var/datum/controller/process/garbage_collector/garbage_collector
var/list/delayed_garbage = list()

/datum/controller/process/garbage_collector
	var/garbage_collect = 1			// Whether or not to actually do work
	var/collection_timeout = 300	//deciseconds to wait to let running procs finish before we just say fuck it and force del() the object
	var/max_checks_multiplier = 5	//multiplier (per-decisecond) for calculating max number of tests per tick. These tests check if our GC'd objects are actually GC'd
	var/max_forcedel_multiplier = 1	//multiplier (per-decisecond) for calculating max number of force del() calls per tick.

	var/dels 		= 0			// number of del()'s we've done this tick
	var/hard_dels 	= 0			// number of hard dels in total
	var/list/destroyed = list() // list of refID's of things that should be garbage collected
								// refID's are associated with the time at which they time out and need to be manually del()
								// we do this so we aren't constantly locating them and preventing them from being gc'd

	var/list/logging = list()	// list of all types that have failed to GC associated with the number of times that's happened.
								// the types are stored as strings

/datum/controller/process/garbage_collector/setup()
	name = "garbage"
	schedule_interval = 2 SECONDS

	if(!garbage_collector)
		garbage_collector = src

	for(var/garbage in delayed_garbage)
		qdel(garbage)
	delayed_garbage.Cut()
	delayed_garbage = null

/datum/controller/process/garbage_collector/doWork()
	if(!garbage_collect)
		return

	dels = 0
	var/time_to_kill = world.time - collection_timeout // Anything qdel() but not GC'd BEFORE this time needs to be manually del()
	var/checkRemain = max_checks_multiplier * schedule_interval
	var/maxDels = max_forcedel_multiplier * schedule_interval

	while(destroyed.len && --checkRemain >= 0)
		if(dels >= maxDels)
			#ifdef GC_DEBUG
			testing("GC: Reached max force dels per tick [dels] vs [maxDels]")
			#endif
			break // Server's already pretty pounded, everything else can wait 2 seconds
		var/refID = destroyed[1]
		var/GCd_at_time = destroyed[refID]
		if(GCd_at_time > time_to_kill)
			#ifdef GC_DEBUG
			testing("GC: [refID] not old enough, breaking at [world.time] for [GCd_at_time - time_to_kill] deciseconds until [GCd_at_time + collection_timeout]")
			#endif
			break // Everything else is newer, skip them
		var/atom/A = locate(refID)
		#ifdef GC_DEBUG
		testing("GC: [refID] old enough to test: GCd_at_time: [GCd_at_time] time_to_kill: [time_to_kill] current: [world.time]")
		#endif
		if(A && A.gcDestroyed == GCd_at_time) // So if something else coincidently gets the same ref, it's not deleted by mistake
			// Something's still referring to the qdel'd object.  Kill it.
			testing("GC: -- \ref[A] | [A.type] was unable to be GC'd and was deleted --")
			logging["[A.type]"]++
			del(A)
			++dels
			++hard_dels
		#ifdef GC_DEBUG
		else
			testing("GC: [refID] properly GC'd at [world.time] with timeout [GCd_at_time]")
		#endif
		destroyed.Cut(1, 2)

/datum/controller/process/garbage_collector/proc/AddTrash(datum/A)
	if(!istype(A) || !isnull(A.gcDestroyed))
		return
	#ifdef GC_DEBUG
	testing("GC: AddTrash(\ref[A] - [A.type])")
	#endif
	A.gcDestroyed = world.time
	destroyed -= "\ref[A]" // Removing any previous references that were GC'd so that the current object will be at the end of the list.
	destroyed["\ref[A]"] = world.time

/datum/controller/process/garbage_collector/getStatName()
	return ..()+"([garbage_collector.destroyed.len]/[garbage_collector.dels]/[garbage_collector.hard_dels])"

// Should be treated as a replacement for the 'del' keyword.
// Datums passed to this will be given a chance to clean up references to allow the GC to collect them.
/proc/qdel(var/datum/A)
	if(!A)
		return
	if(!istype(A))
		warning("qdel() passed object of type [A.type]. qdel() can only handle /datum types.")
		del(A)
		if(garbage_collector)
			garbage_collector.dels++
			garbage_collector.hard_dels++
	else if(isnull(A.gcDestroyed))
		// Let our friend know they're about to get collected
		. = !A.Destroy()
		if(. && A)
			A.finalize_qdel()

/datum/proc/finalize_qdel()
	if(IsPooled(src))
		PlaceInPool(src)
	else
		del(src)

/atom/finalize_qdel()
	if(IsPooled(src))
		PlaceInPool(src)
	else
		if(garbage_collector)
			garbage_collector.AddTrash(src)
		else
			delayed_garbage |= src

/icon/finalize_qdel()
	del(src)

/image/finalize_qdel()
	del(src)

/mob/finalize_qdel()
	del(src)

/turf/finalize_qdel()
	del(src)

// Default implementation of clean-up code.
// This should be overridden to remove all references pointing to the object being destroyed.
// Return true if the the GC controller should allow the object to continue existing. (Useful if pooling objects.)
/datum/proc/Destroy()
	tag = null
	return

#ifdef TESTING
/client/var/running_find_references

/mob/verb/create_thing()
	set category = "Debug"
	set name = "Create Thing"

	var/path = input("Enter path")
	var/atom/thing = new path(loc)
	thing.find_references()

/atom/verb/find_references()
	set category = "Debug"
	set name = "Find References"
	set background = 1
	set src in world

	if(!usr || !usr.client)
		return

	if(usr.client.running_find_references)
		testing("CANCELLED search for references to a [usr.client.running_find_references].")
		usr.client.running_find_references = null
		return

	if(alert("Running this will create a lot of lag until it finishes.  You can cancel it by running it again.  Would you like to begin the search?", "Find References", "Yes", "No") == "No")
		return

	// Remove this object from the list of things to be auto-deleted.
	if(garbage_collector)
		garbage_collector.destroyed -= "\ref[src]"

	usr.client.running_find_references = type
	testing("Beginning search for references to a [type].")
	var/list/things = list()
	for(var/client/thing)
		things += thing
	for(var/datum/thing)
		things += thing
	for(var/atom/thing)
		things += thing
	testing("Collected list of things in search for references to a [type]. ([things.len] Thing\s)")
	for(var/datum/thing in things)
		if(!usr.client.running_find_references) return
		for(var/varname in thing.vars)
			var/variable = thing.vars[varname]
			if(variable == src)
				testing("Found [src.type] \ref[src] in [thing.type]'s [varname] var.")
			else if(islist(variable))
				if(src in variable)
					testing("Found [src.type] \ref[src] in [thing.type]'s [varname] list var.")
	testing("Completed search for references to a [type].")
	usr.client.running_find_references = null

/client/verb/purge_all_destroyed_objects()
	set category = "Debug"
	if(garbage_collector)
		while(garbage_collector.destroyed.len)
			var/datum/o = locate(garbage_collector.destroyed[1])
			if(istype(o) && o.gcDestroyed)
				del(o)
				garbage_collector.dels++
			garbage_collector.destroyed.Cut(1, 2)
#endif

#ifdef GC_DEBUG
#undef GC_DEBUG
#endif