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use crate::guard::guard_on_unwind;
use crate::{SinglePlace, SlicePlace};

use core::{mem, slice};

use rust_alloc::alloc::Layout;
use rust_alloc::alloc::{alloc, alloc_zeroed, dealloc, handle_alloc_error};
use rust_alloc::boxed::Box;

#[inline]
unsafe fn emplace(
    layout: Layout,
    a: unsafe fn(Layout) -> *mut u8,
    f: impl FnOnce(*mut ()),
) -> *mut () {
    if layout.size() == 0 {
        let ptr = layout.align() as *mut ();
        f(ptr);
        return ptr;
    }

    let ptr = a(layout).cast::<()>();
    if ptr.is_null() {
        handle_alloc_error(layout)
    }
    guard_on_unwind(|| f(ptr), || dealloc(ptr.cast(), layout));
    ptr
}

/// Allocates memory and initialize it.
#[inline]
pub fn emplace_with(layout: Layout, f: impl FnOnce(*mut ())) -> *mut () {
    unsafe { emplace(layout, alloc, f) }
}

/// Allocates zeroed memory and initialize it.
#[inline]
pub fn emplace_zeroed_with(layout: Layout, f: impl FnOnce(*mut ())) -> *mut () {
    unsafe { emplace(layout, alloc_zeroed, f) }
}

impl<T> SinglePlace<T> for Box<T> {
    unsafe fn emplace_with(f: impl FnOnce(&mut mem::MaybeUninit<T>)) -> Self {
        let ptr = emplace_with(Layout::new::<T>(), |ptr| f(&mut *ptr.cast()));
        Self::from_raw(ptr.cast())
    }

    unsafe fn emplace_zeroed_with(f: impl FnOnce(&mut mem::MaybeUninit<T>)) -> Self {
        let ptr = emplace_zeroed_with(Layout::new::<T>(), |ptr| f(&mut *ptr.cast()));
        Self::from_raw(ptr.cast())
    }
}

impl<T> SlicePlace<T> for Box<[T]> {
    unsafe fn emplace_with(len: usize, f: impl FnOnce(&mut [mem::MaybeUninit<T>])) -> Self {
        let layout = Layout::array::<T>(len).expect("invalid layout");
        let ptr = emplace_with(layout, |ptr| f(slice::from_raw_parts_mut(ptr.cast(), len)));
        Self::from_raw(slice::from_raw_parts_mut(ptr.cast(), len))
    }

    unsafe fn emplace_zeroed_with(len: usize, f: impl FnOnce(&mut [mem::MaybeUninit<T>])) -> Self {
        let layout = Layout::array::<T>(len).expect("invalid layout");
        let ptr = emplace_zeroed_with(layout, |ptr| f(slice::from_raw_parts_mut(ptr.cast(), len)));
        Self::from_raw(slice::from_raw_parts_mut(ptr.cast(), len))
    }
}