SwitftUI Lazy Staggered Vertical Grid

LazyStaggeredVGrid.swift

//
//  LazyStaggedVGrid.swift
//
//  Created by Ricardo Markiewicz on 20/08/2023.
//  Copyright © 2023 orgName. No rights reserved.
//
//  https://twitter.com/Gazeria/status/1693356336019333382
//

import SwiftUI

struct LazyStaggeredVGrid: Layout {
    func sizeThatFits(
        proposal: ProposedViewSize, // Size that is proposed to me
        subviews: Subviews,         // proxy to my childs (e.g. items)
        cache: inout ()
    ) -> CGSize {
        return proposal.replacingUnspecifiedDimensions()
    }

    func placeSubviews(
        in bounds: CGRect,         // Region where I need to place my subviews into
        proposal: ProposedViewSize,
        subviews: Subviews,
        cache: inout ()
    ) {
        var lastItemCol1: ViewSpacing? = nil
        var lastItemCol2: ViewSpacing? = nil
        let width = (proposal.width ?? 0) / 2
        var col1 = 0.0
        var col2 = 0.0

        let childProposal = ProposedViewSize(width: width, height: nil)
        subviews.enumerated().forEach({ (index, subview) in
            let h = subview.sizeThatFits(childProposal).height

            var spacingX: CGFloat = 0
            if lastItemCol1 != nil {
                spacingX = lastItemCol1!.distance(to: subview.spacing, along: .horizontal)
            } else {
                spacingX = subview.spacing.distance(to: subview.spacing, along: .horizontal)
            }

            var x = 0.0
            var y = 0.0
            if (col1 > col2) {
                // Adding to Col2
                let spacingY: CGFloat
                if lastItemCol2 != nil {
                    spacingY = lastItemCol2!.distance(to: subview.spacing, along: .vertical)
                } else {
                    spacingY = 0
                }

                // Coordinates
                x = width + spacingX / 2
                y = col2 + spacingY

                // Finish
                lastItemCol2 = subview.spacing
                col2 += h + spacingY
            } else {
                // Adding to Col1
                let spacingY: CGFloat
                if lastItemCol1 != nil {
                    spacingY = lastItemCol1!.distance(to: subview.spacing, along: .vertical)
                } else {
                    spacingY = 0
                }

                // Coordinates
                y = col1 + spacingY
                x = 0

                // Finish
                lastItemCol1 = subview.spacing
                col1 += h + spacingY
            }
            let sizeProposal = ProposedViewSize(
                width: width - spacingX / 2,
                height: h
            )

            subview.place(at: CGPoint(x: x, y: y), proposal: sizeProposal)
        })
    }
}