use dashmap::DashMap;
use std::time::Instant;

/// Sliding window rate limiter.
pub struct RateLimiter {
    /// Map of key -> list of request timestamps
    windows: DashMap<String, Vec<Instant>>,
    /// Maximum requests per window
    max_requests: u64,
    /// Window duration in seconds
    window_seconds: u64,
}

impl RateLimiter {
    pub fn new(max_requests: u64, window_seconds: u64) -> Self {
        Self {
            windows: DashMap::new(),
            max_requests,
            window_seconds,
        }
    }

    /// Check if a request is allowed for the given key.
    /// Returns true if allowed, false if rate limited.
    pub fn check(&self, key: &str) -> bool {
        let now = Instant::now();
        let window = std::time::Duration::from_secs(self.window_seconds);

        let mut entry = self.windows.entry(key.to_string()).or_default();
        let timestamps = entry.value_mut();

        // Remove expired entries
        timestamps.retain(|t| now.duration_since(*t) < window);

        if timestamps.len() as u64 >= self.max_requests {
            false
        } else {
            timestamps.push(now);
            true
        }
    }

    /// Clean up expired entries (call periodically).
    pub fn cleanup(&self) {
        let now = Instant::now();
        let window = std::time::Duration::from_secs(self.window_seconds);

        self.windows.retain(|_, timestamps| {
            timestamps.retain(|t| now.duration_since(*t) < window);
            !timestamps.is_empty()
        });
    }
}

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

    #[test]
    fn test_allow_under_limit() {
        let limiter = RateLimiter::new(5, 60);
        for _ in 0..5 {
            assert!(limiter.check("client-1"));
        }
    }

    #[test]
    fn test_block_over_limit() {
        let limiter = RateLimiter::new(3, 60);
        assert!(limiter.check("client-1"));
        assert!(limiter.check("client-1"));
        assert!(limiter.check("client-1"));
        assert!(!limiter.check("client-1")); // 4th request blocked
    }

    #[test]
    fn test_different_keys_independent() {
        let limiter = RateLimiter::new(2, 60);
        assert!(limiter.check("client-a"));
        assert!(limiter.check("client-a"));
        assert!(!limiter.check("client-a")); // blocked
        // Different key should still be allowed
        assert!(limiter.check("client-b"));
        assert!(limiter.check("client-b"));
    }

    #[test]
    fn test_cleanup_removes_expired() {
        let limiter = RateLimiter::new(100, 0); // 0 second window = immediately expired
        limiter.check("client-1");
        // Sleep briefly to let entries expire
        std::thread::sleep(std::time::Duration::from_millis(10));
        limiter.cleanup();
        // After cleanup, the key should be allowed again (entries expired)
        assert!(limiter.check("client-1"));
    }
}