package meta

import (
	"encoding/binary"
	"errors"
	"fmt"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/util/logicerr"
	"go.etcd.io/bbolt"
)

// version contains current metabase version.
const version = 3

var (
	versionKey = []byte("version")
	upgradeKey = []byte("upgrade")
)

// ErrOutdatedVersion is returned on initializing
// an existing metabase that is not compatible with
// the current code version.
var ErrOutdatedVersion = logicerr.New("invalid version, resynchronization is required")

var ErrIncompletedUpgrade = logicerr.New("metabase upgrade is not completed")

var errVersionUndefinedNoInfoBucket = errors.New("version undefined: no info bucket")

func checkVersion(tx *bbolt.Tx, initialized bool) error {
	var knownVersion bool

	b := tx.Bucket(shardInfoBucket)
	if b != nil {
		data := b.Get(versionKey)
		if len(data) == 8 {
			knownVersion = true

			stored := binary.LittleEndian.Uint64(data)
			if stored != version {
				return fmt.Errorf("%w: expected=%d, stored=%d", ErrOutdatedVersion, version, stored)
			}
		}
		data = b.Get(upgradeKey)
		if len(data) > 0 {
			return ErrIncompletedUpgrade
		}
	}

	if !initialized {
		// new database, write version
		return updateVersion(tx, version)
	} else if !knownVersion {
		// db is initialized but no version
		// has been found; that could happen
		// if the db is corrupted or the version
		// is <2 (is outdated and requires resync
		// anyway)
		return ErrOutdatedVersion
	}

	return nil
}

func updateVersion(tx *bbolt.Tx, version uint64) error {
	data := make([]byte, 8)
	binary.LittleEndian.PutUint64(data, version)

	b, err := tx.CreateBucketIfNotExists(shardInfoBucket)
	if err != nil {
		return fmt.Errorf("create auxiliary bucket: %w", err)
	}
	return b.Put(versionKey, data)
}

func currentVersion(tx *bbolt.Tx) (uint64, error) {
	b := tx.Bucket(shardInfoBucket)
	if b == nil {
		return 0, errVersionUndefinedNoInfoBucket
	}
	data := b.Get(versionKey)
	if len(data) != 8 {
		return 0, fmt.Errorf("version undefined: invalid version data length %d", len(data))
	}
	return binary.LittleEndian.Uint64(data), nil
}