// Copyright 2025 the libevm authors.
//
// The libevm additions to go-ethereum are free software: you can redistribute
// them and/or modify them under the terms of the GNU Lesser General Public License
// as published by the Free Software Foundation, either version 3 of the License,
// or (at your option) any later version.
//
// The libevm additions are distributed in the hope that they will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
// General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see
// <http://www.gnu.org/licenses/>.

package ethtest

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"math/big"
	"testing"

	"github.com/stretchr/testify/require"

	"github.com/ava-labs/libevm/crypto"
)

// UNSAFEDeterministicPrivateKey returns a new [crypto.S256] private key,
// deterministically generated from the `seed`.
func UNSAFEDeterministicPrivateKey(tb testing.TB, seed []byte) *ecdsa.PrivateKey {
	tb.Helper()

	curve := crypto.S256()
	d := privateKeyScalar(tb, seed, curve)

	x, y := curve.ScalarBaseMult(d.Bytes())
	return &ecdsa.PrivateKey{
		D: d,
		PublicKey: ecdsa.PublicKey{
			X:     x,
			Y:     y,
			Curve: curve,
		},
	}
}

func privateKeyScalar(tb testing.TB, seed []byte, curve elliptic.Curve) *big.Int {
	tb.Helper()

	s := crypto.NewKeccakState()
	_, err := s.Write(seed)
	require.NoError(tb, err, "%T.Write()", s)

	buf := make([]byte, 32)
	for {
		_, err := s.Read(buf)
		require.NoError(tb, err, "%T.Read()", s)
		d := new(big.Int).SetBytes(buf)

		if isZero := d.Sign() == 0; !isZero && d.Cmp(curve.Params().N) == -1 {
			return d
		}
	}
}