package api

import (
	"context"
	"encoding/json"
	"errors"
	"log/slog"
	"net/http"
	"net/mail"
	"net/url"
	"strconv"
	"strings"
	"time"

	"github.com/google/uuid"

	"github.com/alchemistkay/guestguard/internal/auth"
	"github.com/alchemistkay/guestguard/internal/domain"
	"github.com/alchemistkay/guestguard/internal/ratelimit"
	"github.com/alchemistkay/guestguard/internal/storage"
)

const refreshCookieName = "gg_refresh"

type authHandler struct {
	logger        *slog.Logger
	users         *storage.UserRepo
	verifications *storage.EmailVerificationRepo
	resets        *storage.PasswordResetRepo
	refreshes     *storage.RefreshTokenRepo
	hasher        *auth.PasswordHasher
	signer        *auth.JWTSigner
	emails        auth.EmailSender
	lockout       *auth.LockoutTracker
	limiter       *ratelimit.Limiter

	publicBaseURL        string
	emailVerificationTTL time.Duration
	passwordResetTTL     time.Duration
	refreshTTL           time.Duration
	cookieDomain         string
	cookieSecure         bool
}

type authHandlerDeps struct {
	Logger        *slog.Logger
	Users         *storage.UserRepo
	Verifications *storage.EmailVerificationRepo
	Resets        *storage.PasswordResetRepo
	Refreshes     *storage.RefreshTokenRepo
	Hasher        *auth.PasswordHasher
	Signer        *auth.JWTSigner
	Emails        auth.EmailSender
	Lockout       *auth.LockoutTracker
	Limiter       *ratelimit.Limiter

	PublicBaseURL        string
	EmailVerificationTTL time.Duration
	PasswordResetTTL     time.Duration
	RefreshTTL           time.Duration
	CookieDomain         string
	CookieSecure         bool
}

func newAuthHandler(d authHandlerDeps) *authHandler {
	return &authHandler{
		logger:               d.Logger,
		users:                d.Users,
		verifications:        d.Verifications,
		resets:               d.Resets,
		refreshes:            d.Refreshes,
		hasher:               d.Hasher,
		signer:               d.Signer,
		emails:               d.Emails,
		lockout:              d.Lockout,
		limiter:              d.Limiter,
		publicBaseURL:        strings.TrimRight(d.PublicBaseURL, "/"),
		emailVerificationTTL: d.EmailVerificationTTL,
		passwordResetTTL:     d.PasswordResetTTL,
		refreshTTL:           d.RefreshTTL,
		cookieDomain:         d.CookieDomain,
		cookieSecure:         d.CookieSecure,
	}
}

// --- request/response types ---

type signupRequest struct {
	Email        string `json:"email"`
	Name         string `json:"name"`
	Password     string `json:"password"`
	AcceptTerms  bool   `json:"accept_terms"`
}

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

type verifyEmailRequest struct {
	Token string `json:"token"`
}

type forgotPasswordRequest struct {
	Email string `json:"email"`
}

type resetPasswordRequest struct {
	Token       string `json:"token"`
	NewPassword string `json:"new_password"`
}

type authSuccess struct {
	AccessToken string       `json:"access_token"`
	ExpiresAt   time.Time    `json:"expires_at"`
	User        *domain.User `json:"user"`
}

// --- handlers ---

// POST /auth/signup
func (h *authHandler) signup(w http.ResponseWriter, r *http.Request) {
	var req signupRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	if _, err := mail.ParseAddress(req.Email); err != nil {
		writeError(w, http.StatusBadRequest, "email is invalid")
		return
	}
	if strings.TrimSpace(req.Name) == "" {
		writeError(w, http.StatusBadRequest, "name is required")
		return
	}
	hash, err := h.hasher.Hash(req.Password)
	if err != nil {
		if errors.Is(err, auth.ErrPasswordTooShort) || errors.Is(err, auth.ErrPasswordTooLong) {
			writeError(w, http.StatusBadRequest, err.Error())
			return
		}
		h.logger.Error("hash password", "err", err)
		writeError(w, http.StatusInternalServerError, "failed to create user")
		return
	}

	u, err := h.users.Create(r.Context(), storage.CreateUserParams{
		Email:        req.Email,
		Name:         req.Name,
		PasswordHash: hash,
		AcceptTerms:  req.AcceptTerms,
	})
	if err != nil {
		if errors.Is(err, domain.ErrEmailTaken) {
			// Don't leak which addresses are registered. Still return 201 and
			// trigger a "if-you-already-have-an-account" email asynchronously
			// (skipped for the stub). On real auth this should send a "you
			// tried to sign up again, here's a reset link" email.
			h.logger.Info("signup attempted with existing email", "email", req.Email)
			writeJSON(w, http.StatusCreated, map[string]string{"status": "verification_sent"})
			return
		}
		h.logger.Error("create user", "err", err)
		writeError(w, http.StatusInternalServerError, "failed to create user")
		return
	}

	if err := h.sendVerificationEmail(r.Context(), u); err != nil {
		h.logger.Error("send verification email", "err", err, "user_id", u.ID)
		// Don't fail the signup — user can request a resend.
	}
	writeJSON(w, http.StatusCreated, map[string]string{"status": "verification_sent"})
}

// POST /auth/login
func (h *authHandler) login(w http.ResponseWriter, r *http.Request) {
	var req loginRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	if req.Email == "" || req.Password == "" {
		writeError(w, http.StatusBadRequest, "email and password required")
		return
	}

	// Per-(IP + email) sliding-window — 10 per 5 minutes per the plan.
	if !h.checkRate(w, r, "login", clientIP(r)+"|"+strings.ToLower(strings.TrimSpace(req.Email)),
		10, 5*time.Minute) {
		return
	}

	u, err := h.users.GetByEmail(r.Context(), req.Email)
	if err != nil || u.PasswordHash == "" {
		_, _ = h.lockout.RecordFailure(r.Context(), req.Email, nil)
		writeError(w, http.StatusUnauthorized, "invalid email or password")
		return
	}

	// If the account is already locked, reject before doing a bcrypt compare.
	locked, _ := h.lockout.IsLocked(r.Context(), u.ID)
	if locked {
		writeError(w, http.StatusForbidden, "account locked — reset your password to unlock")
		return
	}

	if err := h.hasher.Verify(u.PasswordHash, req.Password); err != nil {
		locked, _ := h.lockout.RecordFailure(r.Context(), req.Email, &u.ID)
		if locked {
			writeError(w, http.StatusForbidden, "account locked — reset your password to unlock")
			return
		}
		writeError(w, http.StatusUnauthorized, "invalid email or password")
		return
	}
	if !u.EmailVerified {
		writeError(w, http.StatusForbidden, "email not verified")
		return
	}

	h.lockout.ClearOnSuccess(r.Context(), req.Email)
	if err := h.issueSession(w, r, u); err != nil {
		h.logger.Error("issue session", "err", err, "user_id", u.ID)
		writeError(w, http.StatusInternalServerError, "failed to start session")
		return
	}
}

// checkRate consults the limiter (when one is configured) and writes a 429
// response if the budget is exhausted. Returns false if the caller should
// stop handling the request.
func (h *authHandler) checkRate(w http.ResponseWriter, r *http.Request, name, key string, limit int, window time.Duration) bool {
	if h.limiter == nil || key == "" {
		return true
	}
	res, err := h.limiter.Allow(r.Context(), name, key, limit, window)
	if err != nil {
		h.logger.Warn("ratelimit error (failing open)", "rule", name, "err", err)
		return true
	}
	if !res.Allowed {
		retry := int(res.RetryAfter.Round(time.Second).Seconds())
		if retry < 1 {
			retry = 1
		}
		w.Header().Set("Retry-After", strconv.Itoa(retry))
		writeJSON(w, http.StatusTooManyRequests, map[string]any{
			"error":       "rate limit exceeded",
			"retry_after": retry,
		})
		return false
	}
	return true
}

// POST /auth/refresh
func (h *authHandler) refresh(w http.ResponseWriter, r *http.Request) {
	cookie, err := r.Cookie(refreshCookieName)
	if err != nil || cookie.Value == "" {
		writeError(w, http.StatusUnauthorized, "missing refresh token")
		return
	}
	oldHash := auth.HashOpaque(cookie.Value)

	existing, err := h.refreshes.Get(r.Context(), oldHash)
	if err != nil {
		if errors.Is(err, domain.ErrAuthTokenNotFound) {
			h.clearRefreshCookie(w)
			writeError(w, http.StatusUnauthorized, "invalid refresh token")
			return
		}
		h.logger.Error("lookup refresh", "err", err)
		writeError(w, http.StatusInternalServerError, "refresh failed")
		return
	}
	if existing.RevokedAt != nil {
		// Replay of a revoked token. Revoke the family.
		_ = h.refreshes.RevokeAllForUser(r.Context(), existing.UserID)
		h.clearRefreshCookie(w)
		writeError(w, http.StatusUnauthorized, "refresh token reused")
		return
	}
	if time.Now().After(existing.ExpiresAt) {
		h.clearRefreshCookie(w)
		writeError(w, http.StatusUnauthorized, "refresh token expired")
		return
	}

	u, err := h.users.GetByID(r.Context(), existing.UserID)
	if err != nil {
		h.clearRefreshCookie(w)
		writeError(w, http.StatusUnauthorized, "user not found")
		return
	}

	newRaw, newHash, err := auth.NewOpaqueToken()
	if err != nil {
		h.logger.Error("mint refresh", "err", err)
		writeError(w, http.StatusInternalServerError, "refresh failed")
		return
	}
	exp := time.Now().Add(h.refreshTTL)
	if err := h.refreshes.Rotate(r.Context(), oldHash, storage.CreateRefreshTokenParams{
		Hash:      newHash,
		UserID:    u.ID,
		ExpiresAt: exp,
		UserAgent: r.UserAgent(),
		IPAddress: clientIP(r),
	}); err != nil {
		if errors.Is(err, domain.ErrRefreshTokenRevoked) {
			h.clearRefreshCookie(w)
			writeError(w, http.StatusUnauthorized, "refresh token reused")
			return
		}
		h.logger.Error("rotate refresh", "err", err)
		writeError(w, http.StatusInternalServerError, "refresh failed")
		return
	}

	access, accessExp, err := h.signer.Issue(u.ID, time.Now())
	if err != nil {
		h.logger.Error("sign access", "err", err)
		writeError(w, http.StatusInternalServerError, "refresh failed")
		return
	}
	h.setRefreshCookie(w, newRaw, exp)
	writeJSON(w, http.StatusOK, authSuccess{
		AccessToken: access,
		ExpiresAt:   accessExp,
		User:        u,
	})
}

// POST /auth/logout
func (h *authHandler) logout(w http.ResponseWriter, r *http.Request) {
	cookie, err := r.Cookie(refreshCookieName)
	if err == nil && cookie.Value != "" {
		_ = h.refreshes.Revoke(r.Context(), auth.HashOpaque(cookie.Value))
	}
	h.clearRefreshCookie(w)
	w.WriteHeader(http.StatusNoContent)
}

// POST /auth/verify-email
func (h *authHandler) verifyEmail(w http.ResponseWriter, r *http.Request) {
	var req verifyEmailRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil || req.Token == "" {
		writeError(w, http.StatusBadRequest, "token required")
		return
	}
	uid, err := h.verifications.Consume(r.Context(), auth.HashOpaque(req.Token))
	if err != nil {
		switch {
		case errors.Is(err, domain.ErrAuthTokenNotFound):
			writeError(w, http.StatusBadRequest, "invalid token")
		case errors.Is(err, domain.ErrAuthTokenConsumed):
			writeError(w, http.StatusBadRequest, "token already used")
		case errors.Is(err, domain.ErrAuthTokenExpired):
			writeError(w, http.StatusBadRequest, "token expired")
		default:
			h.logger.Error("consume verification", "err", err)
			writeError(w, http.StatusInternalServerError, "verification failed")
		}
		return
	}
	if err := h.users.MarkEmailVerified(r.Context(), uid); err != nil {
		h.logger.Error("mark verified", "err", err, "user_id", uid)
		writeError(w, http.StatusInternalServerError, "verification failed")
		return
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "verified"})
}

// POST /auth/forgot-password
func (h *authHandler) forgotPassword(w http.ResponseWriter, r *http.Request) {
	var req forgotPasswordRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	if !h.checkRate(w, r, "forgot_password", clientIP(r)+"|"+strings.ToLower(strings.TrimSpace(req.Email)),
		3, time.Hour) {
		return
	}
	// Always respond 202 to avoid leaking whether the email exists.
	defer func() { writeJSON(w, http.StatusAccepted, map[string]string{"status": "if_known_email_sent"}) }()

	u, err := h.users.GetByEmail(r.Context(), req.Email)
	if err != nil {
		return
	}
	raw, hash, err := auth.NewOpaqueToken()
	if err != nil {
		h.logger.Error("mint reset", "err", err)
		return
	}
	exp := time.Now().Add(h.passwordResetTTL)
	if err := h.resets.Create(r.Context(), u.ID, hash, exp); err != nil {
		h.logger.Error("persist reset", "err", err)
		return
	}
	link := h.publicBaseURL + "/reset-password/" + url.PathEscape(raw)
	if err := h.emails.SendPasswordReset(r.Context(), u.Email, u.Name, link); err != nil {
		h.logger.Error("send reset email", "err", err)
	}
}

// POST /auth/reset-password
func (h *authHandler) resetPassword(w http.ResponseWriter, r *http.Request) {
	var req resetPasswordRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil || req.Token == "" {
		writeError(w, http.StatusBadRequest, "token and new_password required")
		return
	}
	newHash, err := h.hasher.Hash(req.NewPassword)
	if err != nil {
		if errors.Is(err, auth.ErrPasswordTooShort) || errors.Is(err, auth.ErrPasswordTooLong) {
			writeError(w, http.StatusBadRequest, err.Error())
			return
		}
		h.logger.Error("hash password", "err", err)
		writeError(w, http.StatusInternalServerError, "reset failed")
		return
	}
	uid, err := h.resets.Consume(r.Context(), auth.HashOpaque(req.Token))
	if err != nil {
		switch {
		case errors.Is(err, domain.ErrAuthTokenNotFound):
			writeError(w, http.StatusBadRequest, "invalid token")
		case errors.Is(err, domain.ErrAuthTokenConsumed):
			writeError(w, http.StatusBadRequest, "token already used")
		case errors.Is(err, domain.ErrAuthTokenExpired):
			writeError(w, http.StatusBadRequest, "token expired")
		default:
			h.logger.Error("consume reset", "err", err)
			writeError(w, http.StatusInternalServerError, "reset failed")
		}
		return
	}
	if err := h.users.UpdatePasswordHash(r.Context(), uid, newHash); err != nil {
		h.logger.Error("update password", "err", err, "user_id", uid)
		writeError(w, http.StatusInternalServerError, "reset failed")
		return
	}
	// Invalidate all existing sessions.
	_ = h.refreshes.RevokeAllForUser(r.Context(), uid)
	// Resetting the password is the canonical "unlock" path for the
	// account lockout that triggers after repeated bad-credential attempts.
	if u, err := h.users.GetByID(r.Context(), uid); err == nil {
		_ = h.lockout.ClearForUser(r.Context(), uid, u.Email)
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "password_reset"})
}

// --- helpers ---

func (h *authHandler) sendVerificationEmail(ctx context.Context, u *domain.User) error {
	raw, hash, err := auth.NewOpaqueToken()
	if err != nil {
		return err
	}
	if err := h.verifications.Create(ctx, u.ID, hash, time.Now().Add(h.emailVerificationTTL)); err != nil {
		return err
	}
	link := h.publicBaseURL + "/verify-email?token=" + url.QueryEscape(raw)
	return h.emails.SendVerification(ctx, u.Email, u.Name, link)
}

func (h *authHandler) issueSession(w http.ResponseWriter, r *http.Request, u *domain.User) error {
	access, accessExp, err := h.signer.Issue(u.ID, time.Now())
	if err != nil {
		return err
	}
	raw, hash, err := auth.NewOpaqueToken()
	if err != nil {
		return err
	}
	refreshExp := time.Now().Add(h.refreshTTL)
	if err := h.refreshes.Create(r.Context(), storage.CreateRefreshTokenParams{
		Hash:      hash,
		UserID:    u.ID,
		ExpiresAt: refreshExp,
		UserAgent: r.UserAgent(),
		IPAddress: clientIP(r),
	}); err != nil {
		return err
	}
	h.setRefreshCookie(w, raw, refreshExp)
	writeJSON(w, http.StatusOK, authSuccess{
		AccessToken: access,
		ExpiresAt:   accessExp,
		User:        u,
	})
	return nil
}

func (h *authHandler) setRefreshCookie(w http.ResponseWriter, value string, expires time.Time) {
	http.SetCookie(w, &http.Cookie{
		Name:     refreshCookieName,
		Value:    value,
		Path:     "/auth",
		Domain:   h.cookieDomain,
		Expires:  expires,
		MaxAge:   int(time.Until(expires).Seconds()),
		HttpOnly: true,
		Secure:   h.cookieSecure,
		SameSite: http.SameSiteLaxMode,
	})
}

func (h *authHandler) clearRefreshCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{
		Name:     refreshCookieName,
		Value:    "",
		Path:     "/auth",
		Domain:   h.cookieDomain,
		MaxAge:   -1,
		HttpOnly: true,
		Secure:   h.cookieSecure,
		SameSite: http.SameSiteLaxMode,
	})
}

// --- requireAuth middleware ---

type ctxKey int

const userIDCtxKey ctxKey = iota

func UserIDFromContext(ctx context.Context) (uuid.UUID, bool) {
	v, ok := ctx.Value(userIDCtxKey).(uuid.UUID)
	return v, ok
}

func requireAuth(signer *auth.JWTSigner) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			h := r.Header.Get("Authorization")
			if !strings.HasPrefix(h, "Bearer ") {
				writeError(w, http.StatusUnauthorized, "missing bearer token")
				return
			}
			raw := strings.TrimSpace(strings.TrimPrefix(h, "Bearer "))
			claims, err := signer.Parse(raw)
			if err != nil {
				if errors.Is(err, auth.ErrExpiredJWT) {
					writeError(w, http.StatusUnauthorized, "token expired")
					return
				}
				writeError(w, http.StatusUnauthorized, "invalid token")
				return
			}
			ctx := context.WithValue(r.Context(), userIDCtxKey, claims.UserID)
			next.ServeHTTP(w, r.WithContext(ctx))
		})
	}
}