use task::{Task, Queue};
use worker_state::{
    WorkerState,
    WORKER_SHUTDOWN,
    WORKER_SLEEPING,
};

use std::cell::UnsafeCell;
use std::sync::atomic::Ordering::{AcqRel};
use std::sync::atomic::AtomicUsize;
use std::sync::{Mutex, Condvar};

use deque;

#[derive(Debug)]
pub(crate) struct WorkerEntry {
    // Worker state. This is mutated when notifying the worker.
    pub state: AtomicUsize,

    // Next entry in the parked Trieber stack
    next_sleeper: UnsafeCell<usize>,

    // Worker half of deque
    pub deque: deque::Deque<Task>,

    // Stealer half of deque
    pub steal: deque::Stealer<Task>,

    // Park mutex
    pub park_mutex: Mutex<()>,

    // Park condvar
    pub park_condvar: Condvar,

    // MPSC queue of jobs submitted to the worker from an external source.
    pub inbound: Queue,
}

impl WorkerEntry {
    pub fn new() -> Self {
        let w = deque::Deque::new();
        let s = w.stealer();

        WorkerEntry {
            state: AtomicUsize::new(WorkerState::default().into()),
            next_sleeper: UnsafeCell::new(0),
            deque: w,
            steal: s,
            inbound: Queue::new(),
            park_mutex: Mutex::new(()),
            park_condvar: Condvar::new(),
        }
    }

    #[inline]
    pub fn submit_internal(&self, task: Task) {
        self.push_internal(task);
    }

    /// Submits a task to the worker. This assumes that the caller is external
    /// to the worker. Internal submissions go through another path.
    ///
    /// Returns `false` if the worker needs to be spawned.
    pub fn submit_external(&self, task: Task, mut state: WorkerState) -> bool {
        // Push the task onto the external queue
        self.push_external(task);

        loop {
            let mut next = state;
            next.notify();

            let actual = self.state.compare_and_swap(
                state.into(), next.into(),
                AcqRel).into();

            if state == actual {
                break;
            }

            state = actual;
        }

        match state.lifecycle() {
            WORKER_SLEEPING => {
                // The worker is currently sleeping, the condition variable must
                // be signaled
                self.wakeup();
                true
            }
            WORKER_SHUTDOWN => false,
            _ => true,
        }
    }

    #[inline]
    fn push_external(&self, task: Task) {
        self.inbound.push(task);
    }

    #[inline]
    pub fn push_internal(&self, task: Task) {
        self.deque.push(task);
    }

    #[inline]
    pub fn wakeup(&self) {
        let _lock = self.park_mutex.lock().unwrap();
        self.park_condvar.notify_one();
    }

    #[inline]
    pub fn next_sleeper(&self) -> usize {
        unsafe { *self.next_sleeper.get() }
    }

    #[inline]
    pub fn set_next_sleeper(&self, val: usize) {
        unsafe { *self.next_sleeper.get() = val; }
    }
}