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use std::any::{Any, TypeId};
use std::fmt;

use fxhash::FxHashMap;

#[derive(Default)]
/// A type map of extensions.
pub struct Extensions {
    map: Option<FxHashMap<TypeId, Box<dyn Any>>>,
}

impl Extensions {
    /// Create an empty `Extensions`.
    #[inline]
    pub fn new() -> Extensions {
        Extensions { map: None }
    }

    /// Insert a value into this `Extensions`.
    ///
    /// If a extension of this type already exists, it will
    /// be returned.
    pub fn insert<T: 'static>(&mut self, val: T) -> Option<T> {
        self.map
            .get_or_insert_with(|| FxHashMap::default())
            .insert(TypeId::of::<T>(), Box::new(val))
            .and_then(|boxed| (boxed as Box<dyn Any + 'static>).downcast().ok().map(|boxed| *boxed))

    }

    /// Check if container contains typed value
    pub fn contains<T: 'static>(&self) -> bool {
        self.map.as_ref().and_then(|m| m.get(&TypeId::of::<T>())).is_some()
    }

    /// Get a reference to a typed value previously inserted on this `Extensions`.
    pub fn get<T: 'static>(&self) -> Option<&T> {
        self.map
            .as_ref()
            .and_then(|m| m.get(&TypeId::of::<T>()))
            .and_then(|boxed| (&**boxed as &(dyn Any + 'static)).downcast_ref())
    }

    /// Get a mutable reference to a typed value previously inserted on this `Extensions`.
    pub fn get_mut<T: 'static>(&mut self) -> Option<&mut T> {
        self.map
            .as_mut()
            .and_then(|m| m.get_mut(&TypeId::of::<T>()))
            .and_then(|boxed| (&mut **boxed as &mut (dyn Any + 'static)).downcast_mut())
    }

    /// Remove a typed value from this `Extensions`.
    ///
    /// If a value of this type exists, it will be returned.
    pub fn remove<T: 'static>(&mut self) -> Option<T> {
        self.map
            .as_mut()
            .and_then(|m| m.remove(&TypeId::of::<T>()))
            .and_then(|boxed| (boxed as Box<dyn Any + 'static>).downcast().ok().map(|boxed| *boxed))
    }

    /// Clear the `Extensions` of all inserted values.
    #[inline]
    pub fn clear(&mut self) {
        self.map = None;
    }
}

impl fmt::Debug for Extensions {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Extensions").finish()
    }
}

#[test]
fn test_extensions() {
    #[derive(Debug, PartialEq)]
    struct MyType(i32);

    let mut extensions = Extensions::new();

    extensions.insert(5i32);
    extensions.insert(MyType(10));

    assert_eq!(extensions.get(), Some(&5i32));
    assert_eq!(extensions.get_mut(), Some(&mut 5i32));

    assert_eq!(extensions.remove::<i32>(), Some(5i32));
    assert!(extensions.get::<i32>().is_none());

    assert_eq!(extensions.get::<bool>(), None);
    assert_eq!(extensions.get(), Some(&MyType(10)));
}