DraggableUITableViewWithContextMenu.swift

//
//  ViewController.swift
//
//  Created by @imaizume on 2021/09/03.
//

import UIKit

class ViewController: UIViewController {

    private var list: [String] = ["Apple", "Banana", "Chocolate", "Donut"]

    override func viewDidLoad() {
        super.viewDidLoad()

        // Initialize UITableView.
        let tableView: UITableView = .init()
        view.addSubview(tableView)
        tableView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            view.leadingAnchor.constraint(equalTo: tableView.leadingAnchor, constant: 0),
            view.trailingAnchor.constraint(equalTo: tableView.trailingAnchor, constant: 0),
            view.topAnchor.constraint(equalTo: tableView.topAnchor, constant: 0),
            view.bottomAnchor.constraint(equalTo: tableView.bottomAnchor, constant: 0)
        ])

        // Set data source and delegate.
        tableView.delegate = self
        tableView.dataSource = self

        // Set drag and drop delegate.
        tableView.dragInteractionEnabled = true
        tableView.dragDelegate = self
        tableView.dropDelegate = self
    }
}

extension ViewController: UITableViewDragDelegate {
    func tableView(_ tableView: UITableView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
        [.init(itemProvider: .init())]
    }
}

extension ViewController: UITableViewDropDelegate {
    func tableView(_ tableView: UITableView, dropSessionDidUpdate session: UIDropSession, withDestinationIndexPath destinationIndexPath: IndexPath?
    ) -> UITableViewDropProposal {
        if session.localDragSession != nil {
            return .init(operation: .move, intent: .insertAtDestinationIndexPath)
        } else {
            return .init(operation: .cancel, intent: .unspecified)
        }
    }

    func tableView(_ tableView: UITableView, performDropWith coordinator: UITableViewDropCoordinator) {
        guard let item = coordinator.items.first,
              let destinationIndexPath = coordinator.destinationIndexPath,
              let sourceIndexPath = item.sourceIndexPath else { return }

        tableView.performBatchUpdates({ [weak self] in
            guard let strongSelf = self else { return }
            let element = strongSelf.list.remove(at: sourceIndexPath.row)
            strongSelf.list.insert(element, at: destinationIndexPath.row)
            tableView.deleteRows(at: [sourceIndexPath], with: .automatic)
            tableView.insertRows(at: [destinationIndexPath], with: .automatic)
        }, completion: nil)
        coordinator.drop(item.dragItem, toRowAt: destinationIndexPath)
    }
}

extension ViewController: UIGestureRecognizerDelegate {
    func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
        true
    }
}

extension ViewController: UITableViewDelegate {
    func tableView(_ tableView: UITableView, canMoveRowAt indexPath: IndexPath) -> Bool {
        true
    }

    func tableView(_ tableView: UITableView, contextMenuConfigurationForRowAt indexPath: IndexPath, point: CGPoint) -> UIContextMenuConfiguration? {
        let configuration = UIContextMenuConfiguration(identifier: nil, previewProvider: nil) { actions -> UIMenu? in
            let copy: UIAction = .init(title: "Copy", image: UIImage(systemName: "doc.on.doc"), identifier: nil) { action in
                if let cell = tableView.cellForRow(at: indexPath) {
                    UIPasteboard.general.string = cell.textLabel?.text
                }
            }
            return .init(title: "Menu", image: nil, identifier: nil, children: [copy])
        }
        return configuration
    }
}

extension ViewController: UITableViewDataSource {
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        list.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = UITableViewCell()
        guard indexPath.row < list.count else { return cell }
        cell.textLabel?.text = list[indexPath.row]
        return cell
    }
}