package sftpd

import (
	"errors"
	"fmt"
	"io"
	"os"
	"sync"
	"time"

	"github.com/eikenb/pipeat"

	"github.com/drakkan/sftpgo/dataprovider"
	"github.com/drakkan/sftpgo/logger"
	"github.com/drakkan/sftpgo/metrics"
	"github.com/drakkan/sftpgo/vfs"
)

const (
	transferUpload = iota
	transferDownload
)

var (
	errTransferClosed = errors.New("transfer already closed")
)

// Transfer contains the transfer details for an upload or a download.
// It implements the io Reader and Writer interface to handle files downloads and uploads
type Transfer struct {
	file           *os.File
	writerAt       *vfs.PipeWriter
	readerAt       *pipeat.PipeReaderAt
	cancelFn       func()
	path           string
	start          time.Time
	bytesSent      int64
	bytesReceived  int64
	user           dataprovider.User
	connectionID   string
	transferType   int
	lastActivity   time.Time
	protocol       string
	transferError  error
	minWriteOffset int64
	initialSize    int64
	lock           *sync.Mutex
	isNewFile      bool
	isFinished     bool
	requestPath    string
}

// TransferError is called if there is an unexpected error.
// For example network or client issues
func (t *Transfer) TransferError(err error) {
	t.lock.Lock()
	defer t.lock.Unlock()
	if t.transferError != nil {
		return
	}
	t.transferError = err
	if t.cancelFn != nil {
		t.cancelFn()
	}
	elapsed := time.Since(t.start).Nanoseconds() / 1000000
	logger.Warn(logSender, t.connectionID, "Unexpected error for transfer, path: %#v, error: \"%v\" bytes sent: %v, "+
		"bytes received: %v transfer running since %v ms", t.path, t.transferError, t.bytesSent, t.bytesReceived, elapsed)
}

// ReadAt reads len(p) bytes from the File to download starting at byte offset off and updates the bytes sent.
// It handles download bandwidth throttling too
func (t *Transfer) ReadAt(p []byte, off int64) (n int, err error) {
	t.lastActivity = time.Now()
	var readed int
	var e error
	if t.readerAt != nil {
		readed, e = t.readerAt.ReadAt(p, off)
	} else {
		readed, e = t.file.ReadAt(p, off)
	}
	t.lock.Lock()
	t.bytesSent += int64(readed)
	t.lock.Unlock()
	if e != nil && e != io.EOF {
		t.TransferError(e)
		return readed, e
	}
	t.handleThrottle()
	return readed, e
}

// WriteAt writes len(p) bytes to the uploaded file starting at byte offset off and updates the bytes received.
// It handles upload bandwidth throttling too
func (t *Transfer) WriteAt(p []byte, off int64) (n int, err error) {
	t.lastActivity = time.Now()
	if off < t.minWriteOffset {
		err := fmt.Errorf("Invalid write offset: %v minimum valid value: %v", off, t.minWriteOffset)
		t.TransferError(err)
		return 0, err
	}
	var written int
	var e error
	if t.writerAt != nil {
		written, e = t.writerAt.WriteAt(p, off)
	} else {
		written, e = t.file.WriteAt(p, off)
	}
	t.lock.Lock()
	t.bytesReceived += int64(written)
	t.lock.Unlock()
	if e != nil {
		t.TransferError(e)
		return written, e
	}
	t.handleThrottle()
	return written, e
}

// Close it is called when the transfer is completed.
// It closes the underlying file, logs the transfer info, updates the user quota (for uploads)
// and executes any defined action.
// If there is an error no action will be executed and, in atomic mode, we try to delete
// the temporary file
func (t *Transfer) Close() error {
	t.lock.Lock()
	defer t.lock.Unlock()
	if t.isFinished {
		return errTransferClosed
	}
	err := t.closeIO()
	defer removeTransfer(t) //nolint:errcheck
	t.isFinished = true
	numFiles := 0
	if t.isNewFile {
		numFiles = 1
	}
	metrics.TransferCompleted(t.bytesSent, t.bytesReceived, t.transferType, t.transferError)
	if t.transferType == transferUpload && t.file != nil && t.file.Name() != t.path {
		if t.transferError == nil || uploadMode == uploadModeAtomicWithResume {
			err = os.Rename(t.file.Name(), t.path)
			logger.Debug(logSender, t.connectionID, "atomic upload completed, rename: %#v -> %#v, error: %v",
				t.file.Name(), t.path, err)
		} else {
			err = os.Remove(t.file.Name())
			logger.Warn(logSender, t.connectionID, "atomic upload completed with error: \"%v\", delete temporary file: %#v, "+
				"deletion error: %v", t.transferError, t.file.Name(), err)
			if err == nil {
				numFiles--
				t.bytesReceived = 0
			}
		}
	}
	elapsed := time.Since(t.start).Nanoseconds() / 1000000
	if t.transferType == transferDownload {
		logger.TransferLog(downloadLogSender, t.path, elapsed, t.bytesSent, t.user.Username, t.connectionID, t.protocol)
		go executeAction(newActionNotification(t.user, operationDownload, t.path, "", "", t.bytesSent, t.transferError)) //nolint:errcheck
	} else {
		logger.TransferLog(uploadLogSender, t.path, elapsed, t.bytesReceived, t.user.Username, t.connectionID, t.protocol)
		go executeAction(newActionNotification(t.user, operationUpload, t.path, "", "", t.bytesReceived+t.minWriteOffset, //nolint:errcheck
			t.transferError))
	}
	if t.transferError != nil {
		logger.Warn(logSender, t.connectionID, "transfer error: %v, path: %#v", t.transferError, t.path)
		if err == nil {
			err = t.transferError
		}
	}
	t.updateQuota(numFiles)
	return err
}

func (t *Transfer) closeIO() error {
	var err error
	if t.writerAt != nil {
		err = t.writerAt.Close()
		if err != nil {
			t.transferError = err
		}
	} else if t.readerAt != nil {
		err = t.readerAt.Close()
	} else {
		err = t.file.Close()
	}
	return err
}

func (t *Transfer) updateQuota(numFiles int) bool {
	// S3 uploads are atomic, if there is an error nothing is uploaded
	if t.file == nil && t.transferError != nil {
		return false
	}
	if t.transferType == transferUpload && (numFiles != 0 || t.bytesReceived > 0) {
		vfolder, err := t.user.GetVirtualFolderForPath(t.requestPath)
		if err == nil {
			dataprovider.UpdateVirtualFolderQuota(dataProvider, vfolder.BaseVirtualFolder, numFiles, //nolint:errcheck
				t.bytesReceived-t.initialSize, false)
			if vfolder.IsIncludedInUserQuota() {
				dataprovider.UpdateUserQuota(dataProvider, t.user, numFiles, t.bytesReceived-t.initialSize, false) //nolint:errcheck
			}
		} else {
			dataprovider.UpdateUserQuota(dataProvider, t.user, numFiles, t.bytesReceived-t.initialSize, false) //nolint:errcheck
		}
		return true
	}
	return false
}

func (t *Transfer) handleThrottle() {
	var wantedBandwidth int64
	var trasferredBytes int64
	if t.transferType == transferDownload {
		wantedBandwidth = t.user.DownloadBandwidth
		trasferredBytes = t.bytesSent
	} else {
		wantedBandwidth = t.user.UploadBandwidth
		trasferredBytes = t.bytesReceived
	}
	if wantedBandwidth > 0 {
		// real and wanted elapsed as milliseconds, bytes as kilobytes
		realElapsed := time.Since(t.start).Nanoseconds() / 1000000
		// trasferredBytes / 1000 = KB/s, we multiply for 1000 to get milliseconds
		wantedElapsed := 1000 * (trasferredBytes / 1000) / wantedBandwidth
		if wantedElapsed > realElapsed {
			toSleep := time.Duration(wantedElapsed - realElapsed)
			time.Sleep(toSleep * time.Millisecond)
		}
	}
}

// used for ssh commands.
// It reads from src until EOF so it does not treat an EOF from Read as an error to be reported.
// EOF from Write is reported as error
func (t *Transfer) copyFromReaderToWriter(dst io.Writer, src io.Reader, maxWriteSize int64) (int64, error) {
	var written int64
	var err error
	if maxWriteSize < 0 {
		return 0, errQuotaExceeded
	}
	buf := make([]byte, 32768)
	for {
		t.lastActivity = time.Now()
		nr, er := src.Read(buf)
		if nr > 0 {
			nw, ew := dst.Write(buf[0:nr])
			if nw > 0 {
				written += int64(nw)
				if t.transferType == transferDownload {
					t.bytesSent = written
				} else {
					t.bytesReceived = written
				}
				if maxWriteSize > 0 && written > maxWriteSize {
					err = errQuotaExceeded
					break
				}
			}
			if ew != nil {
				err = ew
				break
			}
			if nr != nw {
				err = io.ErrShortWrite
				break
			}
		}
		if er != nil {
			if er != io.EOF {
				err = er
			}
			break
		}
		t.handleThrottle()
	}
	t.transferError = err
	if t.bytesSent > 0 || t.bytesReceived > 0 || err != nil {
		metrics.TransferCompleted(t.bytesSent, t.bytesReceived, t.transferType, t.transferError)
	}
	return written, err
}