// Copyright 2020 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package fuse

import (
	"gvisor.dev/gvisor/pkg/abi/linux"
	"gvisor.dev/gvisor/pkg/context"
	"gvisor.dev/gvisor/pkg/errors/linuxerr"
	"gvisor.dev/gvisor/pkg/sentry/vfs"
	"gvisor.dev/gvisor/pkg/usermem"
)

// +stateify savable
type directoryFD struct {
	fileDescription
}

// Allocate implements directoryFD.Allocate.
func (*directoryFD) Allocate(ctx context.Context, mode, offset, length uint64) error {
	return linuxerr.EISDIR
}

// PRead implements vfs.FileDescriptionImpl.PRead.
func (*directoryFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
	return 0, linuxerr.EISDIR
}

// Read implements vfs.FileDescriptionImpl.Read.
func (*directoryFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
	return 0, linuxerr.EISDIR
}

// PWrite implements vfs.FileDescriptionImpl.PWrite.
func (*directoryFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
	return 0, linuxerr.EISDIR
}

// Write implements vfs.FileDescriptionImpl.Write.
func (*directoryFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
	return 0, linuxerr.EISDIR
}

// OnClose implements vfs.FileDescriptionImpl.OnClose.
func (*directoryFD) OnClose(ctx context.Context) error {
	return nil
}

// Seek implements vfs.FileDescriptionImpl.Seek.
func (dir *directoryFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
	switch whence {
	case linux.SEEK_SET:
		if offset < 0 {
			return 0, linuxerr.EINVAL
		}
		dir.off.Store(offset)
		return offset, nil
	case linux.SEEK_CUR:
		newOffset := dir.off.Load() + offset
		if newOffset < 0 {
			return 0, linuxerr.EINVAL
		}
		dir.off.Store(newOffset)
		return newOffset, nil
	default:
		return 0, linuxerr.EINVAL
	}
}

// IterDirents implements vfs.FileDescriptionImpl.IterDirents.
func (dir *directoryFD) IterDirents(ctx context.Context, callback vfs.IterDirentsCallback) error {
	in := linux.FUSEReadIn{
		Fh:     dir.Fh,
		Offset: uint64(dir.off.Load()),
		Size:   linux.FUSE_PAGE_SIZE,
		Flags:  dir.statusFlags(),
	}

	// TODO(gVisor.dev/issue/3404): Support FUSE_READDIRPLUS.
	var out linux.FUSEDirents
	if err := dir.inode().call(ctx, linux.FUSE_READDIR, &in, &out); err != nil {
		return err
	}

	for _, fuseDirent := range out.Dirents {
		if len(fuseDirent.Name) == 0 {
			return linuxerr.EIO
		}
		nextOff := int64(fuseDirent.Meta.Off)
		dirent := vfs.Dirent{
			Name:    fuseDirent.Name,
			Type:    uint8(fuseDirent.Meta.Type),
			Ino:     fuseDirent.Meta.Ino,
			NextOff: nextOff,
		}

		if err := callback.Handle(dirent); err != nil {
			return err
		}
		dir.off.Store(nextOff)
	}

	return nil
}
