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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/>.

    //! Panic utilities

    use std::thread;
    use std::sync::Arc;
    use std::default::Default;

    use parking_lot::Mutex;

    /// Thread-safe closure for handling possible panics
    pub trait OnPanicListener: Send + Sync + 'static {
    	/// Invoke listener
    	fn call(&mut self, arg: &str);
    }

    /// Forwards panics from child
    pub trait ForwardPanic {
    	/// Attach `on_panic` listener to `child` and rethrow all panics
    	fn forward_from<S>(&self, child: &S) where S : MayPanic;
    }

    /// Trait indicating that the structure catches some of the panics (most probably from spawned threads)
    /// and it's possbile to be notified when one of the threads panics.
    pub trait MayPanic {
    	/// `closure` will be invoked whenever panic in thread is caught
    	fn on_panic<F>(&self, closure: F) where F: OnPanicListener;
    }

    struct PanicGuard<'a> {
    	handler: &'a PanicHandler,
    }

    impl<'a> Drop for PanicGuard<'a> {
    	fn drop(&mut self) {
    		if thread::panicking() {
    			self.handler.notify_all("Panic!".to_owned());
    		}
    	}
    }

    /// Structure that allows to catch panics and notify listeners
    pub struct PanicHandler {
    	listeners: Mutex<Vec<Box<OnPanicListener>>>
    }

    impl Default for PanicHandler {
    	fn default() -> Self {
    		PanicHandler::new()
    	}
    }

    impl PanicHandler {
    	/// Creates new `PanicHandler` wrapped in `Arc`
    	pub fn new_in_arc() -> Arc<Self> {
    		Arc::new(Self::new())
    	}

    	/// Creates new `PanicHandler`
    	pub fn new() -> Self {
    		PanicHandler {
    			listeners: Mutex::new(vec![])
    		}
    	}

    	/// Invoke closure and catch any possible panics.
    	/// In case of panic notifies all listeners about it.
    	#[cfg_attr(feature="dev", allow(deprecated))]
    	pub fn catch_panic<G, R>(&self, g: G) -> thread::Result<R> where G: FnOnce() -> R + Send + 'static {
    		let _guard = PanicGuard { handler: self };
    		let result = g();
    		Ok(result)
    	}

    	/// Notifies all listeners in case there is a panic.
    	/// You should use `catch_panic` instead of calling this method explicitly.
    	pub fn notify_all(&self, r: String) {
    		let mut listeners = self.listeners.lock();
    		for mut listener in &mut **listeners {
    			listener.call(&r);
    		}
    	}
    }

    impl MayPanic for PanicHandler {
    	fn on_panic<F>(&self, closure: F) where F: OnPanicListener {
    		self.listeners.lock().push(Box::new(closure));
    	}
    }

    impl ForwardPanic for Arc<PanicHandler> {
    	fn forward_from<S>(&self, child: &S) where S : MayPanic {
    		let p = self.clone();
    		child.on_panic(move |t| p.notify_all(t));
    	}
    }

    impl<F> OnPanicListener for F
    	where F: FnMut(String) + Send + Sync + 'static {
    	fn call(&mut self, arg: &str) {
    		self(arg.to_owned())
    	}
    }

    #[test]
    #[ignore] // panic forwarding doesnt work on the same thread in beta
    fn should_notify_listeners_about_panic () {
    	use parking_lot::RwLock;
    	// given
    	let invocations = Arc::new(RwLock::new(vec![]));
    	let i = invocations.clone();
    	let p = PanicHandler::new();
    	p.on_panic(move |t| i.write().push(t));

    	// when
    	p.catch_panic(|| panic!("Panic!")).unwrap_err();

    	// then
    	assert!(invocations.read()[0] == "Panic!");
    }

    #[test]
    #[ignore] // panic forwarding doesnt work on the same thread in beta
    fn should_notify_listeners_about_panic_when_string_is_dynamic () {
    	use parking_lot::RwLock;
    	// given
    	let invocations = Arc::new(RwLock::new(vec![]));
    	let i = invocations.clone();
    	let p = PanicHandler::new();
    	p.on_panic(move |t| i.write().push(t));

    	// when
    	p.catch_panic(|| panic!("Panic: {}", 1)).unwrap_err();

    	// then
    	assert!(invocations.read()[0] == "Panic: 1");
    }

    #[test]
    fn should_notify_listeners_about_panic_in_other_thread () {
    	use std::thread;
    	use parking_lot::RwLock;
    	// given
    	let invocations = Arc::new(RwLock::new(vec![]));
    	let i = invocations.clone();
    	let p = PanicHandler::new();
    	p.on_panic(move |t| i.write().push(t));

    	// when
    	let t = thread::spawn(move ||
    		p.catch_panic(|| panic!("Panic!")).unwrap()
    	);
    	t.join().unwrap_err();

    	// then
    	assert!(invocations.read()[0] == "Panic!");
    }

    #[test]
    #[ignore] // panic forwarding doesnt work on the same thread in beta
    fn should_forward_panics () {
    	use parking_lot::RwLock;
    	// given
    	let invocations = Arc::new(RwLock::new(vec![]));
    	let i = invocations.clone();
    	let p = PanicHandler::new_in_arc();
    	p.on_panic(move |t| i.write().push(t));

    	let p2 = PanicHandler::new();
    	p.forward_from(&p2);

    	// when
    	p2.catch_panic(|| panic!("Panic!")).unwrap_err();

    	// then
    	assert!(invocations.read()[0] == "Panic!");
    }

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