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    // Copyright 2015-2017 Parity Technologies (UK) Ltd.
    // This file is part of Parity.

    // Parity is free software: you can redistribute it and/or modify
    // it under the terms of the GNU General Public License as published by
    // the Free Software Foundation, either version 3 of the License, or
    // (at your option) any later version.

    // Parity is distributed in the hope that it will be useful,
    // but WITHOUT ANY WARRANTY; without even the implied warranty of
    // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    // GNU General Public License for more details.

    // You should have received a copy of the GNU General Public License
    // along with Parity.  If not, see <http://www.gnu.org/licenses/>.

    //! Engine timeout transitioning calls `Engine.step()` on timeout.

    use std::sync::Weak;
    use time::Duration;
    use io::{IoContext, IoHandler, TimerToken};
    use engines::Engine;

    /// Timeouts lookup
    pub trait Timeouts<S: Sync + Send + Clone>: Send + Sync {
    	/// Return the first timeout.
    	fn initial(&self) -> Duration;

    	/// Get a timeout based on step.
    	fn timeout(&self, step: &S) -> Duration;
    }

    /// Timeout transition handling.
    pub struct TransitionHandler<S: Sync + Send + Clone>  {
    	engine: Weak<Engine>,
    	timeouts: Box<Timeouts<S>>,
    }

    impl <S> TransitionHandler<S> where S: Sync + Send + Clone {
    	/// New step caller by timeouts.
    	pub fn new(engine: Weak<Engine>, timeouts: Box<Timeouts<S>>) -> Self {
    		TransitionHandler {
    			engine: engine,
    			timeouts: timeouts,
    		}
    	}
    }

    /// Timer token representing the consensus step timeouts.
    pub const ENGINE_TIMEOUT_TOKEN: TimerToken = 23;

    fn set_timeout<S: Sync + Send + Clone>(io: &IoContext<S>, timeout: Duration) {
    	io.register_timer_once(ENGINE_TIMEOUT_TOKEN, timeout.num_milliseconds() as u64)
    		.unwrap_or_else(|e| warn!(target: "engine", "Failed to set consensus step timeout: {}.", e))
    }

    impl <S> IoHandler<S> for TransitionHandler<S> where S: Sync + Send + Clone + 'static {
    	fn initialize(&self, io: &IoContext<S>) {
    		set_timeout(io, self.timeouts.initial());
    	}

    	/// Call step after timeout.
    	fn timeout(&self, _io: &IoContext<S>, timer: TimerToken) {
    		if timer == ENGINE_TIMEOUT_TOKEN {
    			if let Some(engine) = self.engine.upgrade() {
    				engine.step();
    			}
    		}
    	}

    	/// Set a new timer on message.
    	fn message(&self, io: &IoContext<S>, next: &S) {
    		if let Err(io_err) = io.clear_timer(ENGINE_TIMEOUT_TOKEN) {
    			warn!(target: "engine", "Could not remove consensus timer {}.", io_err)
    		}
    		set_timeout(io, self.timeouts.timeout(next));
    	}
    }

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