ocelot-desktop/src/main/scala/ocelot/desktop/util/animation/ValueAnimation.scala

package ocelot.desktop.util.animation

import ocelot.desktop.ui.UiHandler
import ocelot.desktop.util.animation.easing.{Easing, EasingFunction}

class ValueAnimation(init: Float = 0f, speed: Float = 7f) {
  private var _value = init
  private var start = init
  private var end = init
  private var time = 0f
  private var reached = false
  private var _easing: EasingFunction = Easing.easeInOutQuad
  private var nextEasing = _easing

  def easing: EasingFunction = _easing

  def easing_=(value: EasingFunction): Unit = {
    nextEasing = value
    updateEasing()
  }

  def value: Float = _value

  def jump(to: Float): Unit = {
    _value = to
    start = to
    end = to
    updateReached()
  }

  def goto(to: Float): Unit = {
    start = _value
    end = to
    time = 0
    updateReached()
  }

  def update(): Unit = {
    if (reached) return

    val dist = (end - start).abs
    val dt = (UiHandler.dt * speed) / dist
    time = (time + dt).min(1).max(0)

    _value = if (start > end)
      start - time * dist
    else
      start + time * dist

    updateReached()
    if (reached) _easing = nextEasing
  }

  private def updateReached(): Unit = {
    reached = (_value - end).abs < 0.001
  }

  private def updateEasing(): Unit = {
    updateReached()
    if (reached) _easing = nextEasing
  }
}