _, opt := range opts {
		if err := opt(&base); err != nil {
			return err
		}
	}

	if err := validateSnapshot(&base); err != nil {
		return err
	}

	return update(ctx, s.db, func(tx *bolt.Tx) error {
		bkt := getSnapshotterBucket(tx, ns, s.name)
		if bkt == nil {
			return errors.Wrapf(errdefs.ErrNotFound,
				"can not find snapshotter %q", s.name)
		}

		bbkt, err := bkt.CreateBucket([]byte(name))
		if err != nil {
			if err == bolt.ErrBucketExists {
				err = errors.Wrapf(errdefs.ErrAlreadyExists, "snapshot %q", name)
			}
			return err
		}
		if err := addSnapshotLease(ctx, tx, s.name, name); err != nil {
			return err
		}

		obkt := bkt.Bucket([]byte(key))
		if obkt == nil {
			return errors.Wrapf(errdefs.ErrNotFound, "snapshot %v does not exist", key)
		}

		bkey := string(obkt.Get(bucketKeyName))

		sid, err := bkt.NextSequence()
		if err != nil {
			return err
		}

		nameKey := createKey(sid, ns, name)

		if err := bbkt.Put(bucketKeyName, []byte(nameKey)); err != nil {
			return err
		}

		parent := obkt.Get(bucketKeyParent)
		if len(parent) > 0 {
			pbkt := bkt.Bucket(parent)
			if pbkt == nil {
				return errors.Wrapf(errdefs.ErrNotFound, "parent snapshot %v does not exist", string(parent))
			}

			cbkt, err := pbkt.CreateBucketIfNotExists(bucketKeyChildren)
			if err != nil {
				return err
			}
			if err := cbkt.Delete([]byte(key)); err != nil {
				return err
			}
			if err := cbkt.Put([]byte(name), nil); err != nil {
				return err
			}

			if err := bbkt.Put(bucketKeyParent, parent); err != nil {
				return err
			}
		}
		ts := time.Now().UTC()
		if err := boltutil.WriteTimestamps(bbkt, ts, ts); err != nil {
			return err
		}
		if err := boltutil.WriteLabels(bbkt, base.Labels); err != nil {
			return err
		}

		if err := bkt.DeleteBucket([]byte(key)); err != nil {
			return err
		}
		if err := removeSnapshotLease(ctx, tx, s.name, key); err != nil {
			return err
		}

		// TODO: Consider doing this outside of transaction to lessen
		// metadata lock time
		return s.Snapshotter.Commit(ctx, nameKey, bkey)
	})

}

func (s *snapshotter) Remove(ctx context.Context, key string) error {
	s.l.RLock()
	defer s.l.RUnlock()

	ns, err := namespaces.NamespaceRequired(ctx)
	if err != nil {
		return err
	}

	return update(ctx, s.db, func(tx *bolt.Tx) error {
		var sbkt *bolt.Bucket
		bkt := getSnapshotterBucket(tx, ns, s.name)
		if bkt != nil {
			sbkt = bkt.Bucket([]byte(key))
		}
		if sbkt == nil {
			return errors.Wrapf(errdefs.ErrNotFound, "snapshot %v does not exist", key)
		}

		cbkt := sbkt.Bucket(bucketKeyChildren)
		if cbkt != nil {
			if child, _ := cbkt.Cursor().First(); child != nil {
				return errors.Wrap(errdefs.ErrFailedPrecondition, "cannot remove snapshot with child")
			}
		}

		parent := sbkt.Get(bucketKeyParent)
		if len(parent) > 0 {
			pbkt := bkt.Bucket(parent)
			if pbkt == nil {
				return errors.Wrapf(errdefs.ErrNotFound, "parent snapshot %v does not exist", string(parent))
			}
			cbkt := pbkt.Bucket(bucketKeyChildren)
			if cbkt != nil {
				if err := cbkt.Delete([]byte(key)); err != nil {
					return errors.Wrap(err, "failed to remove child link")
				}
			}
		}

		if err := bkt.DeleteBucket([]byte(key)); err != nil {
			return err
		}
		if err := removeSnapshotLease(ctx, tx, s.name, key); err != nil {
			return err
		}

		// Mark snapshotter as dirty for triggering garbage collection
		s.db.dirtyL.Lock()
		s.db.dirtySS[s.name] = struct{}{}
		s.db.dirtyL.Unlock()

		return nil
	})
}

type infoPair struct {
	bkey string
	info snapshots.Info
}

func (s *snapshotter) Walk(ctx context.Context, fn func(context.Context, snapshots.Info) error) error {
	ns, err := namespaces.NamespaceRequired(ctx)
	if err != nil {
		return err
	}

	var (
		batchSize = 100
		pairs     = []infoPair{}
		lastKey   string
	)

	for {
		if err := view(ctx, s.db, func(tx *bolt.Tx) error {
			bkt := getSnapshotterBucket(tx, ns, s.name)
			if bkt == nil {
				return nil
			}

			c := bkt.Cursor()

			var k, v []byte
			if lastKey == "" {
				k, v = c.First()
			} else {
				k, v = c.Seek([]byte(lastKey))
			}

			for k != nil {
				if v == nil {
					if len(pairs) >= batchSize {
						break
					}
					sbkt := bkt.Bucket(k)

					pair := infoPair{
						bkey: string(sbkt.Get(bucketKeyName)),
						info: snapshots.Info{
							Name:   string(k),
							Parent: string(sbkt.Get(bucketKeyParent)),
						},
					}

					err := boltutil.ReadTimestamps(sbkt, &pair.info.Created, &pair.info.Updated)
					if err != nil {
						return err
					}
					pair.info.Labels, err = boltutil.ReadLabels(sbkt)
					if err != nil {
						return err
					}

					pairs = append(pairs, pair)
				}

				k, v = c.Next()
			}

			lastKey = string(k)

			return nil
		}); err != nil {
			return err
		}

		for _, pair := range pairs {
			info, err := s.Snapshotter.Stat(ctx, pair.bkey)
			if err != nil {
				if errdefs.IsNotFound(err) {
					continue
				}
				return err
			}

			if err := fn(ctx, overlayInfo(info, pair.info)); err != nil {
				return err
			}
		}

		if lastKey == "" {
			break
		}

		pairs = pairs[:0]

	}

	return nil
}

func validateSnapshot(info *snapshots.Info) error {
	for k, v := range info.Labels {
		if err := labels.Validate(k, v); err != nil {
			return errors.Wrapf(err, "info.Labels")
		}
	}

	return nil
}

type cleaner interface {
	Cleanup(ctx context.Context) error
}

func (s *snapshotter) garbageCollect(ctx context.Context) (d time.Duration, err error) {
	s.l.Lock()
	t1 := time.Now()
	defer func() {
		s.l.Unlock()
		if err == nil {
			if c, ok := s.Snapshotter.(cleaner); ok {
				err = c.Cleanup(ctx)
			}
		}
		if err == nil {
			d = time.Since(t1)
		}
	}()

	seen := map[string]struct{}{}
	if err := s.db.View(func(tx *bolt.Tx) error {
		v1bkt := tx.Bucket(bucketKeyVersion)
		if v1bkt == nil {
			return nil
		}

		// iterate through each namespace
		v1c := v1bkt.Cursor()

		for k, v := v1c.First(); k != nil; k, v = v1c.Next() {
			if v != nil {
				continue
			}

			sbkt := v1bkt.Bucket(k).Bucket(bucketKeyObjectSnapshots)
			if sbkt == nil {
				continue
			}

			// Load specific snapshotter
			ssbkt := sbkt.Bucket([]byte(s.name))
			if ssbkt == nil {
				continue
			}

			if err := ssbkt.ForEach(func(sk, sv []byte) error {
				if sv == nil {
					bkey := ssbkt.Bucket(sk).Get(bucketKeyName)
					if len(bkey) > 0 {
						seen[string(bkey)] = struct{}{}
					}
				}
				return nil
			}); err != nil {
				return err
			}
		}

		return nil
	}); err != nil {
		return 0, err
	}

	roots, err := s.walkTree(ctx, seen)
	if err != nil {
		return 0, err
	}

	// TODO: Unlock before removal (once nodes are fully unavailable).
	// This could be achieved through doing prune inside the lock
	// and having a cleanup method which actually performs the
	// deletions on the snapshotters which support it.

	for _, node := range roots {
		if err := s.pruneBranch(ctx, node); err != nil {
			return 0, err
		}
	}

	return
}

type treeNode struct {
	info     snapshots.Info
	remove   bool
	children []*treeNode
}

func (s *snapshotter) walkTree(ctx context.Context, seen map[string]struct{}) ([]*treeNode, error) {
	roots := []*treeNode{}
	nodes := map[string]*treeNode{}

	if err := s.Snapshotter.Walk(ctx, func(ctx context.Context, info snapshots.Info) error {
		_, isSeen := seen[info.Name]
		node, ok := nodes[info.Name]
		if !ok {
			node = &treeNode{}
			nodes[info.Name] = node
		}

		node.remove = !isSeen
		node.info = info

		if info.Parent == "" {
			roots = append(roots, node)
		} else {
			parent, ok := nodes[info.Parent]
			if !ok {
				parent = &treeNode{}
				nodes[info.Parent] = parent
			}
			parent.children = append(parent.children, node)
		}

		return nil
	}); err != nil {
		return nil, err
	}

	return roots, nil
}

func (s *snapshotter) pruneBranch(ctx context.Context, node *treeNode) error {
	for _, child := range node.children {
		if err := s.pruneBranch(ctx, child); err != nil {
			return err
		}
	}

	if node.remove {
		logger := log.G(ctx).WithField("snapshotter", s.name)
		if err := s.Snapshotter.Remove(ctx, node.info.Name); err != nil {
			if !errdefs.IsFailedPrecondition(err) {
				return err
			}
			logger.WithError(err).WithField("key", node.info.Name).Warnf("failed to remove snapshot")
		} else {
			logger.WithField("key", node.info.Name).Debug("removed snapshot")
		}
	}

	return nil
}

// Close closes s.Snapshotter but not db
func (s *snapshotter) Close() error {
	return s.Snapshotter.Close()
}
