extends Node

signal unfreeze

const END_VALUE: int = 1

var is_active: bool = false
var time_start: int
var duration_ms: int
var start_value: float


func start(duration: int = 1, strength: float = 0.9):
    time_start = OS.get_ticks_msec()
    duration_ms = duration * 1000
    start_value = 1 - strength
    Engine.time_scale = start_value
    is_active = true


func _process(_delta: float) -> void:
    if is_active:
        var current_time = OS.get_ticks_msec() - time_start
        var value = circl_ease_in(current_time, start_value, END_VALUE, duration_ms)
        if current_time >= duration_ms:
            is_active = false
            value = END_VALUE
            emit_signal('unfreeze')
        Engine.time_scale = value
    return


func circl_ease_in(t, b, c, d):
    t /= d
    return -c * (sqrt(1 - t * t) - 1) + b