class_name PresentationNavRequestBudget
extends RefCounted

const MAX_NEW_REQUESTS_PER_FRAME := 2

var _pending_by_id: Dictionary = {}
var _in_flight_ids: Dictionary = {}
var _last_drained_frame := -1


func enqueue(stable_id: StringName, priority: int = 0, reason_trace: Array[String] = []) -> bool:
	if stable_id.is_empty() or _pending_by_id.has(stable_id) or _in_flight_ids.has(stable_id):
		return false
	var normalized_trace := reason_trace.duplicate()
	normalized_trace.sort()
	_pending_by_id[stable_id] = {
		"stable_id": stable_id,
		"priority": priority,
		"reason_trace": normalized_trace,
	}
	return true


func take_new_requests(frame_index: int) -> Array[Dictionary]:
	var result: Array[Dictionary] = []
	if frame_index < 0 or frame_index <= _last_drained_frame:
		return result
	_last_drained_frame = frame_index
	var pending: Array[Dictionary] = []
	for request in _pending_by_id.values():
		pending.append((request as Dictionary).duplicate(true))
	pending.sort_custom(_request_before)
	for index in mini(MAX_NEW_REQUESTS_PER_FRAME, pending.size()):
		var request: Dictionary = pending[index]
		var stable_id: StringName = request["stable_id"]
		_pending_by_id.erase(stable_id)
		_in_flight_ids[stable_id] = true
		request["reason_trace"].append("granted_frame_%d" % frame_index)
		result.append(request)
	return result


func complete(stable_id: StringName) -> bool:
	return _in_flight_ids.erase(stable_id)


func cancel(stable_id: StringName) -> bool:
	var changed := _pending_by_id.erase(stable_id)
	return _in_flight_ids.erase(stable_id) or changed


func get_pending_ids() -> Array[StringName]:
	var result: Array[StringName] = []
	for stable_id in _pending_by_id:
		result.append(StringName(stable_id))
	result.sort()
	return result


func get_in_flight_ids() -> Array[StringName]:
	var result: Array[StringName] = []
	for stable_id in _in_flight_ids:
		result.append(StringName(stable_id))
	result.sort()
	return result


func clear() -> void:
	_pending_by_id.clear()
	_in_flight_ids.clear()
	_last_drained_frame = -1


func _request_before(first: Dictionary, second: Dictionary) -> bool:
	if int(first["priority"]) != int(second["priority"]):
		return int(first["priority"]) > int(second["priority"])
	return String(first["stable_id"]) < String(second["stable_id"])