previewPaneApp

//
//  PaneViewController.swift
//  PaneApp
//
//  Created by Vladyslav Bugrym on 18.02.2020.
//  Copyright © 2020 admin. All rights reserved.
//

import UIKit


class PaneViewController:UIViewController {
    
    private lazy var previewPane:PreviewPane = {
        let view = PreviewPane()
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.setupView()
        self.refreshRandomViews()
    }
    
    private func setupView() {
        self.view.backgroundColor = #colorLiteral(red: 0.9995340705, green: 0.988355577, blue: 0.4726552367, alpha: 1)
        self.view.addSubview(previewPane)
        
        let guide = self.view.layoutMarginsGuide
        NSLayoutConstraint.activate([
            self.previewPane.leadingAnchor.constraint(equalTo: guide.leadingAnchor),
            self.previewPane.trailingAnchor.constraint(equalTo: guide.trailingAnchor),
            self.previewPane.centerYAnchor.constraint(equalTo: guide.centerYAnchor)])
    }
    
    private let itemCount = 15
    
    private func refreshRandomViews() {
        var views = [UIView]()
        for count in 0..<itemCount {
            let view = UILabel()
            view.text = "\(count)"
            let size = CGFloat(arc4random_uniform(64)) + 32.0
            view.font = UIFont.systemFont(ofSize: size)
            view.backgroundColor = (count % 2 == 0) ? #colorLiteral(red: 0.8078431487, green: 0.02745098062, blue: 0.3333333433, alpha: 1) : #colorLiteral(red: 0.4666666687, green: 0.7647058964, blue: 0.2666666806, alpha: 1)
            views.append(view)
        }
        previewPane.show(views)
    }
}




class PreviewPane:UIView {
    
    private var overflow = [UIView]()
    
    var spacing:CGFloat = 5.0 {
        didSet {
            stackView.spacing = spacing
        }
    }
    
    private lazy var stackView:UIStackView = {
        let stackView = UIStackView()
        stackView.translatesAutoresizingMaskIntoConstraints = false
        stackView.spacing = spacing
        stackView.alignment = .center
        return stackView
    }()
    
    ///This replaces any views already in the stack view with the new set of views.
    func show(_ items:[UIView]){
        stackView.arrangedSubviews.forEach { (view) in
            view.removeFromSuperview()
        }
        
        items.forEach { (view) in
            stackView.addArrangedSubview(view)
        }
        
        overflow.removeAll()
        
        //The implementation is equivalent
        /**
        stackView.arrangedSubviews.forEach {
            $0.removeFromSuperview()
        }
        
        items.forEach {
            stackView.addArrangedSubview($0)
        } */
         
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        self.setupView()
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        self.setupView()
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        ///After we call super.layoutSubviews() the layout engine has up- dated the bounds and center of our subviews based on the views and constraints.
        while stackView.bounds.width > bounds.width, let extraView = stackView.arrangedSubviews.last {
            extraView.removeFromSuperview()
            overflow.insert(extraView, at: 0)
            updateConstraintsIfNeeded()
            super.layoutSubviews()
        }
        
        while let nextItem = overflow.first, stackView.bounds.width + spacing + nextItem.intrinsicContentSize.width <= bounds.width {
            stackView.addArrangedSubview(nextItem)
            overflow.remove(at: 0)
            updateConstraintsIfNeeded()
            super.layoutSubviews()
        }
            
    }
    
    private func setupView() {
        addSubview(stackView)
        NSLayoutConstraint.activate([
            stackView.centerXAnchor.constraint(equalTo: centerXAnchor),
            stackView.topAnchor.constraint(equalTo: topAnchor),
            stackView.bottomAnchor.constraint(equalTo: bottomAnchor)])
    }
}