MeterAnimation.kt

private sealed class MeterHeadState(val progress: Float) {
    object Low : MeterHeadState(progress = 0f)
    object High : MeterHeadState(progress = 100f)
    class OnIndex(progress: Float) : MeterHeadState(progress)
}

@Composable
private fun rememberMeterHeadState(value: MeterHeadState): MutableState<MeterHeadState> {
    return remember { mutableStateOf(value) }
}

@Composable
private fun updateProgressTransition(index: FGIndex?): State<Float> {
    var currentState by rememberMeterHeadState(MeterHeadState.Low)
    val transition = updateTransition(currentState, label = "meter_head")
    val progress = transition.animateFloat(
        label = "progress",
        transitionSpec = {
            if (currentState is MeterHeadState.OnIndex) {
                spring(
                    Spring.DampingRatioMediumBouncy,
                    stiffness = Spring.StiffnessVeryLow
                )
            } else {
                tween(800, easing = FastOutSlowInEasing)
            }
        }
    ) { state -> state.progress }

    LaunchedEffect(progress, index) {
        val state = getUpdatedState(index, progress.value)
        if (state != null) {
            currentState = state
        }
    }

    return remember(transition) { progress }
}

private fun getUpdatedState(index: FGIndex?, progress: Float): MeterHeadState? {
    if (index != null) {
        return MeterHeadState.OnIndex(index.value.toFloat())
    }

    return when (progress) {
        MeterHeadState.Low.progress -> MeterHeadState.High
        MeterHeadState.High.progress -> MeterHeadState.Low
        else -> null
    }
}