package tlsreload

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

func TestCertificateProviderReloadsPairsAndKeepsLastKnownGoodCertificate(t *testing.T) {
	directory := t.TempDir()
	certificatePath := filepath.Join(directory, "tls.crt")
	keyPath := filepath.Join(directory, "tls.key")
	writeCertificatePair(t, certificatePath, keyPath, "first")

	provider, err := NewCertificateProvider(certificatePath, keyPath)
	if err != nil {
		t.Fatalf("NewCertificateProvider() error = %v", err)
	}
	certificate, err := provider.ServerCertificate(nil)
	if subject := certificateSubject(t, certificate, err); subject != "first" {
		t.Fatalf("initial certificate subject = %q, want first", subject)
	}

	writeCertificatePair(t, certificatePath, keyPath, "second")
	certificate, err = provider.ClientCertificate(nil)
	if subject := certificateSubject(t, certificate, err); subject != "second" {
		t.Fatalf("reloaded certificate subject = %q, want second", subject)
	}

	if err := os.WriteFile(keyPath, []byte("incomplete"), 0o600); err != nil {
		t.Fatalf("break private key: %v", err)
	}
	certificate, err = provider.ServerCertificate(nil)
	if subject := certificateSubject(t, certificate, err); subject != "second" {
		t.Fatalf("fallback certificate subject = %q, want second", subject)
	}
}

func TestCertificateProviderRejectsMissingPaths(t *testing.T) {
	if _, err := NewCertificateProvider("", "key"); err != ErrInvalidCertificatePaths {
		t.Fatalf("NewCertificateProvider(empty certificate) error = %v, want %v", err, ErrInvalidCertificatePaths)
	}
	if _, err := NewCertificateProvider("certificate", ""); err != ErrInvalidCertificatePaths {
		t.Fatalf("NewCertificateProvider(empty key) error = %v, want %v", err, ErrInvalidCertificatePaths)
	}
}

func certificateSubject(t *testing.T, certificate *tls.Certificate, err error) string {
	t.Helper()
	if err != nil {
		t.Fatalf("load certificate: %v", err)
	}
	parsed, err := x509.ParseCertificate(certificate.Certificate[0])
	if err != nil {
		t.Fatalf("parse certificate: %v", err)
	}
	return parsed.Subject.CommonName
}

func writeCertificatePair(t *testing.T, certificatePath, keyPath, commonName string) {
	t.Helper()
	privateKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatalf("generate private key: %v", err)
	}
	now := time.Now()
	template := x509.Certificate{
		SerialNumber: big.NewInt(now.UnixNano()), Subject: pkix.Name{CommonName: commonName},
		NotBefore: now.Add(-time.Minute), NotAfter: now.Add(time.Hour),
		KeyUsage: x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,
	}
	der, err := x509.CreateCertificate(rand.Reader, &template, &template, &privateKey.PublicKey, privateKey)
	if err != nil {
		t.Fatalf("create certificate: %v", err)
	}
	certificate := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der})
	privateDER, err := x509.MarshalPKCS8PrivateKey(privateKey)
	if err != nil {
		t.Fatalf("marshal private key: %v", err)
	}
	key := pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: privateDER})
	if err := os.WriteFile(certificatePath, certificate, 0o600); err != nil {
		t.Fatalf("write certificate: %v", err)
	}
	if err := os.WriteFile(keyPath, key, 0o600); err != nil {
		t.Fatalf("write private key: %v", err)
	}
}