package secp256k1

import (
  "encoding/hex"
  "math/big"
  "testing"
)

func mustDecodeHex(t *testing.T, s string) []byte {
  t.Helper()
  b, err := hex.DecodeString(s)
  if err != nil {
    t.Fatalf("decode hex: %v", err)
  }
  return b
}

// TestBasePointOnCurve confirms the generator satisfies y^2 = x^3 + 7.
func TestBasePointOnCurve(t *testing.T) {
  if !IsOnCurve(&Point{X: Gx, Y: Gy}) {
    t.Fatalf("generator is not on the curve")
  }
}

// TestPointDoublingMatchesScalarMult verifies group consistency: 2*G computed
// via point doubling equals k*G for k=2.
func TestPointDoublingMatchesScalarMult(t *testing.T) {
  g := &Point{X: Gx, Y: Gy}
  viaDouble := Add(g, g)
  viaScalar := ScalarBaseMult(big.NewInt(2))
  if viaDouble.X.Cmp(viaScalar.X) != 0 || viaDouble.Y.Cmp(viaScalar.Y) != 0 {
    t.Fatalf("2G mismatch: double=%v scalar=%v", viaDouble, viaScalar)
  }
  if !IsOnCurve(viaScalar) {
    t.Fatalf("2G not on curve")
  }
}

// TestScalarMultDistributes checks (a+b)G == aG + bG.
func TestScalarMultDistributes(t *testing.T) {
  a := big.NewInt(12345)
  b := big.NewInt(67890)
  sum := new(big.Int).Add(a, b)
  left := ScalarBaseMult(sum)
  right := Add(ScalarBaseMult(a), ScalarBaseMult(b))
  if left.X.Cmp(right.X) != 0 || left.Y.Cmp(right.Y) != 0 {
    t.Fatalf("(a+b)G != aG + bG")
  }
}

// TestPublicKeyKnownValues locks the uncompressed public key for the t3 key.
func TestPublicKeyKnownValues(t *testing.T) {
  priv := mustDecodeHex(t, "a96135266ba58bb5b3a450b8fe7a9d59ea3e6cb0cdb2300e8138d2d2d48e61a8")
  point, err := PublicKey(priv)
  if err != nil {
    t.Fatalf("PublicKey: %v", err)
  }
  raw := make([]byte, 64)
  point.X.FillBytes(raw[0:32])
  point.Y.FillBytes(raw[32:64])
  want := "076e3db946fcb53d575c4e742a9f8ff8c4b57ded53776b2a80d13022e1647adaa1641f3e2210f5f6a3bdd73d073ac029ba79d576093d8a92dd148e448a8e63cb"
  if got := hex.EncodeToString(raw); got != want {
    t.Fatalf("pubkey = %s, want %s", got, want)
  }
  if !IsOnCurve(point) {
    t.Fatalf("derived public key not on curve")
  }
}

// TestSignRecoverRoundTrip signs and recovers for several keys and hashes.
func TestSignRecoverRoundTrip(t *testing.T) {
  privs := []string{
    "a96135266ba58bb5b3a450b8fe7a9d59ea3e6cb0cdb2300e8138d2d2d48e61a8",
    "3252a4cb9b3865c94dbb7d6f50107ca704c1c2b9e3d1eb81753e221c7db8fa25",
    "993638df18a38ef2be9f8c915eb9063647d015edc8fb70e3bcb32469bee39c21",
  }
  hashes := []string{
    "e93945efde601eed484553338e58218f4e81c51261dfda72db2d874f75378fe8",
    "0000000000000000000000000000000000000000000000000000000000000001",
    "ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
  }
  for _, p := range privs {
    priv := mustDecodeHex(t, p)
    wantPoint, _ := PublicKey(priv)
    for _, h := range hashes {
      hash := mustDecodeHex(t, h)
      sig, err := Sign(priv, hash)
      if err != nil {
        t.Fatalf("Sign: %v", err)
      }
      // low-s enforcement
      if sig.S.Cmp(halfN) > 0 {
        t.Fatalf("signature s is not low-s")
      }
      recovered, err := RecoverPublicKey(hash, sig)
      if err != nil {
        t.Fatalf("RecoverPublicKey: %v", err)
      }
      if recovered.X.Cmp(wantPoint.X) != 0 || recovered.Y.Cmp(wantPoint.Y) != 0 {
        t.Fatalf("recovered key differs for priv=%s hash=%s", p, h)
      }
    }
  }
}

// TestSignIsDeterministic confirms RFC6979-style reproducibility.
func TestSignIsDeterministic(t *testing.T) {
  priv := mustDecodeHex(t, "a96135266ba58bb5b3a450b8fe7a9d59ea3e6cb0cdb2300e8138d2d2d48e61a8")
  hash := mustDecodeHex(t, "e93945efde601eed484553338e58218f4e81c51261dfda72db2d874f75378fe8")
  a, err := Sign(priv, hash)
  if err != nil {
    t.Fatalf("Sign: %v", err)
  }
  b, err := Sign(priv, hash)
  if err != nil {
    t.Fatalf("Sign: %v", err)
  }
  if hex.EncodeToString(a.Bytes()) != hex.EncodeToString(b.Bytes()) {
    t.Fatalf("signatures differ for identical inputs")
  }
}

func TestPublicKeyRejectsInvalid(t *testing.T) {
  if _, err := PublicKey(make([]byte, 31)); err == nil {
    t.Fatalf("expected error for short key")
  }
  if _, err := PublicKey(make([]byte, 32)); err == nil {
    t.Fatalf("expected error for zero key")
  }
}