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use crate::{AsIs, BorrowIs, Is, ToOwned};
use core::borrow::{Borrow, BorrowMut};
use core::cmp::Ordering;
use core::fmt;
use core::hash::{Hash, Hasher};
use core::ops::{Deref, DerefMut};

#[cfg(feature = "alloc")]
use alloc::vec::Vec;

/// A stub for [`Vec<T>`] used in a `no_std` environment.
///
/// [`Vec<T>`]: https://doc.rust-lang.org/alloc/vec/struct.Vec.html
#[derive(Clone)]
pub struct VecStub<T>([T; 0]);

impl<T> Default for VecStub<T> {
    fn default() -> Self {
        VecStub([])
    }
}

impl<T> Deref for VecStub<T> {
    type Target = [T];

    fn deref(&self) -> &[T] {
        &self.0
    }
}

impl<T> DerefMut for VecStub<T> {
    fn deref_mut(&mut self) -> &mut [T] {
        &mut self.0
    }
}

impl<T> Borrow<[T]> for VecStub<T> {
    fn borrow(&self) -> &[T] {
        self
    }
}

impl<T> BorrowMut<[T]> for VecStub<T> {
    fn borrow_mut(&mut self) -> &mut [T] {
        self
    }
}

impl<T> PartialEq for VecStub<T>
where
    T: PartialEq,
{
    fn eq(&self, other: &Self) -> bool {
        (**self).eq(&**other)
    }
}

impl<T> Eq for VecStub<T> where T: Eq {}

impl<T> PartialOrd for VecStub<T>
where
    T: PartialOrd,
{
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        (**self).partial_cmp(&**other)
    }
}

impl<T> Ord for VecStub<T>
where
    T: Ord,
{
    fn cmp(&self, other: &Self) -> Ordering {
        (**self).cmp(&**other)
    }
}

impl<T> Hash for VecStub<T>
where
    T: Hash,
{
    fn hash<H: Hasher>(&self, state: &mut H) {
        (**self).hash(state)
    }
}

impl<T> fmt::Debug for VecStub<T>
where
    T: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        (**self).fmt(f)
    }
}

impl<T> BorrowIs for VecStub<T>
where
    T: Clone,
{
    type Is = Self;
}

impl<T> AsIs for VecStub<T>
where
    T: Clone,
{
    fn as_is<'a>(self) -> Is<'a, Self> {
        Is::Owned(self)
    }
}

#[cfg(feature = "alloc")]
impl<T> BorrowIs for Vec<T>
where
    T: Clone,
{
    type Is = Self;
}

#[cfg(feature = "alloc")]
impl<T> AsIs for Vec<T>
where
    T: Clone,
{
    fn as_is<'a>(self) -> Is<'a, Self> {
        Is::Owned(self)
    }
}

impl<T> BorrowIs for [T]
where
    T: Clone,
{
    type Is = Self;
}

impl<T> ToOwned for [T]
where
    T: Clone,
{
    #[cfg(feature = "alloc")]
    type Owned = Vec<T>;

    #[cfg(not(feature = "alloc"))]
    type Owned = VecStub<T>;

    #[cfg(feature = "alloc")]
    fn to_owned(&self) -> Self::Owned {
        alloc::borrow::ToOwned::to_owned(self)
    }

    #[cfg(feature = "alloc")]
    fn clone_into(&self, target: &mut Self::Owned) {
        alloc::borrow::ToOwned::clone_into(self, target)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn vec_stub() {
        let v: VecStub<()> = VecStub::default();

        assert_eq!(v.clone(), v);
        assert_eq!(v < v, [true; 0] < [true; 0]);
        assert_eq!(v.cmp(&v), [true; 0].cmp(&[true; 0]));
    }
}