package ssh

import (
	"bufio"
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"math/rand"
	"net"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/hashicorp/errwrap"
	"github.com/hashicorp/terraform/communicator/remote"
	"github.com/hashicorp/terraform/terraform"
	"golang.org/x/crypto/ssh"
	"golang.org/x/crypto/ssh/agent"
)

const (
	// DefaultShebang is added at the top of a SSH script file
	DefaultShebang = "#!/bin/sh\n"
)

var (
	// randShared is a global random generator object that is shared.  This must be
	// shared since it is seeded by the current time and creating multiple can
	// result in the same values. By using a shared RNG we assure different numbers
	// per call.
	randLock   sync.Mutex
	randShared *rand.Rand

	// enable ssh keeplive probes by default
	keepAliveInterval = 2 * time.Second

	// max time to wait for for a KeepAlive response before considering the
	// connection to be dead.
	maxKeepAliveDelay = 120 * time.Second
)

// Communicator represents the SSH communicator
type Communicator struct {
	connInfo        *connectionInfo
	client          *ssh.Client
	config          *sshConfig
	conn            net.Conn
	address         string
	cancelKeepAlive context.CancelFunc

	lock sync.Mutex
}

type sshConfig struct {
	// The configuration of the Go SSH connection
	config *ssh.ClientConfig

	// connection returns a new connection. The current connection
	// in use will be closed as part of the Close method, or in the
	// case an error occurs.
	connection func() (net.Conn, error)

	// noPty, if true, will not request a pty from the remote end.
	noPty bool

	// sshAgent is a struct surrounding the agent.Agent client and the net.Conn
	// to the SSH Agent. It is nil if no SSH agent is configured
	sshAgent *sshAgent
}

type fatalError struct {
	error
}

func (e fatalError) FatalError() error {
	return e.error
}

// New creates a new communicator implementation over SSH.
func New(s *terraform.InstanceState) (*Communicator, error) {
	connInfo, err := parseConnectionInfo(s)
	if err != nil {
		return nil, err
	}

	config, err := prepareSSHConfig(connInfo)
	if err != nil {
		return nil, err
	}

	// Setup the random number generator once. The seed value is the
	// time multiplied by the PID. This can overflow the int64 but that
	// is okay. We multiply by the PID in case we have multiple processes
	// grabbing this at the same time. This is possible with Terraform and
	// if we communicate to the same host at the same instance, we could
	// overwrite the same files. Multiplying by the PID prevents this.
	randLock.Lock()
	defer randLock.Unlock()
	if randShared == nil {
		randShared = rand.New(rand.NewSource(
			time.Now().UnixNano() * int64(os.Getpid())))
	}

	comm := &Communicator{
		connInfo: connInfo,
		config:   config,
	}

	return comm, nil
}

// Connect implementation of communicator.Communicator interface
func (c *Communicator) Connect(o terraform.UIOutput) (err error) {
	// Grab a lock so we can modify our internal attributes
	c.lock.Lock()
	defer c.lock.Unlock()

	if c.conn != nil {
		c.conn.Close()
	}

	// Set the conn and client to nil since we'll recreate it
	c.conn = nil
	c.client = nil

	if o != nil {
		o.Output(fmt.Sprintf(
			"Connecting to remote host via SSH...\n"+
				"  Host: %s\n"+
				"  User: %s\n"+
				"  Password: %t\n"+
				"  Private key: %t\n"+
				"  Certificate: %t\n"+
				"  SSH Agent: %t\n"+
				"  Checking Host Key: %t",
			c.connInfo.Host, c.connInfo.User,
			c.connInfo.Password != "",
			c.connInfo.PrivateKey != "",
			c.connInfo.Certificate != "",
			c.connInfo.Agent,
			c.connInfo.HostKey != "",
		))

		if c.connInfo.BastionHost != "" {
			o.Output(fmt.Sprintf(
				"Using configured bastion host...\n"+
					"  Host: %s\n"+
					"  User: %s\n"+
					"  Password: %t\n"+
					"  Private key: %t\n"+
					"  Certificate: %t\n"+
					"  SSH Agent: %t\n"+
					"  Checking Host Key: %t",
				c.connInfo.BastionHost, c.connInfo.BastionUser,
				c.connInfo.BastionPassword != "",
				c.connInfo.BastionPrivateKey != "",
				c.connInfo.BastionCertificate != "",
				c.connInfo.Agent,
				c.connInfo.BastionHostKey != "",
			))
		}
	}

	hostAndPort := fmt.Sprintf("%s:%d", c.connInfo.Host, c.connInfo.Port)
	log.Printf("[DEBUG] Connecting to %s for SSH", hostAndPort)
	c.conn, err = c.config.connection()
	if err != nil {
		// Explicitly set this to the REAL nil. Connection() can return
		// a nil implementation of net.Conn which will make the
		// "if c.conn == nil" check fail above. Read here for more information
		// on this psychotic language feature:
		//
		// http://golang.org/doc/faq#nil_error
		c.conn = nil

		log.Printf("[ERROR] connection error: %s", err)
		return err
	}

	log.Printf("[DEBUG] Connection established. Handshaking for user %v", c.connInfo.User)
	sshConn, sshChan, req, err := ssh.NewClientConn(c.conn, hostAndPort, c.config.config)
	if err != nil {
		err = errwrap.Wrapf(fmt.Sprintf("SSH authentication failed (%s@%s): {{err}}", c.connInfo.User, hostAndPort), err)

		// While in theory this should be a fatal error, some hosts may start
		// the ssh service before it is properly configured, or before user
		// authentication data is available.
		// Log the error, and allow the provisioner to retry.
		log.Printf("[WARN] %s", err)
		return err
	}

	c.client = ssh.NewClient(sshConn, sshChan, req)

	if c.config.sshAgent != nil {
		log.Printf("[DEBUG] Telling SSH config to forward to agent")
		if err := c.config.sshAgent.ForwardToAgent(c.client); err != nil {
			return fatalError{err}
		}

		log.Printf("[DEBUG] Setting up a session to request agent forwarding")
		session, err := c.newSession()
		if err != nil {
			return err
		}
		defer session.Close()

		err = agent.RequestAgentForwarding(session)

		if err == nil {
			log.Printf("[INFO] agent forwarding enabled")
		} else {
			log.Printf("[WARN] error forwarding agent: %s", err)
		}
	}

	if err != nil {
		return err
	}

	if o != nil {
		o.Output("Connected!")
	}

	ctx, cancelKeepAlive := context.WithCancel(context.TODO())
	c.cancelKeepAlive = cancelKeepAlive

	// Start a keepalive goroutine to help maintain the connection for
	// long-running commands.
	log.Printf("[DEBUG] starting ssh KeepAlives")
	go func() {
		defer cancelKeepAlive()
		// Along with the KeepAlives generating packets to keep the tcp
		// connection open, we will use the replies to verify liveness of the
		// connection. This will prevent dead connections from blocking the
		// provisioner indefinitely.
		respCh := make(chan error, 1)

		go func() {
			t := time.NewTicker(keepAliveInterval)
			defer t.Stop()
			for {
				select {
				case <-t.C:
					_, _, err := c.client.SendRequest("keepalive@terraform.io", true, nil)
					respCh <- err
				case <-ctx.Done():
					return
				}
			}
		}()

		after := time.NewTimer(maxKeepAliveDelay)
		defer after.Stop()

		for {
			select {
			case err := <-respCh:
				if err != nil {
					log.Printf("[ERROR] ssh keepalive: %s", err)
					sshConn.Close()
					return
				}
			case <-after.C:
				// abort after too many missed keepalives
				log.Println("[ERROR] no reply from ssh server")
				sshConn.Close()
				return
			case <-ctx.Done():
				return
			}
			if !after.Stop() {
				<-after.C
			}
			after.Reset(maxKeepAliveDelay)
		}
	}()

	return nil
}

// Disconnect implementation of communicator.Communicator interface
func (c *Communicator) Disconnect() error {
	c.lock.Lock()
	defer c.lock.Unlock()

	if c.cancelKeepAlive != nil {
		c.cancelKeepAlive()
	}

	if c.config.sshAgent != nil {
		if err := c.config.sshAgent.Close(); err != nil {
			return err
		}
	}

	if c.conn != nil {
		conn := c.conn
		c.conn = nil
		return conn.Close()
	}

	return nil
}

// Timeout implementation of communicator.Communicator interface
func (c *Communicator) Timeout() time.Duration {
	return c.connInfo.TimeoutVal
}

// ScriptPath implementation of communicator.Communicator interface
func (c *Communicator) ScriptPath() string {
	randLock.Lock()
	defer randLock.Unlock()

	return strings.Replace(
		c.connInfo.ScriptPath, "%RAND%",
		strconv.FormatInt(int64(randShared.Int31()), 10), -1)
}

// Start implementation of communicator.Communicator interface
func (c *Communicator) Start(cmd *remote.Cmd) error {
	cmd.Init()

	session, err := c.newSession()
	if err != nil {
		return err
	}

	// Setup our session
	session.Stdin = cmd.Stdin
	session.Stdout = cmd.Stdout
	session.Stderr = cmd.Stderr

	if !c.config.noPty {
		// Request a PTY
		termModes := ssh.TerminalModes{
			ssh.ECHO:          0,     // do not echo
			ssh.TTY_OP_ISPEED: 14400, // input speed = 14.4kbaud
			ssh.TTY_OP_OSPEED: 14400, // output speed = 14.4kbaud
		}

		if err := session.RequestPty("xterm", 80, 40, termModes); err != nil {
			return err
		}
	}

	log.Printf("[DEBUG] starting remote command: %s", cmd.Command)
	err = session.Start(strings.TrimSpace(cmd.Command) + "\n")
	if err != nil {
		return err
	}

	// Start a goroutine to wait for the session to end and set the
	// exit boolean and status.
	go func() {
		defer session.Close()

		err := session.Wait()
		exitStatus := 0
		if err != nil {
			exitErr, ok := err.(*ssh.ExitError)
			if ok {
				exitStatus = exitErr.ExitStatus()
			}
		}

		cmd.SetExitStatus(exitStatus, err)
		log.Printf("[DEBUG] remote command exited with '%d': %s", exitStatus, cmd.Command)
	}()

	return nil
}

// Upload implementation of communicator.Communicator interface
func (c *Communicator) Upload(path string, input io.Reader) error {
	// The target directory and file for talking the SCP protocol
	targetDir := filepath.Dir(path)
	targetFile := filepath.Base(path)

	// On windows, filepath.Dir uses backslash separators (ie. "\tmp").
	// This does not work when the target host is unix.  Switch to forward slash
	// which works for unix and windows
	targetDir = filepath.ToSlash(targetDir)

	// Skip copying if we can get the file size directly from common io.Readers
	size := int64(0)

	switch src := input.(type) {
	case *os.File:
		fi, err := src.Stat()
		if err != nil {
			size = fi.Size()
		}
	case *bytes.Buffer:
		size = int64(src.Len())
	case *bytes.Reader:
		size = int64(src.Len())
	case *strings.Reader:
		size = int64(src.Len())
	}

	scpFunc := func(w io.Writer, stdoutR *bufio.Reader) error {
		return scpUploadFile(targetFile, input, w, stdoutR, size)
	}

	return c.scpSession("scp -vt "+targetDir, scpFunc)
}

// UploadScript implementation of communicator.Communicator interface
func (c *Communicator) UploadScript(path string, input io.Reader) error {
	reader := bufio.NewReader(input)
	prefix, err := reader.Peek(2)
	if err != nil {
		return fmt.Errorf("Error reading script: %s", err)
	}

	var script bytes.Buffer
	if string(prefix) != "#!" {
		script.WriteString(DefaultShebang)
	}

	script.ReadFrom(reader)
	if err := c.Upload(path, &script); err != nil {
		return err
	}

	var stdout, stderr bytes.Buffer
	cmd := &remote.Cmd{
		Command: fmt.Sprintf("chmod 0777 %s", path),
		Stdout:  &stdout,
		Stderr:  &stderr,
	}
	if err := c.Start(cmd); err != nil {
		return fmt.Errorf(
			"Error chmodding script file to 0777 in remote "+
				"machine: %s", err)
	}

	if err := cmd.Wait(); err != nil {
		return fmt.Errorf(
			"Error chmodding script file to 0777 in remote "+
				"machine %v: %s %s", err, stdout.String(), stderr.String())
	}

	return nil
}

// UploadDir implementation of communicator.Communicator interface
func (c *Communicator) UploadDir(dst string, src string) error {
	log.Printf("[DEBUG] Uploading dir '%s' to '%s'", src, dst)
	scpFunc := func(w io.Writer, r *bufio.Reader) error {
		uploadEntries := func() error {
			f, err := os.Open(src)
			if err != nil {
				return err
			}
			defer f.Close()

			entries, err := f.Readdir(-1)
			if err != nil {
				return err
			}

			return scpUploadDir(src, entries, w, r)
		}

		if src[len(src)-1] != '/' {
			log.Printf("[DEBUG] No trailing slash, creating the source directory name")
			return scpUploadDirProtocol(filepath.Base(src), w, r, uploadEntries)
		}
		// Trailing slash, so only upload the contents
		return uploadEntries()
	}

	return c.scpSession("scp -rvt "+dst, scpFunc)
}

func (c *Communicator) newSession() (session *ssh.Session, err error) {
	log.Println("[DEBUG] opening new ssh session")
	if c.client == nil {
		err = errors.New("ssh client is not connected")
	} else {
		session, err = c.client.NewSession()
	}

	if err != nil {
		log.Printf("[WARN] ssh session open error: '%s', attempting reconnect", err)
		if err := c.Connect(nil); err != nil {
			return nil, err
		}

		return c.client.NewSession()
	}

	return session, nil
}

func (c *Communicator) scpSession(scpCommand string, f func(io.Writer, *bufio.Reader) error) error {
	session, err := c.newSession()
	if err != nil {
		return err
	}
	defer session.Close()

	// Get a pipe to stdin so that we can send data down
	stdinW, err := session.StdinPipe()
	if err != nil {
		return err
	}

	// We only want to close once, so we nil w after we close it,
	// and only close in the defer if it hasn't been closed already.
	defer func() {
		if stdinW != nil {
			stdinW.Close()
		}
	}()

	// Get a pipe to stdout so that we can get responses back
	stdoutPipe, err := session.StdoutPipe()
	if err != nil {
		return err
	}
	stdoutR := bufio.NewReader(stdoutPipe)

	// Set stderr to a bytes buffer
	stderr := new(bytes.Buffer)
	session.Stderr = stderr

	// Start the sink mode on the other side
	// TODO(mitchellh): There are probably issues with shell escaping the path
	log.Println("[DEBUG] Starting remote scp process: ", scpCommand)
	if err := session.Start(scpCommand); err != nil {
		return err
	}

	// Call our callback that executes in the context of SCP. We ignore
	// EOF errors if they occur because it usually means that SCP prematurely
	// ended on the other side.
	log.Println("[DEBUG] Started SCP session, beginning transfers...")
	if err := f(stdinW, stdoutR); err != nil && err != io.EOF {
		return err
	}

	// Close the stdin, which sends an EOF, and then set w to nil so that
	// our defer func doesn't close it again since that is unsafe with
	// the Go SSH package.
	log.Println("[DEBUG] SCP session complete, closing stdin pipe.")
	stdinW.Close()
	stdinW = nil

	// Wait for the SCP connection to close, meaning it has consumed all
	// our data and has completed. Or has errored.
	log.Println("[DEBUG] Waiting for SSH session to complete.")
	err = session.Wait()

	// log any stderr before exiting on an error
	scpErr := stderr.String()
	if len(scpErr) > 0 {
		log.Printf("[ERROR] scp stderr: %q", stderr)
	}

	if err != nil {
		if exitErr, ok := err.(*ssh.ExitError); ok {
			// Otherwise, we have an ExitErorr, meaning we can just read
			// the exit status
			log.Printf("[ERROR] %s", exitErr)

			// If we exited with status 127, it means SCP isn't available.
			// Return a more descriptive error for that.
			if exitErr.ExitStatus() == 127 {
				return errors.New(
					"SCP failed to start. This usually means that SCP is not\n" +
						"properly installed on the remote system.")
			}
		}

		return err
	}

	return nil
}

// checkSCPStatus checks that a prior command sent to SCP completed
// successfully. If it did not complete successfully, an error will
// be returned.
func checkSCPStatus(r *bufio.Reader) error {
	code, err := r.ReadByte()
	if err != nil {
		return err
	}

	if code != 0 {
		// Treat any non-zero (really 1 and 2) as fatal errors
		message, _, err := r.ReadLine()
		if err != nil {
			return fmt.Errorf("Error reading error message: %s", err)
		}

		return errors.New(string(message))
	}

	return nil
}

func scpUploadFile(dst string, src io.Reader, w io.Writer, r *bufio.Reader, size int64) error {
	if size == 0 {
		// Create a temporary file where we can copy the contents of the src
		// so that we can determine the length, since SCP is length-prefixed.
		tf, err := ioutil.TempFile("", "terraform-upload")
		if err != nil {
			return fmt.Errorf("Error creating temporary file for upload: %s", err)
		}
		defer os.Remove(tf.Name())
		defer tf.Close()

		log.Println("[DEBUG] Copying input data into temporary file so we can read the length")
		if _, err := io.Copy(tf, src); err != nil {
			return err
		}

		// Sync the file so that the contents are definitely on disk, then
		// read the length of it.
		if err := tf.Sync(); err != nil {
			return fmt.Errorf("Error creating temporary file for upload: %s", err)
		}

		// Seek the file to the beginning so we can re-read all of it
		if _, err := tf.Seek(0, 0); err != nil {
			return fmt.Errorf("Error creating temporary file for upload: %s", err)
		}

		fi, err := tf.Stat()
		if err != nil {
			return fmt.Errorf("Error creating temporary file for upload: %s", err)
		}

		src = tf
		size = fi.Size()
	}

	// Start the protocol
	log.Println("[DEBUG] Beginning file upload...")
	fmt.Fprintln(w, "C0644", size, dst)
	if err := checkSCPStatus(r); err != nil {
		return err
	}

	if _, err := io.Copy(w, src); err != nil {
		return err
	}

	fmt.Fprint(w, "\x00")
	if err := checkSCPStatus(r); err != nil {
		return err
	}

	return nil
}

func scpUploadDirProtocol(name string, w io.Writer, r *bufio.Reader, f func() error) error {
	log.Printf("[DEBUG] SCP: starting directory upload: %s", name)
	fmt.Fprintln(w, "D0755 0", name)
	err := checkSCPStatus(r)
	if err != nil {
		return err
	}

	if err := f(); err != nil {
		return err
	}

	fmt.Fprintln(w, "E")
	if err != nil {
		return err
	}

	return nil
}

func scpUploadDir(root string, fs []os.FileInfo, w io.Writer, r *bufio.Reader) error {
	for _, fi := range fs {
		realPath := filepath.Join(root, fi.Name())

		// Track if this is actually a symlink to a directory. If it is
		// a symlink to a file we don't do any special behavior because uploading
		// a file just works. If it is a directory, we need to know so we
		// treat it as such.
		isSymlinkToDir := false
		if fi.Mode()&os.ModeSymlink == os.ModeSymlink {
			symPath, err := filepath.EvalSymlinks(realPath)
			if err != nil {
				return err
			}

			symFi, err := os.Lstat(symPath)
			if err != nil {
				return err
			}

			isSymlinkToDir = symFi.IsDir()
		}

		if !fi.IsDir() && !isSymlinkToDir {
			// It is a regular file (or symlink to a file), just upload it
			f, err := os.Open(realPath)
			if err != nil {
				return err
			}

			err = func() error {
				defer f.Close()
				return scpUploadFile(fi.Name(), f, w, r, fi.Size())
			}()

			if err != nil {
				return err
			}

			continue
		}

		// It is a directory, recursively upload
		err := scpUploadDirProtocol(fi.Name(), w, r, func() error {
			f, err := os.Open(realPath)
			if err != nil {
				return err
			}
			defer f.Close()

			entries, err := f.Readdir(-1)
			if err != nil {
				return err
			}

			return scpUploadDir(realPath, entries, w, r)
		})
		if err != nil {
			return err
		}
	}

	return nil
}

// ConnectFunc is a convenience method for returning a function
// that just uses net.Dial to communicate with the remote end that
// is suitable for use with the SSH communicator configuration.
func ConnectFunc(network, addr string) func() (net.Conn, error) {
	return func() (net.Conn, error) {
		c, err := net.DialTimeout(network, addr, 15*time.Second)
		if err != nil {
			return nil, err
		}

		if tcpConn, ok := c.(*net.TCPConn); ok {
			tcpConn.SetKeepAlive(true)
		}

		return c, nil
	}
}

// BastionConnectFunc is a convenience method for returning a function
// that connects to a host over a bastion connection.
func BastionConnectFunc(
	bProto string,
	bAddr string,
	bConf *ssh.ClientConfig,
	proto string,
	addr string) func() (net.Conn, error) {
	return func() (net.Conn, error) {
		log.Printf("[DEBUG] Connecting to bastion: %s", bAddr)
		bastion, err := ssh.Dial(bProto, bAddr, bConf)
		if err != nil {
			return nil, fmt.Errorf("Error connecting to bastion: %s", err)
		}

		log.Printf("[DEBUG] Connecting via bastion (%s) to host: %s", bAddr, addr)
		conn, err := bastion.Dial(proto, addr)
		if err != nil {
			bastion.Close()
			return nil, err
		}

		// Wrap it up so we close both things properly
		return &bastionConn{
			Conn:    conn,
			Bastion: bastion,
		}, nil
	}
}

type bastionConn struct {
	net.Conn
	Bastion *ssh.Client
}

func (c *bastionConn) Close() error {
	c.Conn.Close()
	return c.Bastion.Close()
}