package mlkem768

import (
	"bytes"
	"crypto/sha256"
	"errors"
	"testing"
)

func TestGenerateKeyPair(t *testing.T) {
	adapter := New()

	pub, priv, err := adapter.GenerateKeyPair(nil)
	if err != nil {
		t.Fatalf("GenerateKeyPair failed: %v", err)
	}

	if pub.SchemeID() != suiteID {
		t.Errorf("pub.SchemeID() = 0x%04x, want 0x%04x", pub.SchemeID(), suiteID)
	}

	if priv.SchemeID() != suiteID {
		t.Errorf("priv.SchemeID() = 0x%04x, want 0x%04x", priv.SchemeID(), suiteID)
	}

	rawPub := pub.Raw()
	if len(rawPub) != 1184 {
		t.Errorf("pub.Raw() len = %d, want 1184", len(rawPub))
	}

	rawPriv := priv.Raw()
	if len(rawPriv) != 64 {
		t.Errorf("priv.Raw() len = %d, want 64", len(rawPriv))
	}

	expectedKeyID := sha256.Sum256(rawPub[:8])
	if !bytes.Equal(pub.KeyID(), expectedKeyID[:8]) {
		t.Errorf("pub.KeyID() = %x, want %x", pub.KeyID(), expectedKeyID[:8])
	}

	if !bytes.Equal(priv.KeyID(), pub.KeyID()) {
		t.Errorf("priv.KeyID() = %x, want %x", priv.KeyID(), pub.KeyID())
	}
}

func TestEncapsulateReturnOrder(t *testing.T) {
	adapter := New()

	pub, _, err := adapter.GenerateKeyPair(nil)
	if err != nil {
		t.Fatalf("GenerateKeyPair failed: %v", err)
	}

	ct, ss, err := adapter.Encapsulate(pub, nil)
	if err != nil {
		t.Fatalf("Encapsulate failed: %v", err)
	}

	if len(ct) != 1088 {
		t.Errorf("ciphertext len = %d, want 1088", len(ct))
	}

	if len(ss) != 32 {
		t.Errorf("sharedSecret len = %d, want 32", len(ss))
	}
}

func TestRoundTrip(t *testing.T) {
	adapter := New()

	pub, priv, err := adapter.GenerateKeyPair(nil)
	if err != nil {
		t.Fatalf("GenerateKeyPair failed: %v", err)
	}

	ct, ssEnc, err := adapter.Encapsulate(pub, nil)
	if err != nil {
		t.Fatalf("Encapsulate failed: %v", err)
	}

	ssDec, err := adapter.Decapsulate(priv, ct)
	if err != nil {
		t.Fatalf("Decapsulate failed: %v", err)
	}

	if !bytes.Equal(ssEnc, ssDec) {
		t.Fatalf("shared secret mismatch: encapsulate=%x, decapsulate=%x", ssEnc, ssDec)
	}
}

func TestDecapsulateTamperedCiphertext(t *testing.T) {
	adapter := New()

	pub, priv, err := adapter.GenerateKeyPair(nil)
	if err != nil {
		t.Fatalf("GenerateKeyPair failed: %v", err)
	}

	ct, _, err := adapter.Encapsulate(pub, nil)
	if err != nil {
		t.Fatalf("Encapsulate failed: %v", err)
	}

	ct[0] ^= 0xFF

	_, err = adapter.Decapsulate(priv, ct)
	if err == nil {
		t.Fatal("Decapsulate with tampered ciphertext: expected error, got nil")
	}

	if !errors.Is(err, ErrDecapsulationFailed) {
		t.Errorf("Decapsulate error = %v, want ErrDecapsulationFailed", err)
	}
}

func TestRegistryRegistration(t *testing.T) {
	factory, err := DefaultRegistry.Lookup(suiteID)
	if err != nil {
		t.Fatalf("Lookup suiteID 0x%04x failed: %v", suiteID, err)
	}

	instance := factory()
	if instance.SchemeID() != suiteID {
		t.Errorf("factory() SchemeID = 0x%04x, want 0x%04x", instance.SchemeID(), suiteID)
	}
}

func TestFactoryReturnsIndependentInstances(t *testing.T) {
	factory, err := DefaultRegistry.Lookup(suiteID)
	if err != nil {
		t.Fatalf("Lookup suiteID 0x%04x failed: %v", suiteID, err)
	}

	one := factory()
	two := factory()

	if one.SchemeID() != two.SchemeID() {
		t.Error("factory() returned instances with different scheme IDs")
	}
}