NSBrowser Delegate Wrapper

wrapper.swift

import Cocoa

// Insipired by http://dcandi.com/post/cocoa-filesystem-browser/

extension URL {
    var isDirectory: Bool {
        return (try? resourceValues(forKeys: [.isDirectoryKey]))?.isDirectory ?? false
    }
        
    var fileIcon : NSImage {
        (try? resourceValues(forKeys: [.effectiveIconKey]))?.effectiveIcon as? NSImage ?? NSImage()
    }
    
    var smallFileIcon: NSImage{
        let icon = fileIcon
        icon.size = NSMakeSize(16.0, 16.0)
        return icon
    }
}

struct Directory {
    var url: URL
    var contents: [URL]
    init(url: URL) throws {
        self.url = url
        guard url.isDirectory else {
            contents = []
            return
        }
        let urls = try FileManager.default.contentsOfDirectory(
            at: url,
            includingPropertiesForKeys: nil,
            options: FileManager.DirectoryEnumerationOptions.skipsHiddenFiles)
        self.contents = urls
    }
    
    
}

extension Directory: TreeLike {
    var numberOfChildren: Int {
        contents.count
    }
    
    func child(at index: Int) -> Self {
        try! Directory(url: contents[index])
    }
    
    var isLeafItem: Bool {
        !url.isDirectory
    }
    
    var objectValue: String {
        url.lastPathComponent
    }
}

class ViewController: NSViewController {
    let delegate = BrowserDelegate<Directory, FileCell>(rootItem: try! Directory(url: URL(fileURLWithPath: "/")), configure: { cell, dir in
        cell.image = dir.url.smallFileIcon
    })
    
    @IBOutlet var browser: NSBrowser! {
        didSet {
            browser.delegate = delegate
            browser.setCellClass(FileCell.self)
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    override var representedObject: Any? {
        didSet {
        // Update the view, if already loaded.
        }
    }


}

protocol TreeLike {
    associatedtype ObjectValue
    var numberOfChildren: Int { get }
    func child(at index: Int) -> Self
    var isLeafItem: Bool { get }
    var objectValue: ObjectValue { get }
}

final class BrowserDelegate<A: TreeLike, Cell: Any>: NSObject, NSBrowserDelegate {
    var rootItem: A?
    let configure: (Cell, A) -> ()
    init(rootItem: A, configure: @escaping (Cell, A) -> ()) {
        self.rootItem = rootItem
        self.configure = configure
    }
    
    func rootItem(for browser: NSBrowser) -> Any? {
        return rootItem
    }
    
    func browser(_ browser: NSBrowser, numberOfChildrenOfItem item: Any?) -> Int {
        let item = item as! A
        return item.numberOfChildren
    }
    
    func browser(_ browser: NSBrowser, child index: Int, ofItem item: Any?) -> Any {
        let item = item as! A
        return item.child(at: index)
    }
    
    func browser(_ browser: NSBrowser, isLeafItem item: Any?) -> Bool {
        let a = item as! A
        return a.isLeafItem
    }
    
    func browser(_ browser: NSBrowser, objectValueForItem item: Any?) -> Any? {
        let a = item as! A
        return a.objectValue
    }
    
    func browser(_ sender: NSBrowser, willDisplayCell cell: Any, atRow row: Int, column: Int) {
        configure(cell as! Cell, sender.item(atRow: row, inColumn: column) as! A)
    }
}

class FileCell: NSBrowserCell {
    override init(imageCell i: NSImage?) {
        super.init(imageCell: i)
        isLeaf = true
    }
    
    override init(textCell s: String) {
        super.init(textCell: s)
        isLeaf = true
    }
    
    required init(coder c: NSCoder) {
        super.init(coder: c)
        isLeaf = true
    }
}