PopUpButton.swift

//
//  Created by Damiaan on 25/01/2019.
//  Copyright © 2019 Devian. All rights reserved.
//

import AppKit

class PopUpButton<Element>: NSPopUpButton {
	
	var items: SmartCollection<Element> { didSet {bindSmartCollection()} }
	var titleSpecifier: (Element) -> String
	
	required init?(coder: NSCoder) {
		items = SmartCollection()
		titleSpecifier = {return String(describing: $0)}
		super.init(coder: coder)
		
		bindSmartCollection()
	}
	
	func bindSmartCollection() {
		func addItem(for element: Element) {
			super.addItem(withTitle: self.titleSpecifier(element))
		}

		super.removeAllItems()
		items.forEach(addItem)
		items.postReplaceSubscriptions.append { range, elements in
			for index in range.reversed() {
				super.removeItem(at: index)
			}
			elements.forEach(addItem)
		}
		items.postFieldChangeSubscriptions.append { index, _ in
			self.item(at: index)?.title = self.titleSpecifier(self.items[index])
		}
	}

	override func addItem(withTitle title: String) {
		fatalError("use items to add or remove items")
	}
	override func addItems(withTitles itemTitles: [String]) {
		addItem(withTitle: "")
	}
	override func insertItem(withTitle title: String, at index: Int) {
		addItem(withTitle: "")
	}
	
	override func removeItem(at index: Int) {
		items.remove(at: index)
	}
	
	override func removeAllItems() {
		items.removeAll()
	}
	
	override func removeItem(withTitle title: String) {
		let indicesToRemove = items.indices.filter {titleSpecifier(items[$0]) == title}
		for index in indicesToRemove { items.remove(at: index) }
	}
	
	var selectedElement: Element? {
		return indexOfSelectedItem == -1 ? nil : items[indexOfSelectedItem]
	}
}