Tusker/Tusker/Screens/Asset Picker/AssetCollectionsListViewController.swift

//
//  AssetCollectionsListViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 1/1/20.
//  Copyright © 2020 Shadowfacts. All rights reserved.
//

import UIKit
import Photos

class AssetCollectionsListViewController: UITableViewController {

    weak var assetCollectionDelegate: AssetCollectionViewControllerDelegate?
    
    var dataSource: DataSource!

    init() {
        super.init(style: .plain)
        
        title = NSLocalizedString("Collections", comment: "asset collections list title")
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        navigationItem.leftBarButtonItem = UIBarButtonItem(barButtonSystemItem: .cancel, target: self, action: #selector(cancelPressed))

        tableView.register(UINib(nibName: "AllPhotosTableViewCell", bundle: .main), forCellReuseIdentifier: "allPhotosCell")
        tableView.register(UINib(nibName: "AlbumTableViewCell", bundle: .main), forCellReuseIdentifier: "albumCell")
        
        tableView.allowsFocus = true
        tableView.backgroundColor = .appGroupedBackground
        
        dataSource = DataSource(tableView: tableView, cellProvider: { (tableView, indexPath, item) -> UITableViewCell? in
            switch item {
            case .cameraRoll:
                return tableView.dequeueReusableCell(withIdentifier: "allPhotosCell", for: indexPath)

            case let .album(collection):
                let cell = tableView.dequeueReusableCell(withIdentifier: "albumCell", for: indexPath) as! AlbumTableViewCell
                cell.updateUI(album: collection)
                return cell
            }
        })
        
        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
        snapshot.appendSections([.system, .albums, .sharedAlbums, .smartAlbums])
        snapshot.appendItems([.cameraRoll], toSection: .system)
        
        let smartAlbums = PHAssetCollection.fetchAssetCollections(with: .smartAlbum, subtype: .any, options: nil)
        var smartAlbumItems = [Item]()
        smartAlbums.enumerateObjects { (collection, _, _) in
            guard collection.assetCollectionSubtype != .smartAlbumAllHidden else {
                return
            }
            smartAlbumItems.append(.album(collection))
        }
        // sort these manually, using PHFetchOptions.sortDescriptors seems like it just doesn't work with fetchAssetCollections
        smartAlbumItems.sort(by: { $0.title < $1.title })
        snapshot.appendItems(smartAlbumItems, toSection: .smartAlbums)
        
        let albums = PHAssetCollection.fetchAssetCollections(with: .album, subtype: .any, options: nil)
        var albumItems = [Item]()
        var sharedItems = [Item]()
        albums.enumerateObjects { (collection, _, _) in
            if collection.estimatedAssetCount > 0 {
                if collection.assetCollectionSubtype == .albumCloudShared {
                    sharedItems.append(.album(collection))
                } else {
                    albumItems.append(.album(collection))
                }
            }
        }
        albumItems.sort(by: { $0.title < $1.title })
        sharedItems.sort(by: { $0.title < $1.title })
        snapshot.appendItems(albumItems, toSection: .albums)
        snapshot.appendItems(sharedItems, toSection: .sharedAlbums)

        dataSource.apply(snapshot, animatingDifferences: false)
    }
    
    // MARK: - Table view delegate
    
    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        switch dataSource.itemIdentifier(for: indexPath) {
        case nil:
            return
            
        case .cameraRoll:
            let assetCollection = AssetCollectionViewController()
            assetCollection.delegate = assetCollectionDelegate
            show(assetCollection, sender: self)
            
        case let .album(collection):
            let assetCollection = AlbumAssetCollectionViewController(collection: collection)
            assetCollection.delegate = assetCollectionDelegate
            show(assetCollection, sender: self)
        }
    }
    
    // MARK: - Interaction
    
    @objc func cancelPressed() {
        dismiss(animated: true)
    }

}

extension AssetCollectionsListViewController {
    enum Section {
        case system
        case albums
        case sharedAlbums
        case smartAlbums
    }
    enum Item: Hashable {
        case cameraRoll
        case album(PHAssetCollection)
        
        func hash(into hasher: inout Hasher) {
            switch self {
            case .cameraRoll:
                hasher.combine("cameraRoll")
            case let .album(collection):
                hasher.combine("album")
                hasher.combine(collection.localIdentifier)
            }
        }
        
        var title: String {
            switch self {
            case .cameraRoll:
                return "All Photos"
            case .album(let collection):
                return collection.localizedTitle ?? ""
            }
        }
    }
    class DataSource: UITableViewDiffableDataSource<Section, Item> {
        override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
            switch sectionIdentifier(for: section) {
            case .albums:
                return NSLocalizedString("Albums", comment: "albums section title")
            case .sharedAlbums:
                return NSLocalizedString("Shared Albums", comment: "shared albums section title")
            case .smartAlbums:
                return NSLocalizedString("Smart Albums", comment: "smart albums section title")
            default:
                return nil
            }
        }
    }
}