//
//  Account.swift
//  NetNewsWire
//
//  Created by Brent Simmons on 7/1/17.
//  Copyright © 2017 Ranchero Software, LLC. All rights reserved.
//

#if os(iOS)
import UIKit
#endif

import Foundation
import RSCore
import Articles
import RSParser
import RSDatabase
import ArticlesDatabase
import RSWeb
import os.log

// Main thread only.

public extension Notification.Name {
	static let UserDidAddAccount = Notification.Name("UserDidAddAccount")
	static let UserDidDeleteAccount = Notification.Name("UserDidDeleteAccount")
	static let AccountRefreshDidBegin = Notification.Name(rawValue: "AccountRefreshDidBegin")
	static let AccountRefreshDidFinish = Notification.Name(rawValue: "AccountRefreshDidFinish")
	static let AccountRefreshProgressDidChange = Notification.Name(rawValue: "AccountRefreshProgressDidChange")
	static let DownloadArticlesDidUpdateUnreadCounts = Notification.Name(rawValue: "DownloadArticlesDidUpdateUnreadCounts")
	static let AccountDidDownloadArticles = Notification.Name(rawValue: "AccountDidDownloadArticles")
	static let AccountStateDidChange = Notification.Name(rawValue: "AccountStateDidChange")
	static let StatusesDidChange = Notification.Name(rawValue: "StatusesDidChange")
	static let WebFeedMetadataDidChange = Notification.Name(rawValue: "WebFeedMetadataDidChange")
}

public enum AccountType: Int {
	// Raw values should not change since they’re stored on disk.
	case onMyMac = 1
	case feedly = 16
	case feedbin = 17
	case feedWrangler = 18
	case newsBlur = 19
	case freshRSS = 20
	// TODO: more
}

public enum FetchType {
	case starred
	case unread
	case today
	case folder(Folder, Bool)
	case webFeed(WebFeed)
	case articleIDs(Set<String>)
	case search(String)
	case searchWithArticleIDs(String, Set<String>)
}

public final class Account: DisplayNameProvider, UnreadCountProvider, Container, Hashable {

    public struct UserInfoKey {
		public static let account = "account" // UserDidAddAccount, UserDidDeleteAccount
		public static let newArticles = "newArticles" // AccountDidDownloadArticles
		public static let updatedArticles = "updatedArticles" // AccountDidDownloadArticles
		public static let statuses = "statuses" // StatusesDidChange
		public static let articles = "articles" // StatusesDidChange
		public static let articleIDs = "articleIDs" // StatusesDidChange
		public static let webFeeds = "webFeeds" // AccountDidDownloadArticles, StatusesDidChange
	}

	public static let defaultLocalAccountName: String = {
		let defaultName: String
		#if os(macOS)
		defaultName = NSLocalizedString("On My Mac", comment: "Account name")
		#else
		if UIDevice.current.userInterfaceIdiom == .pad {
			defaultName = NSLocalizedString("On My iPad", comment: "Account name")
		} else {
			defaultName = NSLocalizedString("On My iPhone", comment: "Account name")
		}
		#endif
		
		return defaultName
	}()
	
	var log = OSLog(subsystem: Bundle.main.bundleIdentifier!, category: "account")

	public var isDeleted = false
	
	public var containerID: ContainerIdentifier? {
		return ContainerIdentifier.account(accountID)
	}
	
	public var account: Account? {
		return self
	}
	public let accountID: String
	public let type: AccountType
	public var nameForDisplay: String {
		guard let name = name, !name.isEmpty else {
			return defaultName
		}
		return name
	}

	public var name: String? {
		get {
			return metadata.name
		}
		set {
			let currentNameForDisplay = nameForDisplay
			if newValue != metadata.name {
				metadata.name = newValue
				if currentNameForDisplay != nameForDisplay {
					postDisplayNameDidChangeNotification()
				}
			}
		}
	}
	public let defaultName: String
	
	public var isActive: Bool {
		get {
			return metadata.isActive
		}
		set {
			if newValue != metadata.isActive {
				metadata.isActive = newValue
				var userInfo = [AnyHashable: Any]()
				userInfo[UserInfoKey.account] = self
				NotificationCenter.default.post(name: .AccountStateDidChange, object: self, userInfo: userInfo)
			}
		}
	}

	public var topLevelWebFeeds = Set<WebFeed>()
	public var folders: Set<Folder>? = Set<Folder>()
	
	public var sortedFolders: [Folder]? {
		if let folders = folders {
			return Array(folders).sorted(by: { $0.nameForDisplay < $1.nameForDisplay })
		}
		return nil
	}
	
	private var webFeedDictionaryNeedsUpdate = true
	private var _idToWebFeedDictionary = [String: WebFeed]()
	var idToWebFeedDictionary: [String: WebFeed] {
		if webFeedDictionaryNeedsUpdate {
			rebuildWebFeedDictionaries()
		}
		return _idToWebFeedDictionary
	}

	var username: String? {
		get {
			return metadata.username
		}
		set {
			if newValue != metadata.username {
				metadata.username = newValue
			}
		}
	}
	
	public var endpointURL: URL? {
		get {
			return metadata.endpointURL
		}
		set {
			if newValue != metadata.endpointURL {
				metadata.endpointURL = newValue
			}
		}
	}
	
	private var fetchingAllUnreadCounts = false
	var isUnreadCountsInitialized = false

	let dataFolder: String
	let database: ArticlesDatabase
	var delegate: AccountDelegate
	static let saveQueue = CoalescingQueue(name: "Account Save Queue", interval: 1.0)

	private var unreadCounts = [String: Int]() // [feedID: Int]

	private var _flattenedWebFeeds = Set<WebFeed>()
	private var flattenedWebFeedsNeedUpdate = true

	private lazy var opmlFile = OPMLFile(filename: (dataFolder as NSString).appendingPathComponent("Subscriptions.opml"), account: self)
	private lazy var metadataFile = AccountMetadataFile(filename: (dataFolder as NSString).appendingPathComponent("Settings.plist"), account: self)
	var metadata = AccountMetadata() {
		didSet {
			delegate.accountMetadata = metadata
		}
	}

	private lazy var webFeedMetadataFile = WebFeedMetadataFile(filename: (dataFolder as NSString).appendingPathComponent("FeedMetadata.plist"), account: self)
	typealias WebFeedMetadataDictionary = [String: WebFeedMetadata]
	var webFeedMetadata = WebFeedMetadataDictionary()

	var startingUp = true

    public var unreadCount = 0 {
        didSet {
            if unreadCount != oldValue {
                postUnreadCountDidChangeNotification()
            }
        }
    }
    
	public var behaviors: AccountBehaviors {
		return delegate.behaviors
	}
	
	var refreshInProgress = false {
		didSet {
			if refreshInProgress != oldValue {
				if refreshInProgress {
					NotificationCenter.default.post(name: .AccountRefreshDidBegin, object: self)
				}
				else {
					NotificationCenter.default.post(name: .AccountRefreshDidFinish, object: self)
					opmlFile.markAsDirty()
				}
			}
		}
	}

	var refreshProgress: DownloadProgress {
		return delegate.refreshProgress
	}
	
	init?(dataFolder: String, type: AccountType, accountID: String, transport: Transport? = nil) {
		switch type {
		case .onMyMac:
			self.delegate = LocalAccountDelegate()
		case .feedbin:
			self.delegate = FeedbinAccountDelegate(dataFolder: dataFolder, transport: transport)
		case .freshRSS:
			self.delegate = ReaderAPIAccountDelegate(dataFolder: dataFolder, transport: transport)
		case .feedly:
			self.delegate = FeedlyAccountDelegate(dataFolder: dataFolder, transport: transport, api: FeedlyAccountDelegate.environment)
		case .feedWrangler:
			self.delegate = FeedWranglerAccountDelegate(dataFolder: dataFolder, transport: transport)
		default:
			return nil
		}

		self.delegate.accountMetadata = metadata
		
		self.accountID = accountID
		self.type = type
		self.dataFolder = dataFolder

		let databaseFilePath = (dataFolder as NSString).appendingPathComponent("DB.sqlite3")
		self.database = ArticlesDatabase(databaseFilePath: databaseFilePath, accountID: accountID)

		switch type {
		case .onMyMac:
			defaultName = Account.defaultLocalAccountName
		case .feedly:
			defaultName = "Feedly"
		case .feedbin:
			defaultName = "Feedbin"
		case .feedWrangler:
			defaultName = "FeedWrangler"
		case .newsBlur:
			defaultName = "NewsBlur"
		case .freshRSS:
			defaultName = "FreshRSS"
		}

		NotificationCenter.default.addObserver(self, selector: #selector(downloadProgressDidChange(_:)), name: .DownloadProgressDidChange, object: nil)
		NotificationCenter.default.addObserver(self, selector: #selector(unreadCountDidChange(_:)), name: .UnreadCountDidChange, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(batchUpdateDidPerform(_:)), name: .BatchUpdateDidPerform, object: nil)
		NotificationCenter.default.addObserver(self, selector: #selector(displayNameDidChange(_:)), name: .DisplayNameDidChange, object: nil)
		NotificationCenter.default.addObserver(self, selector: #selector(childrenDidChange(_:)), name: .ChildrenDidChange, object: nil)

		metadataFile.load()
		webFeedMetadataFile.load()
		opmlFile.load()

		DispatchQueue.main.async {
			self.database.cleanupDatabaseAtStartup(subscribedToWebFeedIDs: self.flattenedWebFeeds().webFeedIDs())
			self.fetchAllUnreadCounts()
		}

		self.delegate.accountDidInitialize(self)
		startingUp = false
	}
	
	// MARK: - API
	
	public func storeCredentials(_ credentials: Credentials) throws {
		username = credentials.username
		guard let server = delegate.server else {
			assertionFailure()
			return
		}
		try CredentialsManager.storeCredentials(credentials, server: server)
		delegate.credentials = credentials
	}
	
	public func retrieveCredentials(type: CredentialsType) throws -> Credentials? {
		guard let username = self.username, let server = delegate.server else {
			return nil
		}
		return try CredentialsManager.retrieveCredentials(type: type, server: server, username: username)
	}
	
	public func removeCredentials(type: CredentialsType) throws {
		guard let username = self.username, let server = delegate.server else {
			return
		}
		try CredentialsManager.removeCredentials(type: type, server: server, username: username)
	}
	
	public static func validateCredentials(transport: Transport = URLSession.webserviceTransport(), type: AccountType, credentials: Credentials, endpoint: URL? = nil, completion: @escaping (Result<Credentials?, Error>) -> Void) {
		switch type {
		case .feedbin:
			FeedbinAccountDelegate.validateCredentials(transport: transport, credentials: credentials, completion: completion)
		case .freshRSS:
			ReaderAPIAccountDelegate.validateCredentials(transport: transport, credentials: credentials, endpoint: endpoint, completion: completion)
		case .feedWrangler:
			FeedWranglerAccountDelegate.validateCredentials(transport: transport, credentials: credentials, completion: completion)
		default:
			break
		}
	}
	
	internal static func oauthAuthorizationClient(for type: AccountType) -> OAuthAuthorizationClient {
		switch type {
		case .feedly:
			return FeedlyAccountDelegate.environment.oauthAuthorizationClient
		default:
			fatalError("\(type) is not a client for OAuth authorization code granting.")
		}
	}
		
	public static func oauthAuthorizationCodeGrantRequest(for type: AccountType) -> URLRequest {
		let grantingType: OAuthAuthorizationGranting.Type
		switch type {
		case .feedly:
			grantingType = FeedlyAccountDelegate.self
		default:
			fatalError("\(type) does not support OAuth authorization code granting.")
		}
		
		return grantingType.oauthAuthorizationCodeGrantRequest()
	}
	
	public static func requestOAuthAccessToken(with response: OAuthAuthorizationResponse,
											   client: OAuthAuthorizationClient,
											   accountType: AccountType,
											   transport: Transport = URLSession.webserviceTransport(),
											   completion: @escaping (Result<OAuthAuthorizationGrant, Error>) -> ()) {
		let grantingType: OAuthAuthorizationGranting.Type
		
		switch accountType {
		case .feedly:
			grantingType = FeedlyAccountDelegate.self
		default:
			fatalError("\(accountType) does not support OAuth authorization code granting.")
		}
		
		grantingType.requestOAuthAccessToken(with: response, transport: transport, completion: completion)
	}

	public func refreshAll(completion: @escaping (Result<Void, Error>) -> Void) {
		self.delegate.refreshAll(for: self, completion: completion)
	}

	public func syncArticleStatus(completion: ((Result<Void, Error>) -> Void)? = nil) {
		delegate.sendArticleStatus(for: self) { [unowned self] result in
			switch result {
			case .success:
				self.delegate.refreshArticleStatus(for: self) { result in
					switch result {
					case .success:
						completion?(.success(()))
					case .failure(let error):
						completion?(.failure(error))
					}
				}
			case .failure(let error):
				completion?(.failure(error))
			}
		}
	}
	
	public func importOPML(_ opmlFile: URL, completion: @escaping (Result<Void, Error>) -> Void) {
		guard !delegate.isOPMLImportInProgress else {
			completion(.failure(AccountError.opmlImportInProgress))
			return
		}
		
		delegate.importOPML(for: self, opmlFile: opmlFile) { [weak self] result in
			switch result {
			case .success:
				guard let self = self else { return }
				// Reset the last fetch date to get the article history for the added feeds.
				self.metadata.lastArticleFetchStartTime = nil
				self.delegate.refreshAll(for: self, completion: completion)
			case .failure(let error):
				completion(.failure(error))
			}
		}
		
	}
	
	public func suspendNetwork() {
		delegate.suspendNetwork()
	}
	
	public func suspendDatabase() {
		database.suspend()
		save()
		metadataFile.suspend()
		webFeedMetadataFile.suspend()
		opmlFile.suspend()
	}

	/// Re-open the SQLite database and allow database calls.
	/// Call this *before* calling resume.
	public func resumeDatabaseAndDelegate() {
		database.resume()
		delegate.resume()
	}

	/// Reload OPML, etc.
	public func resume() {
		metadataFile.resume()
		webFeedMetadataFile.resume()
		opmlFile.resume()
		metadataFile.load()
		webFeedMetadataFile.load()
		opmlFile.load()
	}

	public func save() {
		metadataFile.save()
		webFeedMetadataFile.save()
		opmlFile.save()
	}
	
	public func prepareForDeletion() {
		delegate.accountWillBeDeleted(self)
	}
	
	func loadOPMLItems(_ items: [RSOPMLItem], parentFolder: Folder?) {
		var feedsToAdd = Set<WebFeed>()

		items.forEach { (item) in

			if let feedSpecifier = item.feedSpecifier {
				let feed = newWebFeed(with: feedSpecifier)
				feedsToAdd.insert(feed)
				return
			}

			guard let folderName = item.titleFromAttributes else {
				// Folder doesn’t have a name, so it won’t be created, and its items will go one level up.
				if let itemChildren = item.children {
					loadOPMLItems(itemChildren, parentFolder: parentFolder)
				}
				return
			}

			if let folder = ensureFolder(with: folderName) {
				folder.externalID = item.attributes?["nnw_externalID"] as? String
				if let itemChildren = item.children {
					loadOPMLItems(itemChildren, parentFolder: folder)
				}
			}
		}

		if let parentFolder = parentFolder {
			for feed in feedsToAdd {
				parentFolder.addWebFeed(feed)
			}
		} else {
			for feed in feedsToAdd {
				addWebFeed(feed)
			}
		}
		
	}
	
	public func resetWebFeedMetadataAndUnreadCounts() {
		for feed in flattenedWebFeeds() {
			feed.metadata = webFeedMetadata(feedURL: feed.url, webFeedID: feed.webFeedID)
		}
		fetchAllUnreadCounts()
		NotificationCenter.default.post(name: .WebFeedMetadataDidChange, object: self, userInfo: nil)
	}
	
	public func markArticles(_ articles: Set<Article>, statusKey: ArticleStatus.Key, flag: Bool) -> Set<Article>? {
		return delegate.markArticles(for: self, articles: articles, statusKey: statusKey, flag: flag)
	}

	@discardableResult
	func ensureFolder(with name: String) -> Folder? {
		// TODO: support subfolders, maybe, some day

		if name.isEmpty {
			return nil
		}

		if let folder = existingFolder(with: name) {
			return folder
		}

		let folder = Folder(account: self, name: name)
		folders!.insert(folder)
		structureDidChange()

		postChildrenDidChangeNotification()
		return folder
	}

	public func ensureFolder(withFolderNames folderNames: [String]) -> Folder? {
		// TODO: support subfolders, maybe, some day.
		// Since we don’t, just take the last name and make sure there’s a Folder.

		guard let folderName = folderNames.last else {
			return nil
		}
		return ensureFolder(with: folderName)
	}

	public func findFolder(withDisplayName displayName: String) -> Folder? {
		return folders?.first(where: { $0.nameForDisplay == displayName })
	}
	
	func newWebFeed(with opmlFeedSpecifier: RSOPMLFeedSpecifier) -> WebFeed {
		let feedURL = opmlFeedSpecifier.feedURL
		let metadata = webFeedMetadata(feedURL: feedURL, webFeedID: feedURL)
		let feed = WebFeed(account: self, url: opmlFeedSpecifier.feedURL, metadata: metadata)
		if let feedTitle = opmlFeedSpecifier.title {
			if feed.name == nil {
				feed.name = feedTitle
			}
		}
		return feed
	}

	public func addWebFeed(_ feed: WebFeed, to container: Container, completion: @escaping (Result<Void, Error>) -> Void) {
		delegate.addWebFeed(for: self, with: feed, to: container, completion: completion)
	}

	public func createWebFeed(url: String, name: String?, container: Container, completion: @escaping (Result<WebFeed, Error>) -> Void) {
		delegate.createWebFeed(for: self, url: url, name: name, container: container, completion: completion)
	}
	
	func createWebFeed(with name: String?, url: String, webFeedID: String, homePageURL: String?) -> WebFeed {
		let metadata = webFeedMetadata(feedURL: url, webFeedID: webFeedID)
		let feed = WebFeed(account: self, url: url, metadata: metadata)
		feed.name = name
		feed.homePageURL = homePageURL
		
		return feed
	}
	
	public func removeWebFeed(_ feed: WebFeed, from container: Container, completion: @escaping (Result<Void, Error>) -> Void) {
		delegate.removeWebFeed(for: self, with: feed, from: container, completion: completion)
	}
	
	public func moveWebFeed(_ feed: WebFeed, from: Container, to: Container, completion: @escaping (Result<Void, Error>) -> Void) {
		delegate.moveWebFeed(for: self, with: feed, from: from, to: to, completion: completion)
	}
	
	public func renameWebFeed(_ feed: WebFeed, to name: String, completion: @escaping (Result<Void, Error>) -> Void) {
		delegate.renameWebFeed(for: self, with: feed, to: name, completion: completion)
	}
	
	public func restoreWebFeed(_ feed: WebFeed, container: Container, completion: @escaping (Result<Void, Error>) -> Void) {
		delegate.restoreWebFeed(for: self, feed: feed, container: container, completion: completion)
	}
	
	public func addFolder(_ name: String, completion: @escaping (Result<Folder, Error>) -> Void) {
		delegate.addFolder(for: self, name: name, completion: completion)
	}
	
	public func removeFolder(_ folder: Folder, completion: @escaping (Result<Void, Error>) -> Void) {
		delegate.removeFolder(for: self, with: folder, completion: completion)
	}
	
	public func renameFolder(_ folder: Folder, to name: String, completion: @escaping (Result<Void, Error>) -> Void) {
		delegate.renameFolder(for: self, with: folder, to: name, completion: completion)
	}

	public func restoreFolder(_ folder: Folder, completion: @escaping (Result<Void, Error>) -> Void) {
		delegate.restoreFolder(for: self, folder: folder, completion: completion)
	}
	
	func clearWebFeedMetadata(_ feed: WebFeed) {
		webFeedMetadata[feed.url] = nil
	}
	
	func addFolder(_ folder: Folder) {
		folders!.insert(folder)
		postChildrenDidChangeNotification()
		structureDidChange()
	}
	
	public func updateUnreadCounts(for webFeeds: Set<WebFeed>, completion: VoidCompletionBlock? = nil) {
		if webFeeds.isEmpty {
			completion?()
			return
		}
		
		database.fetchUnreadCounts(for: webFeeds.webFeedIDs()) { unreadCountDictionaryResult in
			if let unreadCountDictionary = try? unreadCountDictionaryResult.get() {
				for webFeed in webFeeds {
					if let unreadCount = unreadCountDictionary[webFeed.webFeedID] {
						webFeed.unreadCount = unreadCount
					}
				}
			}

			completion?()
		}
	}

	public func fetchArticles(_ fetchType: FetchType) throws -> Set<Article> {
		switch fetchType {
		case .starred:
			return try fetchStarredArticles()
		case .unread:
			return try fetchUnreadArticles()
		case .today:
			return try fetchTodayArticles()
		case .folder(let folder, let readFilter):
			if readFilter {
				return try fetchUnreadArticles(folder: folder)
			} else {
				return try fetchArticles(folder: folder)
			}
		case .webFeed(let webFeed):
			return try fetchArticles(webFeed: webFeed)
		case .articleIDs(let articleIDs):
			return try fetchArticles(articleIDs: articleIDs)
		case .search(let searchString):
			return try fetchArticlesMatching(searchString)
		case .searchWithArticleIDs(let searchString, let articleIDs):
			return try fetchArticlesMatchingWithArticleIDs(searchString, articleIDs)
		}
	}

	public func fetchArticlesAsync(_ fetchType: FetchType, _ completion: @escaping ArticleSetResultBlock) {
		switch fetchType {
		case .starred:
			fetchStarredArticlesAsync(completion)
		case .unread:
			fetchUnreadArticlesAsync(completion)
		case .today:
			fetchTodayArticlesAsync(completion)
		case .folder(let folder, let readFilter):
			if readFilter {
				return fetchUnreadArticlesAsync(folder: folder, completion)
			} else {
				return fetchArticlesAsync(folder: folder, completion)
			}
		case .webFeed(let webFeed):
			fetchArticlesAsync(webFeed: webFeed, completion)
		case .articleIDs(let articleIDs):
			fetchArticlesAsync(articleIDs: articleIDs, completion)
		case .search(let searchString):
			fetchArticlesMatchingAsync(searchString, completion)
		case .searchWithArticleIDs(let searchString, let articleIDs):
			return fetchArticlesMatchingWithArticleIDsAsync(searchString, articleIDs, completion)
		}
	}

	public func fetchUnreadCountForToday(_ completion: @escaping SingleUnreadCountCompletionBlock) {
		database.fetchUnreadCountForToday(for: flattenedWebFeeds().webFeedIDs(), completion: completion)
	}

	public func fetchUnreadCountForStarredArticles(_ completion: @escaping SingleUnreadCountCompletionBlock) {
		database.fetchStarredAndUnreadCount(for: flattenedWebFeeds().webFeedIDs(), completion: completion)
	}

	public func fetchUnreadArticleIDs(_ completion: @escaping ArticleIDsCompletionBlock) {
		database.fetchUnreadArticleIDsAsync(webFeedIDs: flattenedWebFeeds().webFeedIDs(), completion: completion)
	}

	public func fetchStarredArticleIDs(_ completion: @escaping ArticleIDsCompletionBlock) {
		database.fetchStarredArticleIDsAsync(webFeedIDs: flattenedWebFeeds().webFeedIDs(), completion: completion)
	}

	/// Fetch articleIDs for articles that we should have, but don’t. These articles are not userDeleted, and they are either (starred) or (unread and newer than the article cutoff date).
	public func fetchArticleIDsForStatusesWithoutArticlesNewerThanCutoffDate(_ completion: @escaping ArticleIDsCompletionBlock) {
		database.fetchArticleIDsForStatusesWithoutArticlesNewerThanCutoffDate(completion)
	}
	
	public func unreadCount(for webFeed: WebFeed) -> Int {
		return unreadCounts[webFeed.webFeedID] ?? 0
	}

	public func setUnreadCount(_ unreadCount: Int, for webFeed: WebFeed) {
		unreadCounts[webFeed.webFeedID] = unreadCount
	}

	public func structureDidChange() {
		// Feeds were added or deleted. Or folders added or deleted.
		// Or feeds inside folders were added or deleted.
		if !startingUp {
			opmlFile.markAsDirty()
		}
		flattenedWebFeedsNeedUpdate = true
		webFeedDictionaryNeedsUpdate = true
	}

	func update(_ webFeed: WebFeed, with parsedFeed: ParsedFeed, _ completion: @escaping DatabaseCompletionBlock) {
		// Used only by an On My Mac account.
		webFeed.takeSettings(from: parsedFeed)
		let webFeedIDsAndItems = [webFeed.webFeedID: parsedFeed.items]
		update(webFeedIDsAndItems: webFeedIDsAndItems, defaultRead: false, completion: completion)
	}

	func update(webFeedIDsAndItems: [String: Set<ParsedItem>], defaultRead: Bool, completion: @escaping DatabaseCompletionBlock) {
		precondition(Thread.isMainThread)
		guard !webFeedIDsAndItems.isEmpty else {
			completion(nil)
			return
		}
		
		let group = DispatchGroup()
		var possibleError: DatabaseError? = nil
		var newArticles = Set<Article>()
		var updatedArticles = Set<Article>()
		
		for (webFeedID, items) in webFeedIDsAndItems {
			
			group.enter()
			database.update(webFeedID: webFeedID, items: items, defaultRead: defaultRead) { updateArticlesResult in

				switch updateArticlesResult {
				case .success(let newAndUpdatedArticles):
					if let articles = newAndUpdatedArticles.newArticles {
						newArticles.formUnion(articles)
					}
					if let articles = newAndUpdatedArticles.updatedArticles {
						updatedArticles.formUnion(articles)
					}
				case .failure(let databaseError):
					possibleError = databaseError
				}
				
				group.leave()
			}
			
		}
		
		group.notify(queue: DispatchQueue.main) {
			var userInfo = [String: Any]()
			var webFeeds = Set(newArticles.compactMap { $0.webFeed })
			webFeeds.formUnion(Set(updatedArticles.compactMap { $0.webFeed }))
			
			if !newArticles.isEmpty {
				self.updateUnreadCounts(for: webFeeds) {
					NotificationCenter.default.post(name: .DownloadArticlesDidUpdateUnreadCounts, object: self, userInfo: nil)
				}
				userInfo[UserInfoKey.newArticles] = newArticles
			}
			
			if !updatedArticles.isEmpty {
				userInfo[UserInfoKey.updatedArticles] = updatedArticles
			}
			
			userInfo[UserInfoKey.webFeeds] = webFeeds
			NotificationCenter.default.post(name: .AccountDidDownloadArticles, object: self, userInfo: userInfo)
			
			completion(possibleError)
		}
		
	}

	@discardableResult
	func update(_ articles: Set<Article>, statusKey: ArticleStatus.Key, flag: Bool) throws -> Set<Article>? {
		// Returns set of Articles whose statuses did change.
		guard !articles.isEmpty, let updatedStatuses = try database.mark(articles, statusKey: statusKey, flag: flag) else {
			return nil
		}
		
		let updatedArticleIDs = updatedStatuses.articleIDs()
		let updatedArticles = Set(articles.filter{ updatedArticleIDs.contains($0.articleID) })
		
		noteStatusesForArticlesDidChange(updatedArticles)
		return updatedArticles
	}

	/// Mark articleIDs statuses based on statusKey and flag.
	/// Will create statuses in the database and in memory as needed. Sends a .StatusesDidChange notification.
	func mark(articleIDs: Set<String>, statusKey: ArticleStatus.Key, flag: Bool, completion: DatabaseCompletionBlock? = nil) {
		guard !articleIDs.isEmpty else {
			completion?(nil)
			return
		}
		database.mark(articleIDs: articleIDs, statusKey: statusKey, flag: flag) { error in
			if let error = error {
				completion?(error)
				return
			}
			self.noteStatusesForArticleIDsDidChange(articleIDs)
			completion?(nil)
		}
	}

	/// Mark articleIDs as read. Will create statuses in the database and in memory as needed. Sends a .StatusesDidChange notification.
	func markAsRead(_ articleIDs: Set<String>, completion: DatabaseCompletionBlock? = nil) {
		mark(articleIDs: articleIDs, statusKey: .read, flag: true, completion: completion)
	}

	/// Mark articleIDs as unread. Will create statuses in the database and in memory as needed. Sends a .StatusesDidChange notification.
	func markAsUnread(_ articleIDs: Set<String>, completion: DatabaseCompletionBlock? = nil) {
		mark(articleIDs: articleIDs, statusKey: .read, flag: false, completion: completion)
	}

	/// Mark articleIDs as starred. Will create statuses in the database and in memory as needed. Sends a .StatusesDidChange notification.
	func markAsStarred(_ articleIDs: Set<String>, completion: DatabaseCompletionBlock? = nil) {
		mark(articleIDs: articleIDs, statusKey: .starred, flag: true, completion: completion)
	}

	/// Mark articleIDs as unstarred. Will create statuses in the database and in memory as needed. Sends a .StatusesDidChange notification.
	func markAsUnstarred(_ articleIDs: Set<String>, completion: DatabaseCompletionBlock? = nil) {
		mark(articleIDs: articleIDs, statusKey: .starred, flag: false, completion: completion)
	}

	/// Empty caches that can reasonably be emptied. Call when the app goes in the background, for instance.
	func emptyCaches() {
		database.emptyCaches()
	}

	// MARK: - Container

	public func flattenedWebFeeds() -> Set<WebFeed> {
		assert(Thread.isMainThread)
		if flattenedWebFeedsNeedUpdate {
			updateFlattenedWebFeeds()
		}
		return _flattenedWebFeeds
	}

	public func removeWebFeed(_ webFeed: WebFeed) {
		topLevelWebFeeds.remove(webFeed)
		structureDidChange()
		postChildrenDidChangeNotification()
	}
	
	public func removeFeeds(_ webFeeds: Set<WebFeed>) {
		guard !webFeeds.isEmpty else {
			return
		}
		topLevelWebFeeds.subtract(webFeeds)
		structureDidChange()
		postChildrenDidChangeNotification()
	}
	
	public func addWebFeed(_ webFeed: WebFeed) {
		topLevelWebFeeds.insert(webFeed)
		structureDidChange()
		postChildrenDidChangeNotification()
	}

	func addFeedIfNotInAnyFolder(_ webFeed: WebFeed) {
		if !flattenedWebFeeds().contains(webFeed) {
			addWebFeed(webFeed)
		}
	}
	
	func removeFolder(_ folder: Folder) {
		folders?.remove(folder)
		structureDidChange()
		postChildrenDidChangeNotification()
	}
	
	// MARK: - Debug

	public func debugDropConditionalGetInfo() {
		#if DEBUG
			flattenedWebFeeds().forEach{ $0.debugDropConditionalGetInfo() }
		#endif
	}

	public func debugRunSearch() {
		#if DEBUG
			let t1 = Date()
			let articles = try! fetchArticlesMatching("Brent NetNewsWire")
			let t2 = Date()
			print(t2.timeIntervalSince(t1))
			print(articles.count)
		#endif
	}

	// MARK: - Notifications

	@objc func downloadProgressDidChange(_ note: Notification) {
		guard let noteObject = note.object as? DownloadProgress, noteObject === refreshProgress else {
			return
		}

		refreshInProgress = refreshProgress.numberRemaining > 0
		NotificationCenter.default.post(name: .AccountRefreshProgressDidChange, object: self)
	}
	
	@objc func unreadCountDidChange(_ note: Notification) {
		if let feed = note.object as? WebFeed, feed.account === self {
			updateUnreadCount()
		}
	}
    
    @objc func batchUpdateDidPerform(_ note: Notification) {
		flattenedWebFeedsNeedUpdate = true
		rebuildWebFeedDictionaries()
        updateUnreadCount()
    }

	@objc func childrenDidChange(_ note: Notification) {
		guard let object = note.object else {
			return
		}
		if let account = object as? Account, account === self {
			structureDidChange()
			updateUnreadCount()
		}
		if let folder = object as? Folder, folder.account === self {
			structureDidChange()
		}
	}

	@objc func displayNameDidChange(_ note: Notification) {
		if let folder = note.object as? Folder, folder.account === self {
			structureDidChange()
		}
	}

	// MARK: - Hashable

	public func hash(into hasher: inout Hasher) {
		hasher.combine(accountID)
	}

	// MARK: - Equatable

	public class func ==(lhs: Account, rhs: Account) -> Bool {
		return lhs === rhs
	}
}

// MARK: - AccountMetadataDelegate

extension Account: AccountMetadataDelegate {
	func valueDidChange(_ accountMetadata: AccountMetadata, key: AccountMetadata.CodingKeys) {
		metadataFile.markAsDirty()
	}
}

// MARK: - FeedMetadataDelegate

extension Account: WebFeedMetadataDelegate {

	func valueDidChange(_ feedMetadata: WebFeedMetadata, key: WebFeedMetadata.CodingKeys) {
		webFeedMetadataFile.markAsDirty()
		guard let feed = existingWebFeed(withWebFeedID: feedMetadata.webFeedID) else {
			return
		}
		feed.postFeedSettingDidChangeNotification(key)
	}
}

// MARK: - Fetching (Private)

private extension Account {

	func fetchStarredArticles() throws -> Set<Article> {
		return try database.fetchStarredArticles(flattenedWebFeeds().webFeedIDs())
	}

	func fetchStarredArticlesAsync(_ completion: @escaping ArticleSetResultBlock) {
		database.fetchedStarredArticlesAsync(flattenedWebFeeds().webFeedIDs(), completion)
	}

	func fetchUnreadArticles() throws -> Set<Article> {
		return try fetchUnreadArticles(forContainer: self)
	}

	func fetchUnreadArticlesAsync(_ completion: @escaping ArticleSetResultBlock) {
		fetchUnreadArticlesAsync(forContainer: self, completion)
	}

	func fetchTodayArticles() throws -> Set<Article> {
		return try database.fetchTodayArticles(flattenedWebFeeds().webFeedIDs())
	}

	func fetchTodayArticlesAsync(_ completion: @escaping ArticleSetResultBlock) {
		database.fetchTodayArticlesAsync(flattenedWebFeeds().webFeedIDs(), completion)
	}

	func fetchArticles(folder: Folder) throws -> Set<Article> {
		return try fetchArticles(forContainer: folder)
	}

	func fetchArticlesAsync(folder: Folder, _ completion: @escaping ArticleSetResultBlock) {
		fetchArticlesAsync(forContainer: folder, completion)
	}

	func fetchUnreadArticles(folder: Folder) throws -> Set<Article> {
		return try fetchUnreadArticles(forContainer: folder)
	}

	func fetchUnreadArticlesAsync(folder: Folder, _ completion: @escaping ArticleSetResultBlock) {
		fetchUnreadArticlesAsync(forContainer: folder, completion)
	}

	func fetchArticles(webFeed: WebFeed) throws -> Set<Article> {
		let articles = try database.fetchArticles(webFeed.webFeedID)
		validateUnreadCount(webFeed, articles)
		return articles
	}

	func fetchArticlesAsync(webFeed: WebFeed, _ completion: @escaping ArticleSetResultBlock) {
		database.fetchArticlesAsync(webFeed.webFeedID) { [weak self] articleSetResult in
			switch articleSetResult {
			case .success(let articles):
				self?.validateUnreadCount(webFeed, articles)
				completion(.success(articles))
			case .failure(let databaseError):
				completion(.failure(databaseError))
			}
		}
	}

	func fetchArticlesMatching(_ searchString: String) throws -> Set<Article> {
		return try database.fetchArticlesMatching(searchString, flattenedWebFeeds().webFeedIDs())
	}

	func fetchArticlesMatchingWithArticleIDs(_ searchString: String, _ articleIDs: Set<String>) throws -> Set<Article> {
		return try database.fetchArticlesMatchingWithArticleIDs(searchString, articleIDs)
	}
	
	func fetchArticlesMatchingAsync(_ searchString: String, _ completion: @escaping ArticleSetResultBlock) {
		database.fetchArticlesMatchingAsync(searchString, flattenedWebFeeds().webFeedIDs(), completion)
	}

	func fetchArticlesMatchingWithArticleIDsAsync(_ searchString: String, _ articleIDs: Set<String>, _ completion: @escaping ArticleSetResultBlock) {
		database.fetchArticlesMatchingWithArticleIDsAsync(searchString, articleIDs, completion)
	}

	func fetchArticles(articleIDs: Set<String>) throws -> Set<Article> {
		return try database.fetchArticles(articleIDs: articleIDs)
	}

	func fetchArticlesAsync(articleIDs: Set<String>, _ completion: @escaping ArticleSetResultBlock) {
		return database.fetchArticlesAsync(articleIDs: articleIDs, completion)
	}

	func fetchUnreadArticles(webFeed: WebFeed) throws -> Set<Article> {
		let articles = try database.fetchUnreadArticles(Set([webFeed.webFeedID]))
		validateUnreadCount(webFeed, articles)
		return articles
	}

	func fetchUnreadArticlesAsync(for webFeed: WebFeed, completion: @escaping (Set<Article>) -> Void) {
		//		database.fetchUnreadArticlesAsync(for: Set([feed.feedID])) { [weak self] (articles) in
		//			self?.validateUnreadCount(feed, articles)
		//			callback(articles)
		//		}
	}


	func fetchArticles(forContainer container: Container) throws -> Set<Article> {
		let feeds = container.flattenedWebFeeds()
		let articles = try database.fetchArticles(feeds.webFeedIDs())
		validateUnreadCountsAfterFetchingUnreadArticles(feeds, articles)
		return articles
	}

	func fetchArticlesAsync(forContainer container: Container, _ completion: @escaping ArticleSetResultBlock) {
		let webFeeds = container.flattenedWebFeeds()
		database.fetchArticlesAsync(webFeeds.webFeedIDs()) { [weak self] (articleSetResult) in
			switch articleSetResult {
			case .success(let articles):
				self?.validateUnreadCountsAfterFetchingUnreadArticles(webFeeds, articles)
				completion(.success(articles))
			case .failure(let databaseError):
				completion(.failure(databaseError))
			}
		}
	}

	func fetchUnreadArticles(forContainer container: Container) throws -> Set<Article> {
		let feeds = container.flattenedWebFeeds()
		let articles = try database.fetchUnreadArticles(feeds.webFeedIDs())
		validateUnreadCountsAfterFetchingUnreadArticles(feeds, articles)
		return articles
	}

	func fetchUnreadArticlesAsync(forContainer container: Container, _ completion: @escaping ArticleSetResultBlock) {
		let webFeeds = container.flattenedWebFeeds()
		database.fetchUnreadArticlesAsync(webFeeds.webFeedIDs()) { [weak self] (articleSetResult) in
			switch articleSetResult {
			case .success(let articles):
				self?.validateUnreadCountsAfterFetchingUnreadArticles(webFeeds, articles)
				completion(.success(articles))
			case .failure(let databaseError):
				completion(.failure(databaseError))
			}
		}
	}

	func validateUnreadCountsAfterFetchingUnreadArticles(_ webFeeds: Set<WebFeed>, _ articles: Set<Article>) {
		// Validate unread counts. This was the site of a performance slowdown:
		// it was calling going through the entire list of articles once per feed:
		// feeds.forEach { validateUnreadCount($0, articles) }
		// Now we loop through articles exactly once. This makes a huge difference.

		var unreadCountStorage = [String: Int]() // [WebFeedID: Int]
		for article in articles where !article.status.read {
			unreadCountStorage[article.webFeedID, default: 0] += 1
		}
		webFeeds.forEach { (webFeed) in
			let unreadCount = unreadCountStorage[webFeed.webFeedID, default: 0]
			webFeed.unreadCount = unreadCount
		}
	}

	func validateUnreadCount(_ webFeed: WebFeed, _ articles: Set<Article>) {
		// articles must contain all the unread articles for the feed.
		// The unread number should match the feed’s unread count.

		let feedUnreadCount = articles.reduce(0) { (result, article) -> Int in
			if article.webFeed == webFeed && !article.status.read {
				return result + 1
			}
			return result
		}

		webFeed.unreadCount = feedUnreadCount
	}
}

// MARK: - Private

private extension Account {

	func webFeedMetadata(feedURL: String, webFeedID: String) -> WebFeedMetadata {
		if let d = webFeedMetadata[feedURL] {
			assert(d.delegate === self)
			return d
		}
		let d = WebFeedMetadata(webFeedID: webFeedID)
		d.delegate = self
		webFeedMetadata[feedURL] = d
		return d
	}

	func updateFlattenedWebFeeds() {
		var feeds = Set<WebFeed>()
		feeds.formUnion(topLevelWebFeeds)
		for folder in folders! {
			feeds.formUnion(folder.flattenedWebFeeds())
		}

		_flattenedWebFeeds = feeds
		flattenedWebFeedsNeedUpdate = false
	}

	func rebuildWebFeedDictionaries() {
		var idDictionary = [String: WebFeed]()

		flattenedWebFeeds().forEach { (feed) in
			idDictionary[feed.webFeedID] = feed
		}

		_idToWebFeedDictionary = idDictionary
		webFeedDictionaryNeedsUpdate = false
	}
    
    func updateUnreadCount() {
		if fetchingAllUnreadCounts {
			return
		}
		var updatedUnreadCount = 0
		for feed in flattenedWebFeeds() {
			updatedUnreadCount += feed.unreadCount
		}
		unreadCount = updatedUnreadCount
    }
    
    func noteStatusesForArticlesDidChange(_ articles: Set<Article>) {
		let feeds = Set(articles.compactMap { $0.webFeed })
		let statuses = Set(articles.map { $0.status })
		let articleIDs = Set(articles.map { $0.articleID })

        // .UnreadCountDidChange notification will get sent to Folder and Account objects,
        // which will update their own unread counts.
        updateUnreadCounts(for: feeds)
        
		NotificationCenter.default.post(name: .StatusesDidChange, object: self, userInfo: [UserInfoKey.statuses: statuses, UserInfoKey.articles: articles, UserInfoKey.articleIDs: articleIDs, UserInfoKey.webFeeds: feeds])
    }

	func noteStatusesForArticleIDsDidChange(_ articleIDs: Set<String>) {
		fetchAllUnreadCounts()
		NotificationCenter.default.post(name: .StatusesDidChange, object: self, userInfo: [UserInfoKey.articleIDs: articleIDs])
	}

	func fetchAllUnreadCounts() {
		fetchingAllUnreadCounts = true

		database.fetchAllNonZeroUnreadCounts { (unreadCountDictionaryResult) in
			if let unreadCountDictionary = try? unreadCountDictionaryResult.get() {
				self.flattenedWebFeeds().forEach{ (feed) in
					// When the unread count is zero, it won’t appear in unreadCountDictionary.
					if let unreadCount = unreadCountDictionary[feed.webFeedID] {
						feed.unreadCount = unreadCount
					}
					else {
						feed.unreadCount = 0
					}
				}

				self.fetchingAllUnreadCounts = false
				self.updateUnreadCount()
				self.isUnreadCountsInitialized = true
				self.postUnreadCountDidInitializeNotification()
			}
		}
	}
}

// MARK: - Container Overrides

extension Account {

	public func existingWebFeed(withWebFeedID webFeedID: String) -> WebFeed? {
		return idToWebFeedDictionary[webFeedID]
	}
}

// MARK: - OPMLRepresentable

extension Account: OPMLRepresentable {

	public func OPMLString(indentLevel: Int, strictConformance: Bool) -> String {
		var s = ""
		for feed in topLevelWebFeeds.sorted(by: { $0.nameForDisplay < $1.nameForDisplay }) {
			s += feed.OPMLString(indentLevel: indentLevel + 1, strictConformance: strictConformance)
		}
		for folder in folders!.sorted(by: { $0.nameForDisplay < $1.nameForDisplay }) {
			s += folder.OPMLString(indentLevel: indentLevel + 1, strictConformance: strictConformance)
		}
		return s
	}
}