package certs

import (
	"context"
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/hex"
	"encoding/json"
	"encoding/pem"
	"errors"
	"fmt"
	"math/big"
	"net"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"golang.org/x/crypto/acme"
	"debtik/internal/logging"
)

const (
	DefaultCertsDir     = "/etc/debtik/certs"
	DefaultMetadataFile = "certs.json"

	TypeCA     = "ca"
	TypeServer = "server"
	TypeClient = "client"
	TypeACME   = "acme"

	KeyRSA2048   = "RSA-2048"
	KeyRSA4096   = "RSA-4096"
	KeyECDSAP256 = "ECDSA-P256"
)

type CertificateInfo struct {
	ACMERequest      *LetsEncryptRequest `json:"acme_request,omitempty"`
	RenewalError     string              `json:"renewal_error,omitempty"`
	LastRenewAttempt time.Time           `json:"last_renew_attempt,omitempty"`
	ID               string              `json:"id"`
	Name             string              `json:"name"`
	CommonName       string              `json:"common_name"`
	SANs             []string            `json:"sans"`
	IsCA             bool                `json:"is_ca"`
	Issuer           string              `json:"issuer"`
	KeyType          string              `json:"key_type"`
	ValidFrom        time.Time           `json:"valid_from"`
	ValidTo          time.Time           `json:"valid_to"`
	Fingerprint      string              `json:"fingerprint"`
	CertPath         string              `json:"cert_path"`
	KeyPath          string              `json:"key_path"`
	Type             string              `json:"type"`
	Comment          string              `json:"comment,omitempty"`
}

type CreateCARequest struct {
	Name         string `json:"name"`
	CommonName   string `json:"common_name"`
	Organization string `json:"organization,omitempty"`
	Country      string `json:"country,omitempty"`
	Days         int    `json:"days,omitempty"`
	KeyType      string `json:"key_type,omitempty"`
	Comment      string `json:"comment,omitempty"`
}

type CreateCertRequest struct {
	Name         string   `json:"name"`
	CommonName   string   `json:"common_name"`
	CAName       string   `json:"ca_name,omitempty"`
	SANs         []string `json:"sans,omitempty"`
	Days         int      `json:"days,omitempty"`
	KeyType      string   `json:"key_type,omitempty"`
	IsServer     bool     `json:"is_server"`
	Organization string   `json:"organization,omitempty"`
	Country      string   `json:"country,omitempty"`
	Comment      string   `json:"comment,omitempty"`
}

type ImportCertRequest struct {
	Name    string `json:"name"`
	CertPEM string `json:"cert_pem"`
	KeyPEM  string `json:"key_pem"`
	Comment string `json:"comment,omitempty"`
}

type LetsEncryptRequest struct {
	renew   bool
	Name    string `json:"name"`
	Domain  string `json:"domain"`
	Email   string `json:"email"`
	Staging bool   `json:"staging"`
	Comment string `json:"comment,omitempty"`
}

type CertManager struct {
	dir         string
	metaPath    string
	mu          sync.RWMutex
	certs       map[string]*CertificateInfo
	challenges  map[string]string // token -> keyAuth
	challengeMu sync.RWMutex
	renewMu     sync.Mutex
	accountMu   sync.Mutex
}

func NewCertManager(customDir string) (*CertManager, error) {
	d := customDir
	if d == "" {
		d = DefaultCertsDir
	}
	if err := os.MkdirAll(d, 0700); err != nil {
		return nil, fmt.Errorf("failed to create certs directory %s: %w", d, err)
	}

	cm := &CertManager{
		dir:        d,
		metaPath:   filepath.Join(d, DefaultMetadataFile),
		certs:      make(map[string]*CertificateInfo),
		challenges: make(map[string]string),
	}

	if err := cm.load(); err != nil {
		logging.Log("certs,warning", "Warning loading cert metadata: %v", err)
	}

	return cm, nil
}

func (cm *CertManager) load() error {
	cm.mu.Lock()
	defer cm.mu.Unlock()

	data, err := os.ReadFile(cm.metaPath)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return err
	}

	var list []*CertificateInfo
	if err := json.Unmarshal(data, &list); err != nil {
		return err
	}

	for _, c := range list {
		if c.Name != "" {
			cm.certs[strings.ToLower(c.Name)] = c
		}
	}
	return nil
}

func (cm *CertManager) saveLocked() error {
	var list []*CertificateInfo
	for _, c := range cm.certs {
		list = append(list, c)
	}

	data, err := json.MarshalIndent(list, "", "  ")
	if err != nil {
		return err
	}

	tmp := fmt.Sprintf("%s.tmp.%d", cm.metaPath, time.Now().UnixNano())
	if err := os.WriteFile(tmp, data, 0600); err != nil {
		return err
	}
	return os.Rename(tmp, cm.metaPath)
}

// RegisterHTTP01Challenge stores an ACME challenge token and its response for HTTP-01 verification.
func (cm *CertManager) RegisterHTTP01Challenge(token, keyAuth string) {
	cm.challengeMu.Lock()
	defer cm.challengeMu.Unlock()
	cm.challenges[token] = keyAuth
}

// UnregisterHTTP01Challenge removes an ACME challenge token.
func (cm *CertManager) UnregisterHTTP01Challenge(token string) {
	cm.challengeMu.Lock()
	defer cm.challengeMu.Unlock()
	delete(cm.challenges, token)
}

// GetHTTP01Challenge looks up an ACME challenge token for HTTP-01 verification.
func (cm *CertManager) GetHTTP01Challenge(token string) (string, bool) {
	cm.challengeMu.RLock()
	defer cm.challengeMu.RUnlock()
	auth, ok := cm.challenges[token]
	return auth, ok
}

// ListCertificates returns all certificates known to the manager.
func (cm *CertManager) ListCertificates() []*CertificateInfo {
	cm.mu.RLock()
	defer cm.mu.RUnlock()

	var result []*CertificateInfo
	for _, c := range cm.certs {
		copyItem := *c
		result = append(result, &copyItem)
	}
	return result
}

// GetCertificate returns metadata for a certificate by name.
func (cm *CertManager) GetCertificate(name string) (*CertificateInfo, error) {
	cm.mu.RLock()
	defer cm.mu.RUnlock()

	c, ok := cm.certs[strings.ToLower(name)]
	if !ok {
		return nil, fmt.Errorf("certificate %q not found", name)
	}
	copyItem := *c
	return &copyItem, nil
}

// GetTLSCertificate loads a parsed tls.Certificate ready for TLS listeners.
func (cm *CertManager) GetTLSCertificate(name string) (tls.Certificate, error) {
	cm.mu.RLock()
	c, ok := cm.certs[strings.ToLower(name)]
	cm.mu.RUnlock()

	if !ok {
		return tls.Certificate{}, fmt.Errorf("certificate %q not found", name)
	}

	if _, err := os.Stat(c.CertPath); err != nil {
		return tls.Certificate{}, fmt.Errorf("certificate file missing: %w", err)
	}
	if _, err := os.Stat(c.KeyPath); err != nil {
		return tls.Certificate{}, fmt.Errorf("private key file missing: %w", err)
	}

	return tls.LoadX509KeyPair(c.CertPath, c.KeyPath)
}

// ExportPEM returns the PEM encoded certificate and private key content.
func (cm *CertManager) ExportPEM(name string) (certPEM string, keyPEM string, err error) {
	cm.mu.RLock()
	c, ok := cm.certs[strings.ToLower(name)]
	cm.mu.RUnlock()

	if !ok {
		return "", "", fmt.Errorf("certificate %q not found", name)
	}

	certBytes, err := os.ReadFile(c.CertPath)
	if err != nil {
		return "", "", fmt.Errorf("failed to read cert file: %w", err)
	}

	keyBytes, err := os.ReadFile(c.KeyPath)
	if err != nil {
		return "", "", fmt.Errorf("failed to read key file: %w", err)
	}

	return string(certBytes), string(keyBytes), nil
}

// DeleteCertificate removes a certificate, its files, and metadata.
func (cm *CertManager) DeleteCertificate(name string) error {
	cm.mu.Lock()
	defer cm.mu.Unlock()

	key := strings.ToLower(name)
	c, ok := cm.certs[key]
	if !ok {
		return fmt.Errorf("certificate %q not found", name)
	}

	_ = os.Remove(c.CertPath)
	_ = os.Remove(c.KeyPath)
	delete(cm.certs, key)

	if err := cm.saveLocked(); err != nil {
		return err
	}

	logging.Log("certs,info", "Certificate %s deleted", name)
	return nil
}

// CreateCA creates a new Self-Signed Certificate Authority (CA).
func (cm *CertManager) CreateCA(req CreateCARequest) (*CertificateInfo, error) {
	name := strings.TrimSpace(req.Name)
	if name == "" {
		return nil, errors.New("certificate name is required")
	}
	cn := strings.TrimSpace(req.CommonName)
	if cn == "" {
		cn = name
	}

	cm.mu.Lock()
	defer cm.mu.Unlock()

	if _, exists := cm.certs[strings.ToLower(name)]; exists {
		return nil, fmt.Errorf("certificate %q already exists", name)
	}

	days := req.Days
	if days <= 0 {
		days = 3650 // 10 years default for CA
	}

	keyType := req.KeyType
	if keyType == "" {
		keyType = KeyRSA2048
	}

	privKey, pubKey, err := generateKeyPair(keyType)
	if err != nil {
		return nil, fmt.Errorf("failed generating key: %w", err)
	}

	serialNumber, err := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
	if err != nil {
		return nil, fmt.Errorf("failed generating serial: %w", err)
	}

	org := req.Organization
	if org == "" {
		org = "DebTik Network Appliance"
	}
	country := req.Country
	if country == "" {
		country = "GR"
	}

	now := time.Now().UTC()
	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			CommonName:   cn,
			Organization: []string{org},
			Country:      []string{country},
		},
		NotBefore:             now.Add(-1 * time.Hour),
		NotAfter:              now.AddDate(0, 0, days),
		IsCA:                  true,
		KeyUsage:              x509.KeyUsageCertSign | x509.KeyUsageCRLSign | x509.KeyUsageDigitalSignature,
		BasicConstraintsValid: true,
		MaxPathLenZero:        false,
	}

	certBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, pubKey, privKey)
	if err != nil {
		return nil, fmt.Errorf("failed creating CA certificate: %w", err)
	}

	certPath := filepath.Join(cm.dir, fmt.Sprintf("%s.crt", name))
	keyPath := filepath.Join(cm.dir, fmt.Sprintf("%s.key", name))

	if err := savePEM(certPath, "CERTIFICATE", certBytes); err != nil {
		return nil, err
	}
	if err := savePrivateKeyPEM(keyPath, privKey); err != nil {
		_ = os.Remove(certPath)
		return nil, err
	}

	fp := sha256.Sum256(certBytes)
	info := &CertificateInfo{
		ID:          fmt.Sprintf("cert-%d", time.Now().UnixNano()),
		Name:        name,
		CommonName:  cn,
		IsCA:        true,
		Issuer:      "Self-Signed CA",
		KeyType:     keyType,
		ValidFrom:   template.NotBefore,
		ValidTo:     template.NotAfter,
		Fingerprint: formatFingerprint(fp[:]),
		CertPath:    certPath,
		KeyPath:     keyPath,
		Type:        TypeCA,
		Comment:     req.Comment,
	}

	cm.certs[strings.ToLower(name)] = info
	if err := cm.saveLocked(); err != nil {
		return nil, err
	}

	logging.Log("certs,info", "Created new Certificate Authority: %s (CN: %s)", name, cn)
	return info, nil
}

// CreateCertificate issues a server or client certificate signed by a CA or self-signed.
func (cm *CertManager) CreateCertificate(req CreateCertRequest) (*CertificateInfo, error) {
	name := strings.TrimSpace(req.Name)
	if name == "" {
		return nil, errors.New("certificate name is required")
	}
	cn := strings.TrimSpace(req.CommonName)
	if cn == "" {
		return nil, errors.New("common name is required")
	}

	cm.mu.Lock()
	defer cm.mu.Unlock()

	if _, exists := cm.certs[strings.ToLower(name)]; exists {
		return nil, fmt.Errorf("certificate %q already exists", name)
	}

	days := req.Days
	if days <= 0 {
		days = 365 // 1 year default
	}

	keyType := req.KeyType
	if keyType == "" {
		keyType = KeyRSA2048
	}

	privKey, pubKey, err := generateKeyPair(keyType)
	if err != nil {
		return nil, fmt.Errorf("failed generating key: %w", err)
	}

	serialNumber, err := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
	if err != nil {
		return nil, fmt.Errorf("failed generating serial: %w", err)
	}

	org := req.Organization
	if org == "" {
		org = "DebTik Network Appliance"
	}
	country := req.Country
	if country == "" {
		country = "GR"
	}

	now := time.Now().UTC()
	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			CommonName:   cn,
			Organization: []string{org},
			Country:      []string{country},
		},
		NotBefore:             now.Add(-1 * time.Hour),
		NotAfter:              now.AddDate(0, 0, days),
		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,
		BasicConstraintsValid: true,
		IsCA:                  false,
	}

	if req.IsServer {
		template.ExtKeyUsage = append(template.ExtKeyUsage, x509.ExtKeyUsageServerAuth)
	} else {
		template.ExtKeyUsage = append(template.ExtKeyUsage, x509.ExtKeyUsageClientAuth)
	}

	// Process SANs (DNS names & IP addresses)
	sansMap := make(map[string]bool)
	if ip := net.ParseIP(cn); ip != nil {
		template.IPAddresses = append(template.IPAddresses, ip)
		sansMap[cn] = true
	} else if strings.Contains(cn, ".") || cn != "" {
		template.DNSNames = append(template.DNSNames, cn)
		sansMap[cn] = true
	}

	for _, s := range req.SANs {
		s = strings.TrimSpace(s)
		if s == "" || sansMap[s] {
			continue
		}
		sansMap[s] = true
		if ip := net.ParseIP(s); ip != nil {
			template.IPAddresses = append(template.IPAddresses, ip)
		} else {
			template.DNSNames = append(template.DNSNames, s)
		}
	}

	var sansList []string
	for s := range sansMap {
		sansList = append(sansList, s)
	}

	var signerCert *x509.Certificate
	var signerKey crypto.PrivateKey
	issuerName := "Self-Signed"
	var caPEMBytes []byte

	if req.CAName != "" {
		caInfo, ok := cm.certs[strings.ToLower(req.CAName)]
		if !ok || !caInfo.IsCA {
			return nil, fmt.Errorf("signing CA %q not found or is not a CA", req.CAName)
		}
		caCert, caKey, err := loadCertAndKey(caInfo.CertPath, caInfo.KeyPath)
		if err != nil {
			return nil, fmt.Errorf("failed loading CA cert/key: %w", err)
		}
		signerCert = caCert
		signerKey = caKey
		issuerName = caInfo.Name
		caPEMBytes, _ = os.ReadFile(caInfo.CertPath)
	} else {
		signerCert = &template
		signerKey = privKey
	}

	certBytes, err := x509.CreateCertificate(rand.Reader, &template, signerCert, pubKey, signerKey)
	if err != nil {
		return nil, fmt.Errorf("failed creating certificate: %w", err)
	}

	certPath := filepath.Join(cm.dir, fmt.Sprintf("%s.crt", name))
	keyPath := filepath.Join(cm.dir, fmt.Sprintf("%s.key", name))

	// If signed by CA, build chain: [Cert] + [CA Cert]
	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certBytes})
	if len(caPEMBytes) > 0 {
		certPEM = append(certPEM, caPEMBytes...)
	}
	if err := os.WriteFile(certPath, certPEM, 0644); err != nil {
		return nil, err
	}

	if err := savePrivateKeyPEM(keyPath, privKey); err != nil {
		_ = os.Remove(certPath)
		return nil, err
	}

	fp := sha256.Sum256(certBytes)
	info := &CertificateInfo{
		ID:          fmt.Sprintf("cert-%d", time.Now().UnixNano()),
		Name:        name,
		CommonName:  cn,
		SANs:        sansList,
		IsCA:        false,
		Issuer:      issuerName,
		KeyType:     keyType,
		ValidFrom:   template.NotBefore,
		ValidTo:     template.NotAfter,
		Fingerprint: formatFingerprint(fp[:]),
		CertPath:    certPath,
		KeyPath:     keyPath,
		Type:        TypeServer,
		Comment:     req.Comment,
	}
	if !req.IsServer {
		info.Type = TypeClient
	}

	cm.certs[strings.ToLower(name)] = info
	if err := cm.saveLocked(); err != nil {
		return nil, err
	}

	logging.Log("certs,info", "Created new certificate %s (Issuer: %s, CN: %s)", name, issuerName, cn)
	return info, nil
}

// ImportCertificate imports user-provided PEM certificate and private key.
func (cm *CertManager) ImportCertificate(req ImportCertRequest) (*CertificateInfo, error) {
	name := strings.TrimSpace(req.Name)
	if name == "" {
		return nil, errors.New("certificate name is required")
	}

	certBlock, _ := pem.Decode([]byte(req.CertPEM))
	if certBlock == nil || certBlock.Type != "CERTIFICATE" {
		return nil, errors.New("invalid or empty PEM certificate")
	}

	parsedCert, err := x509.ParseCertificate(certBlock.Bytes)
	if err != nil {
		return nil, fmt.Errorf("failed to parse certificate: %w", err)
	}

	// Verify key matches certificate
	_, err = tls.X509KeyPair([]byte(req.CertPEM), []byte(req.KeyPEM))
	if err != nil {
		return nil, fmt.Errorf("private key does not match certificate: %w", err)
	}

	cm.mu.Lock()
	defer cm.mu.Unlock()

	if _, exists := cm.certs[strings.ToLower(name)]; exists {
		return nil, fmt.Errorf("certificate %q already exists", name)
	}

	certPath := filepath.Join(cm.dir, fmt.Sprintf("%s.crt", name))
	keyPath := filepath.Join(cm.dir, fmt.Sprintf("%s.key", name))

	if err := os.WriteFile(certPath, []byte(strings.TrimSpace(req.CertPEM)+"\n"), 0644); err != nil {
		return nil, err
	}
	if err := os.WriteFile(keyPath, []byte(strings.TrimSpace(req.KeyPEM)+"\n"), 0600); err != nil {
		_ = os.Remove(certPath)
		return nil, err
	}

	var sans []string
	for _, dns := range parsedCert.DNSNames {
		sans = append(sans, dns)
	}
	for _, ip := range parsedCert.IPAddresses {
		sans = append(sans, ip.String())
	}

	fp := sha256.Sum256(parsedCert.Raw)
	cType := TypeServer
	if parsedCert.IsCA {
		cType = TypeCA
	}

	keyType := "Unknown"
	switch parsedCert.PublicKeyAlgorithm {
	case x509.RSA:
		keyType = "RSA"
	case x509.ECDSA:
		keyType = "ECDSA"
	}

	info := &CertificateInfo{
		ID:          fmt.Sprintf("cert-%d", time.Now().UnixNano()),
		Name:        name,
		CommonName:  parsedCert.Subject.CommonName,
		SANs:        sans,
		IsCA:        parsedCert.IsCA,
		Issuer:      parsedCert.Issuer.CommonName,
		KeyType:     keyType,
		ValidFrom:   parsedCert.NotBefore,
		ValidTo:     parsedCert.NotAfter,
		Fingerprint: formatFingerprint(fp[:]),
		CertPath:    certPath,
		KeyPath:     keyPath,
		Type:        cType,
		Comment:     req.Comment,
	}

	cm.certs[strings.ToLower(name)] = info
	if err := cm.saveLocked(); err != nil {
		return nil, err
	}

	logging.Log("certs,info", "Imported certificate: %s (CN: %s)", name, info.CommonName)
	return info, nil
}

// IssueLetsEncrypt requests and issues a certificate from Let's Encrypt via ACME HTTP-01 challenge.
func (cm *CertManager) IssueLetsEncrypt(ctx context.Context, req LetsEncryptRequest) (*CertificateInfo, error) {
	name := strings.TrimSpace(req.Name)
	domain := strings.TrimSpace(req.Domain)
	email := strings.TrimSpace(req.Email)

	if domain == "" {
		return nil, errors.New("domain is required for Let's Encrypt")
	}
	if name == "" {
		name = domain
	}

	cm.mu.Lock()
	if old, exists := cm.certs[strings.ToLower(name)]; exists && (!req.renew || old.Type != TypeACME) {
		cm.mu.Unlock()
		return nil, fmt.Errorf("certificate %q already exists", name)
	}
	cm.mu.Unlock()

	logging.Log("certs,info", "Starting Let's Encrypt order for domain %s (Staging=%t)", domain, req.Staging)

	// Generate ACME account key
	accountKey, err := cm.acmeAccountKey(req.Staging)
	if err != nil {
		return nil, fmt.Errorf("failed generating ACME account key: %w", err)
	}

	client := &acme.Client{
		Key: accountKey,
	}
	if req.Staging {
		client.DirectoryURL = "https://acme-staging-v02.api.letsencrypt.org/directory"
	} else {
		client.DirectoryURL = acme.LetsEncryptURL
	}

	// Register account
	account := &acme.Account{}
	if email != "" {
		account.Contact = []string{"mailto:" + email}
	}
	_, err = client.Register(ctx, account, acme.AcceptTOS)
	if err != nil && !strings.Contains(err.Error(), "already exists") {
		return nil, fmt.Errorf("failed registering ACME account: %w", err)
	}

	// Create order for domain
	order, err := client.AuthorizeOrder(ctx, acme.DomainIDs(domain))
	if err != nil {
		return nil, fmt.Errorf("failed requesting order for %s: %w", domain, err)
	}

	// Complete authorization for each authorization URL
	for _, authzURL := range order.AuthzURLs {
		authz, err := client.GetAuthorization(ctx, authzURL)
		if err != nil {
			return nil, fmt.Errorf("failed getting authorization %s: %w", authzURL, err)
		}

		if authz.Status == acme.StatusValid {
			continue
		}

		var challenge *acme.Challenge
		for _, ch := range authz.Challenges {
			if ch.Type == "http-01" {
				challenge = ch
				break
			}
		}
		if challenge == nil {
			return nil, fmt.Errorf("no http-01 challenge available for domain %s", domain)
		}

		keyAuth, err := client.HTTP01ChallengeResponse(challenge.Token)
		if err != nil {
			return nil, fmt.Errorf("failed generating challenge response: %w", err)
		}

		// Register in our web server challenge map
		cm.RegisterHTTP01Challenge(challenge.Token, keyAuth)
		defer cm.UnregisterHTTP01Challenge(challenge.Token)

		// Inform ACME server challenge is ready
		if _, err := client.Accept(ctx, challenge); err != nil {
			return nil, fmt.Errorf("failed accepting challenge: %w", err)
		}

		// Wait for authorization to succeed
		if _, err := client.WaitAuthorization(ctx, challenge.URI); err != nil {
			return nil, fmt.Errorf("ACME authorization failed for %s: %w", domain, err)
		}
	}

	// Generate certificate private key
	certPrivKey, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return nil, fmt.Errorf("failed generating certificate key: %w", err)
	}

	csrTemplate := x509.CertificateRequest{
		Subject:  pkix.Name{CommonName: domain},
		DNSNames: []string{domain},
	}
	csr, err := x509.CreateCertificateRequest(rand.Reader, &csrTemplate, certPrivKey)
	if err != nil {
		return nil, fmt.Errorf("failed creating CSR: %w", err)
	}

	// Finalize order
	certDerList, certURL, err := client.CreateOrderCert(ctx, order.FinalizeURL, csr, true)
	if err != nil {
		return nil, fmt.Errorf("failed finalizing ACME order: %w", err)
	}
	if len(certDerList) == 0 && certURL != "" {
		certDerList, err = client.FetchCert(ctx, certURL, true)
		if err != nil {
			return nil, fmt.Errorf("failed fetching issued cert: %w", err)
		}
	}

	// Build certificate chain in PEM format
	var certPEM []byte
	var firstCert *x509.Certificate
	for idx, der := range certDerList {
		certPEM = append(certPEM, pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der})...)
		if idx == 0 {
			firstCert, _ = x509.ParseCertificate(der)
		}
	}

	certPath := filepath.Join(cm.dir, fmt.Sprintf("%s.crt", name))
	keyPath := filepath.Join(cm.dir, fmt.Sprintf("%s.key", name))

	if err := os.WriteFile(certPath, certPEM, 0644); err != nil {
		return nil, err
	}
	if err := savePrivateKeyPEM(keyPath, certPrivKey); err != nil {
		_ = os.Remove(certPath)
		return nil, err
	}

	cm.mu.Lock()
	defer cm.mu.Unlock()

	var fp [32]byte
	validFrom := time.Now()
	validTo := time.Now().AddDate(0, 0, 90)
	if firstCert != nil {
		fp = sha256.Sum256(firstCert.Raw)
		validFrom = firstCert.NotBefore
		validTo = firstCert.NotAfter
	}

	issuer := "Let's Encrypt"
	if req.Staging {
		issuer = "Let's Encrypt (Staging)"
	}

	requestCopy := req
	requestCopy.Name = name
	requestCopy.renew = false
	info := &CertificateInfo{
		ACMERequest: &requestCopy,
		ID:          fmt.Sprintf("cert-%d", time.Now().UnixNano()),
		Name:        name,
		CommonName:  domain,
		SANs:        []string{domain},
		IsCA:        false,
		Issuer:      issuer,
		KeyType:     KeyRSA2048,
		ValidFrom:   validFrom,
		ValidTo:     validTo,
		Fingerprint: formatFingerprint(fp[:]),
		CertPath:    certPath,
		KeyPath:     keyPath,
		Type:        TypeACME,
		Comment:     req.Comment,
	}

	cm.certs[strings.ToLower(name)] = info
	if err := cm.saveLocked(); err != nil {
		return nil, err
	}

	logging.Log("certs,info", "Successfully issued Let's Encrypt certificate for %s", domain)
	return info, nil
}

// Helpers
func generateKeyPair(keyType string) (crypto.PrivateKey, crypto.PublicKey, error) {
	switch strings.ToUpper(keyType) {
	case KeyRSA4096:
		priv, err := rsa.GenerateKey(rand.Reader, 4096)
		if err != nil {
			return nil, nil, err
		}
		return priv, &priv.PublicKey, nil
	case KeyECDSAP256:
		priv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
		if err != nil {
			return nil, nil, err
		}
		return priv, &priv.PublicKey, nil
	default: // KeyRSA2048
		priv, err := rsa.GenerateKey(rand.Reader, 2048)
		if err != nil {
			return nil, nil, err
		}
		return priv, &priv.PublicKey, nil
	}
}

func savePEM(path, blockType string, data []byte) error {
	block := &pem.Block{Type: blockType, Bytes: data}
	return os.WriteFile(path, pem.EncodeToMemory(block), 0644)
}

func savePrivateKeyPEM(path string, key crypto.PrivateKey) error {
	var block *pem.Block
	switch k := key.(type) {
	case *rsa.PrivateKey:
		block = &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(k)}
	case *ecdsa.PrivateKey:
		b, err := x509.MarshalECPrivateKey(k)
		if err != nil {
			return err
		}
		block = &pem.Block{Type: "EC PRIVATE KEY", Bytes: b}
	default:
		b, err := x509.MarshalPKCS8PrivateKey(key)
		if err != nil {
			return err
		}
		block = &pem.Block{Type: "PRIVATE KEY", Bytes: b}
	}
	return os.WriteFile(path, pem.EncodeToMemory(block), 0600)
}

func loadCertAndKey(certPath, keyPath string) (*x509.Certificate, crypto.PrivateKey, error) {
	certPEM, err := os.ReadFile(certPath)
	if err != nil {
		return nil, nil, err
	}
	block, _ := pem.Decode(certPEM)
	if block == nil {
		return nil, nil, errors.New("failed decoding certificate PEM")
	}
	cert, err := x509.ParseCertificate(block.Bytes)
	if err != nil {
		return nil, nil, err
	}

	keyPEM, err := os.ReadFile(keyPath)
	if err != nil {
		return nil, nil, err
	}
	keyBlock, _ := pem.Decode(keyPEM)
	if keyBlock == nil {
		return nil, nil, errors.New("failed decoding private key PEM")
	}

	if k, err := x509.ParsePKCS1PrivateKey(keyBlock.Bytes); err == nil {
		return cert, k, nil
	}
	if k, err := x509.ParseECPrivateKey(keyBlock.Bytes); err == nil {
		return cert, k, nil
	}
	if k, err := x509.ParsePKCS8PrivateKey(keyBlock.Bytes); err == nil {
		return cert, k, nil
	}

	return nil, nil, errors.New("unrecognized private key format")
}

func formatFingerprint(b []byte) string {
	hexStr := hex.EncodeToString(b)
	var parts []string
	for i := 0; i < len(hexStr); i += 2 {
		parts = append(parts, strings.ToUpper(hexStr[i:i+2]))
	}
	return strings.Join(parts, ":")
}