package webauthn

import (
	"crypto/ed25519"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"errors"
	"testing"
)

func TestVerify_HappyPath(t *testing.T) {
	pub, priv, cred, store := setupCredential(t, "alice")
	_ = pub
	challenge := []byte("challenge-bytes-just-for-the-test")
	a := makeAssertion(t, priv, cred.ID, "trust.basicstack.de", "https://trust.basicstack.de", challenge)

	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
	got, err := Verify(cfg, store, a, challenge)
	if err != nil {
		t.Fatalf("Verify: %v", err)
	}
	if got.ID != cred.ID {
		t.Errorf("credential id mismatch")
	}
}

func TestVerify_WrongChallenge(t *testing.T) {
	_, priv, cred, store := setupCredential(t, "alice")
	challenge := []byte("original-challenge-bytes-xxxxxxxx")
	a := makeAssertion(t, priv, cred.ID, "trust.basicstack.de", "https://trust.basicstack.de", challenge)

	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
	_, err := Verify(cfg, store, a, []byte("different-challenge-bytes-yyyyyy"))
	if !errors.Is(err, ErrChallengeMismatch) {
		t.Fatalf("want ErrChallengeMismatch, got %v", err)
	}
}

func TestVerify_UnknownCredential(t *testing.T) {
	store := NewStore()
	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
	_, err := Verify(cfg, store, Assertion{CredentialID: "nope"}, []byte("c"))
	if !errors.Is(err, ErrCredentialUnknown) {
		t.Fatalf("want ErrCredentialUnknown, got %v", err)
	}
}

func TestVerify_WrongOrigin(t *testing.T) {
	_, priv, cred, store := setupCredential(t, "alice")
	challenge := []byte("challenge-xxx-xxx-xxx-xxx")
	a := makeAssertion(t, priv, cred.ID, "trust.basicstack.de", "https://evil.example", challenge)
	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
	_, err := Verify(cfg, store, a, challenge)
	if err == nil || !errors.Is(err, ErrAssertionInvalid) {
		t.Fatalf("want ErrAssertionInvalid, got %v", err)
	}
}

func TestVerify_WrongType(t *testing.T) {
	_, priv, cred, store := setupCredential(t, "alice")
	challenge := []byte("challenge-xxx-xxx-xxx-xxx")
	a := makeAssertionWithType(t, priv, cred.ID, "trust.basicstack.de", "https://trust.basicstack.de", challenge, "webauthn.create")
	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
	_, err := Verify(cfg, store, a, challenge)
	if !errors.Is(err, ErrAssertionInvalid) {
		t.Fatalf("want ErrAssertionInvalid, got %v", err)
	}
}

func TestVerify_BadSignature(t *testing.T) {
	_, priv, cred, store := setupCredential(t, "alice")
	challenge := []byte("challenge-xxx-xxx-xxx-xxx")
	a := makeAssertion(t, priv, cred.ID, "trust.basicstack.de", "https://trust.basicstack.de", challenge)
	// Tamper with the signature.
	sig, _ := base64.RawURLEncoding.DecodeString(a.Signature)
	sig[0] ^= 0xff
	a.Signature = base64.RawURLEncoding.EncodeToString(sig)

	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
	_, err := Verify(cfg, store, a, challenge)
	if !errors.Is(err, ErrAssertionInvalid) {
		t.Fatalf("want ErrAssertionInvalid, got %v", err)
	}
}

// --- helpers --------------------------------------------------------------

func setupCredential(t *testing.T, userSub string) (ed25519.PublicKey, ed25519.PrivateKey, Credential, *Store) {
	t.Helper()
	pub, priv, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		t.Fatalf("gen key: %v", err)
	}
	idBytes := make([]byte, 16)
	_, _ = rand.Read(idBytes)
	cred := Credential{
		ID:        base64.RawURLEncoding.EncodeToString(idBytes),
		UserSub:   userSub,
		PublicKey: pub,
	}
	store := NewStore()
	if err := store.AddCredential(cred); err != nil {
		t.Fatalf("AddCredential: %v", err)
	}
	return pub, priv, cred, store
}

// makeAssertion signs a mock WebAuthn assertion with the given private
// key over the standard authenticator_data || sha256(clientDataJSON).
func makeAssertion(t *testing.T, priv ed25519.PrivateKey, credID, rpID, origin string, challenge []byte) Assertion {
	return makeAssertionWithType(t, priv, credID, rpID, origin, challenge, "webauthn.get")
}

func makeAssertionWithType(t *testing.T, priv ed25519.PrivateKey, credID, rpID, origin string, challenge []byte, typ string) Assertion {
	t.Helper()
	cd := map[string]string{
		"type":      typ,
		"challenge": base64.RawURLEncoding.EncodeToString(challenge),
		"origin":    origin,
	}
	cdBytes, _ := json.Marshal(cd)
	authData := MakeAuthenticatorData(rpID)
	cdHash := sha256.Sum256(cdBytes)
	signed := append(append([]byte(nil), authData...), cdHash[:]...)
	sig := ed25519.Sign(priv, signed)
	return Assertion{
		CredentialID:      credID,
		ClientDataJSON:    base64.RawURLEncoding.EncodeToString(cdBytes),
		AuthenticatorData: base64.RawURLEncoding.EncodeToString(authData),
		Signature:         base64.RawURLEncoding.EncodeToString(sig),
	}
}