// Copyright (c) 2015-2024 MinIO, Inc.
//
// This file is part of MinIO Object Storage stack
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package cmd

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"path"
	"strings"
	"sync"
	"time"

	"github.com/minio/madmin-go/v3"
	"github.com/minio/minio-go/v7"
	"github.com/minio/minio-go/v7/pkg/credentials"
	xioutil "github.com/minio/minio/internal/ioutil"
	"github.com/minio/pkg/v3/mimedb"
	"github.com/pkg/sftp"
	"golang.org/x/crypto/ssh"
)

// Maximum write offset for incoming SFTP blocks.
// Set to 100MiB to prevent hostile DOS attacks.
const ftpMaxWriteOffset = 100 << 20

type sftpDriver struct {
	permissions *ssh.Permissions
	endpoint    string
}

//msgp:ignore sftpMetrics
type sftpMetrics struct{}

var globalSftpMetrics sftpMetrics

func sftpTrace(s *sftp.Request, startTime time.Time, source string, user string, err error, sz int64) madmin.TraceInfo {
	var errStr string
	if err != nil {
		errStr = err.Error()
	}
	return madmin.TraceInfo{
		TraceType: madmin.TraceFTP,
		Time:      startTime,
		NodeName:  globalLocalNodeName,
		FuncName:  s.Method,
		Duration:  time.Since(startTime),
		Path:      s.Filepath,
		Error:     errStr,
		Bytes:     sz,
		Custom: map[string]string{
			"user":   user,
			"cmd":    s.Method,
			"param":  s.Filepath,
			"source": source,
		},
	}
}

func (m *sftpMetrics) log(s *sftp.Request, user string) func(sz int64, err error) {
	startTime := time.Now()
	source := getSource(2)
	return func(sz int64, err error) {
		globalTrace.Publish(sftpTrace(s, startTime, source, user, err, sz))
	}
}

// NewSFTPDriver initializes sftp.Handlers implementation of following interfaces
//
// - sftp.Fileread
// - sftp.Filewrite
// - sftp.Filelist
// - sftp.Filecmd
func NewSFTPDriver(perms *ssh.Permissions) sftp.Handlers {
	handler := &sftpDriver{endpoint: fmt.Sprintf("127.0.0.1:%s", globalMinioPort), permissions: perms}
	return sftp.Handlers{
		FileGet:  handler,
		FilePut:  handler,
		FileCmd:  handler,
		FileList: handler,
	}
}

func (f *sftpDriver) getMinIOClient() (*minio.Client, error) {
	mcreds := credentials.NewStaticV4(
		f.permissions.CriticalOptions["AccessKey"],
		f.permissions.CriticalOptions["SecretKey"],
		f.permissions.CriticalOptions["SessionToken"],
	)
	return minio.New(f.endpoint, &minio.Options{
		Creds:     mcreds,
		Secure:    globalIsTLS,
		Transport: globalRemoteFTPClientTransport,
	})
}

func (f *sftpDriver) AccessKey() string {
	return f.permissions.CriticalOptions["AccessKey"]
}

func (f *sftpDriver) Fileread(r *sftp.Request) (ra io.ReaderAt, err error) {
	// This is not timing the actual read operation, but the time it takes to prepare the reader.
	stopFn := globalSftpMetrics.log(r, f.AccessKey())
	defer stopFn(0, err)

	flags := r.Pflags()
	if !flags.Read {
		// sanity check
		return nil, os.ErrInvalid
	}

	bucket, object := path2BucketObject(r.Filepath)
	if bucket == "" {
		return nil, errors.New("bucket name cannot be empty")
	}

	clnt, err := f.getMinIOClient()
	if err != nil {
		return nil, err
	}

	obj, err := clnt.GetObject(context.Background(), bucket, object, minio.GetObjectOptions{})
	if err != nil {
		return nil, err
	}

	_, err = obj.Stat()
	if err != nil {
		return nil, err
	}

	return obj, nil
}

// TransferError will catch network errors during transfer.
// When TransferError() is called Close() will also
// be called, so we do not need to Wait() here.
func (w *writerAt) TransferError(err error) {
	_ = w.w.CloseWithError(err)
	_ = w.r.CloseWithError(err)
	w.err = err
}

func (w *writerAt) Close() (err error) {
	switch {
	case len(w.buffer) > 0:
		err = errors.New("some file segments were not flushed from the queue")
		_ = w.w.CloseWithError(err)
	case w.err != nil:
		// No need to close here since both pipes were
		// closing inside TransferError()
		err = w.err
	default:
		err = w.w.Close()
	}
	for i := range w.buffer {
		delete(w.buffer, i)
	}
	w.wg.Wait()
	return err
}

type writerAt struct {
	w      *io.PipeWriter
	r      *io.PipeReader
	wg     *sync.WaitGroup
	buffer map[int64][]byte
	err    error

	nextOffset int64
	m          sync.Mutex
}

func (w *writerAt) WriteAt(b []byte, offset int64) (n int, err error) {
	w.m.Lock()
	defer w.m.Unlock()

	if w.nextOffset == offset {
		n, err = w.w.Write(b)
		w.nextOffset += int64(n)
	} else {
		if offset > w.nextOffset+ftpMaxWriteOffset {
			return 0, fmt.Errorf("write offset %d is too far ahead of next offset %d", offset, w.nextOffset)
		}
		w.buffer[offset] = make([]byte, len(b))
		copy(w.buffer[offset], b)
		n = len(b)
	}

again:
	nextOut, ok := w.buffer[w.nextOffset]
	if ok {
		n, err = w.w.Write(nextOut)
		delete(w.buffer, w.nextOffset)
		w.nextOffset += int64(n)
		if n != len(nextOut) {
			return 0, fmt.Errorf("expected write size %d but wrote %d bytes", len(nextOut), n)
		}
		if err != nil {
			return 0, err
		}
		goto again
	}

	return len(b), nil
}

func (f *sftpDriver) Filewrite(r *sftp.Request) (w io.WriterAt, err error) {
	stopFn := globalSftpMetrics.log(r, f.AccessKey())
	defer func() {
		if err != nil {
			// If there is an error, we never started the goroutine.
			stopFn(0, err)
		}
	}()

	flags := r.Pflags()
	if !flags.Write {
		// sanity check
		return nil, os.ErrInvalid
	}

	bucket, object := path2BucketObject(r.Filepath)
	if bucket == "" {
		return nil, errors.New("bucket name cannot be empty")
	}

	clnt, err := f.getMinIOClient()
	if err != nil {
		return nil, err
	}
	ok, err := clnt.BucketExists(r.Context(), bucket)
	if err != nil {
		return nil, err
	}
	if !ok {
		return nil, os.ErrNotExist
	}

	pr, pw := io.Pipe()

	wa := &writerAt{
		buffer: make(map[int64][]byte),
		w:      pw,
		r:      pr,
		wg:     &sync.WaitGroup{},
	}
	wa.wg.Add(1)
	go func() {
		oi, err := clnt.PutObject(r.Context(), bucket, object, pr, -1, minio.PutObjectOptions{
			ContentType:          mimedb.TypeByExtension(path.Ext(object)),
			DisableContentSha256: true,
		})
		stopFn(oi.Size, err)
		pr.CloseWithError(err)
		wa.wg.Done()
	}()
	return wa, nil
}

func (f *sftpDriver) Filecmd(r *sftp.Request) (err error) {
	stopFn := globalSftpMetrics.log(r, f.AccessKey())
	defer stopFn(0, err)

	clnt, err := f.getMinIOClient()
	if err != nil {
		return err
	}

	switch r.Method {
	case "Setstat", "Rename", "Link", "Symlink":
		return sftp.ErrSSHFxOpUnsupported

	case "Rmdir":
		bucket, prefix := path2BucketObject(r.Filepath)
		if bucket == "" {
			return errors.New("deleting all buckets not allowed")
		}

		cctx, cancel := context.WithCancel(context.Background())
		defer cancel()

		if prefix == "" {
			// if all objects are not deleted yet this call may fail.
			return clnt.RemoveBucket(cctx, bucket)
		}

		objectsCh := make(chan minio.ObjectInfo)

		// Send object names that are needed to be removed to objectsCh
		go func() {
			defer xioutil.SafeClose(objectsCh)
			opts := minio.ListObjectsOptions{
				Prefix:    prefix,
				Recursive: true,
			}
			for object := range clnt.ListObjects(cctx, bucket, opts) {
				if object.Err != nil {
					return
				}
				objectsCh <- object
			}
		}()

		// Call RemoveObjects API
		for err := range clnt.RemoveObjects(context.Background(), bucket, objectsCh, minio.RemoveObjectsOptions{}) {
			if err.Err != nil {
				return err.Err
			}
		}
		return err

	case "Remove":
		bucket, object := path2BucketObject(r.Filepath)
		if bucket == "" {
			return errors.New("bucket name cannot be empty")
		}

		return clnt.RemoveObject(context.Background(), bucket, object, minio.RemoveObjectOptions{})

	case "Mkdir":
		bucket, prefix := path2BucketObject(r.Filepath)
		if bucket == "" {
			return errors.New("bucket name cannot be empty")
		}

		if prefix == "" {
			return clnt.MakeBucket(context.Background(), bucket, minio.MakeBucketOptions{Region: globalSite.Region()})
		}

		dirPath := buildMinioDir(prefix)

		_, err = clnt.PutObject(context.Background(), bucket, dirPath, bytes.NewReader([]byte("")), 0,
			minio.PutObjectOptions{DisableContentSha256: true},
		)
		return err
	}

	return NotImplemented{}
}

type listerAt []os.FileInfo

// Modeled after strings.Reader's ReadAt() implementation
func (f listerAt) ListAt(ls []os.FileInfo, offset int64) (int, error) {
	var n int
	if offset >= int64(len(f)) {
		return 0, io.EOF
	}
	n = copy(ls, f[offset:])
	if n < len(ls) {
		return n, io.EOF
	}
	return n, nil
}

func (f *sftpDriver) Filelist(r *sftp.Request) (la sftp.ListerAt, err error) {
	stopFn := globalSftpMetrics.log(r, f.AccessKey())
	defer stopFn(0, err)

	clnt, err := f.getMinIOClient()
	if err != nil {
		return nil, err
	}

	switch r.Method {
	case "List":
		var files []os.FileInfo

		bucket, prefix := path2BucketObject(r.Filepath)
		if bucket == "" {
			buckets, err := clnt.ListBuckets(r.Context())
			if err != nil {
				return nil, err
			}

			for _, bucket := range buckets {
				files = append(files, &minioFileInfo{
					p:     bucket.Name,
					info:  minio.ObjectInfo{Key: bucket.Name, LastModified: bucket.CreationDate},
					isDir: true,
				})
			}

			return listerAt(files), nil
		}

		prefix = retainSlash(prefix)

		for object := range clnt.ListObjects(r.Context(), bucket, minio.ListObjectsOptions{
			Prefix:    prefix,
			Recursive: false,
		}) {
			if object.Err != nil {
				return nil, object.Err
			}

			if object.Key == prefix {
				continue
			}

			isDir := strings.HasSuffix(object.Key, SlashSeparator)
			files = append(files, &minioFileInfo{
				p:     pathClean(strings.TrimPrefix(object.Key, prefix)),
				info:  object,
				isDir: isDir,
			})
		}

		return listerAt(files), nil

	case "Stat":
		if r.Filepath == SlashSeparator {
			return listerAt{&minioFileInfo{
				p:     r.Filepath,
				isDir: true,
			}}, nil
		}

		bucket, object := path2BucketObject(r.Filepath)
		if bucket == "" {
			return nil, errors.New("bucket name cannot be empty")
		}

		if object == "" {
			ok, err := clnt.BucketExists(context.Background(), bucket)
			if err != nil {
				return nil, err
			}
			if !ok {
				return nil, os.ErrNotExist
			}
			return listerAt{&minioFileInfo{
				p:     pathClean(bucket),
				info:  minio.ObjectInfo{Key: bucket},
				isDir: true,
			}}, nil
		}

		objInfo, err := clnt.StatObject(context.Background(), bucket, object, minio.StatObjectOptions{})
		if err != nil {
			if minio.ToErrorResponse(err).Code == "NoSuchKey" {
				// dummy return to satisfy LIST (stat -> list) behavior.
				return listerAt{&minioFileInfo{
					p:     pathClean(object),
					info:  minio.ObjectInfo{Key: object},
					isDir: true,
				}}, nil
			}
			return nil, err
		}

		isDir := strings.HasSuffix(objInfo.Key, SlashSeparator)
		return listerAt{&minioFileInfo{
			p:     pathClean(object),
			info:  objInfo,
			isDir: isDir,
		}}, nil
	}

	return nil, NotImplemented{}
}