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use std::sync::{Mutex};
use std::collections::HashMap;
use std::ops::{Deref, DerefMut};
use notify_future::NotifyFuture;

struct LockerState {
    pub is_locked: bool,
    pub pending_list: Vec<NotifyFuture<()>>
}

struct LockerManager {
    locker_map: Mutex<HashMap<String, LockerState>>
}

lazy_static::lazy_static! {
    static ref LOCK_MANAGER: LockerManager = LockerManager::new();
}

impl LockerManager {
    pub fn new() -> LockerManager {
        Self {
            locker_map: Mutex::new(HashMap::new())
        }
    }

    pub async fn lock(&self, locker_id: String) {
        let future = {
            let mut locker_map = self.locker_map.lock().unwrap();
            let locker_info = locker_map.get_mut(&locker_id);
            if locker_info.is_none() {
                locker_map.insert(locker_id.clone(), LockerState {
                    is_locked: true,
                    pending_list: Vec::new()
                });
                log::debug!("LockerManager:get locker {}", locker_id);
                return;
            } else {
                let state = locker_info.unwrap();
                if state.is_locked {
                    let future = NotifyFuture::new();
                    state.pending_list.push(future.clone());
                    future
                } else {
                    state.is_locked = true;
                    log::debug!("LockerManager:get locker {}", locker_id);
                    return;
                }
            }
        };
        log::debug!("LockerManager:waiting locker {}", locker_id);
        future.await;
        log::debug!("LockerManager:get locker {}", locker_id);
    }

    pub fn unlock(&self, locker_id: &str) {
        let mut locker_map = self.locker_map.lock().unwrap();
        let locker_info = locker_map.get_mut(locker_id);
        if locker_info.is_some() {
            let state = locker_info.unwrap();
            if state.pending_list.len() > 0 {
                let future = state.pending_list.remove(0);
                future.set_complete(());
            } else {
                state.is_locked = false;
            }
        } else {
            assert!(false);
        }
        log::debug!("LockerManager:free locker {}", locker_id);
    }
}

pub trait IntoString {
    fn into_string(self) -> String;
}

impl IntoString for &str {
    fn into_string(self) -> String {
        self.to_string()
    }
}

impl IntoString for String {
    fn into_string(self) -> String {
        self
    }
}

pub struct Locker {
    locker_id: String,
}

impl Locker {
    pub async fn get_locker<T: IntoString>(locker_id: T) -> Self {
        let id = locker_id.into_string();
        LOCK_MANAGER.lock(id.clone()).await;
        Self {
            locker_id: id
        }
    }
}

impl Drop for Locker {
    fn drop(&mut self) {
        LOCK_MANAGER.unlock(self.locker_id.as_str());
    }
}

pub struct GuardObject<T> {
    _locker: Locker,
    obj: T
}

impl <T> GuardObject<T> {
    pub fn new(locker: Locker, obj: T) -> Self {
        Self {
            _locker: locker,
            obj
        }
    }

    pub fn release_locker(self) -> T {
        self.obj
    }
}

impl <T> Deref for GuardObject<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.obj
    }
}

impl <T> DerefMut for GuardObject<T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.obj
    }
}

#[cfg(test)]
mod test {
    use std::sync::{Arc, Mutex};
    use std::time::Duration;
    use crate::Locker;

    #[test]
    fn test() {
        async_std::task::block_on(async {
            let _locker = Locker::get_locker("test".to_string()).await;
            let i = Arc::new(Mutex::new(0));
            let i_copy = i.clone();
            async_std::task::spawn(async move {
                let _locker = Locker::get_locker("test").await;
                assert_eq!(*i_copy.lock().unwrap(), 1);
            });
            async_std::task::sleep(Duration::from_secs(5)).await;
            *i.lock().unwrap() = 1;
        });
    }
}