# Queuing and management of arbitrary events in a timeline
class EventQueue[E]
	# Comparator used by the queue
	private var event_comparator = new EventComparator

	# Efficient queue
	private var queue = new MinHeap[EventInfo[E]](event_comparator)

	# List of current active event
	private var actives = new Array[EventInfo[E]]

	# List of previously active event
	private var old_actives = new Array[EventInfo[E]]

	# Global time since the creation of the queue
	var time = 0.0

	# Nearest deadline, used to optimise queue access
	#
	# `inf` if no deadline is set
	private var next: Float = inf

	# Register an `event` in the queue to be active in `delay` units of time.
	#
	# If `duration` is given, this is duration after what the event is automatically discarded.
	# If `null`, 0.0 or not given, the event will be executed only once
	# Use `inf` for an event with an infinite duration.
	fun add(event: E, delay: Float, duration: nullable Float): EventInfo[E]
	do
		return add_at(event, time + delay, duration)
	end

	# Register an `event` in the queue executed at a specific time.
	fun add_at(event: E, start: Float, duration: nullable Float): EventInfo[E]
	do
		if start < next then next = start
		var ei = new EventInfo[E](event, self, start, duration or else 0.0)
		queue.add ei

		return ei
	end

	# Add a given amount of time and return all the events that were active during the delay.
	#
	# Note that events that expired during the delay are marked `has_expired` and are still returned.
	fun update(dt: Float): SequenceRead[EventInfo[E]]
	do
		var time = self.time
		time += dt
		self.time = time

		# Switch things
		var tmp = old_actives
		old_actives = actives
		actives = tmp

		# Discard dead events
		actives.clear
		for ei in old_actives do
			if not ei.has_expired then actives.add ei
		end

		# Start new events
		if time >= next then loop
			if queue.is_empty then
				next = inf
				break
			end
			var ei = queue.peek
			if ei.start > time then
				next = ei.start
				break
			end
			ei = queue.take
			if not ei.has_expired then
				actives.add ei
				ei.occurrences = 0
			end
		end

		if actives.is_empty then return actives

		# Update event information
		for ei in actives do ei.update(time, dt)

		return actives
	end
end