use crate::block_device::BLOCK_SIZE;
use crate::disk::block::DataBlock;
use crate::disk::inode::{INODE_PER_BLOCK, InodeMode};
use crate::utils::permissions::{check_access, clear_suid_sgid, get_groups};
use crate::utils::{from_filetype, from_systime, time_now, to_fileattr, to_filetype};
use crate::{AyaFS, TTL};
use fuser::TimeOrNow::{Now, SpecificTime};
use fuser::{FileType, Filesystem, KernelConfig, ReplyAttr, ReplyData, ReplyDirectory, ReplyEmpty, ReplyEntry, ReplyOpen, ReplyWrite, Request, TimeOrNow, ReplyStatfs, FileAttr};
use libc::{
    c_int, EACCES, EBADF, EEXIST, EINVAL, EIO, EISDIR, ENAMETOOLONG, ENOENT, ENOSPC, ENOTDIR,
    ENOTEMPTY, EPERM, O_ACCMODE, O_RDONLY, O_RDWR, O_WRONLY, RENAME_EXCHANGE,
    RENAME_NOREPLACE, R_OK, S_ISGID, S_ISUID, S_IXGRP, S_IXOTH, S_IXUSR, W_OK,
};
use log::debug;
use std::ffi::OsStr;
use std::os::unix::ffi::OsStrExt;
use std::path::Path;
use std::slice;
use std::time::SystemTime;

impl AyaFS {}

impl Filesystem for AyaFS {
    fn init(&mut self, _req: &Request<'_>, _config: &mut KernelConfig) -> Result<(), c_int> {
        debug!("init()");
        Ok(())
    }

    fn destroy(&mut self) {
        debug!("destroy()");
        self.write_back();
    }

    fn lookup(&mut self, req: &Request<'_>, parent: u64, name: &OsStr, reply: ReplyEntry) {
        if name.len() > 255 {
            reply.error(ENAMETOOLONG);
            return;
        }

        let parent = parent as usize;
        if let Some(parent_inode) = self.get_inode(parent) {
            if check_access(
                req.uid(),
                req.gid(),
                parent_inode.uid,
                parent_inode.gid,
                parent_inode.mode,
                R_OK,
            ) {
                let parent_inode = parent_inode.clone();
                match self.lookup_name(parent, &parent_inode, name) {
                    Ok((inode_index, _, inode)) => {
                        let attr = to_fileattr(inode_index as usize, &inode);
                        reply.entry(&TTL, &attr, 0);
                    }
                    Err(err_code) => reply.error(err_code),
                };
            } else {
                reply.error(EACCES);
            }
        } else {
            reply.error(ENOENT);
        }
    }

    fn getattr(&mut self, _req: &Request<'_>, ino: u64, reply: ReplyAttr) {
        if let Some(inode) = self.get_inode(ino as usize) {
            debug!(
                "getattr(ino: {}, incoming_uid: {}, inode_uid: {})",
                ino, _req.uid(), inode.uid,
            );
            reply.attr(&TTL, &to_fileattr(ino as usize, inode));
        } else {
            reply.error(ENOENT);
        }
    }

    fn setattr(
        &mut self,
        req: &Request<'_>,
        ino: u64,
        mode: Option<u32>,
        uid: Option<u32>,
        gid: Option<u32>,
        size: Option<u64>, // 当 setattr 被 ftruncate invoke 时会设置 size
        atime: Option<TimeOrNow>,
        mtime: Option<TimeOrNow>,
        _ctime: Option<SystemTime>,
        fh: Option<u64>,               // 当 setattr 被 ftruncate invoke 时会提供 fh
        _crtime: Option<SystemTime>,   // 忽略
        _chgtime: Option<SystemTime>,  // 忽略
        _bkuptime: Option<SystemTime>, // 忽略
        _flags: Option<u32>,           // 忽略
        reply: ReplyAttr,
    ) {
        if let Some(inode) = self.get_inode_mut(ino as usize) {
            // chmod
            if let Some(mode) = mode {
                debug!("chmod on inode {:#x?} mode {:o}", ino, mode);
                if req.uid() != 0 && req.uid() != inode.uid {
                    reply.error(EPERM);
                    return;
                } // uid == 0 (root) or uid == inode.uid (user itself)

                if req.uid() != 0
                    && req.gid() != inode.gid
                    && !get_groups(req.pid()).contains(&inode.gid)
                {
                    inode.mode = InodeMode((mode & !S_ISGID) as u16);
                } else {
                    inode.mode = InodeMode(mode as u16);
                }

                inode.ctime = time_now();
                reply.attr(&TTL, &to_fileattr(ino as usize, inode));
                return;
            }

            // chown
            if uid.is_some() || gid.is_some() {
                debug!("chown on inode {:#x?} uid {:?} gid {:?}", ino, uid, gid);
                if let Some(uid) = uid {
                    // 虽然只有 root 可以 chown 但是 user chown 自己也是不报错的
                    if req.uid() != 0 && !(uid == inode.uid && uid == req.uid()) {
                        reply.error(EPERM);
                        return;
                    }
                }
                if let Some(gid) = gid {
                    // 只有 root 和 file owner 才可以 chgrp
                    if req.uid() != 0 && req.uid() != inode.uid {
                        reply.error(EPERM);
                        return;
                    }
                    // root 可以任意 chgrp, 非 root 只能修改到用户自己所在的组里
                    if req.gid() != 0 && !get_groups(req.pid()).contains(&gid) {
                        reply.error(EPERM);
                        return;
                    }
                }

                // 可执行文件要清除 suid & sgid
                if inode.mode.0 & (S_IXUSR | S_IXGRP | S_IXOTH) as u16 != 0 {
                    inode.mode = clear_suid_sgid(inode.mode);
                }

                // chown 要清除 suid
                if let Some(uid) = uid {
                    inode.uid = uid;
                    inode.mode.0 &= !S_ISUID as u16;
                }

                if let Some(gid) = gid {
                    inode.gid = gid;
                    if req.uid() != 0 {
                        inode.mode.0 &= !S_ISGID as u16;
                    }
                }
                inode.ctime = time_now();
                reply.attr(&TTL, &to_fileattr(ino as usize, inode));
                return;
            }

            // ftruncate
            if let Some(size) = size {
                // TODO 当大小减小的时候对应 deallocate 块
                debug!("ftruncate on inode {:#x?} size {:?}", ino, size);
                if let Some(file_handle) = fh {
                    let mut inode = inode.clone();
                    let (inode_index, _read, write) =
                        self.file_handle_map.get(&file_handle).unwrap();
                    assert_eq!(ino as usize, *inode_index);
                    if !write {
                        reply.error(EACCES);
                    } else {
                        inode.size = size;
                        reply.attr(&TTL, &to_fileattr(*inode_index, &inode));
                        self.update_inode(*inode_index, inode);
                    }
                } else {
                    if !check_access(req.uid(), req.gid(), inode.uid, inode.gid, inode.mode, W_OK) {
                        reply.error(EACCES);
                    } else {
                        inode.size = size;
                        reply.attr(&TTL, &to_fileattr(ino as usize, &inode));
                    }
                }
                return;
            }

            // time 相关
            if atime.is_some() || mtime.is_some() {
                let current_time = time_now();
                if let Some(atime) = atime {
                    debug!("utimensat on inode {:#x?}, atime {:?}", ino, atime);
                    // root 和 user 可以随意修改 atime, 其他用户只能 touch (即 atime == Now)
                    if req.uid() != 0 && req.uid() != inode.uid && atime != Now {
                        reply.error(EPERM);
                        return;
                    }

                    if req.uid() != 0
                        && req.uid() != inode.uid
                        && check_access(
                            req.uid(),
                            req.gid(),
                            inode.uid,
                            inode.gid,
                            inode.mode,
                            R_OK, // atime 来说是 read TODO 对吗
                        )
                    {
                        reply.error(EACCES);
                        return;
                    }

                    inode.atime = match atime {
                        SpecificTime(time) => from_systime(time),
                        Now => current_time,
                    };
                    inode.ctime = current_time;
                }
                if let Some(mtime) = mtime {
                    debug!("utimensat on inode {:#x?}, mtime {:?}", ino, mtime);
                    // root 和 user 可以随意修改 mtime, 其他用户只能 mtime == Now
                    if req.uid() != 0 && req.uid() != inode.uid && mtime != Now {
                        reply.error(EPERM);
                        return;
                    }

                    if req.uid() != 0
                        && req.uid() != inode.uid
                        && check_access(
                            req.uid(),
                            req.gid(),
                            inode.uid,
                            inode.gid,
                            inode.mode,
                            W_OK, // mtime 来说是 write
                        )
                    {
                        reply.error(EACCES);
                        return;
                    }

                    inode.mtime = match mtime {
                        SpecificTime(time) => from_systime(time),
                        Now => current_time,
                    };
                    inode.ctime = current_time;
                }
            }
            reply.attr(&TTL, &to_fileattr(ino as usize, inode));
            return;
        } else {
            reply.error(ENOENT);
        }
    }

    // 这啥语义啊??
    fn readlink(&mut self, req: &Request<'_>, ino: u64, reply: ReplyData) {
        debug!("readlink(ino: {})", ino);
        if let Some(inode) = self.get_inode(ino as usize) {
            if !inode.is_symlink() {
                reply.error(ENOENT);
                return;
            }
            if !check_access(req.uid(), req.gid(), inode.uid, inode.gid, inode.mode, R_OK) {
                reply.error(EACCES);
                return;
            }
            let path_length = inode.size as usize;
            let mut path = vec![0u8; path_length];
            if path_length < 60 {
                debug!(
                    "symlink path length is {}, reading directly from inode.direct",
                    path_length
                );
                let copy_src = unsafe {
                    let src = (&inode.direct) as *const u32 as *const u8;
                    slice::from_raw_parts(src, path_length)
                };
                path.as_mut_slice().copy_from_slice(copy_src);
            } else {
                debug!(
                    "symlink path length is {}, using original read",
                    path_length
                );
                let inode = inode.clone();
                let mut read_ptr = 0usize;
                while read_ptr < path_length {
                    let block_index = read_ptr / BLOCK_SIZE;
                    let offset = read_ptr % BLOCK_SIZE;

                    let read_length_within_block = if BLOCK_SIZE - offset < path_length - read_ptr {
                        BLOCK_SIZE - offset
                    } else {
                        path_length - read_ptr
                    };

                    if let Some(block) = self.access_block::<DataBlock>(&inode, block_index) {
                        (&mut path[read_ptr..read_ptr + read_length_within_block]).copy_from_slice(
                            &block.block.0[offset..offset + read_length_within_block],
                        );
                        read_ptr += read_length_within_block;
                    } else {
                        reply.error(EIO);
                        return;
                    }
                }
            }
            debug!(
                "readlink path read is {:?}",
                OsStr::from_bytes(path.as_slice())
            );
            reply.data(path.as_slice());
        } else {
            reply.error(ENOENT);
        }
    }

    fn mknod(
        &mut self,
        req: &Request<'_>,
        parent: u64,
        name: &OsStr,
        mode: u32,
        _umask: u32, // umask 是用不到的
        _rdev: u32,  // the device number (only valid if created file is a device)
        reply: ReplyEntry,
    ) {
        debug!(
            "mknod(parent: {}, name: {:?}, mode: {}, umask: {})",
            parent, name, mode, _umask
        );

        let parent = parent as usize;
        if let Some(parent_inode) = self.get_inode(parent) {
            if !check_access(
                req.uid(),
                req.gid(),
                parent_inode.uid,
                parent_inode.gid,
                parent_inode.mode,
                W_OK,
            ) {
                reply.error(EACCES);
                return;
            }

            // parent 不是 IFDIR -> Not a directory
            if !parent_inode.is_dir() {
                reply.error(ENOTDIR);
                return;
            }

            // 文件名长度超过 255, 返回 filename too long
            if name.len() > 255 {
                reply.error(ENAMETOOLONG);
                return;
            }

            let mut parent_inode = parent_inode.clone();
            // 如果已经存在, 返回 already exists
            if self.lookup_name(parent, &parent_inode, name).is_ok() {
                reply.error(EEXIST);
                return;
            }

            let mode = mode as u16;
            if let Some((child_inode_index, child_inode)) =
                self.create_file(mode, req.uid(), req.gid(), 0)
            {
                let mode = child_inode.mode;
                let file_attr = to_fileattr(child_inode_index, child_inode);
                if let Err(err_code) = self.add_direntry(
                    parent,
                    &mut parent_inode,
                    child_inode_index,
                    name,
                    mode.into(),
                ) {
                    reply.error(err_code);
                    return;
                }
                self.update_inode(parent, parent_inode); // 前面 clone 了, 这里写回
                reply.entry(&TTL, &file_attr, 0);
            } else {
                // create_inode 失败 -> no enough space
                reply.error(ENOSPC);
            }
        } else {
            // parent 不存在 -> No such file or directory
            reply.error(ENOENT);
        }
    }

    fn mkdir(
        &mut self,
        req: &Request<'_>,
        parent: u64,
        name: &OsStr,
        mode: u32,
        _umask: u32, // umask 应该也是用不到的
        reply: ReplyEntry,
    ) {
        if let Some(parent_inode) = self.get_inode(parent as usize) {
            // 无权限创建 -> EACCES
            if !check_access(
                req.uid(),
                req.gid(),
                parent_inode.uid,
                parent_inode.gid,
                parent_inode.mode,
                W_OK,
            ) {
                reply.error(EACCES);
                return;
            }

            // parent 不是 IFDIR -> Not a directory
            if !parent_inode.is_dir() {
                reply.error(ENOTDIR);
                return;
            }

            // 文件名长度超过 255 -> filename too long
            if name.len() > 255 {
                reply.error(ENAMETOOLONG);
                return;
            }

            let mut parent_inode = parent_inode.clone();
            // 已经存在 -> File exists
            if self
                .lookup_name(parent as usize, &parent_inode, name)
                .is_ok()
            {
                reply.error(EEXIST);
                return;
            }

            let mode = mode as u16;
            if let Some((child_inode_index, child_inode)) =
                self.create_directory(mode, req.uid(), req.gid(), 0, Some(parent as usize))
            {
                let child_inode = child_inode.clone();
                let file_attr = to_fileattr(child_inode_index, &child_inode);
                if let Err(err_code) = self.add_direntry(
                    parent as usize,
                    &mut parent_inode,
                    child_inode_index,
                    name,
                    child_inode.mode.into(),
                ) {
                    reply.error(err_code);
                    return;
                }
                self.update_inode(parent as usize, parent_inode); // 前面 clone 了, 这里写回
                reply.entry(&TTL, &file_attr, 0);
            } else {
                // create_inode 失败 -> no enough space
                reply.error(ENOSPC);
            }
        } else {
            // parent 不存在 -> No such file or directory
            reply.error(ENOENT);
        }
    }

    fn unlink(&mut self, req: &Request<'_>, parent: u64, name: &OsStr, reply: ReplyEmpty) {
        debug!("unlink(parent: {:#x?}, name: {:?})", parent, name);
        let parent = parent as usize;
        if let Some(parent_inode) = self.get_inode(parent) {
            // 无权限删除 -> EACCES
            if !check_access(
                req.uid(),
                req.gid(),
                parent_inode.uid,
                parent_inode.gid,
                parent_inode.mode,
                W_OK,
            ) {
                reply.error(EACCES);
                return;
            }

            // parent 不是 dir -> ENOTDIR
            if !parent_inode.is_dir() {
                reply.error(ENOTDIR);
                return;
            }

            // 文件名长度超过 255 -> filename too long
            if name.len() > 255 {
                reply.error(ENAMETOOLONG);
                return;
            }

            let mut parent_inode = parent_inode.clone();
            // 不存在 -> No such file or directory
            if let Ok((inode_index, entry_index, mut inode)) =
                self.lookup_name(parent, &parent_inode, name)
            {
                let inode_index = inode_index as usize;

                match inode.file_type() {
                    FileType::RegularFile => {
                        inode.n_links -= 1;
                        if inode.n_links == 0 {
                            // n_links == 0 -> 整个 inode 都要删除掉
                            match self.remove_file(inode_index) {
                                Ok(flag) => debug!("  unlink {}", flag),
                                Err(err_code) => {
                                    reply.error(err_code);
                                    return;
                                }
                            }
                        } else {
                            // n_links > 0 -> 只是移除了一个 hard link, 将改动写回
                            self.update_inode(inode_index, inode);
                        }
                    }
                    FileType::Symlink => {}
                    FileType::Directory => {
                        reply.error(EISDIR);
                        return;
                    }
                    _ => {
                        // Not implemented!
                        reply.error(EIO);
                        return;
                    }
                }

                // 删除 dir entry
                if let Err(err_code) =
                    self.remove_direntry(parent, &mut parent_inode, name, entry_index)
                {
                    reply.error(err_code);
                    return;
                }
                parent_inode.size -= 1;
                self.update_inode(parent, parent_inode);
                reply.ok();
            } else {
                reply.error(ENOENT);
            }
        } else {
            reply.error(ENOENT);
        }
    }

    fn rmdir(&mut self, req: &Request<'_>, parent: u64, name: &OsStr, reply: ReplyEmpty) {
        debug!("rmdir(parent: {:#x?}, name: {:?})", parent, name);
        let parent = parent as usize;
        if let Some(parent_inode) = self.get_inode(parent) {
            // 无权限删除 -> EACCES
            if !check_access(
                req.uid(),
                req.gid(),
                parent_inode.uid,
                parent_inode.gid,
                parent_inode.mode,
                W_OK,
            ) {
                reply.error(EACCES);
                return;
            }

            // parent 不是 dir -> ENOTDIR
            if !parent_inode.is_dir() {
                reply.error(ENOTDIR);
                return;
            }

            // 文件名长度超过 255 -> filename too long
            if name.len() > 255 {
                reply.error(ENAMETOOLONG);
                return;
            }

            let mut parent_inode = parent_inode.clone();
            // 不存在 -> No such file or directory
            if let Ok((inode_index, entry_index, inode)) =
                self.lookup_name(parent, &parent_inode, name)
            {
                let inode_index = inode_index as usize;
                // 要删除的 entry 是一般文件, 不用 rmdir
                if inode.is_file() {
                    reply.error(ENOTDIR);
                    return;
                }

                // 一定有 . 和 .. 所以 size == 2 就是空目录
                // 目录非空 -> ENOTEMPTY
                if inode.size > 2 {
                    reply.error(ENOTEMPTY);
                    return;
                }

                // directory 没有 hard link, 删了就是删了
                match self.remove_dir(inode_index) {
                    Ok(flag) => debug!("  rmdir {}", flag),
                    Err(err_code) => {
                        reply.error(err_code);
                        return;
                    }
                }

                // 删除 dir entry
                if let Err(err_code) =
                    self.remove_direntry(parent, &mut parent_inode, name, entry_index)
                {
                    reply.error(err_code);
                    return;
                }

                parent_inode.size -= 1;
                self.update_inode(parent, parent_inode);
                reply.ok();
            } else {
                reply.error(ENOENT);
            }
        } else {
            reply.error(ENOENT);
        }
    }

    fn symlink(
        &mut self,
        req: &Request<'_>,
        parent: u64,
        link_name: &OsStr,
        target: &Path,
        reply: ReplyEntry,
    ) {
        debug!(
            "symlink(parent: {}, name: {:?}, target: {:?})",
            parent, link_name, target
        );
        let parent = parent as usize;

        // let root_inode_index = 1usize;
        // if let Some(root_inode) = self.get_inode(root_inode_index) {
        //     let mut curr_inode_index = root_inode_index;
        //     let mut curr_inode = root_inode.clone();
        //     for segment in target.iter() {
        //         match self.lookup_name(curr_inode_index, &curr_inode, segment) {
        //             Ok((next_inode_index, _, next_inode)) => {
        //                 curr_inode_index = next_inode_index as usize;
        //                 curr_inode = next_inode;
        //             }
        //             Err(err_code) => {
        //                 reply.error(err_code);
        //                 return;
        //             }
        //         }
        //     }
        // } else {
        //     reply.error(EIO);
        //     return;
        // }

        if let Some(parent_inode) = self.get_inode(parent) {
            if !check_access(
                req.uid(),
                req.gid(),
                parent_inode.uid,
                parent_inode.gid,
                parent_inode.mode,
                W_OK,
            ) {
                reply.error(EACCES);
                return;
            }

            if !parent_inode.is_dir() {
                reply.error(ENOTDIR);
                return;
            }

            if link_name.len() > 255 {
                reply.error(ENAMETOOLONG);
                return;
            }

            let target = target.as_os_str();
            let mut parent_inode = parent_inode.clone();
            if self.lookup_name(parent, &parent_inode, link_name).is_ok() {
                reply.error(EEXIST);
                return;
            }

            if let Some((child_inode_index, child_inode)) =
                self.create_symlink(0o777, req.uid(), req.gid(), 0)
            {
                let mut child_inode = child_inode.clone();
                child_inode.size = target.len() as u64;
                if target.len() < 60 {
                    debug!("create_symlink: target length < 60, allocating in 'direct' section.");
                    let target_path = target.as_bytes();
                    let copy_dst = unsafe {
                        let dst = (&mut child_inode.direct) as *mut u32 as *mut u8;
                        slice::from_raw_parts_mut(dst, target_path.len())
                    };
                    copy_dst.copy_from_slice(target_path);
                } else {
                    debug!("create_symlink: target length >= 60, using original layout.");
                    let mut write_ptr = 0usize;
                    while write_ptr < target.len() {
                        let block_index = write_ptr / BLOCK_SIZE;
                        let offset = write_ptr % BLOCK_SIZE;

                        let write_length_within_block =
                            if BLOCK_SIZE - offset < target.len() - write_ptr {
                                BLOCK_SIZE - offset
                            } else {
                                target.len() - write_ptr
                            };

                        if let Some(block) =
                            self.access_block_mut::<DataBlock>(&child_inode, block_index)
                        {
                            block.block.0[offset..offset + write_length_within_block]
                                .copy_from_slice(
                                    &target.as_bytes()
                                        [write_ptr..write_ptr + write_length_within_block],
                                );
                            write_ptr += write_length_within_block;
                        } else {
                            if let Some((_block_index, block_index_within_inode)) =
                                self.allocate_block_for(&mut child_inode)
                            {
                                let block = self
                                    .access_block_mut::<DataBlock>(
                                        &child_inode,
                                        block_index_within_inode,
                                    )
                                    .unwrap();
                                block.block.0[offset..offset + write_length_within_block]
                                    .copy_from_slice(
                                        &target.as_bytes()
                                            [write_ptr..write_ptr + write_length_within_block],
                                    );
                                write_ptr += write_length_within_block;
                            } else {
                                reply.error(ENOSPC);
                                return;
                            }
                        }
                    }
                }

                let file_attr = to_fileattr(child_inode_index, &child_inode);
                self.update_inode(child_inode_index, child_inode);

                if let Err(err_code) = self.add_direntry(
                    parent,
                    &mut parent_inode,
                    child_inode_index,
                    link_name,
                    from_filetype(FileType::Symlink),
                ) {
                    reply.error(err_code);
                    return;
                }
                self.update_inode(parent, parent_inode);
                reply.entry(&TTL, &file_attr, 0);
            } else {
                reply.error(ENOSPC);
            }
        } else {
            reply.error(ENOENT);
        }
    }

    fn rename(
        &mut self,
        req: &Request<'_>,
        parent: u64,
        name: &OsStr,
        new_parent: u64,
        new_name: &OsStr,
        flags: u32,
        reply: ReplyEmpty,
    ) {
        debug!(
            "rename(parent: {}, name: {:?}, new_parent: {}, new_name: {:?})",
            parent, name, new_parent, new_name
        );

        let parent = parent as usize;
        let new_parent = new_parent as usize;
        if let Some(parent_inode) = self.get_inode(parent) {
            if !check_access(
                req.uid(),
                req.gid(),
                parent_inode.uid,
                parent_inode.gid,
                parent_inode.mode,
                R_OK,
            ) {
                reply.error(EACCES);
                return;
            }

            if name.len() > 255 {
                reply.error(ENAMETOOLONG);
                return;
            }

            let mut parent_inode = parent_inode.clone();
            match self.lookup_name(parent, &parent_inode, name) {
                Ok((_inode_index, entry_index, _inode)) => {
                    if let Some(new_parent_inode) = self.get_inode(new_parent) {
                        if !check_access(
                            req.uid(),
                            req.gid(),
                            new_parent_inode.uid,
                            new_parent_inode.gid,
                            new_parent_inode.mode,
                            W_OK,
                        ) {
                            reply.error(EACCES);
                            return;
                        }
                        if new_name.len() > 255 {
                            reply.error(ENAMETOOLONG);
                            return;
                        }

                        let mut new_parent_inode = new_parent_inode.clone();
                        match self.lookup_name(new_parent, &new_parent_inode, new_name) {
                            Ok((_new_inode_index, new_entry_index, _new_inode)) => {
                                // 新文件存在
                                if flags & RENAME_NOREPLACE != 0 {
                                    // 指定 noreplace 之后不允许覆盖文件
                                    reply.error(EEXIST);
                                    return;
                                }
                                if flags & RENAME_EXCHANGE != 0 {
                                    // 交换两个文件
                                    if let Err(err_code) = self.exchange_direntry(
                                        parent,
                                        &mut parent_inode,
                                        name,
                                        new_parent,
                                        &mut new_parent_inode,
                                        new_name,
                                    ) {
                                        reply.error(err_code);
                                        return;
                                    }
                                } else {
                                    // 用新文件替换旧文件
                                    let dir_entry = self
                                        .get_direntry_by_name(parent, &parent_inode, name)
                                        .unwrap();
                                    if let Err(err_code) = self.remove_direntry(
                                        parent,
                                        &mut parent_inode,
                                        name,
                                        entry_index,
                                    ) {
                                        reply.error(err_code);
                                        return;
                                    }
                                    if let Err(err_code) = self.remove_direntry(
                                        new_parent,
                                        &mut new_parent_inode,
                                        new_name,
                                        new_entry_index,
                                    ) {
                                        reply.error(err_code);
                                        return;
                                    }
                                    if let Err(err_code) = self.add_direntry_2(
                                        new_parent,
                                        &mut new_parent_inode,
                                        new_name,
                                        dir_entry,
                                    ) {
                                        reply.error(err_code);
                                        return;
                                    }
                                }
                                reply.ok();
                            }
                            Err(ENOENT) => {
                                // 新文件不存在, 删除旧的创建新的
                                let dir_entry = self
                                    .get_direntry_by_name(parent, &parent_inode, name)
                                    .unwrap();
                                if let Err(err_code) = self.remove_direntry(
                                    parent,
                                    &mut parent_inode,
                                    name,
                                    entry_index,
                                ) {
                                    reply.error(err_code);
                                    return;
                                }
                                if let Err(err_code) = self.add_direntry_2(
                                    new_parent,
                                    &mut new_parent_inode,
                                    new_name,
                                    dir_entry,
                                ) {
                                    reply.error(err_code);
                                    return;
                                }
                                reply.ok();
                            }
                            Err(err_code) => {
                                // 其他 Err code
                                reply.error(err_code);
                                return;
                            }
                        }
                    } else {
                        reply.error(ENOENT);
                    }
                }
                Err(err_code) => {
                    reply.error(err_code);
                    return;
                }
            }
        } else {
            reply.error(ENOENT);
        }
    }

    fn link(&mut self, req: &Request<'_>, ino: u64, new_parent: u64, new_name: &OsStr, reply: ReplyEntry) {
        let ino = ino as usize;
        let new_parent = new_parent as usize;

        if let Some(parent_inode) = self.get_inode(new_parent) {
            if !check_access(
                req.uid(),
                req.gid(),
                parent_inode.uid,
                parent_inode.gid,
                parent_inode.mode,
                W_OK,
            ) {
                reply.error(EACCES);
                return;
            }

            if !parent_inode.is_dir() {
                reply.error(ENOTDIR);
                return;
            }

            if new_name.len() > 255 {
                reply.error(ENAMETOOLONG);
                return;
            }

            let filetype: FileType;
            let fileattr: FileAttr;
            let mut parent_inode = parent_inode.clone();
            if let Some(inode) = self.get_inode_mut(ino) {
                inode.n_links += 1;
                filetype = inode.file_type();
                fileattr = to_fileattr(ino, inode);
            } else {
                reply.error(ENOENT);
                return;
            }

            if let Err(err_code) = self.add_direntry(
                new_parent,
                &mut parent_inode,
                ino as usize,
                new_name,
                from_filetype(filetype)
            ) {
                reply.error(err_code);
                return;
            }
            self.update_inode(new_parent, parent_inode);
            reply.entry(&TTL, &fileattr, 0);
        } else {
            reply.error(ENOENT);
        }
    }

    fn open(&mut self, req: &Request<'_>, ino: u64, flags: i32, reply: ReplyOpen) {
        debug!("open(ino: {:#x?}, flags: {:#x?})", ino, flags);
        let (access_mask, read, write) = match flags & O_ACCMODE {
            O_RDONLY => {
                // Behavior is undefined, but most filesystems return EACCES
                if flags & libc::O_TRUNC != 0 {
                    reply.error(EACCES);
                    return;
                }
                (R_OK, true, false)
            }
            O_WRONLY => (W_OK, false, true),
            O_RDWR => (R_OK | W_OK, true, true),
            _ => {
                // flag 非法
                reply.error(EINVAL);
                return;
            }
        };

        match self.get_inode(ino as usize) {
            Some(inode) => {
                if !check_access(
                    req.uid(),
                    req.gid(),
                    inode.uid,
                    inode.gid,
                    inode.mode,
                    access_mask,
                ) {
                    reply.error(EACCES);
                    return;
                }
                let fd = self.allocate_file_descriptor(ino as usize, read, write);
                reply.opened(fd, 0);
            }
            None => {
                reply.error(ENOENT);
            }
        }
    }

    // read [offset, offset + size)
    // - EOF < offset + size -> return EOF - offset
    // - EOF > offset + size -> return size
    fn read(
        &mut self,
        req: &Request<'_>,
        ino: u64,
        fh: u64,
        offset: i64,
        size: u32,
        _flags: i32,
        _lock_owner: Option<u64>, // 用不到!
        reply: ReplyData,
    ) {
        assert_eq!(self.file_handle_map.get(&fh).unwrap().0, ino as usize);
        if let Some(inode) = self.get_inode(ino as usize) {
            if inode.is_dir() {
                reply.error(EISDIR);
                return;
            }
            if !check_access(req.uid(), req.gid(), inode.uid, inode.gid, inode.mode, R_OK) {
                reply.error(EACCES);
                return;
            }
            debug!("reading inode {:#x} (offset {} size {})", ino, offset, size);

            if offset as u64 >= inode.size {
                // offset 在 EOF 后面, 直接返回一个 0 长度的空 buffer
                reply.data(&Vec::new());
                return;
            }

            // let read_length = size.min(inode.size.saturating_sub(offset as u32)) as usize;
            // 这和下面那个是等同的但是不利于让人看懂……

            let size = size as u64;
            let read_length = if size.checked_add_signed(offset).unwrap() <= inode.size {
                size // 没有越过 EOF, 读取 size 个 byte
            } else {
                inode.size - offset as u64 // 越过了 EOF, 读取 inode.size - offset 个 byte
            } as usize;

            let mut read_buffer = vec![0u8; read_length];
            let mut read_ptr = 0usize;

            let inode = inode.clone();

            while read_ptr < read_length {
                let current_point = offset as usize + read_ptr;
                let current_block_index = current_point / BLOCK_SIZE;
                let current_offset = current_point % BLOCK_SIZE;

                let read_length_within_block =
                    if BLOCK_SIZE - current_offset < read_length - read_ptr {
                        BLOCK_SIZE - current_offset // 可以读到 block 最后
                    } else {
                        read_length - read_ptr // 读到中途会停下来
                    };

                if let Some(block) = self.access_block::<DataBlock>(&inode, current_block_index) {
                    (&mut read_buffer[read_ptr..read_ptr + read_length_within_block])
                        .copy_from_slice(
                            &block.block.0
                                [current_offset..current_offset + read_length_within_block],
                        );
                    read_ptr += read_length_within_block;
                } else {
                    reply.error(EIO);
                    return;
                }
            }

            reply.data(&read_buffer);
        }
    }

    // 写了多少就返回多少
    fn write(
        &mut self,
        req: &Request<'_>,
        ino: u64,
        fh: u64,
        offset: i64,
        data: &[u8],
        _write_flags: u32,
        _flags: i32,
        _lock_owner: Option<u64>,
        reply: ReplyWrite,
    ) {
        assert_eq!(self.file_handle_map.get(&fh).unwrap().0, ino as usize);
        if let Some(inode) = self.get_inode(ino as usize) {
            if inode.is_dir() {
                reply.error(EISDIR);
                return;
            }
            if !check_access(req.uid(), req.gid(), inode.uid, inode.gid, inode.mode, W_OK) {
                reply.error(EACCES);
                return;
            }
            debug!(
                "writing inode {:#x} (offset {} size {})",
                ino,
                offset,
                data.len()
            );
            let write_length = data.len();
            let mut write_ptr = 0usize;

            let mut inode = inode.clone();

            while write_ptr < write_length {
                let current_point = offset as usize + write_ptr;
                let current_block_index = current_point / BLOCK_SIZE;
                let current_offset = current_point % BLOCK_SIZE;

                let write_length_within_block =
                    if BLOCK_SIZE - current_offset < write_length - write_ptr {
                        BLOCK_SIZE - current_offset // 可以写满 block
                    } else {
                        write_length - write_ptr // 写完 buffer 就停下来
                    };

                // 当前块已分配, 直接往里写
                if let Some(block) = self.access_block_mut::<DataBlock>(&inode, current_block_index)
                {
                    debug!(
                        "writing {} bytes in block {} within inode",
                        write_length_within_block, current_block_index
                    );
                    block.block.0[current_offset..current_offset + write_length_within_block]
                        .copy_from_slice(&data[write_ptr..write_ptr + write_length_within_block]);
                    write_ptr += write_length_within_block;
                } else {
                    // 当前块未分配，尝试分配
                    if let Some((block_index, block_index_within_inode)) =
                        self.allocate_block_for(&mut inode)
                    {
                        debug!("writing {} bytes in allocated block {} within inode, block index is {}", write_length_within_block, block_index_within_inode, block_index);
                        // 能分配, 往里写
                        let block = self
                            .access_block_mut::<DataBlock>(&inode, block_index_within_inode)
                            .unwrap();
                        block.block.0[current_offset..current_offset + write_length_within_block]
                            .copy_from_slice(
                                &data[write_ptr..write_ptr + write_length_within_block],
                            );
                        write_ptr += write_length_within_block;
                    } else {
                        // 分配不了, 没空间了
                        break;
                    }
                }
            }

            inode.size = inode.size.max(offset as u64 + write_length as u64);
            self.update_inode(ino as usize, inode);
            reply.written(write_length as u32);
        } else {
            reply.error(ENOENT);
        }
    }

    fn release(
        &mut self,
        _req: &Request<'_>,
        ino: u64,
        fh: u64,
        _flags: i32,
        _lock_owner: Option<u64>,
        _flush: bool,
        reply: ReplyEmpty,
    ) {
        debug!("release(ino: {:#x?}, fh: {})", ino, fh);
        if self.file_handle_map.contains_key(&fh) {
            self.file_handle_map.remove(&fh);
            reply.ok();
        } else {
            reply.error(EBADF);
        }
    }

    fn opendir(&mut self, req: &Request<'_>, ino: u64, flags: i32, reply: ReplyOpen) {
        debug!("opendir(ino: {:#x?}, flags: {:#x?})", ino, flags);
        let (access_mask, read, write) = match flags & O_ACCMODE {
            O_RDONLY => {
                // Behavior is undefined, but most filesystems return EACCES
                if flags & libc::O_TRUNC != 0 {
                    reply.error(EACCES);
                    return;
                }
                (R_OK, true, false)
            }
            O_WRONLY => (W_OK, false, true),
            O_RDWR => (R_OK | W_OK, true, true),
            _ => {
                // flag 非法
                reply.error(EINVAL);
                return;
            }
        };

        match self.get_inode(ino as usize) {
            Some(inode) => {
                if !check_access(
                    req.uid(),
                    req.gid(),
                    inode.uid,
                    inode.gid,
                    inode.mode,
                    access_mask,
                ) {
                    reply.error(EACCES);
                    return;
                }
                let fd = self.allocate_file_descriptor(ino as usize, read, write);
                reply.opened(fd, 0);
            }
            None => {
                reply.error(ENOENT);
            }
        }
    }

    fn readdir(
        &mut self,
        req: &Request<'_>,
        ino: u64,
        fh: u64, // 如果 invoke 它的 opendir 里有指定 fh, 那么这里会收到 fh 参数
        offset: i64,
        mut reply: ReplyDirectory,
    ) {
        assert_eq!(self.file_handle_map.get(&fh).unwrap().0, ino as usize);
        if let Some(inode) = self.get_inode(ino as usize) {
            if !inode.is_dir() {
                reply.error(ENOTDIR);
                return;
            }

            if !check_access(req.uid(), req.gid(), inode.uid, inode.gid, inode.mode, R_OK) {
                reply.error(EACCES);
                return;
            }

            debug!(
                "reading dir entries from inode {:#x} with offset {}",
                ino, offset
            );
            let inode = inode.clone();

            self.load_direntry_map(ino as usize, &inode).unwrap();
            for (entry_index, (name, dir_entry)) in self
                .dir_entry_map
                .get(&(ino as usize))
                .unwrap()
                .iter()
                .enumerate()
                .skip(offset as usize)
            {
                debug!(
                    "  entry {} from inode {:#x} with name {:?}",
                    entry_index, dir_entry.inode, name
                );
                if reply.add(
                    dir_entry.inode as u64,
                    entry_index as i64 + 1,
                    to_filetype(dir_entry.file_type).expect("not 0x0!"),
                    name,
                ) {
                    break;
                }
            }

            reply.ok();
        } else {
            reply.error(ENOENT);
        }
    }

    fn releasedir(
        &mut self,
        _req: &Request<'_>,
        ino: u64,
        fh: u64,
        _flags: i32,
        reply: ReplyEmpty,
    ) {
        debug!("releasedir(ino: {:#x?}, fh: {})", ino, fh);
        if self.file_handle_map.contains_key(&fh) {
            self.file_handle_map.remove(&fh);
            reply.ok();
        } else {
            reply.error(EBADF);
        }
    }

    fn statfs(&mut self, _req: &Request<'_>, ino: u64, reply: ReplyStatfs) {
        if let Some(_) = self.get_inode(ino as usize) {
            self.super_block.used_inode_number = self.inode_bitmap.count;
            self.super_block.used_block_number = self.data_bitmap.count;

            reply.statfs(
                self.super_block.used_block_number,
                self.super_block.data_block_number - self.super_block.used_block_number,
                self.super_block.data_block_number - self.super_block.used_block_number,
                self.super_block.used_inode_number,
                self.super_block.inode_block_number * INODE_PER_BLOCK as u64 - self.super_block.used_inode_number,
                BLOCK_SIZE as u32,
                255,
                BLOCK_SIZE as u32,
            );
        } else {
            reply.error(ENOENT);
        }
    }

    fn access(&mut self, req: &Request<'_>, ino: u64, mask: i32, reply: ReplyEmpty) {
        // mask:
        // - 要么是 libc::F_OK (aka 0), 检查文件是否存在
        // - 要么是 libc::R_OK,libc::W_OK,libc::X_OK (aka 4/2/1) 构成的 bitmask, 检查是否有对应权限
        debug!("Filesystem::access(ino: {}, mask: {})", ino, mask);

        if let Some(inode) = self.get_inode(ino as usize) {
            debug!("  uid: {}, gid: {}, incoming_uid: {}, incoming_gid: {}, mask: {}", inode.uid, inode.gid, req.uid(), req.gid(), mask);
            if mask == libc::F_OK // 只要检查是否存在
                || check_access(req.uid(), req.gid(), inode.uid, inode.gid, inode.mode, mask)
            // 需要检查 rwx 权限
            {
                reply.ok();
            } else {
                reply.error(EACCES);
            }
        } else {
            reply.error(ENOENT);
        }
    }
}