package sftpd

import (
	"fmt"
	"io"
	"math"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"github.com/drakkan/sftpgo/dataprovider"
	"github.com/drakkan/sftpgo/logger"
	"github.com/drakkan/sftpgo/utils"
	"golang.org/x/crypto/ssh"
)

var (
	okMsg   = []byte{0x00}
	warnMsg = []byte{0x01} // must be followed by an optional message and a newline
	errMsg  = []byte{0x02} // must be followed by an optional message and a newline
	newLine = []byte{0x0A}
)

type execMsg struct {
	Command string
}

type scpCommand struct {
	connection Connection
	args       []string
}

func (c *scpCommand) handle() error {
	var err error
	addConnection(c.connection)
	defer removeConnection(c.connection)
	destPath := c.getDestPath()
	commandType := c.getCommandType()
	c.connection.Log(logger.LevelDebug, logSenderSCP, "handle scp command, args: %v user: %v command type: %v, dest path: %#v",
		c.args, c.connection.User.Username, commandType, destPath)
	if commandType == "-t" {
		// -t means "to", so upload
		err = c.handleRecursiveUpload()
		if err != nil {
			return err
		}

	} else if commandType == "-f" {
		// -f means "from" so download
		err = c.readConfirmationMessage()
		if err != nil {
			return err
		}
		err = c.handleDownload(destPath)
		if err != nil {
			return err
		}
	} else {
		err = fmt.Errorf("scp command not supported, args: %v", c.args)
	}
	c.sendExitStatus(err)
	return err
}

func (c *scpCommand) handleRecursiveUpload() error {
	var err error
	numDirs := 0
	destPath := c.getDestPath()
	for {
		err = c.sendConfirmationMessage()
		if err != nil {
			return err
		}
		command, err := c.getNextUploadProtocolMessage()
		if err != nil {
			return err
		}
		if strings.HasPrefix(command, "E") {
			numDirs--
			c.connection.Log(logger.LevelDebug, logSenderSCP, "received end dir command, num dirs: %v", numDirs)
			if numDirs == 0 {
				// upload is now complete send confirmation message
				err = c.sendConfirmationMessage()
				if err != nil {
					return err
				}
			} else {
				// the destination dir is now the parent directory
				destPath = filepath.Join(destPath, "..")
			}
		} else {
			sizeToRead, name, err := c.parseUploadMessage(command)
			if err != nil {
				return err
			}
			if strings.HasPrefix(command, "D") {
				numDirs++
				destPath = path.Join(destPath, name)
				err = c.handleCreateDir(destPath)
				if err != nil {
					return err
				}
				c.connection.Log(logger.LevelDebug, logSenderSCP, "received start dir command, num dirs: %v destPath: %#v", numDirs, destPath)
			} else if strings.HasPrefix(command, "C") {
				err = c.handleUpload(c.getFileUploadDestPath(destPath, name), sizeToRead)
				if err != nil {
					return err
				}
			}
		}
		if err != nil || numDirs == 0 {
			break
		}
	}
	return err
}

func (c *scpCommand) handleCreateDir(dirPath string) error {
	updateConnectionActivity(c.connection.ID)
	if !c.connection.User.HasPerm(dataprovider.PermCreateDirs) {
		err := fmt.Errorf("Permission denied")
		c.connection.Log(logger.LevelWarn, logSenderSCP, "error creating dir: %#v, permission denied", dirPath)
		c.sendErrorMessage(err.Error())
		return err
	}

	p, err := c.connection.buildPath(dirPath)
	if err != nil {
		c.connection.Log(logger.LevelWarn, logSenderSCP, "error creating dir: %#v, invalid file path, err: %v", dirPath, err)
		c.sendErrorMessage(err.Error())
		return err
	}

	err = c.createDir(p)
	if err != nil {
		return err
	}
	c.connection.Log(logger.LevelDebug, mkdirLogSender, "created dir %#v", dirPath)
	return nil
}

// we need to close the transfer if we have an error
func (c *scpCommand) getUploadFileData(sizeToRead int64, transfer *Transfer) error {
	err := c.sendConfirmationMessage()
	if err != nil {
		transfer.TransferError(err)
		transfer.Close()
		return err
	}

	if sizeToRead > 0 {
		remaining := sizeToRead
		buf := make([]byte, int64(math.Min(32768, float64(sizeToRead))))
		for {
			n, err := c.connection.channel.Read(buf)
			if err != nil {
				c.sendErrorMessage(err.Error())
				transfer.TransferError(err)
				transfer.Close()
				return err
			}
			transfer.WriteAt(buf[:n], sizeToRead-remaining)
			remaining -= int64(n)
			if remaining <= 0 {
				break
			}
			if remaining < int64(len(buf)) {
				buf = make([]byte, remaining)
			}
		}
	}
	err = c.readConfirmationMessage()
	if err != nil {
		transfer.TransferError(err)
		transfer.Close()
		return err
	}
	err = transfer.Close()
	if err != nil {
		c.sendErrorMessage(err.Error())
		return err
	}
	return c.sendConfirmationMessage()
}

func (c *scpCommand) handleUploadFile(requestPath, filePath string, sizeToRead int64, isNewFile bool) error {
	if !c.connection.hasSpace(true) {
		err := fmt.Errorf("denying file write due to space limit")
		c.connection.Log(logger.LevelWarn, logSenderSCP, "error uploading file: %#v, err: %v", filePath, err)
		c.sendErrorMessage(err.Error())
		return err
	}

	if _, err := os.Stat(filepath.Dir(requestPath)); os.IsNotExist(err) {
		if !c.connection.User.HasPerm(dataprovider.PermCreateDirs) {
			err := fmt.Errorf("Permission denied")
			c.connection.Log(logger.LevelWarn, logSenderSCP, "error uploading file: %#v, permission denied", requestPath)
			c.sendErrorMessage(err.Error())
			return err
		}
	}

	file, err := os.Create(filePath)
	if err != nil {
		c.connection.Log(logger.LevelError, logSenderSCP, "error creating file %#v: %v", requestPath, err)
		c.sendErrorMessage(err.Error())
		return err
	}

	utils.SetPathPermissions(filePath, c.connection.User.GetUID(), c.connection.User.GetGID())

	transfer := Transfer{
		file:           file,
		path:           requestPath,
		start:          time.Now(),
		bytesSent:      0,
		bytesReceived:  0,
		user:           c.connection.User,
		connectionID:   c.connection.ID,
		transferType:   transferUpload,
		lastActivity:   time.Now(),
		isNewFile:      isNewFile,
		protocol:       c.connection.protocol,
		transferError:  nil,
		isFinished:     false,
		minWriteOffset: 0,
	}
	addTransfer(&transfer)

	return c.getUploadFileData(sizeToRead, &transfer)
}

func (c *scpCommand) handleUpload(uploadFilePath string, sizeToRead int64) error {
	var err error

	updateConnectionActivity(c.connection.ID)
	if !c.connection.User.HasPerm(dataprovider.PermUpload) {
		err := fmt.Errorf("Permission denied")
		c.connection.Log(logger.LevelWarn, logSenderSCP, "cannot upload file: %#v, permission denied", uploadFilePath)
		c.sendErrorMessage(err.Error())
		return err
	}

	p, err := c.connection.buildPath(uploadFilePath)
	if err != nil {
		c.connection.Log(logger.LevelWarn, logSenderSCP, "error uploading file: %#v, err: %v", uploadFilePath, err)
		c.sendErrorMessage(err.Error())
		return err
	}
	filePath := p
	if isAtomicUploadEnabled() {
		filePath = getUploadTempFilePath(p)
	}
	stat, statErr := os.Stat(p)
	if os.IsNotExist(statErr) {
		return c.handleUploadFile(p, filePath, sizeToRead, true)
	}

	if statErr != nil {
		c.connection.Log(logger.LevelError, logSenderSCP, "error performing file stat %#v: %v", p, statErr)
		c.sendErrorMessage(err.Error())
		return err
	}

	if stat.IsDir() {
		c.connection.Log(logger.LevelWarn, logSenderSCP, "attempted to open a directory for writing to: %#v", p)
		err = fmt.Errorf("Attempted to open a directory for writing: %#v", p)
		c.sendErrorMessage(err.Error())
		return err
	}

	if !c.connection.User.HasPerm(dataprovider.PermOverwrite) {
		err := fmt.Errorf("Permission denied")
		c.connection.Log(logger.LevelWarn, logSenderSCP, "cannot overwrite file: %#v, permission denied", uploadFilePath)
		c.sendErrorMessage(err.Error())
		return err
	}

	if isAtomicUploadEnabled() {
		err = os.Rename(p, filePath)
		if err != nil {
			c.connection.Log(logger.LevelError, logSenderSCP, "error renaming existing file for atomic upload, source: %#v, dest: %#v, err: %v",
				p, filePath, err)
			c.sendErrorMessage(err.Error())
			return err
		}
	}

	dataprovider.UpdateUserQuota(dataProvider, c.connection.User, 0, -stat.Size(), false)

	return c.handleUploadFile(p, filePath, sizeToRead, false)
}

func (c *scpCommand) sendDownloadProtocolMessages(dirPath string, stat os.FileInfo) error {
	var err error
	if c.sendFileTime() {
		modTime := stat.ModTime().UnixNano() / 1000000000
		tCommand := fmt.Sprintf("T%v 0 %v 0\n", modTime, modTime)
		err = c.sendProtocolMessage(tCommand)
		if err != nil {
			return err
		}
		err = c.readConfirmationMessage()
		if err != nil {
			return err
		}
	}

	fileMode := fmt.Sprintf("D%v 0 %v\n", getFileModeAsString(stat.Mode(), stat.IsDir()), filepath.Base(dirPath))
	err = c.sendProtocolMessage(fileMode)
	if err != nil {
		return err
	}
	err = c.readConfirmationMessage()
	return err
}

// we send first all the files in the roor directory and then the directories
// for each directory we recursively call this method again
func (c *scpCommand) handleRecursiveDownload(dirPath string, stat os.FileInfo) error {
	var err error
	if c.isRecursive() {
		c.connection.Log(logger.LevelDebug, logSenderSCP, "recursive download, dir path: %#v", dirPath)
		err = c.sendDownloadProtocolMessages(dirPath, stat)
		if err != nil {
			return err
		}
		files, err := getDirContents(dirPath)
		if err != nil {
			c.sendErrorMessage(err.Error())
			return err
		}
		var dirs []string
		for _, file := range files {
			filePath := c.connection.User.GetRelativePath(filepath.Join(dirPath, file.Name()))
			if file.Mode().IsRegular() || file.Mode()&os.ModeSymlink == os.ModeSymlink {
				err = c.handleDownload(filePath)
				if err != nil {
					break
				}
			} else if file.IsDir() {
				dirs = append(dirs, filePath)
			}
		}
		if err != nil {
			c.sendErrorMessage(err.Error())
			return err
		}
		for _, dir := range dirs {
			err = c.handleDownload(dir)
			if err != nil {
				break
			}
		}
		if err != nil {
			c.sendErrorMessage(err.Error())
			return err
		}
		err = c.sendProtocolMessage("E\n")
		if err != nil {
			return err
		}
		err = c.readConfirmationMessage()
		if err != nil {
			return err
		}
		return err
	}
	err = fmt.Errorf("Unable to send directory for non recursive copy")
	c.sendErrorMessage(err.Error())
	return err
}

func (c *scpCommand) sendDownloadFileData(filePath string, stat os.FileInfo, transfer *Transfer) error {
	var err error
	if c.sendFileTime() {
		modTime := stat.ModTime().UnixNano() / 1000000000
		tCommand := fmt.Sprintf("T%v 0 %v 0\n", modTime, modTime)
		err = c.sendProtocolMessage(tCommand)
		if err != nil {
			return err
		}
		err = c.readConfirmationMessage()
		if err != nil {
			return err
		}
	}

	fileSize := stat.Size()
	readed := int64(0)
	fileMode := fmt.Sprintf("C%v %v %v\n", getFileModeAsString(stat.Mode(), stat.IsDir()), fileSize, filepath.Base(filePath))
	err = c.sendProtocolMessage(fileMode)
	if err != nil {
		return err
	}
	err = c.readConfirmationMessage()
	if err != nil {
		return err
	}

	buf := make([]byte, 32768)
	for {
		n, err := transfer.ReadAt(buf, readed)
		if err == nil || err == io.EOF {
			if n > 0 {
				_, err = c.connection.channel.Write(buf[:n])
			}
		}
		readed += int64(n)
		if err != nil {
			break
		}
	}
	if err != nil && err != io.EOF {
		c.sendErrorMessage(err.Error())
		return err
	}
	err = c.sendConfirmationMessage()
	if err != nil {
		return err
	}
	err = c.readConfirmationMessage()
	return err
}

func (c *scpCommand) handleDownload(filePath string) error {
	var err error

	updateConnectionActivity(c.connection.ID)

	if !c.connection.User.HasPerm(dataprovider.PermDownload) {
		err := fmt.Errorf("Permission denied")
		c.connection.Log(logger.LevelWarn, logSenderSCP, "error downloading file: %#v, permission denied", filePath)
		c.sendErrorMessage(err.Error())
		return err
	}
	p, err := c.connection.buildPath(filePath)
	if err != nil {
		err := fmt.Errorf("Invalid file path")
		c.connection.Log(logger.LevelWarn, logSenderSCP, "error downloading file: %#v, invalid file path", filePath)
		c.sendErrorMessage(err.Error())
		return err
	}

	var stat os.FileInfo
	if stat, err = os.Stat(p); os.IsNotExist(err) {
		c.connection.Log(logger.LevelWarn, logSenderSCP, "error downloading file: %#v, err: %v", p, err)
		c.sendErrorMessage(err.Error())
		return err
	}

	if stat.IsDir() {
		err = c.handleRecursiveDownload(p, stat)
		return err
	}

	file, err := os.Open(p)
	if err != nil {
		c.connection.Log(logger.LevelError, logSenderSCP, "could not open file %#v for reading: %v", p, err)
		c.sendErrorMessage(err.Error())
		return err
	}

	transfer := Transfer{
		file:           file,
		path:           p,
		start:          time.Now(),
		bytesSent:      0,
		bytesReceived:  0,
		user:           c.connection.User,
		connectionID:   c.connection.ID,
		transferType:   transferDownload,
		lastActivity:   time.Now(),
		isNewFile:      false,
		protocol:       c.connection.protocol,
		transferError:  nil,
		isFinished:     false,
		minWriteOffset: 0,
	}
	addTransfer(&transfer)

	err = c.sendDownloadFileData(p, stat, &transfer)
	// we need to call Close anyway and return close error if any and
	// if we have no previous error
	if err == nil {
		err = transfer.Close()
	} else {
		transfer.TransferError(err)
		transfer.Close()
	}
	return err
}

// returns the SCP destination path.
// We ensure that the path is absolute and in SFTP (UNIX) format
func (c *scpCommand) getDestPath() string {
	destPath := filepath.ToSlash(c.args[len(c.args)-1])
	if !filepath.IsAbs(destPath) {
		destPath = "/" + destPath
	}
	return destPath
}

func (c *scpCommand) getCommandType() string {
	return c.args[len(c.args)-2]
}

func (c *scpCommand) sendFileTime() bool {
	return utils.IsStringInSlice("-p", c.args)
}

func (c *scpCommand) isRecursive() bool {
	return utils.IsStringInSlice("-r", c.args)
}

// read the SCP confirmation message and the optional text message
// the channel will be closed on errors
func (c *scpCommand) readConfirmationMessage() error {
	var msg strings.Builder
	buf := make([]byte, 1)
	n, err := c.connection.channel.Read(buf)
	if err != nil {
		c.connection.channel.Close()
		return err
	}
	if n == 1 && (buf[0] == warnMsg[0] || buf[0] == errMsg[0]) {
		isError := buf[0] == errMsg[0]
		for {
			n, err = c.connection.channel.Read(buf)
			readed := buf[:n]
			if err != nil || (n == 1 && readed[0] == newLine[0]) {
				break
			}
			if n > 0 {
				msg.WriteString(string(readed))
			}
		}
		c.connection.Log(logger.LevelInfo, logSenderSCP, "scp error message received: %v is error: %v", msg.String(), isError)
		err = fmt.Errorf("%v", msg.String())
		c.connection.channel.Close()
	}
	return err
}

// protool messages are newline terminated
func (c *scpCommand) readProtocolMessage() (string, error) {
	var command strings.Builder
	var err error
	buf := make([]byte, 1)
	for {
		var n int
		n, err = c.connection.channel.Read(buf)
		if err != nil {
			break
		}
		if n > 0 {
			readed := buf[:n]
			if n == 1 && readed[0] == newLine[0] {
				break
			}
			command.WriteString(string(readed))
		}
	}
	if err != nil {
		c.connection.channel.Close()
	}
	return command.String(), err
}

// send an error message and close the channel
func (c *scpCommand) sendErrorMessage(error string) {
	c.connection.channel.Write(errMsg)
	c.connection.channel.Write([]byte(error))
	c.connection.channel.Write(newLine)
	c.connection.channel.Close()
}

// send scp confirmation message and close the channel if an error happen
func (c *scpCommand) sendConfirmationMessage() error {
	_, err := c.connection.channel.Write(okMsg)
	if err != nil {
		c.connection.channel.Close()
	}
	return err
}

// sends a protocol message and close the channel on error
func (c *scpCommand) sendProtocolMessage(message string) error {
	_, err := c.connection.channel.Write([]byte(message))
	if err != nil {
		c.connection.Log(logger.LevelWarn, logSenderSCP, "error sending protocol message: %v, err: %v", message, err)
		c.connection.channel.Close()
	}
	return err
}

// sends the SCP command exit status
func (c *scpCommand) sendExitStatus(err error) {
	status := uint32(0)
	if err != nil {
		status = 1
	}
	ex := exitStatusMsg{
		Status: status,
	}
	c.connection.Log(logger.LevelDebug, logSenderSCP, "send exit status for command with args: %v user: %v err: %v",
		c.args, c.connection.User.Username, err)
	c.connection.channel.SendRequest("exit-status", false, ssh.Marshal(&ex))
	c.connection.channel.Close()
}

// get the next upload protocol message ignoring T command if any
// we use our own user setting for permissions
func (c *scpCommand) getNextUploadProtocolMessage() (string, error) {
	var command string
	var err error
	for {
		command, err = c.readProtocolMessage()
		if err != nil {
			return command, err
		}
		if strings.HasPrefix(command, "T") {
			err = c.sendConfirmationMessage()
			if err != nil {
				return command, err
			}
		} else {
			break
		}
	}
	return command, err
}

func (c *scpCommand) createDir(dirPath string) error {
	var err error
	if err = os.Mkdir(dirPath, 0777); err != nil {
		c.connection.Log(logger.LevelError, logSenderSCP, "error creating dir: %v", dirPath)
		c.sendErrorMessage(err.Error())
		return err
	}
	utils.SetPathPermissions(dirPath, c.connection.User.GetUID(), c.connection.User.GetGID())
	return err
}

// parse protocol messages such as:
// D0755 0 testdir
// or:
// C0644 6 testfile
// and returns file size and file/directory name
func (c *scpCommand) parseUploadMessage(command string) (int64, string, error) {
	var size int64
	var name string
	var err error
	if !strings.HasPrefix(command, "C") && !strings.HasPrefix(command, "D") {
		err = fmt.Errorf("unknown or invalid upload message: %v args: %v user: %v",
			command, c.args, c.connection.User.Username)
		c.connection.Log(logger.LevelWarn, logSenderSCP, "error: %v", err)
		c.sendErrorMessage(err.Error())
		return size, name, err
	}
	parts := strings.Split(command, " ")
	if len(parts) == 3 {
		size, err = strconv.ParseInt(parts[1], 10, 64)
		if err != nil {
			c.connection.Log(logger.LevelWarn, logSenderSCP, "error getting size from upload message: %v", err)
			c.sendErrorMessage(fmt.Sprintf("Error getting size: %v", err))
			return size, name, err
		}
		name = parts[2]
		if len(name) == 0 {
			err = fmt.Errorf("error getting name from upload message, cannot be empty")
			c.connection.Log(logger.LevelWarn, logSenderSCP, "error: %v", err)
			c.sendErrorMessage(err.Error())
			return size, name, err
		}
	} else {
		err = fmt.Errorf("Error splitting upload message: %v", command)
		c.connection.Log(logger.LevelWarn, logSenderSCP, "error: %v", err)
		c.sendErrorMessage(err.Error())
		return size, name, err
	}
	return size, name, err
}

func (c *scpCommand) getFileUploadDestPath(scpDestPath, fileName string) string {
	if !c.isRecursive() {
		// if the upload is not recursive and the destination path does not end with "/"
		// then scpDestPath is the wanted filename, for example:
		// scp fileName.txt user@127.0.0.1:/newFileName.txt
		// or
		// scp fileName.txt user@127.0.0.1:/fileName.txt
		if !strings.HasSuffix(scpDestPath, "/") {
			// but if scpDestPath is an existing directory then we put the uploaded file
			// inside that directory this is as scp command works, for example:
			// scp fileName.txt user@127.0.0.1:/existing_dir
			if p, err := c.connection.buildPath(scpDestPath); err == nil {
				if stat, err := os.Stat(p); err == nil {
					if stat.IsDir() {
						return path.Join(scpDestPath, fileName)
					}
				}
			}
			return scpDestPath
		}
	}
	// if the upload is recursive or scpDestPath has the "/" suffix then the destination
	// file is relative to scpDestPath
	return path.Join(scpDestPath, fileName)
}

func getFileModeAsString(fileMode os.FileMode, isDir bool) string {
	var defaultMode string
	if isDir {
		defaultMode = "0755"
	} else {
		defaultMode = "0644"
	}
	if fileMode == 0 {
		return defaultMode
	}
	modeString := []byte(fileMode.String())
	nullPerm := []byte("-")
	u := 0
	g := 0
	o := 0
	s := 0
	lastChar := len(modeString) - 1
	if fileMode&os.ModeSticky != 0 {
		s++
	}
	if fileMode&os.ModeSetuid != 0 {
		s += 2
	}
	if fileMode&os.ModeSetgid != 0 {
		s += 4
	}
	if modeString[lastChar-8] != nullPerm[0] {
		u += 4
	}
	if modeString[lastChar-7] != nullPerm[0] {
		u += 2
	}
	if modeString[lastChar-6] != nullPerm[0] {
		u++
	}
	if modeString[lastChar-5] != nullPerm[0] {
		g += 4
	}
	if modeString[lastChar-4] != nullPerm[0] {
		g += 2
	}
	if modeString[lastChar-3] != nullPerm[0] {
		g++
	}
	if modeString[lastChar-2] != nullPerm[0] {
		o += 4
	}
	if modeString[lastChar-1] != nullPerm[0] {
		o += 2
	}
	if modeString[lastChar] != nullPerm[0] {
		o++
	}
	return fmt.Sprintf("%v%v%v%v", s, u, g, o)
}

func getDirContents(path string) ([]os.FileInfo, error) {
	var files []os.FileInfo
	f, err := os.Open(path)
	if err != nil {
		return files, err
	}
	files, err = f.Readdir(-1)
	f.Close()
	return files, err
}