func BenchmarkEncryptDecryptReader(b *testing.B) {
	k := crypto.NewRandomKey()

	size := 8 << 20 // 8MiB
	rd := RandomReader(23, size)

	b.ResetTimer()
	b.SetBytes(int64(size))

	buf := bytes.NewBuffer(nil)
	for i := 0; i < b.N; i++ {
		rd.Seek(0, 0)
		buf.Reset()
		wr := crypto.EncryptTo(k, buf)
		_, err := io.Copy(wr, rd)
		OK(b, err)
		OK(b, wr.Close())

		r, err := crypto.DecryptFrom(k, buf)
		OK(b, err)

		_, err = io.Copy(ioutil.Discard, r)
		OK(b, err)
	}
}

func TestDecryptStreamReader(t *testing.T) {
	k := crypto.NewRandomKey()

	tests := []int{5, 23, 2<<18 + 23, 1 << 20}
	if testLargeCrypto {
		tests = append(tests, 7<<20+123)
	}

	for _, size := range tests {
		data := make([]byte, size)
		_, err := io.ReadFull(RandomReader(42, size), data)
		OK(t, err)

		ciphertext := make([]byte, size+crypto.Extension)

		// encrypt with default function
		ciphertext, err = crypto.Encrypt(k, ciphertext, data)
		OK(t, err)
		Assert(t, len(ciphertext) == len(data)+crypto.Extension,
			"wrong number of bytes returned after encryption: expected %d, got %d",
			len(data)+crypto.Extension, len(ciphertext))

		rd, err := crypto.DecryptFrom(k, bytes.NewReader(ciphertext))
		OK(t, err)

		plaintext, err := ioutil.ReadAll(rd)
		OK(t, err)

		Assert(t, bytes.Equal(data, plaintext),
			"wrong plaintext after decryption: expected %02x, got %02x",
			data, plaintext)
	}
}

// NewUnpacker returns a pointer to Unpacker which can be used to read
// individual Blobs from a pack.
func NewUnpacker(k *crypto.Key, rd io.ReadSeeker) (*Unpacker, error) {
	var err error
	ls := binary.Size(uint32(0))

	// reset to the end to read header length
	_, err = rd.Seek(-int64(ls), 2)
	if err != nil {
		return nil, fmt.Errorf("seeking to read header length failed: %v", err)
	}

	var length uint32
	err = binary.Read(rd, binary.LittleEndian, &length)
	if err != nil {
		return nil, fmt.Errorf("reading header length failed: %v", err)
	}

	// reset to the beginning of the header
	_, err = rd.Seek(-int64(ls)-int64(length), 2)
	if err != nil {
		return nil, fmt.Errorf("seeking to read header length failed: %v", err)
	}

	// read header
	hrd, err := crypto.DecryptFrom(k, io.LimitReader(rd, int64(length)))
	if err != nil {
		return nil, err
	}

	var entries []Blob

	pos := uint(0)
	for {
		e := headerEntry{}
		err = binary.Read(hrd, binary.LittleEndian, &e)
		if err == io.EOF {
			break
		}

		if err != nil {
			return nil, err
		}

		entries = append(entries, Blob{
			Type:   e.Type,
			Length: uint(e.Length),
			ID:     e.ID,
			Offset: pos,
		})

		pos += uint(e.Length)
	}

	p := &Unpacker{
		rd:      rd,
		k:       k,
		Entries: entries,
	}

	return p, nil
}

// LoadJSONPack calls LoadBlob() to load a blob from the backend, decrypt the
// data and afterwards call json.Unmarshal on the item.
func (r *Repository) LoadJSONPack(t pack.BlobType, id backend.ID, item interface{}) error {
	// lookup pack
	blob, err := r.idx.Lookup(id)
	if err != nil {
		return err
	}

	// load blob from pack
	rd, err := r.be.GetReader(backend.Data, blob.PackID.String(), blob.Offset, blob.Length)
	if err != nil {
		return err
	}
	defer rd.Close()

	// decrypt
	decryptRd, err := crypto.DecryptFrom(r.key, rd)
	defer decryptRd.Close()
	if err != nil {
		return err
	}

	// decode
	decoder := json.NewDecoder(decryptRd)
	err = decoder.Decode(item)
	if err != nil {
		return err
	}

	return nil
}

// loadIndex loads the index id and merges it with the currently used index.
func (s *Repository) loadIndex(id string) error {
	debug.Log("Repo.loadIndex", "Loading index %v", id[:8])
	before := len(s.idx.pack)

	rd, err := s.be.Get(backend.Index, id)
	defer rd.Close()
	if err != nil {
		return err
	}

	// decrypt
	decryptRd, err := crypto.DecryptFrom(s.key, rd)
	defer decryptRd.Close()
	if err != nil {
		return err
	}

	idx, err := DecodeIndex(decryptRd)
	if err != nil {
		debug.Log("Repo.loadIndex", "error while decoding index %v: %v", id, err)
		return err
	}

	s.idx.Merge(idx)

	after := len(s.idx.pack)
	debug.Log("Repo.loadIndex", "Loaded index %v, added %v blobs", id[:8], after-before)

	return nil
}

func newDecryptReadCloser(key *crypto.Key, rd io.ReadCloser) (io.ReadCloser, error) {
	dr, err := crypto.DecryptFrom(key, rd)
	if err != nil {
		return nil, err
	}

	return &decryptReadCloser{r: rd, dr: dr}, nil
}

func BenchmarkDecryptReader(b *testing.B) {
	size := 8 << 20 // 8MiB
	buf := Random(23, size)
	k := crypto.NewRandomKey()

	ciphertext := make([]byte, len(buf)+crypto.Extension)
	_, err := crypto.Encrypt(k, ciphertext, buf)
	OK(b, err)

	rd := bytes.NewReader(ciphertext)

	b.ResetTimer()
	b.SetBytes(int64(size))

	for i := 0; i < b.N; i++ {
		rd.Seek(0, 0)
		decRd, err := crypto.DecryptFrom(k, rd)
		OK(b, err)

		_, err = io.Copy(ioutil.Discard, decRd)
		OK(b, err)
	}
}

// LoadJSONUnpacked decrypts the data and afterwards calls json.Unmarshal on
// the item.
func (r *Repository) LoadJSONUnpacked(t backend.Type, id backend.ID, item interface{}) error {
	// load blob from backend
	rd, err := r.be.Get(t, id.String())
	if err != nil {
		return err
	}
	defer rd.Close()

	// decrypt
	decryptRd, err := crypto.DecryptFrom(r.key, rd)
	defer decryptRd.Close()
	if err != nil {
		return err
	}

	// decode
	decoder := json.NewDecoder(decryptRd)
	err = decoder.Decode(item)
	if err != nil {
		return err
	}

	return nil
}

// LoadIndex loads the index id from backend and returns it.
func LoadIndex(repo *Repository, id string) (*Index, error) {
	debug.Log("LoadIndex", "Loading index %v", id[:8])

	rd, err := repo.be.Get(backend.Index, id)
	defer rd.Close()
	if err != nil {
		return nil, err
	}

	// decrypt
	decryptRd, err := crypto.DecryptFrom(repo.key, rd)
	defer decryptRd.Close()
	if err != nil {
		return nil, err
	}

	idx, err := DecodeIndex(decryptRd)
	if err != nil {
		debug.Log("LoadIndex", "error while decoding index %v: %v", id, err)
		return nil, err
	}

	return idx, nil
}