package meta

import (
	"context"
	"errors"
	"fmt"
	"strconv"

	objectV2 "git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/object"
	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	"go.etcd.io/bbolt"
)

// FilterExpired return expired items from addresses.
// Address considered expired if metabase does contain information about expiration and
// expiration epoch is less than epoch.
func (db *DB) FilterExpired(ctx context.Context, epoch uint64, addresses []oid.Address) ([]oid.Address, error) {
	db.modeMtx.RLock()
	defer db.modeMtx.RUnlock()

	if db.mode.NoMetabase() {
		return nil, ErrDegradedMode
	}

	result := make([]oid.Address, 0, len(addresses))
	containerIDToObjectIDs := make(map[cid.ID][]oid.ID)
	for _, addr := range addresses {
		containerIDToObjectIDs[addr.Container()] = append(containerIDToObjectIDs[addr.Container()], addr.Object())
	}

	err := db.boltDB.View(func(tx *bbolt.Tx) error {
		for containerID, objectIDs := range containerIDToObjectIDs {
			select {
			case <-ctx.Done():
				return ErrInterruptIterator
			default:
			}

			expiredNeoFS, err := selectExpiredObjectIDs(tx, objectV2.SysAttributeExpEpochNeoFS, epoch, containerID, objectIDs)
			if err != nil {
				return err
			}

			expiredSys, err := selectExpiredObjectIDs(tx, objectV2.SysAttributeExpEpoch, epoch, containerID, objectIDs)
			if err != nil {
				return err
			}

			for _, o := range expiredNeoFS {
				var a oid.Address
				a.SetContainer(containerID)
				a.SetObject(o)
				result = append(result, a)
			}

			for _, o := range expiredSys {
				var a oid.Address
				a.SetContainer(containerID)
				a.SetObject(o)
				result = append(result, a)
			}
		}
		return nil
	})

	if err != nil {
		return nil, err
	}
	return result, nil
}

func isExpiredWithAttribute(tx *bbolt.Tx, attr string, addr oid.Address, currEpoch uint64) bool {
	// bucket with objects that have expiration attr
	attrKey := make([]byte, bucketKeySize+len(attr))
	expirationBucket := tx.Bucket(attributeBucketName(addr.Container(), attr, attrKey))
	if expirationBucket != nil {
		// bucket that contains objects that expire in the current epoch
		prevEpochBkt := expirationBucket.Bucket([]byte(strconv.FormatUint(currEpoch-1, 10)))
		if prevEpochBkt != nil {
			rawOID := objectKey(addr.Object(), make([]byte, objectKeySize))
			if prevEpochBkt.Get(rawOID) != nil {
				return true
			}
		}
	}

	return false
}

func selectExpiredObjectIDs(tx *bbolt.Tx, attr string, epoch uint64, containerID cid.ID, objectIDs []oid.ID) ([]oid.ID, error) {
	result := make([]oid.ID, 0)
	notResolved := make(map[oid.ID]struct{})
	for _, oid := range objectIDs {
		notResolved[oid] = struct{}{}
	}

	expiredBuffer := make([]oid.ID, 0)
	objectKeyBuffer := make([]byte, objectKeySize)

	expirationBucketKey := make([]byte, bucketKeySize+len(attr))
	expirationBucket := tx.Bucket(attributeBucketName(containerID, attr, expirationBucketKey))
	if expirationBucket == nil {
		return result, nil // all not expired
	}

	err := expirationBucket.ForEach(func(epochExpBucketKey, _ []byte) error {
		bucketExpiresAfter, err := strconv.ParseUint(string(epochExpBucketKey), 10, 64)
		if err != nil {
			return fmt.Errorf("could not parse expiration epoch: %w", err)
		} else if bucketExpiresAfter >= epoch {
			return nil
		}

		epochExpirationBucket := expirationBucket.Bucket(epochExpBucketKey)
		if epochExpirationBucket == nil {
			return nil
		}

		expiredBuffer = expiredBuffer[:0]
		for oid := range notResolved {
			key := objectKey(oid, objectKeyBuffer)
			if epochExpirationBucket.Get(key) != nil {
				expiredBuffer = append(expiredBuffer, oid)
			}
		}

		for _, oid := range expiredBuffer {
			delete(notResolved, oid)
			result = append(result, oid)
		}

		if len(notResolved) == 0 {
			return errBreakBucketForEach
		}

		return nil
	})

	if err != nil && !errors.Is(err, errBreakBucketForEach) {
		return nil, err
	}

	return result, nil
}