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pub struct Context<F: crate::SequenceFactory = crate::TimeSequenceFactory> {
	sequence_factory: F,
	sequence: F::Sequence,
	session: Session,
}

impl Default for Context<crate::TimeSequenceFactory> {
	fn default() -> Self {
		Self::new()
	}
}

impl<SequenceFactory: crate::SequenceFactory + Default> Context<SequenceFactory> {
	pub fn new() -> Self {
		Context {
			sequence_factory: Default::default(),
			sequence: SequenceFactory::base(),
			session: Session::new(),
		}
	}
}

impl<SequenceFactory: crate::SequenceFactory> Context<SequenceFactory> {
	pub fn next_sequence(&mut self) -> Sequence<SequenceFactory> {
		let next = self.sequence_factory.acquire(self.sequence.clone());
		assert!(next > self.sequence);

		self.sequence = next.clone();

		Sequence {
			value: next,
			session: self.session.clone(),
		}
	}

	pub fn session(&self) -> Session {
		self.session.clone()
	}
}

pub struct Sequence<SequenceFactory: crate::SequenceFactory> {
	value: SequenceFactory::Sequence,
	session: Session,
}

impl<T: crate::SequenceFactory> std::fmt::Debug for Sequence<T>
	where T::Sequence: std::fmt::Debug
{
	fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
		write!(f, "Sequence({:?}, {:?})", self.value, self.session)
	}
}


impl<SequenceFactory: crate::SequenceFactory> Default for Sequence<SequenceFactory> {
	fn default() -> Self {
		Sequence {
			value: SequenceFactory::base(),
			session: Session(u64::min_value()),
		}
	}
}

impl<SequenceFactory: crate::SequenceFactory> Clone for Sequence<SequenceFactory> {
	fn clone(&self) -> Self {
		Sequence {
			value: self.value.clone(),
			session: self.session.clone(),
		}
	}
}

impl<SequenceFactory: crate::SequenceFactory> std::cmp::PartialEq for Sequence<SequenceFactory> {
	fn eq(&self, that: &Self) -> bool {
		let Sequence{ref value, ref session} = self;
		(value, session) == (&that.value, &that.session)
	}
}

impl<SequenceFactory: crate::SequenceFactory> std::cmp::Eq for Sequence<SequenceFactory> {
}

impl<SequenceFactory: crate::SequenceFactory> std::cmp::PartialOrd for Sequence<SequenceFactory> {
	fn partial_cmp(&self, that: &Self) -> Option<std::cmp::Ordering> {
		let Sequence{ref value, ref session} = self;
		std::cmp::PartialOrd::partial_cmp(
			&(value, session),
			&(&that.value, &that.session))
	}
}

impl<SequenceFactory: crate::SequenceFactory> std::cmp::Ord for Sequence<SequenceFactory> {
	fn cmp(&self, that: &Self) -> std::cmp::Ordering {
		let Sequence{ref value, ref session} = self;
		(value, session).cmp(&(&that.value, &that.session))
	}
}

#[derive(Clone,Eq,PartialEq,Hash,Ord,PartialOrd)]
pub struct Session(u64);

impl Session {
	pub fn new() -> Self {
		Self::unsafe_from_u64(rand::Rng::gen(&mut rand::thread_rng()))
	}

	/// Create a session from the provided value.
	///
	/// WARNING: If the same session id is used concurrently it may cause unspecified behaviour including crashes.
	pub fn unsafe_from_u64(session: u64) -> Self {
		Session(session)
	}
}

impl std::fmt::Debug for Session {
	fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
		write!(f, "Session({:x})", self.0)
	}
}