// Components/Categories/CategoriesComponent.swift

final class CategoriesComponent: UIViewController, Component {

    // Props

    private let connector: CategoriesConnector!
    var props: CategoriesProps! {
        didSet {
            guard props != oldValue else {
                return
            }
            render()
        }
    }
    private var categories: [CategoriesProps.CategoryInfo] = []


    // UI Props

    @IBOutlet weak var collectionView: UICollectionView!
    @IBOutlet weak var activityIndicator: UIActivityIndicatorView!


    // MARK: - Initializator

    init(connector: CategoriesConnector) {
        self.connector = connector
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }


    // MARK: - UIKit lifecycle

    override func viewDidLoad() {
        super.viewDidLoad()

        setup()
        connector.connect(to: self)

        props.loadCategoriesList.execute()
    }


    // MARK: - Component lifecycle

    func setup() {
        collectionView.register(CategoryCell.nib, forCellWithReuseIdentifier: CategoryCell.nibIdentifier)
        collectionView.delegate = self
        collectionView.dataSource = self
    }

    func render() {
        switch props.state {
        case let .idle(categories: newCategories):
            collectionView.isHidden = false
            activityIndicator.isHidden = true

            let changes = diff(old: categories, new: newCategories)
            collectionView.reload(changes: changes, updateData: { [weak self] in
                self?.categories = newCategories
            })

        case .loading:
            collectionView.isHidden = true
            activityIndicator.isHidden = false
            activityIndicator.startAnimating()
        }
    }

}