// authapi.go — the WebAuthn ceremony endpoints (unauthenticated: they ARE the
// gate) + logout + whoami. register/* is authorised by the one-time enrol token
// from the CLI; login/* is usernameless (discoverable passkey). A successful
// login mints the server-side session (session.go).
package main

import (
	"fmt"
	"log"
	"net/http"
	"sync"
	"time"

	"github.com/go-webauthn/webauthn/protocol"
	"github.com/go-webauthn/webauthn/webauthn"
)

// ceremony holds the in-flight WebAuthn SessionData between begin and finish,
// plus the enrol claims for a registration. Short-lived, in-memory.
type ceremony struct {
	sess    *webauthn.SessionData
	name    string
	jti     string
	exp     int64
	expires time.Time
}

type ceremonyStore struct {
	mu sync.Mutex
	m  map[string]ceremony
}

func newCeremonyStore() *ceremonyStore { return &ceremonyStore{m: map[string]ceremony{}} }

func (c *ceremonyStore) put(sess *webauthn.SessionData, name, jti string, exp int64) string {
	id := randToken()
	c.mu.Lock()
	now := time.Now()
	for k, v := range c.m {
		if now.After(v.expires) {
			delete(c.m, k)
		}
	}
	c.m[id] = ceremony{sess: sess, name: name, jti: jti, exp: exp, expires: now.Add(5 * time.Minute)}
	c.mu.Unlock()
	return id
}

func (c *ceremonyStore) take(id string) (ceremony, bool) {
	c.mu.Lock()
	defer c.mu.Unlock()
	cer, ok := c.m[id]
	if ok {
		delete(c.m, id)
	}
	if ok && time.Now().After(cer.expires) {
		return ceremony{}, false
	}
	return cer, ok
}

func (s *server) authRoutes(mux *http.ServeMux) {
	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/plain")
		_, _ = w.Write([]byte("ok\n"))
	})
	if s.wa == nil {
		return // insecure/dev mode has no passkey ceremonies
	}
	mux.HandleFunc("POST /auth/register/begin", s.handleRegisterBegin)
	mux.HandleFunc("POST /auth/register/finish", s.handleRegisterFinish)
	mux.HandleFunc("POST /auth/login/begin", s.handleLoginBegin)
	mux.HandleFunc("POST /auth/login/finish", s.handleLoginFinish)
	mux.HandleFunc("POST /auth/logout", s.handleLogout)
}

// register/begin — authorised by the one-time enrol token (?token=).
func (s *server) handleRegisterBegin(w http.ResponseWriter, r *http.Request) {
	claims, err := verifyEnrollToken(s.enrollKey, r.URL.Query().Get("token"))
	if err != nil {
		writeErr(w, http.StatusUnauthorized, "invalid enrolment token: "+err.Error())
		return
	}
	if s.creds.tokenUsed(claims.JTI) {
		writeErr(w, http.StatusConflict, "enrolment token already used")
		return
	}
	user := s.creds.getOrCreate(claims.Name)
	sel := protocol.AuthenticatorSelection{
		ResidentKey:        protocol.ResidentKeyRequirementRequired,
		RequireResidentKey: protocol.ResidentKeyRequired(),
		UserVerification:   protocol.VerificationRequired,
	}
	options, sessionData, err := s.wa.BeginRegistration(user, webauthn.WithAuthenticatorSelection(sel))
	if err != nil {
		writeErr(w, http.StatusInternalServerError, "begin registration: "+err.Error())
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"cid": s.ceremonies.put(sessionData, claims.Name, claims.JTI, claims.Exp), "options": options})
}

func (s *server) handleRegisterFinish(w http.ResponseWriter, r *http.Request) {
	cer, ok := s.ceremonies.take(r.URL.Query().Get("cid"))
	if !ok || cer.sess == nil {
		writeErr(w, http.StatusBadRequest, "unknown or expired ceremony")
		return
	}
	if s.creds.tokenUsed(cer.jti) {
		writeErr(w, http.StatusConflict, "enrolment token already used")
		return
	}
	user := s.creds.getOrCreate(cer.name)
	cred, err := s.wa.FinishRegistration(user, *cer.sess, r)
	if err != nil {
		writeErr(w, http.StatusBadRequest, "registration failed: "+err.Error())
		return
	}
	if err := s.creds.addCredential(cer.name, *cred); err != nil {
		writeErr(w, http.StatusInternalServerError, err.Error())
		return
	}
	s.creds.markTokenUsed(cer.jti, cer.exp)
	log.Printf("audit ADMIN-ENROL name=%q (passkey registered)", cer.name)
	writeJSON(w, http.StatusOK, map[string]any{"admin": cer.name, "registered": true})
}

// login/begin — usernameless discoverable login.
func (s *server) handleLoginBegin(w http.ResponseWriter, r *http.Request) {
	options, sessionData, err := s.wa.BeginDiscoverableLogin(webauthn.WithUserVerification(protocol.VerificationRequired))
	if err != nil {
		writeErr(w, http.StatusInternalServerError, "begin login: "+err.Error())
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"cid": s.ceremonies.put(sessionData, "", "", 0), "options": options})
}

func (s *server) handleLoginFinish(w http.ResponseWriter, r *http.Request) {
	cer, ok := s.ceremonies.take(r.URL.Query().Get("cid"))
	if !ok || cer.sess == nil {
		writeErr(w, http.StatusBadRequest, "unknown or expired ceremony")
		return
	}
	var matched *adminUser
	handler := func(rawID, userHandle []byte) (webauthn.User, error) {
		u, ok := s.creds.byHandle(userHandle)
		if !ok {
			return nil, fmt.Errorf("unknown passkey")
		}
		matched = u
		return u, nil
	}
	cred, err := s.wa.FinishDiscoverableLogin(handler, *cer.sess, r)
	if err != nil || matched == nil {
		writeErr(w, http.StatusUnauthorized, "login failed")
		return
	}
	s.creds.updateCredential(matched.IDb, *cred) // persist the signature counter
	id, csrf := s.sessions.create(matched.Name)
	setSessionCookie(w, id, s.cfg.sessionTTL)
	log.Printf("audit ADMIN-LOGIN name=%q", matched.Name)
	writeJSON(w, http.StatusOK, map[string]any{"admin": matched.Name, "csrf": csrf})
}

func (s *server) handleLogout(w http.ResponseWriter, r *http.Request) {
	if c, err := r.Cookie(sessionCookie); err == nil {
		s.sessions.delete(c.Value)
	}
	clearSessionCookie(w)
	w.WriteHeader(http.StatusNoContent)
}

// handleWhoami is session-gated (registered under /api): lets the SPA resume an
// existing session on reload and recover the CSRF token.
func (s *server) handleWhoami(w http.ResponseWriter, r *http.Request) {
	sess, _ := sessionFrom(r)
	writeJSON(w, http.StatusOK, map[string]any{"admin": adminName(r), "csrf": sess.csrf})
}