import SwiftUI

//自动换行
//https://stackoverflow.com/questions/58842453/hstack-with-wrap RelativeJoe的回答
public struct OverflowGrid: Layout {
   private var horizontalSpacing: CGFloat
   private var vericalSpacing: CGFloat
   public init(horizontalSpacing: CGFloat, vericalSpacing: CGFloat? = nil) {
      self.horizontalSpacing = horizontalSpacing
      self.vericalSpacing = vericalSpacing ?? horizontalSpacing
   }
   public func sizeThatFits(proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) -> CGSize {
      let height = subviews.max(by: {$0.dimensions(in: proposal).height > $1.dimensions(in: proposal).height})?.dimensions(in: proposal).height ?? 0
      var rows = [CGFloat]()
      subviews.indices.forEach { index in
         let rowIndex = rows.count - 1
         let subViewWidth = subviews[index].dimensions(in: proposal).width
         guard !rows.isEmpty else {
            rows.append(subViewWidth)
            return
         }
         let newWidth = rows[rowIndex] + subViewWidth + horizontalSpacing
         if newWidth < proposal.width ?? 0 {
            rows[rowIndex] += (rows[rowIndex] > 0 ? horizontalSpacing: 0) + subViewWidth
         }else {
            rows.append(subViewWidth)
         }
      }
      let count = CGFloat(rows.count)
      return CGSize(width: rows.max() ?? 0, height: count * height + (count - 1) * vericalSpacing)
      
   }
   public func placeSubviews(in bounds: CGRect, proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) {
      let height = subviews.max(by: {$0.dimensions(in: proposal).height > $1.dimensions(in: proposal).height})?.dimensions(in: proposal).height ?? 0
      guard !subviews.isEmpty else {return}
      var x = bounds.minX
      var y = height/2 + bounds.minY
      subviews.indices.forEach { index in
         let subView = subviews[index]
         x += subView.dimensions(in: proposal).width/2
         subviews[index].place(at: CGPoint(x: x, y: y), anchor: .center, proposal: ProposedViewSize(width: subView.dimensions(in: proposal).width, height: subView.dimensions(in: proposal).height))
         x += horizontalSpacing + subView.dimensions(in: proposal).width/2
         if x > bounds.width {
            x = bounds.minX
            y += height + vericalSpacing
         }
      }
   }
}