package main

import (
	"context"
	"sync"
	"syscall"

	"9fans.net/go/plan9"
	"9fans.net/go/plan9/client"
	"github.com/hanwen/go-fuse/v2/fs"
	"github.com/hanwen/go-fuse/v2/fuse"
)

// p9Dir is a FUSE directory node backed by a 9P path.
type p9Dir struct {
	fs.Inode
	fsys *client.Fsys
	path string // 9P path (empty string = root)
}

// p9File is a FUSE file node backed by a 9P path.
type p9File struct {
	fs.Inode
	fsys *client.Fsys
	path string
	mu   sync.Mutex
}

var _ = (fs.NodeGetattrer)((*p9Dir)(nil))
var _ = (fs.NodeReaddirer)((*p9Dir)(nil))
var _ = (fs.NodeLookuper)((*p9Dir)(nil))

var _ = (fs.NodeGetattrer)((*p9File)(nil))
var _ = (fs.NodeOpener)((*p9File)(nil))
var _ = (fs.NodeReader)((*p9File)(nil))
var _ = (fs.NodeWriter)((*p9File)(nil))
var _ = (fs.NodeSetattrer)((*p9File)(nil))

func p9path(base, name string) string {
	if base == "" {
		return name
	}
	return base + "/" + name
}

// --- p9Dir ---

func (d *p9Dir) Getattr(ctx context.Context, fh fs.FileHandle, out *fuse.AttrOut) syscall.Errno {
	out.Mode = 0555 | syscall.S_IFDIR
	return 0
}

func (d *p9Dir) Readdir(ctx context.Context) (fs.DirStream, syscall.Errno) {
	path := d.path
	if path == "" {
		path = "/"
	}
	fid, err := d.fsys.Open(path, plan9.OREAD)
	if err != nil {
		return nil, syscall.EIO
	}
	defer fid.Close()
	dirs, err := fid.Dirreadall()
	if err != nil {
		return nil, syscall.EIO
	}
	entries := make([]fuse.DirEntry, len(dirs))
	for i, dir := range dirs {
		m := uint32(dir.Mode) & 0777
		if dir.Mode&plan9.DMDIR != 0 {
			m |= syscall.S_IFDIR
		}
		entries[i] = fuse.DirEntry{Name: dir.Name, Mode: m}
	}
	return fs.NewListDirStream(entries), 0
}

func (d *p9Dir) Lookup(ctx context.Context, name string, out *fuse.EntryOut) (*fs.Inode, syscall.Errno) {
	child := p9path(d.path, name)
	dir, err := d.fsys.Stat(child)
	if err != nil {
		return nil, syscall.ENOENT
	}
	if dir.Mode&plan9.DMDIR != 0 {
		out.Mode = uint32(dir.Mode)&0777 | syscall.S_IFDIR
		node := &p9Dir{fsys: d.fsys, path: child}
		return d.NewInode(ctx, node, fs.StableAttr{Mode: syscall.S_IFDIR}), 0
	}
	out.Mode = uint32(dir.Mode) & 0777
	out.Size = dir.Length
	node := &p9File{fsys: d.fsys, path: child}
	return d.NewInode(ctx, node, fs.StableAttr{}), 0
}

// --- p9File ---

func (f *p9File) Getattr(ctx context.Context, fh fs.FileHandle, out *fuse.AttrOut) syscall.Errno {
	dir, err := f.fsys.Stat(f.path)
	if err != nil {
		return syscall.ENOENT
	}
	// Report all files as rw so the kernel doesn't block writes;
	// the 9P server enforces actual permissions.
	out.Mode = 0666
	out.Size = dir.Length
	return 0
}

func (f *p9File) Setattr(ctx context.Context, fh fs.FileHandle, in *fuse.SetAttrIn, out *fuse.AttrOut) syscall.Errno {
	// Accept truncate silently — 9P files are append/overwrite on write.
	out.Mode = 0666
	return 0
}

func (f *p9File) Open(ctx context.Context, flags uint32) (fs.FileHandle, uint32, syscall.Errno) {
	return nil, fuse.FOPEN_DIRECT_IO, 0
}

func (f *p9File) Read(ctx context.Context, fh fs.FileHandle, dest []byte, off int64) (fuse.ReadResult, syscall.Errno) {
	f.mu.Lock()
	defer f.mu.Unlock()
	fid, err := f.fsys.Open(f.path, plan9.OREAD)
	if err != nil {
		return nil, syscall.EIO
	}
	defer fid.Close()
	// The 9fans client doesn't support Seek; read from offset by reading and discarding.
	// For small offsets this is fine; large seeks on big files would need a smarter approach.
	if off > 0 {
		buf := make([]byte, min(off, 8192))
		remaining := off
		for remaining > 0 {
			n := int64(len(buf))
			if n > remaining {
				n = remaining
			}
			nr, err := fid.Read(buf[:n])
			if err != nil || nr == 0 {
				break
			}
			remaining -= int64(nr)
		}
	}
	n, err := fid.Read(dest)
	if err != nil && n == 0 {
		return nil, syscall.EIO
	}
	return fuse.ReadResultData(dest[:n]), 0
}

func (f *p9File) Write(ctx context.Context, fh fs.FileHandle, data []byte, off int64) (uint32, syscall.Errno) {
	f.mu.Lock()
	defer f.mu.Unlock()
	fid, err := f.fsys.Open(f.path, plan9.OWRITE)
	if err != nil {
		return 0, syscall.EACCES
	}
	n, err := fid.Write(data)
	if err != nil {
		fid.Close()
		return 0, syscall.EIO
	}
	if err := fid.Close(); err != nil {
		return 0, syscall.EACCES
	}
	return uint32(n), 0
}

func min(a, b int64) int64 {
	if a < b {
		return a
	}
	return b
}