// Take a look at the license at the top of the repository in the LICENSE file.

use std::{future::Future, panic, ptr};

use futures_channel::oneshot;

use crate::translate::*;

/// The `GThreadPool` struct represents a thread pool.
///
/// A thread pool is useful when you wish to asynchronously fork out the execution of work
/// and continue working in your own thread. If that will happen often, the overhead of starting
/// and destroying a thread each time might be too high. In such cases reusing already started
/// threads seems like a good idea. And it indeed is, but implementing this can be tedious
/// and error-prone.
///
/// Therefore GLib provides thread pools for your convenience. An added advantage is, that the
/// threads can be shared between the different subsystems of your program, when they are using GLib.
///
/// To create a new thread pool, you use [`new()`][Self::new()].
/// It is destroyed by `GLib::ThreadPool::free()`.
///
/// If you want to execute a certain task within a thread pool, use [`push()`][Self::push()].
///
/// To get the current number of running threads you call [`num_threads()`][Self::num_threads()].
/// To get the number of still unprocessed tasks you call [`unprocessed()`][Self::unprocessed()].
/// To control the maximum number of threads for a thread pool, you use
/// [`max_threads()`][Self::max_threads()]. and [`set_max_threads()`][Self::set_max_threads()].
///
/// Finally you can control the number of unused threads, that are kept alive by GLib for future use.
/// The current number can be fetched with [`num_unused_threads()`][Self::num_unused_threads()].
/// The maximum number can be controlled by [`max_unused_threads()`][Self::max_unused_threads()] and
/// [`set_max_unused_threads()`][Self::set_max_unused_threads()]. All currently unused threads
/// can be stopped by calling [`stop_unused_threads()`][Self::stop_unused_threads()].
#[derive(Debug)]
#[doc(alias = "GThreadPool")]
pub struct ThreadPool(ptr::NonNull<ffi::GThreadPool>);

unsafe impl Send for ThreadPool {}
unsafe impl Sync for ThreadPool {}

// rustdoc-stripper-ignore-next
/// A handle to a thread running on a [`ThreadPool`].
///
/// Like [`std::thread::JoinHandle`] for a GLib thread. The return value from the task can be
/// retrieved by calling [`ThreadHandle::join`]. Dropping the handle "detaches" the thread,
/// allowing it to complete but discarding the return value.
#[derive(Debug)]
pub struct ThreadHandle<T> {
    rx: std::sync::mpsc::Receiver<std::thread::Result<T>>,
}

impl<T> ThreadHandle<T> {
    // rustdoc-stripper-ignore-next
    /// Waits for the associated thread to finish.
    ///
    /// Blocks until the associated thread returns. Returns `Ok` with the value returned from the
    /// thread, or `Err` if the thread panicked. This function will return immediately if the
    /// associated thread has already finished.
    #[inline]
    pub fn join(self) -> std::thread::Result<T> {
        self.rx.recv().unwrap()
    }
}

impl ThreadPool {
    #[doc(alias = "g_thread_pool_new")]
    pub fn shared(max_threads: Option<u32>) -> Result<Self, crate::Error> {
        unsafe {
            let mut err = ptr::null_mut();
            let pool = ffi::g_thread_pool_new(
                Some(spawn_func),
                ptr::null_mut(),
                max_threads.map(|v| v as i32).unwrap_or(-1),
                ffi::GFALSE,
                &mut err,
            );
            if pool.is_null() {
                Err(from_glib_full(err))
            } else {
                Ok(ThreadPool(ptr::NonNull::new_unchecked(pool)))
            }
        }
    }

    #[doc(alias = "g_thread_pool_new")]
    pub fn exclusive(max_threads: u32) -> Result<Self, crate::Error> {
        unsafe {
            let mut err = ptr::null_mut();
            let pool = ffi::g_thread_pool_new(
                Some(spawn_func),
                ptr::null_mut(),
                max_threads as i32,
                ffi::GTRUE,
                &mut err,
            );
            if pool.is_null() {
                Err(from_glib_full(err))
            } else {
                Ok(ThreadPool(ptr::NonNull::new_unchecked(pool)))
            }
        }
    }

    /// Inserts @data into the list of tasks to be executed by @self.
    ///
    /// When the number of currently running threads is lower than the
    /// maximal allowed number of threads, a new thread is started (or
    /// reused) with the properties given to g_thread_pool_new().
    /// Otherwise, @data stays in the queue until a thread in this pool
    /// finishes its previous task and processes @data.
    ///
    /// @error can be [`None`] to ignore errors, or non-[`None`] to report
    /// errors. An error can only occur when a new thread couldn't be
    /// created. In that case @data is simply appended to the queue of
    /// work to do.
    ///
    /// Before version 2.32, this function did not return a success status.
    ///
    /// # Returns
    ///
    /// [`true`] on success, [`false`] if an error occurred
    #[doc(alias = "g_thread_pool_push")]
    pub fn push<T: Send + 'static, F: FnOnce() -> T + Send + 'static>(
        &self,
        func: F,
    ) -> Result<ThreadHandle<T>, crate::Error> {
        let (tx, rx) = std::sync::mpsc::sync_channel(1);
        unsafe {
            let func: Box<dyn FnOnce() + Send + 'static> = Box::new(move || {
                let _ = tx.send(panic::catch_unwind(panic::AssertUnwindSafe(func)));
            });
            let func = Box::new(func);
            let mut err = ptr::null_mut();

            let func = Box::into_raw(func);
            let ret: bool = from_glib(ffi::g_thread_pool_push(
                self.0.as_ptr(),
                func as *mut _,
                &mut err,
            ));
            if ret {
                Ok(ThreadHandle { rx })
            } else {
                let _ = Box::from_raw(func);
                Err(from_glib_full(err))
            }
        }
    }

    pub fn push_future<T: Send + 'static, F: FnOnce() -> T + Send + 'static>(
        &self,
        func: F,
    ) -> Result<impl Future<Output = std::thread::Result<T>> + Send + Sync + 'static, crate::Error>
    {
        let (sender, receiver) = oneshot::channel();

        self.push(move || {
            let _ = sender.send(panic::catch_unwind(panic::AssertUnwindSafe(func)));
        })?;

        Ok(async move { receiver.await.expect("Dropped before executing") })
    }

    /// Sets the maximal allowed number of threads for @self.
    /// A value of -1 means that the maximal number of threads
    /// is unlimited. If @self is an exclusive thread pool, setting
    /// the maximal number of threads to -1 is not allowed.
    ///
    /// Setting @max_threads to 0 means stopping all work for @self.
    /// It is effectively frozen until @max_threads is set to a non-zero
    /// value again.
    ///
    /// A thread is never terminated while calling @func, as supplied by
    /// g_thread_pool_new(). Instead the maximal number of threads only
    /// has effect for the allocation of new threads in g_thread_pool_push().
    /// A new thread is allocated, whenever the number of currently
    /// running threads in @self is smaller than the maximal number.
    ///
    /// @error can be [`None`] to ignore errors, or non-[`None`] to report
    /// errors. An error can only occur when a new thread couldn't be
    /// created.
    ///
    /// Before version 2.32, this function did not return a success status.
    /// ## `max_threads`
    /// a new maximal number of threads for @self,
    ///     or -1 for unlimited
    ///
    /// # Returns
    ///
    /// [`true`] on success, [`false`] if an error occurred
    #[doc(alias = "g_thread_pool_set_max_threads")]
    pub fn set_max_threads(&self, max_threads: Option<u32>) -> Result<(), crate::Error> {
        unsafe {
            let mut err = ptr::null_mut();
            let ret: bool = from_glib(ffi::g_thread_pool_set_max_threads(
                self.0.as_ptr(),
                max_threads.map(|v| v as i32).unwrap_or(-1),
                &mut err,
            ));
            if ret {
                Ok(())
            } else {
                Err(from_glib_full(err))
            }
        }
    }

    /// Returns the maximal number of threads for @self.
    ///
    /// # Returns
    ///
    /// the maximal number of threads
    #[doc(alias = "g_thread_pool_get_max_threads")]
    #[doc(alias = "get_max_threads")]
    pub fn max_threads(&self) -> Option<u32> {
        unsafe {
            let max_threads = ffi::g_thread_pool_get_max_threads(self.0.as_ptr());
            if max_threads == -1 {
                None
            } else {
                Some(max_threads as u32)
            }
        }
    }

    /// Returns the number of threads currently running in @self.
    ///
    /// # Returns
    ///
    /// the number of threads currently running
    #[doc(alias = "g_thread_pool_get_num_threads")]
    #[doc(alias = "get_num_threads")]
    pub fn num_threads(&self) -> u32 {
        unsafe { ffi::g_thread_pool_get_num_threads(self.0.as_ptr()) }
    }

    /// Returns the number of tasks still unprocessed in @self.
    ///
    /// # Returns
    ///
    /// the number of unprocessed tasks
    #[doc(alias = "g_thread_pool_unprocessed")]
    #[doc(alias = "get_unprocessed")]
    pub fn unprocessed(&self) -> u32 {
        unsafe { ffi::g_thread_pool_unprocessed(self.0.as_ptr()) }
    }

    /// Sets the maximal number of unused threads to @max_threads.
    /// If @max_threads is -1, no limit is imposed on the number
    /// of unused threads.
    ///
    /// The default value is 2.
    /// ## `max_threads`
    /// maximal number of unused threads
    #[doc(alias = "g_thread_pool_set_max_unused_threads")]
    pub fn set_max_unused_threads(max_threads: Option<u32>) {
        unsafe {
            ffi::g_thread_pool_set_max_unused_threads(max_threads.map(|v| v as i32).unwrap_or(-1))
        }
    }

    /// Returns the maximal allowed number of unused threads.
    ///
    /// # Returns
    ///
    /// the maximal number of unused threads
    #[doc(alias = "g_thread_pool_get_max_unused_threads")]
    #[doc(alias = "get_max_unused_threads")]
    pub fn max_unused_threads() -> Option<u32> {
        unsafe {
            let max_unused_threads = ffi::g_thread_pool_get_max_unused_threads();
            if max_unused_threads == -1 {
                None
            } else {
                Some(max_unused_threads as u32)
            }
        }
    }

    /// Returns the number of currently unused threads.
    ///
    /// # Returns
    ///
    /// the number of currently unused threads
    #[doc(alias = "g_thread_pool_get_num_unused_threads")]
    #[doc(alias = "get_num_unused_threads")]
    pub fn num_unused_threads() -> u32 {
        unsafe { ffi::g_thread_pool_get_num_unused_threads() }
    }

    /// Stops all currently unused threads. This does not change the
    /// maximal number of unused threads. This function can be used to
    /// regularly stop all unused threads e.g. from g_timeout_add().
    #[doc(alias = "g_thread_pool_stop_unused_threads")]
    pub fn stop_unused_threads() {
        unsafe {
            ffi::g_thread_pool_stop_unused_threads();
        }
    }

    /// This function will set the maximum @interval that a thread
    /// waiting in the pool for new tasks can be idle for before
    /// being stopped. This function is similar to calling
    /// g_thread_pool_stop_unused_threads() on a regular timeout,
    /// except this is done on a per thread basis.
    ///
    /// By setting @interval to 0, idle threads will not be stopped.
    ///
    /// The default value is 15000 (15 seconds).
    /// ## `interval`
    /// the maximum @interval (in milliseconds)
    ///     a thread can be idle
    #[doc(alias = "g_thread_pool_set_max_idle_time")]
    pub fn set_max_idle_time(max_idle_time: u32) {
        unsafe { ffi::g_thread_pool_set_max_idle_time(max_idle_time) }
    }

    /// This function will return the maximum @interval that a
    /// thread will wait in the thread pool for new tasks before
    /// being stopped.
    ///
    /// If this function returns 0, threads waiting in the thread
    /// pool for new work are not stopped.
    ///
    /// # Returns
    ///
    /// the maximum @interval (milliseconds) to wait
    ///     for new tasks in the thread pool before stopping the
    ///     thread
    #[doc(alias = "g_thread_pool_get_max_idle_time")]
    #[doc(alias = "get_max_idle_time")]
    pub fn max_idle_time() -> u32 {
        unsafe { ffi::g_thread_pool_get_max_idle_time() }
    }
}

impl Drop for ThreadPool {
    #[inline]
    fn drop(&mut self) {
        unsafe {
            ffi::g_thread_pool_free(self.0.as_ptr(), ffi::GFALSE, ffi::GTRUE);
        }
    }
}

unsafe extern "C" fn spawn_func(func: ffi::gpointer, _data: ffi::gpointer) {
    let func: Box<Box<dyn FnOnce()>> = Box::from_raw(func as *mut _);
    func()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_push() {
        use std::sync::mpsc;

        let p = ThreadPool::exclusive(1).unwrap();
        let (sender, receiver) = mpsc::channel();

        let handle = p
            .push(move || {
                sender.send(true).unwrap();
                123
            })
            .unwrap();

        assert_eq!(handle.join().unwrap(), 123);
        assert_eq!(receiver.recv(), Ok(true));
    }

    #[test]
    fn test_push_future() {
        let c = crate::MainContext::new();
        let p = ThreadPool::shared(None).unwrap();

        let fut = p.push_future(|| true).unwrap();

        let res = c.block_on(fut);
        assert!(res.unwrap());
    }
}