package cbk_test

import (
	"strings"
	"testing"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"golang.org/x/crypto/nacl/box"

	"sneak.berlin/go/x/pkg/bip39wordlist"
	"sneak.berlin/go/x/pkg/cbk"
)

// vectorRepeats is how many times "abandon" appears in the standard BIP39
// test vector for all-zero 128-bit entropy, which ends with "about".
const vectorRepeats = bip39wordlist.MinWordCount - 1

// The keys below were pinned when the derivation was first implemented.
// If this test starts failing, the derivation has changed and every key
// anyone has derived with this package is no longer reproducible.
const (
	vectorPublicKeyHex = "db9c1ec248805579d0b0fe2d5a4814f96009f66a11c91260487b79167f881b20"

	vectorPrivateKeyHex = "eec3d5da4e348bd16df93b61c595bb5f75645f9aa468e72513be033a72b3d053"
)

// vectorMnemonic returns the standard BIP39 test vector for all-zero
// 128-bit entropy.
func vectorMnemonic() string {
	return strings.Repeat("abandon ", vectorRepeats) + "about"
}

func TestNewMatchesPinnedVector(t *testing.T) {
	t.Parallel()

	keypair, err := cbk.FromMnemonic(vectorMnemonic())
	require.NoError(t, err)

	assert.Equal(t, vectorPublicKeyHex, keypair.PublicKeyHex())
	assert.Equal(t, vectorPrivateKeyHex, keypair.PrivateKeyHex())
}

func TestNewNormalizesMnemonic(t *testing.T) {
	t.Parallel()

	canonical, err := cbk.FromMnemonic(vectorMnemonic())
	require.NoError(t, err)

	messy, err := cbk.New(cbk.Params{
		Mnemonic: "  ABANDON\tAbandon " + strings.Repeat("abandon  ", 9) +
			"\nabout\n",
		Passphrase: "",
	})
	require.NoError(t, err)

	assert.Equal(t, canonical, messy)
}

func TestNewPassphraseChangesKeys(t *testing.T) {
	t.Parallel()

	plain, err := cbk.FromMnemonic(vectorMnemonic())
	require.NoError(t, err)

	extraWord := "TREZOR"

	withExtraWord, err := cbk.New(cbk.Params{
		Mnemonic:   vectorMnemonic(),
		Passphrase: extraWord,
	})
	require.NoError(t, err)

	assert.NotEqual(t, plain.PublicKey, withExtraWord.PublicKey)
	assert.NotEqual(t, plain.PrivateKey, withExtraWord.PrivateKey)

	again, err := cbk.New(cbk.Params{
		Mnemonic:   vectorMnemonic(),
		Passphrase: extraWord,
	})
	require.NoError(t, err)

	assert.Equal(t, withExtraWord, again, "derivation is deterministic")
}

func TestNewRejectsInvalidMnemonic(t *testing.T) {
	t.Parallel()

	_, err := cbk.FromMnemonic("abandon bogus about")
	require.ErrorIs(t, err, bip39wordlist.ErrInvalidWordCount)

	_, err = cbk.FromMnemonic(strings.Repeat("abandon ", vectorRepeats) + "bogus")
	require.ErrorIs(t, err, bip39wordlist.ErrUnknownWord)
}

func TestKeyAccessors(t *testing.T) {
	t.Parallel()

	keypair, err := cbk.FromMnemonic(vectorMnemonic())
	require.NoError(t, err)

	assert.Equal(t, keypair.PublicKey[:], keypair.PublicKeyBytes())
	assert.Equal(t, keypair.PrivateKey[:], keypair.PrivateKeyBytes())
	assert.Len(t, keypair.PublicKeyBytes(), cbk.KeySize)
	assert.Len(t, keypair.PrivateKeyBytes(), cbk.KeySize)
	assert.Equal(t, keypair.PublicKey.Hex(), keypair.PublicKeyHex())
	assert.Equal(t, keypair.PrivateKey.Hex(), keypair.PrivateKeyHex())
}

func TestKeyFromHexRoundTrip(t *testing.T) {
	t.Parallel()

	keypair, err := cbk.FromMnemonic(vectorMnemonic())
	require.NoError(t, err)

	parsed, err := cbk.KeyFromHex(keypair.PublicKeyHex())
	require.NoError(t, err)
	assert.Equal(t, keypair.PublicKey, parsed)
}

func TestKeyFromHexRejectsBadInput(t *testing.T) {
	t.Parallel()

	_, err := cbk.KeyFromHex("abcd")
	require.ErrorIs(t, err, cbk.ErrInvalidKeyHex)

	notHex := "zz" + keypairForTest(t).PublicKeyHex()[2:]

	_, err = cbk.KeyFromHex(notHex)
	require.ErrorIs(t, err, cbk.ErrInvalidKeyHex)
}

func TestSealOpenRoundTrip(t *testing.T) {
	t.Parallel()

	alice := keypairForTest(t)
	bob := keypairForTest(t)
	message := []byte("the quick brown fox jumps over the lazy dog")

	sealed, err := alice.Seal(message, bob.PublicKey)
	require.NoError(t, err)
	assert.Len(t, sealed, cbk.NonceSize+len(message)+box.Overhead)

	opened, err := bob.Open(sealed, alice.PublicKey)
	require.NoError(t, err)
	assert.Equal(t, message, opened)
}

func TestSealUsesFreshNonces(t *testing.T) {
	t.Parallel()

	alice := keypairForTest(t)
	bob := keypairForTest(t)
	message := []byte("same message twice")

	first, err := alice.Seal(message, bob.PublicKey)
	require.NoError(t, err)

	second, err := alice.Seal(message, bob.PublicKey)
	require.NoError(t, err)

	assert.NotEqual(t, first, second)
}

func TestOpenRejectsTamperingAndWrongKeys(t *testing.T) {
	t.Parallel()

	alice := keypairForTest(t)
	bob := keypairForTest(t)
	eve := keypairForTest(t)
	message := []byte("for bob only")

	sealed, err := alice.Seal(message, bob.PublicKey)
	require.NoError(t, err)

	_, err = eve.Open(sealed, alice.PublicKey)
	require.ErrorIs(t, err, cbk.ErrOpenFailed, "wrong recipient")

	_, err = bob.Open(sealed, eve.PublicKey)
	require.ErrorIs(t, err, cbk.ErrOpenFailed, "wrong sender")

	tampered := append([]byte(nil), sealed...)
	tampered[len(tampered)-1] ^= 0x01

	_, err = bob.Open(tampered, alice.PublicKey)
	require.ErrorIs(t, err, cbk.ErrOpenFailed, "modified ciphertext")

	_, err = bob.Open(sealed[:cbk.NonceSize-1], alice.PublicKey)
	require.ErrorIs(t, err, cbk.ErrSealedTooShort)
}

// keypairForTest derives a keypair from a freshly generated mnemonic.
func keypairForTest(t *testing.T) cbk.CryptoBoxKeypair {
	t.Helper()

	mnemonic, err := bip39wordlist.GenerateMnemonic(bip39wordlist.MaxWordCount)
	require.NoError(t, err)

	keypair, err := cbk.FromMnemonic(mnemonic)
	require.NoError(t, err)

	return keypair
}