BitcoinParse.swift

import UIKit

class ViewController: UIViewController {
    
    let imageView: UIImageView = {
        let img = UIImageView()
        img.translatesAutoresizingMaskIntoConstraints = false
        img.image = UIImage(named: "bitstampIcon")
        return img
    }()
    
    let priceLabel: UILabel = {
       let priceLabel = UILabel()
        priceLabel.translatesAutoresizingMaskIntoConstraints = false
        priceLabel.text = "N/A"
        priceLabel.numberOfLines = 0
        priceLabel.textAlignment = .center
        priceLabel.font = UIFont.boldSystemFont(ofSize: 40)
        return priceLabel
    }()
    
    let refreshButton: UIButton = {
        let button = UIButton()
        button.translatesAutoresizingMaskIntoConstraints = false
        button.backgroundColor = UIColor.gray
        button.setTitle("Refresh", for: .normal)
        button.layer.cornerRadius = 5
        button.titleLabel?.font = UIFont.boldSystemFont(ofSize: 40)
        
        button.addTarget(self, action: #selector(handlePriceUpdate), for: .touchUpInside)
        return button
    }()
    
    @objc func handlePriceUpdate() {
        fetchData()
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = UIColor.white
        
        view.addSubview(priceLabel)
        view.addSubview(imageView)
        view.addSubview(refreshButton)
        
        setupPriceLabel()
        setupImageView()
        setupRefreshButton()
        
        fetchData()
    }
    
    func setupImageView() {
        //x, y, width and height constraints
        imageView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        imageView.bottomAnchor.constraint(equalTo: priceLabel.topAnchor).isActive = true
        imageView.widthAnchor.constraint(equalToConstant: 150).isActive = true
        imageView.heightAnchor.constraint(equalToConstant: 150).isActive = true
    }
    
    func setupPriceLabel() {
        //x, y, width and height constraints
        priceLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        priceLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
        priceLabel.widthAnchor.constraint(equalTo: view.widthAnchor, constant: -40).isActive = true
        priceLabel.heightAnchor.constraint(equalToConstant: 50).isActive = true
        
    }
    
    func setupRefreshButton() {
        //x, y, width and height constraints
        refreshButton.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        refreshButton.topAnchor.constraint(equalTo: priceLabel.bottomAnchor, constant: 16).isActive = true
        refreshButton.widthAnchor.constraint(equalTo: view.widthAnchor, constant: -40).isActive = true
        refreshButton.heightAnchor.constraint(equalToConstant: 50).isActive = true
        
    }
    
    
    
}

extension ViewController {
    //fetch & parse json from api
    func fetchData() {
        let urlString = "https://www.bitstamp.net/api/v2/ticker/btcusd/"
        let url = URL(string: urlString)
        let urlRequest = URLRequest(url: url!)
        
        let task = URLSession.shared.dataTask(with: urlRequest) { (data, response, error) in
            if error != nil {
                print(error)
                return
            }
            do {
                let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as! [String : AnyObject]
                if let price = json["last"] as? String, let low = json["low"] as? String, let high = json["high"] as? String {
                    self.priceLabel.text = price
                }

            } catch let error {
                print(error)
            }
        }
        task.resume()
    }
    
}