ProductsViewController

//
//  ProductsViewController.swift
//  Created by nori on 2020/03/15.
//  Copyright © 2020 nori. All rights reserved.
//

import UIKit
import Instantiate
import Firebase
import Ballcap
import SwiftUI
import SwiftUICell

class ProductsViewController: DataSourceViewController<Commerce.Product>, UICollectionViewDelegate {

    enum Section: Int {
        case main
    }

    struct _Cell: Cell {
        var text: String
        var body: some View {
            Text(text)
        }
    }

    lazy var dataSource: UICollectionViewDiffableDataSource<Section, ItemIdentifier> = {
        let dataSource = UICollectionViewDiffableDataSource<Section, ItemIdentifier>(collectionView: self.collectionView) { (collectionView, indexPath, id) -> UICollectionViewCell? in
            guard let data: Commerce.Product.Model = self.products[indexPath.item].data else { return nil }
            let cell = SwiftUICell<_Cell>.dequeue(
                collectionView: collectionView,
                indexPath: indexPath,
                contentView: _Cell(text: data.name), parent: self)

            return cell
        }
        return dataSource
    }()

    lazy var collectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        layout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
        layout.scrollDirection = .vertical
        let view: UICollectionView = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
        view.alwaysBounceVertical = false
        view.backgroundColor = .secondarySystemBackground
        view.delegate = self
        view.register(content: _Cell.self)
        return view
    }()

    var products: [Commerce.Product] = []

    override func loadView() {
        super.loadView()
        self.view.addSubview(collectionView)
        self.view.backgroundColor = .secondarySystemBackground
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        var snapshot: NSDiffableDataSourceSnapshot<Section, ItemIdentifier> = NSDiffableDataSourceSnapshot()
        snapshot.appendSections([.main])
        self.dataSource.apply(snapshot, animatingDifferences: true)
        self._dataSource
            .onChanged({ [weak self] (querySnapstho, dataSourceSnapshot) in
                guard var snapshot: NSDiffableDataSourceSnapshot<Section, ItemIdentifier> = self?.dataSource.snapshot() else { return }
                snapshot.deleteItems(dataSourceSnapshot.before.map { ItemIdentifier(rawValue: $0.path) })
                snapshot.appendItems(dataSourceSnapshot.after.map { ItemIdentifier(rawValue: $0.path) }, toSection: .main)
                self?.dataSource.apply(snapshot, animatingDifferences: true)
            })
            .get()
    }

}

struct _Cell_Previews: PreviewProvider {
    static var previews: some View {
        ProductsViewController._Cell(text: "text")
            .previewLayout(.fixed(width: UIScreen.main.bounds.width, height: 120))
    }
}