// Copyright 2020 TiKV Project Authors. Licensed under Apache-2.0.

use super::key_handle::{KeyHandle, KeyHandleGuard};

use crossbeam_skiplist::SkipMap;
use std::{
    ops::Bound,
    sync::{Arc, Weak},
};
use txn_types::{Key, Lock};

#[derive(Clone)]
pub struct LockTable(pub Arc<SkipMap<Key, Weak<KeyHandle>>>);

impl Default for LockTable {
    fn default() -> Self {
        LockTable(Arc::new(SkipMap::new()))
    }
}

impl LockTable {
    pub async fn lock_key(&self, key: &Key) -> KeyHandleGuard {
        loop {
            // Create a KeyHandle first, but do not bind it to the lock table first.
            // If we fail to insert the handle into the table, this handle should be dropped
            // without removing any entry from the table.
            let handle = Arc::new(KeyHandle::new(key.clone()));
            let weak = Arc::downgrade(&handle);
            let weak2 = weak.clone();
            let guard = handle.lock().await;

            let entry = self.0.get_or_insert(key.clone(), weak);
            if entry.value().ptr_eq(&weak2) {
                // If the weak ptr returned by `get_or_insert` equals to the one we inserted,
                // `guard` refers to the KeyHandle in the lock table. Now, we can bind the handle
                // to the table.

                // SAFETY: The `table` field in `KeyHandle` is only accessed through the `set_table`
                // or the `drop` method. It's impossible to have a concurrent `drop` here and `set_table`
                // is only called here. So there is no concurrent access to the `table` field in `KeyHandle`.
                unsafe {
                    guard.handle().set_table(self.clone());
                }
                return guard;
            } else if let Some(handle) = entry.value().upgrade() {
                return handle.lock().await;
            }
        }
    }

    pub fn check_key<E>(
        &self,
        key: &Key,
        check_fn: impl FnOnce(&Lock) -> Result<(), E>,
    ) -> Result<(), E> {
        if let Some(lock_ref) = self.get(key) {
            return lock_ref.with_lock(|lock| {
                if let Some(lock) = &*lock {
                    return check_fn(lock);
                }
                Ok(())
            });
        }
        Ok(())
    }

    pub fn check_range<E>(
        &self,
        start_key: Option<&Key>,
        end_key: Option<&Key>,
        mut check_fn: impl FnMut(&Key, &Lock) -> Result<(), E>,
    ) -> Result<(), E> {
        let e = self.find_first(start_key, end_key, |handle| {
            handle.with_lock(|lock| {
                lock.as_ref()
                    .and_then(|lock| check_fn(&handle.key, lock).err())
            })
        });
        if let Some(e) = e { Err(e) } else { Ok(()) }
    }

    /// Gets the handle of the key.
    pub fn get(&self, key: &Key) -> Option<Arc<KeyHandle>> {
        self.0.get(key).and_then(|e| e.value().upgrade())
    }

    /// Finds the first handle in the given range that `pred` returns `Some`.
    /// The `Some` return value of `pred` will be returned by `find_first`.
    pub fn find_first<'m, T>(
        &'m self,
        start_key: Option<&Key>,
        end_key: Option<&Key>,
        mut pred: impl FnMut(Arc<KeyHandle>) -> Option<T>,
    ) -> Option<T> {
        let lower_bound = start_key.map(Bound::Included).unwrap_or(Bound::Unbounded);
        let upper_bound = end_key.map(Bound::Excluded).unwrap_or(Bound::Unbounded);

        for e in self.0.range((lower_bound, upper_bound)) {
            let res = e.value().upgrade().and_then(&mut pred);
            if res.is_some() {
                return res;
            }
        }
        None
    }

    /// Iterates all handles and call a specified function on each of them.
    pub fn for_each(&self, mut f: impl FnMut(Arc<KeyHandle>)) {
        for entry in self.0.iter() {
            if let Some(handle) = entry.value().upgrade() {
                f(handle);
            }
        }
    }

    /// Removes the key and its key handle from the map.
    pub fn remove(&self, key: &Key) {
        self.0.remove(key);
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use std::{
        sync::atomic::{AtomicUsize, Ordering},
        time::Duration,
    };
    use tokio::time::delay_for;
    use txn_types::LockType;

    #[tokio::test]
    async fn test_lock_key() {
        let lock_table = LockTable::default();

        let counter = Arc::new(AtomicUsize::new(0));
        let mut handles = Vec::new();
        for _ in 0..100 {
            let lock_table = lock_table.clone();
            let counter = counter.clone();
            let handle = tokio::spawn(async move {
                let _guard = lock_table.lock_key(&Key::from_raw(b"k")).await;
                // Modify an atomic counter with a mutex guard. The value of the counter
                // should remain unchanged if the mutex works.
                let counter_val = counter.fetch_add(1, Ordering::SeqCst) + 1;
                delay_for(Duration::from_millis(1)).await;
                assert_eq!(counter.load(Ordering::SeqCst), counter_val);
            });
            handles.push(handle);
        }
        for handle in handles {
            handle.await.unwrap();
        }
        assert_eq!(counter.load(Ordering::SeqCst), 100);
    }

    fn ts_check(lock: &Lock, ts: u64) -> Result<(), Lock> {
        if lock.ts.into_inner() < ts {
            Err(lock.clone())
        } else {
            Ok(())
        }
    }

    #[tokio::test]
    async fn test_check_key() {
        let lock_table = LockTable::default();
        let key_k = Key::from_raw(b"k");

        // no lock found
        assert!(lock_table.check_key(&key_k, |_| Err(())).is_ok());

        let lock = Lock::new(
            LockType::Lock,
            b"k".to_vec(),
            10.into(),
            100,
            None,
            10.into(),
            1,
            10.into(),
        );
        let guard = lock_table.lock_key(&key_k).await;
        guard.with_lock(|l| {
            *l = Some(lock.clone());
        });

        // lock passes check_fn
        assert!(lock_table.check_key(&key_k, |l| ts_check(l, 5)).is_ok());

        // lock does not pass check_fn
        assert_eq!(lock_table.check_key(&key_k, |l| ts_check(l, 20)), Err(lock));
    }

    #[tokio::test]
    async fn test_check_range() {
        let lock_table = LockTable::default();

        let lock_k = Lock::new(
            LockType::Lock,
            b"k".to_vec(),
            20.into(),
            100,
            None,
            20.into(),
            1,
            20.into(),
        );
        let guard = lock_table.lock_key(&Key::from_raw(b"k")).await;
        guard.with_lock(|l| {
            *l = Some(lock_k.clone());
        });

        let lock_l = Lock::new(
            LockType::Lock,
            b"l".to_vec(),
            10.into(),
            100,
            None,
            10.into(),
            1,
            10.into(),
        );
        let guard = lock_table.lock_key(&Key::from_raw(b"l")).await;
        guard.with_lock(|l| {
            *l = Some(lock_l.clone());
        });

        // no lock found
        assert!(
            lock_table
                .check_range(
                    Some(&Key::from_raw(b"m")),
                    Some(&Key::from_raw(b"n")),
                    |_, _| Err(())
                )
                .is_ok()
        );

        // lock passes check_fn
        assert!(
            lock_table
                .check_range(None, Some(&Key::from_raw(b"z")), |_, l| ts_check(l, 5))
                .is_ok()
        );

        // first lock does not pass check_fn
        assert_eq!(
            lock_table.check_range(Some(&Key::from_raw(b"a")), None, |_, l| ts_check(l, 25)),
            Err(lock_k)
        );

        // first lock passes check_fn but the second does not
        assert_eq!(
            lock_table.check_range(None, None, |_, l| ts_check(l, 15)),
            Err(lock_l)
        );
    }

    #[tokio::test]
    async fn test_lock_table_for_each() {
        let lock_table: LockTable = LockTable::default();

        let mut found_locks = Vec::new();
        let mut expect_locks = Vec::new();

        let collect = |h: Arc<KeyHandle>, to: &mut Vec<_>| {
            let lock = h.with_lock(|l| l.clone());
            to.push((h.key.clone(), lock));
        };

        lock_table.for_each(|h| collect(h, &mut found_locks));
        assert!(found_locks.is_empty());

        let lock_a = Lock::new(
            LockType::Lock,
            b"a".to_vec(),
            20.into(),
            100,
            None,
            20.into(),
            1,
            20.into(),
        );
        let guard_a = lock_table.lock_key(&Key::from_raw(b"a")).await;
        guard_a.with_lock(|l| {
            *l = Some(lock_a.clone());
        });
        expect_locks.push((Key::from_raw(b"a"), Some(lock_a.clone())));

        lock_table.for_each(|h| collect(h, &mut found_locks));
        assert_eq!(found_locks, expect_locks);
        found_locks.clear();

        let lock_b = Lock::new(
            LockType::Lock,
            b"b".to_vec(),
            30.into(),
            120,
            None,
            30.into(),
            2,
            30.into(),
        )
        .use_async_commit(vec![b"c".to_vec()]);
        let guard_b = lock_table.lock_key(&Key::from_raw(b"b")).await;
        guard_b.with_lock(|l| {
            *l = Some(lock_b.clone());
        });
        expect_locks.push((Key::from_raw(b"b"), Some(lock_b.clone())));

        lock_table.for_each(|h| collect(h, &mut found_locks));
        assert_eq!(found_locks, expect_locks);
    }

    #[tokio::test]
    async fn test_lock_key_when_handle_exists() {
        let lock_table: LockTable = LockTable::default();
        let key = Key::from_raw(b"key");

        let guard = lock_table.lock_key(&key).await;
        let handle = lock_table.get(&key).unwrap();
        drop(guard);
        // The handle is still alive in the table.
        assert!(Arc::ptr_eq(&handle, &lock_table.get(&key).unwrap()));

        let guard2 = lock_table.lock_key(&key).await;

        // After we drop the original handle, make sure the new guard refers
        // to the KeyHandle in the table.
        drop(handle);
        assert!(Arc::ptr_eq(guard2.handle(), &lock_table.get(&key).unwrap()));

        // After dropping guard2, a new guard should be different to the old one.
        let old_ptr = Arc::as_ptr(guard2.handle());
        drop(guard2);
        let guard3 = lock_table.lock_key(&key).await;
        assert_ne!(old_ptr, Arc::as_ptr(guard3.handle()));
        assert!(Arc::ptr_eq(guard3.handle(), &lock_table.get(&key).unwrap()));
    }
}