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use crate::Pred;
use std::borrow::Borrow;
use std::cmp::Ordering;
use std::fmt::{Debug, Display, Formatter, Result as FmtResult};
use std::hash::Hash;
use std::hash::Hasher;
std_prelude!();

#[derive(Clone, Copy)]
/// A reference to a value that is accepted by a given predicate.
pub struct PetRef<'a, T: ?Sized, P>(&'a T, P);

impl<'a, T: ?Sized, P: Pred<T>> PetRef<'a, T, P> {
    /// Attempts to create a new `PetRef<'a, T, P>` from a reference `t`.
    ///
    /// If `P` accepts `t`, then the result is a `Some(..)` referring to `t`.
    /// Otherwise, `None` is returned.
    pub fn new(t: &'a T) -> Option<Self> {
        if P::accept(t) {
            Some(Self(t, P::default()))
        } else {
            None
        }
    }

    /// Creates a new `PetRef<'a, T, P>` from a reference `t` without checking if `P` accepts `t`.
    pub unsafe fn new_unchecked(t: &'a T) -> Self {
        Self(t, P::default())
    }

    /// Retrieves the reference contained in this `PetRef<'a, T, P>`.
    pub fn value(&self) -> &'a T {
        self.0
    }
}

impl<'a, T: ?Sized, P> AsRef<T> for PetRef<'a, T, P> {
    fn as_ref(&self) -> &T {
        self.0
    }
}
impl<'a, T: ?Sized, P> Borrow<T> for PetRef<'a, T, P> {
    fn borrow(&self) -> &T {
        self.0
    }
}

impl<'a, 'b, T: ?Sized, P, Q> PartialEq<PetRef<'b, T, Q>> for PetRef<'a, T, P>
where
    T: PartialEq,
{
    fn eq(&self, o: &PetRef<'b, T, Q>) -> bool {
        self.0.eq(&o.0)
    }
    fn ne(&self, o: &PetRef<'b, T, Q>) -> bool {
        self.0.ne(&o.0)
    }
}

impl<'a, 'b, T: ?Sized, P, Q> PartialOrd<PetRef<'b, T, Q>> for PetRef<'a, T, P>
where
    T: PartialOrd,
{
    fn partial_cmp(&self, o: &PetRef<'b, T, Q>) -> Option<Ordering> {
        self.0.partial_cmp(&o.0)
    }
    fn lt(&self, o: &PetRef<'b, T, Q>) -> bool {
        self.0.lt(&o.0)
    }
    fn le(&self, o: &PetRef<'b, T, Q>) -> bool {
        self.0.le(&o.0)
    }
    fn gt(&self, o: &PetRef<'b, T, Q>) -> bool {
        self.0.gt(&o.0)
    }
    fn ge(&self, o: &PetRef<'b, T, Q>) -> bool {
        self.0.ge(&o.0)
    }
}

impl<'a, T: ?Sized, P> Eq for PetRef<'a, T, P> where T: Eq {}
impl<'a, T: ?Sized, P> Ord for PetRef<'a, T, P>
where
    T: Ord,
{
    fn cmp(&self, o: &Self) -> Ordering {
        self.0.cmp(&o.0)
    }
}

impl<'a, T, P> Hash for PetRef<'a, T, P>
where
    T: Hash,
{
    fn hash<H>(&self, state: &mut H)
    where
        H: Hasher,
    {
        self.0.hash(state)
    }
}

impl<'a, T: ?Sized, P> Debug for PetRef<'a, T, P>
where
    T: Debug,
    P: Debug,
{
    fn fmt(&self, f: &mut Formatter) -> FmtResult {
        write!(f, "PetRef<{:?}>({:?})", self.1, self.0)
    }
}

impl<'a, T, P> Display for PetRef<'a, T, P>
where
    T: Display,
{
    fn fmt(&self, f: &mut Formatter) -> FmtResult {
        self.0.fmt(f)
    }
}