package acme

import (
	"context"
	"crypto/rand"
	"crypto/x509"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"

	"git.wntrmute.dev/mc/metacrypt/internal/engine"
)

// directoryResponse is the ACME directory object (RFC 8555 §7.1.1).
type directoryResponse struct {
	Meta       *directoryMeta `json:"meta,omitempty"`
	NewNonce   string         `json:"newNonce"`
	NewAccount string         `json:"newAccount"`
	NewOrder   string         `json:"newOrder"`
	RevokeCert string         `json:"revokeCert"`
	KeyChange  string         `json:"keyChange"`
}

type directoryMeta struct {
	TermsOfService          string   `json:"termsOfService,omitempty"`
	Website                 string   `json:"website,omitempty"`
	CAAIdentities           []string `json:"caaIdentities,omitempty"`
	ExternalAccountRequired bool     `json:"externalAccountRequired"`
}

// handleDirectory serves the ACME directory (GET /acme/{mount}/directory).
// No nonce or authentication required.
func (h *Handler) handleDirectory(w http.ResponseWriter, r *http.Request) {
	base := h.baseURL + "/acme/" + h.mount
	dir := directoryResponse{
		NewNonce:   base + "/new-nonce",
		NewAccount: base + "/new-account",
		NewOrder:   base + "/new-order",
		RevokeCert: base + "/revoke-cert",
		KeyChange:  base + "/key-change",
		Meta: &directoryMeta{
			ExternalAccountRequired: true,
		},
	}
	w.Header().Set("Content-Type", "application/json")
	_ = json.NewEncoder(w).Encode(dir)
}

// handleNewNonce serves HEAD and GET /acme/{mount}/new-nonce.
func (h *Handler) handleNewNonce(w http.ResponseWriter, r *http.Request) {
	h.addNonceHeader(w)
	w.Header().Set("Cache-Control", "no-store")
	if r.Method == http.MethodHead {
		w.WriteHeader(http.StatusOK)
	} else {
		w.WriteHeader(http.StatusNoContent)
	}
}

// newAccountPayload is the payload for the new-account request.
type newAccountPayload struct {
	Contact                []string        `json:"contact,omitempty"`
	ExternalAccountBinding json.RawMessage `json:"externalAccountBinding,omitempty"`
	TermsOfServiceAgreed   bool            `json:"termsOfServiceAgreed"`
	OnlyReturnExisting     bool            `json:"onlyReturnExisting"`
}

// handleNewAccount handles POST /acme/{mount}/new-account.
func (h *Handler) handleNewAccount(w http.ResponseWriter, r *http.Request) {
	parsed, err := h.parseAndVerifyNewAccountJWS(r)
	if err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemMalformed, err.Error())
		return
	}
	// Validate URL in header.
	if parsed.Header.URL != h.baseURL+"/acme/"+h.mount+"/new-account" {
		h.writeACMEError(w, http.StatusBadRequest, ProblemMalformed, "JWS URL mismatch")
		return
	}
	// Consume nonce.
	if err := h.nonces.Consume(parsed.Header.Nonce); err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemBadNonce, "invalid or expired nonce")
		return
	}

	var payload newAccountPayload
	if len(parsed.Payload) > 0 {
		if err := json.Unmarshal(parsed.Payload, &payload); err != nil {
			h.writeACMEError(w, http.StatusBadRequest, ProblemMalformed, "invalid payload")
			return
		}
	}

	ctx := r.Context()

	// Check if account already exists for this JWK.
	jwkJSON, _ := json.Marshal(parsed.Header.JWK)
	kid := thumbprintKey(jwkJSON)
	existingPath := h.barrierPrefix() + "accounts/" + kid + ".json"
	existing, _ := h.barrier.Get(ctx, existingPath)
	if existing != nil {
		var acc Account
		if err := json.Unmarshal(existing, &acc); err == nil {
			if payload.OnlyReturnExisting || acc.Status == StatusValid {
				w.Header().Set("Location", h.accountURL(acc.ID))
				h.writeJSON(w, http.StatusOK, h.accountToWire(&acc))
				return
			}
		}
	}

	if payload.OnlyReturnExisting {
		h.writeACMEError(w, http.StatusBadRequest, ProblemAccountDoesNotExist, "account does not exist")
		return
	}

	// EAB is required.
	if len(payload.ExternalAccountBinding) == 0 {
		h.writeACMEError(w, http.StatusBadRequest, ProblemExternalAccountRequired, "external account binding required")
		return
	}

	// Parse and verify EAB.
	eabParsed, err := ParseJWS(payload.ExternalAccountBinding)
	if err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemMalformed, "invalid EAB JWS")
		return
	}
	eabKID := eabParsed.Header.KID
	eabCred, err := h.GetEAB(ctx, eabKID)
	if err != nil {
		h.writeACMEError(w, http.StatusUnauthorized, ProblemUnauthorized, "unknown EAB key ID")
		return
	}
	if eabCred.Used {
		h.writeACMEError(w, http.StatusUnauthorized, ProblemUnauthorized, "EAB key already used")
		return
	}
	if err := VerifyEAB(payload.ExternalAccountBinding, eabKID, eabCred.HMACKey, jwkJSON); err != nil {
		h.writeACMEError(w, http.StatusUnauthorized, ProblemUnauthorized, "EAB verification failed")
		return
	}
	if err := h.MarkEABUsed(ctx, eabKID); err != nil {
		h.logger.Error("acme: mark EAB used", "error", err)
	}

	// Create account.
	acc := &Account{
		ID:            kid,
		Status:        StatusValid,
		Contact:       payload.Contact,
		JWK:           jwkJSON,
		CreatedAt:     time.Now(),
		MCIASUsername: eabCred.CreatedBy,
	}
	data, _ := json.Marshal(acc)
	if err := h.barrier.Put(ctx, existingPath, data); err != nil {
		h.logger.Error("acme: store account", "error", err)
		h.writeACMEError(w, http.StatusInternalServerError, ProblemServerInternal, "failed to store account")
		return
	}

	w.Header().Set("Location", h.accountURL(acc.ID))
	h.writeJSON(w, http.StatusCreated, h.accountToWire(acc))
}

// newOrderPayload is the payload for the new-order request.
type newOrderPayload struct {
	NotBefore   string       `json:"notBefore,omitempty"`
	NotAfter    string       `json:"notAfter,omitempty"`
	Identifiers []Identifier `json:"identifiers"`
}

// handleNewOrder handles POST /acme/{mount}/new-order.
func (h *Handler) handleNewOrder(w http.ResponseWriter, r *http.Request) {
	acc, parsed, err := h.authenticateRequest(r, h.baseURL+"/acme/"+h.mount+"/new-order")
	if err != nil {
		h.writeACMEError(w, http.StatusUnauthorized, ProblemUnauthorized, err.Error())
		return
	}

	var payload newOrderPayload
	if err := json.Unmarshal(parsed.Payload, &payload); err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemMalformed, "invalid payload")
		return
	}
	if len(payload.Identifiers) == 0 {
		h.writeACMEError(w, http.StatusBadRequest, ProblemMalformed, "identifiers required")
		return
	}

	// Validate identifier types.
	for _, id := range payload.Identifiers {
		if id.Type != IdentifierDNS && id.Type != IdentifierIP {
			h.writeACMEError(w, http.StatusBadRequest, ProblemUnsupportedIdentifier,
				fmt.Sprintf("unsupported identifier type: %s", id.Type))
			return
		}
	}

	ctx := r.Context()

	// Look up default issuer from config.
	cfg, _ := h.loadConfig(ctx)
	if cfg.DefaultIssuer == "" {
		h.writeACMEError(w, http.StatusInternalServerError, ProblemServerInternal,
			"no default issuer configured for this ACME mount; set acme_issuer via the management API")
		return
	}

	orderID := newID()
	now := time.Now()
	orderExpiry := now.Add(7 * 24 * time.Hour)

	// Create one authorization per identifier.
	var authzIDs []string
	for _, id := range payload.Identifiers {
		authzID := newID()
		authzIDs = append(authzIDs, authzID)

		// Create two challenges: http-01 and dns-01.
		httpChallengeID := newID()
		dnsChallengeID := newID()

		httpChallenge := &Challenge{
			ID:      httpChallengeID,
			AuthzID: authzID,
			Type:    ChallengeHTTP01,
			Status:  StatusPending,
			Token:   newToken(),
		}
		dnsChallenge := &Challenge{
			ID:      dnsChallengeID,
			AuthzID: authzID,
			Type:    ChallengeDNS01,
			Status:  StatusPending,
			Token:   newToken(),
		}
		authz := &Authorization{
			ID:           authzID,
			AccountID:    acc.ID,
			Status:       StatusPending,
			Identifier:   id,
			ChallengeIDs: []string{httpChallengeID, dnsChallengeID},
			ExpiresAt:    orderExpiry,
		}

		challPrefix := h.barrierPrefix() + "challenges/"
		authzPrefix := h.barrierPrefix() + "authz/"

		httpData, _ := json.Marshal(httpChallenge)
		dnsData, _ := json.Marshal(dnsChallenge)
		authzData, _ := json.Marshal(authz)

		if err := h.barrier.Put(ctx, challPrefix+httpChallengeID+".json", httpData); err != nil {
			h.logger.Error("acme: store challenge", "error", err)
			h.writeACMEError(w, http.StatusInternalServerError, ProblemServerInternal, "failed to create authorization")
			return
		}
		if err := h.barrier.Put(ctx, challPrefix+dnsChallengeID+".json", dnsData); err != nil {
			h.logger.Error("acme: store challenge", "error", err)
			h.writeACMEError(w, http.StatusInternalServerError, ProblemServerInternal, "failed to create authorization")
			return
		}
		if err := h.barrier.Put(ctx, authzPrefix+authzID+".json", authzData); err != nil {
			h.logger.Error("acme: store authz", "error", err)
			h.writeACMEError(w, http.StatusInternalServerError, ProblemServerInternal, "failed to create authorization")
			return
		}
	}

	order := &Order{
		ID:          orderID,
		AccountID:   acc.ID,
		Status:      StatusPending,
		Identifiers: payload.Identifiers,
		AuthzIDs:    authzIDs,
		ExpiresAt:   orderExpiry,
		CreatedAt:   now,
		IssuerName:  cfg.DefaultIssuer,
	}
	orderData, _ := json.Marshal(order)
	if err := h.barrier.Put(ctx, h.barrierPrefix()+"orders/"+orderID+".json", orderData); err != nil {
		h.logger.Error("acme: store order", "error", err)
		h.writeACMEError(w, http.StatusInternalServerError, ProblemServerInternal, "failed to create order")
		return
	}

	w.Header().Set("Location", h.orderURL(orderID))
	h.writeJSON(w, http.StatusCreated, h.orderToWire(order))
}

// handleGetAuthz handles POST /acme/{mount}/authz/{id} (POST-as-GET, empty payload).
func (h *Handler) handleGetAuthz(w http.ResponseWriter, r *http.Request) {
	authzID := chi.URLParam(r, "id")
	reqURL := h.baseURL + "/acme/" + h.mount + "/authz/" + authzID
	_, _, err := h.authenticateRequest(r, reqURL)
	if err != nil {
		h.writeACMEError(w, http.StatusUnauthorized, ProblemUnauthorized, err.Error())
		return
	}

	authz, err := h.loadAuthz(r.Context(), authzID)
	if err != nil {
		h.writeACMEError(w, http.StatusNotFound, ProblemMalformed, "authorization not found")
		return
	}

	h.writeJSON(w, http.StatusOK, h.authzToWire(r.Context(), authz))
}

// handleChallenge handles POST /acme/{mount}/challenge/{type}/{id}.
func (h *Handler) handleChallenge(w http.ResponseWriter, r *http.Request) {
	challType := chi.URLParam(r, "type")
	challID := chi.URLParam(r, "id")
	reqURL := h.baseURL + "/acme/" + h.mount + "/challenge/" + challType + "/" + challID

	acc, _, err := h.authenticateRequest(r, reqURL)
	if err != nil {
		h.writeACMEError(w, http.StatusUnauthorized, ProblemUnauthorized, err.Error())
		return
	}

	ctx := r.Context()
	chall, err := h.loadChallenge(ctx, challID)
	if err != nil {
		h.writeACMEError(w, http.StatusNotFound, ProblemMalformed, "challenge not found")
		return
	}
	if chall.Status != StatusPending {
		// Already processing or completed; return current state.
		h.writeJSON(w, http.StatusOK, h.challengeToWire(chall))
		return
	}

	// Mark as processing.
	chall.Status = StatusProcessing
	if err := h.saveChallenge(ctx, chall); err != nil {
		h.writeACMEError(w, http.StatusInternalServerError, ProblemServerInternal, "failed to update challenge")
		return
	}

	// Return challenge immediately; validate asynchronously.
	h.writeJSON(w, http.StatusOK, h.challengeToWire(chall))

	// Launch validation goroutine.
	go h.validateChallenge(context.Background(), chall, acc.JWK) //nolint:gosec
}

// handleFinalize handles POST /acme/{mount}/finalize/{id}.
func (h *Handler) handleFinalize(w http.ResponseWriter, r *http.Request) {
	orderID := chi.URLParam(r, "id")
	reqURL := h.baseURL + "/acme/" + h.mount + "/finalize/" + orderID

	acc, parsed, err := h.authenticateRequest(r, reqURL)
	if err != nil {
		h.writeACMEError(w, http.StatusUnauthorized, ProblemUnauthorized, err.Error())
		return
	}

	ctx := r.Context()
	order, err := h.loadOrder(ctx, orderID)
	if err != nil {
		h.writeACMEError(w, http.StatusNotFound, ProblemMalformed, "order not found")
		return
	}
	if order.AccountID != acc.ID {
		h.writeACMEError(w, http.StatusUnauthorized, ProblemUnauthorized, "order belongs to different account")
		return
	}
	if order.Status != StatusReady {
		h.writeACMEError(w, http.StatusForbidden, ProblemOrderNotReady, "order is not ready")
		return
	}

	// Parse payload: {"csr": "<base64url DER>"}
	var finalizePayload struct {
		CSR string `json:"csr"`
	}
	if err := json.Unmarshal(parsed.Payload, &finalizePayload); err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemMalformed, "invalid payload")
		return
	}
	csrDER, err := base64.RawURLEncoding.DecodeString(finalizePayload.CSR)
	if err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemBadCSR, "invalid CSR encoding")
		return
	}
	csr, err := x509.ParseCertificateRequest(csrDER)
	if err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemBadCSR, "invalid CSR: "+err.Error())
		return
	}
	if err := csr.CheckSignature(); err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemBadCSR, "CSR signature invalid")
		return
	}

	// Verify CSR identifiers match order identifiers.
	if err := h.validateCSRIdentifiers(csr, order.Identifiers); err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemBadCSR, err.Error())
		return
	}

	// Issue certificate via CA engine.
	// Build SANs from order identifiers.
	var dnsNames, ipAddrs []string
	for _, id := range order.Identifiers {
		switch id.Type {
		case IdentifierDNS:
			dnsNames = append(dnsNames, id.Value)
		case IdentifierIP:
			ipAddrs = append(ipAddrs, id.Value)
		}
	}

	issueReq := &engine.Request{
		Operation: "issue",
		CallerInfo: &engine.CallerInfo{
			Username: acc.MCIASUsername,
			Roles:    []string{"user"},
			IsAdmin:  false,
		},
		Data: map[string]interface{}{
			"issuer":       order.IssuerName,
			"profile":      "server",
			"common_name":  csr.Subject.CommonName,
			"dns_names":    dnsNames,
			"ip_addresses": ipAddrs,
		},
	}

	resp, err := h.engines.HandleRequest(ctx, h.mount, issueReq)
	if err != nil {
		h.logger.Error("acme: issue cert", "error", err)
		h.writeACMEError(w, http.StatusInternalServerError, ProblemServerInternal, "certificate issuance failed")
		return
	}

	certPEM, _ := resp.Data["chain_pem"].(string)
	expiresStr, _ := resp.Data["expires_at"].(string)
	certID := newID()

	var expiresAt time.Time
	if expiresStr != "" {
		expiresAt, _ = time.Parse(time.RFC3339, expiresStr)
	}

	issuedCert := &IssuedCert{
		ID:        certID,
		OrderID:   orderID,
		AccountID: acc.ID,
		CertPEM:   certPEM,
		IssuedAt:  time.Now(),
		ExpiresAt: expiresAt,
	}
	certData, _ := json.Marshal(issuedCert)
	if err := h.barrier.Put(ctx, h.barrierPrefix()+"certs/"+certID+".json", certData); err != nil {
		h.logger.Error("acme: store cert", "error", err)
	}

	order.Status = StatusValid
	order.CertID = certID
	orderData, _ := json.Marshal(order)
	_ = h.barrier.Put(ctx, h.barrierPrefix()+"orders/"+orderID+".json", orderData)

	h.writeJSON(w, http.StatusOK, h.orderToWire(order))
}

// handleGetCert handles POST /acme/{mount}/cert/{id} (POST-as-GET).
func (h *Handler) handleGetCert(w http.ResponseWriter, r *http.Request) {
	certID := chi.URLParam(r, "id")
	reqURL := h.baseURL + "/acme/" + h.mount + "/cert/" + certID

	_, _, err := h.authenticateRequest(r, reqURL)
	if err != nil {
		h.writeACMEError(w, http.StatusUnauthorized, ProblemUnauthorized, err.Error())
		return
	}

	data, err := h.barrier.Get(r.Context(), h.barrierPrefix()+"certs/"+certID+".json")
	if err != nil || data == nil {
		h.writeACMEError(w, http.StatusNotFound, ProblemMalformed, "certificate not found")
		return
	}
	var cert IssuedCert
	if err := json.Unmarshal(data, &cert); err != nil {
		h.writeACMEError(w, http.StatusInternalServerError, ProblemServerInternal, "failed to load certificate")
		return
	}
	if cert.Revoked {
		h.writeACMEError(w, http.StatusNotFound, ProblemAlreadyRevoked, "certificate has been revoked")
		return
	}

	h.addNonceHeader(w)
	w.Header().Set("Content-Type", "application/pem-certificate-chain")
	w.WriteHeader(http.StatusOK)
	_, _ = w.Write([]byte(cert.CertPEM))
}

// handleRevokeCert handles POST /acme/{mount}/revoke-cert.
func (h *Handler) handleRevokeCert(w http.ResponseWriter, r *http.Request) {
	_, parsed, err := h.authenticateRequest(r, h.baseURL+"/acme/"+h.mount+"/revoke-cert")
	if err != nil {
		h.writeACMEError(w, http.StatusUnauthorized, ProblemUnauthorized, err.Error())
		return
	}

	var revokePayload struct {
		Certificate string `json:"certificate"` // base64url DER
	}
	if err := json.Unmarshal(parsed.Payload, &revokePayload); err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemMalformed, "invalid payload")
		return
	}

	// Find cert by matching the DER bytes.
	ctx := r.Context()
	certDER, err := base64.RawURLEncoding.DecodeString(revokePayload.Certificate)
	if err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemMalformed, "invalid certificate encoding")
		return
	}
	targetCert, err := x509.ParseCertificate(certDER)
	if err != nil {
		h.writeACMEError(w, http.StatusBadRequest, ProblemMalformed, "invalid certificate")
		return
	}

	paths, err := h.barrier.List(ctx, h.barrierPrefix()+"certs/")
	if err != nil {
		h.writeACMEError(w, http.StatusInternalServerError, ProblemServerInternal, "failed to list certificates")
		return
	}

	for _, p := range paths {
		if !strings.HasSuffix(p, ".json") {
			continue
		}
		data, _ := h.barrier.Get(ctx, h.barrierPrefix()+"certs/"+p)
		if data == nil {
			continue
		}
		var cert IssuedCert
		if err := json.Unmarshal(data, &cert); err != nil {
			continue
		}
		// Match by serial number encoded in PEM.
		issuedCertDER, err := pemToDER(cert.CertPEM)
		if err != nil {
			continue
		}
		issuedCert, err := x509.ParseCertificate(issuedCertDER)
		if err != nil {
			continue
		}
		if issuedCert.SerialNumber.Cmp(targetCert.SerialNumber) == 0 {
			cert.Revoked = true
			updated, _ := json.Marshal(cert)
			_ = h.barrier.Put(ctx, h.barrierPrefix()+"certs/"+p, updated)
			h.addNonceHeader(w)
			w.WriteHeader(http.StatusOK)
			return
		}
	}

	h.writeACMEError(w, http.StatusNotFound, ProblemMalformed, "certificate not found")
}

// --- Authentication helpers ---

// authenticateRequest parses and verifies a JWS request, consuming the nonce
// and validating the URL. Returns the account and parsed JWS.
// For new-account requests, use parseAndVerifyNewAccountJWS instead.
func (h *Handler) authenticateRequest(r *http.Request, expectedURL string) (*Account, *ParsedJWS, error) {
	body, err := readBody(r)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to read body: %w", err)
	}
	parsed, err := ParseJWS(body)
	if err != nil {
		return nil, nil, fmt.Errorf("invalid JWS: %w", err)
	}
	if parsed.Header.URL != expectedURL {
		return nil, nil, errors.New("JWS URL mismatch")
	}
	if err := h.nonces.Consume(parsed.Header.Nonce); err != nil {
		return nil, nil, errors.New("invalid or expired nonce")
	}

	// Look up account by KID.
	if parsed.Header.KID == "" {
		return nil, nil, errors.New("KID required for authenticated requests")
	}
	// KID is the full account URL; extract the ID.
	accID := extractIDFromURL(parsed.Header.KID, "/account/")
	if accID == "" {
		// Try treating KID directly as the account ID (thumbprint).
		accID = parsed.Header.KID
	}

	acc, err := h.loadAccount(r.Context(), accID)
	if err != nil {
		return nil, nil, errors.New("account not found")
	}
	if acc.Status != StatusValid {
		return nil, nil, fmt.Errorf("account status is %s", acc.Status)
	}

	// Verify JWS signature against account key.
	pubKey, err := ParseJWK(acc.JWK)
	if err != nil {
		return nil, nil, fmt.Errorf("invalid account key: %w", err)
	}
	if err := VerifyJWS(parsed, pubKey); err != nil {
		return nil, nil, fmt.Errorf("signature verification failed: %w", err)
	}
	return acc, parsed, nil
}

// parseAndVerifyNewAccountJWS parses a new-account JWS where the key is
// embedded in the JWK header field (not a KID).
func (h *Handler) parseAndVerifyNewAccountJWS(r *http.Request) (*ParsedJWS, error) {
	body, err := readBody(r)
	if err != nil {
		return nil, fmt.Errorf("failed to read body: %w", err)
	}
	parsed, err := ParseJWS(body)
	if err != nil {
		return nil, fmt.Errorf("invalid JWS: %w", err)
	}
	if len(parsed.Header.JWK) == 0 {
		return nil, errors.New("JWK required in header for new-account")
	}
	pubKey, err := ParseJWK(parsed.Header.JWK)
	if err != nil {
		return nil, fmt.Errorf("invalid JWK: %w", err)
	}
	if err := VerifyJWS(parsed, pubKey); err != nil {
		return nil, fmt.Errorf("signature verification failed: %w", err)
	}
	return parsed, nil
}

// --- Barrier helpers ---

func (h *Handler) loadAccount(ctx context.Context, id string) (*Account, error) {
	data, err := h.barrier.Get(ctx, h.barrierPrefix()+"accounts/"+id+".json")
	if err != nil || data == nil {
		return nil, errors.New("account not found")
	}
	var acc Account
	return &acc, json.Unmarshal(data, &acc)
}

func (h *Handler) loadOrder(ctx context.Context, id string) (*Order, error) {
	data, err := h.barrier.Get(ctx, h.barrierPrefix()+"orders/"+id+".json")
	if err != nil || data == nil {
		return nil, errors.New("order not found")
	}
	var order Order
	return &order, json.Unmarshal(data, &order)
}

func (h *Handler) loadAuthz(ctx context.Context, id string) (*Authorization, error) {
	data, err := h.barrier.Get(ctx, h.barrierPrefix()+"authz/"+id+".json")
	if err != nil || data == nil {
		return nil, errors.New("authorization not found")
	}
	var authz Authorization
	return &authz, json.Unmarshal(data, &authz)
}

func (h *Handler) loadChallenge(ctx context.Context, id string) (*Challenge, error) {
	paths, err := h.barrier.List(ctx, h.barrierPrefix()+"challenges/")
	if err != nil {
		return nil, errors.New("challenge not found")
	}
	for _, p := range paths {
		if !strings.Contains(p, id) {
			continue
		}
		data, err := h.barrier.Get(ctx, h.barrierPrefix()+"challenges/"+p)
		if err != nil || data == nil {
			continue
		}
		var chall Challenge
		if err := json.Unmarshal(data, &chall); err != nil {
			continue
		}
		if chall.ID == id {
			return &chall, nil
		}
	}
	return nil, errors.New("challenge not found")
}

func (h *Handler) saveChallenge(ctx context.Context, chall *Challenge) error {
	data, err := json.Marshal(chall)
	if err != nil {
		return err
	}
	return h.barrier.Put(ctx, h.barrierPrefix()+"challenges/"+chall.ID+".json", data)
}

// --- Wire format helpers ---

func (h *Handler) accountToWire(acc *Account) map[string]interface{} {
	return map[string]interface{}{
		"status":  acc.Status,
		"contact": acc.Contact,
		"orders":  h.baseURL + "/acme/" + h.mount + "/account/" + acc.ID + "/orders",
	}
}

func (h *Handler) orderToWire(order *Order) map[string]interface{} {
	authzURLs := make([]string, len(order.AuthzIDs))
	for i, id := range order.AuthzIDs {
		authzURLs[i] = h.authzURL(id)
	}
	m := map[string]interface{}{
		"status":         order.Status,
		"expires":        order.ExpiresAt.Format(time.RFC3339),
		"identifiers":    order.Identifiers,
		"authorizations": authzURLs,
		"finalize":       h.finalizeURL(order.ID),
	}
	if order.CertID != "" {
		m["certificate"] = h.certURL(order.CertID)
	}
	return m
}

func (h *Handler) authzToWire(ctx context.Context, authz *Authorization) map[string]interface{} {
	var challenges []map[string]interface{}
	for _, challID := range authz.ChallengeIDs {
		chall, err := h.loadChallenge(ctx, challID)
		if err != nil {
			continue
		}
		challenges = append(challenges, h.challengeToWire(chall))
	}
	return map[string]interface{}{
		"status":     authz.Status,
		"expires":    authz.ExpiresAt.Format(time.RFC3339),
		"identifier": authz.Identifier,
		"challenges": challenges,
	}
}

func (h *Handler) challengeToWire(chall *Challenge) map[string]interface{} {
	m := map[string]interface{}{
		"type":   chall.Type,
		"status": chall.Status,
		"url":    h.challengeURL(chall.Type, chall.ID),
		"token":  chall.Token,
	}
	if chall.ValidatedAt != nil {
		m["validated"] = chall.ValidatedAt.Format(time.RFC3339)
	}
	if chall.Error != nil {
		m["error"] = chall.Error
	}
	return m
}

// --- Validation helpers ---

func (h *Handler) validateCSRIdentifiers(csr *x509.CertificateRequest, identifiers []Identifier) error {
	// Build expected sets from order.
	expectedDNS := make(map[string]bool)
	expectedIP := make(map[string]bool)
	for _, id := range identifiers {
		switch id.Type {
		case IdentifierDNS:
			expectedDNS[id.Value] = true
		case IdentifierIP:
			expectedIP[id.Value] = true
		}
	}

	// Verify DNS SANs match.
	for _, name := range csr.DNSNames {
		if !expectedDNS[name] {
			return fmt.Errorf("CSR contains unexpected DNS SAN: %s", name)
		}
		delete(expectedDNS, name)
	}
	if len(expectedDNS) > 0 {
		missing := make([]string, 0, len(expectedDNS))
		for k := range expectedDNS {
			missing = append(missing, k)
		}
		return fmt.Errorf("CSR missing DNS SANs: %s", strings.Join(missing, ", "))
	}

	// Verify IP SANs match.
	for _, ip := range csr.IPAddresses {
		ipStr := ip.String()
		if !expectedIP[ipStr] {
			return fmt.Errorf("CSR contains unexpected IP SAN: %s", ipStr)
		}
		delete(expectedIP, ipStr)
	}
	if len(expectedIP) > 0 {
		missing := make([]string, 0, len(expectedIP))
		for k := range expectedIP {
			missing = append(missing, k)
		}
		return fmt.Errorf("CSR missing IP SANs: %s", strings.Join(missing, ", "))
	}
	return nil
}

// --- Misc helpers ---

// newID generates a random URL-safe ID.
func newID() string {
	b := make([]byte, 16)
	rand.Read(b)
	return base64.RawURLEncoding.EncodeToString(b)
}

// newToken generates a random 32-byte base64url-encoded ACME challenge token.
func newToken() string {
	b := make([]byte, 32)
	rand.Read(b)
	return base64.RawURLEncoding.EncodeToString(b)
}

// thumbprintKey returns the JWK thumbprint of a JSON-encoded public key,
// used as the account ID / barrier key.
func thumbprintKey(jwk []byte) string {
	t, err := ThumbprintJWK(jwk)
	if err != nil {
		return newID()
	}
	return t
}

// extractIDFromURL extracts the last path segment after a known prefix.
func extractIDFromURL(url, prefix string) string {
	idx := strings.LastIndex(url, prefix)
	if idx < 0 {
		return ""
	}
	return url[idx+len(prefix):]
}

// readBody reads and returns the full request body.
func readBody(r *http.Request) ([]byte, error) {
	if r.Body == nil {
		return nil, errors.New("empty body")
	}
	defer func() { _ = r.Body.Close() }()
	buf := make([]byte, 0, 4096)
	tmp := make([]byte, 512)
	for {
		n, err := r.Body.Read(tmp)
		buf = append(buf, tmp[:n]...)
		if err != nil {
			break
		}
		if len(buf) > 1<<20 {
			return nil, errors.New("request body too large")
		}
	}
	return buf, nil
}