/*

    Copyright (C) 2016 Apple Inc. All Rights Reserved.

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    Contains the `ImageListController` view controller subclass that displays the images in an `ImageCollection`.

*/

import Cocoa

/**

    `ImageListController` displays the `ImageFiles` in a given `ImageCollection` in 

    an `NSCollectionView. It can be given a selection handler to report when an 

    `ImageFile` is selected.

*/

class ImageListController: NSViewController, NSCollectionViewDataSource, NSCollectionViewDelegate {

    // MARK: Properties

    override var nibName: String {

        return "ImageListController"

    }

    fileprivate static let imageCollectionViewItemIdentifier = "ImageItem"

    @IBOutlet var collectionView: NSCollectionView!

    // MARK: Image File / Collection Management

    var imageSelectionHandler: ((ImageFile?) -> Void)?

    var imageCollections = [ImageCollection]() {

        didSet {

            // Observe the new collections for changes, and unobserve the old collections.

            for collection in oldValue {

                NotificationCenter.default.removeObserver(self, name: NSNotification.Name(rawValue: ImageCollection.imagesDidChangeNotification), object: collection)

            }

            for collection in imageCollections {

                NotificationCenter.default.addObserver(self, selector: #selector(ImageListController.imageCollectionDidChange(_:)), name: NSNotification.Name(rawValue: ImageCollection.imagesDidChangeNotification), object: collection)

            }

            guard isViewLoaded else { return }

            reloadCollectionViewAndSelectFirstItemIfNecessary()

        }

    }

    @objc func imageCollectionDidChange(_ notification: Notification) {

        reloadCollectionViewAndSelectFirstItemIfNecessary()

    }

    deinit {

        NotificationCenter.default.removeObserver(self)

    }

    // MARK: Life Cycle

    override func viewDidLoad() {

        // Tell the CollectionView to use the ImageCollectionViewItem nib for its items.

        let nib = NSNib(nibNamed: "ImageCollectionViewItem", bundle: nil)

        collectionView.register(nib, forItemWithIdentifier: ImageListController.imageCollectionViewItemIdentifier)

        collectionView.dataSource = self

        collectionView.delegate = self

        // Create a grid layout that is somewhat flexible for the various widths it might have.

        let gridLayout = NSCollectionViewGridLayout()

        gridLayout.minimumItemSize = NSSize(width: 100, height: 100)

        gridLayout.maximumItemSize = NSSize(width: 175, height: 175)

        gridLayout.minimumInteritemSpacing = 10

        gridLayout.margins = EdgeInsets(top: 10, left: 10, bottom: 10, right: 10)

        collectionView.collectionViewLayout = gridLayout

        reloadCollectionViewAndSelectFirstItemIfNecessary()

        super.viewDidLoad()

    }

    fileprivate func reloadCollectionViewAndSelectFirstItemIfNecessary() {

        collectionView.reloadData()

        // If the `collectionView` has no selection, attempt to select the first available item.

        guard collectionView.selectionIndexPaths.isEmpty else { return }

        // Get the collections that contain images.

        let populatedCollections = imageCollections.filter { !$0.images.isEmpty }

        // Find the first `ImageCollection` that actually has images displayed.

        guard let firstPopulatedCollection = populatedCollections.first else { return }

        /*

            Get the index path to that collection's first image -- section is the 

            index of the collection, item index is 0.

        */

        let firstPopulatedIndex = imageCollections.index(of: firstPopulatedCollection)!

        // Programmatically change the selection, and handle the changed selection.

        collectionView.selectionIndexPaths = [

            IndexPath(item: 0, section: firstPopulatedIndex)

        ]

        handleSelectionChanged()

    }

    // MARK: Collection View Data Source / Delegate

    func numberOfSections(in collectionView: NSCollectionView) -> Int {

        return imageCollections.count

    }

    func collectionView(_ collectionView: NSCollectionView, numberOfItemsInSection section: Int) -> Int {

        return imageCollections[section].images.count

    }

    func collectionView(_ collectionView: NSCollectionView, itemForRepresentedObjectAt indexPath: IndexPath) -> NSCollectionViewItem {

        let item = collectionView.makeItem(withIdentifier: ImageListController.imageCollectionViewItemIdentifier, for: indexPath)

        if let imageItem = item as? ImageCollectionViewItem {

            // The section maps to the index of the `ImageCollection`.

            let imageCollection = imageCollections[(indexPath as NSIndexPath).section]

            imageItem.imageFile = imageCollection.images[(indexPath as NSIndexPath).item]

        }

        return item

    }

    func collectionView(_ collectionView: NSCollectionView, didSelectItemsAt indexPaths: Set<IndexPath>) {

        handleSelectionChanged()

    }

    func collectionView(_ collectionView: NSCollectionView, didDeselectItemsAt indexPaths: Set<IndexPath>) {

        handleSelectionChanged()

    }

    fileprivate func handleSelectionChanged() {

        guard let imageSelectionHandler = imageSelectionHandler else { return }

        /*

            The collection view does not support multiple selection, so just check 

            the first index.

        */

        let selectedImage: ImageFile?

        if let selectedIndexPath = collectionView.selectionIndexPaths.first

           , (selectedIndexPath as NSIndexPath).section != -1 && (selectedIndexPath as NSIndexPath).item != -1 {

            // There is a selected index path, get the image at that path.

            selectedImage = imageCollections[(selectedIndexPath as NSIndexPath).section].images[(selectedIndexPath as NSIndexPath).item]

        }

        else {

            /*

                There is no selected index path -- the collection view supports

                empty selection, there is no selected image.

            */

            selectedImage = nil

        }

        imageSelectionHandler(selectedImage)

    }

}