use std::collections::{BTreeSet, HashMap};
use std::ffi::{OsStr, OsString};
use std::fs::File;
use std::fs::OpenOptions;
use std::io;
use std::os::fd::{AsFd, AsRawFd};
use std::os::unix::ffi::{OsStrExt, OsStringExt};
use std::os::unix::fs::FileExt;
use std::os::unix::fs::OpenOptionsExt;
use std::path::{Path, PathBuf};
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::{Arc, Mutex};
use std::time::{Duration, SystemTime, UNIX_EPOCH};

use fuser::{
    BsdFileFlags, Config, CopyFileRangeFlags, Errno, FileAttr, FileHandle, FileType, Filesystem,
    FopenFlags, Generation, INodeNo, InitFlags, KernelConfig, LockFlags, LockOwner, MountOption,
    OpenFlags, RenameFlags as FuseRenameFlags, ReplyAttr, ReplyCreate, ReplyData, ReplyDirectory,
    ReplyEmpty, ReplyEntry, ReplyLock, ReplyLseek, ReplyOpen, ReplyStatfs, ReplyWrite, ReplyXattr,
    Request, TimeOrNow, WriteFlags,
};
use nix::fcntl::{FcntlArg, fcntl};
use rustix::fs::{
    FallocateFlags, FlockOperation, Mode, OFlags, RenameFlags, SeekFrom, Timestamps, UTIME_NOW,
    UTIME_OMIT, XattrFlags, copy_file_range, fallocate, fchmod, fchown, fgetxattr, flistxattr,
    flock as bsd_flock, fremovexattr, fsetxattr, fstat, fstatvfs, ftruncate, futimens, mknodat,
    seek,
};
use rustix::process::{Gid, Uid};
use rustix::time::Timespec;

use crate::backing::{BackingRoot, validate_name, validate_relative};
use crate::classifier::tracked_paths_from_index;
use crate::classifier::{Classification, ClassificationSnapshot, GitClassifier};

const TTL: Duration = Duration::ZERO;

#[derive(Clone, Debug)]
pub struct MountConfiguration {
    pub workspace: PathBuf,
    pub isolated_state: PathBuf,
    pub mountpoint: PathBuf,
    pub global_excludes: Option<PathBuf>,
    pub threads: usize,
}

pub(crate) struct RouterConfiguration {
    pub workspace_label: PathBuf,
    pub workspace: File,
    pub isolated_state: File,
    pub mountpoint: PathBuf,
    pub global_excludes: Option<PathBuf>,
    pub isolate_ignored: bool,
    pub threads: usize,
}

pub struct IgnoredWorkspace {
    host: BackingRoot,
    isolated: BackingRoot,
    classifier: GitClassifier,
    isolate_ignored: bool,
    nodes: Mutex<NodeTable>,
    files: Mutex<HashMap<u64, Arc<OpenFile>>>,
    directories: Mutex<HashMap<u64, DirectoryStream>>,
    posix_lock_files: Mutex<HashMap<PosixLockKey, Arc<File>>>,
    next_handle: AtomicU64,
}

fn mount_config(threads: usize) -> Config {
    let mut config = Config::default();
    config.mount_options.extend([
        MountOption::FSName("lazaret-ignored-workspace".to_owned()),
        MountOption::RW,
        MountOption::Exec,
        MountOption::NoSuid,
        MountOption::NoDev,
        MountOption::DefaultPermissions,
    ]);
    config.n_threads = Some(threads.max(1));
    config.clone_fd = true;
    config
}

impl IgnoredWorkspace {
    /// # Errors
    /// Refuses roots that are not distinct, descriptor-openable directories in a Git workspace.
    pub fn open(
        workspace: &Path,
        isolated_state: &Path,
        global_excludes: Option<PathBuf>,
    ) -> io::Result<Self> {
        let workspace = workspace.canonicalize()?;
        let isolated_state = isolated_state.canonicalize()?;
        if workspace == isolated_state {
            return Err(io::Error::other("workspace and isolated roots must differ"));
        }
        let host = BackingRoot::open(&workspace)?;
        let isolated = BackingRoot::open(&isolated_state)?;
        Self::from_roots(workspace, host, isolated, global_excludes)
    }

    /// # Errors
    /// Refuses aliased or non-directory authorities and unreadable Git policy inputs.
    pub fn from_authorities(
        workspace_label: PathBuf,
        workspace: File,
        isolated_state: File,
        global_excludes: Option<PathBuf>,
    ) -> io::Result<Self> {
        let host = BackingRoot::from_file(workspace)?;
        let isolated = BackingRoot::from_file(isolated_state)?;
        Self::from_roots(workspace_label, host, isolated, global_excludes)
    }

    /// # Errors
    /// Refuses aliased or non-directory authorities and unreadable Git policy inputs.
    pub fn from_authorities_with_policy(
        workspace_label: PathBuf,
        workspace: File,
        isolated_state: File,
        global_excludes: Option<PathBuf>,
        isolate_ignored: bool,
    ) -> io::Result<Self> {
        let host = BackingRoot::from_file(workspace)?;
        let isolated = BackingRoot::from_file(isolated_state)?;
        Self::from_roots_with_policy(
            workspace_label,
            host,
            isolated,
            global_excludes,
            isolate_ignored,
        )
    }

    fn from_roots(
        workspace_label: PathBuf,
        host: BackingRoot,
        isolated: BackingRoot,
        global_excludes: Option<PathBuf>,
    ) -> io::Result<Self> {
        Self::from_roots_with_policy(workspace_label, host, isolated, global_excludes, true)
    }

    fn from_roots_with_policy(
        workspace_label: PathBuf,
        host: BackingRoot,
        isolated: BackingRoot,
        global_excludes: Option<PathBuf>,
        isolate_ignored: bool,
    ) -> io::Result<Self> {
        if host.identity()? == isolated.identity()? {
            return Err(io::Error::other("workspace and isolated authorities alias"));
        }
        let classifier_root = BackingRoot::from_file(host.duplicate()?)?;
        let classifier =
            GitClassifier::from_root(workspace_label, classifier_root, global_excludes)?;
        Ok(Self {
            host,
            isolated,
            classifier,
            isolate_ignored,
            nodes: Mutex::new(NodeTable::new()),
            files: Mutex::new(HashMap::new()),
            directories: Mutex::new(HashMap::new()),
            posix_lock_files: Mutex::new(HashMap::new()),
            next_handle: AtomicU64::new(1),
        })
    }

    /// # Errors
    /// Returns mount or daemon I/O failures.
    pub fn mount(configuration: MountConfiguration) -> io::Result<()> {
        let filesystem = Self::open(
            &configuration.workspace,
            &configuration.isolated_state,
            configuration.global_excludes,
        )?;
        let config = mount_config(configuration.threads);
        fuser::mount2(filesystem, configuration.mountpoint, &config)
    }

    /// # Errors
    /// Returns mount, readiness, control-channel, unmount, or daemon I/O failures.
    pub(crate) fn serve_from_authorities(
        configuration: RouterConfiguration,
        ready: impl FnOnce() -> io::Result<()>,
    ) -> io::Result<()> {
        let filesystem = Self::from_authorities_with_policy(
            configuration.workspace_label,
            configuration.workspace,
            configuration.isolated_state,
            configuration.global_excludes,
            configuration.isolate_ignored,
        )?;
        let session = fuser::spawn_mount2(
            filesystem,
            configuration.mountpoint,
            &mount_config(configuration.threads),
        )?;
        if let Err(error) = ready() {
            let _ = session.umount_and_join();
            return Err(error);
        }
        std::io::copy(&mut std::io::stdin().lock(), &mut std::io::sink())?;
        session.umount_and_join()
    }

    fn root(&self, backing: Classification) -> &BackingRoot {
        match backing {
            Classification::Host => &self.host,
            Classification::Isolated => &self.isolated,
        }
    }

    fn path_for(&self, inode: INodeNo) -> io::Result<PathBuf> {
        self.nodes
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner)
            .path(inode)
            .ok_or_else(|| io::Error::from_raw_os_error(libc::ENOENT))
    }

    fn child_path(&self, parent: INodeNo, name: &OsStr) -> io::Result<PathBuf> {
        validate_name(name)?;
        let path = self.path_for(parent)?.join(name);
        validate_relative(&path)?;
        Ok(path)
    }

    fn inode_for(&self, entry: &ResolvedEntry) -> INodeNo {
        if entry.path.as_os_str().is_empty() {
            return INodeNo::ROOT;
        }
        self.nodes
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner)
            .inode(entry)
    }

    fn resolve(&self, snapshot: &ClassificationSnapshot, path: &Path) -> io::Result<ResolvedEntry> {
        let host = self.host.stat(path).ok();
        let isolated = self.isolated.stat(path).ok();
        let directory = isolated
            .as_ref()
            .or(host.as_ref())
            .is_some_and(|stat| stat.st_mode & libc::S_IFMT == libc::S_IFDIR);
        let backing = self.classify(snapshot, path, directory);
        if snapshot.is_tracked(path) {
            if let (Some(host), Some(isolated)) = (&host, &isolated)
                && host.st_mode & libc::S_IFMT != isolated.st_mode & libc::S_IFMT
            {
                return Err(io::Error::from_raw_os_error(libc::EIO));
            }
            if backing == Classification::Host && host.is_none() && isolated.is_some() {
                return Err(io::Error::from_raw_os_error(libc::EIO));
            }
        }
        let stat = match backing {
            Classification::Host => host,
            Classification::Isolated => isolated,
        }
        .ok_or_else(|| io::Error::from_raw_os_error(libc::ENOENT))?;
        Ok(ResolvedEntry {
            path: path.to_path_buf(),
            backing,
            stat,
        })
    }

    fn create_backing(
        &self,
        snapshot: &ClassificationSnapshot,
        path: &Path,
        directory: bool,
    ) -> io::Result<Classification> {
        let backing = self.classify(snapshot, path, directory);
        if backing == Classification::Isolated {
            self.isolated.ensure_parent_directories(path)?;
        }
        Ok(backing)
    }

    fn classify(
        &self,
        snapshot: &ClassificationSnapshot,
        path: &Path,
        directory: bool,
    ) -> Classification {
        if self.isolate_ignored {
            snapshot.classify(path, directory)
        } else {
            Classification::Host
        }
    }

    fn open_file(&self, inode: INodeNo, flags: i32) -> io::Result<u64> {
        let path = self.path_for(inode)?;
        let snapshot = self.classifier.snapshot_for(&path);
        let entry = self.resolve(&snapshot, &path)?;
        let file = self
            .root(entry.backing)
            .open_entry(&path, open_flags(flags), Mode::empty())?;
        let handle = self.next_handle.fetch_add(1, Ordering::Relaxed);
        self.files
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner)
            .insert(
                handle,
                Arc::new(OpenFile {
                    file,
                    backing: entry.backing,
                    access_mode: flags & libc::O_ACCMODE,
                }),
            );
        Ok(handle)
    }

    fn visible_entries(
        &self,
        directory: &Path,
        snapshot: &ClassificationSnapshot,
    ) -> io::Result<Vec<DirectoryEntry>> {
        let mut names = BTreeSet::new();
        for root in [&self.host, &self.isolated] {
            match root.entries(directory) {
                Ok(entries) => names.extend(entries),
                Err(error) if error.kind() == io::ErrorKind::NotFound => {}
                Err(error) => return Err(error),
            }
        }
        let mut entries = Vec::new();
        for name in names {
            let path = directory.join(&name);
            if let Ok(entry) = self.resolve(snapshot, &path) {
                entries.push(DirectoryEntry {
                    inode: self.inode_for(&entry),
                    kind: file_type(entry.stat.st_mode)?,
                    name,
                });
            }
        }
        Ok(entries)
    }

    fn reply_entry(&self, path: &Path, reply: ReplyEntry) {
        let snapshot = self.classifier.snapshot_for(path);
        match self
            .resolve(&snapshot, path)
            .and_then(|entry| self.attributes(&entry))
        {
            Ok(attributes) => reply.entry(&TTL, &attributes, Generation(0)),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn attributes(&self, entry: &ResolvedEntry) -> io::Result<FileAttr> {
        let stat = entry.stat;
        Ok(FileAttr {
            ino: self.inode_for(entry),
            size: u64::try_from(stat.st_size)
                .map_err(|_| io::Error::other("negative file size"))?,
            blocks: u64::try_from(stat.st_blocks)
                .map_err(|_| io::Error::other("negative block count"))?,
            atime: system_time(stat.st_atime, stat.st_atime_nsec),
            mtime: system_time(stat.st_mtime, stat.st_mtime_nsec),
            ctime: system_time(stat.st_ctime, stat.st_ctime_nsec),
            crtime: UNIX_EPOCH,
            kind: file_type(stat.st_mode)?,
            perm: (stat.st_mode & 0o7777) as u16,
            nlink: u32::try_from(stat.st_nlink).unwrap_or(u32::MAX),
            uid: stat.st_uid,
            gid: stat.st_gid,
            rdev: u32::try_from(stat.st_rdev).unwrap_or(u32::MAX),
            blksize: u32::try_from(stat.st_blksize).unwrap_or(u32::MAX),
            flags: 0,
        })
    }

    fn with_file<T>(
        &self,
        handle: FileHandle,
        operation: impl FnOnce(&OpenFile) -> io::Result<T>,
    ) -> io::Result<T> {
        let open = self
            .files
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner)
            .get(&handle.0)
            .cloned()
            .ok_or_else(|| io::Error::from_raw_os_error(libc::EBADF))?;
        operation(&open)
    }

    fn posix_lock_file(&self, open: &OpenFile, owner: LockOwner) -> io::Result<Arc<File>> {
        let stat = fstat(open.file.as_fd())?;
        let key = PosixLockKey {
            backing: open.backing,
            device: stat.st_dev,
            inode: stat.st_ino,
            owner: owner.0,
        };
        let mut files = self
            .posix_lock_files
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner);
        if let Some(file) = files.get(&key) {
            return Ok(Arc::clone(file));
        }
        let mut options = OpenOptions::new();
        match open.access_mode {
            libc::O_RDONLY => {
                options.read(true);
            }
            libc::O_WRONLY => {
                options.write(true);
            }
            libc::O_RDWR => {
                options.read(true).write(true);
            }
            _ => return Err(io::Error::from_raw_os_error(libc::EINVAL)),
        }
        let file = Arc::new(
            options
                .custom_flags(libc::O_CLOEXEC)
                .open(format!("/proc/self/fd/{}", open.file.as_raw_fd()))?,
        );
        let reopened = fstat(file.as_fd())?;
        if (reopened.st_dev, reopened.st_ino) != (stat.st_dev, stat.st_ino) {
            return Err(io::Error::other("lock descriptor identity changed"));
        }
        files.insert(key, Arc::clone(&file));
        Ok(file)
    }

    fn release_posix_locks(&self, open: &OpenFile, owner: LockOwner) -> io::Result<()> {
        let stat = fstat(open.file.as_fd())?;
        self.posix_lock_files
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner)
            .remove(&PosixLockKey {
                backing: open.backing,
                device: stat.st_dev,
                inode: stat.st_ino,
                owner: owner.0,
            });
        Ok(())
    }
}

impl Filesystem for IgnoredWorkspace {
    fn init(&mut self, _request: &Request, config: &mut KernelConfig) -> io::Result<()> {
        config
            .add_capabilities(
                InitFlags::FUSE_AUTO_INVAL_DATA
                    | InitFlags::FUSE_POSIX_ACL
                    | InitFlags::FUSE_POSIX_LOCKS
                    | InitFlags::FUSE_FLOCK_LOCKS,
            )
            .map_err(|unsupported| {
                io::Error::other(format!(
                    "required FUSE capabilities are unavailable: {unsupported:?}"
                ))
            })
    }

    fn lookup(&self, _request: &Request, parent: INodeNo, name: &OsStr, reply: ReplyEntry) {
        match self.child_path(parent, name) {
            Ok(path) => self.reply_entry(&path, reply),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn getattr(
        &self,
        _request: &Request,
        inode: INodeNo,
        handle: Option<FileHandle>,
        reply: ReplyAttr,
    ) {
        let result = if let Some(handle) = handle {
            self.with_file(handle, |open| {
                let stat = fstat(open.file.as_fd())?;
                let path = self.path_for(inode)?;
                self.attributes(&ResolvedEntry {
                    path,
                    backing: open.backing,
                    stat,
                })
            })
        } else {
            self.path_for(inode).and_then(|path| {
                let snapshot = self.classifier.snapshot_for(&path);
                self.resolve(&snapshot, &path)
                    .and_then(|entry| self.attributes(&entry))
            })
        };
        match result {
            Ok(attributes) => reply.attr(&TTL, &attributes),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn setattr(
        &self,
        _request: &Request,
        inode: INodeNo,
        mode: Option<u32>,
        uid: Option<u32>,
        gid: Option<u32>,
        size: Option<u64>,
        atime: Option<TimeOrNow>,
        mtime: Option<TimeOrNow>,
        _ctime: Option<SystemTime>,
        handle: Option<FileHandle>,
        _crtime: Option<SystemTime>,
        _chgtime: Option<SystemTime>,
        _bkuptime: Option<SystemTime>,
        _flags: Option<BsdFileFlags>,
        reply: ReplyAttr,
    ) {
        let operation = |open: &OpenFile| -> io::Result<FileAttr> {
            if let Some(mode) = mode {
                fchmod(open.file.as_fd(), Mode::from_raw_mode(mode & 0o7777))?;
            }
            if uid.is_some() || gid.is_some() {
                fchown(
                    open.file.as_fd(),
                    uid.map(Uid::from_raw),
                    gid.map(Gid::from_raw),
                )?;
            }
            if let Some(size) = size {
                ftruncate(open.file.as_fd(), size)?;
            }
            if atime.is_some() || mtime.is_some() {
                futimens(
                    open.file.as_fd(),
                    &Timestamps {
                        last_access: timestamp(atime),
                        last_modification: timestamp(mtime),
                    },
                )?;
            }
            let path = self.path_for(inode)?;
            self.attributes(&ResolvedEntry {
                path,
                backing: open.backing,
                stat: fstat(open.file.as_fd())?,
            })
        };
        let result = if let Some(handle) = handle {
            self.with_file(handle, operation)
        } else {
            let path = match self.path_for(inode) {
                Ok(path) => path,
                Err(error) => {
                    reply.error(errno(&error));
                    return;
                }
            };
            let snapshot = self.classifier.snapshot_for(&path);
            let entry = match self.resolve(&snapshot, &path) {
                Ok(entry) => entry,
                Err(error) => {
                    reply.error(errno(&error));
                    return;
                }
            };
            if entry.stat.st_mode & libc::S_IFMT == libc::S_IFLNK {
                if mode.is_some() || uid.is_some() || gid.is_some() || size.is_some() {
                    Err(io::Error::from_raw_os_error(libc::EOPNOTSUPP))
                } else {
                    self.root(entry.backing)
                        .set_symlink_times(
                            &path,
                            &Timestamps {
                                last_access: timestamp(atime),
                                last_modification: timestamp(mtime),
                            },
                        )
                        .and_then(|()| {
                            self.root(entry.backing).stat(&path).and_then(|stat| {
                                self.attributes(&ResolvedEntry {
                                    path,
                                    backing: entry.backing,
                                    stat,
                                })
                            })
                        })
                }
            } else {
                let flags = if size.is_some() {
                    libc::O_RDWR
                } else {
                    libc::O_RDONLY
                };
                self.open_file(inode, flags).and_then(|handle| {
                    let result = self.with_file(FileHandle(handle), operation);
                    self.files
                        .lock()
                        .unwrap_or_else(std::sync::PoisonError::into_inner)
                        .remove(&handle);
                    result
                })
            }
        };
        match result {
            Ok(attributes) => reply.attr(&TTL, &attributes),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn readlink(&self, _request: &Request, inode: INodeNo, reply: ReplyData) {
        let result = self.path_for(inode).and_then(|path| {
            let snapshot = self.classifier.snapshot_for(&path);
            let entry = self.resolve(&snapshot, &path)?;
            self.root(entry.backing).readlink(&path)
        });
        match result {
            Ok(bytes) => reply.data(&bytes),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn mknod(
        &self,
        _request: &Request,
        parent: INodeNo,
        name: &OsStr,
        mode: u32,
        umask: u32,
        rdev: u32,
        reply: ReplyEntry,
    ) {
        if matches!(mode & libc::S_IFMT, libc::S_IFCHR | libc::S_IFBLK) {
            reply.error(Errno::EPERM);
            return;
        }
        let result = (|| {
            let path = self.child_path(parent, name)?;
            let snapshot = self.classifier.snapshot_for(&path);
            let backing = self.create_backing(&snapshot, &path, false)?;
            let root = self.root(backing);
            let parent_path = path.parent().unwrap_or_else(|| Path::new(""));
            let directory = root.open_directory(parent_path)?;
            mknodat(
                directory.as_fd(),
                name,
                rustix::fs::FileType::from_raw_mode(mode),
                Mode::from_raw_mode(mode & !umask),
                rustix::fs::makedev(rdev >> 8, rdev & 0xff),
            )?;
            Ok(path)
        })();
        match result {
            Ok(path) => self.reply_entry(&path, reply),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn mkdir(
        &self,
        _request: &Request,
        parent: INodeNo,
        name: &OsStr,
        mode: u32,
        umask: u32,
        reply: ReplyEntry,
    ) {
        let result = (|| {
            let path = self.child_path(parent, name)?;
            let snapshot = self.classifier.snapshot_for(&path);
            let backing = self.create_backing(&snapshot, &path, true)?;
            self.root(backing)
                .mkdir(&path, Mode::from_raw_mode((mode & !umask) & 0o7777))?;
            Ok(path)
        })();
        match result {
            Ok(path) => self.reply_entry(&path, reply),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn unlink(&self, _request: &Request, parent: INodeNo, name: &OsStr, reply: ReplyEmpty) {
        self.remove(parent, name, false, reply);
    }

    fn rmdir(&self, _request: &Request, parent: INodeNo, name: &OsStr, reply: ReplyEmpty) {
        self.remove(parent, name, true, reply);
    }

    fn symlink(
        &self,
        _request: &Request,
        parent: INodeNo,
        name: &OsStr,
        target: &Path,
        reply: ReplyEntry,
    ) {
        let result = (|| {
            let path = self.child_path(parent, name)?;
            let snapshot = self.classifier.snapshot_for(&path);
            let backing = self.create_backing(&snapshot, &path, false)?;
            self.root(backing).symlink(target, &path)?;
            Ok(path)
        })();
        match result {
            Ok(path) => self.reply_entry(&path, reply),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn rename(
        &self,
        _request: &Request,
        parent: INodeNo,
        name: &OsStr,
        new_parent: INodeNo,
        new_name: &OsStr,
        flags: FuseRenameFlags,
        reply: ReplyEmpty,
    ) {
        if flags.contains(FuseRenameFlags::RENAME_WHITEOUT) {
            reply.error(Errno::EOPNOTSUPP);
            return;
        }
        let result = (|| {
            let source = self.child_path(parent, name)?;
            let destination = self.child_path(new_parent, new_name)?;
            let snapshot = self.classifier.snapshot_for_paths(&[&source, &destination]);
            let source_entry = self.resolve(&snapshot, &source)?;
            let destination_backing = self.classify(
                &snapshot,
                &destination,
                source_entry.stat.st_mode & libc::S_IFMT == libc::S_IFDIR,
            );
            if source_entry.backing != destination_backing {
                return Err(io::Error::from_raw_os_error(libc::EXDEV));
            }
            if destination == Path::new(".git/index") {
                self.require_index_publication_safe(source_entry.backing, &source, &snapshot)?;
            }
            let flags = RenameFlags::from_bits_retain(flags.bits());
            self.root(source_entry.backing)
                .rename(&source, &destination, flags)
        })();
        reply_result(result, reply);
    }

    fn link(
        &self,
        _request: &Request,
        inode: INodeNo,
        new_parent: INodeNo,
        new_name: &OsStr,
        reply: ReplyEntry,
    ) {
        let result = (|| {
            let source = self.path_for(inode)?;
            let destination = self.child_path(new_parent, new_name)?;
            let snapshot = self.classifier.snapshot_for_paths(&[&source, &destination]);
            let source_entry = self.resolve(&snapshot, &source)?;
            let destination_backing = self.classify(&snapshot, &destination, false);
            if source_entry.backing != destination_backing {
                return Err(io::Error::from_raw_os_error(libc::EXDEV));
            }
            self.root(source_entry.backing)
                .link(&source, &destination)?;
            Ok(destination)
        })();
        match result {
            Ok(path) => self.reply_entry(&path, reply),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn open(&self, _request: &Request, inode: INodeNo, flags: OpenFlags, reply: ReplyOpen) {
        match self.open_file(inode, flags.0) {
            Ok(handle) => reply.opened(FileHandle(handle), FopenFlags::empty()),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn read(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        offset: u64,
        size: u32,
        _flags: OpenFlags,
        _lock_owner: Option<LockOwner>,
        reply: ReplyData,
    ) {
        let result = self.with_file(handle, |open| {
            let mut bytes = vec![0; size as usize];
            let read = open.file.read_at(&mut bytes, offset)?;
            bytes.truncate(read);
            Ok(bytes)
        });
        match result {
            Ok(bytes) => reply.data(&bytes),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn write(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        offset: u64,
        data: &[u8],
        _write_flags: WriteFlags,
        flags: OpenFlags,
        _lock_owner: Option<LockOwner>,
        reply: ReplyWrite,
    ) {
        let result = self.with_file(handle, |open| {
            let offset = if flags.0 & libc::O_APPEND != 0 {
                open.file.metadata()?.len()
            } else {
                offset
            };
            open.file.write_at(data, offset)
        });
        match result {
            Ok(written) => reply.written(u32::try_from(written).unwrap_or(u32::MAX)),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn flush(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        owner: LockOwner,
        reply: ReplyEmpty,
    ) {
        let result = self.with_file(handle, |open| {
            self.release_posix_locks(open, owner)?;
            open.file.sync_data()
        });
        reply_result(result, reply);
    }

    fn release(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        _flags: OpenFlags,
        owner: Option<LockOwner>,
        _flush: bool,
        reply: ReplyEmpty,
    ) {
        let open = self
            .files
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner)
            .remove(&handle.0);
        let result = match (open, owner) {
            (Some(open), Some(owner)) => self.release_posix_locks(&open, owner),
            (Some(_), None) => Ok(()),
            (None, _) => Err(io::Error::from_raw_os_error(libc::EBADF)),
        };
        reply_result(result, reply);
    }

    fn fsync(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        datasync: bool,
        reply: ReplyEmpty,
    ) {
        let result = self.with_file(handle, |open| {
            if datasync {
                open.file.sync_data()
            } else {
                open.file.sync_all()
            }
        });
        reply_result(result, reply);
    }

    fn getlk(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        owner: LockOwner,
        start: u64,
        end: u64,
        typ: i32,
        _pid: u32,
        flags: LockFlags,
        reply: ReplyLock,
    ) {
        if unsupported_lock_flags(flags) {
            reply.error(Errno::EOPNOTSUPP);
            return;
        }
        if flags.contains(LockFlags::FUSE_LK_FLOCK) {
            reply.locked(0, u64::MAX, libc::F_UNLCK, 0);
            return;
        }
        let result = self.with_file(handle, |open| {
            let file = self.posix_lock_file(open, owner)?;
            let mut lock = record_lock(start, end, typ)?;
            fcntl(file.as_fd(), FcntlArg::F_OFD_GETLK(&mut lock))?;
            fuse_lock(&lock)
        });
        match result {
            Ok((start, end, typ, pid)) => reply.locked(start, end, typ, pid),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn setlk(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        owner: LockOwner,
        start: u64,
        end: u64,
        typ: i32,
        _pid: u32,
        sleep: bool,
        flags: LockFlags,
        reply: ReplyEmpty,
    ) {
        if unsupported_lock_flags(flags) {
            reply.error(Errno::EOPNOTSUPP);
            return;
        }
        let result = self.with_file(handle, |open| {
            if flags.contains(LockFlags::FUSE_LK_FLOCK) {
                if (start, end) != (0, i64::MAX as u64) {
                    return Err(io::Error::from_raw_os_error(libc::EINVAL));
                }
                return Ok(bsd_flock(
                    open.file.as_fd(),
                    bsd_lock_operation(typ, sleep)?,
                )?);
            }
            let file = self.posix_lock_file(open, owner)?;
            let lock = record_lock(start, end, typ)?;
            let command = if sleep {
                FcntlArg::F_OFD_SETLKW(&lock)
            } else {
                FcntlArg::F_OFD_SETLK(&lock)
            };
            fcntl(file.as_fd(), command)?;
            Ok(())
        });
        reply_result(result, reply);
    }

    fn opendir(&self, _request: &Request, inode: INodeNo, _flags: OpenFlags, reply: ReplyOpen) {
        let result = (|| {
            let path = self.path_for(inode)?;
            let snapshot = self.classifier.snapshot_for(&path);
            let entry = self.resolve(&snapshot, &path)?;
            let directory = self.root(entry.backing).open_directory(&path)?;
            let mut entries = vec![
                DirectoryEntry {
                    inode,
                    kind: FileType::Directory,
                    name: OsString::from("."),
                },
                DirectoryEntry {
                    inode: if path.as_os_str().is_empty() {
                        INodeNo::ROOT
                    } else {
                        let parent = path.parent().unwrap_or_else(|| Path::new(""));
                        let parent_entry = self.resolve(&snapshot, parent)?;
                        self.inode_for(&parent_entry)
                    },
                    kind: FileType::Directory,
                    name: OsString::from(".."),
                },
            ];
            entries.extend(self.visible_entries(&path, &snapshot)?);
            let handle = self.next_handle.fetch_add(1, Ordering::Relaxed);
            self.directories
                .lock()
                .unwrap_or_else(std::sync::PoisonError::into_inner)
                .insert(
                    handle,
                    DirectoryStream {
                        directory,
                        entries,
                        _snapshot: snapshot,
                    },
                );
            Ok(handle)
        })();
        match result {
            Ok(handle) => reply.opened(FileHandle(handle), FopenFlags::empty()),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn readdir(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        offset: u64,
        mut reply: ReplyDirectory,
    ) {
        let directories = self
            .directories
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner);
        let Some(directory) = directories.get(&handle.0) else {
            reply.error(Errno::EBADF);
            return;
        };
        for (index, entry) in directory
            .entries
            .iter()
            .enumerate()
            .skip(usize::try_from(offset).unwrap_or(usize::MAX))
        {
            if reply.add(entry.inode, (index + 1) as u64, entry.kind, &entry.name) {
                break;
            }
        }
        reply.ok();
    }

    fn releasedir(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        _flags: OpenFlags,
        reply: ReplyEmpty,
    ) {
        self.directories
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner)
            .remove(&handle.0);
        reply.ok();
    }

    fn fsyncdir(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        datasync: bool,
        reply: ReplyEmpty,
    ) {
        let directories = self
            .directories
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner);
        let result = directories
            .get(&handle.0)
            .ok_or_else(|| io::Error::from_raw_os_error(libc::EBADF))
            .and_then(|stream| {
                if datasync {
                    stream.directory.sync_data()
                } else {
                    stream.directory.sync_all()
                }
            });
        reply_result(result, reply);
    }

    fn statfs(&self, _request: &Request, _inode: INodeNo, reply: ReplyStatfs) {
        match self
            .host
            .duplicate()
            .and_then(|file| Ok(fstatvfs(file.as_fd())?))
        {
            Ok(stat) => reply.statfs(
                stat.f_blocks,
                stat.f_bfree,
                stat.f_bavail,
                stat.f_files,
                stat.f_ffree,
                u32::try_from(stat.f_bsize).unwrap_or(u32::MAX),
                u32::try_from(stat.f_namemax).unwrap_or(u32::MAX),
                u32::try_from(stat.f_frsize).unwrap_or(u32::MAX),
            ),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn setxattr(
        &self,
        _request: &Request,
        inode: INodeNo,
        name: &OsStr,
        value: &[u8],
        flags: i32,
        position: u32,
        reply: ReplyEmpty,
    ) {
        if position != 0 || !writable_xattr(name) {
            reply.error(Errno::ENOTSUP);
            return;
        }
        let result = self.with_temporary_file(inode, |file| {
            Ok(fsetxattr(
                file.as_fd(),
                name,
                value,
                XattrFlags::from_bits_retain(u32::from_ne_bytes(flags.to_ne_bytes())),
            )?)
        });
        reply_result(result, reply);
    }

    fn getxattr(
        &self,
        _request: &Request,
        inode: INodeNo,
        name: &OsStr,
        size: u32,
        reply: ReplyXattr,
    ) {
        let result = self.with_temporary_file(inode, |file| {
            let mut bytes = vec![0; 64 * 1024];
            let length = fgetxattr(file.as_fd(), name, &mut bytes)?;
            bytes.truncate(length);
            Ok(bytes)
        });
        reply_xattr(result, size, reply);
    }

    fn listxattr(&self, _request: &Request, inode: INodeNo, size: u32, reply: ReplyXattr) {
        let result = self.with_temporary_file(inode, |file| {
            let mut bytes = vec![0; 64 * 1024];
            let length = flistxattr(file.as_fd(), &mut bytes)?;
            bytes.truncate(length);
            Ok(bytes)
        });
        reply_xattr(result, size, reply);
    }

    fn removexattr(&self, _request: &Request, inode: INodeNo, name: &OsStr, reply: ReplyEmpty) {
        if !writable_xattr(name) {
            reply.error(Errno::ENOTSUP);
            return;
        }
        let result = self.with_temporary_file(inode, |file| Ok(fremovexattr(file.as_fd(), name)?));
        reply_result(result, reply);
    }

    fn create(
        &self,
        _request: &Request,
        parent: INodeNo,
        name: &OsStr,
        mode: u32,
        umask: u32,
        flags: i32,
        reply: ReplyCreate,
    ) {
        let result = (|| {
            let path = self.child_path(parent, name)?;
            let snapshot = self.classifier.snapshot_for(&path);
            let backing = self.create_backing(&snapshot, &path, false)?;
            let file = self.root(backing).open_entry(
                &path,
                open_flags(flags) | OFlags::CREATE,
                Mode::from_raw_mode((mode & !umask) & 0o7777),
            )?;
            let stat = fstat(file.as_fd())?;
            let attributes = self.attributes(&ResolvedEntry {
                path,
                backing,
                stat,
            })?;
            let handle = self.next_handle.fetch_add(1, Ordering::Relaxed);
            self.files
                .lock()
                .unwrap_or_else(std::sync::PoisonError::into_inner)
                .insert(
                    handle,
                    Arc::new(OpenFile {
                        file,
                        backing,
                        access_mode: flags & libc::O_ACCMODE,
                    }),
                );
            Ok((attributes, handle))
        })();
        match result {
            Ok((attributes, handle)) => reply.created(
                &TTL,
                &attributes,
                Generation(0),
                FileHandle(handle),
                FopenFlags::empty(),
            ),
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn fallocate(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        offset: u64,
        length: u64,
        mode: i32,
        reply: ReplyEmpty,
    ) {
        let result = self.with_file(handle, |open| {
            Ok(fallocate(
                open.file.as_fd(),
                FallocateFlags::from_bits_retain(u32::from_ne_bytes(mode.to_ne_bytes())),
                offset,
                length,
            )?)
        });
        reply_result(result, reply);
    }

    fn lseek(
        &self,
        _request: &Request,
        _inode: INodeNo,
        handle: FileHandle,
        offset: i64,
        whence: i32,
        reply: ReplyLseek,
    ) {
        let position = match whence {
            libc::SEEK_SET => u64::try_from(offset).ok().map(SeekFrom::Start),
            libc::SEEK_CUR => Some(SeekFrom::Current(offset)),
            libc::SEEK_END => Some(SeekFrom::End(offset)),
            libc::SEEK_DATA => u64::try_from(offset).ok().map(SeekFrom::Data),
            libc::SEEK_HOLE => u64::try_from(offset).ok().map(SeekFrom::Hole),
            _ => None,
        };
        let result = position
            .ok_or_else(|| io::Error::from_raw_os_error(libc::EINVAL))
            .and_then(|position| {
                self.with_file(handle, |open| Ok(seek(open.file.as_fd(), position)?))
            });
        match result {
            Ok(position) => match i64::try_from(position) {
                Ok(position) => reply.offset(position),
                Err(_) => reply.error(Errno::EOVERFLOW),
            },
            Err(error) => reply.error(errno(&error)),
        }
    }

    fn copy_file_range(
        &self,
        _request: &Request,
        _inode_in: INodeNo,
        handle_in: FileHandle,
        offset_in: u64,
        _inode_out: INodeNo,
        handle_out: FileHandle,
        offset_out: u64,
        length: u64,
        flags: CopyFileRangeFlags,
        reply: ReplyWrite,
    ) {
        if !flags.is_empty() {
            reply.error(Errno::EINVAL);
            return;
        }
        let files = self
            .files
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner);
        let result = (|| {
            let input = files
                .get(&handle_in.0)
                .ok_or_else(|| io::Error::from_raw_os_error(libc::EBADF))?;
            let output = files
                .get(&handle_out.0)
                .ok_or_else(|| io::Error::from_raw_os_error(libc::EBADF))?;
            if input.backing != output.backing {
                return Err(io::Error::from_raw_os_error(libc::EXDEV));
            }
            let mut input_offset = offset_in;
            let mut output_offset = offset_out;
            copy_file_range(
                input.file.as_fd(),
                Some(&mut input_offset),
                output.file.as_fd(),
                Some(&mut output_offset),
                usize::try_from(length).unwrap_or(usize::MAX),
            )
            .map_err(io::Error::from)
        })();
        match result {
            Ok(written) => reply.written(u32::try_from(written).unwrap_or(u32::MAX)),
            Err(error) => reply.error(errno(&error)),
        }
    }
}

impl IgnoredWorkspace {
    fn remove(&self, parent: INodeNo, name: &OsStr, directory: bool, reply: ReplyEmpty) {
        let result = (|| {
            let path = self.child_path(parent, name)?;
            let snapshot = self.classifier.snapshot_for(&path);
            let entry = self.resolve(&snapshot, &path)?;
            self.root(entry.backing).unlink(&path, directory)
        })();
        reply_result(result, reply);
    }

    fn with_temporary_file<T>(
        &self,
        inode: INodeNo,
        operation: impl FnOnce(&File) -> io::Result<T>,
    ) -> io::Result<T> {
        let path = self.path_for(inode)?;
        let snapshot = self.classifier.snapshot_for(&path);
        let entry = self.resolve(&snapshot, &path)?;
        let file = self
            .root(entry.backing)
            .open_entry(&path, OFlags::RDONLY, Mode::empty())?;
        operation(&file)
    }

    fn require_index_publication_safe(
        &self,
        backing: Classification,
        source: &Path,
        snapshot: &ClassificationSnapshot,
    ) -> io::Result<()> {
        let bytes = self.root(backing).read_file(source, 512 * 1024 * 1024)?;
        for path in tracked_paths_from_index(&bytes)? {
            let path = PathBuf::from(OsString::from_vec(path));
            if snapshot.is_tracked(&path) {
                continue;
            }
            let host = self.host.stat(&path).ok();
            let isolated = self.isolated.stat(&path).ok();
            if let Some(isolated) = isolated {
                let compatible = host.is_some_and(|host| {
                    host.st_mode & libc::S_IFMT == isolated.st_mode & libc::S_IFMT
                });
                if !compatible {
                    return Err(io::Error::from_raw_os_error(libc::EBUSY));
                }
            }
        }
        Ok(())
    }
}

struct ResolvedEntry {
    path: PathBuf,
    backing: Classification,
    stat: rustix::fs::Stat,
}

struct OpenFile {
    file: File,
    backing: Classification,
    access_mode: i32,
}

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
struct PosixLockKey {
    backing: Classification,
    device: u64,
    inode: u64,
    owner: u64,
}

struct DirectoryStream {
    directory: File,
    entries: Vec<DirectoryEntry>,
    _snapshot: ClassificationSnapshot,
}

struct DirectoryEntry {
    inode: INodeNo,
    kind: FileType,
    name: OsString,
}

struct NodeTable {
    paths: HashMap<u64, PathBuf>,
    inodes: HashMap<NodeKey, u64>,
    next_inode: u64,
}

impl NodeTable {
    fn new() -> Self {
        Self {
            paths: HashMap::from([(INodeNo::ROOT.0, PathBuf::new())]),
            inodes: HashMap::new(),
            next_inode: 2,
        }
    }

    fn path(&self, inode: INodeNo) -> Option<PathBuf> {
        self.paths.get(&inode.0).cloned()
    }

    fn inode(&mut self, entry: &ResolvedEntry) -> INodeNo {
        let key = NodeKey {
            path: entry.path.clone(),
            backing: entry.backing,
            device: entry.stat.st_dev,
            inode: entry.stat.st_ino,
        };
        if let Some(inode) = self.inodes.get(&key) {
            return INodeNo(*inode);
        }
        let inode = self.next_inode;
        self.next_inode = self.next_inode.saturating_add(1);
        self.paths.insert(inode, entry.path.clone());
        self.inodes.insert(key, inode);
        INodeNo(inode)
    }
}

#[derive(Clone, Debug, Eq, Hash, PartialEq)]
struct NodeKey {
    path: PathBuf,
    backing: Classification,
    device: u64,
    inode: u64,
}

fn open_flags(flags: i32) -> OFlags {
    let mut result = OFlags::from_bits_retain(u32::from_ne_bytes(flags.to_ne_bytes()));
    result.remove(OFlags::CREATE | OFlags::EXCL | OFlags::NOFOLLOW | OFlags::CLOEXEC);
    result
}

fn file_type(mode: u32) -> io::Result<FileType> {
    match mode & libc::S_IFMT {
        libc::S_IFREG => Ok(FileType::RegularFile),
        libc::S_IFDIR => Ok(FileType::Directory),
        libc::S_IFLNK => Ok(FileType::Symlink),
        libc::S_IFIFO => Ok(FileType::NamedPipe),
        libc::S_IFSOCK => Ok(FileType::Socket),
        libc::S_IFCHR => Ok(FileType::CharDevice),
        libc::S_IFBLK => Ok(FileType::BlockDevice),
        _ => Err(io::Error::from_raw_os_error(libc::EOPNOTSUPP)),
    }
}

fn system_time(seconds: i64, nanoseconds: u64) -> SystemTime {
    if seconds >= 0 {
        UNIX_EPOCH
            + Duration::new(
                u64::try_from(seconds).unwrap_or(0),
                u32::try_from(nanoseconds).unwrap_or(999_999_999),
            )
    } else {
        UNIX_EPOCH
    }
}

fn timestamp(value: Option<TimeOrNow>) -> Timespec {
    match value {
        Some(TimeOrNow::Now) => Timespec {
            tv_sec: 0,
            tv_nsec: UTIME_NOW,
        },
        Some(TimeOrNow::SpecificTime(value)) => {
            let duration = value.duration_since(UNIX_EPOCH).unwrap_or_default();
            Timespec {
                tv_sec: i64::try_from(duration.as_secs()).unwrap_or(i64::MAX),
                tv_nsec: i64::from(duration.subsec_nanos()),
            }
        }
        None => Timespec {
            tv_sec: 0,
            tv_nsec: UTIME_OMIT,
        },
    }
}

fn writable_xattr(name: &OsStr) -> bool {
    matches!(
        name.as_bytes(),
        b"system.posix_acl_access" | b"system.posix_acl_default"
    ) || name.as_bytes().starts_with(b"user.")
}

fn unsupported_lock_flags(flags: LockFlags) -> bool {
    flags.bits() & !LockFlags::FUSE_LK_FLOCK.bits() != 0
}

fn bsd_lock_operation(typ: i32, sleep: bool) -> io::Result<FlockOperation> {
    match (typ, sleep) {
        (libc::F_RDLCK, true) => Ok(FlockOperation::LockShared),
        (libc::F_RDLCK, false) => Ok(FlockOperation::NonBlockingLockShared),
        (libc::F_WRLCK, true) => Ok(FlockOperation::LockExclusive),
        (libc::F_WRLCK, false) => Ok(FlockOperation::NonBlockingLockExclusive),
        (libc::F_UNLCK, true) => Ok(FlockOperation::Unlock),
        (libc::F_UNLCK, false) => Ok(FlockOperation::NonBlockingUnlock),
        _ => Err(io::Error::from_raw_os_error(libc::EINVAL)),
    }
}

fn record_lock(start: u64, end: u64, typ: i32) -> io::Result<libc::flock> {
    if start > end {
        return Err(io::Error::from_raw_os_error(libc::EINVAL));
    }
    let start_u64 = start;
    let start =
        i64::try_from(start_u64).map_err(|_| io::Error::from_raw_os_error(libc::EOVERFLOW))?;
    let length = if end == u64::MAX {
        0
    } else {
        let length = end
            .checked_sub(start_u64)
            .and_then(|length| length.checked_add(1))
            .ok_or_else(|| io::Error::from_raw_os_error(libc::EOVERFLOW))?;
        i64::try_from(length).map_err(|_| io::Error::from_raw_os_error(libc::EOVERFLOW))?
    };
    let typ = i16::try_from(typ).map_err(|_| io::Error::from_raw_os_error(libc::EINVAL))?;
    let whence =
        i16::try_from(libc::SEEK_SET).map_err(|_| io::Error::from_raw_os_error(libc::EINVAL))?;
    if !matches!(
        i32::from(typ),
        libc::F_RDLCK | libc::F_WRLCK | libc::F_UNLCK
    ) {
        return Err(io::Error::from_raw_os_error(libc::EINVAL));
    }
    Ok(libc::flock {
        l_type: typ,
        l_whence: whence,
        l_start: start,
        l_len: length,
        l_pid: 0,
    })
}

fn fuse_lock(lock: &libc::flock) -> io::Result<(u64, u64, i32, u32)> {
    let start =
        u64::try_from(lock.l_start).map_err(|_| io::Error::from_raw_os_error(libc::EOVERFLOW))?;
    let end = if lock.l_len == 0 {
        u64::MAX
    } else {
        let length =
            u64::try_from(lock.l_len).map_err(|_| io::Error::from_raw_os_error(libc::EOVERFLOW))?;
        start
            .checked_add(length.saturating_sub(1))
            .ok_or_else(|| io::Error::from_raw_os_error(libc::EOVERFLOW))?
    };
    Ok((
        start,
        end,
        i32::from(lock.l_type),
        u32::from_ne_bytes(lock.l_pid.to_ne_bytes()),
    ))
}

fn errno(error: &io::Error) -> Errno {
    Errno::from_i32(error.raw_os_error().unwrap_or(libc::EIO))
}

fn reply_result(result: io::Result<()>, reply: ReplyEmpty) {
    match result {
        Ok(()) => reply.ok(),
        Err(error) => reply.error(errno(&error)),
    }
}

fn reply_xattr(result: io::Result<Vec<u8>>, size: u32, reply: ReplyXattr) {
    match result {
        Ok(bytes) if size == 0 => reply.size(u32::try_from(bytes.len()).unwrap_or(u32::MAX)),
        Ok(bytes) if bytes.len() <= size as usize => reply.data(&bytes),
        Ok(_) => reply.error(Errno::ERANGE),
        Err(error) => reply.error(errno(&error)),
    }
}

#[cfg(test)]
mod tests {
    use std::fs::{self, OpenOptions};
    use std::io::{Read, Seek, Write};
    use std::os::fd::{AsFd, AsRawFd};
    use std::sync::atomic::{AtomicU64, Ordering};

    use fuser::{Config, LockOwner, MountOption};
    use nix::fcntl::{FcntlArg, fcntl};

    use super::{Classification, IgnoredWorkspace, OpenFile, fuse_lock, record_lock};

    static SEQUENCE: AtomicU64 = AtomicU64::new(0);

    #[test]
    fn posix_lock_owners_use_distinct_backing_lock_domains() {
        let fixture = Fixture::new();
        repository(&fixture.workspace);
        let path = fixture.workspace.join("ordinary");
        fs::write(&path, b"lock").unwrap();
        let filesystem =
            IgnoredWorkspace::open(&fixture.workspace, &fixture.isolated, None).unwrap();
        let open = OpenFile {
            file: OpenOptions::new()
                .read(true)
                .write(true)
                .open(path)
                .unwrap(),
            backing: Classification::Host,
            access_mode: libc::O_RDWR,
        };
        let first_owner = LockOwner(101);
        let second_owner = LockOwner(202);
        let first = filesystem.posix_lock_file(&open, first_owner).unwrap();
        let second = filesystem.posix_lock_file(&open, second_owner).unwrap();
        assert_ne!(first.as_raw_fd(), second.as_raw_fd());

        let lock = record_lock(0, 0, libc::F_WRLCK).unwrap();
        fcntl(first.as_fd(), FcntlArg::F_OFD_SETLK(&lock)).unwrap();
        let error = fcntl(second.as_fd(), FcntlArg::F_OFD_SETLK(&lock)).unwrap_err();
        assert_eq!(error, nix::errno::Errno::EAGAIN);

        drop(first);
        filesystem.release_posix_locks(&open, first_owner).unwrap();
        fcntl(second.as_fd(), FcntlArg::F_OFD_SETLK(&lock)).unwrap();
    }

    #[test]
    fn record_lock_ranges_round_trip() {
        for (start, end) in [(0, 0), (7, 19), (11, u64::MAX)] {
            let lock = record_lock(start, end, libc::F_RDLCK).unwrap();
            assert_eq!(fuse_lock(&lock).unwrap(), (start, end, libc::F_RDLCK, 0));
        }
    }

    #[test]
    fn disabled_isolation_routes_ignored_paths_to_the_host_backing() {
        let fixture = Fixture::new();
        repository(&fixture.workspace);
        fs::write(fixture.workspace.join(".gitignore"), b"ignored/\n").unwrap();
        let filesystem = IgnoredWorkspace::from_authorities_with_policy(
            fixture.workspace.clone(),
            fs::File::open(&fixture.workspace).unwrap(),
            fs::File::open(&fixture.isolated).unwrap(),
            None,
            false,
        )
        .unwrap();
        let path = std::path::Path::new("ignored/item");
        let snapshot = filesystem.classifier.snapshot_for(path);
        assert_eq!(
            filesystem.classify(&snapshot, path, false),
            Classification::Host
        );
    }

    #[test]
    #[ignore = "requires a usable host FUSE device"]
    fn physical_router_preserves_lock_domains_across_transition() {
        let fixture = Fixture::new();
        repository(&fixture.workspace);
        fs::write(fixture.workspace.join(".gitignore"), b"ignored/\n").unwrap();
        fs::create_dir(fixture.workspace.join("ignored")).unwrap();
        fs::write(fixture.workspace.join("ignored/locked"), b"host").unwrap();
        fs::create_dir(fixture.isolated.join("ignored")).unwrap();
        fs::write(fixture.isolated.join("ignored/locked"), b"isolated").unwrap();

        let filesystem =
            IgnoredWorkspace::open(&fixture.workspace, &fixture.isolated, None).unwrap();
        let mut config = Config::default();
        config.mount_options.extend([
            MountOption::RW,
            MountOption::DefaultPermissions,
            MountOption::NoDev,
            MountOption::NoSuid,
        ]);
        let session = fuser::spawn_mount2(filesystem, &fixture.mountpoint, &config).unwrap();

        let mounted_path = fixture.mountpoint.join("ignored/locked");
        let old = OpenOptions::new()
            .read(true)
            .write(true)
            .open(&mounted_path)
            .unwrap();
        let lock = record_lock(0, 0, libc::F_WRLCK).unwrap();
        fcntl(old.as_fd(), FcntlArg::F_SETLK(&lock)).unwrap();

        fs::write(fixture.workspace.join(".gitignore"), b"different/\n").unwrap();
        let new = OpenOptions::new()
            .read(true)
            .write(true)
            .open(&mounted_path)
            .unwrap();
        assert_eq!(fs::read(&mounted_path).unwrap(), b"host");

        let isolated = OpenOptions::new()
            .read(true)
            .write(true)
            .open(fixture.isolated.join("ignored/locked"))
            .unwrap();
        assert_eq!(
            fcntl(isolated.as_fd(), FcntlArg::F_OFD_SETLK(&lock)).unwrap_err(),
            nix::errno::Errno::EAGAIN
        );
        let host = OpenOptions::new()
            .read(true)
            .write(true)
            .open(fixture.workspace.join("ignored/locked"))
            .unwrap();
        fcntl(host.as_fd(), FcntlArg::F_OFD_SETLK(&lock)).unwrap();
        let unlock = record_lock(0, 0, libc::F_UNLCK).unwrap();
        fcntl(host.as_fd(), FcntlArg::F_OFD_SETLK(&unlock)).unwrap();

        fcntl(new.as_fd(), FcntlArg::F_SETLK(&lock)).unwrap();
        assert_eq!(
            fcntl(host.as_fd(), FcntlArg::F_OFD_SETLK(&lock)).unwrap_err(),
            nix::errno::Errno::EAGAIN
        );
        drop(old);
        fcntl(isolated.as_fd(), FcntlArg::F_OFD_SETLK(&lock)).unwrap();
        drop(new);
        fcntl(host.as_fd(), FcntlArg::F_OFD_SETLK(&lock)).unwrap();

        session.umount_and_join().unwrap();
    }

    #[test]
    #[ignore = "requires a usable host FUSE device"]
    fn physical_router_preserves_routes_transitions_and_cross_route_atomicity() {
        let fixture = Fixture::new();
        repository(&fixture.workspace);
        fs::write(fixture.workspace.join(".gitignore"), b"ignored/\n").unwrap();
        fs::create_dir(fixture.workspace.join("ignored")).unwrap();
        fs::write(fixture.workspace.join("ignored/sentinel"), b"host").unwrap();
        fs::create_dir(fixture.isolated.join("ignored")).unwrap();
        fs::write(fixture.isolated.join("ignored/sentinel"), b"isolated").unwrap();

        let filesystem =
            IgnoredWorkspace::open(&fixture.workspace, &fixture.isolated, None).unwrap();
        let mut config = Config::default();
        config.mount_options.extend([
            MountOption::RW,
            MountOption::DefaultPermissions,
            MountOption::NoDev,
            MountOption::NoSuid,
        ]);
        let session = fuser::spawn_mount2(filesystem, &fixture.mountpoint, &config).unwrap();

        assert_eq!(
            fs::read(fixture.mountpoint.join("ignored/sentinel")).unwrap(),
            b"isolated"
        );
        fs::write(fixture.mountpoint.join("ordinary"), b"bidirectional").unwrap();
        assert_eq!(
            fs::read(fixture.workspace.join("ordinary")).unwrap(),
            b"bidirectional"
        );

        let mut pinned = OpenOptions::new()
            .read(true)
            .write(true)
            .open(fixture.mountpoint.join("ignored/sentinel"))
            .unwrap();
        fs::write(fixture.workspace.join(".gitignore"), b"different/\n").unwrap();
        assert_eq!(
            fs::read(fixture.mountpoint.join("ignored/sentinel")).unwrap(),
            b"host"
        );
        pinned.write_all(b"-pinned").unwrap();
        pinned.flush().unwrap();
        let mut pinned_bytes = Vec::new();
        pinned.rewind().unwrap();
        pinned.read_to_end(&mut pinned_bytes).unwrap();
        assert_eq!(pinned_bytes, b"-pinnedd");
        assert_eq!(
            fs::read(fixture.workspace.join("ignored/sentinel")).unwrap(),
            b"host"
        );

        fs::write(fixture.workspace.join("host-source"), b"source").unwrap();
        fs::write(fixture.workspace.join(".gitignore"), b"destination\n").unwrap();
        let error = fs::rename(
            fixture.mountpoint.join("host-source"),
            fixture.mountpoint.join("destination"),
        )
        .unwrap_err();
        assert_eq!(error.raw_os_error(), Some(libc::EXDEV));
        assert_eq!(
            fs::read(fixture.workspace.join("host-source")).unwrap(),
            b"source"
        );
        assert!(!fixture.isolated.join("destination").exists());

        drop(pinned);
        session.umount_and_join().unwrap();
    }

    fn repository(root: &std::path::Path) {
        fs::create_dir_all(root.join(".git/info")).unwrap();
        fs::create_dir_all(root.join(".git/hooks")).unwrap();
        fs::write(root.join(".git/config"), b"[core]\nignoreCase = false\n").unwrap();
        fs::write(root.join(".git/info/exclude"), b"").unwrap();
        let mut index = b"DIRC".to_vec();
        index.extend_from_slice(&2u32.to_be_bytes());
        index.extend_from_slice(&0u32.to_be_bytes());
        index.extend_from_slice(&[0; 20]);
        fs::write(root.join(".git/index"), index).unwrap();
    }

    struct Fixture {
        root: std::path::PathBuf,
        workspace: std::path::PathBuf,
        isolated: std::path::PathBuf,
        mountpoint: std::path::PathBuf,
    }

    impl Fixture {
        fn new() -> Self {
            let sequence = SEQUENCE.fetch_add(1, Ordering::Relaxed);
            let root = std::env::current_dir()
                .unwrap()
                .join("target/ignored-workspace-tests")
                .join(format!("physical-{}-{sequence}", std::process::id()));
            let workspace = root.join("workspace");
            let isolated = root.join("isolated");
            let mountpoint = root.join("mountpoint");
            fs::create_dir_all(&workspace).unwrap();
            fs::create_dir(&isolated).unwrap();
            fs::create_dir(&mountpoint).unwrap();
            Self {
                root,
                workspace,
                isolated,
                mountpoint,
            }
        }
    }

    impl Drop for Fixture {
        fn drop(&mut self) {
            fs::remove_dir_all(&self.root).unwrap();
        }
    }
}