lottie/src/main/java/com/airbnb/lottie/NumberKeyframeAnimation.java

package com.airbnb.lottie;

import android.view.animation.Interpolator;

import java.util.List;

import static com.airbnb.lottie.MiscUtils.lerp;

class NumberKeyframeAnimation<T extends Number> extends KeyframeAnimation<T> {
  private final List<T> values;
  private final Class<T> klass;

  NumberKeyframeAnimation(long duration, LottieComposition composition, List<Float> keyTimes,
      Class<T> klass, List<T> values, List<Interpolator> interpolators) {
    super(duration, composition, keyTimes, interpolators);
    this.klass = klass;
    if (keyTimes.size() != values.size()) {
      throw new IllegalArgumentException(
          "Key times and values must be the same length " + keyTimes + " vs " + values);
    }
    this.values = values;
  }

  @Override T getValue() {
    if (progress <= 0f) {
      return values.get(0);
    } else if (progress >= 1f) {
      return values.get(values.size() - 1);
    }

    int keyframeIndex = getKeyframeIndex();

    float startKeytime = keyTimes.get(keyframeIndex);
    float endKeytime = keyTimes.get(keyframeIndex + 1);

    float percentageIntoFrame = 0;
    if (!isDiscrete) {
      percentageIntoFrame = (progress - startKeytime) / (endKeytime - startKeytime);
      if (interpolators != null) {
        percentageIntoFrame =
            interpolators.get(keyframeIndex).getInterpolation(percentageIntoFrame);
      }
    }

    Number startValue = values.get(keyframeIndex);
    Number endValue = values.get(keyframeIndex + 1);

    if (klass.isAssignableFrom(Integer.class)) {
      return klass.cast(lerp(startValue.intValue(), endValue.intValue(), percentageIntoFrame));
    } else {
      return klass.cast(lerp(startValue.floatValue(), endValue.floatValue(), percentageIntoFrame));
    }
  }
}