package certs

import (
	"context"
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/tls"
	"crypto/x509"
	"encoding/json"
	"encoding/pem"
	"errors"
	"fmt"
	"net/http"
	"os"
	"regexp"
	"strings"
	"sync"
	"time"

	"github.com/go-acme/lego/v4/certcrypto"
	"github.com/go-acme/lego/v4/certificate"
	"github.com/go-acme/lego/v4/challenge/dns01"
	"github.com/go-acme/lego/v4/lego"
	"github.com/go-acme/lego/v4/registration"

	"jarl/internal/acme"
	"jarl/internal/auth"
	"jarl/internal/engine"
	"jarl/internal/model"
)

// Account is the ACME account certificates are obtained with. Its key is
// kept in Jarl's database (and so in backups), like TSIG secrets.
type Account struct {
	Directory    string    `json:"directory"`
	Email        string    `json:"email,omitempty"`
	URI          string    `json:"uri,omitempty"` // the account at the CA
	RegisteredAt time.Time `json:"registered_at"`
	KeyPEM       string    `json:"key_pem,omitempty"`
}

const metaAccount = "acme.account"

// account returns the stored account (nil when there is none).
func (m *Manager) account(ctx context.Context) *Account {
	raw, err := m.store.GetMeta(ctx, metaAccount)
	if err != nil {
		return nil
	}
	var a Account
	if json.Unmarshal([]byte(raw), &a) != nil {
		return nil
	}
	return &a
}

type legoUser struct {
	email string
	reg   *registration.Resource
	key   crypto.PrivateKey
}

func (u *legoUser) GetEmail() string                        { return u.email }
func (u *legoUser) GetRegistration() *registration.Resource { return u.reg }
func (u *legoUser) GetPrivateKey() crypto.PrivateKey        { return u.key }

// ErrTermsNotAgreed means acme.account.agree_tos isn't set.
var ErrTermsNotAgreed = errors.New("acme.account.agree_tos isn't set")

func (m *Manager) httpClient() (*http.Client, error) {
	tr := http.DefaultTransport.(*http.Transport).Clone()
	tr.TLSClientConfig = &tls.Config{MinVersion: tls.VersionTLS12}
	if m.cfg.CABundle != "" {
		pem, err := os.ReadFile(m.cfg.CABundle)
		if err != nil {
			return nil, fmt.Errorf("acme.ca_bundle: %w", err)
		}
		pool, err := x509.SystemCertPool()
		if err != nil || pool == nil {
			pool = x509.NewCertPool()
		}
		if !pool.AppendCertsFromPEM(pem) {
			return nil, fmt.Errorf("acme.ca_bundle: no certificates in %s", m.cfg.CABundle)
		}
		tr.TLSClientConfig.RootCAs = pool
	}
	return &http.Client{Timeout: 2 * time.Minute, Transport: tr}, nil
}

// client returns a lego client for the account (registering it when
// needed) that makes keys of keyType.
func (m *Manager) client(ctx context.Context, keyType string) (*lego.Client, error) {
	dir := m.cfg.Directory
	hc, err := m.httpClient()
	if err != nil {
		return nil, err
	}
	a := m.account(ctx)
	user := &legoUser{email: m.cfg.Email}
	if a != nil && a.Directory == dir && a.KeyPEM != "" {
		if user.key, err = parseKey(a.KeyPEM); err != nil {
			return nil, fmt.Errorf("the stored ACME account key: %w", err)
		}
		if a.URI != "" {
			user.reg = &registration.Resource{URI: a.URI}
		}
	} else {
		k, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
		if err != nil {
			return nil, err
		}
		user.key = k
	}
	cfg := lego.NewConfig(user)
	cfg.CADirURL, cfg.HTTPClient, cfg.UserAgent = dir, hc, "jarl/"+m.cfg.Version
	cfg.Certificate.KeyType = legoKeyType(keyType)
	cfg.Certificate.Timeout = 90 * time.Second
	c, err := lego.NewClient(cfg)
	if err != nil {
		return nil, fmt.Errorf("ACME server %s: %w", dir, err)
	}
	if user.reg != nil && (a.Email == m.cfg.Email) {
		return c, nil
	}
	if user.reg != nil {
		// Only the email changed: update the account.
		if reg, err := c.Registration.UpdateRegistration(registration.RegisterOptions{TermsOfServiceAgreed: true}); err == nil {
			user.reg = reg
			return c, m.saveAccount(ctx, user, dir)
		}
	}
	if !m.cfg.AgreeTOS {
		tos := c.GetToSURL()
		if tos == "" {
			tos = "on the CA's website"
		}
		return nil, fmt.Errorf("%w: Jarl registers an account with %s only after you accept its terms of service (%s): set acme.account.agree_tos: true in jarl.yaml and restart jarld", ErrTermsNotAgreed, dir, tos)
	}
	var reg *registration.Resource
	if m.cfg.EABKeyID != "" {
		reg, err = c.Registration.RegisterWithExternalAccountBinding(registration.RegisterEABOptions{TermsOfServiceAgreed: true, Kid: m.cfg.EABKeyID, HmacEncoded: m.cfg.EABHMAC})
	} else {
		if c.GetExternalAccountRequired() {
			return nil, fmt.Errorf("%s needs External Account Binding: set acme.account.eab_kid and eab_hmac in jarl.yaml (from the CA's dashboard)", dir)
		}
		reg, err = c.Registration.Register(registration.RegisterOptions{TermsOfServiceAgreed: true})
	}
	if err != nil {
		return nil, fmt.Errorf("registering the ACME account: %w", err)
	}
	user.reg = reg
	m.log.Info("ACME account registered", "directory", dir, "account", reg.URI)
	return c, m.saveAccount(ctx, user, dir)
}

func (m *Manager) saveAccount(ctx context.Context, u *legoUser, dir string) error {
	der, err := x509.MarshalPKCS8PrivateKey(u.key)
	if err != nil {
		return err
	}
	a := Account{Directory: dir, Email: u.email, URI: u.reg.URI, RegisteredAt: time.Now().UTC(),
		KeyPEM: string(pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: der}))}
	b, _ := json.Marshal(a)
	return m.store.SetMeta(ctx, metaAccount, string(b))
}

func parseKey(s string) (crypto.PrivateKey, error) {
	b, _ := pem.Decode([]byte(s))
	if b == nil {
		return nil, errors.New("not PEM")
	}
	return x509.ParsePKCS8PrivateKey(b.Bytes)
}

func legoKeyType(t string) certcrypto.KeyType {
	switch t {
	case "ec384":
		return certcrypto.EC384
	case "rsa2048":
		return certcrypto.RSA2048
	case "rsa3072":
		return certcrypto.RSA3072
	case "rsa4096":
		return certcrypto.RSA4096
	}
	return certcrypto.EC256
}

// KeyTypes are the key types a certificate Jarl obtains can have.
var KeyTypes = []string{"ec256", "ec384", "rsa2048", "rsa3072", "rsa4096"}

// provider answers DNS-01 challenges for one issue: in a zone Jarl serves,
// or at Porkbun, as route decides for each name.
type provider struct {
	m        *Manager
	ctx      context.Context
	cert     *model.Certificate
	mu       sync.Mutex
	cleanups map[string]func() error
	routes   []Route
}

func (p *provider) Present(domain, token, keyAuth string) error {
	info := dns01.GetChallengeInfo(domain, keyAuth)
	st, err := p.m.store.LoadState(p.ctx)
	if err != nil {
		return err
	}
	r := p.m.route(p.ctx, st, p.cert.Challenge, domain, info.EffectiveFQDN)
	p.mu.Lock()
	p.routes = append(p.routes, r)
	p.mu.Unlock()
	if r.Error != "" {
		return errors.New(r.Error)
	}
	key := info.EffectiveFQDN + " " + info.Value
	var cleanup func() error
	switch r.Route {
	case model.ChallengeJarl:
		if err := p.m.publish(p.ctx, p.cert, info.EffectiveFQDN, info.Value, true); err != nil {
			return err
		}
		cleanup = func() error {
			return p.m.publish(context.WithoutCancel(p.ctx), p.cert, info.EffectiveFQDN, info.Value, false)
		}
	case model.ChallengePorkbun:
		zone := strings.TrimSuffix(r.Zone, ".")
		id, err := p.m.cfg.Porkbun.CreateTXT(p.ctx, zone, strings.TrimSuffix(info.EffectiveFQDN, "."), info.Value)
		if err != nil {
			return fmt.Errorf("publishing the challenge for %s at Porkbun: %w", domain, err)
		}
		cleanup = func() error { return p.m.cfg.Porkbun.DeleteRecord(context.WithoutCancel(p.ctx), zone, id) }
	}
	p.mu.Lock()
	p.cleanups[key] = cleanup
	p.mu.Unlock()
	return nil
}

func (p *provider) CleanUp(domain, token, keyAuth string) error {
	info := dns01.GetChallengeInfo(domain, keyAuth)
	key := info.EffectiveFQDN + " " + info.Value
	p.mu.Lock()
	f := p.cleanups[key]
	delete(p.cleanups, key)
	p.mu.Unlock()
	if f == nil {
		return nil
	}
	if err := f(); err != nil {
		p.m.log.Warn("removing an ACME challenge record failed", "certificate", p.cert.Name, "record", info.EffectiveFQDN, "err", err)
		return err
	}
	return nil
}

// Timeout is how long lego waits for the record to reach every name
// server of the zone: Porkbun's take a few minutes.
func (p *provider) Timeout() (timeout, interval time.Duration) {
	if p.m.cfg.PropagationTimeout > 0 {
		return p.m.cfg.PropagationTimeout, 2 * time.Second
	}
	return 10 * time.Minute, 10 * time.Second
}

// publish writes (or removes) a challenge TXT record in the Jarl zone that
// holds name, in every view that has it, and returns once named serves it.
func (m *Manager) publish(ctx context.Context, c *model.Certificate, name, value string, set bool) error {
	st, err := m.store.LoadState(ctx)
	if err != nil {
		return err
	}
	zones := acme.Zones(name, primaryZones(st), "")
	if len(zones) == 0 {
		return fmt.Errorf("no primary zone in Jarl contains %s", strings.TrimSuffix(name, "."))
	}
	var reqs []engine.Request
	for _, r := range acme.Requests(name, zones, []string{value}, set, acme.DefaultTTL) {
		reqs = append(reqs, engine.Request{Op: r.Op, ID: r.ID, BaseVersion: r.BaseVersion, Data: r.Data})
	}
	desc := acme.Description(name, set) + " (certificate " + c.Name + ")"
	if _, err := m.eng.Submit(ctx, reqs, auth.System, "acme", desc, engine.ApplyOptions{}); err != nil {
		return fmt.Errorf("writing the challenge record %s: %w", strings.TrimSuffix(name, "."), err)
	}
	return nil
}

// obtain gets a new certificate for c from the CA. old is the certificate
// it replaces (nil for the first), so the CA can link them (ARI).
func (m *Manager) obtain(ctx context.Context, c *model.Certificate, old *x509.Certificate) (*certificate.Resource, []Route, error) {
	m.legoMu.Lock()
	defer m.legoMu.Unlock()
	client, err := m.client(ctx, c.KeyType)
	if err != nil {
		return nil, nil, err
	}
	p := &provider{m: m, ctx: ctx, cert: c, cleanups: map[string]func() error{}}
	opts := []dns01.ChallengeOption{dns01.AddRecursiveNameservers(m.cfg.Resolvers), dns01.AddDNSTimeout(10 * time.Second)}
	if m.cfg.SkipPropagationCheck {
		opts = append(opts, dns01.DisableAuthoritativeNssPropagationRequirement())
	}
	if err := client.Challenge.SetDNS01Provider(p, opts...); err != nil {
		return nil, nil, err
	}
	req := certificate.ObtainRequest{Domains: c.Domains, Bundle: true}
	if old != nil {
		if id, err := certificate.MakeARICertID(old); err == nil {
			req.ReplacesCertID = id
		}
	}
	res, err := client.Certificate.Obtain(req)
	if err != nil && req.ReplacesCertID != "" && len(p.routes) == 0 && ctx.Err() == nil {
		// The CA refused the order itself, before any challenge: it may
		// not link the new certificate to the old one (another CA, one
		// already replaced, or its own bug). Ask for a plain new one.
		m.log.Info("the CA refused to link the renewal to the old certificate; asking for a new one", "certificate", c.Name, "err", cleanLegoError(err))
		req.ReplacesCertID = ""
		res, err = client.Certificate.Obtain(req)
	}
	if err != nil {
		return nil, p.routes, cleanLegoError(err)
	}
	return res, p.routes, nil
}

// renewalInfo asks the CA when to renew (ARI, RFC 9773). nil, nil when
// it doesn't say.
func (m *Manager) renewalInfo(ctx context.Context, c *model.Certificate, leaf *x509.Certificate) (*time.Time, error) {
	m.legoMu.Lock()
	defer m.legoMu.Unlock()
	client, err := m.client(ctx, c.KeyType)
	if err != nil {
		return nil, err
	}
	ri, err := client.Certificate.GetRenewalInfo(certificate.RenewalInfoRequest{Cert: leaf})
	if err != nil {
		if strings.Contains(err.Error(), "does not advertise a renewal info endpoint") {
			return nil, nil
		}
		return nil, err
	}
	// A time within the CA's window (now if it has started); never later
	// than two thirds into the lifetime, in case the window is odd.
	at := ri.ShouldRenewAt(time.Now(), 10*365*24*time.Hour)
	if at == nil {
		return nil, nil
	}
	t := at.UTC().Truncate(time.Second)
	if limit := twoThirds(leaf.NotBefore, leaf.NotAfter); t.After(limit) {
		t = limit
	}
	return &t, nil
}

func twoThirds(nb, na time.Time) time.Time {
	return nb.Add(na.Sub(nb) * 2 / 3).UTC().Truncate(time.Second)
}

// cleanLegoError shortens lego's errors, which wrap each name's problem in
// several prefixes and the whole ACME problem document:
//
//	error: one or more domains had a problem:
//	[a.example.com] [a.example.com] acme: error presenting token: MSG
//	[b.example.com] acme: error: 403 :: urn:ietf:params:acme:error:unauthorized :: MSG
//
// becomes "a.example.com: MSG; b.example.com: the CA refused (unauthorized): MSG".
func cleanLegoError(err error) error {
	msg := strings.TrimSpace(strings.Replace(err.Error(), "error: one or more domains had a problem:", "", 1))
	var out []string
	for _, line := range strings.Split(msg, "\n") {
		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}
		domain := ""
		for strings.HasPrefix(line, "[") {
			end := strings.Index(line, "] ")
			if end < 0 {
				break
			}
			if domain == "" {
				domain = line[1:end]
			}
			line = line[end+2:]
		}
		for _, p := range []string{"acme: error presenting token: ", "acme: error: ", "acme: "} {
			line = strings.TrimPrefix(line, p)
		}
		if m := acmeProblemRe.FindStringSubmatch(line); m != nil {
			line = "the CA refused (" + m[2] + "): " + m[3]
		}
		if domain != "" {
			line = domain + ": " + line
		}
		out = append(out, line)
	}
	if len(out) == 0 {
		return err
	}
	return errors.New(strings.Join(out, "; "))
}

// acmeProblemRe matches "403 :: urn:ietf:params:acme:error:unauthorized :: detail".
var acmeProblemRe = regexp.MustCompile(`^(\d+) :: urn:ietf:params:acme:error:(\w+) :: (.*)$`)