TableViewManager

import CoreData
import UIKit

protocol TableViewManagerDelegate: AnyObject {

    associatedtype Cell: UITableViewCell
    associatedtype Header: UITableViewHeaderFooterView
    associatedtype Footer: UITableViewHeaderFooterView
    associatedtype Object: NSManagedObject

    func configureCell(_ cell: Cell, for object: Object)
    func configureHeader(_ header: Header, for title: String?)
    func configureFooter(_ footer: Footer, for title: String?)

}

// MARK: -

extension TableViewManagerDelegate {

    func configureHeader(
        _ header: UITableViewHeaderFooterView,
        for title: String?
    ) { }

    func configureFooter(
        _ footer: UITableViewHeaderFooterView,
        for title: String?
    ) { }

}

// MARK: -

class TableViewManager<Delegate: TableViewManagerDelegate>:
    NSObject,
    UITableViewDataSource,
    UITableViewDelegate,
    NSFetchedResultsControllerDelegate
{

    // MARK: - Types

    typealias Cell = Delegate.Cell
    typealias Header = Delegate.Header
    typealias Footer = Delegate.Footer
    typealias Object = Delegate.Object

    // MARK: - Variables

    weak var delegate: Delegate?

    private let tableView: UITableView
    private let frc: NSFetchedResultsController<Object>

    // MARK: - Lifecycle

    init(
        tableView: UITableView,
        frc: NSFetchedResultsController<Object>
    ) {
        self.tableView = tableView
        self.frc = frc

        super.init()
    }

    // MARK: - Public

    func object(at indexPath: IndexPath) -> Object {
        return frc.object(at: indexPath)
    }

    func title(at section: Int) -> String? {
        return frc.sections?[safe: section]?.name ?? nil
    }

    // MARK: - UITableViewDataSource

    func numberOfSections(
        in tableView: UITableView
    ) -> Int {
        return frc.sections?.count ?? 0
    }

    func tableView(
        _ tableView: UITableView,
        numberOfRowsInSection section: Int
    ) -> Int {
        return frc.sections?[section].numberOfObjects ?? 0
    }

    func tableView(
        _ tableView: UITableView,
        cellForRowAt indexPath: IndexPath
    ) -> UITableViewCell {
        guard let cell = tableView.dequeueReusableCell(
            withIdentifier: Cell.name,
            for: indexPath
        ) as? Cell else {
            fatalError("Failed to get \(Cell.name)")
        }
        delegate?.configureCell(cell, for: object(at: indexPath))
        return cell
    }

    // MARK: - UITableViewDelegate

    func tableView(
        _ tableView: UITableView,
        viewForHeaderInSection section: Int
    ) -> UIView? {
        guard let header = tableView.dequeueReusableHeaderFooterView(
            withIdentifier: Header.name
        ) as? Header else {
            fatalError("Failed to get \(Header.name)")
        }
        delegate?.configureHeader(header, for: title(at: section))
        return header
    }

    func tableView(
        _ tableView: UITableView,
        viewForFooterInSection section: Int
    ) -> UIView? {
        guard let footer = tableView.dequeueReusableHeaderFooterView(
            withIdentifier: Footer.name
        ) as? Footer else {
            fatalError("Failed to get \(Footer.name)")
        }
        delegate?.configureFooter(footer, for: title(at: section))
        return footer
    }

}

// MARK: -

class TestViewController: UIViewController, TableViewManagerDelegate {

    func configureCell(
        _ cell: UITableViewCell,
        for object: NSManagedObject
    ) {

    }

}