#![cfg(any(
    target_os = "linux",
    target_os = "android",
    all(target_os = "emscripten", target_feature = "atomics"),
    target_os = "freebsd",
    target_os = "openbsd",
    target_os = "dragonfly",
    target_os = "fuchsia",
))]

use crate::sync::atomic::AtomicU32;
use crate::time::Duration;

/// 等待 futex_wake 操作唤醒我们。
///
/// 如果 futex 不包含预期值，则直接返回。
///
/// 在超时时返回 false，在所有其他情况下返回 true。
#[cfg(any(target_os = "linux", target_os = "android", target_os = "freebsd"))]
pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
    use super::time::Timespec;
    use crate::ptr::null;
    use crate::sync::atomic::Ordering::Relaxed;

    // 将超时计算为绝对时间规格。
    //
    // 溢出四舍五入到无限超时 (None)。
    let timespec = timeout
        .and_then(|d| Timespec::now(libc::CLOCK_MONOTONIC).checked_add_duration(&d))
        .and_then(|t| t.to_timespec());

    loop {
        // 如果值已经改变，则无需等待。
        if futex.load(Relaxed) != expected {
            return true;
        }

        let r = unsafe {
            cfg_if::cfg_if! {
                if #[cfg(target_os = "freebsd")] {
                    // FreeBSD 没有 futex()，但有 _umtx_op(UMTX_OP_WAIT_UINT_PRIVATE)，几乎相同。
                    // 它通过 _umtx_time 结构体中的标志支持绝对超时。
                    //
                    //
                    let umtx_timeout = timespec.map(|t| libc::_umtx_time {
                        _timeout: t,
                        _flags: libc::UMTX_ABSTIME,
                        _clockid: libc::CLOCK_MONOTONIC as u32,
                    });
                    let umtx_timeout_ptr = umtx_timeout.as_ref().map_or(null(), |t| t as *const _);
                    let umtx_timeout_size = umtx_timeout.as_ref().map_or(0, |t| crate::mem::size_of_val(t));
                    libc::_umtx_op(
                        futex as *const AtomicU32 as *mut _,
                        libc::UMTX_OP_WAIT_UINT_PRIVATE,
                        expected as libc::c_ulong,
                        crate::ptr::invalid_mut(umtx_timeout_size),
                        umtx_timeout_ptr as *mut _,
                    )
                } else if #[cfg(any(target_os = "linux", target_os = "android"))] {
                    // 使用 FUTEX_WAIT_BITSET 而不是 FUTEX_WAIT 能够给出绝对时间而不是相对时间。
                    //
                    libc::syscall(
                        libc::SYS_futex,
                        futex as *const AtomicU32,
                        libc::FUTEX_WAIT_BITSET | libc::FUTEX_PRIVATE_FLAG,
                        expected,
                        timespec.as_ref().map_or(null(), |t| t as *const libc::timespec),
                        null::<u32>(), // 该参数未用于 FUTEX_WAIT_BITSET。
                        !0u32,         // 一个完整的位掩码，使其表现得像一个普通的 FUTEX_WAIT。
                    )
                } else {
                    compile_error!("unknown target_os");
                }
            }
        };

        match (r < 0).then(super::os::errno) {
            Some(libc::ETIMEDOUT) => return false,
            Some(libc::EINTR) => continue,
            _ => return true,
        }
    }
}

/// 在这个 futex 上唤醒一个在 futex_wait 上被阻塞的线程。
///
/// 如果这实际上唤醒了这样一个线程，则返回 true，如果没有线程在此 futex 上等待，则返回 false。
///
///
/// 在某些平台上，这总是返回 false。
#[cfg(any(target_os = "linux", target_os = "android"))]
pub fn futex_wake(futex: &AtomicU32) -> bool {
    let ptr = futex as *const AtomicU32;
    let op = libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG;
    unsafe { libc::syscall(libc::SYS_futex, ptr, op, 1) > 0 }
}

/// 唤醒在这个 futex 上等待 futex_wait 的所有线程。
#[cfg(any(target_os = "linux", target_os = "android"))]
pub fn futex_wake_all(futex: &AtomicU32) {
    let ptr = futex as *const AtomicU32;
    let op = libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG;
    unsafe {
        libc::syscall(libc::SYS_futex, ptr, op, i32::MAX);
    }
}

// FreeBSD 没有告诉我们有多少线程被唤醒，所以它总是返回 false。
#[cfg(target_os = "freebsd")]
pub fn futex_wake(futex: &AtomicU32) -> bool {
    use crate::ptr::null_mut;
    unsafe {
        libc::_umtx_op(
            futex as *const AtomicU32 as *mut _,
            libc::UMTX_OP_WAKE_PRIVATE,
            1,
            null_mut(),
            null_mut(),
        )
    };
    false
}

#[cfg(target_os = "freebsd")]
pub fn futex_wake_all(futex: &AtomicU32) {
    use crate::ptr::null_mut;
    unsafe {
        libc::_umtx_op(
            futex as *const AtomicU32 as *mut _,
            libc::UMTX_OP_WAKE_PRIVATE,
            i32::MAX as libc::c_ulong,
            null_mut(),
            null_mut(),
        )
    };
}

#[cfg(target_os = "openbsd")]
pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
    use super::time::Timespec;
    use crate::ptr::{null, null_mut};

    // 溢出四舍五入到无限超时 (None)。
    let timespec = timeout
        .and_then(|d| Timespec::zero().checked_add_duration(&d))
        .and_then(|t| t.to_timespec());

    let r = unsafe {
        libc::futex(
            futex as *const AtomicU32 as *mut u32,
            libc::FUTEX_WAIT,
            expected as i32,
            timespec.as_ref().map_or(null(), |t| t as *const libc::timespec),
            null_mut(),
        )
    };

    r == 0 || super::os::errno() != libc::ETIMEDOUT
}

#[cfg(target_os = "openbsd")]
pub fn futex_wake(futex: &AtomicU32) -> bool {
    use crate::ptr::{null, null_mut};
    unsafe {
        libc::futex(futex as *const AtomicU32 as *mut u32, libc::FUTEX_WAKE, 1, null(), null_mut())
            > 0
    }
}

#[cfg(target_os = "openbsd")]
pub fn futex_wake_all(futex: &AtomicU32) {
    use crate::ptr::{null, null_mut};
    unsafe {
        libc::futex(
            futex as *const AtomicU32 as *mut u32,
            libc::FUTEX_WAKE,
            i32::MAX,
            null(),
            null_mut(),
        );
    }
}

#[cfg(target_os = "dragonfly")]
pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
    // 超时 0 表示无限。
    // 我们将较小的超时舍入到 1 毫秒。
    // 溢出被四舍五入到无限超时。
    let timeout_ms =
        timeout.and_then(|d| Some(i32::try_from(d.as_millis()).ok()?.max(1))).unwrap_or(0);

    let r = unsafe {
        libc::umtx_sleep(futex as *const AtomicU32 as *const i32, expected as i32, timeout_ms)
    };

    r == 0 || super::os::errno() != libc::ETIMEDOUT
}

// DragonflyBSD 没有告诉我们有多少线程被唤醒，所以它总是返回 false。
#[cfg(target_os = "dragonfly")]
pub fn futex_wake(futex: &AtomicU32) -> bool {
    unsafe { libc::umtx_wakeup(futex as *const AtomicU32 as *const i32, 1) };
    false
}

#[cfg(target_os = "dragonfly")]
pub fn futex_wake_all(futex: &AtomicU32) {
    unsafe { libc::umtx_wakeup(futex as *const AtomicU32 as *const i32, i32::MAX) };
}

#[cfg(target_os = "emscripten")]
extern "C" {
    fn emscripten_futex_wake(addr: *const AtomicU32, count: libc::c_int) -> libc::c_int;
    fn emscripten_futex_wait(
        addr: *const AtomicU32,
        val: libc::c_uint,
        max_wait_ms: libc::c_double,
    ) -> libc::c_int;
}

#[cfg(target_os = "emscripten")]
pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
    unsafe {
        emscripten_futex_wait(
            futex,
            expected,
            timeout.map_or(f64::INFINITY, |d| d.as_secs_f64() * 1000.0),
        ) != -libc::ETIMEDOUT
    }
}

#[cfg(target_os = "emscripten")]
pub fn futex_wake(futex: &AtomicU32) -> bool {
    unsafe { emscripten_futex_wake(futex, 1) > 0 }
}

#[cfg(target_os = "emscripten")]
pub fn futex_wake_all(futex: &AtomicU32) {
    unsafe { emscripten_futex_wake(futex, i32::MAX) };
}

#[cfg(target_os = "fuchsia")]
pub mod zircon {
    pub type zx_futex_t = crate::sync::atomic::AtomicU32;
    pub type zx_handle_t = u32;
    pub type zx_status_t = i32;
    pub type zx_time_t = i64;

    pub const ZX_HANDLE_INVALID: zx_handle_t = 0;

    pub const ZX_TIME_INFINITE: zx_time_t = zx_time_t::MAX;

    pub const ZX_OK: zx_status_t = 0;
    pub const ZX_ERR_INVALID_ARGS: zx_status_t = -10;
    pub const ZX_ERR_BAD_HANDLE: zx_status_t = -11;
    pub const ZX_ERR_WRONG_TYPE: zx_status_t = -12;
    pub const ZX_ERR_BAD_STATE: zx_status_t = -20;
    pub const ZX_ERR_TIMED_OUT: zx_status_t = -21;

    extern "C" {
        pub fn zx_clock_get_monotonic() -> zx_time_t;
        pub fn zx_futex_wait(
            value_ptr: *const zx_futex_t,
            current_value: zx_futex_t,
            new_futex_owner: zx_handle_t,
            deadline: zx_time_t,
        ) -> zx_status_t;
        pub fn zx_futex_wake(value_ptr: *const zx_futex_t, wake_count: u32) -> zx_status_t;
        pub fn zx_futex_wake_single_owner(value_ptr: *const zx_futex_t) -> zx_status_t;
        pub fn zx_thread_self() -> zx_handle_t;
    }
}

#[cfg(target_os = "fuchsia")]
pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
    // 如果超时时间长于 i64 的大小，则永远休眠。
    let deadline = timeout
        .and_then(|d| {
            i64::try_from(d.as_nanos())
                .ok()?
                .checked_add(unsafe { zircon::zx_clock_get_monotonic() })
        })
        .unwrap_or(zircon::ZX_TIME_INFINITE);

    unsafe {
        zircon::zx_futex_wait(futex, AtomicU32::new(expected), zircon::ZX_HANDLE_INVALID, deadline)
            != zircon::ZX_ERR_TIMED_OUT
    }
}

// Fuchsia 没有告诉我们有多少线程被唤醒，所以它总是返回 false。
#[cfg(target_os = "fuchsia")]
pub fn futex_wake(futex: &AtomicU32) -> bool {
    unsafe { zircon::zx_futex_wake(futex, 1) };
    false
}

#[cfg(target_os = "fuchsia")]
pub fn futex_wake_all(futex: &AtomicU32) {
    unsafe { zircon::zx_futex_wake(futex, u32::MAX) };
}