#![forbid(unsafe_op_in_unsafe_fn)]

#[cfg(target_feature = "atomics")]
use crate::io;
use crate::mem;
#[cfg(target_feature = "atomics")]
use crate::num::NonZero;
#[cfg(target_feature = "atomics")]
use crate::sys::os;
use crate::time::Duration;
#[cfg(target_feature = "atomics")]
use crate::{cmp, ptr};

// Add a few symbols not in upstream `libc` just yet.
#[cfg(target_feature = "atomics")]
mod libc {
    pub use libc::*;

    pub use crate::ffi;

    // defined in wasi-libc
    // https://github.com/WebAssembly/wasi-libc/blob/a6f871343313220b76009827ed0153586361c0d5/libc-top-half/musl/include/alltypes.h.in#L108
    #[repr(C)]
    union pthread_attr_union {
        __i: [ffi::c_int; if size_of::<ffi::c_long>() == 8 { 14 } else { 9 }],
        __vi: [ffi::c_int; if size_of::<ffi::c_long>() == 8 { 14 } else { 9 }],
        __s: [ffi::c_ulong; if size_of::<ffi::c_long>() == 8 { 7 } else { 9 }],
    }

    #[repr(C)]
    pub struct pthread_attr_t {
        __u: pthread_attr_union,
    }

    #[allow(non_camel_case_types)]
    pub type pthread_t = *mut ffi::c_void;

    pub const _SC_NPROCESSORS_ONLN: ffi::c_int = 84;

    unsafe extern "C" {
        pub fn pthread_create(
            native: *mut pthread_t,
            attr: *const pthread_attr_t,
            f: extern "C" fn(*mut ffi::c_void) -> *mut ffi::c_void,
            value: *mut ffi::c_void,
        ) -> ffi::c_int;
        pub fn pthread_join(native: pthread_t, value: *mut *mut ffi::c_void) -> ffi::c_int;
        pub fn pthread_attr_init(attrp: *mut pthread_attr_t) -> ffi::c_int;
        pub fn pthread_attr_setstacksize(
            attr: *mut pthread_attr_t,
            stack_size: libc::size_t,
        ) -> ffi::c_int;
        pub fn pthread_attr_destroy(attr: *mut pthread_attr_t) -> ffi::c_int;
        pub fn pthread_detach(thread: pthread_t) -> ffi::c_int;
    }
}

#[cfg(target_feature = "atomics")]
pub struct Thread {
    id: libc::pthread_t,
}

#[cfg(target_feature = "atomics")]
impl Drop for Thread {
    fn drop(&mut self) {
        let ret = unsafe { libc::pthread_detach(self.id) };
        debug_assert_eq!(ret, 0);
    }
}

pub const DEFAULT_MIN_STACK_SIZE: usize = 1024 * 1024;

#[cfg(target_feature = "atomics")]
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> {
        let p = Box::into_raw(Box::new(p));
        let mut native: libc::pthread_t = unsafe { mem::zeroed() };
        let mut attr: libc::pthread_attr_t = unsafe { mem::zeroed() };
        assert_eq!(unsafe { libc::pthread_attr_init(&mut attr) }, 0);

        let stack_size = cmp::max(stack, DEFAULT_MIN_STACK_SIZE);

        match unsafe { libc::pthread_attr_setstacksize(&mut attr, stack_size) } {
            0 => {}
            n => {
                assert_eq!(n, libc::EINVAL);
                // EINVAL means |stack_size| is either too small or not a
                // multiple of the system page size. Because it's definitely
                // >= PTHREAD_STACK_MIN, it must be an alignment issue.
                // Round up to the nearest page and try again.
                let page_size = os::page_size();
                let stack_size =
                    (stack_size + page_size - 1) & (-(page_size as isize - 1) as usize - 1);
                assert_eq!(unsafe { libc::pthread_attr_setstacksize(&mut attr, stack_size) }, 0);
            }
        };

        let ret = unsafe { libc::pthread_create(&mut native, &attr, thread_start, p as *mut _) };
        // Note: if the thread creation fails and this assert fails, then p will
        // be leaked. However, an alternative design could cause double-free
        // which is clearly worse.
        assert_eq!(unsafe { libc::pthread_attr_destroy(&mut attr) }, 0);

        return if ret != 0 {
            // The thread failed to start and as a result p was not consumed. Therefore, it is
            // safe to reconstruct the box so that it gets deallocated.
            unsafe {
                drop(Box::from_raw(p));
            }
            Err(io::Error::from_raw_os_error(ret))
        } else {
            Ok(Thread { id: native })
        };

        extern "C" fn thread_start(main: *mut libc::c_void) -> *mut libc::c_void {
            unsafe {
                // Finally, let's run some code.
                Box::from_raw(main as *mut Box<dyn FnOnce()>)();
            }
            ptr::null_mut()
        }
    }

    pub fn join(self) {
        let id = mem::ManuallyDrop::new(self).id;
        let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
        if ret != 0 {
            rtabort!("failed to join thread: {}", io::Error::from_raw_os_error(ret));
        }
    }
}

#[cfg(target_feature = "atomics")]
pub fn available_parallelism() -> io::Result<NonZero<usize>> {
    match unsafe { libc::sysconf(libc::_SC_NPROCESSORS_ONLN) } {
        -1 => Err(io::Error::last_os_error()),
        cpus => NonZero::new(cpus as usize).ok_or(io::Error::UNKNOWN_THREAD_COUNT),
    }
}

pub fn yield_now() {
    let ret = unsafe { wasi::sched_yield() };
    debug_assert_eq!(ret, Ok(()));
}

pub fn sleep(dur: Duration) {
    let mut nanos = dur.as_nanos();
    while nanos > 0 {
        const USERDATA: wasi::Userdata = 0x0123_45678;

        let clock = wasi::SubscriptionClock {
            id: wasi::CLOCKID_MONOTONIC,
            timeout: u64::try_from(nanos).unwrap_or(u64::MAX),
            precision: 0,
            flags: 0,
        };
        nanos -= u128::from(clock.timeout);

        let in_ = wasi::Subscription {
            userdata: USERDATA,
            u: wasi::SubscriptionU { tag: 0, u: wasi::SubscriptionUU { clock } },
        };
        unsafe {
            let mut event: wasi::Event = mem::zeroed();
            let res = wasi::poll_oneoff(&in_, &mut event, 1);
            match (res, event) {
                (
                    Ok(1),
                    wasi::Event {
                        userdata: USERDATA,
                        error: wasi::ERRNO_SUCCESS,
                        type_: wasi::EVENTTYPE_CLOCK,
                        ..
                    },
                ) => {}
                _ => panic!("thread::sleep(): unexpected result of poll_oneoff"),
            }
        }
    }
}
