AdaptivePagingScrollViewStep02.swift

struct AdaptivePagingScrollView: View {
    
    /// {  * * *  States  * * * }
    
    // 01
    private func countOffset(for pageIndex: Int) -> CGFloat {
        
        let activePageOffset = CGFloat(pageIndex) * (itemWidth + itemPadding)
        return leadingOffset - activePageOffset
    }
    
    // 02
    private func countPageIndex(for offset: CGFloat) -> Int {
        
        guard itemsAmount > 0 else { return 0 }
        
        let offset = countLogicalOffset(offset)
        let floatIndex = (offset)/(itemWidth + itemPadding)
        
        var index = Int(round(floatIndex))
        if max(index, 0) > itemsAmount {
            index = itemsAmount
        }
        
        return min(max(index, 0), itemsAmount - 1)
    }
    
    // 03
    private func countCurrentScrollOffset() -> CGFloat {
        return countOffset(for: currentPageIndex) + gestureDragOffset
    }

    // 04
    private func countLogicalOffset(_ trueOffset: CGFloat) -> CGFloat {
        return (trueOffset-leadingOffset) * -1.0
    }
    
    /// {  * * *  Body  * * * }
}