/**
     * Create a baked animation
     * @param babylonTransformNode BabylonJS mesh
     * @param animation BabylonJS animation corresponding to the BabylonJS mesh
     * @param animationChannelTargetPath animation target channel
     * @param minFrame minimum animation frame
     * @param maxFrame maximum animation frame
     * @param fps frames per second of the animation
     * @param inputs input key frames of the animation
     * @param outputs output key frame data of the animation
     * @param convertToRightHandedSystem converts the values to right-handed
     * @param useQuaternion specifies if quaternions should be used
     */
    private static _CreateBakedAnimation(babylonTransformNode: TransformNode, animation: Animation, animationChannelTargetPath: AnimationChannelTargetPath, minFrame: number, maxFrame: number, fps: number, sampleRate: number, inputs: number[], outputs: number[][], minMaxFrames: { min: number, max: number }, convertToRightHandedSystem: boolean, useQuaternion: boolean) {
        let value: number | Vector3 | Quaternion;
        let quaternionCache: Quaternion = Quaternion.Identity();
        let previousTime: Nullable<number> = null;
        let time: number;
        let maxUsedFrame: Nullable<number> = null;
        let currKeyFrame: Nullable<IAnimationKey> = null;
        let nextKeyFrame: Nullable<IAnimationKey> = null;
        let prevKeyFrame: Nullable<IAnimationKey> = null;
        let endFrame: Nullable<number> = null;
        minMaxFrames.min = Tools.FloatRound(minFrame / fps);

        let keyFrames = animation.getKeys();

        for (let i = 0, length = keyFrames.length; i < length; ++i) {
            endFrame = null;
            currKeyFrame = keyFrames[i];

            if (i + 1 < length) {
                nextKeyFrame = keyFrames[i + 1];
                if (currKeyFrame.value.equals(nextKeyFrame.value)) {
                    if (i === 0) { // set the first frame to itself
                        endFrame = currKeyFrame.frame;
                    }
                    else {
                        continue;
                    }
                }
                else {
                    endFrame = nextKeyFrame.frame;
                }
            }
            else {
                // at the last key frame
                prevKeyFrame = keyFrames[i - 1];
                if (currKeyFrame.value.equals(prevKeyFrame.value)) {
                    continue;
                }
                else {
                    endFrame = maxFrame;
                }
            }
            if (endFrame) {
                for (let f = currKeyFrame.frame; f <= endFrame; f += sampleRate) {
                    time = Tools.FloatRound(f / fps);
                    if (time === previousTime) {
                        continue;
                    }
                    previousTime = time;
                    maxUsedFrame = time;
                    value = animation._interpolate(f, 0, undefined, animation.loopMode);

                    _GLTFAnimation._SetInterpolatedValue(babylonTransformNode, value, time, animation, animationChannelTargetPath, quaternionCache, inputs, outputs, convertToRightHandedSystem, useQuaternion);
                }
            }
        }
        if (maxUsedFrame) {
            minMaxFrames.max = maxUsedFrame;
        }
    }

    /**
     * Creates cubic spline animation from the animation key frames
     * @param babylonTransformNode BabylonJS mesh
     * @param animation BabylonJS animation
     * @param animationChannelTargetPath The target animation channel
     * @param frameDelta The difference between the last and first frame of the animation
     * @param inputs Array to store the key frame times
     * @param outputs Array to store the key frame data
     * @param convertToRightHandedSystem Specifies if the position data should be converted to right handed
     * @param useQuaternion Specifies if quaternions are used in the animation
     */
    private static _CreateCubicSplineAnimation(babylonTransformNode: TransformNode, animation: Animation, animationChannelTargetPath: AnimationChannelTargetPath, frameDelta: number, inputs: number[], outputs: number[][], convertToRightHandedSystem: boolean, useQuaternion: boolean) {
        animation.getKeys().forEach(function(keyFrame) {
            inputs.push(keyFrame.frame / animation.framePerSecond); // keyframes in seconds.
            _GLTFAnimation.AddSplineTangent(
                babylonTransformNode,
                _TangentType.INTANGENT,
                outputs,
                animationChannelTargetPath,
                AnimationSamplerInterpolation.CUBICSPLINE,
                keyFrame,
                frameDelta,
                useQuaternion,
                convertToRightHandedSystem
            );
            _GLTFAnimation._AddKeyframeValue(keyFrame, animation, outputs, animationChannelTargetPath, babylonTransformNode, convertToRightHandedSystem, useQuaternion);

            _GLTFAnimation.AddSplineTangent(
                babylonTransformNode,
                _TangentType.OUTTANGENT,
                outputs,
                animationChannelTargetPath,
                AnimationSamplerInterpolation.CUBICSPLINE,
                keyFrame,
                frameDelta,
                useQuaternion,
                convertToRightHandedSystem
            );
        });
    }

    /**
     * @ignore
     *
     * Creates glTF channel animation from BabylonJS animation.
     * @param babylonTransformNode - BabylonJS mesh.
     * @param animation - animation.
     * @param animationChannelTargetPath - The target animation channel.
     * @param convertToRightHandedSystem - Specifies if the values should be converted to right-handed.
     * @param useQuaternion - Specifies if quaternions are used.
     * @returns nullable IAnimationData
     */
    public static _CreateNodeAnimation(babylonTransformNode: TransformNode, animation: Animation, animationChannelTargetPath: AnimationChannelTargetPath, convertToRightHandedSystem: boolean, useQuaternion: boolean, animationSampleRate: number): Nullable<_IAnimationData> {
        const inputs: number[] = [];
        const outputs: number[][] = [];
        const keyFrames = animation.getKeys();
        const minMaxKeyFrames = _GLTFAnimation.calculateMinMaxKeyFrames(keyFrames);
        const interpolationOrBake = _GLTFAnimation._DeduceInterpolation(keyFrames, animationChannelTargetPath, useQuaternion);
        const frameDelta = minMaxKeyFrames.max - minMaxKeyFrames.min;

        const interpolation = interpolationOrBake.interpolationType;
        const shouldBakeAnimation = interpolationOrBake.shouldBakeAnimation;

        if (shouldBakeAnimation) {
            _GLTFAnimation._CreateBakedAnimation(babylonTransformNode, animation, animationChannelTargetPath, minMaxKeyFrames.min, minMaxKeyFrames.max, animation.framePerSecond, animationSampleRate, inputs, outputs, minMaxKeyFrames, convertToRightHandedSystem, useQuaternion);
        }
        else {
            if (interpolation === AnimationSamplerInterpolation.LINEAR || interpolation === AnimationSamplerInterpolation.STEP) {
                _GLTFAnimation._CreateLinearOrStepAnimation(babylonTransformNode, animation, animationChannelTargetPath, frameDelta, inputs, outputs, convertToRightHandedSystem, useQuaternion);

            }
            else if (interpolation === AnimationSamplerInterpolation.CUBICSPLINE) {
                _GLTFAnimation._CreateCubicSplineAnimation(babylonTransformNode, animation, animationChannelTargetPath, frameDelta, inputs, outputs, convertToRightHandedSystem, useQuaternion);
            }
            else {
                _GLTFAnimation._CreateBakedAnimation(babylonTransformNode, animation, animationChannelTargetPath, minMaxKeyFrames.min, minMaxKeyFrames.max, animation.framePerSecond, animationSampleRate, inputs, outputs, minMaxKeyFrames, convertToRightHandedSystem, useQuaternion);
            }
        }

        if (inputs.length && outputs.length) {
            const result: _IAnimationData = {
                inputs: inputs,
                outputs: outputs,
                samplerInterpolation: interpolation,
                inputsMin: shouldBakeAnimation ? minMaxKeyFrames.min : Tools.FloatRound(minMaxKeyFrames.min / animation.framePerSecond),
                inputsMax: shouldBakeAnimation ? minMaxKeyFrames.max : Tools.FloatRound(minMaxKeyFrames.max / animation.framePerSecond)
            };

            return result;
        }

        return null;
    }

 /**
  * Creates linear animation from the animation key frames
  * @param babylonTransformNode BabylonJS mesh
  * @param animation BabylonJS animation
  * @param animationChannelTargetPath The target animation channel
  * @param frameDelta The difference between the last and first frame of the animation
  * @param inputs Array to store the key frame times
  * @param outputs Array to store the key frame data
  * @param convertToRightHandedSystem Specifies if the position data should be converted to right handed
  * @param useQuaternion Specifies if quaternions are used in the animation
  */
 private static _CreateLinearOrStepAnimation(babylonTransformNode: TransformNode, animation: Animation, animationChannelTargetPath: AnimationChannelTargetPath, frameDelta: number, inputs: number[], outputs: number[][], convertToRightHandedSystem: boolean, useQuaternion: boolean) {
     for (let keyFrame of animation.getKeys()) {
         inputs.push(keyFrame.frame / animation.framePerSecond); // keyframes in seconds.
         _GLTFAnimation._AddKeyframeValue(keyFrame, animation, outputs, animationChannelTargetPath, babylonTransformNode, convertToRightHandedSystem, useQuaternion);
     }
 }