package main

import (
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/meshcore-analyzer/users"
)

const (
	sessionCookieName = "cs_session"
	csrfHeader        = "X-CS-CSRF"
)

// deviceScopeRX is the scope of CoreDrive RX device tokens: the routes
// bearerScopeFor lists.
const deviceScopeRX = "rx"

// bearerScopeFor returns the scope a device token needs on path, or ""
// when no device token may use it (spec: /api/auth/me, /api/auth/logout,
// /api/account/companions*, /api/account/settings).
func bearerScopeFor(path string) string {
	switch {
	case path == "/api/auth/me", path == "/api/auth/logout", path == "/api/account/settings",
		path == "/api/account/companions", strings.HasPrefix(path, "/api/account/companions/"):
		return deviceScopeRX
	}
	return ""
}

// bearerCORSPath reports whether path takes cross-origin writes from an
// allowlisted origin: the device-token login and the bearer routes.
func bearerCORSPath(path string) bool {
	return path == "/api/auth/device-token" || bearerScopeFor(path) != ""
}

// bearerToken returns the token of an "Authorization: Bearer" header and
// whether the request is to be judged on it. A request that carries the
// session cookie is not: the cookie decides, so an auth proxy that adds its
// own Authorization header does not break browser logins.
func bearerToken(r *http.Request) (string, bool) {
	if c, err := r.Cookie(sessionCookieName); err == nil && c.Value != "" {
		return "", false
	}
	const prefix = "Bearer "
	h := r.Header.Get("Authorization")
	if len(h) < len(prefix) || !strings.EqualFold(h[:len(prefix)], prefix) {
		return "", false
	}
	return strings.TrimSpace(h[len(prefix):]), true
}

// bearerUser resolves a device token for r. The code is 0 on success, 401
// for an unknown, expired or web token or an inactive account, and 403
// when the token's scope does not cover the route. A use more than a day
// after the last one extends the token by DeviceSessionTTL (sliding).
func (a *authService) bearerUser(r *http.Request, tok string) (*users.User, *users.Session, int) {
	if tok == "" {
		return nil, nil, http.StatusUnauthorized
	}
	sess, err := a.st.LookupSession(tok)
	// A web token as a bearer would skip the CSRF check: refused.
	if err != nil || sess.Kind != users.SessionKindDevice {
		return nil, nil, http.StatusUnauthorized
	}
	u, err := a.st.GetByID(sess.UserID)
	if err != nil || u.Status != users.StatusActive {
		return nil, nil, http.StatusUnauthorized
	}
	if need := bearerScopeFor(r.URL.Path); need == "" || !sess.HasScope(need) {
		return nil, nil, http.StatusForbidden
	}
	if time.Since(sess.LastSeenAt) > 24*time.Hour {
		_ = a.st.ExtendSession(sess.ID, users.DeviceSessionTTL)
	}
	return u, sess, 0
}

func writeBearerFail(w http.ResponseWriter, code int) {
	if code == http.StatusForbidden {
		writeError(w, http.StatusForbidden, "this token is not allowed on this route")
		return
	}
	writeError(w, http.StatusUnauthorized, "invalid or expired token")
}

func (a *authService) setSessionCookie(w http.ResponseWriter, raw string, expires time.Time) {
	http.SetCookie(w, &http.Cookie{
		Name: sessionCookieName, Value: raw, Path: "/",
		Expires: expires, MaxAge: int(time.Until(expires).Seconds()),
		HttpOnly: true, Secure: a.set.secureCookie, SameSite: http.SameSiteLaxMode,
	})
}

func (a *authService) clearSessionCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{Name: sessionCookieName, Value: "", Path: "/", MaxAge: -1,
		HttpOnly: true, Secure: a.set.secureCookie, SameSite: http.SameSiteLaxMode})
}

// currentUser returns the active user behind the session cookie, or nils.
// A session last seen more than a day ago is extended (sliding expiry)
// and its cookie re-issued.
func (a *authService) currentUser(w http.ResponseWriter, r *http.Request) (*users.User, *users.Session) {
	c, err := r.Cookie(sessionCookieName)
	if err != nil || c.Value == "" {
		return nil, nil
	}
	sess, err := a.st.LookupSession(c.Value)
	// A device token is a bearer credential only: sent as the cookie it
	// must not pass as a browser session.
	if err != nil || sess.Kind != users.SessionKindWeb {
		return nil, nil
	}
	u, err := a.st.GetByID(sess.UserID)
	if err != nil || u.Status != users.StatusActive {
		return nil, nil
	}
	if time.Since(sess.LastSeenAt) > 24*time.Hour {
		if err := a.st.ExtendSession(sess.ID, a.set.sessionTTL); err == nil {
			a.setSessionCookie(w, c.Value, time.Now().Add(a.set.sessionTTL))
		}
	}
	return u, sess
}

// originOK requires the request's Origin (or, if absent, Referer) to be the
// configured publicBaseUrl's origin.
func (a *authService) originOK(r *http.Request) bool {
	want := a.set.baseURL.Scheme + "://" + a.set.baseURL.Host
	if o := r.Header.Get("Origin"); o != "" {
		return strings.EqualFold(o, want)
	}
	if ref := r.Header.Get("Referer"); ref != "" {
		u, err := url.Parse(ref)
		return err == nil && strings.EqualFold(u.Scheme+"://"+u.Host, want)
	}
	return false
}

func (a *authService) csrfOK(r *http.Request, sess *users.Session) bool {
	return a.originOK(r) && constantTimeEqual(r.Header.Get(csrfHeader), sess.CSRFToken)
}

func isSafeMethod(m string) bool { return m == http.MethodGet || m == http.MethodHead }

type authedHandler func(w http.ResponseWriter, r *http.Request, u *users.User, sess *users.Session)

// withUser requires a logged-in active user. A request with an
// Authorization: Bearer header and no session cookie is judged on that
// device token alone (scope check, no CSRF: browsers never attach it on
// their own).
// Otherwise the cookie session is used, and state-changing methods must
// pass the origin + CSRF-token check.
func (s *Server) withUser(h authedHandler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if tok, ok := bearerToken(r); ok {
			u, sess, code := s.auth.bearerUser(r, tok)
			if code != 0 {
				writeBearerFail(w, code)
				return
			}
			h(w, r, u, sess)
			return
		}
		u, sess := s.auth.currentUser(w, r)
		if u == nil {
			writeError(w, http.StatusUnauthorized, "not logged in")
			return
		}
		if !isSafeMethod(r.Method) && !s.auth.csrfOK(r, sess) {
			writeError(w, http.StatusForbidden, "CSRF check failed")
			return
		}
		h(w, r, u, sess)
	}
}

// adminSessionOK is the one place that decides whether a session user may
// act as admin: state-changing methods must pass the origin + CSRF check,
// and the role must be admin. It writes the 403 itself when not.
func (a *authService) adminSessionOK(w http.ResponseWriter, r *http.Request, u *users.User, sess *users.Session) bool {
	if !isSafeMethod(r.Method) && !a.csrfOK(r, sess) {
		writeError(w, http.StatusForbidden, "CSRF check failed")
		return false
	}
	if u.Role != users.RoleAdmin {
		writeError(w, http.StatusForbidden, "admin role required")
		return false
	}
	return true
}

// withAdmin requires a logged-in admin (see adminSessionOK).
func (s *Server) withAdmin(h authedHandler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if _, ok := bearerToken(r); ok {
			writeBearerFail(w, http.StatusForbidden)
			return
		}
		u, sess := s.auth.currentUser(w, r)
		if u == nil {
			writeError(w, http.StatusUnauthorized, "not logged in")
			return
		}
		if !s.auth.adminSessionOK(w, r, u, sess) {
			return
		}
		h(w, r, u, sess)
	}
}

// requireOrigin guards unauthenticated state-changing endpoints (login CSRF).
func (s *Server) requireOrigin(h http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if !s.auth.originOK(r) {
			writeError(w, http.StatusForbidden, "request origin not allowed")
			return
		}
		h(w, r)
	}
}