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use std::borrow::BorrowMut;
use std::ops::Deref;

#[cfg(feature = "std")]
use anchor::BoxAnchor;
use anchor::{Anchor, IdentityAnchor, StackAnchor};
use RefMove;

/// Anchored by-move borrowing.
///
/// This is different from [`BorrowMove`][BorrowMove] in that the user has to
/// provide an **anchored** self when invoking [`borrow_move`][borrow_move].
///
/// This extra step is required to achieve safe by-move borrowing.
/// The point is that it's caller's responsibility to ensure the space is
/// valid until `'a` expires.
///
/// [BorrowMove]: trait.BorrowMove.html
/// [borrow_move]: ../anchor/trait.Anchor.html#tymethod.borrow_move
pub trait BorrowInterior<Borrowed: ?Sized>: BorrowMut<Borrowed> + Sized {
    /// The anchor type we use for this pair of borrowing.
    type Anchor: Anchor<Self, Borrowed>;
}

impl<T> BorrowInterior<T> for T {
    type Anchor = StackAnchor<T>;
}

impl<'a, T: ?Sized> BorrowInterior<T> for RefMove<'a, T> {
    type Anchor = IdentityAnchor<'a, T>;
}

// TODO: make T: ?Sized once rust-lang/rust#53033 lands
#[cfg(feature = "std")]
impl<T> BorrowInterior<T> for Box<T> {
    type Anchor = BoxAnchor<T>;
}

/// Provides `anchor` and `anchor_box` methods.
pub trait AnchorExt: Sized {
    /// Wraps the value by `StackAnchor`.
    /// With `#![feature(nll)]` enabled you can write `.anchor().borrow_move()`
    /// to create `RefMove` pointing to the stack.
    fn anchor(self) -> StackAnchor<Self> {
        StackAnchor::anchor_from(self)
    }

    /// Wraps the value by `BoxAnchor` or `IdentityAnchor`.
    /// With `#![feature(nll)]` enabled you can write `.anchor_box().borrow_move()`
    /// to create `RefMove` pointing to the heap.
    fn anchor_box(self) -> Self::Anchor
    where
        Self: Deref,
        Self: BorrowInterior<<Self as Deref>::Target>,
    {
        Self::Anchor::anchor_from(self)
    }
}

impl<T> AnchorExt for T {}

/// Unanchored by-move reborrowing.
///
/// Unlike [`BorrowInterior`][BorrowInterior] the definition of `BorrowMove`
/// is similar to the one in `BorrowMut` and very straightforward.
///
/// However, it cannot provide a *starting point* of the by-move borrowing,
/// namely getting `RefMove<T>` from `T` or `Box<T>`.
///
/// Both stack-borrowing and heap-borrowing need some tweak to ensure validity.
/// That's what [`BorrowInterior`][BorrowInterior] provides.
///
/// [BorrowInterior]: trait.BorrowInterior.html
pub trait BorrowMove<Borrowed: ?Sized>: BorrowMut<Borrowed> {
    fn borrow_move<'a>(self: RefMove<'a, Self>) -> RefMove<'a, Borrowed>;
}

impl<T: ?Sized> BorrowMove<T> for T {
    fn borrow_move<'a>(self: RefMove<'a, Self>) -> RefMove<'a, T> {
        self
    }
}

impl<'a, T: ?Sized> BorrowMove<T> for RefMove<'a, T> {
    fn borrow_move<'b>(self: RefMove<'b, Self>) -> RefMove<'b, T> {
        self.into_inner()
    }
}

macro_rules! define_array_borrow {
    ($($n:expr),*) => {
        $(
            impl<T> BorrowMove<[T]> for [T; $n] {
                fn borrow_move<'a>(self: RefMove<'a, Self>) -> RefMove<'a, [T]> {
                    self
                }
            }
        )*
    };
}

define_array_borrow!(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15);
define_array_borrow!(16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32);