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// Copyright 2020 Jean Pierre Dudey. See the LICENSE-MIT and
// LICENSE-APACHE files at the top-level directory of this
// distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! # tokio-udev
//!
//! This library implements an stream of device events from `udev`
//! asynchronously.
//!
//! # Usage
//!
//! First put the dependency on your crate's `Cargo.toml`. For example:
//!
//! ```toml
//! [dependencies]
//! tokio-udev = "0.1"
//! ```
//!
//! Then import it in your crate root as:
//!
//! ```rust
//! use tokio_udev;
//! ```

#![cfg(target_os = "linux")]

pub use mio_udev::{
    Attribute, Attributes, Device, Enumerator, Event, EventType, Properties,
    Property,
};

use futures_core::stream::Stream;
use std::ffi::OsStr;
use std::io;
use std::pin::Pin;
use std::sync::Mutex;
use std::task::Poll;
use tokio::io::unix::AsyncFd;

/// Monitors for device events.
///
/// A monitor communicates with the kernel over a socket. Filtering events is
/// performed efficiently in the kernel, and only events that match the filters
/// are received by the socket. Filters must be setup before listening for
/// events.
pub struct MonitorBuilder {
    builder: mio_udev::MonitorBuilder,
}

impl MonitorBuilder {
    /// Creates a new `MonitorSocket`.
    #[inline(always)]
    pub fn new() -> io::Result<Self> {
        Ok(MonitorBuilder {
            builder: mio_udev::MonitorBuilder::new()?,
        })
    }

    fn map(builder: mio_udev::MonitorBuilder) -> Self {
        MonitorBuilder { builder }
    }

    /// Adds a filter that matches events for devices with the given subsystem.
    #[inline(always)]
    pub fn match_subsystem<T>(self, subsystem: T) -> io::Result<Self>
    where
        T: AsRef<OsStr>,
    {
        self.builder.match_subsystem::<T>(subsystem).map(Self::map)
    }

    /// Adds a filter that matches events for devices with the given subsystem
    /// and device type.
    #[inline(always)]
    pub fn match_subsystem_devtype<T, U>(
        self,
        subsystem: T,
        devtype: U,
    ) -> io::Result<Self>
    where
        T: AsRef<OsStr>,
        U: AsRef<OsStr>,
    {
        self.builder
            .match_subsystem_devtype::<T, U>(subsystem, devtype)
            .map(Self::map)
    }

    /// Adds a filter that matches events for devices with the given tag.
    #[inline(always)]
    pub fn match_tag<T>(self, tag: T) -> io::Result<Self>
    where
        T: AsRef<OsStr>,
    {
        self.builder.match_tag::<T>(tag).map(Self::map)
    }

    /// Removes all filters currently set on the monitor.
    #[inline(always)]
    pub fn clear_filters(self) -> io::Result<Self> {
        self.builder.clear_filters().map(Self::map)
    }

    /// Listens for events matching the current filters.
    ///
    /// This method consumes the `MonitorBuilder`.
    pub fn listen(self) -> io::Result<MonitorSocket> {
        MonitorSocket::new(self.builder.listen()?)
    }
}

/// Asynchronous stream of device events.
pub struct MonitorSocket {
    inner: Mutex<Inner>,
}

impl MonitorSocket {
    fn new(monitor: mio_udev::MonitorSocket) -> io::Result<MonitorSocket> {
        Ok(MonitorSocket {
            inner: Mutex::new(Inner::new(monitor)?),
        })
    }
}

unsafe impl Send for MonitorSocket {}
unsafe impl Sync for MonitorSocket {}

impl Stream for MonitorSocket {
    type Item = Result<mio_udev::Event, io::Error>;

    fn poll_next(
        self: Pin<&mut Self>,
        ctx: &mut std::task::Context,
    ) -> Poll<Option<Self::Item>> {
        self.inner.lock().unwrap().poll_receive(ctx)
    }
}

struct Inner {
    fd: AsyncFd<mio_udev::MonitorSocket>,
}

impl Inner {
    fn new(monitor: mio_udev::MonitorSocket) -> io::Result<Inner> {
        Ok(Inner {
            fd: AsyncFd::new(monitor)?,
        })
    }

    fn poll_receive(
        &mut self,
        ctx: &mut std::task::Context,
    ) -> Poll<Option<Result<mio_udev::Event, io::Error>>> {
        match self.fd.poll_read_ready(ctx) {
            Poll::Ready(Ok(mut ready_guard)) => {
                ready_guard.clear_ready();
                Poll::Ready(self.fd.get_mut().next().map(Ok))
            }
            Poll::Ready(Err(err)) => Poll::Ready(Some(Err(err))),
            Poll::Pending => Poll::Pending,
        }
    }
}