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A library for 2D OpenGL and OpenAL support based on LWJGL 3

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package io.github.mwttg.pixelartillery2d.graphic;

import java.util.List;

final class AnimationTimingUnit {

  private final List delaysInMs;
  private final AnimationType type;
  private final int maxFrames;
  private int currentFrame;
  private long lastTick;
  private int alternatingSummand;

  private AnimationTimingUnit(final List delaysInMs, final AnimationType type) {
    this.delaysInMs = delaysInMs;
    this.type = type;
    this.maxFrames = delaysInMs.size();
    this.currentFrame = 0;
    this.lastTick = System.currentTimeMillis();
    this.alternatingSummand = 1;
  }

  static AnimationTimingUnit create(final List delaysInMs) {
    return new AnimationTimingUnit(delaysInMs, AnimationType.LOOP);
  }

  static AnimationTimingUnit create(final List delaysInMs, final AnimationType type) {
    return new AnimationTimingUnit(delaysInMs, type);
  }

  void reset() {
    lastTick = System.currentTimeMillis();
    currentFrame = 0;
  }

  int getCurrentFrame() {
    final var now = System.currentTimeMillis();
    if (now - lastTick > delaysInMs.get(currentFrame)) {
      lastTick = System.currentTimeMillis();
      nextFrame();
    }
    return currentFrame;
  }

  private void nextFrame() {
    switch (type) {
      case LOOP -> loopAnimation();
      case ONCE -> onceAnimation();
      case ALTERNATING -> alternatingAnimation();
      default -> throw new IllegalStateException("Unexpected value: " + type);
    }
  }

  private void loopAnimation() {
    currentFrame++;
    if (currentFrame >= maxFrames) {
      currentFrame = 0;
    }
  }

  private void onceAnimation() {
    if (currentFrame < maxFrames - 1) {
      currentFrame++;
    }
  }

  private void alternatingAnimation() {
    if (currentFrame >= maxFrames - 1) {
      alternatingSummand = -1;
    }
    if (currentFrame < 1) {
      alternatingSummand = 1;
    }
    currentFrame = currentFrame + alternatingSummand;
  }
}