0001-single-source-of-truth-005.swift

final class ViewController: UIViewController {
    
    // MARK: - Views -
    @IBOutlet private weak var firstNumberTextField: UITextField!
    @IBOutlet private weak var secondNumberTextField: UITextField!
    @IBOutlet private weak var operationTextField: UITextField!
    @IBOutlet private weak var resultLabel: UILabel!
    
    private var operationPickerView: UIPickerView!
    
    // MARK: - Attributes -
    private let viewModel = ViewModel()
    private var cancellables: [AnyCancellable] = []

    // MARK: - Life Cycle -
    override func viewDidLoad() {
        super.viewDidLoad()
    
        firstNumberTextField.addTarget(self,
            action: #selector(firstNumberTextFieldChanged),
            for: .editingChanged
        )
        
        secondNumberTextField.addTarget(self,
            action: #selector(secondNumberTextFieldChanged),
            for: .editingChanged
        )
        
        operationPickerView = UIPickerView()
        operationPickerView.delegate = self
        operationPickerView.dataSource = self
        operationTextField.inputView = operationPickerView
        
        bindToViewModel()
    }

    // MARK: - Private methods -
    private func bindToViewModel() {
        viewModel.$operationText
            .assign(to: \.text, on: operationTextField)
            .add(to: &cancellables)
        
        viewModel.$result
            .assign(to: \.text, on: resultLabel)
            .add(to: &cancellables)
    }
    
    // MARK: - Actions -
    @objc private func firstNumberTextFieldChanged() {
        viewModel.firstNumberText = firstNumberTextField.text
    }
    
    @objc private func secondNumberTextFieldChanged() {
        viewModel.secondNumberText = secondNumberTextField.text
    }
    
}

extension ViewController: UIPickerViewDelegate, UIPickerViewDataSource {
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }
    
    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return MathOperation.allCases.count
    }
    
    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return MathOperation.allCases[row].rawValue
    }
    
    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        viewModel.operation = MathOperation.allCases[row]
    }
}