package server

//go:generate python sri.py templates/*.html
//go:generate go-bindata --nocompress --pkg server static/... templates/...

import (
	"bytes"
	"context"
	"encoding/gob"
	"encoding/json"
	"fmt"
	"html/template"
	"io"
	"io/ioutil"
	"log"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

	assetfs "github.com/elazarl/go-bindata-assetfs"
	"github.com/gorilla/csrf"
	"github.com/gorilla/mux"
	"github.com/gorilla/sessions"
	"github.com/rs/cors"

	"git.autistici.org/id/auth"
	authclient "git.autistici.org/id/auth/client"
	ksclient "git.autistici.org/id/keystore/client"

	"git.autistici.org/id/go-sso/httputil"
	"git.autistici.org/id/go-sso/server/device"
)

const authSessionKey = "_auth"

type authSession struct {
	*httputil.ExpiringSession

	// User name and other information (like group membership).
	Username string
	UserInfo *auth.UserInfo

	// Services the user has logged in to from this session.
	Services []string
}

// AddService adds a service to the current session (if it's not
// already there).
func (s *authSession) AddService(service string) {
	for _, svc := range s.Services {
		if svc == service {
			return
		}
	}
	s.Services = append(s.Services, service)
}

// By default, make users log in again after (almost) one day.
var defaultAuthSessionLifetime = 20 * time.Hour

func newAuthSession(ttl time.Duration, username string, userinfo *auth.UserInfo) *authSession {
	return &authSession{
		ExpiringSession: httputil.NewExpiringSession(ttl),
		Username:        username,
		UserInfo:        userinfo,
	}
}

func init() {
	gob.Register(&authSession{})
}

// Returns the URL of the login handler on the target service.
func serviceLoginCallback(service, destination, token string) string {
	v := make(url.Values)
	v.Set("t", token)
	v.Set("d", destination)
	return fmt.Sprintf("https://%ssso_login?%s", service, v.Encode())
}

// Returns the URL of the logout handler on the target service.
func serviceLogoutCallback(service string) string {
	return fmt.Sprintf("https://%ssso_logout", service)
}

// Server for the SSO protocol. Provides the HTTP interface to a
// LoginService.
type Server struct {
	authSessionStore    sessions.Store
	authSessionLifetime time.Duration
	loginHandler        *loginHandler
	loginService        *LoginService
	keystore            ksclient.Client
	keystoreGroups      []string
	csrfSecret          []byte
	renderer            *renderer
	urlPrefix           string
	homepageRedirectURL string
	allowedOrigins      []string

	// User-configurable static data that we serve from memory.
	siteLogo    *staticContent
	siteFavicon *staticContent
}

func sl2bl(sl []string) [][]byte {
	var out [][]byte
	for _, s := range sl {
		out = append(out, []byte(s))
	}
	return out
}

// New returns a new Server.
func New(loginService *LoginService, authClient authclient.Client, config *Config) (*Server, error) {
	urlPrefix := strings.TrimRight(config.URLPrefix, "/")
	sessionSecrets := sl2bl(config.SessionSecrets)
	store := sessions.NewCookieStore(sessionSecrets...)
	store.Options = &sessions.Options{
		HttpOnly: true,
		Secure:   true,
		MaxAge:   0,
		Path:     urlPrefix + "/",
	}

	renderer := newRenderer(config)
	s := &Server{
		authSessionLifetime: defaultAuthSessionLifetime,
		authSessionStore:    store,
		loginService:        loginService,
		urlPrefix:           urlPrefix,
		homepageRedirectURL: config.HomepageRedirectURL,
		allowedOrigins:      config.AllowedCORSOrigins,
		renderer:            renderer,
	}
	if config.CSRFSecret != "" {
		s.csrfSecret = []byte(config.CSRFSecret)
	}
	if config.AuthSessionLifetimeSeconds > 0 {
		s.authSessionLifetime = time.Duration(config.AuthSessionLifetimeSeconds) * time.Second
	}

	if config.SiteLogo != "" {
		siteLogo, err := loadStaticContent(config.SiteLogo)
		if err != nil {
			return nil, err
		}
		s.siteLogo = siteLogo
	}
	if config.SiteFavicon != "" {
		siteFavicon, err := loadStaticContent(config.SiteFavicon)
		if err != nil {
			return nil, err
		}
		s.siteFavicon = siteFavicon
	}

	if config.KeyStore != nil {
		ks, err := ksclient.New(config.KeyStore)
		if err != nil {
			return nil, err
		}
		log.Printf("keystore client enabled")
		s.keystore = ks
		s.keystoreGroups = config.KeyStoreEnableGroups
	}

	devMgr, err := device.New(config.DeviceManager)
	if err != nil {
		return nil, err
	}
	s.loginHandler = newLoginHandler(s.loginCallback, devMgr, authClient,
		config.AuthService, config.U2FAppID, config.URLPrefix,
		renderer, sessionSecrets...)

	return s, nil
}

func inAnyGroups(groups, ref []string) bool {
	for _, rr := range ref {
		for _, gg := range groups {
			if gg == rr {
				return true
			}
		}
	}
	return false
}

// We unlock the keystore if the following conditions are met:
// keystore_enable_groups is set, userinfo is not nil, and the groups match.
func (h *Server) maybeUnlockKeystore(ctx context.Context, username, password string, userinfo *auth.UserInfo) (bool, error) {
	if h.keystore == nil {
		return false, nil
	}

	var shard string
	if len(h.keystoreGroups) > 0 {
		if userinfo == nil {
			return false, nil
		}
		if !inAnyGroups(userinfo.Groups, h.keystoreGroups) {
			return false, nil
		}
		shard = userinfo.Shard
	}
	return true, h.keystore.Open(ctx, shard, username, password, int(h.authSessionLifetime.Seconds()))
}

func (h *Server) loginCallback(w http.ResponseWriter, req *http.Request, username, password string, userinfo *auth.UserInfo) error {
	// Open the keystore for this user with the password used to
	// authenticate. Set the TTL to the duration of the
	// authenticated session.
	decrypted, err := h.maybeUnlockKeystore(req.Context(), username, password, userinfo)
	if err != nil {
		log.Printf("failed to unlock keystore for user %s: %v", username, err)
		return err
	}

	var kmsg string
	if decrypted {
		kmsg = " (key unlocked)"
	}
	log.Printf("successful login for user %s%s", username, kmsg)

	// Create cookie-based session for the authenticated user.
	session := newAuthSession(h.authSessionLifetime, username, userinfo)
	httpSession, _ := h.authSessionStore.Get(req, authSessionKey) // nolint
	httpSession.Values["data"] = session
	return httpSession.Save(req, w)
}

func (h *Server) redirectToLogin(w http.ResponseWriter, req *http.Request) {
	http.Redirect(w, req, h.loginHandler.makeLoginURL(req), http.StatusFound)
}

func (h *Server) withAuth(f func(http.ResponseWriter, *http.Request, *authSession), authFail func(http.ResponseWriter, *http.Request)) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
		httpSession, err := h.authSessionStore.Get(req, authSessionKey)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		session, ok := httpSession.Values["data"].(*authSession)
		if ok && session.Valid() {
			f(w, req, session)
			return
		}
		httpSession.Options.MaxAge = -1
		delete(httpSession.Values, "data")
		if err := httpSession.Save(req, w); err != nil {
			log.Printf("error saving session: %v", err)
		}
		authFail(w, req)
	})
}

// Token signing handler. Authorizes an authenticated user to a service by
// signing a token with the user's identity. The client is redirected back to
// the original service, with the signed token.
func (h *Server) handleHomepage(w http.ResponseWriter, req *http.Request, session *authSession) {
	// Extract the authorization request parameters from the HTTP
	// request query args.
	//
	// *NOTE*: we do not want to parse the request body, in case
	// it is a POST request redirected from a 307, so we do not
	// call req.FormValue() but look directly into request.URL
	// instead.
	username := session.Username
	service := req.URL.Query().Get("s")
	destination := req.URL.Query().Get("d")
	nonce := req.URL.Query().Get("n")
	groupsStr := req.URL.Query().Get("g")

	// If the above parameters are unset, we're probably faced with a user
	// that reached this URL by other means. Redirect them to the
	// configured homepageRedirectURL, or at least return a slightly more
	// user-friendly error.
	if service == "" || destination == "" {
		if h.homepageRedirectURL != "" {
			http.Redirect(w, req, h.homepageRedirectURL, http.StatusFound)
		} else {
			http.Error(w, "You are not supposed to reach this page directly. Use the back button in your browser instead.", http.StatusBadRequest)
		}
		return
	}

	// Compute the intersection of the user's groups and the
	// requested groups, to obtain the group memberships to grant.
	var groups []string
	if groupsStr != "" {
		reqGroups := strings.Split(groupsStr, ",")
		if len(reqGroups) > 0 && session.UserInfo != nil {
			groups = intersectGroups(reqGroups, session.UserInfo.Groups)
			// We only make this check here as a convenience to
			// the user (we may be able to show a nicer UI): the
			// actual group ACL must be applied on the destination
			// service, because the 'g' parameter is untrusted at
			// this stage.
			if len(groups) == 0 {
				http.Error(w, "Forbidden", http.StatusForbidden)
				return
			}
		}
	}

	// Make the authorization request.
	token, err := h.loginService.Authorize(username, service, destination, nonce, groups)
	if err != nil {
		log.Printf("auth error: %v: user=%s service=%s destination=%s nonce=%s groups=%s", err, username, service, destination, nonce, groupsStr)
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	session.AddService(service)
	if err := sessions.Save(req, w); err != nil {
		log.Printf("error saving session: %v", err)
	}

	// Redirect to service callback.
	callbackURL := serviceLoginCallback(service, destination, token)
	http.Redirect(w, req, callbackURL, http.StatusFound)
}

func (h *Server) alreadyLoggedOut(w http.ResponseWriter, req *http.Request) {
	http.Error(w, "You do not seem to be logged in", http.StatusBadRequest)
}

type logoutServiceInfo struct {
	URL  string `json:"url"`
	Name string `json:"name"`
}

func (h *Server) handleLogout(w http.ResponseWriter, req *http.Request, session *authSession) {
	var svcs []logoutServiceInfo
	for _, svc := range session.Services {
		svcs = append(svcs, logoutServiceInfo{
			Name: svc,
			URL:  serviceLogoutCallback(svc),
		})
	}

	svcJSON, _ := json.Marshal(svcs) // nolint
	data := map[string]interface{}{
		"Services":             svcs,
		"ServicesJSON":         string(svcJSON),
		"IncludeLogoutScripts": true,
	}

	// Clear the local session. Ignore errors.
	httpSession, _ := h.authSessionStore.Get(req, authSessionKey) // nolint
	delete(httpSession.Values, "data")
	httpSession.Options.MaxAge = -1
	httpSession.Save(req, w) // nolint

	// Close the keystore.
	if h.keystore != nil {
		var shard string
		if session.UserInfo != nil {
			shard = session.UserInfo.Shard
		}
		if err := h.keystore.Close(req.Context(), shard, session.Username); err != nil {
			log.Printf("failed to wipe keystore for user %s: %v", session.Username, err)
		}
	}

	w.Header().Set("Content-Security-Policy", logoutContentSecurityPolicy)

	body, err := h.renderer.Render(req, "logout.html", data)
	if err != nil {
		log.Printf("template error in logout(): %v", err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	w.Write(body) // nolint
}

func (h *Server) handleExchange(w http.ResponseWriter, req *http.Request) {
	curToken := req.FormValue("cur_tkt")
	curService := req.FormValue("cur_svc")
	curNonce := req.FormValue("cur_nonce")
	newService := req.FormValue("new_svc")
	newNonce := req.FormValue("new_nonce")

	token, err := h.loginService.Exchange(curToken, curService, curNonce, newService, newNonce)
	switch {
	case err == ErrUnauthorized:
		log.Printf("unauthorized exchange request (%s -> %s)", curService, newService)
		http.Error(w, "Forbidden", http.StatusForbidden)
		return
	case err != nil:
		log.Printf("exchange error (%s -> %s): %v", curService, newService, err)
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	w.Header().Set("Content-Type", "text/plain")
	io.WriteString(w, token) // nolint
}

func (h *Server) urlFor(path string) string {
	return h.urlPrefix + path
}

// Handler returns the http.Handler for the SSO server application.
func (h *Server) Handler() http.Handler {
	// The root HTTP handler. This must be a gorilla/mux.Router since
	// sessions depend on it.
	//
	// If a URL prefix is set, we can't just add a StripPrefix in
	// front of everything, as the handlers need access to the
	// actual full request URL, so we just inject the prefix
	// everywhere.
	root := mux.NewRouter()

	// If we have customized content, serve it from well-known URLs.
	if h.siteLogo != nil {
		root.Handle(h.urlFor("/img/site_logo"), h.siteLogo)
	}
	if h.siteFavicon != nil {
		root.Handle(h.urlFor("/favicon.ico"), h.siteFavicon)
	}

	// Serve static content to anyone.
	staticPath := h.urlFor("/static/")
	root.PathPrefix(staticPath).Handler(http.StripPrefix(staticPath, http.FileServer(&assetfs.AssetFS{
		Asset:     Asset,
		AssetDir:  AssetDir,
		AssetInfo: AssetInfo,
		Prefix:    "static",
	})))

	// Build the main IDP application router, with optional CSRF
	// protection.
	m := http.NewServeMux()
	m.Handle(h.urlFor("/login"), h.loginHandler)
	m.Handle(h.urlFor("/logout"), h.withAuth(h.handleLogout, h.alreadyLoggedOut))
	idph := http.Handler(m)
	if h.csrfSecret != nil {
		idph = csrf.Protect(h.csrfSecret)(idph)
	}

	// Add the SSO provider endpoints (root path and /exchange),
	// which do not need CSRF. We use a HandlerFunc to bypass the
	// '/' dispatch semantics of the standard http.ServeMux.
	ssoh := h.withAuth(h.handleHomepage, h.redirectToLogin)
	userh := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		switch {
		case r.Method == "GET" && r.URL.Path == h.urlFor("/"):
			ssoh.ServeHTTP(w, r)
		case r.URL.Path == h.urlFor("/exchange"):
			h.handleExchange(w, r)
		default:
			idph.ServeHTTP(w, r)
		}
	})

	// Add CORS headers around user-facing routes.
	c := cors.New(cors.Options{
		AllowedOrigins:   h.allowedOrigins,
		AllowCredentials: true,
		MaxAge:           86400,
	})

	// User-facing routes require cache-busting and CSP headers.
	root.PathPrefix(h.urlFor("/")).Handler(withDynamicHeaders(c.Handler(userh)))

	return root
}

// A relatively strict CSP.
const contentSecurityPolicy = "default-src 'none'; img-src 'self' data:; script-src 'self'; style-src 'self'; connect-src 'self';"

// Slightly looser CSP for the logout page: it needs to load remote
// images.
const logoutContentSecurityPolicy = "default-src 'none'; img-src *; script-src 'self'; style-src 'self'; connect-src *;"

func withDynamicHeaders(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Pragma", "no-cache")
		w.Header().Set("Cache-Control", "no-store")
		w.Header().Set("Expires", "-1")
		w.Header().Set("X-Frame-Options", "NONE")
		w.Header().Set("X-XSS-Protection", "1; mode=block")
		w.Header().Set("X-Content-Type-Options", "nosniff")
		if w.Header().Get("Content-Security-Policy") == "" {
			w.Header().Set("Content-Security-Policy", contentSecurityPolicy)
		}
		h.ServeHTTP(w, r)
	})
}

// Parse the templates that are embedded with the binary (in bindata.go).
func parseEmbeddedTemplates() *template.Template {
	root := template.New("").Funcs(template.FuncMap{
		"json": toJSON,
	})
	files, err := AssetDir("templates")
	if err != nil {
		log.Fatalf("no asset dir for templates: %v", err)
	}
	for _, f := range files {
		b, err := Asset("templates/" + f)
		if err != nil {
			log.Fatalf("could not read embedded template %s: %v", f, err)
		}
		if _, err := root.New(f).Parse(string(b)); err != nil {
			log.Fatalf("error parsing template %s: %v", f, err)
		}
	}
	return root
}

type renderer struct {
	tpl *template.Template

	urlPrefix          string
	siteName           string
	siteLogo           string
	siteFavicon        string
	accountRecoveryURL string
}

func newRenderer(config *Config) *renderer {
	return &renderer{
		tpl:                parseEmbeddedTemplates(),
		urlPrefix:          strings.TrimRight(config.URLPrefix, "/"),
		accountRecoveryURL: config.AccountRecoveryURL,
		siteName:           config.SiteName,
		siteLogo:           config.SiteLogo,
		siteFavicon:        config.SiteFavicon,
	}
}

func (r *renderer) Render(req *http.Request, templateName string, data map[string]interface{}) ([]byte, error) {
	data["CSRFField"] = csrf.TemplateField(req)
	data["URLPrefix"] = r.urlPrefix
	data["AccountRecoveryURL"] = r.accountRecoveryURL
	data["SiteName"] = r.siteName
	data["SiteLogo"] = r.siteLogo
	data["SiteFavicon"] = r.siteFavicon

	var buf bytes.Buffer
	if err := r.tpl.ExecuteTemplate(&buf, templateName, data); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}

type staticContent struct {
	modtime time.Time
	name    string
	data    []byte
}

func loadStaticContent(path string) (*staticContent, error) {
	stat, err := os.Stat(path)
	if err != nil {
		return nil, err
	}
	data, err := ioutil.ReadFile(path) // #nosec
	if err != nil {
		return nil, err
	}
	return &staticContent{
		name:    path,
		modtime: stat.ModTime(),
		data:    data,
	}, nil
}

func (c *staticContent) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	http.ServeContent(w, req, c.name, c.modtime, bytes.NewReader(c.data))
}