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    use std::time::Instant;
    use std::collections::hash_map::Entry;
    use std::collections::HashMap;
    use util::interval::{Interval, RealInterval};

    use message::{Command, Payload};
    use message::types::{Ping, Pong};

    // delay somewhere near communication timeout
    const ENORMOUS_PING_DELAY: f64 = 10f64;

    #[derive(Default, Clone, Debug)]
    pub struct RunningAverage {
    	count: u64,
    	bytes: u64,
    }

    impl RunningAverage {
    	fn new(initial: usize) -> Self {
    		RunningAverage { count: 1, bytes: initial as u64 }
    	}

    	fn add(&mut self, bytes: usize) {
    		self.count += 1;
    		// self.count guaranteed to be at least 1, since self.count min value is 0 and we just added 1 above
    		// so division by zero is impossible; qed
    		//
    		// let x = self.bytes
    		// let y = bytes, y >= 0
    		// to not overflow, this following be true:
    		// x + (y - x) / c >= 0
    		// so
    		// y / c  >= 0
    		// which is true by usize definition;
    		// qed
    		self.bytes = (self.bytes as i64 + ((bytes as i64 - self.bytes as i64) / self.count as i64)) as u64;
    	}

    	pub fn val(&self) -> u64 {
    		self.bytes
    	}
    }

    pub enum Flow { Receive, Send }

    #[derive(Default, Clone)]
    pub struct PeerStats<T: Interval = RealInterval> {
    	pub last_send: u32,
    	pub last_recv: u32,

    	pub total_send: u64,
    	pub total_recv: u64,

    	pub avg_ping: f64,
    	pub min_ping: Option<f64>,

    	send_avg: HashMap<Command, RunningAverage>,
    	recv_avg: HashMap<Command, RunningAverage>,

    	last_ping: Option<Instant>,
    	ping_count: u64,

    	interval: T,
    }

    impl<I: Interval> PeerStats<I> {

    	pub fn with_interval(interval: I) -> PeerStats<I> {
    		PeerStats {
    			interval: interval,
    			.. PeerStats::default()
    		}
    	}

    	pub fn report_send(&mut self, command: Command, bytes: usize) {
    		self.total_send += bytes as u64;
    		self.last_send = ::time::get_time().sec as u32;

    		if command == Ping::command() {
    			self.report_ping_send();
    		}

    		match self.send_avg.entry(command) {
    			Entry::Occupied(mut avg) => {
    				avg.get_mut().add(bytes);
    			},
    			Entry::Vacant(entry) => {
    				entry.insert(RunningAverage::new(bytes));
    			},
    		}
    	}

    	fn report_ping_send(&mut self) {
    		self.last_ping = Some(self.interval.now());
    		self.ping_count += 1;
    	}

    	fn report_pong_recv(&mut self) {
    		if let Some(last_ping) = self.last_ping {
    			let dur = self.interval.elapsed(last_ping);
    			let update = if dur.as_secs() > 10 {
    				ENORMOUS_PING_DELAY
    			}
    			else {
    				// max is 10, checked above, dur.as_secs() as u32 cannot overflow; qed
    				f64::from(dur.as_secs() as u32) + f64::from(dur.subsec_nanos()) / 1e9
    			};
    			self.min_ping = Some(self.min_ping.unwrap_or(ENORMOUS_PING_DELAY).min(update));
    			self.avg_ping += (update - self.avg_ping) / (self.ping_count as f64);
    		}
    	}

    	pub fn report_recv(&mut self, command: Command, bytes: usize) {
    		self.total_recv += bytes as u64;
    		self.last_recv = ::time::get_time().sec as u32;

    		if command == Pong::command() {
    			self.report_pong_recv();
    		}

    		match self.recv_avg.entry(command) {
    			Entry::Occupied(mut avg) => {
    				avg.get_mut().add(bytes);
    			},
    			Entry::Vacant(entry) => {
    				entry.insert(RunningAverage::new(bytes));
    			},
    		}
    	}

    	pub fn avg<T>(&self, dir: Flow, cmd: T) -> u64
    		where T: Into<Command>
    	{
    		match dir {
    			Flow::Receive => self.recv_avg.get(&cmd.into()).and_then(|x| Some(x.val())).unwrap_or_default(),
    			Flow::Send => self.send_avg.get(&cmd.into()).and_then(|x| Some(x.val())).unwrap_or_default(),
    		}
    	}
    }

    #[cfg(test)]
    mod tests {

    	use super::{RunningAverage, PeerStats, Flow};
    	use util::interval::{FixedIntervalSpawner, RealInterval};

    	#[test]
    	fn avg() {
    		let mut avg = RunningAverage::new(10);
    		avg.add(12);

    		assert_eq!(avg.bytes, 11);
    	}

    	#[test]
    	fn avg_l() {
    		let mut avg = RunningAverage::new(10);
    		avg.add(12);
    		avg.add(20);
    		avg.add(28);
    		avg.add(12);

    		assert_eq!(avg.bytes, 16);
    	}

    	#[test]
    	fn smoky() {
    		let mut stats = PeerStats::<FixedIntervalSpawner>::with_interval(FixedIntervalSpawner::new(50));
    		stats.report_send("ping".into(), 200);

    		assert_eq!(stats.send_avg[&"ping".into()].val(), 200);

    		stats.report_recv("pong".into(), 50);
    		assert!(stats.avg_ping > 0.03);
    		assert!(stats.avg_ping < 0.1);
    	}

    	#[test]
    	fn avg_t() {
    		let mut stats = PeerStats::<RealInterval>::default();
    		stats.report_send("inv".into(), 200);
    		stats.report_send("inv".into(), 300);

    		assert_eq!(stats.avg(Flow::Send, "inv"), 250);

    		let mut stats = PeerStats::<RealInterval>::default();
    		stats.report_recv("inv".into(), 2000);
    		stats.report_recv("inv".into(), 3000);

    		assert_eq!(stats.avg(Flow::Receive, "inv"), 2500);
    	}
    }

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