walleth 0.1.0

use super::Observer;

/// A store for state that can be subscribed to
pub struct Observable<S> {
	state: S,
	observers: Vec<Observer<S>>,
}

impl<S> Observable<S>
where
	S: Clone,
{
	pub fn new(initial_state: S) -> Self {
		Observable {
			state: initial_state,
			observers: vec![],
		}
	}

	/// Get the current state
	pub fn get_state(&self) -> &S {
		&self.state
	}

	/// Set the current state
	/// This will call all event listeners with the new state
	pub fn set_state(&mut self, new_state: S) -> () {
		self.state = new_state;
		self.emit();
	}

	/// Update the current state
	/// This will call all event listeners with the new state
	/// The updater function will be called with a mutable reference to the current state
	/// allowing you to mutate the state
	///
	/// # Example
	///
	/// ```
	/// use walleth::Observable;
	///
	/// let mut store = Observable::new(0);
	/// store.update(|state| {
	///   *state = 1;
	/// });
	///
	/// assert_eq!(store.get_state(), &1);
	/// ```
	///
	pub fn update<F>(&mut self, updater: F) -> ()
	where
		F: Fn(&mut S),
	{
		updater(&mut self.state);
		self.emit();
	}

	/// Subscribe to state changes
	/// Returns the id of the subscriber
	pub fn subscribe<F>(&mut self, subscriber: F) -> usize
	where
		F: 'static + FnMut(&S),
	{
		self.observers
			.push(Observer::new(self.observers.len(), Box::new(subscriber)));
		self.observers.len() - 1
	}

	/// Unsubscribe from state changes
	pub fn unsubscribe(&mut self, id: usize) -> () {
		self.observers.retain(|observer| observer.id != id);
	}

	/// Emit the current state to all subscribers
	fn emit(&mut self) -> () {
		for observer in &mut self.observers {
			(observer.callback)(&self.state);
		}
	}
}