rememberSnapFlingBehavior.kt

import androidx.compose.animation.core.Animatable
import androidx.compose.animation.core.calculateTargetValue
import androidx.compose.animation.rememberSplineBasedDecay
import androidx.compose.foundation.gestures.FlingBehavior
import androidx.compose.foundation.gestures.ScrollScope
import androidx.compose.foundation.lazy.LazyListState
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember

@Composable
private fun rememberSnapFlingBehavior(state: LazyListState): FlingBehavior {
    val flingSpec = rememberSplineBasedDecay<Float>()

    return remember {
        object : FlingBehavior {
            override suspend fun ScrollScope.performFling(initialVelocity: Float): Float {
                val firstItem = state.layoutInfo.visibleItemsInfo.first()
                
                /** Current offset of the first visible element from the screen's start */
                val firstItemOffset = -firstItem.offset.toFloat()

                /** Target offset that would be reached by default */
                val targetOffset = flingSpec.calculateTargetValue(
                    initialValue = firstItemOffset,
                    initialVelocity = initialVelocity
                )

                /** The element's final visibility rate: 0 - hidden, 1 - fully visible */
                val visibilityRate = 1 - (targetOffset / firstItem.size)

                val scrollDistance = if (visibilityRate > 0.5f) {
                    /** Scroll to the left, up to the current element's start */
                    -firstItemOffset
                } else {
                    /** Scroll to the right, up to the next element */
                    firstItem.size - firstItemOffset
                }

                /** Scrolling with animation up to target value */
                var consumedScrollDistance = 0f
                Animatable(0f)
                    .animateTo(
                        targetValue = scrollDistance,
                        initialVelocity = initialVelocity,
                    ) {
                        consumedScrollDistance += scrollBy(value - consumedScrollDistance)
                    }
                if (consumedScrollDistance < scrollDistance) {
                    scrollBy(scrollDistance - consumedScrollDistance)
                }

                return 0f
            }
        }
    }
}