use dashmap::DashMap;
use fnv::FnvBuildHasher;
use std::sync::Arc;
use std::thread::{current, park, park_timeout, Thread};
use std::time::Duration;
use thiserror::Error;

/// Error that can occur during wait/notify calls.
#[derive(Debug, Error)]
// Non-exhaustive to allow for future variants without breaking changes!
#[non_exhaustive]
pub enum WaiterError {
    /// Wait/Notify is not implemented for this memory
    Unimplemented,
    /// To many waiter for an address
    TooManyWaiters,
}

impl std::fmt::Display for WaiterError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "WaiterError")
    }
}

/// A location in memory for a Waiter
#[derive(Hash, Eq, PartialEq, Clone, Copy, Debug)]
pub struct NotifyLocation {
    /// The address of the Waiter location
    pub address: u32,
}

#[derive(Debug)]
struct NotifyWaiter {
    pub thread: Thread,
    pub notified: bool,
}
#[derive(Debug, Default)]
struct NotifyMap {
    pub map: DashMap<NotifyLocation, Vec<NotifyWaiter>, FnvBuildHasher>,
}

/// HashMap of Waiters for the Thread/Notify opcodes
#[derive(Debug)]
pub struct ThreadConditions {
    inner: Arc<NotifyMap>, // The Hasmap with the Notify for the Notify/wait opcodes
}

impl ThreadConditions {
    /// Create a new ThreadConditions
    pub fn new() -> Self {
        Self {
            inner: Arc::new(NotifyMap::default()),
        }
    }

    // To implement Wait / Notify, a HasMap, behind a mutex, will be used
    // to track the address of waiter. The key of the hashmap is based on the memory
    // and waiter threads are "park"'d (with or without timeout)
    // Notify will wake the waiters by simply "unpark" the thread
    // as the Thread info is stored on the HashMap
    // once unparked, the waiter thread will remove it's mark on the HashMap
    // timeout / awake is tracked with a boolean in the HashMap
    // because `park_timeout` doesn't gives any information on why it returns

    /// Add current thread to the waiter hash
    pub fn do_wait(
        &mut self,
        dst: NotifyLocation,
        timeout: Option<Duration>,
    ) -> Result<u32, WaiterError> {
        // fetch the notifier
        if self.inner.map.len() >= 1 << 32 {
            return Err(WaiterError::TooManyWaiters);
        }
        self.inner
            .map
            .entry(dst)
            .or_insert_with(Vec::new)
            .push(NotifyWaiter {
                thread: current(),
                notified: false,
            });
        if let Some(timeout) = timeout {
            park_timeout(timeout);
        } else {
            park();
        }
        let mut bindding = self.inner.map.get_mut(&dst).unwrap();
        let v = bindding.value_mut();
        let id = current().id();
        let mut ret = 0;
        v.retain(|cond| {
            if cond.thread.id() == id {
                ret = if cond.notified { 0 } else { 2 };
                false
            } else {
                true
            }
        });
        let empty = v.is_empty();
        drop(bindding);
        if empty {
            self.inner.map.remove(&dst);
        }
        Ok(ret)
    }

    /// Notify waiters from the wait list
    pub fn do_notify(&mut self, dst: NotifyLocation, count: u32) -> u32 {
        let mut count_token = 0u32;
        if let Some(mut v) = self.inner.map.get_mut(&dst) {
            for waiter in v.value_mut() {
                if count_token < count && !waiter.notified {
                    waiter.notified = true; // mark as was waiked up
                    waiter.thread.unpark(); // wakeup!
                    count_token += 1;
                }
            }
        }
        count_token
    }
}

impl Clone for ThreadConditions {
    fn clone(&self) -> Self {
        Self {
            inner: self.inner.clone(),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn threadconditions_notify_nowaiters() {
        let mut conditions = ThreadConditions::new();
        let dst = NotifyLocation { address: 0 };
        let ret = conditions.do_notify(dst, 1);
        assert_eq!(ret, 0);
    }

    #[test]
    fn threadconditions_notify_1waiter() {
        use std::thread;

        let mut conditions = ThreadConditions::new();
        let mut threadcond = conditions.clone();

        thread::spawn(move || {
            let dst = NotifyLocation { address: 0 };
            let ret = threadcond.do_wait(dst, None).unwrap();
            assert_eq!(ret, 0);
        });
        thread::sleep(Duration::from_millis(10));
        let dst = NotifyLocation { address: 0 };
        let ret = conditions.do_notify(dst, 1);
        assert_eq!(ret, 1);
    }

    #[test]
    fn threadconditions_notify_waiter_timeout() {
        use std::thread;

        let mut conditions = ThreadConditions::new();
        let mut threadcond = conditions.clone();

        thread::spawn(move || {
            let dst = NotifyLocation { address: 0 };
            let ret = threadcond
                .do_wait(dst, Some(Duration::from_millis(1)))
                .unwrap();
            assert_eq!(ret, 2);
        });
        thread::sleep(Duration::from_millis(50));
        let dst = NotifyLocation { address: 0 };
        let ret = conditions.do_notify(dst, 1);
        assert_eq!(ret, 0);
    }

    #[test]
    fn threadconditions_notify_waiter_mismatch() {
        use std::thread;

        let mut conditions = ThreadConditions::new();
        let mut threadcond = conditions.clone();

        thread::spawn(move || {
            let dst = NotifyLocation { address: 8 };
            let ret = threadcond
                .do_wait(dst, Some(Duration::from_millis(10)))
                .unwrap();
            assert_eq!(ret, 2);
        });
        thread::sleep(Duration::from_millis(1));
        let dst = NotifyLocation { address: 0 };
        let ret = conditions.do_notify(dst, 1);
        assert_eq!(ret, 0);
        thread::sleep(Duration::from_millis(100));
    }

    #[test]
    fn threadconditions_notify_2waiters() {
        use std::thread;

        let mut conditions = ThreadConditions::new();
        let mut threadcond = conditions.clone();
        let mut threadcond2 = conditions.clone();

        thread::spawn(move || {
            let dst = NotifyLocation { address: 0 };
            let ret = threadcond.do_wait(dst, None).unwrap();
            assert_eq!(ret, 0);
        });
        thread::spawn(move || {
            let dst = NotifyLocation { address: 0 };
            let ret = threadcond2.do_wait(dst, None).unwrap();
            assert_eq!(ret, 0);
        });
        thread::sleep(Duration::from_millis(20));
        let dst = NotifyLocation { address: 0 };
        let ret = conditions.do_notify(dst, 5);
        assert_eq!(ret, 2);
    }
}