rifts 0.3.1

//! Dedupe store — drops messages that have already been seen within
//! the dedupe window (spec §11.2).
//!
//! Keyed by `(topic, dedupe_key)`. A background sweep evicts old
//! entries; a read returns whether the key has been seen.

use std::time::Duration;

use dashmap::DashMap;

use crate::now_ms;

/// In-memory deduplication store.
///
/// Each entry is keyed by `(topic, dedupe_key)` and stores the epoch
/// millisecond at which it expires.  `check_and_record` is the main
/// entry point: it atomically checks and records, returning `true` if
/// the message should be processed (fresh) or `false` if it is a
/// duplicate.
#[derive(Debug, Default)]
pub struct DedupeStore {
    inner: DashMap<(String, String), i64>,
}

impl DedupeStore {
    /// Create an empty dedupe store.
    pub fn new() -> Self {
        Self::default()
    }

    /// Returns `true` if the key is fresh (i.e. the message should be
    /// processed); `false` if it has been seen within the window.
    ///
    /// If the key exists but its previous entry has already expired,
    /// the entry is renewed and the message is treated as fresh.
    pub fn check_and_record(&self, topic: &str, key: &str, window: Duration) -> bool {
        let now = now_ms();
        let expires = now + window.as_millis() as i64;
        let k = (topic.to_string(), key.to_string());
        // DashMap 6.x 的 entry() 是原子的：and_modify 与 or_insert_with 闭包
        // 互斥——同一 key 只有一个闭包会执行。这避免了原先 get_mut → insert
        // 两步之间的竞争窗口。
        let mut is_fresh = false;
        self.inner
            .entry(k)
            .and_modify(|v| {
                if *v <= now {
                    *v = expires;
                    is_fresh = true;
                }
            })
            .or_insert_with(|| {
                is_fresh = true;
                expires
            });
        is_fresh
    }

    /// Drop expired entries. Returns number of removed entries.
    ///
    /// Should be called periodically from a background task to bound
    /// memory usage.
    pub fn sweep(&self) -> usize {
        let now = now_ms();
        let expired: Vec<(String, String)> = self
            .inner
            .iter()
            .filter(|kv| *kv.value() <= now)
            .map(|kv| (kv.key().0.clone(), kv.key().1.clone()))
            .collect();
        let mut removed = 0;
        for k in expired {
            if self.inner.remove(&k).is_some() {
                removed += 1;
            }
        }
        removed
    }

    /// Number of tracked keys.
    pub fn len(&self) -> usize {
        self.inner.len()
    }

    /// Returns `true` if the store is empty.
    pub fn is_empty(&self) -> bool {
        self.inner.is_empty()
    }
}

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

    #[test]
    fn fresh_then_duplicate() {
        let d = DedupeStore::new();
        assert!(d.check_and_record("t", "k", Duration::from_secs(60)));
        assert!(!d.check_and_record("t", "k", Duration::from_secs(60)));
    }

    #[test]
    fn per_topic() {
        let d = DedupeStore::new();
        assert!(d.check_and_record("t1", "k", Duration::from_secs(60)));
        assert!(d.check_and_record("t2", "k", Duration::from_secs(60)));
    }

    #[test]
    fn sweep_drops_expired() {
        let d = DedupeStore::new();
        // 0-ms window — entries are immediately expired.
        d.check_and_record("t", "k", Duration::from_millis(0));
        // Manually expire it.
        d.inner.insert(("t".into(), "k".into()), 0);
        assert_eq!(d.sweep(), 1);
    }

    #[test]
    fn concurrent_dedup_returns_one_fresh() {
        use std::sync::Arc;
        use std::thread;
        let store = Arc::new(DedupeStore::new());
        let w = Duration::from_secs(60);
        let handles: Vec<_> = (0..8)
            .map(|_| {
                let s = store.clone();
                thread::spawn(move || s.check_and_record("t", "k", w))
            })
            .collect();
        let results: Vec<bool> = handles.into_iter().map(|h| h.join().unwrap()).collect();
        let fresh_count = results.iter().filter(|&&b| b).count();
        assert_eq!(fresh_count, 1, "exactly one thread should see fresh");
    }
}