package ssl

import (
	"context"
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/sha256"
	"crypto/x509"
	"encoding/hex"
	"encoding/pem"
	"errors"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/go-acme/lego/v4/certcrypto"
	"github.com/go-acme/lego/v4/certificate"
	"github.com/go-acme/lego/v4/challenge/http01"
	"github.com/go-acme/lego/v4/lego"
	"github.com/go-acme/lego/v4/registration"
)

type ACMEUser struct {
	Email        string
	Registration *registration.Resource
	key          *ecdsa.PrivateKey
}

func (u *ACMEUser) GetEmail() string                        { return u.Email }
func (u *ACMEUser) GetRegistration() *registration.Resource { return u.Registration }
func (u *ACMEUser) GetPrivateKey() crypto.PrivateKey        { return u.key }

type challengeProvider struct {
	webroot   string
	store     *ChallengeStore
	httpAddr  string
	httpSrv   *http01.ProviderServer
}

func (p *challengeProvider) Present(domain, token, keyAuth string) error {
	p.store.Set(token, keyAuth)
	dir := filepath.Join(p.webroot, ".well-known", "acme-challenge")
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return err
	}
	if err := os.WriteFile(filepath.Join(dir, token), []byte(keyAuth), 0o644); err != nil {
		return err
	}
	if p.httpSrv != nil {
		return p.httpSrv.Present(domain, token, keyAuth)
	}
	return nil
}

func (p *challengeProvider) CleanUp(domain, token, keyAuth string) error {
	p.store.Delete(token)
	_ = os.Remove(filepath.Join(p.webroot, ".well-known", "acme-challenge", token))
	if p.httpSrv != nil {
		return p.httpSrv.CleanUp(domain, token, keyAuth)
	}
	return nil
}

type Issuer struct {
	staging     bool
	storageDir  string
	acmeHTTPAddr string
	store       *ChallengeStore
	mu          sync.Mutex
	clients     map[string]*lego.Client
}

func NewIssuer(staging bool, storageDir, acmeHTTPAddr string, store *ChallengeStore) *Issuer {
	return &Issuer{
		staging:      staging,
		storageDir:   storageDir,
		acmeHTTPAddr: acmeHTTPAddr,
		store:        store,
		clients:      make(map[string]*lego.Client),
	}
}

func (i *Issuer) Obtain(ctx context.Context, email, domain, webroot string) (*certificate.Resource, error) {
	email = strings.TrimSpace(strings.ToLower(email))
	if email == "" {
		return nil, errors.New("ssl email is not configured")
	}

	client, err := i.getClient(email)
	if err != nil {
		return nil, err
	}

	provider := &challengeProvider{webroot: webroot, store: i.store}
	if i.acmeHTTPAddr != "" {
		port := "80"
		if strings.Contains(i.acmeHTTPAddr, ":") {
			port = strings.TrimPrefix(i.acmeHTTPAddr, ":")
		}
		provider.httpSrv = http01.NewProviderServer("", port)
	}

	if err := client.Challenge.SetHTTP01Provider(provider); err != nil {
		return nil, err
	}

	request := certificate.ObtainRequest{
		Domains: []string{domain},
		Bundle:  true,
	}

	res, err := client.Certificate.Obtain(request)
	if err != nil {
		return nil, fmt.Errorf("acme obtain: %w%s", err, tlsErrorHint(err))
	}

	if err := i.saveToDisk(domain, res); err != nil {
		log.Printf("ssl: save to disk: %v", err)
	}

	return res, nil
}

func tlsErrorHint(err error) string {
	msg := err.Error()
	if strings.Contains(msg, "error:tls") || strings.Contains(msg, "remote error: tls") {
		return " — домен перенаправляет HTTP→HTTPS; нужен nginx location для /.well-known/acme-challenge/ без редиректа"
	}
	return ""
}

func (i *Issuer) getClient(email string) (*lego.Client, error) {
	i.mu.Lock()
	defer i.mu.Unlock()

	if client, ok := i.clients[email]; ok {
		return client, nil
	}

	user, err := i.loadOrCreateUser(email)
	if err != nil {
		return nil, err
	}

	config := lego.NewConfig(user)
	config.Certificate.KeyType = certcrypto.RSA2048
	if i.staging {
		config.CADirURL = lego.LEDirectoryStaging
	} else {
		config.CADirURL = lego.LEDirectoryProduction
	}

	client, err := lego.NewClient(config)
	if err != nil {
		return nil, err
	}

	if user.Registration == nil {
		reg, err := client.Registration.Register(registration.RegisterOptions{TermsOfServiceAgreed: true})
		if err != nil {
			return nil, fmt.Errorf("acme register: %w", err)
		}
		user.Registration = reg
		if err := i.saveAccount(user); err != nil {
			log.Printf("ssl: save acme account: %v", err)
		}
	}

	i.clients[email] = client
	return client, nil
}

func (i *Issuer) accountPath(email string) string {
	sum := sha256.Sum256([]byte(strings.ToLower(email)))
	id := hex.EncodeToString(sum[:8])
	return filepath.Join(i.storageDir, "acme", id, "account.pem")
}

func (i *Issuer) loadOrCreateUser(email string) (*ACMEUser, error) {
	user := &ACMEUser{Email: email}
	path := i.accountPath(email)

	if data, err := os.ReadFile(path); err == nil {
		block, _ := pem.Decode(data)
		if block != nil {
			key, err := x509.ParseECPrivateKey(block.Bytes)
			if err == nil {
				user.key = key
				return user, nil
			}
		}
	}

	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		return nil, err
	}
	user.key = key

	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
		return nil, err
	}
	if err := i.saveAccount(user); err != nil {
		return nil, err
	}
	return user, nil
}

func (i *Issuer) saveAccount(user *ACMEUser) error {
	der, err := x509.MarshalECPrivateKey(user.key)
	if err != nil {
		return err
	}
	pemBytes := pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: der})
	return os.WriteFile(i.accountPath(user.Email), pemBytes, 0o600)
}

func (i *Issuer) saveToDisk(domain string, res *certificate.Resource) error {
	dir := filepath.Join(i.storageDir, "live", sanitizeDomain(domain))
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return err
	}
	if err := os.WriteFile(filepath.Join(dir, "fullchain.pem"), res.Certificate, 0o644); err != nil {
		return err
	}
	return os.WriteFile(filepath.Join(dir, "privkey.pem"), res.PrivateKey, 0o600)
}

func (i *Issuer) Store() *ChallengeStore {
	return i.store
}

func sanitizeDomain(domain string) string {
	return strings.ReplaceAll(domain, "..", "")
}

func CertPaths(storageDir, domain string) (certPath, keyPath string) {
	dir := filepath.Join(storageDir, "live", sanitizeDomain(domain))
	return filepath.Join(dir, "fullchain.pem"), filepath.Join(dir, "privkey.pem")
}

func ParseCertExpiry(certPEM []byte) (time.Time, error) {
	block, _ := pem.Decode(certPEM)
	if block == nil {
		return time.Time{}, errors.New("invalid certificate pem")
	}
	cert, err := x509.ParseCertificate(block.Bytes)
	if err != nil {
		return time.Time{}, err
	}
	return cert.NotAfter, nil
}