package server

import (
	"errors"
	"net/http"
	"sort"
	"strings"
	"time"

	"cc.tiredsysadmin.keeporg/internal/secret"
	"cc.tiredsysadmin.keeporg/internal/store"
)

// The web interface covers what a browser is better at than the command
// line: creating a vault and setting its password, and the administration of
// people — invites, accounts, groups and who reaches which vault. It is not
// a password manager and never shows a vault's contents; the server does not
// open a vault except to merge one.
const webCookie = "keeporg_web"

// webSession is a signed-in browser.
type webSession struct {
	user *store.User
	csrf string
}

// webUser resolves the session cookie, or nil when the browser is not
// signed in.
func (s *Server) webUser(r *http.Request) *webSession {
	c, err := r.Cookie(webCookie)
	if err != nil || c.Value == "" {
		return nil
	}
	var out *webSession
	s.st.Read(func(st *store.State) {
		sess := st.Sessions[c.Value]
		if sess == nil || time.Now().After(sess.ExpiresAt) {
			return
		}
		if u := st.Users[sess.UserID]; u != nil && !u.Disabled {
			cp := *u
			out = &webSession{user: &cp, csrf: sess.CSRF}
		}
	})
	return out
}

// webHandler is a handler that needs a signed-in browser.
type webHandler func(http.ResponseWriter, *http.Request, *webSession)

// webPage serves a page to a signed-in browser, and the sign-in form to
// anyone else.
func (s *Server) webPage(fn webHandler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		sess := s.webUser(r)
		if sess == nil {
			s.renderSignIn(w, "")
			return
		}
		fn(w, r, sess)
	}
}

// webForm accepts a form from a signed-in browser. Every form on every page
// goes through here, so the CSRF check cannot be forgotten on one of them.
func (s *Server) webForm(fn webHandler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		sess := s.webUser(r)
		if sess == nil {
			s.renderSignIn(w, "")
			return
		}
		if err := r.ParseForm(); err != nil || !s.checkCSRF(r, sess) {
			fail(w, http.StatusForbidden, "csrf", "stale form, reload the page")
			return
		}
		fn(w, r, sess)
	}
}

// checkCSRF verifies the form token against the session's.
func (s *Server) checkCSRF(r *http.Request, sess *webSession) bool {
	return sess.csrf != "" && secret.Equal(sess.csrf, r.FormValue("csrf"))
}

func (s *Server) setWebCookie(w http.ResponseWriter, token string, ttl time.Duration) {
	http.SetCookie(w, &http.Cookie{
		Name:     webCookie,
		Value:    token,
		Path:     "/",
		HttpOnly: true,
		Secure:   strings.HasPrefix(s.cfg.ExternalURL, "https://"),
		SameSite: http.SameSiteStrictMode,
		MaxAge:   int(ttl.Seconds()),
	})
}

func (s *Server) handleWebHome(w http.ResponseWriter, r *http.Request) {
	if s.webUser(r) != nil {
		http.Redirect(w, r, "/web/vaults", http.StatusFound)
		return
	}
	s.renderSignIn(w, "")
}

func (s *Server) handleWebSignIn(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		fail(w, http.StatusBadRequest, "bad_request", err.Error())
		return
	}
	var token string
	err := s.st.Update(func(st *store.State) error {
		u, err := checkPassword(st, r.FormValue("username"), r.FormValue("password"),
			r.FormValue("totp"))
		if err != nil {
			return err
		}
		token = s.newSession(st, u.ID, "web").Token
		return nil
	})
	switch {
	case errors.Is(err, errTOTPRequired):
		s.renderSignIn(w, "This account needs its one-time code.")
	case errors.Is(err, errTOTPInvalid):
		s.renderSignIn(w, "That one-time code was rejected.")
	case errors.Is(err, errBadCredentials):
		s.renderSignIn(w, "Unknown user or wrong password.")
	case err != nil:
		s.renderSignIn(w, err.Error())
	default:
		s.setWebCookie(w, token, s.cfg.SessionTTL)
		http.Redirect(w, r, "/web/vaults", http.StatusFound)
	}
}

func (s *Server) handleWebSignOut(w http.ResponseWriter, r *http.Request, _ *webSession) {
	if c, err := r.Cookie(webCookie); err == nil {
		_ = s.st.Update(func(st *store.State) error {
			delete(st.Sessions, c.Value)
			return nil
		})
	}
	s.setWebCookie(w, "", -time.Second)
	http.Redirect(w, r, "/web", http.StatusFound)
}

// webVault is one row of the vault list.
type webVault struct {
	ID       string
	Name     string
	Perm     string
	Strategy string
	Version  int64
	Updated  string
	By       string
	HasKey   bool
}

// webGroup is one option in a group selector.
type webGroup struct {
	ID   string
	Name string
}

func (s *Server) handleWebVaults(w http.ResponseWriter, r *http.Request, sess *webSession) {
	s.renderVaults(w, sess, "", "")
}

func (s *Server) handleWebCreateVault(w http.ResponseWriter, r *http.Request, sess *webSession) {
	password := r.FormValue("password")
	if password != r.FormValue("password2") {
		s.renderVaults(w, sess, "The two vault passwords do not match.", "")
		return
	}
	strategy := store.Strategy(r.FormValue("strategy"))
	if strategy == "" {
		strategy = store.StrategyMerge
	}
	view, err := s.createVault(sess.user, r.FormValue("name"), r.FormValue("group"),
		strategy, password)
	if err != nil {
		s.renderVaults(w, sess, humanError(err), "")
		return
	}
	s.renderVaults(w, sess, "",
		"Created "+view.Name+". Open "+view.Name+".kdbx from your KeepOrg client "+
			"with the password you just set.")
}

func (s *Server) handleWebChangePassword(w http.ResponseWriter, r *http.Request, sess *webSession) {
	next := r.FormValue("new_password")
	if next != r.FormValue("new_password2") {
		s.renderVaults(w, sess, "The two new passwords do not match.", "")
		return
	}
	cookie, _ := r.Cookie(webCookie)
	keep := ""
	if cookie != nil {
		keep = cookie.Value
	}
	err := s.st.Update(func(st *store.State) error {
		return changePassword(st, sess.user.Username, r.FormValue("current_password"),
			r.FormValue("totp"), next, keep)
	})
	switch {
	case errors.Is(err, errTOTPRequired):
		s.renderVaults(w, sess, "Enter your one-time code to change the password.", "")
	case errors.Is(err, errTOTPInvalid):
		s.renderVaults(w, sess, "That one-time code was rejected.", "")
	case errors.Is(err, errBadCredentials):
		s.renderVaults(w, sess, "The current password is wrong.", "")
	case err != nil:
		s.renderVaults(w, sess, err.Error(), "")
	default:
		s.renderVaults(w, sess, "",
			"Password changed. Other sessions on this account were signed out.")
	}
}

// humanError keeps internal wording out of the browser.
func humanError(err error) string {
	if errors.Is(err, errForbidden) {
		return "You do not administer that."
	}
	return err.Error()
}

// vaultRows collects what the signed-in user may see, and the groups they
// may create a vault in.
func (s *Server) vaultRows(u *store.User) ([]webVault, []webGroup) {
	vaults := []webVault{}
	groups := []webGroup{}
	s.st.Read(func(st *store.State) {
		for _, a := range st.Assignments(u.ID) {
			updated := "never"
			if a.DB.Version > 0 {
				updated = a.DB.UpdatedAt.UTC().Format("2006-01-02 15:04 UTC")
			}
			vaults = append(vaults, webVault{
				ID: a.DB.ID, Name: a.DB.Name, Perm: string(a.Perm),
				Strategy: string(a.DB.MergeStrategy), Version: a.DB.Version,
				Updated: updated, By: a.DB.UpdatedBy, HasKey: a.DB.WrappedKey != "",
			})
		}
		for id, g := range st.Groups {
			if st.IsGroupAdmin(u.ID, id) {
				groups = append(groups, webGroup{ID: id, Name: g.Name})
			}
		}
	})
	sort.Slice(groups, func(i, j int) bool { return groups[i].Name < groups[j].Name })
	return vaults, groups
}