use core::ops::{Range, RangeBounds};
use core::{ptr, slice};
use super::Vec;
use crate::alloc::{Allocator, Global};
#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
#[derive(Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
pub struct ExtractIf<
    'a,
    T,
    F,
    #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> {
    vec: &'a mut Vec<T, A>,
    idx: usize,
    end: usize,
    del: usize,
    old_len: usize,
    pred: F,
}
impl<'a, T, F, A: Allocator> ExtractIf<'a, T, F, A> {
    pub(super) fn new<R: RangeBounds<usize>>(vec: &'a mut Vec<T, A>, pred: F, range: R) -> Self {
        let old_len = vec.len();
        let Range { start, end } = slice::range(range, ..old_len);
        unsafe {
            vec.set_len(0);
        }
        ExtractIf { vec, idx: start, del: 0, end, old_len, pred }
    }
    #[unstable(feature = "allocator_api", issue = "32838")]
    #[inline]
    pub fn allocator(&self) -> &A {
        self.vec.allocator()
    }
}
#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
impl<T, F, A: Allocator> Iterator for ExtractIf<'_, T, F, A>
where
    F: FnMut(&mut T) -> bool,
{
    type Item = T;
    fn next(&mut self) -> Option<T> {
        unsafe {
            while self.idx < self.end {
                let i = self.idx;
                let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
                let drained = (self.pred)(&mut v[i]);
                self.idx += 1;
                if drained {
                    self.del += 1;
                    return Some(ptr::read(&v[i]));
                } else if self.del > 0 {
                    let del = self.del;
                    let src: *const T = &v[i];
                    let dst: *mut T = &mut v[i - del];
                    ptr::copy_nonoverlapping(src, dst, 1);
                }
            }
            None
        }
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        (0, Some(self.end - self.idx))
    }
}
#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
impl<T, F, A: Allocator> Drop for ExtractIf<'_, T, F, A> {
    fn drop(&mut self) {
        unsafe {
            if self.idx < self.old_len && self.del > 0 {
                let ptr = self.vec.as_mut_ptr();
                let src = ptr.add(self.idx);
                let dst = src.sub(self.del);
                let tail_len = self.old_len - self.idx;
                src.copy_to(dst, tail_len);
            }
            self.vec.set_len(self.old_len - self.del);
        }
    }
}