//go:build linux

package mount

import (
	"context"
	"errors"
	"fmt"
	"hash/fnv"
	"io"
	"os"
	"path"
	"sync"
	"syscall"
	"time"

	"bazil.org/fuse"
	"bazil.org/fuse/fs"
	"gitea.dddbg.com/youbin/bdrclone/internal/baidu"
)

type FileSystem struct {
	client   *baidu.Client
	readOnly bool
}

func New(client *baidu.Client, readOnly bool) *FileSystem {
	return &FileSystem{client: client, readOnly: readOnly}
}

func (f *FileSystem) Root() (fs.Node, error) {
	return &Dir{fs: f, name: "/"}, nil
}

type Dir struct {
	fs   *FileSystem
	name string
}

func (d *Dir) Attr(_ context.Context, attr *fuse.Attr) error {
	attr.Inode = inode(d.name)
	attr.Mode = os.ModeDir | 0o755
	attr.Mtime = time.Now()
	return nil
}

func (d *Dir) Lookup(ctx context.Context, req *fuse.LookupRequest, _ *fuse.LookupResponse) (fs.Node, error) {
	remote := path.Join(d.name, req.Name)
	entry, err := d.fs.client.Stat(ctx, remote)
	if err != nil {
		if errors.Is(err, baidu.ErrNotFound) {
			return nil, syscall.ENOENT
		}
		return nil, err
	}
	return d.fs.node(d.fs.client.APIPath(entry.Path), entry), nil
}

func (d *Dir) ReadDirAll(ctx context.Context) ([]fuse.Dirent, error) {
	entries, err := d.fs.client.List(ctx, d.name)
	if err != nil {
		return nil, err
	}
	result := make([]fuse.Dirent, 0, len(entries))
	for _, entry := range entries {
		typeID := fuse.DT_File
		if entry.IsDirectory() {
			typeID = fuse.DT_Dir
		}
		result = append(result, fuse.Dirent{Inode: inode(d.fs.client.APIPath(entry.Path)), Name: entry.Name(), Type: typeID})
	}
	return result, nil
}

func (d *Dir) Mkdir(ctx context.Context, req *fuse.MkdirRequest) (fs.Node, error) {
	if d.fs.readOnly {
		return nil, syscall.EROFS
	}
	name := path.Join(d.name, req.Name)
	entry, err := d.fs.client.Mkdir(ctx, name)
	if err != nil {
		return nil, err
	}
	return d.fs.node(name, entry), nil
}

func (d *Dir) Create(ctx context.Context, req *fuse.CreateRequest, resp *fuse.CreateResponse) (fs.Node, fs.Handle, error) {
	if d.fs.readOnly {
		return nil, nil, syscall.EROFS
	}
	name := path.Join(d.name, req.Name)
	tmp, err := os.CreateTemp("", "bdrclone-write-*")
	if err != nil {
		return nil, nil, err
	}
	node := &File{fs: d.fs, name: name, info: baidu.File{Path: d.fs.client.RemotePath(name), ServerFilename: req.Name}}
	handle := &writeHandle{node: node, file: tmp, dirty: true}
	node.active = handle
	resp.Flags |= fuse.OpenDirectIO
	return node, handle, nil
}

func (d *Dir) Remove(ctx context.Context, req *fuse.RemoveRequest) error {
	if d.fs.readOnly {
		return syscall.EROFS
	}
	name := path.Join(d.name, req.Name)
	if req.Dir {
		entries, err := d.fs.client.List(ctx, name)
		if err != nil {
			return err
		}
		if len(entries) > 0 {
			return syscall.ENOTEMPTY
		}
	}
	return d.fs.client.Delete(ctx, name)
}

func (d *Dir) Rename(ctx context.Context, req *fuse.RenameRequest, newDir fs.Node) error {
	if d.fs.readOnly {
		return syscall.EROFS
	}
	destinationDir, ok := newDir.(*Dir)
	if !ok {
		return syscall.ENOTDIR
	}
	return d.fs.client.Move(ctx, path.Join(d.name, req.OldName), path.Join(destinationDir.name, req.NewName))
}

func (f *FileSystem) node(name string, entry baidu.File) fs.Node {
	if entry.IsDirectory() {
		return &Dir{fs: f, name: name}
	}
	return &File{fs: f, name: name, info: entry}
}

type File struct {
	fs     *FileSystem
	name   string
	mu     sync.Mutex
	info   baidu.File
	active *writeHandle
}

func (f *File) Attr(_ context.Context, attr *fuse.Attr) error {
	f.mu.Lock()
	defer f.mu.Unlock()
	attr.Inode = inode(f.name)
	attr.Mode = 0o644
	attr.Size = uint64(f.info.Size)
	attr.Mtime = f.info.ModTime()
	return nil
}

func (f *File) Open(ctx context.Context, req *fuse.OpenRequest, resp *fuse.OpenResponse) (fs.Handle, error) {
	if !req.Flags.IsWriteOnly() && !req.Flags.IsReadWrite() {
		resp.Flags |= fuse.OpenDirectIO
		return &readHandle{file: f}, nil
	}
	if f.fs.readOnly {
		return nil, syscall.EROFS
	}
	f.mu.Lock()
	busy := f.active != nil
	f.mu.Unlock()
	if busy {
		return nil, syscall.EBUSY
	}
	tmp, err := os.CreateTemp("", "bdrclone-write-*")
	if err != nil {
		return nil, err
	}
	if req.Flags&fuse.OpenTruncate == 0 && f.info.Size > 0 {
		body, err := f.fs.client.Open(ctx, f.info, 0, 0)
		if err != nil {
			tmp.Close()
			os.Remove(tmp.Name())
			return nil, err
		}
		_, copyErr := io.Copy(tmp, body)
		closeErr := body.Close()
		if copyErr != nil || closeErr != nil {
			tmp.Close()
			os.Remove(tmp.Name())
			return nil, errors.Join(copyErr, closeErr)
		}
	}
	resp.Flags |= fuse.OpenDirectIO
	handle := &writeHandle{node: f, file: tmp, dirty: req.Flags&fuse.OpenTruncate != 0}
	f.mu.Lock()
	f.active = handle
	f.mu.Unlock()
	return handle, nil
}

func (f *File) Setattr(_ context.Context, req *fuse.SetattrRequest, _ *fuse.SetattrResponse) error {
	if f.fs.readOnly && req.Valid.Size() {
		return syscall.EROFS
	}
	if req.Valid.Size() {
		f.mu.Lock()
		handle := f.active
		f.mu.Unlock()
		if handle == nil {
			return syscall.EBADF
		}
		return handle.truncate(int64(req.Size))
	}
	return nil
}

func (f *File) Fsync(ctx context.Context, _ *fuse.FsyncRequest) error {
	f.mu.Lock()
	handle := f.active
	f.mu.Unlock()
	if handle == nil {
		return nil
	}
	return handle.sync(ctx)
}

type readHandle struct{ file *File }

func (h *readHandle) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
	h.file.mu.Lock()
	info := h.file.info
	h.file.mu.Unlock()
	if req.Offset >= info.Size {
		resp.Data = nil
		return nil
	}
	size := min(int64(req.Size), info.Size-req.Offset)
	body, err := h.file.fs.client.Open(ctx, info, req.Offset, size)
	if err != nil {
		return err
	}
	defer body.Close()
	resp.Data, err = io.ReadAll(io.LimitReader(body, size))
	return err
}

type writeHandle struct {
	node  *File
	file  *os.File
	mu    sync.Mutex
	dirty bool
	done  bool
}

func (h *writeHandle) Read(_ context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
	h.mu.Lock()
	defer h.mu.Unlock()
	buf := make([]byte, req.Size)
	n, err := h.file.ReadAt(buf, req.Offset)
	if err != nil && !errors.Is(err, io.EOF) {
		return err
	}
	resp.Data = buf[:n]
	return nil
}

func (h *writeHandle) Write(_ context.Context, req *fuse.WriteRequest, resp *fuse.WriteResponse) error {
	h.mu.Lock()
	defer h.mu.Unlock()
	n, err := h.file.WriteAt(req.Data, req.Offset)
	resp.Size = n
	if n > 0 {
		h.dirty = true
	}
	return err
}

func (h *writeHandle) Setattr(_ context.Context, req *fuse.SetattrRequest, _ *fuse.SetattrResponse) error {
	if !req.Valid.Size() {
		return nil
	}
	return h.truncate(int64(req.Size))
}

func (h *writeHandle) truncate(size int64) error {
	h.mu.Lock()
	defer h.mu.Unlock()
	if err := h.file.Truncate(size); err != nil {
		return err
	}
	h.dirty = true
	return nil
}

func (h *writeHandle) Fsync(ctx context.Context, _ *fuse.FsyncRequest) error { return h.sync(ctx) }

func (h *writeHandle) Flush(ctx context.Context, _ *fuse.FlushRequest) error {
	return h.sync(ctx)
}

func (h *writeHandle) Release(ctx context.Context, _ *fuse.ReleaseRequest) error {
	err := h.sync(ctx)
	h.mu.Lock()
	if !h.done {
		h.done = true
		closeErr := h.file.Close()
		if err != nil {
			recoveryPath, recoveryErr := preserveFailedWrite(h.file.Name(), h.node.name)
			fmt.Fprintf(os.Stderr, "bdrclone: upload failed for %s; local recovery file: %s\n", h.node.name, recoveryPath)
			err = errors.Join(err, closeErr, recoveryErr)
		} else {
			err = errors.Join(closeErr, os.Remove(h.file.Name()))
		}
	}
	h.mu.Unlock()
	h.node.mu.Lock()
	if h.node.active == h {
		h.node.active = nil
	}
	h.node.mu.Unlock()
	return err
}

func (h *writeHandle) sync(ctx context.Context) error {
	h.mu.Lock()
	defer h.mu.Unlock()
	if !h.dirty || h.done {
		return nil
	}
	stat, err := h.file.Stat()
	if err != nil {
		return err
	}
	if stat.Size() == 0 {
		return errors.New("Baidu Netdisk does not support empty files")
	}
	entry, err := h.node.fs.client.Upload(ctx, h.file, stat.Size(), h.node.name, stat.ModTime(), nil)
	if err != nil {
		return fmt.Errorf("upload %s: %w", h.node.name, err)
	}
	h.node.mu.Lock()
	h.node.info = entry
	h.node.mu.Unlock()
	h.dirty = false
	return nil
}

func inode(name string) uint64 {
	h := fnv.New64a()
	_, _ = h.Write([]byte(name))
	return h.Sum64()
}

var (
	_ fs.FS                  = (*FileSystem)(nil)
	_ fs.Node                = (*Dir)(nil)
	_ fs.NodeRequestLookuper = (*Dir)(nil)
	_ fs.HandleReadDirAller  = (*Dir)(nil)
	_ fs.NodeMkdirer         = (*Dir)(nil)
	_ fs.NodeCreater         = (*Dir)(nil)
	_ fs.NodeRemover         = (*Dir)(nil)
	_ fs.NodeRenamer         = (*Dir)(nil)
	_ fs.Node                = (*File)(nil)
	_ fs.NodeOpener          = (*File)(nil)
	_ fs.NodeSetattrer       = (*File)(nil)
	_ fs.NodeFsyncer         = (*File)(nil)
	_ fs.HandleReader        = (*readHandle)(nil)
	_ fs.HandleReader        = (*writeHandle)(nil)
	_ fs.HandleWriter        = (*writeHandle)(nil)
	_ fs.HandleFlusher       = (*writeHandle)(nil)
	_ fs.HandleReleaser      = (*writeHandle)(nil)
)