use crate::ffi::CStr;
use crate::io;
use crate::num::NonZero;
use crate::sys::unsupported;
use crate::time::{Duration, Instant};

pub struct Thread(!);

pub const DEFAULT_MIN_STACK_SIZE: usize = 1024 * 1024;

impl Thread {
    // unsafe: see thread::Builder::spawn_unchecked for safety requirements
    pub unsafe fn new(
        _stack: usize,
        _name: Option<&str>,
        _p: Box<dyn FnOnce()>,
    ) -> io::Result<Thread> {
        unsupported()
    }

    pub fn yield_now() {}

    pub fn set_name(_name: &CStr) {}

    pub fn sleep(dur: Duration) {
        #[cfg(target_arch = "wasm32")]
        use core::arch::wasm32 as wasm;
        #[cfg(target_arch = "wasm64")]
        use core::arch::wasm64 as wasm;

        use crate::cmp;

        // Use an atomic wait to block the current thread artificially with a
        // timeout listed. Note that we should never be notified (return value
        // of 0) or our comparison should never fail (return value of 1) so we
        // should always only resume execution through a timeout (return value
        // 2).
        let mut nanos = dur.as_nanos();
        while nanos > 0 {
            let amt = cmp::min(i64::MAX as u128, nanos);
            let mut x = 0;
            let val = unsafe { wasm::memory_atomic_wait32(&mut x, 0, amt as i64) };
            debug_assert_eq!(val, 2);
            nanos -= amt;
        }
    }

    pub fn sleep_until(deadline: Instant) {
        let now = Instant::now();

        if let Some(delay) = deadline.checked_duration_since(now) {
            Self::sleep(delay);
        }
    }

    pub fn join(self) {}
}

pub fn available_parallelism() -> io::Result<NonZero<usize>> {
    unsupported()
}

pub mod guard {
    pub type Guard = !;
    pub unsafe fn current() -> Option<Guard> {
        None
    }
    pub unsafe fn init() -> Option<Guard> {
        None
    }
}