import SwiftUI

/// All card positions are calculated in the same transaction as the bookmark flight.
struct LeadCardGrid: Layout {
    let columnCount: Int
    var spacing: CGFloat = 16

    func sizeThatFits(proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) -> CGSize {
        let width = proposal.width ?? 310
        let frames = frames(width: width, subviews: subviews)
        return CGSize(width: width, height: frames.map(\.maxY).max() ?? 0)
    }

    func placeSubviews(in bounds: CGRect, proposal: ProposedViewSize,
                       subviews: Subviews, cache: inout ()) {
        let frames = frames(width: bounds.width, subviews: subviews)
        for (index, subview) in subviews.enumerated() {
            let frame = frames[index]
            subview.place(at: CGPoint(x: bounds.minX + frame.minX, y: bounds.minY + frame.minY),
                          anchor: .topLeading,
                          proposal: ProposedViewSize(width: frame.width, height: frame.height))
        }
    }

    private func frames(width: CGFloat, subviews: Subviews) -> [CGRect] {
        let columns = max(1, columnCount)
        let cardWidth = max(0, (width - CGFloat(columns - 1) * spacing) / CGFloat(columns))
        var frames: [CGRect] = []
        var rowY: CGFloat = 0
        var rowHeight: CGFloat = 0
        for (index, subview) in subviews.enumerated() {
            let column = index % columns
            if column == 0 && index > 0 {
                rowY += rowHeight + spacing
                rowHeight = 0
            }
            let size = subview.sizeThatFits(ProposedViewSize(width: cardWidth, height: nil))
            frames.append(CGRect(x: CGFloat(column) * (cardWidth + spacing), y: rowY,
                                 width: cardWidth, height: size.height))
            rowHeight = max(rowHeight, size.height)
        }
        return frames
    }
}