crius 0.4.0

Crius is a simple hystrix-like circuit breaker
Documentation 
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use std::collections::vec_deque::VecDeque;
use std::time::{Duration, Instant};
use command::Config;

#[derive(PartialEq, Eq, Hash, Copy, Clone, Debug)]
pub enum Point {
    SUCCESS,
    FAILURE,
}

#[derive(Clone, Debug)]
struct Bucket {
    points: Vec<Point>,
    timestamp: Instant,
}

impl Bucket {
    fn new() -> Bucket {
        Bucket {
            points: Vec::new(),
            timestamp: Instant::now(),
        }
    }
}

#[derive(Clone, Debug)]
pub struct Window {
    /// Queue structure holding the window's buckets
    buckets: VecDeque<Bucket>,

    /// Period during which a single bucket is valid
    bucket_ms: Duration,

    /// Maximum number of buckets in a window
    buckets_nr: u32,

    /// Total size of all buckets in a window
    window_size: Duration,
}

impl Window {
    /// Attempt to create a window from a given configuration. Returns
    /// `None` if the duration calculations overflowed.
    pub fn new(config: Config) -> Option<Self> {
        let bucket_ms = Duration::from_millis(config.bucket_size_in_ms);
        let window_size = bucket_ms.checked_mul(config.buckets_in_window);

        window_size.map(|window_size| Window {
            bucket_ms,
            window_size,
            buckets: VecDeque::new(),
            buckets_nr: config.buckets_in_window,
        })
    }

    pub fn add_point(&mut self, point: Point) {
        let current_bucket = self.update_window_returning_latest_bucket();
        current_bucket.points.push(point);
    }

    pub fn clear_window(&mut self) {
        self.buckets.clear();
    }

    /// Returns the points of all currently valid buckets:
    pub fn get_points(&mut self) -> Vec<Point> {
        let threshold = Instant::now() - self.window_size;
        self.buckets
            .iter()
            .filter(|bucket| bucket.timestamp > threshold)
            .fold(vec![], |mut acc, bucket| {
                acc.extend(&bucket.points);
                return acc;
            })
    }

    fn update_window_returning_latest_bucket(&mut self) -> &mut Bucket {
        let now = Instant::now();
        let latest_threshold = self.buckets
            .back()
            .map(|bucket| bucket.timestamp + self.bucket_ms);

        if let Some(threshold) = latest_threshold {
            // Return the latest bucket if it is still current:
            if threshold > now {
                return self.buckets.back_mut().unwrap();
            }

            // Otherwise create and return a new bucket:
            let new_bucket = Bucket {
                points: Vec::new(),
                timestamp: threshold,
            };

            self.buckets.push_back(new_bucket);
            if self.buckets.len() > self.buckets_nr as usize {
                self.buckets.pop_front();
            }
            return self.buckets.back_mut().unwrap();
        } else {
            // Create a bucket if there aren't any in the window currently:
            let first_bucket = Bucket::new();
            self.buckets.push_back(first_bucket);
            return self.buckets.back_mut().unwrap();
        }
    }
}