Tusker/Tusker/Screens/Compose/Asset Picker/AssetCollectionViewController.swift

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

import UIKit
import Photos

private let reuseIdentifier = "assetCell"
private let cameraReuseIdentifier = "showCameraCell"

protocol AssetCollectionViewControllerDelegate: class {
    func shouldSelectAsset(_ asset: PHAsset) -> Bool
    func didSelectAssets(_ assets: [PHAsset])
    func captureFromCamera()
}

class AssetCollectionViewController: UICollectionViewController {

    weak var delegate: AssetCollectionViewControllerDelegate?
    
    var flowLayout: UICollectionViewFlowLayout {
        return collectionViewLayout as! UICollectionViewFlowLayout
    }
    
    var availableWidth: CGFloat!
    var thumbnailSize: CGSize!
    
    let imageManager = PHCachingImageManager()
    var fetchResult: PHFetchResult<PHAsset>!
    
    var selectedAssets: [PHAsset] {
        return collectionView.indexPathsForSelectedItems?.map({ (indexPath) in
            fetchResult.object(at: indexPath.row - 1)
        }) ?? []
    }
    
    init() {
        super.init(collectionViewLayout: UICollectionViewFlowLayout())
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(donePressed))

        collectionView.alwaysBounceVertical = true
        
        collectionView.register(UINib(nibName: "AssetCollectionViewCell", bundle: .main), forCellWithReuseIdentifier: reuseIdentifier)
        collectionView.register(UINib(nibName: "ShowCameraCollectionViewCell", bundle: .main), forCellWithReuseIdentifier: cameraReuseIdentifier)
        
        let options = PHFetchOptions()
        options.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
        fetchResult = fetchAssets(with: options)
        
        collectionView.allowsMultipleSelection = true
        setEditing(true, animated: false)
        
        updateItemsSelected()

        if let singleFingerPanGesture = collectionView.gestureRecognizers?.first(where: {
                $0.name == "multi-select.singleFingerPanGesture"
            }),
            let interactivePopGesture = navigationController?.interactivePopGestureRecognizer {
            singleFingerPanGesture.require(toFail: interactivePopGesture)
        }
    }
    
    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)
    }
    
    open func fetchAssets(with options: PHFetchOptions) -> PHFetchResult<PHAsset> {
        return PHAsset.fetchAssets(with: options)
    }
    
    func updateItemsSelected() {
        let selected = collectionView.indexPathsForSelectedItems?.count ?? 0
        
        navigationItem.title = "\(selected) selected"
    }

    // MARK: UICollectionViewDataSource

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

    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return fetchResult.count + 1
    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        if indexPath.row == 0 {
            return collectionView.dequeueReusableCell(withReuseIdentifier: cameraReuseIdentifier, for: indexPath)
        } else {
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! AssetCollectionViewCell
    
            let asset = fetchResult.object(at: indexPath.row - 1)
    
            cell.updateUI(asset: asset)
            imageManager.requestImage(for: asset, targetSize: thumbnailSize, contentMode: .aspectFill, options: nil) { (image, _) in
                guard let image = image else { return }
                DispatchQueue.main.async {
                    guard cell.assetIdentifier == asset.localIdentifier else { return }
                    cell.thumbnailImage = image
                }
            }

            return cell
        }
    }

    // MARK: UICollectionViewDelegate

    override func collectionView(_ collectionView: UICollectionView, shouldBeginMultipleSelectionInteractionAt indexPath: IndexPath) -> Bool {
        return true
    }
    
    override func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool {
        if indexPath.row > 0,
            let delegate = delegate {
            let asset = fetchResult.object(at: indexPath.row - 1)
            return delegate.shouldSelectAsset(asset)
        }
        return true
    }
    
    override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        if indexPath.row == 0 {
            collectionView.deselectItem(at: indexPath, animated: false)
            delegate?.captureFromCamera()
        } else {
            updateItemsSelected()
        }
    }
    
    override func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
        updateItemsSelected()
    }
    
    override func collectionView(_ collectionView: UICollectionView, contextMenuConfigurationForItemAt indexPath: IndexPath, point: CGPoint) -> UIContextMenuConfiguration? {
        if indexPath.row == 0 {
            return nil
        } else {
            let asset = fetchResult.object(at: indexPath.row - 1)
            return UIContextMenuConfiguration(identifier: nil, previewProvider: { () -> UIViewController? in
                return AssetPreviewViewController(asset: asset)
            }, actionProvider: nil)
        }
    }
    
    // MARK: - Interaction
    
    @objc func donePressed() {
        delegate?.didSelectAssets(selectedAssets)
        dismiss(animated: true)
    }
    
}