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//! A Vec-based SlotMap-esque datastructure and corresponding Key type.

use std::fmt::{Debug, Display, Formatter};
use std::hash::{Hash, Hasher};
use std::marker::PhantomData;
use std::ops::{Index, IndexMut};

/// A key into a SlotVec.
#[repr(transparent)]
pub struct Key<Tag: ?Sized> {
    index: usize,
    _phantom: PhantomData<Tag>,
}
impl<Tag: ?Sized> Key<Tag> {
    /// Creates a Key from a raw index. Avoid using this function directly.
    pub fn from_raw(index: usize) -> Self {
        Key {
            index,
            _phantom: PhantomData,
        }
    }
}
impl<Tag: ?Sized> Clone for Key<Tag> {
    fn clone(&self) -> Self {
        *self
    }
}
impl<Tag: ?Sized> Copy for Key<Tag> {}
impl<Tag: ?Sized> PartialEq for Key<Tag> {
    fn eq(&self, other: &Self) -> bool {
        self.index == other.index
    }
}
impl<Tag: ?Sized> Eq for Key<Tag> {}
impl<Tag: ?Sized> Hash for Key<Tag> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.index.hash(state);
    }
}
impl<Tag: ?Sized> Debug for Key<Tag> {
    fn fmt(&self, f: &mut Formatter) -> std::fmt::Result {
        write!(f, "Key({})", self.index)
    }
}
impl<Tag: ?Sized> Display for Key<Tag> {
    fn fmt(&self, f: &mut Formatter) -> std::fmt::Result {
        write!(f, "{}", self.index)
    }
}

/// A Vec-based SlotMap-esque datastructure without removes.
#[repr(transparent)]
pub struct SlotVec<Tag: ?Sized, Val> {
    slots: Vec<Val>,
    _phantom: PhantomData<Tag>,
}
impl<Tag: ?Sized, Val> SlotVec<Tag, Val> {
    /// Creates a new SlotVec.
    pub fn new() -> Self {
        Self {
            slots: Vec::default(),
            _phantom: PhantomData,
        }
    }

    /// Inserts a value into the SlotVec and returns the key.
    pub fn insert(&mut self, value: Val) -> Key<Tag> {
        let key = Key::from_raw(self.slots.len());
        self.slots.push(value);
        key
    }

    /// Use the provided function to generate a value given the key and insert it into the SlotVec.
    pub fn insert_with_key<F>(&mut self, func: F) -> Key<Tag>
    where
        F: FnOnce(Key<Tag>) -> Val,
    {
        let key = Key::from_raw(self.slots.len());
        self.slots.push((func)(key));
        key
    }

    /// Returns a reference to the value associated with the key.
    pub fn get(&self, key: Key<Tag>) -> Option<&Val> {
        self.slots.get(key.index)
    }

    /// Returns a mutable reference to the value associated with the key.
    pub fn get_mut(&mut self, key: Key<Tag>) -> Option<&mut Val> {
        self.slots.get_mut(key.index)
    }

    /// Returns the number of elements in the SlotVec.
    pub fn len(&self) -> usize {
        self.slots.len()
    }

    /// Returns true if the SlotVec is empty.
    pub fn is_empty(&self) -> bool {
        self.slots.is_empty()
    }
}
impl<Tag: ?Sized, Val> Index<Key<Tag>> for SlotVec<Tag, Val> {
    type Output = Val;

    fn index(&self, key: Key<Tag>) -> &Self::Output {
        self.get(key).unwrap()
    }
}
impl<Tag: ?Sized, Val> IndexMut<Key<Tag>> for SlotVec<Tag, Val> {
    fn index_mut(&mut self, key: Key<Tag>) -> &mut Self::Output {
        self.get_mut(key).unwrap()
    }
}
impl<Key: ?Sized, Val> Default for SlotVec<Key, Val> {
    fn default() -> Self {
        Self::new()
    }
}