use std::{future::Future, time::*, collections::HashMap, hash::Hash};
#[derive(Debug)]
pub struct AsyncCache<K, V, F> {
    func: F,
    cache: HashMap<K, (Instant, V)>,
    interval: Duration
}

impl<K, V, F, Fut> AsyncCache<K, V, F>
where
    F: for<'a> FnMut(&'a K) -> Fut,
    K: Hash + PartialEq + Eq + Clone,
    Fut: Future<Output = Result<V, &'static str>>
{
    pub fn new(interval: Duration, func: F) -> Self {
        Self{
            cache: HashMap::new(),
            interval, func
        }
    }
    
    pub async fn get(&mut self, key: &K) -> Result<&V, &'static str> {
        if self.is_stale(&key) {
            self.renew(&key).await
        } else {
            Ok(&self.cache.get(&key).unwrap().1)
        }
    }

    pub async fn renew(&mut self, key: &K) -> Result<&V, &'static str> {
        let val = (self.func)(&key).await?;
        self.cache.insert(key.clone(), (Instant::now(), val));
        Ok(&self.cache.get(key).unwrap().1)
    }

    pub fn is_stale(&self, key: &K) -> bool {
        if let Some((last_update, _)) = self.cache.get(key) {
            let now = Instant::now();
            now < (*last_update + self.interval)
        }
        else { true }
    }
    
    pub async fn get_opt(&self, key: &K) -> Option<&V> {
        if self.is_stale(key) {
            self.cache.get(key).map(|(_, v)| v)
        }
        else { None }
    }
}

impl<K, V, F, Fut> AsyncCache<K, V, F>
where
    F: for<'a> FnMut(&'a K) -> Fut,
    K: Hash + PartialEq + Eq + Clone,
    V: Clone,
    Fut: Future<Output = Result<V, &'static str>>
{
    pub async fn get_owned(&mut self, key: &K) -> Result<V, &'static str> {
        self.get(key).await.cloned()
    }
}
/*
pub struct AsyncCache<K, V, F> {
    func: F,
    cache: HashMap<K, (Instant, V)>,
    interval: Duration
}

impl<K, V, F> AsyncCache<K, V, F>
where
    for<'a> F: FnMut(&'a K) -> Fut + 'a,
    Fut: Future<Output = V>
{
    pub fn new(interval: Duration, mut func: F) -> Self {
        Self{
            cache: HashMap::new(),
            interval, func
        }
    }

    pub async fn get(&mut self, key: &K) -> &V {
        if self.is_stale(key) {
            self.renew().await
        } else {
            self.cache.get(key)
        }
    }

    pub async fn renew(&mut self, key: &K) -> &V {
        self.cache.get_mut(key).0 = now;
        self.cache.get_mut(key).1 = (self.func)(key).await;
        self.cache.get(key)
    }

    pub fn is_stale(&self, key: &K) -> bool {
        let now = Instant::now();
        let last_update = self.cache.get(key).0;
        now < (last_update + self.interval)
    }
    
    pub fn get_opt(&self, key: &K) -> Option<&T> {
        if self.is_stale(key) {
            Some(self.cache.get(key))
        }
        else { None }
    }
}

impl<K, V, F> AsyncCache<K, V, F>
where
    F: for<'a> FnMut(&'a K) -> Fut + 'a,
    Fut: Future<Output = V>,
    V: Clone
{
    pub async fn get_owned(&mut self, key: &K) -> V {
        self.get(key).await.clone()
    }
}
*/