use crate::num::NonZero;
use crate::thread::ThreadInit;
use crate::time::Duration;
use crate::{io, ptr};

pub type Tid = hermit_abi::Tid;

pub struct Thread {
    tid: Tid,
}

unsafe impl Send for Thread {}
unsafe impl Sync for Thread {}

pub const DEFAULT_MIN_STACK_SIZE: usize = 1 << 20;

impl Thread {
    pub unsafe fn new_with_coreid(
        stack: usize,
        init: Box<ThreadInit>,
        core_id: isize,
    ) -> io::Result<Thread> {
        let data = Box::into_raw(init);
        let tid = unsafe {
            hermit_abi::spawn2(
                thread_start,
                data.expose_provenance(),
                hermit_abi::Priority::into(hermit_abi::NORMAL_PRIO),
                stack,
                core_id,
            )
        };

        return if tid == 0 {
            // The thread failed to start and as a result data was not consumed. Therefore, it is
            // safe to reconstruct the box so that it gets deallocated.
            unsafe {
                drop(Box::from_raw(data));
            }
            Err(io::const_error!(io::ErrorKind::Uncategorized, "unable to create thread!"))
        } else {
            Ok(Thread { tid })
        };

        extern "C" fn thread_start(data: usize) {
            // SAFETY: we are simply recreating the box that was leaked earlier.
            let init =
                unsafe { Box::from_raw(ptr::with_exposed_provenance_mut::<ThreadInit>(data)) };
            let rust_start = init.init();
            rust_start();

            // Run all destructors.
            unsafe {
                crate::sys::thread_local::destructors::run();
            }
            crate::rt::thread_cleanup();
        }
    }

    pub unsafe fn new(stack: usize, init: Box<ThreadInit>) -> io::Result<Thread> {
        unsafe {
            Thread::new_with_coreid(stack, init, -1 /* = no specific core */)
        }
    }

    pub fn join(self) {
        unsafe {
            let _ = hermit_abi::join(self.tid);
        }
    }
}

pub fn available_parallelism() -> io::Result<NonZero<usize>> {
    unsafe { Ok(NonZero::new_unchecked(hermit_abi::available_parallelism())) }
}

#[inline]
pub fn sleep(dur: Duration) {
    let micros = dur.as_micros() + if dur.subsec_nanos() % 1_000 > 0 { 1 } else { 0 };
    let micros = u64::try_from(micros).unwrap_or(u64::MAX);

    unsafe {
        hermit_abi::usleep(micros);
    }
}

#[inline]
pub fn yield_now() {
    unsafe {
        hermit_abi::yield_now();
    }
}