package main

import (
	"context"
	"io"
	"log"
	"os"
	"sort"
	"syscall"

	"bazil.org/fuse"
	"bazil.org/fuse/fs"
)

var _ fs.HandleFlockLocker = (*Handle)(nil)
var _ fs.HandleFlusher = (*Handle)(nil)
var _ fs.HandleLocker = (*Handle)(nil)
var _ fs.HandlePOSIXLocker = (*Handle)(nil)
var _ fs.HandlePoller = (*Handle)(nil)
var _ fs.HandleReadDirAller = (*Handle)(nil)
var _ fs.HandleReader = (*Handle)(nil)
var _ fs.HandleReleaser = (*Handle)(nil)
var _ fs.HandleWriter = (*Handle)(nil)

// var _ fs.HandleReadAller = (*Handle)(nil)

type Handle struct {
	f *os.File
}

// Flush is called each time the file or directory is closed.
// Because there can be multiple file descriptors referring to a
// single opened file, Flush can be called multiple times.
func (h *Handle) Flush(ctx context.Context, req *fuse.FlushRequest) (err error) {
	defer func() { log.Printf("[flush] handle=%q -- err=%v", h.f.Name(), err) }()
	return h.f.Sync()
}

func (h *Handle) ReadDirAll(ctx context.Context) (ents []fuse.Dirent, err error) {
	defer func() { log.Printf("[readdirall] handle=%q -- ents=%d err=%v", h.f.Name(), len(ents), err) }()

	fis, err := h.f.Readdir(-1)
	if err != nil {
		return nil, err
	}

	// Convert FileInfo objects to FUSE directory entries.
	ents = make([]fuse.Dirent, len(fis))
	for i, fi := range fis {
		statt := fi.Sys().(*syscall.Stat_t)
		ents[i] = fuse.Dirent{Inode: statt.Ino, Name: fi.Name()}
	}

	sort.Slice(ents, func(i, j int) bool { return ents[i].Name < ents[j].Name })
	return ents, nil
}

// Read requests to read data from the handle.
//
// There is a page cache in the kernel that normally submits only
// page-aligned reads spanning one or more pages. However, you
// should not rely on this. To see individual requests as
// submitted by the file system clients, set OpenDirectIO.
//
// Note that reads beyond the size of the file as reported by Attr
// are not even attempted (except in OpenDirectIO mode).
func (h *Handle) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) (err error) {
	defer func() {
		log.Printf("[read] handle=%q offset=%d size=%d flags=%#o lockowner=%d fileflags=%#o -- data=%d err=%v",
			h.f.Name(),
			req.Offset,
			req.Size,
			req.Flags,
			req.LockOwner,
			req.FileFlags,
			len(resp.Data),
			err,
		)
	}()

	// TODO: Flags     ReadFlags
	// TODO: LockOwner
	// TODO: FileFlags OpenFlags

	buf := make([]byte, req.Size)
	n, err := h.f.ReadAt(buf, req.Offset)
	if err != nil && err != io.EOF {
		return err
	}
	resp.Data = buf[:n]

	return nil
}

// Write requests to write data into the handle at the given offset.
// Store the amount of data written in resp.Size.
//
// There is a writeback page cache in the kernel that normally submits
// only page-aligned writes spanning one or more pages. However,
// you should not rely on this. To see individual requests as
// submitted by the file system clients, set OpenDirectIO.
//
// Writes that grow the file are expected to update the file size
// (as seen through Attr). Note that file size changes are
// communicated also through Setattr.
func (h *Handle) Write(ctx context.Context, req *fuse.WriteRequest, resp *fuse.WriteResponse) (err error) {
	defer func() {
		log.Printf(
			"[write] handle=%q offset=%d size=%d flags=%#o lockowner=%d fileflags=%#o -- data=%d err=%v",
			h.f.Name(),
			req.Offset,
			len(req.Data),
			req.Flags,
			req.LockOwner,
			req.FileFlags,
			resp.Size,
			err,
		)
	}()

	// Offset    int64
	// Data      []byte
	// Flags     WriteFlags
	// LockOwner LockOwner
	// FileFlags OpenFlags

	resp.Size, err = h.f.WriteAt(req.Data, req.Offset)
	return err
}

func (h *Handle) Release(ctx context.Context, req *fuse.ReleaseRequest) (err error) {
	defer func() { log.Printf("[release] handle=%q -- err=%v", h.f.Name(), err) }()
	return h.f.Close()
}

// Poll checks whether the handle is currently ready for I/O, and
// may request a wakeup when it is.
//
// Poll should always return quickly. Clients waiting for
// readiness can be woken up by passing the return value of
// PollRequest.Wakeup to fs.Server.NotifyPollWakeup or
// fuse.Conn.NotifyPollWakeup.
//
// To allow supporting poll for only some of your Nodes/Handles,
// the default behavior is to report immediate readiness. If your
// FS does not support polling and you want to minimize needless
// requests and log noise, implement NodePoller and return
// syscall.ENOSYS.
//
// The Go runtime uses epoll-based I/O whenever possible, even for
// regular files.
func (h *Handle) Poll(ctx context.Context, req *fuse.PollRequest, resp *fuse.PollResponse) error {
	log.Printf("[poll] handle=%q flags=%#o events=%#o", h.f.Name(), req.Flags, req.Events)

	//type PollRequest struct {
	//    Header `json:"-"`
	//    Handle HandleID
	//
	//    Flags PollFlags
	//    Events PollEvents
	//}

	//type PollResponse struct {
	//    REvents PollEvents
	//}

	panic("TODO")
}

// Lock tries to acquire a lock on a byte range of the node. If a
// conflicting lock is already held, returns syscall.EAGAIN.
//
// LockRequest.LockOwner is a file-unique identifier for this
// lock, and will be seen in calls releasing this lock
// (UnlockRequest, ReleaseRequest, FlushRequest) and also
// in e.g. ReadRequest, WriteRequest.
func (h *Handle) Lock(ctx context.Context, req *fuse.LockRequest) error {
	log.Printf("[lock] handle=%q lockowner=%d lock=%#o lockflags=%#o", h.f.Name(), req.LockOwner, req.Lock, req.LockFlags)

	// type LockRequest struct {
	//     Header
	//     Handle HandleID
	//     // LockOwner is a unique identifier for the originating client, to identify locks.
	//     LockOwner LockOwner
	//     Lock      FileLock
	//     LockFlags LockFlags
	// }

	panic("TODO")
}

// LockWait acquires a lock on a byte range of the node, waiting
// until the lock can be obtained (or context is canceled).
func (h *Handle) LockWait(ctx context.Context, req *fuse.LockWaitRequest) error {
	log.Printf("[lockwait] handle=%q lockowner=%d lock=%#o lockflags=%#o", h.f.Name(), req.LockOwner, req.Lock, req.LockFlags)

	// type LockWaitRequest LockRequest

	panic("TODO")
}

// Unlock releases the lock on a byte range of the node. Locks can
// be released also implicitly, see HandleFlockLocker and
// HandlePOSIXLocker.
func (h *Handle) Unlock(ctx context.Context, req *fuse.UnlockRequest) error {
	log.Printf("[unlock] handle=%q lockowner=%d lock=%#o lockflags=%#o", h.f.Name(), req.LockOwner, req.Lock, req.LockFlags)

	// type UnlockRequest LockRequest

	panic("TODO")
}

// QueryLock returns the current state of locks held for the byte
// range of the node.
//
// See QueryLockRequest for details on how to respond.
//
// To simplify implementing this method, resp.Lock is prefilled to
// have Lock.Type F_UNLCK, and the whole struct should be
// overwritten for in case of conflicting locks.
func (h *Handle) QueryLock(ctx context.Context, req *fuse.QueryLockRequest, resp *fuse.QueryLockResponse) error {
	log.Printf("[querylock] handle=%q lockowner=%d lock=%#o lockflags=%#o", h.f.Name(), req.LockOwner, req.Lock, req.LockFlags)

	// type QueryLockRequest struct {
	//     Header
	//     Handle    HandleID
	//     LockOwner LockOwner
	//     Lock      FileLock
	//     LockFlags LockFlags
	// }

	// type QueryLockResponse struct {
	//     Lock FileLock
	// }

	panic("TODO")
}