metatext/View Controllers/TableViewController.swift

// Copyright © 2020 Metabolist. All rights reserved.

import Combine
import SafariServices
import SwiftUI
import ViewModels

class TableViewController: UITableViewController {
    private let viewModel: CollectionViewModel
    private let identification: Identification
    private let loadingTableFooterView = LoadingTableFooterView()
    private let webfingerIndicatorView = WebfingerIndicatorView()
    private var cancellables = Set<AnyCancellable>()
    private var cellHeightCaches = [CGFloat: [CollectionItemIdentifier: CGFloat]]()

    private lazy var dataSource: TableViewDataSource = {
        .init(tableView: tableView, viewModelProvider: viewModel.viewModel(indexPath:))
    }()

    init(viewModel: CollectionViewModel, identification: Identification) {
        self.viewModel = viewModel
        self.identification = identification

        super.init(style: .plain)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        tableView.dataSource = dataSource
        tableView.prefetchDataSource = self
        tableView.cellLayoutMarginsFollowReadableWidth = true
        tableView.tableFooterView = UIView()

        view.addSubview(webfingerIndicatorView)
        webfingerIndicatorView.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint.activate([
            webfingerIndicatorView.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor),
            webfingerIndicatorView.centerYAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerYAnchor)
        ])

        setupViewModelBindings()
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        viewModel.request(maxId: nil, minId: nil)
    }

    override func scrollViewDidScroll(_ scrollView: UIScrollView) {
        guard scrollView.isDragging else { return }

        let up = scrollView.panGestureRecognizer.translation(in: scrollView.superview).y > 0

        for loadMoreView in visibleLoadMoreViews {
            loadMoreView.directionChanged(up: up)
        }
    }

    override func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        for loadMoreView in visibleLoadMoreViews {
            loadMoreView.finalizeDirectionChange()
        }
    }

    override func tableView(_ tableView: UITableView,
                            willDisplay cell: UITableViewCell,
                            forRowAt indexPath: IndexPath) {
        guard let item = dataSource.itemIdentifier(for: indexPath) else { return }

        var heightCache = cellHeightCaches[tableView.frame.width] ?? [CollectionItemIdentifier: CGFloat]()

        heightCache[item] = cell.frame.height
        cellHeightCaches[tableView.frame.width] = heightCache
    }

    override func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
        guard let item = dataSource.itemIdentifier(for: indexPath) else { return UITableView.automaticDimension }

        return cellHeightCaches[tableView.frame.width]?[item] ?? UITableView.automaticDimension
    }

    override func tableView(_ tableView: UITableView, shouldHighlightRowAt indexPath: IndexPath) -> Bool {
        viewModel.canSelect(indexPath: indexPath)
    }

    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        tableView.deselectRow(at: indexPath, animated: true)

        viewModel.select(indexPath: indexPath)
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        sizeTableHeaderFooterViews()
    }
}

extension TableViewController: UITableViewDataSourcePrefetching {
    func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
        guard
            let maxId = viewModel.nextPageMaxId,
            let indexPath = indexPaths.last,
            indexPath.section == dataSource.numberOfSections(in: tableView) - 1,
            indexPath.row == dataSource.tableView(tableView, numberOfRowsInSection: indexPath.section) - 1
        else { return }

        viewModel.request(maxId: maxId, minId: nil)
    }
}

extension TableViewController {
    func sizeTableHeaderFooterViews() {
        // https://useyourloaf.com/blog/variable-height-table-view-header/
        if let headerView = tableView.tableHeaderView {
            let size = headerView.systemLayoutSizeFitting(
                CGSize(width: tableView.frame.width, height: .greatestFiniteMagnitude),
                withHorizontalFittingPriority: .required,
                verticalFittingPriority: .fittingSizeLevel)

            if headerView.frame.size.height != size.height {
                headerView.frame.size.height = size.height
                tableView.tableHeaderView = headerView
                tableView.layoutIfNeeded()
            }

            view.insertSubview(webfingerIndicatorView, aboveSubview: headerView)
        }

        if let footerView = tableView.tableFooterView {
            let size = footerView.systemLayoutSizeFitting(
                CGSize(width: tableView.frame.width, height: .greatestFiniteMagnitude),
                withHorizontalFittingPriority: .required,
                verticalFittingPriority: .fittingSizeLevel)

            if footerView.frame.size.height != size.height {
                footerView.frame.size.height = size.height
                tableView.tableFooterView = footerView
                tableView.layoutIfNeeded()
            }
        }
    }
}

private extension TableViewController {
    var visibleLoadMoreViews: [LoadMoreView] {
        tableView.visibleCells.compactMap { $0.contentView as? LoadMoreView }
    }

    func setupViewModelBindings() {
        viewModel.title.sink { [weak self] in self?.navigationItem.title = $0 }.store(in: &cancellables)

        viewModel.updates.sink { [weak self] in self?.update($0) }.store(in: &cancellables)

        viewModel.events.receive(on: DispatchQueue.main)
            .sink { [weak self] in self?.handle(event: $0) }
            .store(in: &cancellables)

        viewModel.expandAll.receive(on: DispatchQueue.main)
            .sink { [weak self] in self?.set(expandAllState: $0) }
            .store(in: &cancellables)

        viewModel.loading.receive(on: RunLoop.main).sink { [weak self] in
            guard let self = self else { return }

            self.tableView.tableFooterView = $0 ? self.loadingTableFooterView : UIView()
            self.sizeTableHeaderFooterViews()
        }
        .store(in: &cancellables)

        tableView.publisher(for: \.contentOffset)
            .compactMap { [weak self] _ in self?.tableView.indexPathsForVisibleRows?.first }
            .removeDuplicates()
            .sink { [weak self] in self?.viewModel.viewedAtTop(indexPath: $0) }
            .store(in: &cancellables)
    }

    func update(_ update: CollectionUpdate) {
        var offsetFromNavigationBar: CGFloat?

        if
            let item = update.maintainScrollPosition,
            let indexPath = dataSource.indexPath(for: item),
            let navigationBar = navigationController?.navigationBar {
            let navigationBarMaxY = tableView.convert(navigationBar.bounds, from: navigationBar).maxY
            offsetFromNavigationBar = tableView.rectForRow(at: indexPath).origin.y - navigationBarMaxY
        }

        self.dataSource.apply(update.items.snapshot(), animatingDifferences: false) { [weak self] in
            guard let self = self else { return }

            if
                let item = update.maintainScrollPosition,
                let indexPath = self.dataSource.indexPath(for: item) {
                self.tableView.scrollToRow(at: indexPath, at: .top, animated: false)

                if let offsetFromNavigationBar = offsetFromNavigationBar {
                    self.tableView.contentOffset.y -= offsetFromNavigationBar
                }
            }
        }
    }

    func handle(event: CollectionItemEvent) {
        switch event {
        case .ignorableOutput:
            break
        case let .share(url):
            share(url: url)
        case let.navigation(navigation):
            switch navigation {
            case let .collection(collectionService):
                show(TableViewController(
                        viewModel: CollectionItemsViewModel(
                            collectionService: collectionService,
                            identification: identification),
                        identification: identification),
                     sender: self)
            case let .profile(profileService):
                show(ProfileViewController(
                        viewModel: ProfileViewModel(
                            profileService: profileService,
                            identification: identification),
                        identification: identification),
                     sender: self)
            case let .url(url):
                present(SFSafariViewController(url: url), animated: true)
            case .webfingerStart:
                webfingerIndicatorView.startAnimating()
            case .webfingerEnd:
                webfingerIndicatorView.stopAnimating()
            }
        }
    }

    func set(expandAllState: ExpandAllState) {
        switch expandAllState {
        case .hidden:
            navigationItem.rightBarButtonItem = nil
        case .expand:
            navigationItem.rightBarButtonItem = UIBarButtonItem(
                title: NSLocalizedString("status.show-more", comment: ""),
                image: UIImage(systemName: "eye"),
                primaryAction: UIAction { [weak self] _ in self?.viewModel.toggleExpandAll() })
        case .collapse:
            navigationItem.rightBarButtonItem = UIBarButtonItem(
                title: NSLocalizedString("status.show-less", comment: ""),
                image: UIImage(systemName: "eye.slash"),
                primaryAction: UIAction { [weak self] _ in self?.viewModel.toggleExpandAll() })
        }
    }

    func share(url: URL) {
        let activityViewController = UIActivityViewController(activityItems: [url], applicationActivities: nil)

        present(activityViewController, animated: true, completion: nil)
    }
}