tinylfu-cached 0.0.4

High performance, LFU based in-memory cache.
Documentation 
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use bloomfilter::Bloom;
use log::debug;

use crate::cache::types::{DoorKeeperCapacity, DoorKeeperFalsePositiveRate, KeyHash};

/// DoorKeeper is an implementation of BloomFilter that is used by TinyLFU abstraction to manage the key accesses
/// A Bloom filter is a probabilistic data structure used to test whether an element is a set member.
/// A bloom filter can query against large amounts of data and return either “possibly in the set” or “definitely not in the set”.
/// A bloom filter can have false positives, but false negatives are impossible.
pub(crate) struct DoorKeeper {
    bloom: Bloom<KeyHash>,
}

impl DoorKeeper {
    pub(crate) fn new(capacity: DoorKeeperCapacity, false_positive: DoorKeeperFalsePositiveRate) -> Self {
        DoorKeeper {
            bloom: Bloom::new_for_fp_rate(capacity, false_positive)
        }
    }

    pub(crate) fn add_if_missing(&mut self, key: &KeyHash) -> bool {
        if !self.has(key) {
            debug!("Adding key with hash {} to the doorkeeper", key);
            self.bloom.set(key);
            return true;
        }
        false
    }

    pub(crate) fn has(&self, key: &KeyHash) -> bool {
        self.bloom.check(key)
    }

    pub(crate) fn clear(&mut self) {
        self.bloom.clear();
    }
}

#[cfg(test)]
mod tests {
    use crate::cache::lfu::doorkeeper::DoorKeeper;

    #[test]
    fn add_if_missing() {
        let mut door_keeper = DoorKeeper::new(100, 0.01);
        door_keeper.add_if_missing(&200);

        assert!(door_keeper.has(&200));
        door_keeper.clear();
    }

    #[test]
    fn do_not_add_if_not_missing() {
        let mut door_keeper = DoorKeeper::new(100, 0.01);
        door_keeper.add_if_missing(&200);
        let added = door_keeper.add_if_missing(&200);

        assert!(door_keeper.has(&200));
        assert!(!added);
        door_keeper.clear();
    }

    #[test]
    fn add() {
        let mut door_keeper = DoorKeeper::new(100, 0.01);
        door_keeper.add_if_missing(&200);

        assert!(door_keeper.has(&200));
        door_keeper.clear();
    }

    #[test]
    fn add_multiple_keys() {
        let mut door_keeper = DoorKeeper::new(100, 0.01);
        door_keeper.add_if_missing(&200);
        door_keeper.add_if_missing(&100);

        assert!(door_keeper.has(&100));
        assert!(door_keeper.has(&200));
        door_keeper.clear();
    }

    #[test]
    fn does_not_contain_after_clear() {
        let mut door_keeper = DoorKeeper::new(100, 0.01);
        door_keeper.add_if_missing(&200);
        door_keeper.add_if_missing(&100);

        door_keeper.clear();
        assert!(!door_keeper.has(&100));
        assert!(!door_keeper.has(&200));
    }
}