package main

// @FIXME: Proper handling of various upper/lower case combinations
// @FIXME: Implement missing search filters (in applyFilter)
// @FIXME: Add an initial prefix to the consul key value

import (
	"crypto/tls"
	"encoding/base64"
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"math/rand"
	"os"
	"os/signal"
	"strings"
	"syscall"

	ldap "./ldapserver"
	consul "github.com/hashicorp/consul/api"
	message "github.com/vjeantet/goldap/message"
)

const DEBUG = false

const ATTR_USERPASSWORD = "userpassword"
const ATTR_MEMBEROF = "memberof"
const ATTR_ENTRYUUID = "entryuuid"
const ATTR_CREATORSNAME = "creatorsname"
const ATTR_CREATETIMESTAMP = "createtimestamp"
const ATTR_MODIFIERSNAME = "modifiersname"
const ATTR_MODIFYTIMESTAMP = "modifytimestamp"

type ConfigFile struct {
	Suffix        string   `json:"suffix"`
	BindAddress   string   `json:"bind_address"`
	ConsulHost    string   `json:"consul_host"`
	Acl           []string `json:"acl"`
	SSLCertFile   string   `json:"ssl_cert_file"`
	SSLKeyFile    string   `json:"ssl_key_file"`
	SSLServerName string   `json:"ssl_server_name"`
}

type Config struct {
	Suffix      string
	BindAddress string
	ConsulHost  string

	Acl ACL

	TlsConfig *tls.Config
}

type Server struct {
	logger *log.Logger
	config Config
	kv     *consul.KV
}

type State struct {
	login Login
}

type Entry map[string][]string

var configFlag = flag.String("config", "./config.json", "Configuration file path")

func readConfig() Config {
	config_file := ConfigFile{
		BindAddress: "0.0.0.0:389",
	}

	bytes, err := ioutil.ReadFile(*configFlag)
	if err != nil {
		panic(err)
	}

	err = json.Unmarshal(bytes, &config_file)
	if err != nil {
		panic(err)
	}

	acl, err := ParseACL(config_file.Acl)
	if err != nil {
		panic(err)
	}

	ret := Config{
		Suffix:      config_file.Suffix,
		BindAddress: config_file.BindAddress,
		ConsulHost:  config_file.ConsulHost,
		Acl:         acl,
	}

	if config_file.SSLCertFile != "" && config_file.SSLKeyFile != "" && config_file.SSLServerName != "" {
		cert_txt, err := ioutil.ReadFile(config_file.SSLCertFile)
		if err != nil {
			panic(err)
		}
		key_txt, err := ioutil.ReadFile(config_file.SSLKeyFile)
		if err != nil {
			panic(err)
		}
		cert, err := tls.X509KeyPair(cert_txt, key_txt)
		if err != nil {
			panic(err)
		}
		ret.TlsConfig = &tls.Config{
			MinVersion:   tls.VersionSSL30,
			MaxVersion:   tls.VersionTLS12,
			Certificates: []tls.Certificate{cert},
			ServerName:   config_file.SSLServerName,
		}

	}

	return ret
}

func main() {
	flag.Parse()

	ldap.Logger = log.New(os.Stdout, "[ldapserver] ", log.LstdFlags)

	config := readConfig()

	// Connect to Consul
	consul_config := consul.DefaultConfig()
	if config.ConsulHost != "" {
		consul_config.Address = config.ConsulHost
	}
	consul_client, err := consul.NewClient(consul_config)
	if err != nil {
		panic(err)
	}
	kv := consul_client.KV()

	// Create gobottin server
	gobottin := Server{
		logger: log.New(os.Stdout, "[gobottin] ", log.LstdFlags),
		config: config,
		kv:     kv,
	}
	err = gobottin.init()
	if err != nil {
		panic(err)
	}

	//Create a new LDAP Server
	ldapserver := ldap.NewServer()
	ldapserver.NewUserState = func() ldap.UserState {
		return &State{
			login: Login{
				user:   "ANONYMOUS",
				groups: []string{},
			},
		}
	}

	routes := ldap.NewRouteMux()
	routes.Bind(gobottin.handleBind)
	routes.Search(gobottin.handleSearch)
	routes.Add(gobottin.handleAdd)
	routes.Compare(gobottin.handleCompare)
	routes.Delete(gobottin.handleDelete)
	routes.Modify(gobottin.handleModify)
	ldapserver.Handle(routes)

	if config.TlsConfig != nil {
		secureConn := func(s *ldap.Server) {
			s.Listener = tls.NewListener(s.Listener, config.TlsConfig)
		}
		go ldapserver.ListenAndServe(config.BindAddress, secureConn)
	} else {
		go ldapserver.ListenAndServe(config.BindAddress)
	}

	// When CTRL+C, SIGINT and SIGTERM signal occurs
	// Then stop server gracefully
	ch := make(chan os.Signal)
	signal.Notify(ch, syscall.SIGINT, syscall.SIGTERM)
	<-ch
	close(ch)

	ldapserver.Stop()
}

func (server *Server) init() error {
	path, err := dnToConsul(server.config.Suffix)
	if err != nil {
		return err
	}

	pair, _, err := server.kv.Get(path+"/attribute=objectClass", nil)
	if err != nil {
		return err
	}

	if pair != nil {
		return nil
	}

	base_attributes := Entry{
		"objectClass":           []string{"top", "dcObject", "organization"},
		"structuralObjectClass": []string{"Organization"},
	}
	suffix_dn, err := parseDN(server.config.Suffix)
	if err != nil {
		return err
	}
	base_attributes[suffix_dn[0].Type] = []string{suffix_dn[0].Value}

	err = server.addElements(server.config.Suffix, base_attributes)
	if err != nil {
		return err
	}

	admin_pass := make([]byte, 8)
	rand.Read(admin_pass)
	admin_pass_str := base64.RawURLEncoding.EncodeToString(admin_pass)
	admin_pass_hash := SSHAEncode([]byte(admin_pass_str))

	admin_dn := "cn=admin," + server.config.Suffix
	admin_attributes := Entry{
		"objectClass":           []string{"simpleSecurityObject", "organizationalRole"},
		"description":           []string{"LDAP administrator"},
		"cn":                    []string{"admin"},
		ATTR_USERPASSWORD:       []string{admin_pass_hash},
		"structuralObjectClass": []string{"organizationalRole"},
		"permissions":           []string{"read", "write"},
	}

	err = server.addElements(admin_dn, admin_attributes)
	if err != nil {
		return err
	}

	server.logger.Printf(
		"It seems to be a new installation, we created a default user for you:\n\n    dn:          %s\n    password:    %s\n\nWe didn't use true random, you should replace it as soon as possible.",
		admin_dn,
		admin_pass_str,
	)

	return nil
}

func (server *Server) addElements(dn string, attrs Entry) error {
	prefix, err := dnToConsul(dn)
	if err != nil {
		return err
	}

	for k, v := range attrs {
		path := prefix + "/attribute=" + k
		if len(v) == 0 {
			// If we have zero values, delete associated k/v pair
			_, err := server.kv.Delete(path, nil)
			if err != nil {
				return err
			}
		} else {
			json, err := json.Marshal(v)
			if err != nil {
				return err
			}
			pair := &consul.KVPair{Key: path, Value: json}
			_, err = server.kv.Put(pair, nil)
			if err != nil {
				return err
			}
		}
	}
	return nil
}

func (server *Server) getAttribute(dn string, attr string) ([]string, error) {
	path, err := dnToConsul(dn)
	if err != nil {
		return nil, err
	}

	pair, _, err := server.kv.Get(path+"/attribute="+attr, nil)
	if err != nil {
		return nil, err
	}

	if pair == nil {
		return nil, nil
	}

	return parseValue(pair.Value)
}

func (server *Server) objectExists(dn string) (bool, error) {
	prefix, err := dnToConsul(dn)
	if err != nil {
		return false, err
	}

	data, _, err := server.kv.List(prefix+"/", nil)
	if err != nil {
		return false, err
	}
	return len(data) > 0, nil
}

func (server *Server) checkSuffix(dn string, allow_extend bool) (string, error) {
	suffix := server.config.Suffix
	if len(dn) < len(suffix) {
		if dn != suffix[-len(dn):] || !allow_extend {
			return suffix, fmt.Errorf(
				"Only handling stuff under DN %s", suffix)
		}
		return suffix, nil
	} else {
		if dn[len(dn)-len(suffix):] != suffix {
			return suffix, fmt.Errorf(
				"Only handling stuff under DN %s", suffix)
		}
		return dn, nil
	}
}

func (server *Server) handleBind(s ldap.UserState, w ldap.ResponseWriter, m *ldap.Message) {
	state := s.(*State)
	r := m.GetBindRequest()

	result_code, err := server.handleBindInternal(state, &r)

	res := ldap.NewBindResponse(result_code)
	if err != nil {
		res.SetDiagnosticMessage(err.Error())
		server.logger.Printf("Failed bind for %s: %s", string(r.Name()), err.Error())
	}
	if result_code == ldap.LDAPResultSuccess {
		server.logger.Printf("Successfully bound to %s", string(r.Name()))
	} else {
		server.logger.Printf("Failed to bind to %s (%s)", string(r.Name()), err)
	}
	w.Write(res)
}

func (server *Server) handleBindInternal(state *State, r *message.BindRequest) (int, error) {
	// Check permissions
	if !server.config.Acl.Check(&state.login, "bind", string(r.Name()), []string{}) {
		return ldap.LDAPResultInsufficientAccessRights, nil
	}

	// Try to retrieve password and check for match
	passwd, err := server.getAttribute(string(r.Name()), ATTR_USERPASSWORD)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}
	if passwd == nil {
		return ldap.LDAPResultNoSuchObject, nil
	}

	for _, hash := range passwd {
		valid := SSHAMatches(hash, []byte(r.AuthenticationSimple()))
		if valid {
			groups, err := server.getAttribute(string(r.Name()), ATTR_MEMBEROF)
			if err != nil {
				return ldap.LDAPResultOperationsError, err
			}
			state.login = Login{
				user:   string(r.Name()),
				groups: groups,
			}
			return ldap.LDAPResultSuccess, nil
		}
	}
	return ldap.LDAPResultInvalidCredentials, nil
}

func (server *Server) handleSearch(s ldap.UserState, w ldap.ResponseWriter, m *ldap.Message) {
	state := s.(*State)
	r := m.GetSearchRequest()

	code, err := server.handleSearchInternal(state, w, &r)

	res := ldap.NewResponse(code)
	if err != nil {
		res.SetDiagnosticMessage(err.Error())
	}
	w.Write(message.SearchResultDone(res))
}

func (server *Server) handleSearchInternal(state *State, w ldap.ResponseWriter, r *message.SearchRequest) (int, error) {
	if DEBUG {
		server.logger.Printf("-- SEARCH REQUEST: --")
		server.logger.Printf("Request BaseDn=%s", r.BaseObject())
		server.logger.Printf("Request Filter=%s", r.Filter())
		server.logger.Printf("Request FilterString=%s", r.FilterString())
		server.logger.Printf("Request Attributes=%s", r.Attributes())
		server.logger.Printf("Request TimeLimit=%d", r.TimeLimit().Int())
	}

	if !server.config.Acl.Check(&state.login, "read", string(r.BaseObject()), []string{}) {
		return ldap.LDAPResultInsufficientAccessRights, fmt.Errorf("Please specify a base object on which you have read rights")
	}

	baseObject, err := server.checkSuffix(string(r.BaseObject()), true)
	if err != nil {
		return ldap.LDAPResultInvalidDNSyntax, err
	}
	basePath, err := dnToConsul(baseObject)
	if err != nil {
		return ldap.LDAPResultInvalidDNSyntax, err
	}

	data, _, err := server.kv.List(basePath+"/", nil)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}

	entries, err := parseConsulResult(data)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}
	if DEBUG {
		server.logger.Printf("in %s: %#v", basePath+"/", data)
		server.logger.Printf("%#v", entries)
	}

	for dn, entry := range entries {
		// Filter out if we don't match requested filter
		matched, err := applyFilter(entry, r.Filter())
		if err != nil {
			return ldap.LDAPResultUnwillingToPerform, err
		}
		if !matched {
			continue
		}

		// Filter out if user is not allowed to read this
		if !server.config.Acl.Check(&state.login, "read", dn, []string{}) {
			continue
		}

		e := ldap.NewSearchResultEntry(dn)
		for attr, val := range entry {
			// If attribute is not in request, exclude it from returned entry
			if len(r.Attributes()) > 0 {
				found := false
				for _, requested := range r.Attributes() {
					if strings.EqualFold(string(requested), attr) {
						found = true
						break
					}
				}
				if !found {
					continue
				}
			}
			// If we are not allowed to read attribute, exclude it from returned entry
			if !server.config.Acl.Check(&state.login, "read", dn, []string{attr}) {
				continue
			}
			// Send result
			for _, v := range val {
				e.AddAttribute(message.AttributeDescription(attr),
					message.AttributeValue(v))
			}
		}
		w.Write(e)
	}

	return ldap.LDAPResultSuccess, nil
}

func applyFilter(entry Entry, filter message.Filter) (bool, error) {
	if fAnd, ok := filter.(message.FilterAnd); ok {
		for _, cond := range fAnd {
			res, err := applyFilter(entry, cond)
			if err != nil {
				return false, err
			}
			if !res {
				return false, nil
			}
		}
		return true, nil
	} else if fOr, ok := filter.(message.FilterOr); ok {
		for _, cond := range fOr {
			res, err := applyFilter(entry, cond)
			if err != nil {
				return false, err
			}
			if res {
				return true, nil
			}
		}
		return false, nil
	} else if fNot, ok := filter.(message.FilterNot); ok {
		res, err := applyFilter(entry, fNot.Filter)
		if err != nil {
			return false, err
		}
		return !res, nil
	} else if fPresent, ok := filter.(message.FilterPresent); ok {
		what := string(fPresent)
		// Case insensitive search
		for desc, values := range entry {
			if strings.EqualFold(what, desc) {
				return len(values) > 0, nil
			}
		}
		return false, nil
	} else if fEquality, ok := filter.(message.FilterEqualityMatch); ok {
		desc := string(fEquality.AttributeDesc())
		target := string(fEquality.AssertionValue())
		// Case insensitive attribute search
		for entry_desc, value := range entry {
			if strings.EqualFold(entry_desc, desc) {
				for _, val := range value {
					if val == target {
						return true, nil
					}
				}
				return false, nil
			}
		}
		return false, nil
	} else {
		return false, fmt.Errorf("Unsupported filter: %#v %T", filter, filter)
	}
}

func (server *Server) handleAdd(s ldap.UserState, w ldap.ResponseWriter, m *ldap.Message) {
	state := s.(*State)
	r := m.GetAddRequest()

	code, err := server.handleAddInternal(state, &r)

	res := ldap.NewResponse(code)
	if err != nil {
		res.SetDiagnosticMessage(err.Error())
	}
	if code == ldap.LDAPResultSuccess {
		server.logger.Printf("Successfully added %s", string(r.Entry()))
	} else {
		server.logger.Printf("Failed to add %s (%s)", string(r.Entry()), err)
	}
	w.Write(message.AddResponse(res))
}

func (server *Server) handleAddInternal(state *State, r *message.AddRequest) (int, error) {
	dn := string(r.Entry())

	_, err := server.checkSuffix(dn, false)
	if err != nil {
		return ldap.LDAPResultInvalidDNSyntax, err
	}

	dnSplit, err := parseDN(dn)
	if err != nil {
		return ldap.LDAPResultInvalidDNSyntax, err
	}

	// Check permissions
	attrListStr := []string{}
	for _, attribute := range r.Attributes() {
		attrListStr = append(attrListStr, string(attribute.Type_()))
	}
	if !server.config.Acl.Check(&state.login, "add", dn, attrListStr) {
		return ldap.LDAPResultInsufficientAccessRights, nil
	}

	// Check that object does not already exist
	exists, err := server.objectExists(dn)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}
	if exists {
		return ldap.LDAPResultEntryAlreadyExists, nil
	}

	// Add object

	// If adding a group, track of who the members will be so that their memberOf field can be updated later
	var members []string = nil

	entry := Entry{}
	for _, attribute := range r.Attributes() {
		key := string(attribute.Type_())
		vals_str := []string{}
		for _, val := range attribute.Vals() {
			vals_str = append(vals_str, string(val))
		}

		// Fail if they are trying to write memberOf, we manage this ourselves
		err = checkRestrictedAttr(key)
		if err != nil {
			return ldap.LDAPResultObjectClassViolation, err
		}
		// If they are writing a member key, we have to check they are adding valid members
		if strings.EqualFold(key, "member") {
			members = vals_str
			for _, member := range members {
				_, err := server.checkSuffix(member, false)
				if err != nil {
					return ldap.LDAPResultInvalidDNSyntax, err
				}
				exists, err = server.objectExists(member)
				if err != nil {
					return ldap.LDAPResultOperationsError, err
				}
				if !exists {
					return ldap.LDAPResultNoSuchObject, fmt.Errorf(
						"Cannot add %s to members, it does not exist!",
						member)
				}
			}
		}
		entry[key] = vals_str
	}

	entry[ATTR_CREATORSNAME] = []string{state.login.user}
	entry[ATTR_CREATETIMESTAMP] = []string{genTimestamp()}
	entry[ATTR_ENTRYUUID] = []string{genUuid()}
	entry[dnSplit[0].Type] = []string{dnSplit[0].Value}

	err = server.addElements(dn, entry)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}

	if members != nil {
		for _, member := range members {
			memberGroups, err := server.getAttribute(member, ATTR_MEMBEROF)
			if err != nil {
				return ldap.LDAPResultOperationsError, err
			}
			if memberGroups == nil {
				memberGroups = []string{}
			}

			alreadyMember := false
			for _, mb := range memberGroups {
				if mb == dn {
					alreadyMember = true
					server.logger.Printf("Warning: inconsistency detected, %s was memberOf %s at a time when it didn't exist!",
						member, dn)
					break
				}
			}

			if !alreadyMember {
				memberGroups = append(memberGroups, dn)
				err = server.addElements(member, Entry{
					ATTR_MEMBEROF: memberGroups,
				})
				if err != nil {
					return ldap.LDAPResultOperationsError, err
				}
			}
		}
	}

	return ldap.LDAPResultSuccess, nil
}

func (server *Server) handleCompare(s ldap.UserState, w ldap.ResponseWriter, m *ldap.Message) {
	state := s.(*State)
	r := m.GetCompareRequest()

	code, err := server.handleCompareInternal(state, &r)

	res := ldap.NewResponse(code)
	if err != nil {
		res.SetDiagnosticMessage(err.Error())
	}
	w.Write(message.CompareResponse(res))
}

func (server *Server) handleCompareInternal(state *State, r *message.CompareRequest) (int, error) {
	dn := string(r.Entry())
	attr := string(r.Ava().AttributeDesc())
	expected := string(r.Ava().AssertionValue())

	_, err := server.checkSuffix(dn, false)
	if err != nil {
		return ldap.LDAPResultInvalidDNSyntax, err
	}

	// Check permissions
	if !server.config.Acl.Check(&state.login, dn, "read", []string{attr}) {
		return ldap.LDAPResultInsufficientAccessRights, nil
	}

	// Do query
	exists, err := server.objectExists(dn)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}
	if !exists {
		return ldap.LDAPResultNoSuchObject, fmt.Errorf("Not found: %s", dn)
	}

	values, err := server.getAttribute(dn, attr)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}

	for _, v := range values {
		if v == expected {
			return ldap.LDAPResultCompareTrue, nil
		}
	}

	return ldap.LDAPResultCompareFalse, nil
}

func (server *Server) handleDelete(s ldap.UserState, w ldap.ResponseWriter, m *ldap.Message) {
	state := s.(*State)
	r := m.GetDeleteRequest()

	code, err := server.handleDeleteInternal(state, &r)

	res := ldap.NewResponse(code)
	if err != nil {
		res.SetDiagnosticMessage(err.Error())
	}
	if code == ldap.LDAPResultSuccess {
		server.logger.Printf("Successfully deleted %s", string(r))
	} else {
		server.logger.Printf("Failed to delete %s (%s)", string(r), err)
	}
	w.Write(message.DelResponse(res))
}

func (server *Server) handleDeleteInternal(state *State, r *message.DelRequest) (int, error) {
	dn := string(*r)

	_, err := server.checkSuffix(dn, false)
	if err != nil {
		return ldap.LDAPResultInvalidDNSyntax, err
	}

	// Check for delete permission
	if !server.config.Acl.Check(&state.login, "delete", dn, []string{}) {
		return ldap.LDAPResultInsufficientAccessRights, nil
	}

	// Check that this LDAP entry exists and has no children
	path, err := dnToConsul(dn)
	if err != nil {
		return ldap.LDAPResultInvalidDNSyntax, err
	}

	items, _, err := server.kv.List(path+"/", nil)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}

	if len(items) == 0 {
		return ldap.LDAPResultNoSuchObject, fmt.Errorf("Not found: %s", dn)
	}
	for _, item := range items {
		itemDN, _, err := consulToDN(item.Key)
		if err != nil {
			continue
		}
		if itemDN != dn {
			return ldap.LDAPResultNotAllowedOnNonLeaf, fmt.Errorf(
				"Cannot delete %d as it has children", dn)
		}
	}

	// Retrieve group membership before we delete everything
	memberOf, err := server.getAttribute(dn, ATTR_MEMBEROF)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}

	// Delete the LDAP entry
	_, err = server.kv.DeleteTree(path+"/", nil)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}

	// Delete it from the member list of all the groups it was a member of
	if memberOf != nil {
		for _, group := range memberOf {
			groupMembers, err := server.getAttribute(dn, "member")
			if err != nil {
				return ldap.LDAPResultOperationsError, err
			}

			newMembers := []string{}
			for _, memb := range groupMembers {
				if memb != dn {
					newMembers = append(newMembers, memb)
				}
			}

			err = server.addElements(group, Entry{
				"member": newMembers,
			})
			if err != nil {
				return ldap.LDAPResultOperationsError, err
			}
		}
	}

	return ldap.LDAPResultSuccess, nil
}

func (server *Server) handleModify(s ldap.UserState, w ldap.ResponseWriter, m *ldap.Message) {
	state := s.(*State)
	r := m.GetModifyRequest()

	code, err := server.handleModifyInternal(state, &r)

	res := ldap.NewResponse(code)
	if err != nil {
		res.SetDiagnosticMessage(err.Error())
	}
	if code == ldap.LDAPResultSuccess {
		server.logger.Printf("Successfully modified %s", string(r.Object()))
	} else {
		server.logger.Printf("Failed to modifiy %s (%s)", string(r.Object()), err)
	}
	w.Write(message.ModifyResponse(res))
}

func (server *Server) handleModifyInternal(state *State, r *message.ModifyRequest) (int, error) {
	dn := string(r.Object())

	_, err := server.checkSuffix(dn, false)
	if err != nil {
		return ldap.LDAPResultInvalidDNSyntax, err
	}

	dnSplit, err := parseDN(dn)
	if err != nil {
		return ldap.LDAPResultInvalidDNSyntax, err
	}

	// First permission check with no particular attributes
	if !server.config.Acl.Check(&state.login, "modify", dn, []string{}) {
		return ldap.LDAPResultInsufficientAccessRights, nil
	}

	// Retrieve previous values (by the way, check object exists)
	path, err := dnToConsul(dn)
	if err != nil {
		return ldap.LDAPResultInvalidDNSyntax, err
	}

	items, _, err := server.kv.List(path+"/attribute=", nil)
	if err != nil {
		return ldap.LDAPResultOperationsError, err
	}

	if len(items) == 0 {
		return ldap.LDAPResultNoSuchObject, fmt.Errorf("Not found: %s", dn)
	}

	prevEntry := Entry{}
	for _, item := range items {
		itemDN, attr, err := consulToDN(item.Key)
		if err != nil {
			continue
		}
		if itemDN != dn {
			panic("itemDN != dn in handleModifyInternal")
		}
		vals, err := parseValue(item.Value)
		if err != nil {
			return ldap.LDAPResultOperationsError, err
		}
		prevEntry[attr] = vals
	}

	// Keep track of group members added/deleted
	addMembers, delMembers := []string{}, []string{}

	// Produce new entry values to be saved
	newEntry := Entry{}
	for _, change := range r.Changes() {
		attr := string(change.Modification().Type_())
		values := change.Modification().Vals()

		err = checkRestrictedAttr(attr)
		if err != nil {
			return ldap.LDAPResultObjectClassViolation, err
		}
		if strings.EqualFold(attr, dnSplit[0].Type) {
			return ldap.LDAPResultObjectClassViolation, fmt.Errorf("%s may not be changed as it is part of object path", attr)
		}

		// Check for permission to modify this attribute
		if !server.config.Acl.Check(&state.login, "modify", dn, []string{attr}) {
			return ldap.LDAPResultInsufficientAccessRights, nil
		}

		if change.Operation() == ldap.ModifyRequestChangeOperationAdd {
			newEntry[attr] = prevEntry[attr]
			for _, val := range values {
				present := false
				for _, prevVal := range newEntry[attr] {
					if prevVal == string(val) {
						present = true
						break
					}
				}
				if !present {
					newEntry[attr] = append(newEntry[attr], string(val))
					if strings.EqualFold(attr, "member") {
						addMembers = append(addMembers, string(val))
					}
				}
			}
		} else if change.Operation() == ldap.ModifyRequestChangeOperationDelete {
			if len(values) == 0 {
				// Delete everything
				newEntry[attr] = []string{}
				if strings.EqualFold(attr, "member") {
					delMembers = append(delMembers, prevEntry[attr]...)
				}
			} else {
				// Delete only those specified
				newEntry[attr] = []string{}
				for _, prevVal := range prevEntry[attr] {
					keep := true
					for _, delVal := range values {
						if string(delVal) == prevVal {
							keep = false
							break
						}
					}
					if keep {
						newEntry[attr] = append(newEntry[attr], prevVal)
					} else {
						if strings.EqualFold(attr, "member") {
							delMembers = append(delMembers, prevVal)
						}
					}
				}
			}
		} else if change.Operation() == ldap.ModifyRequestChangeOperationReplace {
			newEntry[attr] = []string{}
			for _, newVal := range values {
				newEntry[attr] = append(newEntry[attr], string(newVal))
			}
			if strings.EqualFold(attr, "member") {
				for _, newMem := range newEntry[attr] {
					mustAdd := true
					for _, prevMem := range prevEntry[attr] {
						if prevMem == newMem {
							mustAdd = false
							break
						}
					}
					if mustAdd {
						addMembers = append(addMembers, newMem)
					}
				}
				for _, prevMem := range prevEntry[attr] {
					mustDel := true
					for _, newMem := range newEntry[attr] {
						if newMem == prevMem {
							mustDel = false
							break
						}
					}
					if mustDel {
						delMembers = append(delMembers, prevMem)
					}
				}
			}
		}
	}

	// Check that added members actually exist
	for _, addMem := range addMembers {
		exists, err := server.objectExists(addMem)
		if err != nil {
			return ldap.LDAPResultOperationsError, err
		}
		if !exists {
			return ldap.LDAPResultNoSuchObject, fmt.Errorf(
				"Cannot add member %s, it does not exist", addMem)
		}
	}

	newEntry[ATTR_MODIFIERSNAME] = []string{state.login.user}
	newEntry[ATTR_MODIFYTIMESTAMP] = []string{genTimestamp()}

	// Save the edited values
	server.addElements(dn, newEntry)

	// Update memberOf for added members and deleted members
	for _, addMem := range addMembers {
		memberOf, err := server.getAttribute(addMem, ATTR_MEMBEROF)
		if err != nil {
			return ldap.LDAPResultOperationsError, err
		}
		if memberOf == nil {
			memberOf = []string{}
		}
		memberOf = append(memberOf, dn)
		err = server.addElements(addMem, Entry{ATTR_MEMBEROF: memberOf})
		if err != nil {
			return ldap.LDAPResultOperationsError, err
		}
	}

	for _, delMem := range delMembers {
		memberOf, err := server.getAttribute(delMem, ATTR_MEMBEROF)
		if err != nil {
			return ldap.LDAPResultOperationsError, err
		}
		if memberOf == nil {
			memberOf = []string{}
		}
		newMemberOf := []string{}
		for _, g := range memberOf {
			if g != dn {
				newMemberOf = append(newMemberOf, g)
			}
		}

		err = server.addElements(delMem, Entry{ATTR_MEMBEROF: newMemberOf})
		if err != nil {
			return ldap.LDAPResultOperationsError, err
		}
	}

	return ldap.LDAPResultSuccess, nil
}