package webapp

import (
	"context"
	"crypto/sha256"
	"crypto/subtle"
	"net/http"
	"strings"
	"time"
)

// requireSession is the middleware chain for authenticated pages.
// On success, the request context carries the *Session so handlers
// can look up the user without re-querying the store. On failure,
// the operator is redirected to /web/login.
//
// When basic auth is configured (WORKER_LOGIN/WORKER_PASSWORD), the
// middleware accepts HTTP Basic credentials on /web/api/* as an
// alternative to the session cookie. The synthetic session is created
// in-memory only (no row in webapp_sessions) so curl -u operators
// don't accumulate dead rows.
//
// First-run password-change enforcement is intentionally OFF: the
// requires_change flag is still recorded on webapp_users and the
// /web/change-password page is still reachable, but the operator is
// not redirected there on first login. The flag is reserved for a
// future "hardening" toggle that operators will opt into (e.g. via
// a config knob or a UI setting). For now the worker ships with
// frictionless first-login so basic auth + standalone bcrypt users
// can both reach the operator console immediately.
func (s *Server) requireSession(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		// Fast-path: HTTP Basic for API consumers when basic auth
		// is configured. Only the /web/api/* prefix is exposed this
		// way so the browser-driven login flow stays intact.
		if s.basicAuthOK && strings.HasPrefix(r.URL.Path, "/web/api/") {
			if s.checkBasicAuth(r) {
				next(w, r)
				return
			}
			w.Header().Set("WWW-Authenticate", basicAuthRealm)
			http.Error(w, "unauthorized", http.StatusUnauthorized)
			return
		}

		sess, err := s.resolveSession(r)
		if err != nil {
			redirectTo(w, r, pathLogin)
			return
		}
		ctx := context.WithValue(r.Context(), ctxKeySession, sess)
		next(w, r.WithContext(ctx))
	}
}

// checkBasicAuth validates the Authorization: Basic header against
// the configured WORKER_LOGIN / WORKER_PASSWORD pair. Login is
// compared in constant time; password is hashed at startup so the
// raw value never enters the request hot path.
func (s *Server) checkBasicAuth(r *http.Request) bool {
	if !s.basicAuthOK {
		return false
	}
	user, pass, ok := r.BasicAuth()
	if !ok {
		return false
	}
	userHash := sha256.Sum256([]byte(user))
	wantUserHash := sha256.Sum256([]byte(s.cfg.BasicAuthLogin))
	if subtle.ConstantTimeCompare(userHash[:], wantUserHash[:]) != 1 {
		return false
	}
	passHash := sha256.Sum256([]byte(pass))
	return subtle.ConstantTimeCompare(passHash[:], s.basicAuthHash[:]) == 1
}

// resolveSession reads the session cookie, validates the row, slides
// the absolute expiry forward on activity, and returns the Session.
// Returns errMissingSession if any step fails.
func (s *Server) resolveSession(r *http.Request) (*Session, error) {
	c, err := r.Cookie(sessionCookieName)
	if err != nil || c.Value == "" {
		return nil, errMissingSession
	}
	sess, err := s.store.GetSession(r.Context(), c.Value)
	if err != nil {
		return nil, errMissingSession
	}
	if err := s.store.TouchSession(r.Context(), sess.ID, s.cfg.SessionIdle, s.cfg.SessionAbs); err != nil {
		return nil, errMissingSession
	}
	sess.LastSeenAt = time.Now().UTC()
	return sess, nil
}

// requireCSRF verifies the double-submit token on state-changing
// requests. The middleware compares the form/header value against
// the session's stored CSRF token. The cookie value is not the
// authoritative source on its own (it is set without HttpOnly so
// that JS on the same origin could read it, but Phase 1 ships no
// JS, so a missing cookie is fine).
func (s *Server) requireCSRF(sess *Session, r *http.Request) bool {
	if sess == nil {
		return false
	}
	if r.Method == http.MethodGet || r.Method == http.MethodHead || r.Method == http.MethodOptions {
		return true
	}
	want := sess.CSRFToken
	if want == "" {
		return false
	}
	// Form value is the primary check; header is a fallback for
	// fetch-style callers.
	if err := r.ParseForm(); err != nil {
		return false
	}
	got := strings.TrimSpace(r.FormValue("csrf_token"))
	if got == "" {
		got = strings.TrimSpace(r.Header.Get("X-CSRF-Token"))
	}
	if got == "" || constantTimeEq(got, want) != 1 {
		return false
	}
	return true
}

// writeSessionCookie sets the session and CSRF cookies. The Secure
// flag is set when the request did not arrive over loopback (i.e.,
// when the operator has gone out of their way to expose the
// webapp over a non-loopback interface).
func (s *Server) writeSessionCookie(w http.ResponseWriter, r *http.Request, sess *Session) {
	if sess == nil {
		return
	}
	secure := !isLoopbackRequest(r)
	http.SetCookie(w, &http.Cookie{
		Name:     sessionCookieName,
		Value:    sess.ID,
		Path:     "/",
		HttpOnly: true,
		Secure:   secure,
		SameSite: http.SameSiteStrictMode,
		Expires:  sess.ExpiresAt,
	})
	http.SetCookie(w, &http.Cookie{
		Name:     csrfCookieName,
		Value:    sess.CSRFToken,
		Path:     "/",
		HttpOnly: false,
		Secure:   secure,
		SameSite: http.SameSiteStrictMode,
		Expires:  sess.ExpiresAt,
	})
}

// clearSessionCookie blanks out the session and CSRF cookies. Used
// on logout and on hard errors (DB failure, etc.).
func clearSessionCookie(w http.ResponseWriter, r *http.Request) {
	secure := !isLoopbackRequest(r)
	for _, name := range []string{sessionCookieName, csrfCookieName} {
		http.SetCookie(w, &http.Cookie{
			Name:     name,
			Value:    "",
			Path:     "/",
			HttpOnly: true,
			Secure:   secure,
			SameSite: http.SameSiteStrictMode,
			Expires:  time.Unix(0, 0),
			MaxAge:   -1,
		})
	}
}