package server

import (
	"context"
	"crypto/subtle"
	"errors"
	"net/http"
	"strings"
	"sync"
	"time"

	"steward/internal/api"
	"steward/internal/auth"
	"steward/internal/model"
	"steward/internal/store"
	"steward/internal/version"
)

const (
	sessionCookie = "steward_session"
	csrfHeader    = "X-CSRF-Token"
)

// rateLimiter limits failed logins and token attempts per key (address or
// user name) over a sliding window.
type rateLimiter struct {
	mu   sync.Mutex
	hits map[string][]time.Time
}

func newRateLimiter() *rateLimiter { return &rateLimiter{hits: map[string][]time.Time{}} }

const (
	failWindow  = 15 * time.Minute
	failsPerIP  = 20
	failsPerKey = 8
)

func (l *rateLimiter) recent(key string, now time.Time) []time.Time {
	var keep []time.Time
	for _, t := range l.hits[key] {
		if now.Sub(t) < failWindow {
			keep = append(keep, t)
		}
	}
	l.hits[key] = keep
	return keep
}

func (l *rateLimiter) blocked(key string, max int) bool {
	l.mu.Lock()
	defer l.mu.Unlock()
	return len(l.recent(key, time.Now())) >= max
}

func (l *rateLimiter) fail(keys ...string) {
	l.mu.Lock()
	defer l.mu.Unlock()
	now := time.Now()
	for _, k := range keys {
		l.hits[k] = append(l.recent(k, now), now)
	}
}

func (l *rateLimiter) reset(key string) {
	l.mu.Lock()
	defer l.mu.Unlock()
	delete(l.hits, key)
}

func (l *rateLimiter) cleanup() {
	l.mu.Lock()
	defer l.mu.Unlock()
	now := time.Now()
	for k := range l.hits {
		if len(l.recent(k, now)) == 0 {
			delete(l.hits, k)
		}
	}
}

var errUnauthenticated = &httpError{http.StatusUnauthorized, "unauthenticated", "authentication required: log in, or send an API token as 'Authorization: Bearer steward_...'"}

// authenticate identifies the caller: the local socket's peer, a bearer
// token or a session cookie (with the CSRF token for changes).
func (s *Server) authenticate(r *http.Request) (*auth.Principal, *model.Session, error) {
	ip := s.clientIP(r)
	if pr := peerOf(r.Context()); pr != nil && r.Header.Get("Authorization") == "" {
		if trustedUID(pr.UID) {
			return socketPrincipal(pr, r.UserAgent()), nil, nil
		}
		return nil, nil, socketDenied(pr)
	}
	if h := r.Header.Get("Authorization"); h != "" {
		scheme, tok, _ := strings.Cut(h, " ")
		if !strings.EqualFold(scheme, "Bearer") {
			return nil, nil, &httpError{http.StatusUnauthorized, "unauthenticated", "unsupported authorization scheme (use Bearer with an API token)"}
		}
		if s.limiter.blocked("ip:"+ip, failsPerIP) {
			return nil, nil, &httpError{http.StatusTooManyRequests, "rate_limited", "too many failed attempts; try again later"}
		}
		p, err := s.tokenPrincipal(r.Context(), strings.TrimSpace(tok), ip, r.UserAgent())
		if err != nil {
			s.limiter.fail("ip:" + ip)
			s.eng.Audit(r.Context(), &auth.Principal{IP: ip, Method: "token"}, "auth.token_failed", "", "failure", err.Error())
			return nil, nil, &httpError{http.StatusUnauthorized, "unauthenticated", "invalid API token: " + err.Error()}
		}
		return p, nil, nil
	}
	c, err := r.Cookie(sessionCookie)
	if err != nil || c.Value == "" {
		return nil, nil, errUnauthenticated
	}
	hash := auth.HashSecret(c.Value)
	se, err := s.store.GetSession(r.Context(), hash)
	if err != nil {
		return nil, nil, &httpError{http.StatusUnauthorized, "session_expired", "your session has expired; please log in again"}
	}
	now := time.Now()
	if now.After(se.ExpiresAt) || now.Sub(se.LastSeenAt) > s.cfg.SessionIdle {
		s.store.DeleteSession(r.Context(), hash)
		return nil, nil, &httpError{http.StatusUnauthorized, "session_expired", "your session has expired; please log in again"}
	}
	u, err := s.store.GetUser(r.Context(), se.UserID)
	if err != nil || u.Disabled {
		s.store.DeleteSession(r.Context(), hash)
		return nil, nil, &httpError{http.StatusUnauthorized, "session_expired", "your account is not available; please log in again"}
	}
	if r.Method != http.MethodGet && r.Method != http.MethodHead {
		got := r.Header.Get(csrfHeader)
		if got == "" || subtle.ConstantTimeCompare([]byte(got), []byte(se.CSRFToken)) != 1 {
			return nil, nil, &httpError{http.StatusForbidden, "csrf", "missing or invalid " + csrfHeader + " header"}
		}
	}
	if now.Sub(se.LastSeenAt) > time.Minute {
		s.store.TouchSession(r.Context(), hash, now)
	}
	return &auth.Principal{User: u, Method: "session", IP: ip, Agent: r.UserAgent()}, se, nil
}

func (s *Server) tokenPrincipal(ctx context.Context, tok, ip, agent string) (*auth.Principal, error) {
	pid, secret, err := auth.ParseToken(tok)
	if err != nil {
		return nil, err
	}
	t, err := s.store.GetTokenByPublicID(ctx, pid)
	if errors.Is(err, store.ErrNotFound) {
		return nil, errors.New("unknown token")
	}
	if err != nil {
		return nil, err
	}
	if !auth.CheckSecret(secret, t.SecretHash) {
		return nil, errors.New("wrong token secret")
	}
	if t.RevokedAt != nil {
		return nil, errors.New("the token was revoked")
	}
	now := time.Now()
	if t.ExpiresAt != nil && now.After(*t.ExpiresAt) {
		return nil, errors.New("the token has expired")
	}
	u, err := s.store.GetUser(ctx, t.UserID)
	if err != nil {
		return nil, err
	}
	if u.Disabled {
		return nil, errors.New("the token's user is disabled")
	}
	if t.LastUsedAt == nil || now.Sub(*t.LastUsedAt) > time.Minute || t.LastUsedIP != ip {
		s.store.TouchToken(ctx, t.ID, ip)
	}
	return &auth.Principal{User: u, Token: t, Method: "token", IP: ip, Agent: agent}, nil
}

// authed wraps a handler with authentication and error handling.
func (s *Server) authed(h handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		r.Body = http.MaxBytesReader(w, r.Body, s.cfg.MaxBodyBytes)
		p, se, err := s.authenticate(r)
		if err != nil {
			s.writeErr(w, r, err, nil)
			return
		}
		ctx := context.WithValue(r.Context(), keyPrincipal, p)
		if se != nil {
			ctx = context.WithValue(ctx, keySession, se)
		}
		r = r.WithContext(ctx)
		if err := h(w, r, p); err != nil {
			s.writeErr(w, r, err, nil)
		}
	}
}

// public wraps an unauthenticated handler.
func (s *Server) public(h func(w http.ResponseWriter, r *http.Request) error) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		r.Body = http.MaxBytesReader(w, r.Body, 1<<20)
		if err := h(w, r); err != nil {
			s.writeErr(w, r, err, nil)
		}
	}
}

func (s *Server) cookieSecure(r *http.Request) bool {
	switch s.cfg.CookieSecure {
	case "always":
		return true
	case "never":
		return false
	}
	return s.isHTTPS(r)
}

func (s *Server) login(w http.ResponseWriter, r *http.Request) error {
	var in api.Login
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	ip := s.clientIP(r)
	name := strings.TrimSpace(in.Username)
	userKey := "user:" + strings.ToLower(name)
	who := &auth.Principal{User: &model.User{Username: name}, IP: ip, Method: "session"}
	if s.limiter.blocked("ip:"+ip, failsPerIP) || s.limiter.blocked(userKey, failsPerKey) {
		s.eng.Audit(r.Context(), who, "auth.login_blocked", "user "+name, "denied", "too many failed attempts")
		return &httpError{http.StatusTooManyRequests, "rate_limited", "too many failed login attempts; wait a few minutes and try again"}
	}
	u, err := s.store.GetUserByName(r.Context(), name)
	hash := ""
	if err == nil {
		hash = u.PasswordHash
	}
	ok := auth.CheckPassword(hash, in.Password)
	if err != nil || !ok || u.Disabled || u.PasswordHash == "" {
		s.limiter.fail("ip:"+ip, userKey)
		reason := "wrong username or password"
		if err == nil && u.Disabled && ok {
			reason = "account disabled"
		}
		s.eng.Audit(r.Context(), who, "auth.login_failed", "user "+name, "failure", reason)
		return &httpError{http.StatusUnauthorized, "login_failed", "wrong username or password"}
	}
	s.limiter.reset(userKey)
	id, csrf := auth.NewSessionID()
	now := time.Now()
	se := &model.Session{IDHash: auth.HashSecret(id), UserID: u.ID, CSRFToken: csrf, CreatedAt: now, ExpiresAt: now.Add(s.cfg.SessionLifetime), LastSeenAt: now, IP: ip, UserAgent: r.UserAgent()}
	if err := s.store.CreateSession(r.Context(), se); err != nil {
		return err
	}
	s.store.TouchLogin(r.Context(), u.ID)
	http.SetCookie(w, &http.Cookie{Name: sessionCookie, Value: id, Path: "/", HttpOnly: true, Secure: s.cookieSecure(r), SameSite: http.SameSiteStrictMode, Expires: se.ExpiresAt})
	p := &auth.Principal{User: u, Method: "session", IP: ip, Agent: r.UserAgent()}
	s.eng.Audit(r.Context(), p, "auth.login", "user "+u.Username, "success", "")
	writeJSON(w, http.StatusOK, s.whoamiOf(p, se))
	return nil
}

func (s *Server) logout(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if se, ok := r.Context().Value(keySession).(*model.Session); ok {
		s.store.DeleteSession(r.Context(), se.IDHash)
	}
	http.SetCookie(w, &http.Cookie{Name: sessionCookie, Value: "", Path: "/", HttpOnly: true, Secure: s.cookieSecure(r), SameSite: http.SameSiteStrictMode, MaxAge: -1})
	s.eng.Audit(r.Context(), p, "auth.logout", "user "+p.Name(), "success", "")
	w.WriteHeader(http.StatusNoContent)
	return nil
}

func (s *Server) whoamiOf(p *auth.Principal, se *model.Session) api.Whoami {
	out := api.Whoami{User: p.User, Admin: p.IsAdmin(), Method: p.Method, Permissions: p.Permissions(), Build: version.Info()}
	if se != nil {
		out.CSRFToken = se.CSRFToken
	}
	return out
}

func (s *Server) whoami(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	se, _ := r.Context().Value(keySession).(*model.Session)
	writeJSON(w, http.StatusOK, s.whoamiOf(p, se))
	return nil
}