exfat-slim 0.5.0

// the file system exposed through shared references using the actor pattern and the Embassy async runtime

use core::sync::atomic::{AtomicU32, Ordering};

use alloc::{
    // borrow::Cow,
    borrow::Cow,
    collections::btree_map::{BTreeMap, Entry},
    string::{String, ToString},
    vec,
    vec::Vec,
};

use crate::info;
use embassy_sync::{
    blocking_mutex::raw::CriticalSectionRawMutex,
    channel::Channel,
    mutex::Mutex,
    semaphore::{FairSemaphore, Semaphore},
    signal::Signal,
};

use crate::asynchronous::{
    BlockDevice, boot_sector,
    directory::{DirectoryEntry, DirectoryIterator},
    directory_entry::{self},
    error::ExFatError,
    file::{File, Metadata, OpenOptions},
    file_system::{ExFatResult, FileSystem},
};

static REQ: Channel<CriticalSectionRawMutex, Req, 8> = Channel::new();

// to keep the API simple this error type is not generic
// as a result the BlockDevice error is turned into an error_code
// look for implementations of the ErrorCode trate to see what these codes mean in your codebase
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
#[derive(thiserror::Error, Debug, Clone, Copy)]
pub enum Error {
    #[error("io error code {error_code}")]
    Io { error_code: u8 },

    #[error("no sd card")]
    NoCard,

    #[error("directory entry ({0:?})")]
    DirectoryEntry(#[from] directory_entry::Error),

    #[error("boot sector not valid exFAT ({0:?})")]
    NotExFat(#[from] boot_sector::Error),

    #[error("end of fat chain")]
    EndOfFatChain,

    #[error("invalid uft16 string encountered ({reason})")]
    InvalidUtf16String { reason: &'static str },

    #[error("invalid file name ({reason})")]
    InvalidFileName { reason: &'static str },

    #[error("invalid file system ({reason})")]
    InvalidFileSystem { reason: &'static str },

    #[error("file not found")]
    FileNotFound,

    #[error("directory not found")]
    DirectoryNotFound,

    #[error("invalid utf8 bytes")]
    Utf8Error,

    #[error("disk is full")]
    DiskFull,

    #[error("invalid cluster id ({0})")]
    InvalidClusterId(u32),

    #[error("invalid sector id ({0})")]
    InvalidSectorId(u32),

    #[error("directory is not empty")]
    DirectoryNotEmpty,

    #[error("write not enabled")]
    WriteNotEnabled,

    #[error("read not enabled")]
    ReadNotEnabled,

    #[error("file already exists")]
    AlreadyExists,

    #[error("cannot seek past the end of the valid data in the file")]
    SeekOutOfRange,

    #[error("attempt to change the allocation bitmap to a value with no effect")]
    InvalidAllocation {
        allocated: bool,
        allocated_new: bool,
        index: usize,
        lba: u32,
    },

    #[error("the combination of flags set when opening the file is not valid")]
    InvalidOptions,

    #[error("unexpected response from file system actor")]
    UnexpectedResponse,

    #[error("no more file handles")]
    ExhaustedFileHandles,

    #[error("invalid file handle")]
    InvalidFileHandle,

    #[error("unexpected error occured: {0}")]
    Unexpected(&'static str),
}

impl<E> From<ExFatError<E>> for Error
where
    E: BlockDeviceError,
{
    fn from(value: ExFatError<E>) -> Self {
        match value {
            ExFatError::Io(e) => {
                if e.no_card() {
                    Error::NoCard
                } else {
                    Error::Io {
                        error_code: e.to_error_code(),
                    }
                }
            }
            ExFatError::AlreadyExists => Error::AlreadyExists,
            ExFatError::DirectoryEntry(e) => Error::DirectoryEntry(e),
            ExFatError::DirectoryNotEmpty => Error::DirectoryNotEmpty,
            ExFatError::DirectoryNotFound => Error::DirectoryNotFound,
            ExFatError::DiskFull => Error::DiskFull,
            ExFatError::EndOfFatChain => Error::EndOfFatChain,
            ExFatError::FileNotFound => Error::FileNotFound,
            ExFatError::InvalidAllocation {
                allocated,
                allocated_new,
                index,
                lba,
            } => Error::InvalidAllocation {
                allocated,
                allocated_new,
                index,
                lba,
            },
            ExFatError::InvalidClusterId(id) => Error::InvalidClusterId(id),
            ExFatError::InvalidFileName { reason } => Error::InvalidFileName { reason },
            ExFatError::InvalidFileSystem { reason } => Error::InvalidFileSystem { reason },
            ExFatError::InvalidOptions => Error::InvalidOptions,
            ExFatError::InvalidSectorId(id) => Error::InvalidSectorId(id),
            ExFatError::InvalidUtf16String { reason } => Error::InvalidUtf16String { reason },
            ExFatError::NotExFat(e) => Error::NotExFat(e),
            ExFatError::ReadNotEnabled => Error::ReadNotEnabled,
            ExFatError::SeekOutOfRange => Error::SeekOutOfRange,
            ExFatError::Utf8Error => Error::Utf8Error,
            ExFatError::WriteNotEnabled => Error::WriteNotEnabled,
            ExFatError::Unexpected(reason) => Error::Unexpected(reason),
        }
    }
}

impl OpenOptions {
    pub async fn open(&self, path: &str) -> Result<FileHandle, Error> {
        let token = ReplyPool::acquire().await;
        let req = Req {
            op: Op::OpenFile {
                path: path.to_string(),
                options: self.clone(),
            },
            reply: token,
        };
        REQ.send(req).await;
        let resp = ReplyPool::wait(token).await?;

        match resp {
            Resp::FileOpen { handle } => Ok(handle),
            _ => Err(Error::UnexpectedResponse),
        }
    }
}

enum Op {
    ReadToString { path: String },
    Read { path: String },
    OpenFile { path: String, options: OpenOptions },
    ReadFile { handle: FileHandle, len: usize },
    ReadFileToEnd { handle: FileHandle },
    ReadFileToString { handle: FileHandle },
    WriteFile { handle: FileHandle, buffer: Vec<u8> },
    SeekFile { handle: FileHandle, position: u64 },
    CloseFile { handle: FileHandle },
    FlushFile { handle: FileHandle },
    Metadata { handle: FileHandle },
    OpenDirectory { path: String },
    DirectoryNextEntry { handle: DirectoryHandle },
    Exists { path: String },
    RemoveFile { path: String },
    CreateDirectory { path: String },
    Copy { from_path: String, to_path: String },
    Rename { from_path: String, to_path: String },
    RemoveDir { path: String },
    Write { path: String, buffer: Vec<u8> },
}

struct Req {
    op: Op,
    reply: ReplyToken,
}

pub struct DirectoryHandle(u32);

impl DirectoryHandle {
    pub async fn next_entry(&self) -> Result<Option<DirectoryEntry>, Error> {
        let token = ReplyPool::acquire().await;
        let req = Req {
            op: Op::DirectoryNextEntry {
                handle: DirectoryHandle(self.0),
            },
            reply: token,
        };
        REQ.send(req).await;
        let resp = ReplyPool::wait(token).await?;

        match resp {
            Resp::DirectoryEntry { data } => Ok(data),
            _ => Err(Error::UnexpectedResponse),
        }
    }
}

pub struct FileHandle(u32);

impl FileHandle {
    pub async fn read(&self, buf: &mut [u8]) -> Result<Option<usize>, Error> {
        let token = ReplyPool::acquire().await;
        let req = Req {
            op: Op::ReadFile {
                handle: FileHandle(self.0),
                len: buf.len(),
            },
            reply: token,
        };
        REQ.send(req).await;
        let resp = ReplyPool::wait(token).await?;

        match resp {
            Resp::Read { data } => {
                if data.is_empty() {
                    Ok(None)
                } else {
                    buf.copy_from_slice(&data);
                    Ok(Some(data.len()))
                }
            }
            _ => Err(Error::UnexpectedResponse),
        }
    }

    pub async fn read_to_end(&self) -> Result<Vec<u8>, Error> {
        let token = ReplyPool::acquire().await;
        let req = Req {
            op: Op::ReadFileToEnd {
                handle: FileHandle(self.0),
            },
            reply: token,
        };
        REQ.send(req).await;
        let resp = ReplyPool::wait(token).await?;

        match resp {
            Resp::Read { data } => Ok(data),
            _ => Err(Error::UnexpectedResponse),
        }
    }

    pub async fn read_to_string(&self) -> Result<String, Error> {
        let token = ReplyPool::acquire().await;
        let req = Req {
            op: Op::ReadFileToString {
                handle: FileHandle(self.0),
            },
            reply: token,
        };
        REQ.send(req).await;
        let resp = ReplyPool::wait(token).await?;

        match resp {
            Resp::ReadToString { data } => Ok(data),
            _ => Err(Error::UnexpectedResponse),
        }
    }

    pub async fn write(&self, buffer: impl Into<Cow<'_, [u8]>>) -> Result<(), Error> {
        let buffer: Cow<'_, [u8]> = buffer.into();
        if buffer.is_empty() {
            return Ok(());
        }

        let token = ReplyPool::acquire().await;
        let req = Req {
            op: Op::WriteFile {
                handle: FileHandle(self.0),
                buffer: buffer.into(),
            },
            reply: token,
        };
        REQ.send(req).await;
        let resp = ReplyPool::wait(token).await?;

        match resp {
            Resp::Ok => Ok(()),
            _ => Err(Error::UnexpectedResponse),
        }
    }

    pub async fn seek(&self, position: u64) -> Result<(), Error> {
        let token = ReplyPool::acquire().await;
        let req = Req {
            op: Op::SeekFile {
                handle: FileHandle(self.0),
                position,
            },
            reply: token,
        };
        REQ.send(req).await;
        let resp = ReplyPool::wait(token).await?;

        match resp {
            Resp::Ok => Ok(()),
            _ => Err(Error::UnexpectedResponse),
        }
    }

    pub async fn metdata(&self) -> Result<Metadata, Error> {
        let token = ReplyPool::acquire().await;
        let req = Req {
            op: Op::Metadata {
                handle: FileHandle(self.0),
            },
            reply: token,
        };
        REQ.send(req).await;
        let resp = ReplyPool::wait(token).await?;

        match resp {
            Resp::Metadata { data } => Ok(data),
            _ => Err(Error::UnexpectedResponse),
        }
    }

    // this performs a flush and waits for the operation to complete, consuming file handle
    pub async fn close(self) -> Result<(), Error> {
        let token = ReplyPool::acquire().await;
        let req = Req {
            op: Op::CloseFile {
                handle: FileHandle(self.0),
            },
            reply: token,
        };
        REQ.send(req).await;
        let resp = ReplyPool::wait(token).await?;

        match resp {
            Resp::Ok => Ok(()),
            _ => Err(Error::UnexpectedResponse),
        }
    }

    // this writes all outstanding metadata relating to changes to the file to disk
    // and returns when that operation is complete.
    // This includes file length (directory entry) FAT and allocation tables
    // The file is kept open
    pub async fn flush(&self) -> Result<(), Error> {
        let token = ReplyPool::acquire().await;
        let req = Req {
            op: Op::FlushFile {
                handle: FileHandle(self.0),
            },
            reply: token,
        };
        REQ.send(req).await;
        let resp = ReplyPool::wait(token).await?;

        match resp {
            Resp::Ok => Ok(()),
            _ => Err(Error::UnexpectedResponse),
        }
    }
}

impl Drop for FileHandle {
    // this will make a best effort attempt to close the file
    // but not wait for confirmation that the operation was completed.
    // If you want to be sure that the file was closed without error
    // then call the close or flush functions explicitly
    fn drop(&mut self) {
        // TODO: get this to work

        /*
        let handle = FileHandle(self.0);
        if let Some(reply) = ReplyPool::try_acquire() {
            let req = Req {
                op: Op::CloseFile { handle },
                reply,
            };
            REQ.try_send(req).ok();
        }*/
    }
}

pub async fn open(path: &str, options: OpenOptions) -> Result<FileHandle, Error> {
    let token = ReplyPool::acquire().await;
    let req = Req {
        op: Op::OpenFile {
            path: path.to_string(),
            options,
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::FileOpen { handle } => Ok(handle),
        _ => Err(Error::UnexpectedResponse),
    }
}

pub async fn read_to_string(path: &str) -> Result<String, Error> {
    let token = ReplyPool::acquire().await;
    let req = Req {
        op: Op::ReadToString {
            path: path.to_string(),
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::ReadToString { data: string } => Ok(string),
        _ => Err(Error::UnexpectedResponse),
    }
}

pub async fn read(path: &str) -> Result<Vec<u8>, Error> {
    let token = ReplyPool::acquire().await;
    let req = Req {
        op: Op::Read {
            path: path.to_string(),
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::Read { data } => Ok(data),
        _ => Err(Error::UnexpectedResponse),
    }
}

pub async fn read_dir(path: &str) -> Result<DirectoryHandle, Error> {
    let token = ReplyPool::acquire().await;
    let req = Req {
        op: Op::OpenDirectory {
            path: path.to_string(),
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::DirectoryOpen { handle } => Ok(handle),
        _ => Err(Error::UnexpectedResponse),
    }
}

pub async fn exists(path: &str) -> Result<bool, Error> {
    let token = ReplyPool::acquire().await;
    let req = Req {
        op: Op::Exists {
            path: path.to_string(),
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::Exists { exists } => Ok(exists),
        _ => Err(Error::UnexpectedResponse),
    }
}

pub async fn remove_file(path: &str) -> Result<(), Error> {
    let token = ReplyPool::acquire().await;
    let req = Req {
        op: Op::RemoveFile {
            path: path.to_string(),
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::Ok => Ok(()),
        _ => Err(Error::UnexpectedResponse),
    }
}

pub async fn create_directory(path: &str) -> Result<(), Error> {
    let token = ReplyPool::acquire().await;
    let req = Req {
        op: Op::CreateDirectory {
            path: path.to_string(),
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::Ok => Ok(()),
        _ => Err(Error::UnexpectedResponse),
    }
}

pub async fn copy(path_from: &str, path_to: &str) -> Result<(), Error> {
    let token = ReplyPool::acquire().await;
    let req = Req {
        op: Op::Copy {
            from_path: path_from.to_string(),
            to_path: path_to.to_string(),
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::Ok => Ok(()),
        _ => Err(Error::UnexpectedResponse),
    }
}

pub async fn rename(path_from: &str, path_to: &str) -> Result<(), Error> {
    let token = ReplyPool::acquire().await;
    let req = Req {
        op: Op::Rename {
            from_path: path_from.to_string(),
            to_path: path_to.to_string(),
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::Ok => Ok(()),
        _ => Err(Error::UnexpectedResponse),
    }
}

pub async fn remove_directory(path: &str) -> Result<(), Error> {
    let token = ReplyPool::acquire().await;
    let req = Req {
        op: Op::RemoveDir {
            path: path.to_string(),
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::Ok => Ok(()),
        _ => Err(Error::UnexpectedResponse),
    }
}

pub async fn write(path: &str, buffer: impl Into<Cow<'_, [u8]>>) -> Result<(), Error> {
    let token = ReplyPool::acquire().await;
    let buffer: Cow<'_, [u8]> = buffer.into();

    let req = Req {
        op: Op::Write {
            path: path.to_string(),
            buffer: buffer.into(),
        },
        reply: token,
    };
    REQ.send(req).await;
    let resp = ReplyPool::wait(token).await?;

    match resp {
        Resp::Ok => Ok(()),
        _ => Err(Error::UnexpectedResponse),
    }
}

#[derive(Clone, Copy, Debug)]
struct ReplyToken {
    pub slot: u8,
    pub seq: u32,
}

struct ReplySignal {
    seq: u32,
    resp: Result<Resp, Error>,
}

const REPLY_SLOTS: usize = 4;

// Each slot carries (seq, Resp). seq prevents stale wakeups.
static REPLY_SIGNALS: [Signal<CriticalSectionRawMutex, ReplySignal>; REPLY_SLOTS] =
    [Signal::new(), Signal::new(), Signal::new(), Signal::new()];

// Semaphore limits number of in-flight requests to REPLY_SLOTS.
static FREE_SLOTS: FairSemaphore<CriticalSectionRawMutex, REPLY_SLOTS> =
    FairSemaphore::new(REPLY_SLOTS);

// Slot bitmap, protected by a Mutex (portable in Embassy).
static SLOT_BITMAP: Mutex<CriticalSectionRawMutex, u32> = Mutex::new(0);

// Monotonic sequence generator.
static SEQ: AtomicU32 = AtomicU32::new(1);

fn claim_slot_locked(bitmap: &mut u32) -> u8 {
    // Find a 0 bit and set it.
    for i in 0..REPLY_SLOTS {
        let mask = 1u32 << i;
        if (*bitmap & mask) == 0 {
            *bitmap |= mask;
            return i as u8;
        }
    }
    // Should be unreachable due to semaphore gating.
    0
}

fn release_slot_locked(bitmap: &mut u32, slot: u8) {
    let mask = 1u32 << (slot as u32);
    *bitmap &= !mask;
}

enum Resp {
    Ok,
    ReadToString { data: String },
    Read { data: Vec<u8> },
    FileOpen { handle: FileHandle },
    DirectoryOpen { handle: DirectoryHandle },
    Metadata { data: Metadata },
    DirectoryEntry { data: Option<DirectoryEntry> },
    Exists { exists: bool },
}

struct Handles<T> {
    handles: BTreeMap<u32, T>,
    next_handle: u32,
}

impl<T> Handles<T> {
    fn new() -> Self {
        Self {
            handles: BTreeMap::new(),
            next_handle: 0,
        }
    }

    pub fn clear(&mut self) {
        self.handles.clear();
        // don't reset the handle back to 0 because there might be old handles still out there
    }

    pub fn add(&mut self, item: T) -> Result<u32, Error> {
        let mut counter: u32 = 0;
        loop {
            let handle = self.next_handle.wrapping_add(1);
            self.next_handle = handle;

            match self.handles.entry(handle) {
                Entry::Occupied(_) => {
                    // file is still available here because it was not moved
                }
                Entry::Vacant(v) => {
                    v.insert(item); // moved only if key was absent
                    return Ok(handle);
                }
            }

            counter += 1;
            if counter == u32::MAX {
                return Err(Error::ExhaustedFileHandles);
            }
        }
    }

    pub fn remove(&mut self, handle: u32) -> Result<T, Error> {
        self.handles.remove(&handle).ok_or(Error::InvalidFileHandle)
    }

    pub fn get(&mut self, handle: u32) -> Result<&mut T, Error> {
        self.handles
            .get_mut(&handle)
            .ok_or(Error::InvalidFileHandle)
    }
}

struct ReplyPool;

impl ReplyPool {
    /// Acquire a reply slot and create a token.
    pub async fn acquire() -> ReplyToken {
        // Ensure a slot is available.
        FREE_SLOTS.acquire(1).await.unwrap();

        // Claim an actual slot id.
        let slot = {
            let mut bm = SLOT_BITMAP.lock().await;
            claim_slot_locked(&mut bm)
        };

        let seq = SEQ.fetch_add(1, Ordering::Relaxed);
        ReplyToken { slot, seq }
    }

    /// Acquire a reply slot and create a token.
    pub fn _try_acquire() -> Option<ReplyToken> {
        // Ensure a slot is available.
        FREE_SLOTS.try_acquire(1)?;

        // Claim an actual slot id.
        let slot = {
            let mut bm = SLOT_BITMAP.try_lock().ok()?;
            claim_slot_locked(&mut bm)
        };

        let seq = SEQ.fetch_add(1, Ordering::Relaxed);
        Some(ReplyToken { slot, seq })
    }

    /// Wait for completion of a specific token; releases the slot afterwards.
    pub async fn wait(token: ReplyToken) -> Result<Resp, Error> {
        let slot = token.slot as usize;

        loop {
            let ReplySignal { seq, resp } = REPLY_SIGNALS[slot].wait().await;
            if seq == token.seq {
                // Release slot back to pool.
                {
                    let mut bm = SLOT_BITMAP.lock().await;
                    release_slot_locked(&mut bm, token.slot);
                }
                FREE_SLOTS.release(1);
                return resp;
            }
            // If mismatched (rare; usually only after reset/reuse bugs), keep waiting.
        }
    }

    /// Actor-side: complete a request.
    pub fn complete(token: ReplyToken, resp: Result<Resp, Error>) {
        let signal = ReplySignal {
            seq: token.seq,
            resp,
        };
        REPLY_SIGNALS[token.slot as usize].signal(signal);
    }
}

pub trait BlockDeviceError {
    fn to_error_code(&self) -> u8;
    fn no_card(&self) -> bool;
}

struct FsManager<D, const SIZE: usize, const N: usize>
where
    D: BlockDevice<SIZE>,
{
    dev: Option<D>,
    file_system: Option<FileSystem<D, SIZE, N>>,
    files: Handles<File>,
    directories: Handles<DirectoryIterator<SIZE>>,
}

impl<D, const SIZE: usize, const N: usize> FsManager<D, SIZE, N>
where
    D: BlockDevice<SIZE>,
{
    pub fn new(dev: D) -> Self {
        Self {
            dev: Some(dev),
            file_system: None,
            files: Handles::new(),
            directories: Handles::new(),
        }
    }

    pub async fn mount(
        &mut self,
    ) -> ExFatResult<
        (
            &mut FileSystem<D, SIZE, N>,
            &mut Handles<File>,
            &mut Handles<DirectoryIterator<SIZE>>,
        ),
        D,
        SIZE,
    > {
        if let Some(dev) = self.dev.take() {
            let mut file_system = FileSystem::new(dev);
            info!("mounting file system");
            match file_system.mount().await {
                Ok(()) => {
                    self.files.clear();
                    self.file_system = Some(file_system);
                    Ok((
                        self.file_system.as_mut().unwrap(),
                        &mut self.files,
                        &mut self.directories,
                    ))
                }
                Err(e) => {
                    let dev = file_system.unmount();
                    self.dev = Some(dev);
                    return Err(e);
                }
            }
        } else if let Some(file_system) = self.file_system.as_mut() {
            return Ok((file_system, &mut self.files, &mut self.directories));
        } else {
            panic!("neither dev or file_system are set")
        }
    }

    pub fn unmount(&mut self) {
        if let Some(file_system) = self.file_system.take() {
            let dev = file_system.unmount();
            self.dev = Some(dev);
        }
    }
}

pub async fn fs_actor_task<D, const SIZE: usize, const N: usize>(device: D)
where
    D: BlockDevice<SIZE>,
    D::Error: BlockDeviceError,
{
    let mut fs_manager: FsManager<D, SIZE, N> = FsManager::new(device);
    let rx = REQ.receiver();

    loop {
        let Req { op, reply } = rx.receive().await;

        match handle_req(op, &mut fs_manager).await {
            Ok(resp) => {
                ReplyPool::complete(reply, Ok(resp));
            }
            Err(Error::NoCard) => {
                fs_manager.unmount();
                info!("no card, unmounted");
                ReplyPool::complete(reply, Err(Error::NoCard))
            }
            Err(e) => {
                ReplyPool::complete(reply, Err(e));
            }
        }
    }
}

async fn handle_req<D, const SIZE: usize, const N: usize>(
    op: Op,
    fs_manager: &mut FsManager<D, SIZE, N>,
) -> Result<Resp, Error>
where
    D: BlockDevice<SIZE>,
    D::Error: BlockDeviceError,
{
    let (file_system, files, dirs) = fs_manager.mount().await?;

    let resp = match op {
        Op::ReadToString { path } => {
            let data = file_system.read_to_string(&path).await?;
            Resp::ReadToString { data }
        }
        Op::Read { path } => {
            let data = file_system.read(&path).await?;
            Resp::Read { data }
        }
        Op::OpenFile { path, options } => {
            let file = file_system.open(&path, options).await?;
            let handle = FileHandle(files.add(file).unwrap());
            Resp::FileOpen { handle }
        }
        Op::ReadFileToString { handle } => {
            let file = files.get(handle.0)?;
            let data = file.read_to_string(file_system).await?;
            Resp::ReadToString { data }
        }
        Op::ReadFileToEnd { handle } => {
            let file = files.get(handle.0)?;
            let mut data = Vec::new();
            file.read_to_end(file_system, &mut data).await?;
            Resp::Read { data }
        }
        Op::SeekFile { handle, position } => {
            let file = files.get(handle.0)?;
            file.seek(file_system, position).await?;
            Resp::Ok
        }
        Op::ReadFile { handle, len } => {
            let file = files.get(handle.0)?;
            let mut data = vec![0u8; len];
            file.read(file_system, &mut data).await?;
            Resp::Read { data }
        }
        Op::WriteFile { handle, buffer } => {
            let file = files.get(handle.0)?;
            file.write(file_system, &buffer).await?;
            Resp::Ok
        }
        Op::CloseFile { handle } => {
            let file = files.remove(handle.0)?;
            file.close(file_system).await?;
            Resp::Ok
        }
        Op::FlushFile { handle } => {
            let file = files.get(handle.0)?;
            file.flush(file_system).await?;
            Resp::Ok
        }
        Op::Metadata { handle } => {
            let file = files.get(handle.0)?;
            let data = file.metadata();
            Resp::Metadata { data }
        }
        Op::OpenDirectory { path } => {
            let dir = file_system.read_dir(&path).await?;
            let handle = DirectoryHandle(dirs.add(dir).unwrap());
            Resp::DirectoryOpen { handle }
        }
        Op::DirectoryNextEntry { handle } => {
            let dir = dirs.get(handle.0)?;
            let data = dir.next_entry(file_system).await?;
            Resp::DirectoryEntry { data }
        }
        Op::Exists { path } => {
            let exists = file_system.exists(&path).await?;
            Resp::Exists { exists }
        }
        Op::RemoveFile { path } => {
            file_system.remove_file(&path).await?;
            Resp::Ok
        }
        Op::CreateDirectory { path } => {
            file_system.create_directory(&path).await?;
            Resp::Ok
        }
        Op::Copy { from_path, to_path } => {
            file_system.copy(&from_path, &to_path).await?;
            Resp::Ok
        }
        Op::Rename { from_path, to_path } => {
            file_system.rename(&from_path, &to_path).await?;
            Resp::Ok
        }
        Op::RemoveDir { path } => {
            file_system.remove_dir(&path).await?;
            Resp::Ok
        }
        Op::Write { path, buffer } => {
            file_system.write(&path, &buffer).await?;
            Resp::Ok
        }
    };

    Ok(resp)
}