vds_ios/VDS/Components/Buttons/ButtonGroup/ButtonGroup.swift

//
//  ButtonGroup.swift
//  VDS
//
//  Created by Matt Bruce on 11/3/22.
//

import Foundation
import UIKit
import VDSColorTokens
import VDSFormControlsTokens
import Combine

@objc(VDSButtonGroup)
open class ButtonGroup: View, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout, UICollectionViewDelegate, ButtongGroupPositionLayoutDelegate {

    //--------------------------------------------------
    // MARK: - Properties
    //--------------------------------------------------
    //An object containing number of Button components per row, in each viewport
    open var rowQuantityPhone: Int = 0 { didSet { didChange() } }

    open var rowQuantityTablet: Int = 0 { didSet { didChange() } }

    public var rowQuantity: Int { UIDevice.isIPad ? rowQuantityTablet : rowQuantityPhone }

    //If provided, aligns TextLink/TextLinkCaret alignment when rowQuantity is set one.
    open var textPosition: TextPosition = .center { didSet { didChange() }}

    open var buttons: [Buttonable] = [] { didSet { didChange() }}

    //If provided, width of Button components will be rendered based on this value. If omitted, default button widths are rendered.
    open var buttonWidth: CGFloat? {
        didSet {
            buttons.forEach { button in
                if let button = button as? Button {
                    button.width = buttonWidth
                }
            }
            didChange()
        }
    }

    //--------------------------------------------------
    // MARK: - Private Properties
    //--------------------------------------------------
    private let lineSpacing: CGFloat = 12.0
    private let itemSpacing: CGFloat = 16.0
    private let estimatedCellHeight: CGFloat = 40.0
    private let estimatedCellWidth: CGFloat = 150.0

    fileprivate lazy var collectionView: SelfSizingCollectionView = {
        let positionLayout = ButtonGroupPositionLayout().with {
            $0.position = .center
            $0.delegate = self
        }

        return SelfSizingCollectionView(frame: .zero, collectionViewLayout: positionLayout).with {
            $0.backgroundColor = .clear
            $0.showsHorizontalScrollIndicator = false
            $0.showsVerticalScrollIndicator = false
            $0.isScrollEnabled = false
            $0.translatesAutoresizingMaskIntoConstraints = false
            $0.dataSource = self
            $0.delegate = self
            $0.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "collectionViewCell")
        }
    }()

    //--------------------------------------------------
    // MARK: - Overrides
    //--------------------------------------------------
    override public var disabled: Bool {
        didSet {
            buttons.forEach { button in
                button.disabled = disabled
            }
        }
    }

    override public var surface: Surface {
        didSet {
            buttons.forEach { button in
                button.surface = surface
            }
        }
    }


    //--------------------------------------------------
    // MARK: - Initializers
    //--------------------------------------------------
    required public init() {
        super.init(frame: .zero)
        initialSetup()
    }

    public override init(frame: CGRect) {
        super.init(frame: .zero)
        initialSetup()
    }

    public required init?(coder: NSCoder) {
        super.init(coder: coder)
        initialSetup()
    }
    //--------------------------------------------------
    // MARK: - Public Functions
    //--------------------------------------------------
    open override func setup() {
        super.setup()
        isAccessibilityElement = true
        accessibilityTraits = .button
        addSubview(collectionView)
        collectionView.pinToSuperView()
    }

    //--------------------------------------------------
    // MARK: - Overrides
    //--------------------------------------------------
    open override func updateView() {
        super.updateView()
        collectionView.reloadData()
    }
    
    open override func layoutSubviews() {
        super.layoutSubviews()
        // Accounts for any collection size changes
        DispatchQueue.main.async {
            self.collectionView.collectionViewLayout.invalidateLayout()
        }
    }

    //--------------------------------------------------
    // MARK: - UICollectionViewDataSource
    //--------------------------------------------------
    public func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

    public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return buttons.count
    }

    public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let button = buttons[indexPath.row]
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "collectionViewCell", for: indexPath)
        cell.subviews.forEach { $0.removeFromSuperview() }
        cell.subviews.forEach { $0.removeFromSuperview() }
        cell.addSubview(button)
        button.pinToSuperView()
        return cell
    }
    
    public func collectionView(_ collectionView: UICollectionView, sizeForItemAtIndexPath indexPath: IndexPath) -> CGSize {
        buttons[indexPath.row].intrinsicContentSize
    }
    
    public func collectionView(_ collectionView: UICollectionView, insetsForItemsInSection section: Int) -> UIEdgeInsets {
        UIEdgeInsets.zero
    }
    
    public func collectionView(_ collectionView: UICollectionView, itemSpacingInSection section: Int) -> CGFloat {
        itemSpacing
    }
}

final class SelfSizingCollectionView: UICollectionView {

    private var contentSizeObservation: NSKeyValueObservation?

    // MARK: - Lifecycle

    override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
        super.init(frame: frame, collectionViewLayout: layout)
        self.setupContentSizeObservation()
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        self.setupContentSizeObservation()
    }

    // MARK: - UIView

    override var intrinsicContentSize: CGSize {
        let contentSize = self.contentSize
        //print(#function, contentSize)
        return CGSize(width: UIView.noIntrinsicMetric, height: contentSize.height)
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        //print(type(of: self), #function)
        super.traitCollectionDidChange(previousTraitCollection)

        // We need to handle any change that will affect layout and/or anything that affects size of a UILabel
        if self.traitCollection.hasDifferentTextAppearance(comparedTo: previousTraitCollection) {
            self.collectionViewLayout.invalidateLayout()
        }
    }

    override func systemLayoutSizeFitting(_ targetSize: CGSize, withHorizontalFittingPriority horizontalFittingPriority: UILayoutPriority, verticalFittingPriority: UILayoutPriority) -> CGSize {
        let size = super.systemLayoutSizeFitting(targetSize, withHorizontalFittingPriority: horizontalFittingPriority, verticalFittingPriority: verticalFittingPriority)
        //print(type(of: self), #function, targetSize, "->", size)
        return size
    }

    // MARK: - Private

    private func setupContentSizeObservation() {
        // Observing the value of contentSize seems to be the only reliable way to get the contentSize after the collection view lays out its subviews.
        self.contentSizeObservation = self.observe(\.contentSize, options: [.old, .new]) { [weak self] _, change in
            // If we don't specify `options: [.old, .new]`, the change.oldValue and .newValue will always be `nil`.
            if change.newValue != change.oldValue {
                self?.invalidateIntrinsicContentSize()
            }
        }
    }
}

extension UITraitCollection {

    func hasDifferentTextAppearance(comparedTo traitCollection: UITraitCollection?) -> Bool {
        var result = self.preferredContentSizeCategory != traitCollection?.preferredContentSizeCategory

        if #available(iOS 13.0, *) {
            result = result || self.legibilityWeight != traitCollection?.legibilityWeight
        }

        return result
    }
}