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//! **This module is experimental**
//!
//! This module provides threadsafe versions of FrozenMap and FrozenVec,
//! ideal for use as a cache.
//!
//! These lock internally, however locks only last as long as the method calls
//!

use std::borrow::Borrow;
use std::collections::HashMap;
use std::hash::Hash;

use stable_deref_trait::StableDeref;

use std::sync::RwLock;

/// Append-only threadsafe version of `std::collections::HashMap` where
/// insertion does not require mutable access
pub struct FrozenMap<K, V> {
    map: RwLock<HashMap<K, V>>
}

impl<K: Eq + Hash, V: StableDeref> FrozenMap<K, V> {
    // these should never return &K or &V
    // these should never delete any entries

    pub fn new() -> Self {
        Self {
            map: RwLock::new(Default::default()),
        }
    }

    pub fn insert(&self, k: K, v: V) -> &V::Target {
        let mut map = self.map.write().unwrap();
        let ret = unsafe {
            let inserted = &**map.entry(k).or_insert(v);
            &* (inserted as *const _)
        };
        ret
    }

    pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V::Target>
    where
        K: Borrow<Q>,
        Q: Hash + Eq,
    {
        let map = self.map.read().unwrap();
        let ret = unsafe {
            map.get(k).map(|x| &*(&**x as *const V::Target))
        };
        ret
    }

    // TODO add more
}

/// Append-only threadsafe version of `std::vec::Vec` where
/// insertion does not require mutable access
pub struct FrozenVec<T> {
    vec: RwLock<Vec<T>>,
}

impl<T: StableDeref> FrozenVec<T> {
    pub fn new() -> Self {
        Self {
            vec: RwLock::new(Default::default()),
        }
    }

    // these should never return &T
    // these should never delete any entries

    pub fn push(&self, val: T) {
        let mut vec = self.vec.write().unwrap();
        vec.push(val);
    }

    /// Push, immediately getting a reference to the element
    pub fn push_get(&self, val: T) -> &T::Target {
        let mut vec = self.vec.write().unwrap();
        vec.push(val);
        unsafe {
            &*(&**vec.get_unchecked(vec.len() - 1) as *const T::Target)
        }
    }


    pub fn get(&self, index: usize) -> Option<&T::Target> {
        let vec = self.vec.read().unwrap();
        unsafe {
            vec.get(index).map(|x| &*(&**x as *const T::Target))
        }
    }

    // TODO add more
}