class_name TickClock
extends RefCounted
## Turns frame time into a whole number of simulation ticks.

## Most ticks one frame may run. After a long stall the simulation catches
## up only this far and drops the rest, instead of freezing to catch up.
const MAX_TICKS_PER_FRAME := 5

var seconds_per_tick: float
var paused := false

var _accumulated := 0.0


func _init(ticks_per_second: int) -> void:
	seconds_per_tick = 1.0 / ticks_per_second


## Returns how many ticks to run for a frame that took `delta` seconds.
func advance(delta: float) -> int:
	if paused:
		return 0
	_accumulated += delta
	var ticks := int(_accumulated / seconds_per_tick)
	if ticks > MAX_TICKS_PER_FRAME:
		_accumulated = 0.0
		return MAX_TICKS_PER_FRAME
	_accumulated -= ticks * seconds_per_tick
	return ticks