//
//  TimelineViewController.swift
//  NetNewsWire
//
//  Created by Brent Simmons on 7/26/15.
//  Copyright © 2015 Ranchero Software, LLC. All rights reserved.
//

import Foundation
import RSCore
import Articles
import Account
import os.log

protocol TimelineDelegate: AnyObject {
	func timelineSelectionDidChange(_: TimelineViewController, selectedArticles: [Article]?)
	func timelineRequestedFeedSelection(_: TimelineViewController, feed: Feed)
	func timelineInvalidatedRestorationState(_: TimelineViewController)
}

enum TimelineShowFeedName {
	case none
	case byline
	case feed
}

final class TimelineViewController: NSViewController, UndoableCommandRunner, UnreadCountProvider {

	@IBOutlet var tableView: TimelineTableView!

	private var readFilterEnabledTable = [SidebarItemIdentifier: Bool]()
	var isReadFiltered: Bool? {
		guard representedObjects?.count == 1, let timelineFeed = representedObjects?.first as? SidebarItem else {
			return nil
		}
		guard timelineFeed.defaultReadFilterType != .alwaysRead else {
			return nil
		}
		if let feedID = timelineFeed.sidebarItemID, let readFilterEnabled = readFilterEnabledTable[feedID] {
			return readFilterEnabled
		} else {
			return timelineFeed.defaultReadFilterType == .read
		}
	}

	var isCleanUpAvailable: Bool {
		let isEligibleForCleanUp: Bool?

		if representedObjects?.count == 1, let timelineFeed = representedObjects?.first as? SidebarItem, timelineFeed.defaultReadFilterType == .alwaysRead {
			isEligibleForCleanUp = true
		} else {
			isEligibleForCleanUp = isReadFiltered
		}

		guard isEligibleForCleanUp ?? false else { return false }

		let readSelectedCount = selectedArticles.filter({ $0.status.read }).count
		let readArticleCount = articles.count - unreadCount
		let availableToCleanCount = readArticleCount - readSelectedCount

		return availableToCleanCount > 0
	}

	var representedObjects: [AnyObject]? {
		didSet {
			if !representedObjectArraysAreEqual(oldValue, representedObjects) {
				unreadCount = 0

				selectionDidChange(nil)
				if showsSearchResults {
					fetchAndReplaceArticlesAsync()
				} else {
					fetchAndReplaceArticlesSync()
					if articles.count > 0 {
						tableView.scrollRowToVisible(0)
					}
					updateUnreadCount()
				}
			}
		}
	}

	weak var delegate: TimelineDelegate?
	var sharingServiceDelegate: NSSharingServiceDelegate?

	var showsSearchResults = false
	var selectedArticles: [Article] {
		return Array(articles.articlesForIndexes(tableView.selectedRowIndexes))
	}

	var hasAtLeastOneSelectedArticle: Bool {
		return tableView.selectedRow != -1
	}

	var articles = ArticleArray() {
		didSet {
			defer {
				updateUnreadCount()
			}

			if articles == oldValue {
				return
			}

			if articles.representSameArticlesInSameOrder(as: oldValue) {
				// When the array is the same — same articles, same order —
				// but some data in some of the articles may have changed.
				// Just reload visible cells in this case: don’t call reloadData.
				articleRowMap = [String: [Int]]()
				reloadVisibleCells()
				return
			}

			if let representedObjects = representedObjects, representedObjects.count == 1 && representedObjects.first is Feed {
				showFeedNames = {
					for article in articles {
						if !article.byline().isEmpty {
							return .byline
						}
					}
					return .none
				}()
			} else {
				showFeedNames = .feed
			}

			articleRowMap = [String: [Int]]()
			tableView.reloadData()
		}
	}

	var unreadCount: Int = 0 {
		didSet {
			if unreadCount != oldValue {
				postUnreadCountDidChangeNotification()
			}
		}
	}

	var undoableCommands = [UndoableCommand]()

	private var fetchSerialNumber = 0
	private let fetchRequestQueue = FetchRequestQueue()
	private var exceptionArticleFetcher: ArticleFetcher?
	private var articleRowMap = [String: [Int]]() // articleID: rowIndex
	private var cellAppearance: TimelineCellAppearance!
	private var cellAppearanceWithIcon: TimelineCellAppearance!
	private var showFeedNames: TimelineShowFeedName = .none {
		didSet {
			if showFeedNames != oldValue {
				updateShowIcons()
				updateTableViewRowHeight()
				reloadVisibleCells()
			}
		}
	}

	private var showIcons = false
	private var currentRowHeight: CGFloat = 0.0

	private var didRegisterForNotifications = false
	static let fetchAndMergeArticlesQueue = CoalescingQueue(name: "Fetch and Merge Articles", interval: 0.5, maxInterval: 2.0)

	private var sortDirection = AppDefaults.shared.timelineSortDirection {
		didSet {
			if sortDirection != oldValue {
				sortParametersDidChange()
			}
		}
	}
	private var groupByFeed = AppDefaults.shared.timelineGroupByFeed {
		didSet {
			if groupByFeed != oldValue {
				sortParametersDidChange()
			}
		}
	}
	private var fontSize: FontSize = AppDefaults.shared.timelineFontSize {
		didSet {
			if fontSize != oldValue {
				fontSizeDidChange()
			}
		}
	}

	private var previouslySelectedArticles: ArticleArray?

	private var oneSelectedArticle: Article? {
		return selectedArticles.count == 1 ? selectedArticles.first : nil
	}

	private let keyboardDelegate = TimelineKeyboardDelegate()
	private var timelineShowsSeparatorsObserver: NSKeyValueObservation?

	convenience init(delegate: TimelineDelegate) {
		self.init(nibName: "TimelineTableView", bundle: nil)
		self.delegate = delegate
	}

	override func viewDidLoad() {
		cellAppearance = TimelineCellAppearance(showIcon: false, fontSize: fontSize)
		cellAppearanceWithIcon = TimelineCellAppearance(showIcon: true, fontSize: fontSize)

		updateRowHeights()
		tableView.rowHeight = currentRowHeight
		tableView.target = self
		tableView.doubleAction = #selector(openArticleInBrowser(_:))
		tableView.setDraggingSourceOperationMask(.copy, forLocal: false)
		tableView.keyboardDelegate = keyboardDelegate
		tableView.style = .inset

		if !didRegisterForNotifications {
			NotificationCenter.default.addObserver(self, selector: #selector(statusesDidChange(_:)), name: .StatusesDidChange, object: nil)
			NotificationCenter.default.addObserver(self, selector: #selector(feedIconDidBecomeAvailable(_:)), name: .feedIconDidBecomeAvailable, object: nil)
			NotificationCenter.default.addObserver(self, selector: #selector(avatarDidBecomeAvailable(_:)), name: .AvatarDidBecomeAvailable, object: nil)
			NotificationCenter.default.addObserver(self, selector: #selector(faviconDidBecomeAvailable(_:)), name: .FaviconDidBecomeAvailable, object: nil)
			NotificationCenter.default.addObserver(self, selector: #selector(accountDidDownloadArticles(_:)), name: .AccountDidDownloadArticles, object: nil)
			NotificationCenter.default.addObserver(self, selector: #selector(accountStateDidChange(_:)), name: .AccountStateDidChange, object: nil)
			NotificationCenter.default.addObserver(self, selector: #selector(accountsDidChange(_:)), name: .UserDidAddAccount, object: nil)
			NotificationCenter.default.addObserver(self, selector: #selector(accountsDidChange(_:)), name: .UserDidDeleteAccount, object: nil)
			NotificationCenter.default.addObserver(self, selector: #selector(containerChildrenDidChange(_:)), name: .ChildrenDidChange, object: nil)
			NotificationCenter.default.addObserver(self, selector: #selector(userDefaultsDidChange(_:)), name: UserDefaults.didChangeNotification, object: nil)
			didRegisterForNotifications = true
		}
	}

	override func viewDidAppear() {
		sharingServiceDelegate = SharingServiceDelegate(self.view.window)
	}

	// MARK: - API

	func markAllAsRead(completion: (() -> Void)? = nil) {
		guard let undoManager = undoManager, let markReadCommand = MarkStatusCommand(initialArticles: articles, markingRead: true, undoManager: undoManager, completion: completion) else {
			return
		}
		runCommand(markReadCommand)
	}

	func canMarkAllAsRead() -> Bool {
		return articles.canMarkAllAsRead()
	}

	func canMarkSelectedArticlesAsRead() -> Bool {
		return selectedArticles.canMarkAllAsRead()
	}

	func representsThisObjectOnly(_ object: AnyObject) -> Bool {
		guard let representedObjects = representedObjects else {
			return false
		}
		if representedObjects.count != 1 {
			return false
		}
		return representedObjects.first! === object
	}

	func cleanUp() {
		fetchAndReplacePreservingSelection()
	}

	func toggleReadFilter() {
		guard let filter = isReadFiltered, let feedID = (representedObjects?.first as? SidebarItem)?.sidebarItemID else { return }
		readFilterEnabledTable[feedID] = !filter
		delegate?.timelineInvalidatedRestorationState(self)
		fetchAndReplacePreservingSelection()
	}

	// MARK: State Restoration

	func saveState(to state: inout [AnyHashable: Any]) {
		state[UserInfoKey.readArticlesFilterStateKeys] = readFilterEnabledTable.keys.compactMap { $0.userInfo }
		state[UserInfoKey.readArticlesFilterStateValues] = readFilterEnabledTable.values.compactMap( { $0 })

		if selectedArticles.count == 1 {
			state[UserInfoKey.articlePath] = selectedArticles.first!.pathUserInfo
		}
	}

	func restoreState(from state: [AnyHashable: Any]) {
		guard let readArticlesFilterStateKeys = state[UserInfoKey.readArticlesFilterStateKeys] as? [[AnyHashable: AnyHashable]],
			let readArticlesFilterStateValues = state[UserInfoKey.readArticlesFilterStateValues] as? [Bool] else {
			return
		}

		for i in 0..<readArticlesFilterStateKeys.count {
			if let feedIdentifier = SidebarItemIdentifier(userInfo: readArticlesFilterStateKeys[i]) {
				readFilterEnabledTable[feedIdentifier] = readArticlesFilterStateValues[i]
			}
		}

		if let articlePathUserInfo = state[UserInfoKey.articlePath] as? [AnyHashable: Any],
			let accountID = articlePathUserInfo[ArticlePathKey.accountID] as? String,
			let account = AccountManager.shared.existingAccount(with: accountID),
			let articleID = articlePathUserInfo[ArticlePathKey.articleID] as? String {

			exceptionArticleFetcher = SingleArticleFetcher(account: account, articleID: articleID)
			fetchAndReplaceArticlesSync()

			if let selectedIndex = articles.firstIndex(where: { $0.articleID == articleID }) {
				tableView.selectRow(selectedIndex)
				DispatchQueue.main.async {
					self.tableView.scrollTo(row: selectedIndex)
				}
				focus()
			}

		} else {

			fetchAndReplaceArticlesSync()

		}

	}

	// MARK: - Actions

	@objc func openArticleInBrowser(_ sender: Any?) {
		if let link = oneSelectedArticle?.preferredLink {
			Browser.open(link, invertPreference: NSApp.currentEvent?.modifierFlags.contains(.shift) ?? false)
		}
	}

	@IBAction func toggleStatusOfSelectedArticles(_ sender: Any?) {
		guard !selectedArticles.isEmpty else {
			return
		}
		let articles = selectedArticles
		let status = articles.first!.status
		let markAsRead = !status.read

		if markAsRead {
			markSelectedArticlesAsRead(sender)
		} else {
			markSelectedArticlesAsUnread(sender)
		}
	}

	@IBAction func markSelectedArticlesAsRead(_ sender: Any?) {
		guard let undoManager = undoManager, let markReadCommand = MarkStatusCommand(initialArticles: selectedArticles, markingRead: true, undoManager: undoManager) else {
			return
		}
		runCommand(markReadCommand)
	}

	@IBAction func markSelectedArticlesAsUnread(_ sender: Any?) {
		guard let undoManager = undoManager, let markUnreadCommand = MarkStatusCommand(initialArticles: selectedArticles, markingRead: false, undoManager: undoManager) else {
			return
		}
		runCommand(markUnreadCommand)
	}

	@IBAction func copy(_ sender: Any?) {
		NSPasteboard.general.copyObjects(selectedArticles)
	}

	@IBAction func selectNextUp(_ sender: Any?) {
		guard let lastSelectedRow = tableView.selectedRowIndexes.last else {
			return
		}

		let nextRowIndex = lastSelectedRow - 1
		if nextRowIndex <= 0 {
			tableView.scrollTo(row: 0, extraHeight: 0)
		}

		tableView.selectRow(nextRowIndex)

		let followingRowIndex = nextRowIndex - 1
		if followingRowIndex < 0 {
			return
		}

		tableView.scrollToRowIfNotVisible(followingRowIndex)

	}

	@IBAction func selectNextDown(_ sender: Any?) {
		guard let firstSelectedRow = tableView.selectedRowIndexes.first else {
			return
		}

		let tableMaxIndex = tableView.numberOfRows - 1
		let nextRowIndex = firstSelectedRow + 1
		if nextRowIndex >= tableMaxIndex {
			tableView.scrollTo(row: tableMaxIndex, extraHeight: 0)
		}

		tableView.selectRow(nextRowIndex)

		let followingRowIndex = nextRowIndex + 1
		if followingRowIndex > tableMaxIndex {
			return
		}

		tableView.scrollToRowIfNotVisible(followingRowIndex)

	}

	func toggleReadStatusForSelectedArticles() {
		// If any one of the selected articles is unread, then mark them as read.
		// If all articles are read, then mark them as unread them.

		let commandStatus = markReadCommandStatus()
		let markingRead: Bool
		switch commandStatus {
		case .canMark:
			markingRead = true
		case .canUnmark:
			markingRead = false
		case .canDoNothing:
			return
		}

		guard let undoManager = undoManager, let markStarredCommand = MarkStatusCommand(initialArticles: selectedArticles, markingRead: markingRead, undoManager: undoManager) else {
			return
		}

		runCommand(markStarredCommand)
	}

	func toggleStarredStatusForSelectedArticles() {

		// If any one of the selected articles is not starred, then star them.
		// If all articles are starred, then unstar them.

		let commandStatus = markStarredCommandStatus()
		let starring: Bool
		switch commandStatus {
		case .canMark:
			starring = true
		case .canUnmark:
			starring = false
		case .canDoNothing:
			return
		}

		guard let undoManager = undoManager, let markStarredCommand = MarkStatusCommand(initialArticles: selectedArticles, markingStarred: starring, undoManager: undoManager) else {
			return
		}
		runCommand(markStarredCommand)
	}

	func markStarredCommandStatus() -> MarkCommandValidationStatus {
		return MarkCommandValidationStatus.statusFor(selectedArticles) { $0.anyArticleIsUnstarred() }
	}

	func markReadCommandStatus() -> MarkCommandValidationStatus {
		let articles = selectedArticles

		if articles.anyArticleIsUnread() {
			return .canMark
		}

		if articles.anyArticleIsReadAndCanMarkUnread() {
			return .canUnmark
		}

		return .canDoNothing
	}

	func markOlderArticlesRead() {
		markOlderArticlesRead(selectedArticles)
	}

	func markAboveArticlesRead() {
		markAboveArticlesRead(selectedArticles)
	}

	func markBelowArticlesRead() {
		markBelowArticlesRead(selectedArticles)
	}

	func canMarkAboveArticlesAsRead() -> Bool {
		guard let first = selectedArticles.first else { return false }
		return articles.articlesAbove(article: first).canMarkAllAsRead()
	}

	func canMarkBelowArticlesAsRead() -> Bool {
		guard let last = selectedArticles.last else { return false }
		return articles.articlesBelow(article: last).canMarkAllAsRead()
	}

	func markOlderArticlesRead(_ selectedArticles: [Article]) {
		// Mark articles older than the selectedArticles(s) as read.

		var cutoffDate: Date?
		for article in selectedArticles {
			if cutoffDate == nil {
				cutoffDate = article.logicalDatePublished
			} else if cutoffDate! > article.logicalDatePublished {
				cutoffDate = article.logicalDatePublished
			}
		}
		if cutoffDate == nil {
			return
		}

		let articlesToMark = articles.filter { $0.logicalDatePublished < cutoffDate! }
		if articlesToMark.isEmpty {
			return
		}

		guard let undoManager = undoManager, let markReadCommand = MarkStatusCommand(initialArticles: articlesToMark, markingRead: true, undoManager: undoManager) else {
			return
		}
		runCommand(markReadCommand)
	}

	func markAboveArticlesRead(_ selectedArticles: [Article]) {
		guard let first = selectedArticles.first else { return }
		let articlesToMark = articles.articlesAbove(article: first)
		guard !articlesToMark.isEmpty else { return }
		guard let undoManager = undoManager, let markReadCommand = MarkStatusCommand(initialArticles: articlesToMark, markingRead: true, undoManager: undoManager) else {
			return
		}
		runCommand(markReadCommand)
	}

	func markBelowArticlesRead(_ selectedArticles: [Article]) {
		guard let last = selectedArticles.last else { return }
		let articlesToMark = articles.articlesBelow(article: last)
		guard !articlesToMark.isEmpty else { return }
		guard let undoManager = undoManager, let markReadCommand = MarkStatusCommand(initialArticles: articlesToMark, markingRead: true, undoManager: undoManager) else {
			return
		}
		runCommand(markReadCommand)
	}

	// MARK: - Navigation

	func goToDeepLink(for userInfo: [AnyHashable: Any]) {
		guard let articleID = userInfo[ArticlePathKey.articleID] as? String else { return }

		if isReadFiltered ?? false {
			if let accountName = userInfo[ArticlePathKey.accountName] as? String,
				let account = AccountManager.shared.existingActiveAccount(forDisplayName: accountName) {
				exceptionArticleFetcher = SingleArticleFetcher(account: account, articleID: articleID)
				fetchAndReplaceArticlesSync()
			}
		}

		guard let ix = articles.firstIndex(where: { $0.articleID == articleID }) else {	return }

		NSCursor.setHiddenUntilMouseMoves(true)
		tableView.selectRow(ix)
		tableView.scrollTo(row: ix)
	}

	func goToNextUnread(wrappingToTop wrapping: Bool = false) {
		guard let ix = indexOfNextUnreadArticle() else {
			return
		}
		NSCursor.setHiddenUntilMouseMoves(true)
		tableView.selectRow(ix)
		tableView.scrollTo(row: ix)
	}

	func canGoToNextUnread(wrappingToTop wrapping: Bool = false) -> Bool {
		guard let _ = indexOfNextUnreadArticle(wrappingToTop: wrapping) else {
			return false
		}
		return true
	}

	func indexOfNextUnreadArticle(wrappingToTop wrapping: Bool = false) -> Int? {
		return articles.rowOfNextUnreadArticle(tableView.selectedRow, wrappingToTop: wrapping)
	}

	func focus() {
		guard let window = tableView.window else {
			return
		}

		window.makeFirstResponderUnlessDescendantIsFirstResponder(tableView)
		if !hasAtLeastOneSelectedArticle && articles.count > 0 {
			tableView.selectRowAndScrollToVisible(0)
		}
	}

	// MARK: - Notifications

	@objc func statusesDidChange(_ note: Notification) {
		guard let articleIDs = note.userInfo?[Account.UserInfoKey.articleIDs] as? Set<String> else {
			return
		}
		reloadVisibleCells(for: articleIDs)
		updateUnreadCount()
	}

	@objc func feedIconDidBecomeAvailable(_ note: Notification) {
		guard showIcons, let feed = note.userInfo?[UserInfoKey.feed] as? Feed else {
			return
		}
		let indexesToReload = tableView.indexesOfAvailableRowsPassingTest { (row) -> Bool in
			guard let article = articles.articleAtRow(row) else {
				return false
			}
			return feed == article.feed
		}
		if let indexesToReload = indexesToReload {
			reloadCells(for: indexesToReload)
		}
	}

	@objc func avatarDidBecomeAvailable(_ note: Notification) {
		guard showIcons, let avatarURL = note.userInfo?[UserInfoKey.url] as? String else {
			return
		}

		let indexesToReload = tableView.indexesOfAvailableRowsPassingTest { (row) -> Bool in
			guard let article = articles.articleAtRow(row), let authors = article.authors, !authors.isEmpty else {
				return false
			}
			for author in authors {
				if author.avatarURL == avatarURL {
					return true
				}
			}
			return false
		}
		if let indexesToReload = indexesToReload {
			reloadCells(for: indexesToReload)
		}
	}

	@objc func faviconDidBecomeAvailable(_ note: Notification) {
		if showIcons {
			queueReloadAvailableCells()
		}
	}

	@objc func accountDidDownloadArticles(_ note: Notification) {
		guard let feeds = note.userInfo?[Account.UserInfoKey.feeds] as? Set<Feed> else {
			return
		}

		let shouldFetchAndMergeArticles = representedObjectsContainsAnyFeed(feeds) || representedObjectsContainsAnyPseudoFeed()
		if shouldFetchAndMergeArticles {
			queueFetchAndMergeArticles()
		}
	}

	@objc func accountStateDidChange(_ note: Notification) {
		if representedObjectsContainsAnyPseudoFeed() {
			fetchAndReplaceArticlesAsync()
		}
	}

	@objc func accountsDidChange(_ note: Notification) {
		if representedObjectsContainsAnyPseudoFeed() {
			fetchAndReplaceArticlesAsync()
		}
	}

	@objc func containerChildrenDidChange(_ note: Notification) {
		if representedObjectsContainsAnyPseudoFeed() || representedObjectsContainAnyFolder() {
			fetchAndReplaceArticlesAsync()
		}
	}

	@objc func userDefaultsDidChange(_ note: Notification) {
		self.fontSize = AppDefaults.shared.timelineFontSize
		self.sortDirection = AppDefaults.shared.timelineSortDirection
		self.groupByFeed = AppDefaults.shared.timelineGroupByFeed
	}

	// MARK: - Reloading Data

	private func cellForRowView(_ rowView: NSView) -> NSView? {
		for oneView in rowView.subviews where oneView is TimelineTableCellView {
			return oneView
		}
		return nil
	}

	private func reloadVisibleCells() {
		guard let indexes = tableView.indexesOfAvailableRows() else {
			return
		}
		reloadVisibleCells(for: indexes)
	}

	private func reloadVisibleCells(for articles: [Article]) {
		reloadVisibleCells(for: Set(articles.articleIDs()))
	}

	private func reloadVisibleCells(for articles: Set<Article>) {
		reloadVisibleCells(for: articles.articleIDs())
	}

	private func reloadVisibleCells(for articleIDs: Set<String>) {
		if articleIDs.isEmpty {
			return
		}
		let indexes = indexesForArticleIDs(articleIDs)
		reloadVisibleCells(for: indexes)
	}

	private func reloadVisibleCells(for indexes: IndexSet) {
		let indexesToReload = tableView.indexesOfAvailableRowsPassingTest { (row) -> Bool in
			return indexes.contains(row)
		}
		if let indexesToReload = indexesToReload {
			reloadCells(for: indexesToReload)
		}
	}

	private func reloadCells(for indexes: IndexSet) {
		if indexes.isEmpty {
			return
		}
		tableView.reloadData(forRowIndexes: indexes, columnIndexes: NSIndexSet(index: 0) as IndexSet)
	}

	// MARK: - Cell Configuring

	private func calculateRowHeight() -> CGFloat {

		let prototypeID = "prototype"
		let status = ArticleStatus(articleID: prototypeID, read: false, starred: false, dateArrived: Date())
		let prototypeArticle = Article(accountID: prototypeID, articleID: prototypeID, feedID: prototypeID, uniqueID: prototypeID, title: Constants.prototypeText, contentHTML: nil, contentText: nil, url: nil, externalURL: nil, summary: nil, imageURL: nil, datePublished: nil, dateModified: nil, authors: nil, status: status)

		let prototypeCellData = TimelineCellData(article: prototypeArticle, showFeedName: .feed, feedName: "Prototype Feed Name", byline: nil, iconImage: nil, showIcon: false, featuredImage: nil)
		let height = TimelineCellLayout.height(for: 100, cellData: prototypeCellData, appearance: cellAppearance)
		return height
	}

	private func updateRowHeights() {
		currentRowHeight = calculateRowHeight()
		updateTableViewRowHeight()
	}

	@objc func fetchAndMergeArticles() {
		guard let representedObjects = representedObjects else {
			return
		}

		fetchUnsortedArticlesAsync(for: representedObjects) { [weak self] (unsortedArticles) in
			// Merge articles by articleID. For any unique articleID in current articles, add to unsortedArticles.
			guard let strongSelf = self else {
				return
			}
			let unsortedArticleIDs = unsortedArticles.articleIDs()
			var updatedArticles = unsortedArticles
			for article in strongSelf.articles {
				if !unsortedArticleIDs.contains(article.articleID) {
					updatedArticles.insert(article)
				}
			}
			strongSelf.performBlockAndRestoreSelection {
				strongSelf.replaceArticles(with: updatedArticles)
			}
		}
	}
}

// MARK: - NSMenuDelegate

extension TimelineViewController: NSMenuDelegate {

	public func menuNeedsUpdate(_ menu: NSMenu) {
		menu.removeAllItems()
		guard let contextualMenu = contextualMenuForClickedRows() else {
			return
		}
		menu.takeItems(from: contextualMenu)
	}
}

// MARK: - NSUserInterfaceValidations

extension TimelineViewController: NSUserInterfaceValidations {

	func validateUserInterfaceItem(_ item: NSValidatedUserInterfaceItem) -> Bool {
		if item.action == #selector(openArticleInBrowser(_:)) {
			if let item = item as? NSMenuItem, item.keyEquivalentModifierMask.contains(.shift) {
				item.title = Browser.titleForOpenInBrowserInverted
			}

			let currentLink = oneSelectedArticle?.preferredLink
			return currentLink != nil
		}

		if item.action == #selector(copy(_:)) {
			return NSPasteboard.general.canCopyAtLeastOneObject(selectedArticles)
		}

		return true
	}
}

// MARK: - NSTableViewDataSource

extension TimelineViewController: NSTableViewDataSource {
	func numberOfRows(in tableView: NSTableView) -> Int {
		return articles.count
	}

	func tableView(_ tableView: NSTableView, objectValueFor tableColumn: NSTableColumn?, row: Int) -> Any? {
		return articles.articleAtRow(row) ?? nil
	}

	func tableView(_ tableView: NSTableView, pasteboardWriterForRow row: Int) -> NSPasteboardWriting? {
		guard let article = articles.articleAtRow(row) else {
			return nil
		}
		return ArticlePasteboardWriter(article: article)
	}
}

// MARK: - NSTableViewDelegate

extension TimelineViewController: NSTableViewDelegate {
	private static let rowViewIdentifier = NSUserInterfaceItemIdentifier(rawValue: "timelineRow")

	func tableView(_ tableView: NSTableView, rowViewForRow row: Int) -> NSTableRowView? {
		if let rowView: TimelineTableRowView = tableView.makeView(withIdentifier: TimelineViewController.rowViewIdentifier, owner: nil) as? TimelineTableRowView {
			return rowView
		}
		let rowView = TimelineTableRowView()
		rowView.identifier = TimelineViewController.rowViewIdentifier
		return rowView
	}

	private static let timelineCellIdentifier = NSUserInterfaceItemIdentifier(rawValue: "timelineCell")

	func tableView(_ tableView: NSTableView, viewFor tableColumn: NSTableColumn?, row: Int) -> NSView? {

		func configure(_ cell: TimelineTableCellView) {
			cell.cellAppearance = showIcons ? cellAppearanceWithIcon : cellAppearance
			if let article = articles.articleAtRow(row) {
				configureTimelineCell(cell, article: article)
			} else {
				makeTimelineCellEmpty(cell)
			}
		}

		if let cell = tableView.makeView(withIdentifier: TimelineViewController.timelineCellIdentifier, owner: nil) as? TimelineTableCellView {
			configure(cell)
			return cell
		}

		let cell = TimelineTableCellView()
		cell.identifier = TimelineViewController.timelineCellIdentifier
		configure(cell)
		return cell
	}

	func tableViewSelectionDidChange(_ notification: Notification) {
		if selectedArticles.isEmpty {
			selectionDidChange(nil)
			return
		}

		if selectedArticles.count == 1 {
			let article = selectedArticles.first!
			if !article.status.read {
				markArticles(Set([article]), statusKey: .read, flag: true)
			}
		}

		selectionDidChange(selectedArticles)
	}

	private func selectionDidChange(_ selectedArticles: ArticleArray?) {
		guard selectedArticles != previouslySelectedArticles else { return }
		previouslySelectedArticles = selectedArticles
		delegate?.timelineSelectionDidChange(self, selectedArticles: selectedArticles)
		delegate?.timelineInvalidatedRestorationState(self)
	}

	private func configureTimelineCell(_ cell: TimelineTableCellView, article: Article) {
		cell.objectValue = article
		let iconImage = article.iconImage()
		cell.cellData = TimelineCellData(article: article, showFeedName: showFeedNames, feedName: article.feed?.nameForDisplay, byline: article.byline(), iconImage: iconImage, showIcon: showIcons, featuredImage: nil)
	}

	private func iconFor(_ article: Article) -> IconImage? {
		if !showIcons {
			return nil
		}
		return IconImageCache.shared.imageForArticle(article)
	}

	private func avatarForAuthor(_ author: Author) -> IconImage? {
		return AuthorAvatarDownloader.shared.image(for: author)
	}

	private func makeTimelineCellEmpty(_ cell: TimelineTableCellView) {
		cell.objectValue = nil
		cell.cellData = TimelineCellData()
	}

	private func toggleArticleRead(_ article: Article) {
		guard let undoManager = undoManager, let markUnreadCommand = MarkStatusCommand(initialArticles: [article], markingRead: !article.status.read, undoManager: undoManager) else {
			return
		}
		self.runCommand(markUnreadCommand)
	}

	private func toggleArticleStarred(_ article: Article) {
		guard let undoManager = undoManager, let markUnreadCommand = MarkStatusCommand(initialArticles: [article], markingStarred: !article.status.starred, undoManager: undoManager) else {
			return
		}
		self.runCommand(markUnreadCommand)
	}

	func tableView(_ tableView: NSTableView, rowActionsForRow row: Int, edge: NSTableView.RowActionEdge) -> [NSTableViewRowAction] {

		guard let article = articles.articleAtRow(row) else {
			return []
		}

		switch edge {
			case .leading:
				let action = NSTableViewRowAction(style: .regular, title: article.status.read ? "Unread" : "Read") { (_, _) in
					self.toggleArticleRead(article)
					tableView.rowActionsVisible = false
				}
				action.image = article.status.read ? AppAssets.swipeMarkUnreadImage : AppAssets.swipeMarkReadImage
				return [action]

			case .trailing:
				let action = NSTableViewRowAction(style: .regular, title: article.status.starred ? "Unstar" : "Star") { (_, _) in
					self.toggleArticleStarred(article)
					tableView.rowActionsVisible = false
				}
				action.backgroundColor = AppAssets.starColor
				action.image = article.status.starred ? AppAssets.swipeMarkUnstarredImage : AppAssets.swipeMarkStarredImage
				return [action]

			@unknown default:
				os_log(.error, "Unknown table row edge: %ld", edge.rawValue)
		}

		return []
	}
}

// MARK: - Private

private extension TimelineViewController {

	func fetchAndReplacePreservingSelection() {
		if let article = oneSelectedArticle, let account = article.account {
			exceptionArticleFetcher = SingleArticleFetcher(account: account, articleID: article.articleID)
		}
		performBlockAndRestoreSelection {
			fetchAndReplaceArticlesSync()
		}
	}

	@objc func reloadAvailableCells() {
		if let indexesToReload = tableView.indexesOfAvailableRows() {
			reloadCells(for: indexesToReload)
		}
	}

	func updateUnreadCount() {
		var count = 0
		for article in articles {
			if !article.status.read {
				count += 1
			}
		}
		unreadCount = count
	}

	func queueReloadAvailableCells() {
		CoalescingQueue.standard.add(self, #selector(reloadAvailableCells))
	}

	func updateTableViewRowHeight() {
		tableView.rowHeight = currentRowHeight
	}

	func updateShowIcons() {
		if showFeedNames == .feed {
			self.showIcons = true
			return
		}

		if showFeedNames == .none {
			self.showIcons = false
			return
		}

		for article in articles {
			if let authors = article.authors {
				for author in authors {
					if author.avatarURL != nil {
						self.showIcons = true
						return
					}
				}
			}
		}

		self.showIcons = false
	}

	func emptyTheTimeline() {
		if !articles.isEmpty {
			articles = [Article]()
		}
	}

	func sortParametersDidChange() {
		performBlockAndRestoreSelection {
			let unsortedArticles = Set(articles)
			replaceArticles(with: unsortedArticles)
		}
	}

	func selectedArticleIDs() -> [String] {
		return selectedArticles.articleIDs()
	}

	func restoreSelection(_ articleIDs: [String]) {
		selectArticles(articleIDs)
		if tableView.selectedRow != -1 {
			tableView.scrollRowToVisible(tableView.selectedRow)
		}
	}

	func performBlockAndRestoreSelection(_ block: (() -> Void)) {
		let savedSelection = selectedArticleIDs()
		block()
		restoreSelection(savedSelection)
	}

	func rows(for articleID: String) -> [Int]? {
		updateArticleRowMapIfNeeded()
		return articleRowMap[articleID]
	}

	func rows(for article: Article) -> [Int]? {
		return rows(for: article.articleID)
	}

	func updateArticleRowMap() {
		var rowMap = [String: [Int]]()
		var index = 0
		for article in articles {
			if var indexes = rowMap[article.articleID] {
				indexes.append(index)
				rowMap[article.articleID] = indexes
			} else {
				rowMap[article.articleID] = [index]
			}
			index += 1
		}
		articleRowMap = rowMap
	}

	func updateArticleRowMapIfNeeded() {
		if articleRowMap.isEmpty {
			updateArticleRowMap()
		}
	}

	func indexesForArticleIDs(_ articleIDs: Set<String>) -> IndexSet {
		var indexes = IndexSet()

		for articleID in articleIDs {
			guard let rowsIndex = rows(for: articleID) else {
				continue
			}
			for rowIndex in rowsIndex {
				indexes.insert(rowIndex)
			}
		}

		return indexes
	}

	// MARK: - Appearance Change

	private func fontSizeDidChange() {
		cellAppearance = TimelineCellAppearance(showIcon: false, fontSize: fontSize)
		cellAppearanceWithIcon = TimelineCellAppearance(showIcon: true, fontSize: fontSize)
		updateRowHeights()
		performBlockAndRestoreSelection {
			tableView.reloadData()
		}
	}

	// MARK: - Fetching Articles

	func fetchAndReplaceArticlesSync() {
		// To be called when the user has made a change of selection in the sidebar.
		// It blocks the main thread, so that there’s no async delay,
		// so that the entire display refreshes at once.
		// It’s a better user experience this way.
		cancelPendingAsyncFetches()
		guard var representedObjects = representedObjects else {
			emptyTheTimeline()
			return
		}

		if exceptionArticleFetcher != nil {
			representedObjects.append(exceptionArticleFetcher as AnyObject)
			exceptionArticleFetcher = nil
		}

		let fetchedArticles = fetchUnsortedArticlesSync(for: representedObjects)
		replaceArticles(with: fetchedArticles)
	}

	func fetchAndReplaceArticlesAsync() {
		// To be called when we need to do an entire fetch, but an async delay is okay.
		// Example: we have the Today feed selected, and the calendar day just changed.
		cancelPendingAsyncFetches()
		guard var representedObjects = representedObjects else {
			emptyTheTimeline()
			return
		}

		if exceptionArticleFetcher != nil {
			representedObjects.append(exceptionArticleFetcher as AnyObject)
			exceptionArticleFetcher = nil
		}

		fetchUnsortedArticlesAsync(for: representedObjects) { [weak self] (articles) in
			self?.replaceArticles(with: articles)
		}
	}

	func cancelPendingAsyncFetches() {
		fetchSerialNumber += 1
		fetchRequestQueue.cancelAllRequests()
	}

	func replaceArticles(with unsortedArticles: Set<Article>) {
		articles = Array(unsortedArticles).sortedByDate(sortDirection, groupByFeed: groupByFeed)
	}

	func fetchUnsortedArticlesSync(for representedObjects: [Any]) -> Set<Article> {
		cancelPendingAsyncFetches()
		let fetchers = representedObjects.compactMap { $0 as? ArticleFetcher }
		if fetchers.isEmpty {
			return Set<Article>()
		}

		var fetchedArticles = Set<Article>()
		for fetchers in fetchers {
			if (fetchers as? SidebarItem)?.readFiltered(readFilterEnabledTable: readFilterEnabledTable) ?? true {
				if let articles = try? fetchers.fetchUnreadArticles() {
					fetchedArticles.formUnion(articles)
				}
			} else {
				if let articles = try? fetchers.fetchArticles() {
					fetchedArticles.formUnion(articles)
				}
			}
		}
		return fetchedArticles
	}

	func fetchUnsortedArticlesAsync(for representedObjects: [Any], completion: @escaping ArticleSetBlock) {
		// The callback will *not* be called if the fetch is no longer relevant — that is,
		// if it’s been superseded by a newer fetch, or the timeline was emptied, etc., it won’t get called.
		precondition(Thread.isMainThread)
		cancelPendingAsyncFetches()
		let fetchers = representedObjects.compactMap { $0 as? ArticleFetcher }
		let fetchOperation = FetchRequestOperation(id: fetchSerialNumber, readFilterEnabledTable: readFilterEnabledTable, fetchers: fetchers) { [weak self] (articles, operation) in
			precondition(Thread.isMainThread)
			guard !operation.isCanceled, let strongSelf = self, operation.id == strongSelf.fetchSerialNumber else {
				return
			}
			completion(articles)
		}
		fetchRequestQueue.add(fetchOperation)
	}

	func selectArticles(_ articleIDs: [String]) {
		let indexesToSelect = indexesForArticleIDs(Set(articleIDs))
		if indexesToSelect.isEmpty {
			tableView.deselectAll(self)
			return
		}
		tableView.selectRowIndexes(indexesToSelect, byExtendingSelection: false)
	}

	func queueFetchAndMergeArticles() {
		TimelineViewController.fetchAndMergeArticlesQueue.add(self, #selector(fetchAndMergeArticles))
	}

	func representedObjectArraysAreEqual(_ objects1: [AnyObject]?, _ objects2: [AnyObject]?) -> Bool {
		if objects1 == nil && objects2 == nil {
			return true
		}
		guard let objects1 = objects1, let objects2 = objects2 else {
			return false
		}
		if objects1.count != objects2.count {
			return false
		}

		var ix = 0
		for oneObject in objects1 {
			if oneObject !== objects2[ix] {
				return false
			}
			ix += 1
		}
		return true
	}

	func representedObjectsContainsAnyPseudoFeed() -> Bool {
		return representedObjects?.contains(where: { $0 is PseudoFeed}) ?? false
	}

	func representedObjectsContainsTodayFeed() -> Bool {
		return representedObjects?.contains(where: { $0 === SmartFeedsController.shared.todayFeed }) ?? false
	}

	func representedObjectsContainAnyFolder() -> Bool {
		return representedObjects?.contains(where: { $0 is Folder }) ?? false
	}

	func representedObjectsContainsAnyFeed(_ feeds: Set<Feed>) -> Bool {
		// Return true if there’s a match or if a folder contains (recursively) one of feeds

		guard let representedObjects = representedObjects else {
			return false
		}
		for representedObject in representedObjects {
			if let feed = representedObject as? Feed {
				for oneFeed in feeds {
					if feed.feedID == oneFeed.feedID || feed.url == oneFeed.url {
						return true
					}
				}
			} else if let folder = representedObject as? Folder {
				for oneFeed in feeds {
					if folder.hasFeed(with: oneFeed.feedID) || folder.hasFeed(withURL: oneFeed.url) {
						return true
					}
				}
			}
		}
		return false
	}
}