package DupletListModule
/** Turns a class into a linked list where each instance knows it's previous
	and next member in the list */
public module DupletListModule
	static thistype firstActive = null
	static thistype lastActive = null
	static thistype firstInactive = null
	static thistype lastInactive = null
	static int activeSize = 0
	static int inactiveSize = 0
	thistype prev
	thistype next
	boolean active = true
	boolean linked = false

	construct()
		addToActive()

	function deactivate()
		if active and linked
			active = false
			removeFromActive()
			addToInactive()

	function activate()
		if not active and linked
			active = true
			removeFromInactive()
			addToActive()

	function remove()
		if not linked
			return
		if active
			active = false
			removeFromActive()
		else
			removeFromInactive()

	function removeFromActive()
		activeSize--
		if this != firstActive
			prev.next = next
		else
			firstActive = next
		if this != lastActive
			next.prev = prev	
		else
			lastActive = prev
		if firstActive != null
			if firstActive == lastActive
				firstActive.prev = null
			else
				firstActive.prev = lastActive
		linked = false
		prev = null
		next = null

	function removeFromInactive()
		inactiveSize--
		if this != firstInactive
			prev.next = next
		else
			firstInactive = next
		if this != lastInactive
			next.prev = prev	
		else
			lastInactive = prev
		if firstInactive != null
			if firstInactive == lastInactive
				firstInactive.prev = null
			else
				firstInactive.prev = lastInactive
		linked = false
		prev = null
		next = null
	
	function addToActive()
		activeSize++
		if activeSize == 1
			firstActive = this
			prev = null	
		else
			prev = lastActive
			lastActive.next = this
			firstActive.prev = this
		next = null
		lastActive = this
		linked = true

	function addToInactive()
		inactiveSize++
		if inactiveSize == 1
			firstInactive = this
			prev = null	
		else
			prev = lastInactive
			lastInactive.next = this
			firstInactive.prev = this
		next = null
		lastInactive = this
		linked = true

			
	ondestroy
		remove()
	
	/** an iterator which iterates over all instances of this class */
	static function iterator() returns Iterator
		return new Iterator()
		
	static class Iterator
		DupletListModule.thistype current = firstActive
		DupletListModule.thistype lastReturned = null

		private function syncCurrent()
			// Re-anchor from the last returned active node so iteration survives
			// removals/deactivations of what used to be `current`.
			if lastReturned != null and lastReturned.active
				current = lastReturned.next

		function hasNext() returns boolean
			syncCurrent()
			return current != null
	
		function next() returns DupletListModule.thistype
			syncCurrent()
			let res = current
			current = current.next
			lastReturned = res
			return res
 		
		function close() 
			destroy this

		function reset()
			current = firstActive
			lastReturned = null