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use std::thread::{self, JoinHandle};

#[cfg(target_os = "linux")]
use libc::{
    c_int, cpu_set_t, sched_get_priority_max, sched_get_priority_min,
    sched_param, sched_setaffinity, sched_setscheduler, CPU_SET,
    CPU_ZERO, SCHED_FIFO,
};

#[cfg(target_os = "linux")]
use rand::Rng;

use super::*;

#[cfg(target_os = "linux")]
const POLICY: c_int = SCHED_FIFO;

#[cfg(target_os = "linux")]
pub fn prioritize(prio: c_int) {
    pin_cpu();

    let param = sched_param {
        sched_priority: prio,
    };
    let ret = unsafe {
        sched_setscheduler(0, POLICY, &param as *const sched_param)
    };

    assert_eq!(
        ret,
        0,
        "setscheduler is expected to return zero, was {}: {:?}",
        ret,
        std::io::Error::last_os_error()
    );

    thread::yield_now();
}

#[cfg(target_os = "linux")]
fn pin_cpu() {
    unsafe {
        let mut cpu_set: cpu_set_t = std::mem::zeroed();
        CPU_ZERO(&mut cpu_set);
        CPU_SET(0, &mut cpu_set);
        let ret =
            sched_setaffinity(0, 1, &cpu_set as *const cpu_set_t);
        assert_eq!(
            ret,
            0,
            "sched_setaffinity is expected to return 0, was {}: {:?}",
            ret,
            std::io::Error::last_os_error()
        );
    }
}

/// Spawn a thread with a thread priority determined by a
/// (possibly pre-seeded) `rand::Rng`.
#[cfg(target_os = "linux")]
pub fn spawn_with_random_prio<F, T>(f: F) -> JoinHandle<T>
where
    F: FnOnce() -> T,
    F: Send + 'static,
    T: Send + 'static,
{
    let min = unsafe { sched_get_priority_min(POLICY) };
    let max = unsafe { sched_get_priority_max(POLICY) };

    prioritize(thread_rng().gen_range(min, max));

    let prio = thread_rng().gen_range(min, max);

    let context = context();

    thread::spawn(move || {
        prioritize(prio);

        set_context(context);

        f()
    })
}

/// Spawn a thread with a specific realtime priority.
#[cfg(target_os = "linux")]
pub fn spawn_with_prio<F, T>(prio: c_int, f: F) -> JoinHandle<T>
where
    F: FnOnce() -> T,
    F: Send + 'static,
    T: Send + 'static,
{
    let context = context();

    thread::spawn(move || {
        prioritize(prio);

        set_context(context);

        f()
    })
}

/// Spawn a thread and transfer the deterministic Context.
pub fn spawn<F, T>(f: F) -> JoinHandle<T>
where
    F: FnOnce() -> T,
    F: Send + 'static,
    T: Send + 'static,
{
    let context = context();

    thread::spawn(move || {
        set_context(context);

        f()
    })
}

#[test]
fn ensure_context_is_inherited() {
    use std::ops::Add;
    use std::time::Duration;

    let time = UNIX_EPOCH.add(Duration::from_millis(55));
    context::set_time(time.clone());

    let child_time = spawn(|| context::now())
        .join()
        .expect("child should not crash");

    assert_eq!(time, child_time);
}

#[test]
#[ignore]
#[cfg(target_os = "linux")]
fn gogogo() {
    fn f1() {
        for _ in 0..10 {
            println!("1");
        }
    }
    fn f2() {
        for _ in 0..10 {
            println!("2");
        }
    }
    fn f3() {
        for _ in 0..10 {
            println!("3");
        }
    }

    // it's important to prioritize the spawner!
    prioritize(4);

    let threads = vec![
        spawn_with_prio(3, f1),
        spawn_with_prio(2, f2),
        spawn_with_prio(1, f3),
    ];

    for t in threads.into_iter() {
        t.join().unwrap();
    }
}