MVVM-C ViewModel

CountryListViewModel.swift

import Foundation

private struct CountryListEndpoint: EndpointReprsentable {
    
    var httpMethod: HTTPMethod { .get }
    var urlPath: URLPath { .name }
    let pathComponent: String?
    
}

protocol CountryListViewModelLoadingErrorDelegate: class {
    func didFailLoading(error: Error)
}

class CountryListViewModel: ViewModel, Searchable, CountryListDatasource {
    
    private enum Constants {
        static let title = "Countries"
        static let loadingMessage = "Loading countries..."
    }
    
    var screenTitle: String { Constants.title }
    var didUpdate: (() -> Void)?
    var didChangeState: ((_ isLoading: Bool, _ loadingMessage: String?) -> Void)?
    weak var loadingErrorDelegate: CountryListViewModelLoadingErrorDelegate?
    private let requestManager: RequestManager
    
    // MARK: - ViewModel
    
    private var countries = [Country]() {
        didSet {
            didUpdate?()
        }
    }
    
    private(set) var isLoading: Bool = false {
        didSet {
            didChangeState?(isLoading, isLoading ? Constants.loadingMessage : nil)
        }
    }
    
    // MARK: - Object lifecycle
    
    init(requestManager: RequestManager) {
        self.requestManager = requestManager
    }
    
    // MARK: - Searchable
    
    func searchFor(keyword: String) {
        let endpoint = CountryListEndpoint(pathComponent: keyword)
        
        isLoading = true
        requestManager.performRequest(endPoint: endpoint, completionQueue: .main, parser: JSONParser()) {
            [weak self] (result: Result<[Country], Error>) in
            
            guard let self = self else { return }
            self.isLoading = false
            
            switch result {
            case .success(let countries):
                self.countries = countries
            case .failure(let error):
                self.loadingErrorDelegate?.didFailLoading(error: error)
            }
        }
    }
    
}

// MARK: - CountryListDatasource

extension CountryListViewModel {
    
    var numberOfSections: Int { 1 }
    
    func numberOfRows(in section: Int) -> Int { countries.count }
    
    func country(at indexPath: IndexPath) -> Country? { countries[indexPath.row] }
    
    func itemForRow(at indexPath: IndexPath) -> CountryListItemRepresentable { countries[indexPath.row] }
    
}