package identity_test

import (
	"crypto/ed25519"
	"encoding/json"
	"testing"

	"git.n1ko.dev/Niko/niko_trust/internal/address"
	"git.n1ko.dev/Niko/niko_trust/internal/identity"
	"git.n1ko.dev/Niko/niko_trust/internal/identity/signer"
)

func mustSigner(t *testing.T) *signer.Signer {
	t.Helper()
	s, err := signer.Generate()
	if err != nil {
		t.Fatal(err)
	}
	return s
}

func TestGenerateProducesUsableIdentity(t *testing.T) {
	s := mustSigner(t)
	id := s.Identity()

	if id.IsZero() {
		t.Fatal("generated identity is zero")
	}
	if _, err := identity.Parse(id.String()); err != nil {
		t.Fatalf("generated address does not parse: %v", err)
	}
	if err := address.ValidatePubKey(id.PubKey()); err != nil {
		t.Fatalf("generated key fails validation: %v", err)
	}
	if !id.Address().Equal(s.Address()) {
		t.Fatal("signer address and identity address disagree")
	}
}

func TestGenerateIsUnique(t *testing.T) {
	seen := make(map[string]bool)
	for i := 0; i < 200; i++ {
		s := mustSigner(t)
		addr := s.Identity().String()
		if seen[addr] {
			t.Fatalf("duplicate identity generated: %s", addr)
		}
		seen[addr] = true
	}
}

func TestSignAndVerify(t *testing.T) {
	s := mustSigner(t)
	id := s.Identity()
	msg := []byte("canonical protocol bytes")

	sig := s.Sign(msg)
	if len(sig) != identity.SignatureSize {
		t.Fatalf("signature size = %d", len(sig))
	}
	if !id.Verify(msg, sig) {
		t.Fatal("valid signature did not verify")
	}
	if err := id.VerifyErr(msg, sig); err != nil {
		t.Fatalf("VerifyErr on a valid signature: %v", err)
	}
}

// TestVerifyRejectsTampering covers the modification cases in the threat
// model: a changed message, a changed signature, and a signature made by a
// different identity.
func TestVerifyRejectsTampering(t *testing.T) {
	s := mustSigner(t)
	other := mustSigner(t)
	id := s.Identity()
	msg := []byte("trust1abc says trust1bca minecraft.op = true")
	sig := s.Sign(msg)

	t.Run("modified message", func(t *testing.T) {
		for i := range msg {
			bad := make([]byte, len(msg))
			copy(bad, msg)
			bad[i] ^= 0x01
			if id.Verify(bad, sig) {
				t.Fatalf("verified a message modified at byte %d", i)
			}
		}
	})

	t.Run("modified signature", func(t *testing.T) {
		for i := range sig {
			bad := make([]byte, len(sig))
			copy(bad, sig)
			bad[i] ^= 0x01
			if id.Verify(msg, bad) {
				t.Fatalf("verified a signature modified at byte %d", i)
			}
		}
	})

	t.Run("wrong signer", func(t *testing.T) {
		if other.Identity().Verify(msg, sig) {
			t.Fatal("a signature verified under the wrong identity")
		}
		if id.Verify(msg, other.Sign(msg)) {
			t.Fatal("another identity's signature verified under this one")
		}
	})

	t.Run("truncated and extended", func(t *testing.T) {
		if id.Verify(msg, sig[:len(sig)-1]) {
			t.Fatal("verified a truncated signature")
		}
		if id.Verify(msg, append(append([]byte{}, sig...), 0)) {
			t.Fatal("verified an over-long signature")
		}
		if id.Verify(msg, nil) {
			t.Fatal("verified a nil signature")
		}
		if id.Verify(msg, []byte{}) {
			t.Fatal("verified an empty signature")
		}
	})

	t.Run("empty message is still bound", func(t *testing.T) {
		empty := s.Sign(nil)
		if !id.Verify(nil, empty) {
			t.Fatal("signature over an empty message did not verify")
		}
		if id.Verify([]byte("x"), empty) {
			t.Fatal("empty-message signature verified over other content")
		}
	})
}

// TestZeroIdentityVerifiesNothing ensures an uninitialised Identity cannot be
// used to accept data. Fail-closed behaviour matters because a zero value is
// what a struct field holds when a caller forgets to populate it.
func TestZeroIdentityVerifiesNothing(t *testing.T) {
	var zero identity.Identity
	s := mustSigner(t)
	msg := []byte("m")

	if !zero.IsZero() {
		t.Fatal("zero value must report IsZero")
	}
	if zero.Verify(msg, s.Sign(msg)) {
		t.Fatal("the zero identity verified a signature")
	}
	if zero.Verify(nil, nil) {
		t.Fatal("the zero identity verified empty input")
	}
	if err := zero.VerifyErr(msg, s.Sign(msg)); err == nil {
		t.Fatal("VerifyErr on the zero identity returned nil")
	}
	if zero.Equal(zero) {
		t.Fatal("the zero identity must not equal itself")
	}
}

func TestEqualIgnoresAlias(t *testing.T) {
	s := mustSigner(t)
	a, err := identity.FromPubKey(s.Public())
	if err != nil {
		t.Fatal(err)
	}
	b, err := identity.Parse(s.Identity().String())
	if err != nil {
		t.Fatal(err)
	}
	if !a.Equal(b) {
		t.Fatal("the same key must produce equal identities")
	}
	if !a.Equal(s.Identity()) {
		t.Fatal("identity from signer differs from identity from key")
	}
	if a.Equal(mustSigner(t).Identity()) {
		t.Fatal("different keys must not be equal")
	}
}

func TestFromPubKeyRejectsBadKeys(t *testing.T) {
	if _, err := identity.FromPubKey(make([]byte, 32)); err == nil {
		t.Fatal("accepted the all-zero key")
	}
	if _, err := identity.FromPubKey(make([]byte, 31)); err == nil {
		t.Fatal("accepted a short key")
	}
	if _, err := identity.FromPubKey(nil); err == nil {
		t.Fatal("accepted a nil key")
	}
}

func TestJSONRoundTrip(t *testing.T) {
	s := mustSigner(t)
	id := s.Identity()

	type envelope struct {
		Issuer identity.Identity `json:"issuer"`
	}
	b, err := json.Marshal(envelope{Issuer: id})
	if err != nil {
		t.Fatal(err)
	}

	var back envelope
	if err := json.Unmarshal(b, &back); err != nil {
		t.Fatal(err)
	}
	if !back.Issuer.Equal(id) {
		t.Fatal("identity did not survive a JSON round trip")
	}

	// Decoding must validate, so a hostile document cannot inject a
	// degenerate key through the JSON path.
	var bad envelope
	if err := json.Unmarshal([]byte(`{"issuer":"trust1qqqqqqqqqqqqqqqq"}`), &bad); err == nil {
		t.Fatal("unmarshal accepted an invalid address")
	}
}

func TestPubKeyIsCopied(t *testing.T) {
	s := mustSigner(t)
	id := s.Identity()
	k := id.PubKey()
	for i := range k {
		k[i] = 0
	}
	if err := address.ValidatePubKey(id.PubKey()); err != nil {
		t.Fatalf("identity key was mutated through a returned copy: %v", err)
	}
}

func TestSignerFromSeedAndPrivateKey(t *testing.T) {
	orig := mustSigner(t)
	seed := orig.Seed()

	fromSeed, err := signer.FromSeed(seed)
	if err != nil {
		t.Fatal(err)
	}
	if !fromSeed.Identity().Equal(orig.Identity()) {
		t.Fatal("seed did not restore the same identity")
	}

	fromPriv, err := signer.FromPrivateKey(orig.PrivateKey())
	if err != nil {
		t.Fatal(err)
	}
	if !fromPriv.Identity().Equal(orig.Identity()) {
		t.Fatal("private key did not restore the same identity")
	}

	// Signatures from a restored key must verify under the original identity.
	msg := []byte("restored")
	if !orig.Identity().Verify(msg, fromSeed.Sign(msg)) {
		t.Fatal("signature from a seed-restored key did not verify")
	}

	for _, n := range []int{0, 31, 33, 64} {
		if _, err := signer.FromSeed(make([]byte, n)); err == nil {
			t.Errorf("FromSeed accepted a %d-byte seed", n)
		}
	}
	for _, n := range []int{0, 32, 63, 65} {
		if _, err := signer.FromPrivateKey(make([]byte, n)); err == nil {
			t.Errorf("FromPrivateKey accepted a %d-byte key", n)
		}
	}
}

// TestFromPrivateKeyRejectsInconsistentKey covers a tampered key file whose
// public half no longer matches its seed. Such a key would sign under one
// identity while claiming another.
func TestFromPrivateKeyRejectsInconsistentKey(t *testing.T) {
	a := mustSigner(t)
	b := mustSigner(t)

	frankenstein := make(ed25519.PrivateKey, ed25519.PrivateKeySize)
	copy(frankenstein[:32], a.PrivateKey()[:32]) // seed from a
	copy(frankenstein[32:], b.Public())          // public half from b

	if _, err := signer.FromPrivateKey(frankenstein); err == nil {
		t.Fatal("accepted a private key whose public half does not match its seed")
	}
}

func TestSeedAndPrivateKeyAreCopies(t *testing.T) {
	s := mustSigner(t)
	id := s.Identity()

	seed := s.Seed()
	for i := range seed {
		seed[i] = 0
	}
	priv := s.PrivateKey()
	for i := range priv {
		priv[i] = 0
	}

	msg := []byte("still works")
	if !id.Verify(msg, s.Sign(msg)) {
		t.Fatal("signer was corrupted by a caller mutating returned key material")
	}
}

func TestGenerateFromDeterministicSource(t *testing.T) {
	src := func() *zeroReader { return &zeroReader{} }
	a, err := signer.GenerateFrom(src())
	if err != nil {
		t.Fatal(err)
	}
	b, err := signer.GenerateFrom(src())
	if err != nil {
		t.Fatal(err)
	}
	if !a.Identity().Equal(b.Identity()) {
		t.Fatal("the same entropy must yield the same identity")
	}
	if a.Identity().Equal(mustSigner(t).Identity()) {
		t.Fatal("a random identity collided with the deterministic one")
	}
}

type zeroReader struct{}

func (z *zeroReader) Read(p []byte) (int, error) {
	for i := range p {
		p[i] = 0
	}
	return len(p), nil
}

func BenchmarkVerify(b *testing.B) {
	s, _ := signer.Generate()
	id := s.Identity()
	msg := []byte("canonical protocol bytes for benchmarking")
	sig := s.Sign(msg)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		if !id.Verify(msg, sig) {
			b.Fatal("verification failed")
		}
	}
}