package ssl

import (
	"context"
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/x509"
	"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/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 webrootProvider struct {
	webroot string
	store   *ChallengeStore
}

func (p *webrootProvider) 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
	}
	return os.WriteFile(filepath.Join(dir, token), []byte(keyAuth), 0o644)
}

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

type Issuer struct {
	email      string
	staging    bool
	storageDir string
	store      *ChallengeStore
	mu         sync.Mutex
	client     *lego.Client
}

func NewIssuer(email string, staging bool, storageDir string, store *ChallengeStore) *Issuer {
	return &Issuer{
		email:      email,
		staging:    staging,
		storageDir: storageDir,
		store:      store,
	}
}

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

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

	provider := &webrootProvider{webroot: webroot, store: i.store}
	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", err)
	}

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

	return res, nil
}

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

	if i.client != nil {
		return i.client, nil
	}

	user, err := i.loadOrCreateUser()
	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.client = client
	return client, nil
}

func (i *Issuer) accountPath() string {
	return filepath.Join(i.storageDir, "acme", "account.pem")
}

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

	if data, err := os.ReadFile(i.accountPath()); 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(i.accountPath()), 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(), 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
}