use std::collections::{HashMap, VecDeque};
use anyhow::anyhow;
use tokio::sync::RwLock;

pub struct MessageHistory {
    map: RwLock<HashMap<String, VecDeque<String>>>,
    maxlen: usize
}

impl MessageHistory {
    pub fn new(maxlen: usize) -> MessageHistory {
        MessageHistory {
            map: RwLock::new(HashMap::new()),
            maxlen
        }
    }

    pub fn max_len(&self) -> usize {
        self.maxlen
    }

    pub async fn last_msg(&self, user: &str) -> Option<String> {
        let map = self.map.read().await;
        map.get(user).and_then(|d| d.get(0)).map(|s| s.to_string())
    }

    pub async fn last_msgs(&self, user: &str, count: usize) -> Option<Vec<String>> {
        let map = self.map.read().await;
        if let Some(deque) = map.get(user) {
            let count = if deque.len() < count { deque.len() } else {count};
            Some(deque.range(..count).rev().map(ToString::to_string).collect())
        } else {
            None
        }
    }

    pub async fn add_message(&self, user: &str, message: &str) {
        let mut map = self.map.write().await;
        if let Some(deque) = map.get_mut(user) {
            if deque.len() == self.maxlen {
                deque.remove(deque.len()-1);
            }
            deque.push_front(message.to_string());
        } else {
            let mut deque = VecDeque::with_capacity(self.maxlen);
            deque.push_front(message.to_string());
            map.insert(user.to_string(), deque);
        }
    }
}