// Copyright 2015 Google Inc. All Rights Reserved.
//
// 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 (
	"fmt"
	"syscall"
	"unsafe"

	"github.com/jacobsa/fuse/fuseops"
	"github.com/jacobsa/fuse/internal/buffer"
	"github.com/jacobsa/fuse/internal/fusekernel"
)

// Return the response that should be sent to the kernel. If the op requires no
// response, return a nil response.
func kernelResponse(
	fuseID uint64,
	op interface{},
	opErr error,
	protocol fusekernel.Protocol) (msg []byte) {
	// If the user replied with an error, create room enough just for the result
	// header and fill it in with an error. Otherwise create an appropriate
	// response.
	var b buffer.OutMessage
	if opErr != nil {
		b = buffer.NewOutMessage(0)
		if errno, ok := opErr.(syscall.Errno); ok {
			b.OutHeader().Error = -int32(errno)
		} else {
			b.OutHeader().Error = -int32(syscall.EIO)
		}
	} else {
		b = kernelResponseForOp(op, protocol)
	}

	msg = b.Bytes()

	// Fill in the rest of the header, if a response is required.
	if msg != nil {
		h := b.OutHeader()
		h.Unique = fuseID
		h.Len = uint32(len(msg))
	}

	return
}

// Like kernelResponse, but assumes the user replied with a nil error to the
// op. Returns a nil response if no response is required.
func kernelResponseForOp(
	op interface{},
	protocol fusekernel.Protocol) (b buffer.OutMessage) {
	// Create the appropriate output message
	switch o := op.(type) {
	case *fuseops.LookUpInodeOp:
		size := fusekernel.EntryOutSize(protocol)
		b = buffer.NewOutMessage(size)
		out := (*fusekernel.EntryOut)(b.Grow(size))
		convertChildInodeEntry(&o.Entry, out)

	case *fuseops.GetInodeAttributesOp:
		size := fusekernel.AttrOutSize(protocol)
		b = buffer.NewOutMessage(size)
		out := (*fusekernel.AttrOut)(b.Grow(size))
		out.AttrValid, out.AttrValidNsec = convertExpirationTime(
			o.AttributesExpiration)
		convertAttributes(o.Inode, &o.Attributes, &out.Attr)

	case *fuseops.SetInodeAttributesOp:
		size := fusekernel.AttrOutSize(protocol)
		b = buffer.NewOutMessage(size)
		out := (*fusekernel.AttrOut)(b.Grow(size))
		out.AttrValid, out.AttrValidNsec = convertExpirationTime(
			o.AttributesExpiration)
		convertAttributes(o.Inode, &o.Attributes, &out.Attr)

	case *fuseops.ForgetInodeOp:
		// No response.

	case *fuseops.MkDirOp:
		size := fusekernel.EntryOutSize(protocol)
		b = buffer.NewOutMessage(size)
		out := (*fusekernel.EntryOut)(b.Grow(size))
		convertChildInodeEntry(&o.Entry, out)

	case *fuseops.CreateFileOp:
		eSize := fusekernel.EntryOutSize(protocol)
		b = buffer.NewOutMessage(eSize + unsafe.Sizeof(fusekernel.OpenOut{}))

		e := (*fusekernel.EntryOut)(b.Grow(eSize))
		convertChildInodeEntry(&o.Entry, e)

		oo := (*fusekernel.OpenOut)(b.Grow(unsafe.Sizeof(fusekernel.OpenOut{})))
		oo.Fh = uint64(o.Handle)

	case *fuseops.CreateSymlinkOp:
		size := fusekernel.EntryOutSize(protocol)
		b = buffer.NewOutMessage(size)
		out := (*fusekernel.EntryOut)(b.Grow(size))
		convertChildInodeEntry(&o.Entry, out)

	case *fuseops.RenameOp:
		b = buffer.NewOutMessage(0)

	case *fuseops.RmDirOp:
		b = buffer.NewOutMessage(0)

	case *fuseops.UnlinkOp:
		b = buffer.NewOutMessage(0)

	case *fuseops.OpenDirOp:
		b = buffer.NewOutMessage(unsafe.Sizeof(fusekernel.OpenOut{}))
		out := (*fusekernel.OpenOut)(b.Grow(unsafe.Sizeof(fusekernel.OpenOut{})))
		out.Fh = uint64(o.Handle)

	case *fuseops.ReadDirOp:
		b = buffer.NewOutMessage(uintptr(len(o.Data)))
		b.Append(o.Data)

	case *fuseops.ReleaseDirHandleOp:
		b = buffer.NewOutMessage(0)

	case *fuseops.OpenFileOp:
		b = buffer.NewOutMessage(unsafe.Sizeof(fusekernel.OpenOut{}))
		out := (*fusekernel.OpenOut)(b.Grow(unsafe.Sizeof(fusekernel.OpenOut{})))
		out.Fh = uint64(o.Handle)

	case *fuseops.ReadFileOp:
		b = buffer.NewOutMessage(uintptr(len(o.Data)))
		b.Append(o.Data)

	case *fuseops.WriteFileOp:
		b = buffer.NewOutMessage(unsafe.Sizeof(fusekernel.WriteOut{}))
		out := (*fusekernel.WriteOut)(b.Grow(unsafe.Sizeof(fusekernel.WriteOut{})))
		out.Size = uint32(len(o.Data))

	case *fuseops.SyncFileOp:
		b = buffer.NewOutMessage(0)

	case *fuseops.FlushFileOp:
		b = buffer.NewOutMessage(0)

	case *fuseops.ReleaseFileHandleOp:
		b = buffer.NewOutMessage(0)

	case *fuseops.ReadSymlinkOp:
		b = buffer.NewOutMessage(uintptr(len(o.Target)))
		b.AppendString(o.Target)

	case *statFSOp:
		b = buffer.NewOutMessage(unsafe.Sizeof(fusekernel.StatfsOut{}))
		b.Grow(unsafe.Sizeof(fusekernel.StatfsOut{}))

	case *interruptOp:
		// No response.

	case *initOp:
		b = buffer.NewOutMessage(unsafe.Sizeof(fusekernel.InitOut{}))
		out := (*fusekernel.InitOut)(b.Grow(unsafe.Sizeof(fusekernel.InitOut{})))

		out.Major = o.Library.Major
		out.Minor = o.Library.Minor
		out.MaxReadahead = o.MaxReadahead
		out.Flags = uint32(o.Flags)
		out.MaxWrite = o.MaxWrite

	default:
		panic(fmt.Sprintf("Unknown op: %#v", op))
	}

	return
}

////////////////////////////////////////////////////////////////////////
// Internal
////////////////////////////////////////////////////////////////////////

// A sentinel used for unknown ops. The user is expected to respond with a
// non-nil error.
type unknownOp struct {
	opCode uint32
	inode  fuseops.InodeID
}

type statFSOp struct {
}

type interruptOp struct {
	FuseID uint64
}

type initOp struct {
	// In
	Kernel fusekernel.Protocol

	// Out
	Library      fusekernel.Protocol
	MaxReadahead uint32
	Flags        fusekernel.InitFlags
	MaxWrite     uint32
}