package customerauth

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"net/mail"
	"net/url"
	"strconv"
	"strings"
	"time"

	"git.k6n.net/mats/go-cart-actor/pkg/actor"
	"git.k6n.net/mats/go-cart-actor/pkg/profile"
	messages "git.k6n.net/mats/go-cart-actor/proto/profile"
	"google.golang.org/protobuf/proto"
)

// minPasswordLen is the minimum accepted password length at registration and
// password reset.
const minPasswordLen = 8

// Token lifetimes for the email-verification and password-reset links.
const (
	verifyTokenTTL = 24 * time.Hour
	resetTokenTTL  = 1 * time.Hour
)

// Storefront paths (appended to Options.BaseURL) that the verification and reset
// links point at. The page reads the token from the query string and POSTs it
// back to /verify or /reset.
const (
	verifyLinkPath = "/account/verify"
	resetLinkPath  = "/account/reset"
)

// ProfileApplier is the subset of the profile grain pool the auth server needs.
// The pool (and the UCP adapter's ProfileApplier) already satisfies it.
type ProfileApplier interface {
	Get(ctx context.Context, id uint64) (*profile.ProfileGrain, error)
	Apply(ctx context.Context, id uint64, mutation ...proto.Message) (*actor.MutationResult[profile.ProfileGrain], error)
}

// Server exposes password signup/login, email verification, password reset and
// identity-linking over HTTP, backed by the credential store (email→id+hash) and
// the profile grain pool.
type Server struct {
	store           Credentials
	applier         ProfileApplier
	signer          *Signer
	ttl             time.Duration
	limiter         Limiter
	notifier        Notifier
	baseURL         string
	requireVerified bool
}

// Options configures optional auth-server behavior. The zero value is valid: an
// in-memory login limiter (5 failures / 15m), a logging notifier, and no
// verified-email requirement for login.
type Options struct {
	// Limiter throttles failed logins and reset requests. Nil installs a default
	// in-memory limiter (5 failures / 15m). Inject a RedisLoginLimiter for a
	// horizontally-scaled deployment.
	Limiter Limiter
	// Notifier delivers verification and reset links. Nil installs LogNotifier.
	Notifier Notifier
	// BaseURL is the public origin used to build links in messages, e.g.
	// "https://shop.tornberg.me". The verify/reset paths are appended to it.
	BaseURL string
	// RequireVerifiedEmail, when true, blocks login until the email is verified.
	// Off by default so pre-existing accounts (which carry no verification
	// record) keep working.
	RequireVerifiedEmail bool
}

// NewServer builds an auth server. ttl<=0 falls back to DefaultSessionTTL.
func NewServer(store Credentials, applier ProfileApplier, signer *Signer, ttl time.Duration, opts Options) *Server {
	if ttl <= 0 {
		ttl = DefaultSessionTTL
	}
	if opts.Limiter == nil {
		opts.Limiter = NewLoginLimiter(0, 0)
	}
	if opts.Notifier == nil {
		opts.Notifier = LogNotifier{}
	}
	return &Server{
		store:           store,
		applier:         applier,
		signer:          signer,
		ttl:             ttl,
		limiter:         opts.Limiter,
		notifier:        opts.Notifier,
		baseURL:         strings.TrimRight(opts.BaseURL, "/"),
		requireVerified: opts.RequireVerifiedEmail,
	}
}

// Handler returns the router for the auth endpoints. Mount it under /ucp/v1/auth
// (the prefix is stripped by the caller).
func (s *Server) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("POST /register", s.handleRegister)
	mux.HandleFunc("POST /login", s.handleLogin)
	mux.HandleFunc("POST /logout", s.handleLogout)
	mux.HandleFunc("GET /me", s.handleMe)
	mux.HandleFunc("POST /verify-request", s.handleVerifyRequest)
	mux.HandleFunc("POST /verify", s.handleVerify)
	mux.HandleFunc("POST /reset-request", s.handleResetRequest)
	mux.HandleFunc("POST /reset", s.handleResetComplete)
	mux.HandleFunc("POST /link-cart", s.handleLinkCart)
	mux.HandleFunc("POST /link-checkout", s.handleLinkCheckout)
	mux.HandleFunc("POST /link-order", s.handleLinkOrder)
	return mux
}

// ---------------------------------------------------------------------------
// Request/response payloads
// ---------------------------------------------------------------------------

type registerRequest struct {
	Email    string `json:"email"`
	Password string `json:"password"`
	Name     string `json:"name,omitempty"`
	Phone    string `json:"phone,omitempty"`
}

type loginRequest struct {
	Email    string `json:"email"`
	Password string `json:"password"`
}

type linkCartRequest struct {
	CartID string `json:"cartId"`
}

type linkCheckoutRequest struct {
	CheckoutID string `json:"checkoutId"`
	CartID     string `json:"cartId"`
}

type linkOrderRequest struct {
	OrderReference string `json:"orderReference"`
	CartID         string `json:"cartId"`
	Status         string `json:"status,omitempty"`
}

// tokenRequest carries a verification token.
type tokenRequest struct {
	Token string `json:"token"`
}

// resetRequest asks for a password-reset link to be sent to an email.
type resetRequest struct {
	Email string `json:"email"`
}

// resetCompleteRequest carries a reset token and the new password.
type resetCompleteRequest struct {
	Token    string `json:"token"`
	Password string `json:"password"`
}

// EmailPreferencesResponse mirrors the UCP email preferences type for the
// customer-facing API.
type EmailPreferencesResponse struct {
	OrderEmails     *bool `json:"orderEmails,omitempty"`
	MarketingEmails *bool `json:"marketingEmails,omitempty"`
}

// CustomerResponse mirrors the UCP customer projection (kept local to avoid an
// import cycle with internal/ucp). The password hash is never included.
type CustomerResponse struct {
	ID        string            `json:"id"`
	Name      string            `json:"name,omitempty"`
	Email     string            `json:"email,omitempty"`
	Phone     string            `json:"phone,omitempty"`
	Language  string            `json:"language,omitempty"`
	Currency  string            `json:"currency,omitempty"`
	AvatarURL string            `json:"avatarUrl,omitempty"`
	Addresses []AddressResponse `json:"addresses"`
	Orders    []OrderRef        `json:"orders"`

	// EmailPreferences carries the customer's current email opt-in/out state.
	EmailPreferences *EmailPreferencesResponse `json:"emailPreferences,omitempty"`

	// EmailVerified reflects whether the email-verification flow has completed.
	EmailVerified bool `json:"emailVerified"`
}

type AddressResponse struct {
	ID                uint32 `json:"id"`
	Label             string `json:"label,omitempty"`
	FullName          string `json:"fullName,omitempty"`
	AddressLine1      string `json:"addressLine1"`
	AddressLine2      string `json:"addressLine2,omitempty"`
	City              string `json:"city"`
	Zip               string `json:"zip"`
	Country           string `json:"country"`
	IsDefaultShipping bool   `json:"isDefaultShipping,omitempty"`
	IsDefaultBilling  bool   `json:"isDefaultBilling,omitempty"`
}

type OrderRef struct {
	OrderReference string `json:"orderReference"`
	Status         string `json:"status,omitempty"`
}

// ---------------------------------------------------------------------------
// Handlers
// ---------------------------------------------------------------------------

func (s *Server) handleRegister(w http.ResponseWriter, r *http.Request) {
	var req registerRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeErr(w, http.StatusBadRequest, "invalid request body")
		return
	}
	email := NormalizeEmail(req.Email)
	if !validEmail(email) {
		writeErr(w, http.StatusBadRequest, "a valid email is required")
		return
	}
	if len(req.Password) < minPasswordLen {
		writeErr(w, http.StatusBadRequest, "password must be at least 8 characters")
		return
	}
	if _, exists := s.store.Get(r.Context(), email); exists {
		writeErr(w, http.StatusConflict, "an account with this email already exists")
		return
	}

	hash, err := HashPassword(req.Password)
	if err != nil {
		writeErr(w, http.StatusInternalServerError, "could not hash password")
		return
	}

	rawID, err := profile.NewProfileId()
	if err != nil {
		writeErr(w, http.StatusInternalServerError, "could not generate id")
		return
	}
	id := uint64(rawID)

	set := &messages.SetProfile{Email: &email}
	if req.Name != "" {
		set.Name = &req.Name
	}
	if req.Phone != "" {
		set.Phone = &req.Phone
	}
	if _, err := s.applier.Apply(r.Context(), id, set); err != nil {
		writeErr(w, http.StatusInternalServerError, "could not create profile")
		return
	}

	// Persist the credential only after the profile is created. If this fails
	// the profile exists but is unreachable by login — acceptable and rare.
	if err := s.store.Register(r.Context(), email, id, hash, time.Now().UTC().Format(time.RFC3339)); err != nil {
		if err == ErrEmailExists {
			writeErr(w, http.StatusConflict, "an account with this email already exists")
			return
		}
		writeErr(w, http.StatusInternalServerError, "could not store credentials")
		return
	}

	// Send the verification link (best-effort, via the configured notifier).
	s.sendVerification(email)

	s.issueSession(w, r, id)
	s.writeCustomer(w, r, http.StatusCreated, rawID.String(), id)
}

func (s *Server) handleLogin(w http.ResponseWriter, r *http.Request) {
	var req loginRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeErr(w, http.StatusBadRequest, "invalid request body")
		return
	}
	key := NormalizeEmail(req.Email)
	if ok, retry := s.limiter.Allowed(r.Context(), key); !ok {
		w.Header().Set("Retry-After", strconv.Itoa(int(retry.Seconds())+1))
		writeErr(w, http.StatusTooManyRequests, "too many attempts, try again later")
		return
	}
	rec, ok := s.store.Get(r.Context(), req.Email)
	// Always run a verify (even on miss, against the stored hash if present) and
	// return a single generic error so the response does not reveal whether the
	// email exists.
	if !ok || !VerifyPassword(req.Password, rec.Hash) {
		s.limiter.RecordFailure(r.Context(), key)
		writeErr(w, http.StatusUnauthorized, "invalid email or password")
		return
	}
	if s.requireVerified && rec.VerifiedAt == "" {
		writeErr(w, http.StatusForbidden, "email not verified")
		return
	}
	s.limiter.Reset(r.Context(), key)
	s.issueSession(w, r, rec.ProfileID)
	s.writeCustomer(w, r, http.StatusOK, profile.ProfileId(rec.ProfileID).String(), rec.ProfileID)
}

func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
	ClearSession(w, r)
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (s *Server) handleMe(w http.ResponseWriter, r *http.Request) {
	id, ok := s.requireSession(w, r)
	if !ok {
		return
	}
	s.writeCustomer(w, r, http.StatusOK, profile.ProfileId(id).String(), id)
}

// handleVerifyRequest re-sends the email-verification link for the logged-in
// customer. Requires a session so it can't be used to enumerate addresses.
func (s *Server) handleVerifyRequest(w http.ResponseWriter, r *http.Request) {
	id, ok := s.requireSession(w, r)
	if !ok {
		return
	}
	g, err := s.applier.Get(r.Context(), id)
	if err != nil || g.Email == "" {
		writeErr(w, http.StatusInternalServerError, "could not read profile")
		return
	}
	s.sendVerification(NormalizeEmail(g.Email))
	writeJSON(w, http.StatusOK, map[string]string{"status": "sent"})
}

// handleVerify consumes a verification token and marks the email verified. An
// unknown subject still returns success so the endpoint reveals nothing.
func (s *Server) handleVerify(w http.ResponseWriter, r *http.Request) {
	var req tokenRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeErr(w, http.StatusBadRequest, "invalid request body")
		return
	}
	email, err := s.signer.ParsePurpose(purposeVerifyEmail, req.Token)
	if err != nil {
		writeErr(w, http.StatusBadRequest, "invalid or expired token")
		return
	}
	if _, err := s.store.MarkVerified(r.Context(), email, time.Now().UTC().Format(time.RFC3339)); err != nil {
		writeErr(w, http.StatusInternalServerError, "could not record verification")
		return
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "verified"})
}

// handleResetRequest issues a password-reset link for a registered email. It
// always returns 200 (whether or not the email exists) so it never reveals
// account existence, and is rate-limited per email to prevent mail-bombing.
func (s *Server) handleResetRequest(w http.ResponseWriter, r *http.Request) {
	var req resetRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeErr(w, http.StatusBadRequest, "invalid request body")
		return
	}
	email := NormalizeEmail(req.Email)
	limiterKey := "reset:" + email
	if ok, retry := s.limiter.Allowed(r.Context(), limiterKey); !ok {
		w.Header().Set("Retry-After", strconv.Itoa(int(retry.Seconds())+1))
		writeErr(w, http.StatusTooManyRequests, "too many requests, try again later")
		return
	}
	if _, exists := s.store.Get(r.Context(), email); exists {
		token := s.signer.IssuePurpose(purposePasswordReset, email, resetTokenTTL)
		s.notifier.SendPasswordReset(email, s.link(resetLinkPath, token))
	}
	s.limiter.RecordFailure(r.Context(), limiterKey)
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

// handleResetComplete consumes a reset token and replaces the password hash.
func (s *Server) handleResetComplete(w http.ResponseWriter, r *http.Request) {
	var req resetCompleteRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeErr(w, http.StatusBadRequest, "invalid request body")
		return
	}
	if len(req.Password) < minPasswordLen {
		writeErr(w, http.StatusBadRequest, "password must be at least 8 characters")
		return
	}
	email, err := s.signer.ParsePurpose(purposePasswordReset, req.Token)
	if err != nil {
		writeErr(w, http.StatusBadRequest, "invalid or expired token")
		return
	}
	hash, err := HashPassword(req.Password)
	if err != nil {
		writeErr(w, http.StatusInternalServerError, "could not hash password")
		return
	}
	found, err := s.store.UpdateHash(r.Context(), email, hash)
	if err != nil {
		writeErr(w, http.StatusInternalServerError, "could not update password")
		return
	}
	if !found {
		// Token signed for an email no longer present.
		writeErr(w, http.StatusBadRequest, "invalid or expired token")
		return
	}
	s.limiter.Reset(r.Context(), NormalizeEmail(email))
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (s *Server) handleLinkCart(w http.ResponseWriter, r *http.Request) {
	id, ok := s.requireSession(w, r)
	if !ok {
		return
	}
	var req linkCartRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeErr(w, http.StatusBadRequest, "invalid request body")
		return
	}
	cartID, ok := parseBase62(req.CartID)
	if !ok {
		writeErr(w, http.StatusBadRequest, "invalid cartId")
		return
	}
	if _, err := s.applier.Apply(r.Context(), id, &messages.LinkCart{CartId: cartID, Label: "current cart"}); err != nil {
		writeErr(w, http.StatusInternalServerError, "could not link cart")
		return
	}
	s.writeCustomer(w, r, http.StatusOK, profile.ProfileId(id).String(), id)
}

func (s *Server) handleLinkCheckout(w http.ResponseWriter, r *http.Request) {
	id, ok := s.requireSession(w, r)
	if !ok {
		return
	}
	var req linkCheckoutRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeErr(w, http.StatusBadRequest, "invalid request body")
		return
	}
	checkoutID, ok := parseBase62(req.CheckoutID)
	if !ok {
		writeErr(w, http.StatusBadRequest, "invalid checkoutId")
		return
	}
	cartID, _ := parseBase62(req.CartID)
	if _, err := s.applier.Apply(r.Context(), id, &messages.LinkCheckout{CheckoutId: checkoutID, CartId: cartID}); err != nil {
		writeErr(w, http.StatusInternalServerError, "could not link checkout")
		return
	}
	s.writeCustomer(w, r, http.StatusOK, profile.ProfileId(id).String(), id)
}

func (s *Server) handleLinkOrder(w http.ResponseWriter, r *http.Request) {
	id, ok := s.requireSession(w, r)
	if !ok {
		return
	}
	var req linkOrderRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeErr(w, http.StatusBadRequest, "invalid request body")
		return
	}
	if strings.TrimSpace(req.OrderReference) == "" {
		writeErr(w, http.StatusBadRequest, "orderReference is required")
		return
	}
	cartID, _ := parseBase62(req.CartID)
	if _, err := s.applier.Apply(r.Context(), id, &messages.LinkOrder{
		OrderReference: req.OrderReference,
		CartId:         cartID,
		Status:         req.Status,
	}); err != nil {
		writeErr(w, http.StatusInternalServerError, "could not link order")
		return
	}
	s.writeCustomer(w, r, http.StatusOK, profile.ProfileId(id).String(), id)
}

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

func (s *Server) issueSession(w http.ResponseWriter, r *http.Request, id uint64) {
	SetSession(w, r, s.signer.Issue(id, s.ttl), s.ttl)
}

// sendVerification mints a verification token for email and hands the link to
// the notifier. email must already be normalized.
func (s *Server) sendVerification(email string) {
	token := s.signer.IssuePurpose(purposeVerifyEmail, email, verifyTokenTTL)
	s.notifier.SendEmailVerification(email, s.link(verifyLinkPath, token))
}

// link builds an absolute link to a storefront path carrying the token as a
// query parameter. With no configured BaseURL it returns a relative link.
func (s *Server) link(path, token string) string {
	return fmt.Sprintf("%s%s?token=%s", s.baseURL, path, url.QueryEscape(token))
}

// requireSession reads and validates the session cookie, writing 401 on
// failure. It returns the profile id and whether a valid session was present.
func (s *Server) requireSession(w http.ResponseWriter, r *http.Request) (uint64, bool) {
	c, err := r.Cookie(SessionCookieName)
	if err != nil || c.Value == "" {
		writeErr(w, http.StatusUnauthorized, "not authenticated")
		return 0, false
	}
	id, err := s.signer.Parse(c.Value)
	if err != nil {
		writeErr(w, http.StatusUnauthorized, "not authenticated")
		return 0, false
	}
	return id, true
}

// writeCustomer loads the profile grain and writes it as a CustomerResponse.
func (s *Server) writeCustomer(w http.ResponseWriter, r *http.Request, status int, idStr string, id uint64) {
	g, err := s.applier.Get(r.Context(), id)
	if err != nil {
		writeErr(w, http.StatusInternalServerError, "could not read profile")
		return
	}
	resp := grainToCustomer(idStr, g)
	if rec, ok := s.store.Get(r.Context(), g.Email); ok {
		resp.EmailVerified = rec.VerifiedAt != ""
	}
	writeJSON(w, status, resp)
}

func grainToCustomer(id string, g *profile.ProfileGrain) CustomerResponse {
	resp := CustomerResponse{
		ID:        id,
		Name:      g.Name,
		Email:     g.Email,
		Phone:     g.Phone,
		Language:  g.Language,
		Currency:  g.Currency,
		AvatarURL: g.AvatarUrl,
		Addresses: make([]AddressResponse, 0, len(g.Addresses)),
		Orders:    make([]OrderRef, 0, len(g.Orders)),
	}
	for _, a := range g.Addresses {
		resp.Addresses = append(resp.Addresses, AddressResponse{
			ID:                a.Id,
			Label:             a.Label,
			FullName:          a.FullName,
			AddressLine1:      a.AddressLine1,
			AddressLine2:      a.AddressLine2,
			City:              a.City,
			Zip:               a.Zip,
			Country:           a.Country,
			IsDefaultShipping: a.IsDefaultShipping,
			IsDefaultBilling:  a.IsDefaultBilling,
		})
	}
	for _, o := range g.Orders {
		resp.Orders = append(resp.Orders, OrderRef{OrderReference: o.OrderReference, Status: o.Status})
	}
	if g.EmailPreferences != nil {
		resp.EmailPreferences = &EmailPreferencesResponse{
			OrderEmails:     g.EmailPreferences.OrderEmails,
			MarketingEmails: g.EmailPreferences.MarketingEmails,
		}
	}
	return resp
}

// parseBase62 decodes a base62 id (cart/checkout/profile share the scheme).
func parseBase62(s string) (uint64, bool) {
	if s == "" {
		return 0, false
	}
	id, ok := profile.ParseProfileId(s)
	return uint64(id), ok
}

func validEmail(email string) bool {
	if email == "" {
		return false
	}
	_, err := mail.ParseAddress(email)
	return err == nil
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

func writeErr(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, map[string]string{"error": msg})
}