Cleaner impl.

mic_loader.dart

class AnimatingIcon extends StatefulWidget {
  const AnimatingIcon({super.key, this.onTap});
  final VoidCallback? onTap;

  @override
  State<AnimatingIcon> createState() => _AnimatingIconState();
}

class _AnimatingIconState extends State<AnimatingIcon>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;

  @override
  void initState() {
    super.initState();

    _controller = AnimationController(
        vsync: this, duration: const Duration(milliseconds: 850));

    _controller.addStatusListener((status) {
      if (status == AnimationStatus.completed) {
        _controller.reset();
      }

      if (status == AnimationStatus.dismissed) {
        _controller.forward();
      }
    });
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        if (_controller.isAnimating) {
          _controller.reset();
          _controller.stop();
        } else {
          _controller.forward();
        }
        widget.onTap?.call();
      },
      child: MicAnimatingIcon(controller: _controller),
    );
  }
}

class MicAnimatingIcon extends AnimatedWidget {
  final AnimationController controller;
  static const startSize = 100.0;
  static const endSize = 50.0;

  const MicAnimatingIcon({super.key, required this.controller})
      : super(listenable: controller);

  Animation<double> get _sizeStep =>
      _StepTween(startSize: startSize, endSize: endSize).animate(controller);

  Animation<double> get _iconStep =>
      _StepTween(startSize: startSize / 3, endSize: endSize / 2)
          .animate(controller);

  Animation<double> get _sizeStepTwo =>
      Tween<double>(begin: startSize, end: endSize)
          .animate(CurvedAnimation(parent: controller, curve: _StepCurveTwo()));

  @override
  Widget build(BuildContext context) {
    return Stack(
      fit: StackFit.loose,
      clipBehavior: Clip.none,
      alignment: AlignmentDirectional.center,
      children: [
        Container(
          height: startSize,
          width: startSize,
          decoration: const BoxDecoration(
            shape: BoxShape.circle,
            color: Colors.blue,
          ),
        ),
        Container(
          height: _sizeStepTwo.value,
          width: _sizeStepTwo.value,
          decoration: BoxDecoration(
              shape: BoxShape.circle,
              color: Colors.green,
              boxShadow: [
                if (_sizeStepTwo.value >= 0.5)
                  const BoxShadow(
                      color: Colors.black38,
                      offset: Offset(-1, 1),
                      blurRadius: 5,
                      spreadRadius: 0.6),
              ]),
        ),
        Container(
          height: _sizeStep.value,
          width: _sizeStep.value,
          decoration: BoxDecoration(
            shape: BoxShape.circle,
            color: Colors.purple[400],
          ),
          alignment: Alignment.center,
          child: Icon(
            Icons.mic,
            color: Colors.white,
            size: _iconStep.value,
          ),
        ),
      ],
    );
  }
}

class _StepTween extends Tween<double> {
  final double startSize;
  final double endSize;

  _StepTween({required this.startSize, required this.endSize})
      : super(begin: startSize, end: endSize);

  @override
  double lerp(double t) {
    if (t < 0.33) {
      return lerpDouble(startSize, endSize, 0) ?? 0;
    }

    if (t > 0.65) {
      return lerpDouble(startSize, endSize, 1) ?? 0;
    }

    return lerpDouble(startSize, endSize, 0.5) ?? 0;
  }
}

class _StepCurveTwo extends Curve {
  @override
  double transformInternal(double t) {
    if (t < 0.65) {
      return 0;
    }

    return 0.5;
  }
}