package ldap

import (
	"crypto/tls"
	"errors"
	"fmt"
	"strings"

	ldap "github.com/vjeantet/ldapserver"
)

// New returns a new ldap server instance
func New(opts ...Option) *server {
	x := new(server)
	for _, o := range opts {
		o(x)
	}
	x.Server = ldap.NewServer()

	// The underlying server only permits a single handler and aborts
	// the process on a second registration, so a stable delegating
	// handler is registered once and SetDomain swaps the routed mux
	// underneath it.
	x.Handle(x)

	x.buildRoutes()

	return x
}

// buildRoutes (re)creates the route mux. It is called by New and again
// by SetDomain so that the naming-convention dependent routes always
// reflect the current domain without ever leaving duplicates behind.
func (s *server) buildRoutes() {
	routes := ldap.NewRouteMux()
	routes.NotFound(s.guard(s.handleNotFound))
	routes.Abandon(s.guard(s.handleAbandon))
	routes.Bind(s.guard(s.handleBind))

	routes.Search(s.guard(s.handleSearchDSE)).
		BaseDn("").
		Scope(ldap.SearchRequestScopeBaseObject).
		Filter("(objectclass=*)").
		Label("Search - ROOT DSE")

	if len(s.nc) > 0 {
		base := strings.Join(s.nc, ",")

		routes.Search(s.guard(s.handleSearchEntities)).
			BaseDn("ou=entities," + base).
			Scope(ldap.SearchRequestHomeSubtree).
			Label("Search - Entities")

		routes.Search(s.guard(s.handleSearchGroups)).
			BaseDn("ou=groups," + base).
			Scope(ldap.SearchRequestHomeSubtree).
			Label("Search - Groups")
	}

	// Catch-all route for single-entry lookups, registered last so
	// the specific routes above win. Clients such as HashiCorp Vault
	// address one entry directly with a base-object search whose base
	// DN is the entry itself; that DN has no fixed value to match on,
	// so only the scope can be matched here and the DN is dispatched
	// inside the handler. Subtree searches with an unknown base stay
	// unrouted and are still refused outright.
	routes.Search(s.guard(s.handleSearchEntry)).
		Scope(ldap.SearchRequestScopeBaseObject).
		Label("Search - Single Entry")

	s.routes = routes
}

// Serve serves a plaintext DSA on the provided bind string. It
// returns once the listener is bound; the server keeps running in the
// background until Stop is called.
func (s *server) Serve(bind string) error {
	return s.listenAndServe(bind)
}

// ServeTLS serves a TLS encrypted DSA on the provided bindstring
// using a key/cert pair located at the paths provided.  Key and
// certificate should be PEM encoded.
func (s *server) ServeTLS(bind, keypath, certpath string) error {
	cert, err := tls.LoadX509KeyPair(certpath, keypath)
	if err != nil {
		return fmt.Errorf("error creating certificate chain: %s", err)
	}
	cfg := &tls.Config{
		Certificates: []tls.Certificate{cert},
		MinVersion:   tls.VersionTLS12,
	}
	return s.listenAndServe(bind, func(srv *ldap.Server) {
		srv.Listener = tls.NewListener(srv.Listener, cfg)
	})
}

// listenAndServe binds the listening socket synchronously so that
// bind errors are reported to the caller, then serves in the
// background. The underlying server assigns its Listener field before
// invoking the option functions it is handed, so closing the started
// channel from an option guarantees that bookkeeping (and any TLS
// wrapping) is complete, and in a reliably ordered way, before Serve
// returns. Stop depends on reading that field.
func (s *server) listenAndServe(bind string, opts ...func(*ldap.Server)) error {
	started := make(chan struct{})
	failed := make(chan error, 1)
	go func() {
		opts := append(opts, func(*ldap.Server) { close(started) })
		if err := s.Server.ListenAndServe(bind, opts...); err != nil {
			select {
			case <-started:
				s.l.Error("Error from main server thread", "error", err)
			default:
				failed <- err
			}
		}
	}()
	select {
	case <-started:
		return nil
	case err := <-failed:
		return fmt.Errorf("error creating listener: %s", err)
	}
}

func (s *server) handleNotFound(w ldap.ResponseWriter, r *ldap.Message) {
	s.l.Warn("Refusing unrouted operation", "op", r.ProtocolOpName(), "message", r.String())
	writeResult(w, r, ldap.LDAPResultUnwillingToPerform,
		"Operation not implemented by server, searches must use a base DN of ou=entities or ou=groups underneath the naming context")
}

func (s *server) handleAbandon(w ldap.ResponseWriter, m *ldap.Message) {
	var req = m.GetAbandonRequest()
	// retreive the request to abandon, and send a abort signal to it
	if requestToAbandon, ok := m.Client.GetMessageByID(int(req)); ok {
		requestToAbandon.Abandon()
	}
}

// SetDomain configures the naming context from a plain domain name
// such as "example.com". NetAuth has no notion of a base DN, so it is
// supplied here: the domain is split on dots, each label becomes a
// dc component, and dc=netauth is prepended. It must be called after
// New and is safe to call more than once.
func (s *server) SetDomain(domain string) error {
	if domain == "" {
		return errors.New("a domain must be configured")
	}

	labels := strings.Split(domain, ".")
	nc := []string{"dc=netauth"}
	for _, l := range labels {
		l = strings.TrimSpace(l)
		if l == "" {
			return errors.New("domain contains an empty label")
		}
		nc = append(nc, "dc="+l)
	}

	s.nc = nc
	s.buildRoutes()
	return nil
}

// ServeLDAP implements the underlying server's Handler interface. It
// is registered once with the server and forwards to whatever route
// mux is current, which lets SetDomain rebuild routing without
// re-registering a handler (the server aborts on a second
// registration).
func (s *server) ServeLDAP(w ldap.ResponseWriter, r *ldap.Message) {
	if s.routes == nil {
		writeResult(w, r, ldap.LDAPResultUnavailable, "server is not configured with a domain")
		return
	}
	s.routes.ServeLDAP(w, r)
}