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//! An archived version of `Option`.

use core::{cmp, hash};

/// An archived [`Option`].
///
/// It functions identically to [`Option`] but has a different internal
/// representation to allow for archiving.
#[derive(Debug)]
#[cfg_attr(feature = "validation", derive(bytecheck::CheckBytes))]
#[repr(u8)]
pub enum ArchivedOption<T> {
    /// No value
    None,
    /// Some value `T`
    Some(T),
}

impl<T> ArchivedOption<T> {
    /// Returns `true` if the option is a `None` value.
    #[inline]
    pub fn is_none(&self) -> bool {
        match self {
            ArchivedOption::None => true,
            ArchivedOption::Some(_) => false,
        }
    }

    /// Returns `true` if the option is a `Some` value.
    #[inline]
    pub fn is_some(&self) -> bool {
        match self {
            ArchivedOption::None => false,
            ArchivedOption::Some(_) => true,
        }
    }

    /// Converts to an `Option<&T>`.
    #[inline]
    pub fn as_ref(&self) -> Option<&T> {
        match self {
            ArchivedOption::None => None,
            ArchivedOption::Some(value) => Some(value),
        }
    }

    /// Converts to an `Option<&mut T>`.
    #[inline]
    pub fn as_mut(&mut self) -> Option<&mut T> {
        match self {
            ArchivedOption::None => None,
            ArchivedOption::Some(value) => Some(value),
        }
    }

    /// Inserts `v` into the option if it is `None`, then returns a mutable
    /// reference to the contained value.
    #[inline]
    pub fn get_or_insert(&mut self, v: T) -> &mut T {
        self.get_or_insert_with(move || v)
    }

    /// Inserts a value computed from `f` into the option if it is `None`, then
    /// returns a mutable reference to the contained value.
    #[inline]
    pub fn get_or_insert_with<F: FnOnce() -> T>(&mut self, f: F) -> &mut T {
        if let ArchivedOption::Some(ref mut value) = self {
            value
        } else {
            *self = ArchivedOption::Some(f());
            self.as_mut().unwrap()
        }
    }
}

impl<T: Eq> Eq for ArchivedOption<T> {}

impl<T: hash::Hash> hash::Hash for ArchivedOption<T> {
    #[inline]
    fn hash<H: hash::Hasher>(&self, state: &mut H) {
        self.as_ref().hash(state)
    }
}

impl<T: Ord> Ord for ArchivedOption<T> {
    #[inline]
    fn cmp(&self, other: &Self) -> cmp::Ordering {
        self.as_ref().cmp(&other.as_ref())
    }
}

impl<T: PartialEq> PartialEq for ArchivedOption<T> {
    #[inline]
    fn eq(&self, other: &Self) -> bool {
        self.as_ref().eq(&other.as_ref())
    }
}

impl<T: PartialOrd> PartialOrd for ArchivedOption<T> {
    #[inline]
    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
        self.as_ref().partial_cmp(&other.as_ref())
    }
}

impl<T, U: PartialEq<T>> PartialEq<Option<T>> for ArchivedOption<U> {
    #[inline]
    fn eq(&self, other: &Option<T>) -> bool {
        if let ArchivedOption::Some(self_value) = self {
            if let Some(other_value) = other {
                self_value.eq(other_value)
            } else {
                false
            }
        } else {
            other.is_none()
        }
    }
}

impl<T: PartialEq<U>, U> PartialEq<ArchivedOption<T>> for Option<U> {
    #[inline]
    fn eq(&self, other: &ArchivedOption<T>) -> bool {
        other.eq(self)
    }
}