AdaptivePagingScrollViewStep03.swift

 struct AdaptivePagingScrollView: View {
    
    /// {  * * *  States  * * * }
    
    /// {  * * *  Functions  * * * }
    
    var body: some View {
        // 01
        GeometryReader { viewGeometry in
            HStack(alignment: .center, spacing: itemSpacing) {
                ForEach(items.indices, id: \.self) { itemIndex in
                    items[itemIndex].frame(width: itemWidth)
                }
            }
        }
        .onAppear { // 02
            currentScrollOffset = countOffset(for: currentPageIndex)
        }
        .background(Color.black.opacity(0.00001)) // hack - this allows gesture recognizing even when background is transparent
        .frame(width: contentWidth)
        .offset(x: self.currentScrollOffset, y: 0)
        .simultaneousGesture( // 03
            DragGesture(minimumDistance: 1, coordinateSpace: .local)
                .onChanged { value in // 04
                    gestureDragOffset = value.translation.width
                    currentScrollOffset = countCurrentScrollOffset()
                }
                .onEnded { value in // 05
                    let cleanOffset = (value.predictedEndTranslation.width - gestureDragOffset)
                    let velocityDiff = cleanOffset * scrollDampingFactor
                    
                    var newPageIndex = countPageIndex(for: currentScrollOffset + velocityDiff)
                    
                    let currentItemOffset = CGFloat(currentPageIndex) * (itemWidth + itemPadding)
                    
                    if currentScrollOffset < -(currentItemOffset),
                       newPageIndex == currentPageIndex {
                        newPageIndex += 1
                    }
                    
                    gestureDragOffset = 0
                    // 06
                    withAnimation(.interpolatingSpring(mass: 0.1,
                                                       stiffness: 20,
                                                       damping: 1.5,
                                                       initialVelocity: 0)) {
                        self.currentPageIndex = newPageIndex
                        self.currentScrollOffset = self.countCurrentScrollOffset()
                    }
                }
        )
    }
}