import UIKit

class TestViewController: UIViewController {

    @IBOutlet weak var tableView: UITableView!
    var dataList: [String] = [String]()
    var fromIndex: Int = 0
    let totalEntries: Int = 100
    let limit: Int = 20

    override func viewDidLoad() {
        super.viewDidLoad()
        tableViewSetup()
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        dataList.removeAll()
        loadMoreItems()
    }

    @objc func loadMoreItems() {

        let endIndex = min(totalEntries, fromIndex + limit)
        for i in fromIndex..<endIndex{
            dataList.append(String(i))
        }
        fromIndex = endIndex
        tableView.reloadData()

        // Dismissing activity indicator from footer...
        self.tableView.tableFooterView = nil
    }
}

extension TestViewController: UITableViewDelegate, UITableViewDataSource {

    func tableViewSetup() {
        tableView.dataSource = self
        tableView.delegate = self
        tableView.rowHeight = 40
    }

    func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return dataList.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
        return cell
    }

    func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        cell.textLabel?.text = dataList[indexPath.row]
        if indexPath.row == dataList.count - 1 && totalEntries > dataList.count{

            // Adding Activity Indicator as footerView in tableView
            let spinner = UIActivityIndicatorView(activityIndicatorStyle: .gray)
            spinner.startAnimating()
            spinner.frame = CGRect(x: CGFloat(0), y: CGFloat(0), width: tableView.bounds.width, height: CGFloat(44))
            self.tableView.tableFooterView = spinner
            self.tableView.tableFooterView?.isHidden = false

            // Call loadMore() method
            self.perform(#selector(loadMoreItems), with: nil, afterDelay: 2.0)

        }
    }
}