foxtive-worker 0.1.0

use async_trait::async_trait;
use std::sync::Arc;

use governor::{Quota, RateLimiter};
use governor::state::{NotKeyed, InMemoryState};
use governor::clock::DefaultClock;

use crate::error::{WorkerError, WorkerResult};
use crate::message::ReceivedMessage;
use crate::middleware::{MessageHandler, Middleware};

/// Middleware that rate limits message processing using a token bucket algorithm.
///
/// This middleware prevents overwhelming downstream systems by limiting the rate
/// at which messages are processed. When the rate limit is exceeded, messages
/// are rejected with a `WorkerError::RateLimited` error.
///
/// # Example
/// ```rust,no_run
/// use foxtive_worker::RateLimitMiddleware;
///
/// // Allow 100 messages per second with burst capacity of 50
/// let middleware = RateLimitMiddleware::new(100, 50);
/// ```
pub struct RateLimitMiddleware {
    limiter: Arc<RateLimiter<NotKeyed, InMemoryState, DefaultClock>>,
    name: String,
}

impl std::fmt::Debug for RateLimitMiddleware {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("RateLimitMiddleware")
            .field("name", &self.name)
            .finish()
    }
}

impl RateLimitMiddleware {
    /// Create a new rate limiter middleware.
    ///
    /// # Arguments
    /// * `rate` - Sustained rate in messages per second
    /// * `burst` - Maximum burst capacity (max tokens)
    pub fn new(rate: u64, burst: u32) -> Self {
        let quota = Quota::per_second(std::num::NonZeroU32::new(rate as u32).unwrap_or(std::num::NonZeroU32::new(1).unwrap()))
            .allow_burst(std::num::NonZeroU32::new(burst).unwrap_or(std::num::NonZeroU32::new(1).unwrap()));

        Self {
            limiter: Arc::new(RateLimiter::direct(quota)),
            name: format!("rate-limit-{}rps", rate),
        }
    }

    /// Create a rate limiter with equal rate and burst capacity.
    pub fn with_rate(rate: u64) -> Self {
        Self::new(rate, rate as u32)
    }
}

#[async_trait]
impl Middleware for RateLimitMiddleware {
    fn name(&self) -> &str {
        &self.name
    }

    async fn handle(
        &self,
        message: ReceivedMessage<serde_json::Value>,
        next: Box<dyn MessageHandler>,
    ) -> WorkerResult<()> {
        match self.limiter.check() {
            Ok(_) => {
                next.handle(message).await
            }
            Err(_) => {
                Err(WorkerError::ProcessingFailed(format!(
                    "Rate limit exceeded for middleware '{}'",
                    self.name
                )))
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::message::{Message, MessageMetadata, AckHandle};
    use std::sync::Arc;
    use tokio::time::{self, Duration};

    struct SuccessHandler;

    #[async_trait]
    impl MessageHandler for SuccessHandler {
        async fn handle(&self, _message: ReceivedMessage<serde_json::Value>) -> WorkerResult<()> {
            Ok(())
        }
    }

    fn create_test_message() -> ReceivedMessage<serde_json::Value> {
        #[derive(Debug)]
        struct MockAckHandle;

        #[async_trait]
        impl AckHandle for MockAckHandle {
            async fn ack(&self) -> WorkerResult<()> {
                Ok(())
            }

            async fn nack(&self, _requeue: bool) -> WorkerResult<()> {
                Ok(())
            }
        }

        let message = Message {
            id: "test-1".to_string(),
            payload: serde_json::json!({"test": "data"}),
            metadata: MessageMetadata::new("test-queue"),
        };
        ReceivedMessage::new(message, Arc::new(MockAckHandle))
    }

    #[tokio::test]
    async fn test_rate_limit_allows_within_limit() {
        let rate = 10;
        let burst = 10;
        let middleware = RateLimitMiddleware::new(rate, burst);
        
        // Should allow up to burst capacity
        for _ in 0..burst {
            let message = create_test_message();
            assert!(middleware.handle(message, Box::new(SuccessHandler)).await.is_ok());
        }
    }

    #[tokio::test]
    async fn test_rate_limit_rejects_over_limit() {
        let rate = 10;
        let burst = 5;
        let middleware = RateLimitMiddleware::new(rate, burst);
        
        // Consume all tokens
        for _ in 0..burst {
            let message = create_test_message();
            middleware.handle(message, Box::new(SuccessHandler)).await.unwrap();
        }
        
        // Next should fail
        let message = create_test_message();
        let result = middleware.handle(message, Box::new(SuccessHandler)).await;
        assert!(result.is_err());
        if let Err(WorkerError::ProcessingFailed(_)) = result {
            // Success: rate limited
        } else {
            panic!("Expected ProcessingFailed (rate limited)");
        }
    }

    #[tokio::test]
    async fn test_rate_limit_with_custom_burst() {
        let rate = 100;
        let burst = 20;
        let middleware = RateLimitMiddleware::new(rate, burst);
        
        // Should allow burst of 20
        for _ in 0..burst {
            let message = create_test_message();
            assert!(middleware.handle(message, Box::new(SuccessHandler)).await.is_ok());
        }
        
        // 21st should fail
        let message = create_test_message();
        assert!(middleware.handle(message, Box::new(SuccessHandler)).await.is_err());
        
        let message = create_test_message();
        if let Err(WorkerError::ProcessingFailed(_)) = middleware.handle(message, Box::new(SuccessHandler)).await {
            // Success: rate limited
        } else {
            panic!("Expected ProcessingFailed (rate limited)");
        }
    }

    #[tokio::test]
    async fn test_rate_limit_refills_over_time() {
        let rate = 1; // 1 message per second
        let burst = 1;
        let middleware = RateLimitMiddleware::new(rate, burst);

        // Consume the initial token
        let message = create_test_message();
        assert!(middleware.handle(message, Box::new(SuccessHandler)).await.is_ok());

        // Next message should be rate-limited immediately
        let message = create_test_message();
        assert!(middleware.handle(message, Box::new(SuccessHandler)).await.is_err());

        // Wait for a token to refill (slightly more than 1 second)
        time::sleep(Duration::from_millis(1100)).await;

        // Now it should allow another message
        let message = create_test_message();
        assert!(middleware.handle(message, Box::new(SuccessHandler)).await.is_ok());
    }
}