PhotoRank/PhotoRank/Asset Picker/AssetPickerViewControler.swift

//
//  AssetCollectionViewController.swift
//  PhotoRank
//
//  Created by Shadowfacts on 8/3/19.
//  Copyright © 2019 Shadowfacts. All rights reserved.
//

import UIKit
import Photos

private let reuseIdentifier = "AssetCell"

class AssetPickerViewController: UICollectionViewController {
    
    var continueButton: UIBarButtonItem!
    
    var flowLayout: UICollectionViewFlowLayout {
        return collectionViewLayout as! UICollectionViewFlowLayout
    }
    
    var availableWidth: CGFloat!
    var thumbnailSize: CGSize!
    
    var fetchResult: PHFetchResult<PHAsset>!
    
    init() {
        super.init(collectionViewLayout: UICollectionViewFlowLayout())
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        collectionView.alwaysBounceVertical = true
        
        // Register cell classes
        self.collectionView!.register(UINib(nibName: "AssetCollectionViewCell", bundle: .main), forCellWithReuseIdentifier: reuseIdentifier)

        let options = PHFetchOptions()
        options.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
        // get all photos except live photos
        options.predicate = NSPredicate(format: "mediaType == %d && !((mediaSubtypes & %d) == %d)", PHAssetMediaType.image.rawValue, PHAssetMediaSubtype.photoLive.rawValue, PHAssetMediaSubtype.photoLive.rawValue)
        fetchResult = PHAsset.fetchAssets(with: options)
        
        collectionView.allowsMultipleSelection = true
        setEditing(true, animated: false)
        
        continueButton = UIBarButtonItem(title: "Continue", style: .done, target: self, action: #selector(continueButtonPressed))
        updateItemsSelected()
        navigationItem.rightBarButtonItem = continueButton
    }
    
    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        
        let availableWidth = view.bounds.inset(by: view.safeAreaInsets).width
        
        if self.availableWidth != availableWidth {
            self.availableWidth = availableWidth
            
            let size = (availableWidth - 8) / 3
            flowLayout.itemSize = CGSize(width: size, height: size)
            flowLayout.minimumInteritemSpacing = 4
            flowLayout.minimumLineSpacing = 4
        }
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        let scale = UIScreen.main.scale
        let cellSize = flowLayout.itemSize
        thumbnailSize = CGSize(width: cellSize.width * scale, height: cellSize.height * scale)
    }

    func updateItemsSelected() {
        let selected = collectionView.indexPathsForSelectedItems?.count ?? 0
        continueButton.isEnabled = selected >= 2
        
        navigationItem.title = "\(selected) selected"
    }
    
    @objc func continueButtonPressed() {
        let indexPaths = collectionView.indexPathsForSelectedItems!
        let assets = fetchResult.objects(at: IndexSet(indexPaths.map { $0.item }))
        
        let comparison = AssetComparisonViewController(assets: assets)
        show(comparison, sender: nil)
    }

    // MARK: UICollectionViewDataSource

    override func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }


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

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! AssetCollectionViewCell
    
        let asset = fetchResult.object(at: indexPath.row)
        
        cell.assetIdentifier = asset.localIdentifier
        PhotosHelper.requestThumbnail(for: asset, targetSize: thumbnailSize) { (image) in
            DispatchQueue.main.async {
                if cell.assetIdentifier == asset.localIdentifier {
                    cell.thumbnailImage = image
                }
            }
        }

        return cell
    }

    // MARK: UICollectionViewDelegate
    
    override func collectionView(_ collectionView: UICollectionView, shouldBeginMultipleSelectionInteractionAt indexPath: IndexPath) -> Bool {
        return true
    }
    
    override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        updateItemsSelected()
    }
    
    override func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
        updateItemsSelected()
    }
    
    /*
    // Uncomment these methods to specify if an action menu should be displayed for the specified item, and react to actions performed on the item
    override func collectionView(_ collectionView: UICollectionView, shouldShowMenuForItemAt indexPath: IndexPath) -> Bool {
        return false
    }

    override func collectionView(_ collectionView: UICollectionView, canPerformAction action: Selector, forItemAt indexPath: IndexPath, withSender sender: Any?) -> Bool {
        return false
    }

    override func collectionView(_ collectionView: UICollectionView, performAction action: Selector, forItemAt indexPath: IndexPath, withSender sender: Any?) {
    
    }
    */
    
}