// Copyright 2014 The Gogs Authors. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.

// Package ldap provide functions & structure to query a LDAP ldap directory
// For now, it's mainly tested again an MS Active Directory service, see README.md for more information
package ldap

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

	"github.com/gogits/gogs/modules/ldap"
	"github.com/gogits/gogs/modules/log"
)

// Basic LDAP authentication service
type Source struct {
	Name             string // canonical name (ie. corporate.ad)
	Host             string // LDAP host
	Port             int    // port number
	UseSSL           bool   // Use SSL
	SkipVerify       bool
	BindDN           string // DN to bind with
	BindPassword     string // Bind DN password
	UserBase         string // Base search path for users
	UserDN           string // Template for the DN of the user for simple auth
	AttributeName    string // First name attribute
	AttributeSurname string // Surname attribute
	AttributeMail    string // E-mail attribute
	Filter           string // Query filter to validate entry
	AdminFilter      string // Query filter to check if user is admin
	Enabled          bool   // if this source is disabled
}

func (ls *Source) sanitizedUserQuery(username string) (string, bool) {
	// See http://tools.ietf.org/search/rfc4515
	badCharacters := "\x00()*\\"
	if strings.ContainsAny(username, badCharacters) {
		log.Debug("'%s' contains invalid query characters. Aborting.", username)
		return "", false
	}

	return fmt.Sprintf(ls.Filter, username), true
}

func (ls *Source) sanitizedUserDN(username string) (string, bool) {
	// See http://tools.ietf.org/search/rfc4514: "special characters"
	badCharacters := "\x00()*\\,='\"#+;<> "
	if strings.ContainsAny(username, badCharacters) {
		log.Debug("'%s' contains invalid DN characters. Aborting.", username)
		return "", false
	}

	return fmt.Sprintf(ls.UserDN, username), true
}

func (ls *Source) FindUserDN(name string) (string, bool) {
	l, err := ldapDial(ls)
	if err != nil {
		log.Error(4, "LDAP Connect error, %s:%v", ls.Host, err)
		ls.Enabled = false
		return "", false
	}
	defer l.Close()

	log.Trace("Search for LDAP user: %s", name)
	if ls.BindDN != "" && ls.BindPassword != "" {
		err = l.Bind(ls.BindDN, ls.BindPassword)
		if err != nil {
			log.Debug("Failed to bind as BindDN[%s]: %v", ls.BindDN, err)
			return "", false
		}
		log.Trace("Bound as BindDN %s", ls.BindDN)
	} else {
		log.Trace("Proceeding with anonymous LDAP search.")
	}

	// A search for the user.
	userFilter, ok := ls.sanitizedUserQuery(name)
	if !ok {
		return "", false
	}

	log.Trace("Searching using filter %s", userFilter)
	search := ldap.NewSearchRequest(
		ls.UserBase, ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0,
		false, userFilter, []string{}, nil)

	// Ensure we found a user
	sr, err := l.Search(search)
	if err != nil || len(sr.Entries) < 1 {
		log.Debug("Failed search using filter[%s]: %v", userFilter, err)
		return "", false
	} else if len(sr.Entries) > 1 {
		log.Debug("Filter '%s' returned more than one user.", userFilter)
		return "", false
	}

	userDN := sr.Entries[0].DN
	if userDN == "" {
		log.Error(4, "LDAP search was succesful, but found no DN!")
		return "", false
	}

	return userDN, true
}

// searchEntry : search an LDAP source if an entry (name, passwd) is valid and in the specific filter
func (ls *Source) SearchEntry(name, passwd string, directBind bool) (string, string, string, bool, bool) {
	var userDN string
	if directBind {
		log.Trace("LDAP will bind directly via UserDN template: %s", ls.UserDN)

		var ok bool
		userDN, ok = ls.sanitizedUserDN(name)
		if !ok {
			return "", "", "", false, false
		}
	} else {
		log.Trace("LDAP will use BindDN.")

		var found bool
		userDN, found = ls.FindUserDN(name)
		if !found {
			return "", "", "", false, false
		}
	}

	l, err := ldapDial(ls)
	if err != nil {
		log.Error(4, "LDAP Connect error (%s): %v", ls.Host, err)
		ls.Enabled = false
		return "", "", "", false, false
	}
	defer l.Close()

	log.Trace("Binding with userDN: %s", userDN)
	err = l.Bind(userDN, passwd)
	if err != nil {
		log.Debug("LDAP auth. failed for %s, reason: %v", userDN, err)
		return "", "", "", false, false
	}

	log.Trace("Bound successfully with userDN: %s", userDN)
	userFilter, ok := ls.sanitizedUserQuery(name)
	if !ok {
		return "", "", "", false, false
	}

	search := ldap.NewSearchRequest(
		userDN, ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false, userFilter,
		[]string{ls.AttributeName, ls.AttributeSurname, ls.AttributeMail},
		nil)

	sr, err := l.Search(search)
	if err != nil {
		log.Error(4, "LDAP Search failed unexpectedly! (%v)", err)
		return "", "", "", false, false
	} else if len(sr.Entries) < 1 {
		if directBind {
			log.Error(4, "User filter inhibited user login.")
		} else {
			log.Error(4, "LDAP Search failed unexpectedly! (0 entries)")
		}

		return "", "", "", false, false
	}

	name_attr := sr.Entries[0].GetAttributeValue(ls.AttributeName)
	sn_attr := sr.Entries[0].GetAttributeValue(ls.AttributeSurname)
	mail_attr := sr.Entries[0].GetAttributeValue(ls.AttributeMail)

	admin_attr := false
	if len(ls.AdminFilter) > 0 {
		search = ldap.NewSearchRequest(
			userDN, ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false, ls.AdminFilter,
			[]string{ls.AttributeName},
			nil)

		sr, err = l.Search(search)
		if err != nil {
			log.Error(4, "LDAP Admin Search failed unexpectedly! (%v)", err)
		} else if len(sr.Entries) < 1 {
			log.Error(4, "LDAP Admin Search failed")
		} else {
			admin_attr = true
		}
	}

	return name_attr, sn_attr, mail_attr, admin_attr, true
}

func ldapDial(ls *Source) (*ldap.Conn, error) {
	if ls.UseSSL {
		log.Debug("Using TLS for LDAP without verifying: %v", ls.SkipVerify)
		return ldap.DialTLS("tcp", fmt.Sprintf("%s:%d", ls.Host, ls.Port), &tls.Config{
			InsecureSkipVerify: ls.SkipVerify,
		})
	} else {
		return ldap.Dial("tcp", fmt.Sprintf("%s:%d", ls.Host, ls.Port))
	}
}
