Example viewModel

RandomMusicViewModel.swift

//
//  RandomMusicViewModel.swift
//
//  Created by Vasiliy Savchuk on 2/6/17.
//  Copyright © 2017 All rights reserved.
//

class RandomMusicViewModel: ViewModelTitleProtocol, ViewModelProtocol, ViewModelTypeProtocol {
    var dataSource: Array<JSONDecodable> =  Array()
    var type: CellType = .randomMusicCell
    private let backendService: BackendService = BackendService()
    var canLoad = true
    var perPage = 10
    var page = 1
    
    var imageUrl: URL {
        let track: Track = self.dataSource.first as! Track
        if let album = track.albums.first { return URL(string: API.url + album.cover.thumblUrlX3)! }
        return URL(string: API.url + "")!
    }
    
    //MARK: - Lifecicle Object
    
    init() {
        NotificationCenter.observe(self, selector: #selector(loadNext(notification:)), name: Notification.Name.Player.loadNext)
    }

    //MARK: - Methods
    
    func loadDataFromDB() -> Results<Object>? {
        return nil
    }
    
    func load(perPage: Int = 10, page: Int = 1, handler:@escaping () -> Void) {
        if canLoad == false { return }
        let existIds = dataSource.map { ($0 as! Track).id }
        backendService.parameters = ["per_page": perPage, "page": page, "exist_ids" : existIds]
        backendService.getRandom { [weak self] json in
            let items = json.map({ Track.init(json: $0.1) })
            if items.count < perPage {  self?.canLoad = false  }
            if page > 1 {
                let _ = items.map({self?.dataSource.append($0)})
                self?.updatePlayerIfNeededWith(tracks: items)
            } else {
                self?.dataSource = items
            }
            handler()
        }
    }
    
    private func updatePlayerIfNeededWith(tracks: [Track]) {
        guard let viewModel = Player.sharedInstance.viewModel as? RandomMusicViewModel else { return }
        if viewModel == self {
            Player.sharedInstance.addTracksToTheEnd(array: tracks)
        }
    }

    @objc func loadNext(notification: Notification) {
        let viewModel = notification.userInfo?["viewModel"]
        guard let vm = viewModel as? RandomMusicViewModel else { return }
        if vm == self {
            if canLoad == false { return }
            page += 1
            load(perPage: perPage, page: page, handler:{})
        }
    }
    
    func nameOfTitle() -> String {
        return ""
    }
    
    public static func == (lhs: RandomMusicViewModel, rhs: RandomMusicViewModel) -> Bool {
        if lhs.dataSource.count != rhs.dataSource.count { return false }
        for (index, item) in lhs.dataSource.enumerated() {
            let item2 = rhs.dataSource[index] as! Track
            if (item as! Track).id != item2.id {
                return false
            }
        }
        return true
    }
}