func (d *datastore) Delete(key ds.Key) (err error) {
	err = d.DB.Delete(key.Bytes(), nil)
	if err == leveldb.ErrNotFound {
		return ds.ErrNotFound
	}
	return err
}

// Returns ErrInvalidType if value is not of type []byte.
//
// Note: using sync = false.
// see http://godoc.org/github.com/syndtr/goleveldb/leveldb/opt#WriteOptions
func (d *datastore) Put(key ds.Key, value interface{}) (err error) {
	val, ok := value.([]byte)
	if !ok {
		return ds.ErrInvalidType
	}
	return d.DB.Put(key.Bytes(), val, nil)
}

// InvertKey returns a b58 decoded Datastore key
// TODO: this is hacky because it encodes every path component. some
// path components may be proper strings already...
func (b58KeyConverter) InvertKey(dsk ds.Key) ds.Key {
	k := ds.NewKey("/")
	for _, n := range dsk.Namespaces() {
		k = k.ChildString(string(b58.Decode(n)))
	}
	return k
}

func (d *datastore) Get(key ds.Key) (value interface{}, err error) {
	val, err := d.DB.Get(key.Bytes(), nil)
	if err != nil {
		if err == leveldb.ErrNotFound {
			return nil, ds.ErrNotFound
		}
		return nil, err
	}
	return val, nil
}

// PrefixTransform constructs a KeyTransform with a pair of functions that
// add or remove the given prefix key.
//
// Warning: will panic if prefix not found when it should be there. This is
// to avoid insidious data inconsistency errors.
func PrefixTransform(prefix ds.Key) ktds.KeyTransform {
	return &ktds.Pair{

		// Convert adds the prefix
		Convert: func(k ds.Key) ds.Key {
			return prefix.Child(k)
		},

		// Invert removes the prefix. panics if prefix not found.
		Invert: func(k ds.Key) ds.Key {
			if !prefix.IsAncestorOf(k) {
				fmt.Errorf("Expected prefix (%s) in key (%s)", prefix, k)
				panic("expected prefix not found")
			}

			s := strings.TrimPrefix(k.String(), prefix.String())
			return ds.NewKey(s)
		},
	}
}

// KeyFilename returns the filename associated with `key`
func (d *Datastore) KeyFilename(key ds.Key) string {
	return filepath.Join(d.path, key.String(), ".dsobject")
}

// KeyFromDsKey returns a Datastore key
func KeyFromDsKey(dsk ds.Key) Key {
	return Key(dsk.BaseNamespace())
}

func (d *Datastore) Has(key ds.Key) (exists bool, err error) {
	id := d.KeyHash(key)
	return core.Exists(false, d.Index(key), key.Type(), id)
}

// Returns the ElasticSearch index for given key. If the datastore specifies
// an index, use that. Else, key.Parent
func (d *Datastore) Index(key ds.Key) string {
	if len(d.index) > 0 {
		return d.index
	}
	return key.Parent().BaseNamespace()
}

// Hash a key and return the first 16 hex chars of its blake2b hash.
// basically: Blake2b(key).HexString[:16]
func BlakeKeyHash(key ds.Key) string {
	h := blake2.NewBlake2B()
	h.Write(key.Bytes())
	d := h.Sum(nil)
	return fmt.Sprintf("%x", d)[:16]
}