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
	token 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
		seen time.Time
	)
	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, token: c.Value}
			seen = sess.LastSeenAt
		}
	})
	if out != nil {
		s.markSeen(c.Value, seen)
	}
	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, r, "")
			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, r, "")
			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, r, "")
}

// preCookie carries a token that the sign-in form must echo. Without it a
// page elsewhere could post the form with its own credentials and sign a
// visitor in to the attacker's account, where whatever they then create
// lands. Strict, so a cross-site post does not carry it.
const preCookie = "keeporg_pre"

// preSessionToken returns this browser's sign-in form token, issuing one if
// it has none.
func (s *Server) preSessionToken(w http.ResponseWriter, r *http.Request) string {
	if c, err := r.Cookie(preCookie); err == nil && len(c.Value) == 64 {
		return c.Value
	}
	tok := secret.Token()
	http.SetCookie(w, &http.Cookie{
		Name: preCookie, Value: tok, Path: "/web", HttpOnly: true,
		Secure:   strings.HasPrefix(s.cfg.ExternalURL, "https://"),
		SameSite: http.SameSiteStrictMode,
	})
	return tok
}

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
	}
	if c, err := r.Cookie(preCookie); err != nil || !secret.Equal(c.Value, r.FormValue("pre")) {
		s.renderSignIn(w, r, "The sign-in form had expired. Sign in again.")
		return
	}
	var token string
	err := s.signIn(r, r.FormValue("username"), r.FormValue("password"), r.FormValue("totp"),
		func(st *store.State, u *store.User) error {
			token = s.newBrowserSession(st, u.ID, r).Token
			return nil
		})
	var throttled *errThrottled
	switch {
	case errors.As(err, &throttled):
		s.renderSignIn(w, r, throttled.Error())
	case errors.Is(err, errTOTPRequired):
		s.renderSignIn(w, r, "This account needs its one-time code.")
	case errors.Is(err, errTOTPInvalid):
		s.renderSignIn(w, r, "That one-time code was rejected.")
	case errors.Is(err, errBadCredentials):
		s.renderSignIn(w, r, "Unknown user or wrong password.")
	case err != nil:
		s.renderSignIn(w, r, 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.")
}

// webDeleteVault is what the confirmation page shows before a vault goes.
type webDeleteVault struct {
	ID      string
	Name    string
	Group   string
	Version int64
	Updated string
	Grants  int
	// NeedsName marks an account with no password of its own, which confirms
	// by typing the vault's name instead; NeedsTOTP marks one with a second
	// factor enrolled.
	NeedsName bool
	NeedsTOTP bool
}

// deleteVaultView gathers what is about to be destroyed, or nil when the
// caller does not administer the vault.
func (s *Server) deleteVaultView(u *store.User, id string) *webDeleteVault {
	var out *webDeleteVault
	s.st.Read(func(st *store.State) {
		db := st.Databases[id]
		if db == nil || st.DatabasePerm(u.ID, id) != store.PermAdmin {
			return
		}
		v := &webDeleteVault{ID: db.ID, Name: db.Name, Version: db.Version, Updated: "never"}
		if db.Version > 0 {
			v.Updated = db.UpdatedAt.UTC().Format("2006-01-02 15:04 UTC")
		}
		if g := st.Groups[db.OwnerGroupID]; g != nil {
			v.Group = g.Name
		}
		for _, gr := range st.Grants {
			if gr.DatabaseID == id {
				v.Grants++
			}
		}
		if target := st.Users[u.ID]; target != nil {
			v.NeedsName = target.PassHash == ""
			v.NeedsTOTP = target.TOTPConfirmed
		}
		out = v
	})
	return out
}

func (s *Server) handleWebDeleteVaultPage(w http.ResponseWriter, r *http.Request, sess *webSession) {
	s.renderDeleteVault(w, sess, r.PathValue("id"), "")
}

func (s *Server) handleWebDeleteVault(w http.ResponseWriter, r *http.Request, sess *webSession) {
	id := r.PathValue("id")
	name, err := s.deleteDatabase(r, sess.user, id, r.FormValue("password"),
		r.FormValue("totp"), r.FormValue("confirm_name"))
	var throttled *errThrottled
	switch {
	case errors.As(err, &throttled):
		s.renderDeleteVault(w, sess, id, throttled.Error())
	case errors.Is(err, errReauth):
		s.renderDeleteVault(w, sess, id, "Enter your account password.")
	case errors.Is(err, errTOTPRequired):
		s.renderDeleteVault(w, sess, id, "Enter your one-time code as well.")
	case errors.Is(err, errBadCredentials):
		s.renderDeleteVault(w, sess, id, "Your account password or one-time code is wrong.")
	case errors.Is(err, errConfirmName):
		s.renderDeleteVault(w, sess, id, "Type the vault's name exactly as it is shown.")
	case err != nil:
		s.renderDeleteVault(w, sess, id, humanError(err))
	default:
		s.renderVaults(w, sess, "", "Deleted "+name+" and every version of it. "+
			"Copies already on people's computers stay where they are.")
	}
}

// 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
}