/*
	Copyright 2019 Stellar Project
	Permission is hereby granted, free of charge, to any person obtaining a copy of
	this software and associated documentation files (the "Software"), to deal in the
	Software without restriction, including without limitation the rights to use, copy,
	modify, merge, publish, distribute, sublicense, and/or sell copies of the Software,
	and to permit persons to whom the Software is furnished to do so, subject to the
	following conditions:
	The above copyright notice and this permission notice shall be included in all copies
	or substantial portions of the Software.
	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
	INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
	PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
	FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
	TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
	USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

package main

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"os"
	"path"
	"path/filepath"
	"sync"
	"time"

	v1 "github.com/crosbymichael/guard/api/v1"
	"github.com/gliderlabs/ssh"
	"github.com/gomodule/redigo/redis"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
	"google.golang.org/grpc"
)

const (
	ipsKey          = "gatekeeper/ips"
	configKeyPrefix = "gatekeeper/config/"
)

type ServerConfig struct {
	ListenPort  int
	DBPath      string
	KeysPath    string
	HostKeyPath string
	RedisURL    string
	Subnet      string
	GuardAddr   string
	GuardTunnel string
	GuardDNS    string
}

type Server struct {
	cfg        *ServerConfig
	publicKeys []ssh.PublicKey
	mu         *sync.Mutex
}

func NewServer(cfg *ServerConfig) (*Server, error) {
	if cfg.ListenPort == 0 {
		cfg.ListenPort = 2222
	}
	return &Server{
		cfg: cfg,
		mu:  &sync.Mutex{},
	}, nil
}

func (s *Server) Run() error {
	if err := s.loadKeys(); err != nil {
		return err
	}

	ssh.Handle(func(session ssh.Session) {
		id := s.getID(session.PublicKey())
		config, err := s.getConfig(id)
		if err != nil {
			logrus.Error(err)
			return
		}
		logrus.Debugf("config: id=%s", id)
		io.WriteString(session, config)
	})

	pubKeyOption := ssh.PublicKeyAuth(func(ctx ssh.Context, key ssh.PublicKey) bool {
		return s.isAuthorized(ctx, key)
	})

	logrus.Infof("starting ssh server on port %d", s.cfg.ListenPort)
	opts := []ssh.Option{
		pubKeyOption,
	}
	if _, err := os.Stat(s.cfg.HostKeyPath); err == nil {
		opts = append(opts, ssh.HostKeyFile(s.cfg.HostKeyPath))
	}
	return ssh.ListenAndServe(fmt.Sprintf(":%d", s.cfg.ListenPort), nil, opts...)
}

func (s *Server) loadKeys() error {
	s.mu.Lock()
	defer s.mu.Unlock()

	if s.cfg.KeysPath == "" {
		return nil
	}

	keys, err := ioutil.ReadDir(s.cfg.KeysPath)
	if err != nil {
		return err
	}

	pubKeys := []ssh.PublicKey{}
	for _, k := range keys {
		logrus.Debugf("loading public key %s", k.Name())
		p := filepath.Join(s.cfg.KeysPath, k.Name())
		data, err := ioutil.ReadFile(p)
		if err != nil {
			return err
		}
		k, _, _, _, err := ssh.ParseAuthorizedKey(data)
		if err != nil {
			return err
		}
		pubKeys = append(pubKeys, k)
	}

	s.publicKeys = pubKeys
	return nil
}

func (s *Server) isAuthorized(ctx ssh.Context, key ssh.PublicKey) bool {
	for _, k := range s.publicKeys {
		if ssh.KeysEqual(key, k) {
			return true
		}
	}
	logrus.WithFields(logrus.Fields{
		"user": ctx.User(),
		"addr": ctx.RemoteAddr(),
	}).Warn("access denied")
	return false
}

func (s *Server) getConfig(id string) (string, error) {
	c, err := s.getConn()
	if err != nil {
		return "", err
	}
	defer c.Close()
	key := path.Join(configKeyPrefix, id)
	cfg, err := redis.String(c.Do("GET", key))
	if err != nil && err != redis.ErrNil {
		return "", err
	}
	if cfg != "" {
		return cfg, nil
	}

	conn, err := grpc.Dial(s.cfg.GuardAddr, grpc.WithInsecure())
	if err != nil {
		return "", errors.Wrap(err, "error connecting to guard server")
	}
	defer conn.Close()
	ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
	defer cancel()

	client := v1.NewWireguardClient(conn)

	ip, ipnet, err := s.getOrAllocateIP(id, s.cfg.Subnet)
	if err != nil {
		return "", err
	}

	r, err := client.NewPeer(ctx, &v1.NewPeerRequest{
		ID:      s.cfg.GuardTunnel,
		PeerID:  id,
		Address: ip.String() + "/32",
	})
	if err != nil {
		return "", err
	}
	// generate peer tunnel config
	t := &v1.Tunnel{
		PrivateKey: r.Peer.PrivateKey,
		Address:    r.Peer.AllowedIPs[0],
		DNS:        s.cfg.GuardDNS,
		Peers: []*v1.Peer{
			{
				ID:         r.Tunnel.ID,
				PublicKey:  r.Tunnel.PublicKey,
				Endpoint:   net.JoinHostPort(r.Tunnel.Endpoint, r.Tunnel.ListenPort),
				AllowedIPs: []string{ipnet.String()},
			},
		},
	}
	b := bytes.NewBuffer(nil)
	t.Render(b)
	if _, err := c.Do("SET", key, b.String()); err != nil {
		return "", err
	}
	return b.String(), nil
}