package blobgen_test

import (
	"bytes"
	"io"
	"testing"

	"filippo.io/age"
	"github.com/stretchr/testify/require"
	"sneak.berlin/go/vaultik/internal/blobgen"
)

// TestReaderRejectsHeaderNonceTruncation guards against a stream cut right
// after the age header plus its 16-byte nonce. age.Decrypt still succeeds on
// such an object, and the zstd decoder maps the age reader's
// io.ErrUnexpectedEOF to a clean io.EOF at frame start, so without the extra
// check the truncated stream would read as a valid empty one. Reading it must
// now fail.
func TestReaderRejectsHeaderNonceTruncation(t *testing.T) {
	t.Parallel()

	identity, err := age.GenerateX25519Identity()
	require.NoError(t, err)

	// Encrypting empty plaintext yields header + nonce(16) + a single
	// 16-byte final chunk tag. Dropping the trailing tag leaves exactly the
	// age header plus its nonce — the truncation point that triggers the bug.
	var full bytes.Buffer

	w, err := age.Encrypt(&full, identity.Recipient())
	require.NoError(t, err)
	require.NoError(t, w.Close())

	truncated := full.Bytes()[:full.Len()-16]

	reader, err := blobgen.NewReader(bytes.NewReader(truncated), identity)
	require.NoError(t, err)

	defer func() { _ = reader.Close() }()

	_, err = io.ReadAll(reader)
	require.Error(t, err)
	require.ErrorIs(t, err, io.ErrUnexpectedEOF)
}

// TestReaderReadsGenuinelyEmptyBlob confirms the truncation check does not
// reject a legitimately empty payload: a blob written with no data must round
// trip back to zero bytes with no error.
func TestReaderReadsGenuinelyEmptyBlob(t *testing.T) {
	t.Parallel()

	identity, err := age.GenerateX25519Identity()
	require.NoError(t, err)

	var encrypted bytes.Buffer

	writer, err := blobgen.NewWriter(
		&encrypted, 3, []string{identity.Recipient().String()})
	require.NoError(t, err)
	require.NoError(t, writer.Close())

	reader, err := blobgen.NewReader(bytes.NewReader(encrypted.Bytes()), identity)
	require.NoError(t, err)

	defer func() { _ = reader.Close() }()

	data, err := io.ReadAll(reader)
	require.NoError(t, err)
	require.Empty(t, data)
}