//go:generate go-bindata -pkg bindata -o bindata/bindata.go template/
//go:generate protoc -I pb/ -I$GOPATH/src/github.com/grpc-ecosystem/grpc-gateway/third_party/googleapis pb/user.proto pb/vpn.proto pb/network.proto --go_out=plugins=grpc:pb
//go:generate protoc -I pb/ -I$GOPATH/src/github.com/grpc-ecosystem/grpc-gateway/third_party/googleapis pb/user.proto pb/vpn.proto pb/network.proto --grpc-gateway_out=logtostderr=true:pb
//go:generate protoc -I pb/ -I$GOPATH/src/github.com/grpc-ecosystem/grpc-gateway/third_party/googleapis pb/user.proto pb/vpn.proto pb/network.proto --swagger_out=logtostderr=true:pb

package ovpm

import (
	"bytes"
	"fmt"
	"math/big"
	"net"
	"os"
	"os/exec"
	"strings"
	"text/template"

	"time"

	"github.com/Sirupsen/logrus"
	"github.com/asaskevich/govalidator"
	"github.com/cad/ovpm/bindata"
	"github.com/cad/ovpm/pki"
	"github.com/cad/ovpm/supervisor"
	"github.com/coreos/go-iptables/iptables"
	"github.com/google/uuid"
	"github.com/jinzhu/gorm"
)

const (
	TCPProto string = "tcp"
	UDPProto string = "udp"
)

// DBServer is database model for storing VPN server related stuff.
type DBServer struct {
	gorm.Model
	Name         string `gorm:"unique_index"` // Server name.
	SerialNumber string

	Hostname string // Server's ip address or FQDN
	Port     string // Server's listening port
	Proto    string // Server's proto udp or tcp
	Cert     string // Server RSA certificate.
	Key      string // Server RSA private key.
	CACert   string // Root CA RSA certificate.
	CAKey    string // Root CA RSA key.
	Net      string // VPN network.
	Mask     string // VPN network mask.
	CRL      string // Certificate Revocation List
}

// CheckSerial takes a serial number and checks it against the current server's serial number.
func (s *DBServer) CheckSerial(serial string) bool {
	return serial == s.SerialNumber
}

type _VPNServerConfig struct {
	CertPath     string
	KeyPath      string
	CACertPath   string
	CAKeyPath    string
	CCDPath      string
	CRLPath      string
	DHParamsPath string
	Net          string
	Mask         string
	Port         string
	Proto        string
}

// Init regenerates keys and certs for a Root CA, and saves them in the database.
//
// proto can be either "udp" or "tcp" and if it's "" it defaults to "udp".
func Init(hostname string, port string, proto string) error {
	if port == "" {
		port = DefaultVPNPort
	}

	switch proto {
	case "":
		proto = UDPProto
	case UDPProto:
		proto = UDPProto
	case TCPProto:
		proto = TCPProto
	default:
		return fmt.Errorf("validation error: proto:`%s` should be either 'tcp' or 'udp'", proto)
	}

	if !govalidator.IsNumeric(port) {
		return fmt.Errorf("validation error: port:`%s` should be numeric", port)
	}

	serverName := "default"
	if IsInitialized() {
		if err := Deinit(); err != nil {
			logrus.Errorf("server can not be deleted: %v", err)
			return err
		}
	}

	if !govalidator.IsHost(hostname) {
		return fmt.Errorf("validation error: hostname:`%s` should be either an ip address or a FQDN", hostname)
	}

	ca, err := pki.NewCA()
	if err != nil {
		return fmt.Errorf("can not create ca creds: %s", err)
	}

	srv, err := pki.NewServerCertHolder(ca)
	if err != nil {
		return fmt.Errorf("can not create server cert creds: %s", err)
	}
	serialNumber := uuid.New().String()
	serverInstance := DBServer{
		Name: serverName,

		SerialNumber: serialNumber,
		Hostname:     hostname,
		Proto:        proto,
		Port:         port,
		Cert:         srv.Cert,
		Key:          srv.Key,
		CACert:       ca.Cert,
		CAKey:        ca.Key,
		Net:          _DefaultServerNetwork,
		Mask:         _DefaultServerNetMask,
	}

	db.Create(&serverInstance)

	if db.NewRecord(&serverInstance) {
		return fmt.Errorf("can not create server instance on database")
	}

	users, err := GetAllUsers()
	if err != nil {
		return err
	}
	// Sign all users in the db with the new server
	for _, user := range users {
		err := user.Renew()
		logrus.Infof("user certificate changed for %s, you should run: $ ovpm user export-config --user %s", user.Username, user.Username)
		if err != nil {
			logrus.Errorf("can not sign user %s: %v", user.Username, err)
			continue
		}
	}
	Emit()
	logrus.Infof("server initialized")
	return nil
}

// Deinit deletes the server with the given serverName from the database and frees the allocated resources.
func Deinit() error {
	if !IsInitialized() {
		return fmt.Errorf("server not found")
	}

	db.Unscoped().Delete(&DBServer{})
	db.Unscoped().Delete(&DBRevoked{})
	Emit()
	return nil
}

// DumpsClientConfig generates .ovpn file for the given vpn user and returns it as a string.
func DumpsClientConfig(username string) (string, error) {
	var result bytes.Buffer
	user, err := GetUser(username)
	if err != nil {
		return "", err
	}

	server, err := GetServerInstance()
	if err != nil {
		return "", err
	}

	params := struct {
		Hostname string
		Port     string
		CA       string
		Key      string
		Cert     string
		NoGW     bool
	}{
		Hostname: server.Hostname,
		Port:     server.Port,
		CA:       server.CACert,
		Key:      user.Key,
		Cert:     user.Cert,
		NoGW:     user.NoGW,
	}
	data, err := bindata.Asset("template/client.ovpn.tmpl")
	if err != nil {
		return "", err
	}

	t, err := template.New("client.ovpn").Parse(string(data))
	if err != nil {
		return "", fmt.Errorf("can not parse client.ovpn.tmpl template: %s", err)
	}

	err = t.Execute(&result, params)
	if err != nil {
		return "", fmt.Errorf("can not render client.ovpn: %s", err)
	}

	return result.String(), nil
}

// DumpClientConfig generates .ovpn file for the given vpn user and dumps it to outPath.
func DumpClientConfig(username, path string) error {
	result, err := DumpsClientConfig(username)
	if err != nil {
		return err
	}
	// Wite rendered content into openvpn server conf.
	return emitToFile(path, result, 0)

}

// GetSystemCA returns the system CA from the database if available.
func GetSystemCA() (*pki.CA, error) {
	server := DBServer{}
	db.First(&server)
	if db.NewRecord(&server) {
		return nil, fmt.Errorf("server record does not exists in db")
	}
	return &pki.CA{
		CertHolder: pki.CertHolder{
			Cert: server.CACert,
			Key:  server.CAKey,
		},
	}, nil

}

// vpnProc represents the OpenVPN process that is managed by the ovpm supervisor globally OpenVPN.
var vpnProc supervisor.Supervisable

// StartVPNProc starts the OpenVPN process.
func StartVPNProc() {
	if !IsInitialized() {
		logrus.Error("can not launch OpenVPN because system is not initialized")
		return
	}
	if vpnProc == nil {
		panic(fmt.Sprintf("vpnProc is not initialized!"))
	}
	if vpnProc.Status() == supervisor.RUNNING {
		logrus.Error("OpenVPN is already started")
		return
	}
	vpnProc.Start()
	ensureNatEnabled()
}

// RestartVPNProc restarts the OpenVPN process.
func RestartVPNProc() {
	if !IsInitialized() {
		logrus.Error("can not launch OpenVPN because system is not initialized")
		return
	}
	if vpnProc == nil {
		panic(fmt.Sprintf("vpnProc is not initialized!"))
	}
	vpnProc.Restart()
	ensureNatEnabled()
}

// StopVPNProc stops the OpenVPN process.
func StopVPNProc() {
	if vpnProc == nil {
		panic(fmt.Sprintf("vpnProc is not initialized!"))
	}
	if vpnProc.Status() != supervisor.RUNNING {
		logrus.Error("OpenVPN is already not running")
		return
	}
	vpnProc.Stop()

}

// Emit generates all needed files for the OpenVPN server and dumps them to their corresponding paths defined in the config.
func Emit() error {
	// Check dependencies
	if !checkOpenVPNExecutable() {
		return fmt.Errorf("openvpn executable can not be found! you should install OpenVPN on this machine")
	}

	if !checkOpenSSLExecutable() {
		return fmt.Errorf("openssl executable can not be found! you should install openssl on this machine")

	}

	if !checkIptablesExecutable() {
		return fmt.Errorf("iptables executable can not be found")
	}

	if !IsInitialized() {
		return fmt.Errorf("you should create a server first. e.g. $ ovpm vpn create-server")
	}

	if err := emitServerConf(); err != nil {
		return fmt.Errorf("can not emit server conf: %s", err)
	}

	if err := emitServerCert(); err != nil {
		return fmt.Errorf("can not emit server cert: %s", err)
	}

	if err := emitServerKey(); err != nil {
		return fmt.Errorf("can not emit server key: %s", err)
	}

	if err := emitCACert(); err != nil {
		return fmt.Errorf("can not emit ca cert : %s", err)
	}

	if err := emitCAKey(); err != nil {
		return fmt.Errorf("can not emit ca key: %s", err)
	}

	if err := emitDHParams(); err != nil {
		return fmt.Errorf("can not emit dhparams: %s", err)
	}

	if err := emitCCD(); err != nil {
		return fmt.Errorf("can not emit ccd: %s", err)
	}

	if err := emitIptables(); err != nil {
		return fmt.Errorf("can not emit iptables: %s", err)
	}

	if err := emitCRL(); err != nil {
		return fmt.Errorf("can not emit crl: %s", err)
	}

	logrus.Info("configurations emitted to the filesystem")

	if IsInitialized() {
		for {
			if vpnProc.Status() == supervisor.RUNNING || vpnProc.Status() == supervisor.STOPPED {
				logrus.Info("OpenVPN process is restarting")
				RestartVPNProc()
				break
			}
			time.Sleep(1 * time.Second)
		}
	}

	return nil
}

func emitToFile(path, content string, mode uint) error {
	// When testing don't emit files to the filesystem. Just pretend you did.
	if Testing {
		return nil
	}
	file, err := os.Create(path)
	if err != nil {
		return fmt.Errorf("Cannot create file %s: %v", path, err)

	}
	if mode != 0 {
		file.Chmod(os.FileMode(mode))
	}
	defer file.Close()
	fmt.Fprintf(file, content)
	return nil
}

func emitServerConf() error {
	serverInstance, err := GetServerInstance()
	if err != nil {
		return fmt.Errorf("can not retrieve server: %v", err)
	}
	port := DefaultVPNPort
	if serverInstance.Port != "" {
		port = serverInstance.Port
	}

	var result bytes.Buffer

	server := _VPNServerConfig{
		CertPath:     _DefaultCertPath,
		KeyPath:      _DefaultKeyPath,
		CACertPath:   _DefaultCACertPath,
		CAKeyPath:    _DefaultCAKeyPath,
		CCDPath:      _DefaultVPNCCDPath,
		CRLPath:      _DefaultCRLPath,
		DHParamsPath: _DefaultDHParamsPath,
		Net:          _DefaultServerNetwork,
		Mask:         _DefaultServerNetMask,
		Port:         port,
		Proto:        serverInstance.Proto,
	}
	data, err := bindata.Asset("template/server.conf.tmpl")
	if err != nil {
		return err
	}

	t, err := template.New("server.conf").Parse(string(data))
	if err != nil {
		return fmt.Errorf("can not parse server.conf.tmpl template: %s", err)
	}

	err = t.Execute(&result, server)
	if err != nil {
		return fmt.Errorf("can not render server.conf: %s", err)
	}

	// Wite rendered content into openvpn server conf.
	return emitToFile(_DefaultVPNConfPath, result.String(), 0)
}

// GetServerInstance returns the default server from the database.
func GetServerInstance() (*DBServer, error) {
	var server DBServer
	db.First(&server)
	if db.NewRecord(server) {
		return nil, fmt.Errorf("can not retrieve server from db")
	}
	return &server, nil
}

// IsInitialized checks if there is a default server in the database or not.
func IsInitialized() bool {
	var server DBServer
	db.First(&server)
	if db.NewRecord(server) {
		return false
	}
	return true
}

func emitServerKey() error {
	server, err := GetServerInstance()
	if err != nil {
		return err
	}

	// Write rendered content into key file.
	return emitToFile(_DefaultKeyPath, server.Key, 0600)
}

func emitServerCert() error {
	server, err := GetServerInstance()
	if err != nil {
		return err
	}

	// Write rendered content into the cert file.
	return emitToFile(_DefaultCertPath, server.Cert, 0)
}

func emitCRL() error {
	var revokedDBItems []*DBRevoked
	db.Find(&revokedDBItems)
	var revokedCertSerials []*big.Int
	for _, item := range revokedDBItems {
		bi := big.NewInt(0)
		bi.SetString(item.SerialNumber, 16)
		revokedCertSerials = append(revokedCertSerials, bi)
	}
	systemCA, err := GetSystemCA()
	if err != nil {
		return fmt.Errorf("can not emit CRL: %v", err)
	}
	crl, err := pki.NewCRL(systemCA, revokedCertSerials...)
	if err != nil {
		return fmt.Errorf("can not emit crl: %v", err)
	}

	return emitToFile(_DefaultCRLPath, crl, 0)
}

func emitCACert() error {
	server, err := GetServerInstance()
	if err != nil {
		return err
	}

	// Write rendered content into the ca cert file.
	return emitToFile(_DefaultCACertPath, server.CACert, 0)
}

func emitCAKey() error {
	server, err := GetServerInstance()
	if err != nil {
		return err
	}

	// Write rendered content into the ca key file.
	return emitToFile(_DefaultCAKeyPath, server.CAKey, 0600)
}

func emitCCD() error {
	users, err := GetAllUsers()
	if err != nil {
		return err
	}

	// Filesystem related stuff. Skipping when testing.
	if !Testing {
		// Clean and then create and write rendered ccd data.
		err = os.RemoveAll(_DefaultVPNCCDPath)
		if err != nil {
			if os.IsNotExist(err) {
			} else {
				return err
			}
		}

		if _, err := os.Stat(_DefaultVPNCCDPath); err != nil {
		}

		err = os.Mkdir(_DefaultVPNCCDPath, 0755)
		if err != nil {
			if !os.IsExist(err) {
				return err
			}
		}
	}
	// Render ccd templates for the users.
	for _, user := range users {
		var associatedRoutes [][3]string
		for _, network := range GetAllNetworks() {
			switch network.Type {
			case ROUTE:
				for _, assocUsername := range network.GetAssociatedUsernames() {
					if assocUsername == user.Username {
						via := network.Via
						ip, mask, err := net.ParseCIDR(network.CIDR)
						if err != nil {
							return err
						}
						associatedRoutes = append(associatedRoutes, [3]string{ip.To4().String(), net.IP(mask.Mask).To4().String(), via})
					}
				}
			}
		}
		var result bytes.Buffer
		params := struct {
			IP         string
			NetMask    string
			Routes     [][3]string // [0] is IP, [1] is Netmask, [2] is Via
			RedirectGW bool
		}{IP: user.getIP().String(), NetMask: _DefaultServerNetMask, Routes: associatedRoutes, RedirectGW: !user.NoGW}

		data, err := bindata.Asset("template/ccd.file.tmpl")
		if err != nil {
			return err
		}
		t, err := template.New("ccd.file.tmpl").Parse(string(data))
		if err != nil {
			return fmt.Errorf("can not parse ccd.file.tmpl template: %s", err)
		}

		err = t.Execute(&result, params)
		if err != nil {
			return fmt.Errorf("can not render ccd file %s: %s", user.Username, err)
		}

		err = emitToFile(_DefaultVPNCCDPath+user.Username, result.String(), 0)
		if err != nil {
			return err
		}
	}
	return nil
}

func emitDHParams() error {
	var result bytes.Buffer
	data, err := bindata.Asset("template/dh4096.pem.tmpl")
	if err != nil {
		return err
	}

	t, err := template.New("dh4096.pem.tmpl").Parse(string(data))
	if err != nil {
		return fmt.Errorf("can not parse dh4096.pem template: %s", err)
	}

	err = t.Execute(&result, nil)
	if err != nil {
		return fmt.Errorf("can not render dh4096.pem file: %s", err)
	}

	err = emitToFile(_DefaultDHParamsPath, result.String(), 0)
	if err != nil {
		return err
	}
	return nil
}

func emitIptables() error {
	if Testing {
		return nil
	}
	ipt, err := iptables.NewWithProtocol(iptables.ProtocolIPv4)
	if err != nil {
		return fmt.Errorf("can not create new iptables object: %v", err)
	}

	for _, network := range GetAllNetworks() {
		associatedUsernames := network.GetAssociatedUsernames()
		switch network.Type {
		case SERVERNET:
			users, err := GetAllUsers()
			if err != nil {
				return err
			}
			for _, user := range users {
				var found bool
				for _, auser := range associatedUsernames {
					if user.Username == auser {
						found = true
						break
					}
				}

				userIP, _, err := net.ParseCIDR(user.GetIPNet())
				if err != nil {
					return err
				}
				_, networkIPNet, err := net.ParseCIDR(network.CIDR)
				if err != nil {
					return err
				}

				// get destination network's iface
				iface := interfaceOfIP(networkIPNet)
				if iface == nil {
					logrus.Warnf("network doesn't exist on server %s[SERVERNET]: cant find interface for %s", network.Name, networkIPNet.String())
					return nil
				}
				// enable nat for the user to the destination network n
				if found {
					err = ipt.AppendUnique("nat", "POSTROUTING", "-s", userIP.String(), "-o", iface.Name, "-j", "MASQUERADE")
					if err != nil {
						logrus.Error(err)
						return err
					}
				} else {
					err = ipt.Delete("nat", "POSTROUTING", "-s", userIP.String(), "-o", iface.Name, "-j", "MASQUERADE")
					if err != nil {
						logrus.Debug(err)
					}
				}
			}
		}
	}
	return nil
}

func checkOpenVPNExecutable() bool {
	executable := getOpenVPNExecutable()
	if executable == "" {
		logrus.Error("openvpn is not installed ✘")
		return false
	}
	logrus.Debugf("openvpn executable detected: %s  ✔", executable)
	return true
}

func getOpenVPNExecutable() string {
	cmd := exec.Command("which", "openvpn")
	output, err := cmd.Output()
	if err != nil {
		logrus.Errorf("openvpn is not installed: %s  ✘", err)
		return ""
	}
	logrus.Debugf("openvpn executable detected: %s  ✔", strings.TrimSpace(string(output[:])))
	return strings.TrimSpace(string(output[:]))
}

func checkOpenSSLExecutable() bool {
	cmd := exec.Command("which", "openssl")
	output, err := cmd.Output()
	if err != nil {
		logrus.Errorf("openssl is not installed: %s  ✘", err)
		return false
	}
	logrus.Debugf("openssl executable detected: %s  ✔", strings.TrimSpace(string(output[:])))
	return true
}

func checkIptablesExecutable() bool {
	cmd := exec.Command("which", "iptables")
	output, err := cmd.Output()
	if err != nil {
		logrus.Errorf("iptables is not installed: %s  ✘", err)
		return false
	}
	logrus.Debugf("iptables executable detected: %s  ✔", strings.TrimSpace(string(output[:])))
	return true
}

func ensureBaseDir() {
	if Testing {
		return
	}
	os.Mkdir(varBasePath, 0755)
}

func init() {
	ensureBaseDir()
	var err error
	vpnProc, err = supervisor.NewProcess(getOpenVPNExecutable(), varBasePath, []string{"--config", _DefaultVPNConfPath})
	if err != nil {
		logrus.Errorf("can not create process: %v", err)
	}
}