package busauth

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"math/big"
	"os"
	"path/filepath"
	"testing"
	"time"
)

// writeSelfSigned writes a self-signed cert + key PEM pair to dir and returns
// their paths. It is enough to exercise both LoadCATLSConfig (reads the cert as
// a CA) and ServerTLSConfig (reads the cert+key as a server keypair).
func writeSelfSigned(t *testing.T, dir string) (certPath, keyPath string) {
	t.Helper()
	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatalf("key: %v", err)
	}
	tmpl := &x509.Certificate{
		SerialNumber:          big.NewInt(1),
		Subject:               pkix.Name{CommonName: "unibus-tls-test"},
		NotBefore:             time.Now().Add(-time.Hour),
		NotAfter:              time.Now().Add(time.Hour),
		IsCA:                  true,
		KeyUsage:              x509.KeyUsageCertSign | x509.KeyUsageDigitalSignature,
		BasicConstraintsValid: true,
	}
	der, err := x509.CreateCertificate(rand.Reader, tmpl, tmpl, &key.PublicKey, key)
	if err != nil {
		t.Fatalf("cert: %v", err)
	}
	certPath = filepath.Join(dir, "cert.pem")
	keyPath = filepath.Join(dir, "key.pem")
	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der})
	if err := os.WriteFile(certPath, certPEM, 0o644); err != nil {
		t.Fatalf("write cert: %v", err)
	}
	keyDER, err := x509.MarshalECPrivateKey(key)
	if err != nil {
		t.Fatalf("marshal key: %v", err)
	}
	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: keyDER})
	if err := os.WriteFile(keyPath, keyPEM, 0o600); err != nil {
		t.Fatalf("write key: %v", err)
	}
	return certPath, keyPath
}

// Golden: a valid CA PEM loads into a config with a non-empty RootCAs pool, and
// a valid keypair loads into a config presenting one certificate.
func TestLoadTLSConfigsGolden(t *testing.T) {
	dir := t.TempDir()
	certPath, keyPath := writeSelfSigned(t, dir)

	caCfg, err := LoadCATLSConfig(certPath)
	if err != nil {
		t.Fatalf("LoadCATLSConfig: %v", err)
	}
	if caCfg.RootCAs == nil {
		t.Fatalf("expected a populated RootCAs pool")
	}

	srvCfg, err := ServerTLSConfig(certPath, keyPath)
	if err != nil {
		t.Fatalf("ServerTLSConfig: %v", err)
	}
	if len(srvCfg.Certificates) != 1 {
		t.Fatalf("expected exactly one server certificate, got %d", len(srvCfg.Certificates))
	}
}

// Error path: missing file, and a file that is not valid PEM.
func TestLoadTLSConfigsErrors(t *testing.T) {
	if _, err := LoadCATLSConfig("/no/such/ca.crt"); err == nil {
		t.Fatalf("expected error for missing CA file")
	}
	dir := t.TempDir()
	junk := filepath.Join(dir, "junk.crt")
	if err := os.WriteFile(junk, []byte("not a pem"), 0o644); err != nil {
		t.Fatalf("write junk: %v", err)
	}
	if _, err := LoadCATLSConfig(junk); err == nil {
		t.Fatalf("expected error for non-PEM CA file")
	}
	if _, err := ServerTLSConfig("/no/such/server.crt", "/no/such/server.key"); err == nil {
		t.Fatalf("expected error for missing server keypair")
	}
}