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extern crate time;
use std::mem;
use std::cmp;
use std::hash::Hash;
use std::cell::RefCell;
use std::collections::HashMap;
use std::collections::hash_map::Entry;
use std::ops::{Deref, DerefMut};
pub trait Timer {
fn get_time(&self) -> i64;
}
#[derive(Default)]
pub struct StandardTimer;
impl Timer for StandardTimer {
fn get_time(&self) -> i64 {
time::get_time().sec
}
}
pub struct TransientHashMap<K, V, T = StandardTimer> where T: Timer {
backing: HashMap<K, V>,
timestamps: RefCell<HashMap<K, i64>>,
lifetime: u64,
timer: T
}
impl<K, V> TransientHashMap<K, V, StandardTimer> where K: Eq + Hash {
pub fn new(lifetime: u64) -> Self {
TransientHashMap::new_with_timer(lifetime, Default::default())
}
}
impl<K, V, T> TransientHashMap<K, V, T> where K: Eq + Hash, T: Timer {
pub fn new_with_timer(lifetime: u64, t: T) -> Self {
TransientHashMap {
backing: HashMap::new(),
timestamps: RefCell::new(HashMap::new()),
lifetime: lifetime,
timer: t
}
}
pub fn insert(&mut self, key: K, value: V) -> Option<V> where K: Clone {
self.note_used(key.clone());
self.backing.insert(key, value)
}
pub fn entry(&mut self, key: K) -> Entry<K, V> where K: Clone {
self.note_used(key.clone());
self.backing.entry(key)
}
pub fn get(&self, key: &K) -> Option<&V> where K: Clone {
self.note_used(key.clone());
self.backing.get(key)
}
pub fn get_mut(&mut self, key: &K) -> Option<&mut V> where K: Clone {
self.note_used(key.clone());
self.backing.get_mut(key)
}
pub fn contains_key(&self, key: &K) -> bool where K: Clone {
self.note_used(key.clone());
self.backing.contains_key(key)
}
pub fn remaining_lifetime(&self, key: &K) -> u64 {
let timestamps = self.timestamps.borrow();
match timestamps.get(key) {
None => 0,
Some(time) => cmp::max(0, self.lifetime - (self.timer.get_time() - time) as u64)
}
}
fn note_used(&self, key: K) {
self.timestamps.borrow_mut().insert(key, self.timer.get_time());
}
pub fn prune(&mut self) {
let now = self.timer.get_time();
let timestamps = mem::replace(&mut self.timestamps, RefCell::new(HashMap::new()));
*self.timestamps.borrow_mut() = timestamps.into_inner().into_iter()
.filter(|entry| ((now - entry.1) as u64) < self.lifetime)
.collect();
let backing = mem::replace(&mut self.backing, HashMap::new());
let timestamps = self.timestamps.borrow();
self.backing = backing.into_iter()
.filter(|entry| timestamps.contains_key(&entry.0))
.collect();
}
pub fn direct(&self) -> &HashMap<K, V> {
&self.backing
}
pub fn direct_mut(&mut self) -> &mut HashMap<K, V> {
&mut self.backing
}
}
impl<K, V, T> Deref for TransientHashMap<K, V, T> where T: Timer {
type Target = HashMap<K, V>;
fn deref(&self) -> &Self::Target {
&self.backing
}
}
impl<K, V, T> DerefMut for TransientHashMap<K, V, T> where T: Timer {
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.backing
}
}
#[cfg(test)]
mod test {
use std::cell::RefCell;
use super::{TransientHashMap, Timer};
struct TestTimer<'a> {
time: &'a RefCell<i64>
}
impl<'a> Timer for TestTimer<'a> {
fn get_time(&self) -> i64 {
*self.time.borrow()
}
}
#[test]
fn it_works() {
let time = RefCell::new(0);
let timer = TestTimer {
time: &time
};
let mut t_map = TransientHashMap::new_with_timer(2, timer);
assert_eq!(t_map.remaining_lifetime(&1), 0);
t_map.insert(1, 1);
assert_eq!(t_map.remaining_lifetime(&1), 2);
*time.borrow_mut() = 1;
assert_eq!(t_map.remaining_lifetime(&1), 1);
*time.borrow_mut() = 2;
assert_eq!(t_map.remaining_lifetime(&1), 0);
*time.borrow_mut() = 1;
assert_eq!(t_map.remaining_lifetime(&1), 1);
t_map.prune();
assert_eq!(t_map.remaining_lifetime(&1), 1);
*time.borrow_mut() = 2;
assert_eq!(t_map.remaining_lifetime(&1), 0);
t_map.prune();
assert_eq!(t_map.remaining_lifetime(&1), 0);
*time.borrow_mut() = 1;
assert_eq!(t_map.remaining_lifetime(&1), 0);
}
}