//
//  TimelineModel.swift
//  NetNewsWire
//
//  Created by Maurice Parker on 6/30/20.
//  Copyright © 2020 Ranchero Software. All rights reserved.
//

import Foundation
import Combine
import RSCore
import Account
import Articles

protocol TimelineModelDelegate: class {
	func timelineRequestedWebFeedSelection(_: TimelineModel, webFeed: WebFeed)
}

class TimelineModel: ObservableObject, UndoableCommandRunner {
	
	weak var delegate: TimelineModelDelegate?
	
	@Published var nameForDisplay = ""
	@Published var timelineItems = [TimelineItem]()
	@Published var selectedArticleIDs = Set<String>()
	@Published var selectedArticleID: String? = .none
	@Published var selectedArticles = [Article]()
	@Published var isReadFiltered = false

	var undoManager: UndoManager?
	var undoableCommands = [UndoableCommand]()

	private var selectedArticleIDsCancellable: AnyCancellable?
	private var selectedArticleIDCancellable: AnyCancellable?
	private var selectedArticlesCancellable: AnyCancellable?

	private var fetchSerialNumber = 0
	private let fetchRequestQueue = FetchRequestQueue()
	private var exceptionArticleFetcher: ArticleFetcher?
	
	private var articles = [Article]() {
		didSet {
			articleDictionaryNeedsUpdate = true
		}
	}
	
	private var articleDictionaryNeedsUpdate = true
	private var _idToArticleDictionary = [String: Article]()
	private var idToArticleDictionary: [String: Article] {
		if articleDictionaryNeedsUpdate {
			rebuildArticleDictionaries()
		}
		return _idToArticleDictionary
	}

	private var sortDirection = AppDefaults.shared.timelineSortDirection {
		didSet {
			if sortDirection != oldValue {
				sortParametersDidChange()
			}
		}
	}
	
	private var groupByFeed = AppDefaults.shared.timelineGroupByFeed {
		didSet {
			if groupByFeed != oldValue {
				sortParametersDidChange()
			}
		}
	}
	
	init() {
		NotificationCenter.default.addObserver(self, selector: #selector(statusesDidChange(_:)), name: .StatusesDidChange, object: nil)

		// TODO: This should be rewritten to use Combine correctly
		selectedArticleIDsCancellable = $selectedArticleIDs.sink { [weak self] articleIDs in
			guard let self = self else { return }
			self.selectedArticles = articleIDs.compactMap { self.idToArticleDictionary[$0] }
		}
		
		// TODO: This should be rewritten to use Combine correctly
		selectedArticleIDCancellable = $selectedArticleID.sink { [weak self] articleID in
			guard let self = self else { return }
			if let articleID = articleID, let article = self.idToArticleDictionary[articleID] {
				self.selectedArticles = [article]
			}
		}

		// TODO: This should be rewritten to use Combine correctly
		selectedArticlesCancellable = $selectedArticles.sink { articles in
			if articles.count == 1 {
				let article = articles.first!
				if !article.status.read {
					markArticles(Set([article]), statusKey: .read, flag: true)
				}
			}
		}
	}
	
	// MARK: API
	
	func rebuildTimelineItems(feeds: [Feed]) {
		if feeds.count == 1 {
			nameForDisplay = feeds.first!.nameForDisplay
		} else {
			nameForDisplay = NSLocalizedString("Multiple", comment: "Multiple Feeds")
		}
		fetchAndReplaceArticlesAsync(feeds: feeds)
	}
	
	func toggleReadStatusForSelectedArticles() {
		guard !selectedArticles.isEmpty else {
			return
		}
		if selectedArticles.anyArticleIsUnread() {
			markSelectedArticlesAsRead()
		} else {
			markSelectedArticlesAsUnread()
		}
	}

	func markSelectedArticlesAsRead() {
		guard let undoManager = undoManager, let markReadCommand = MarkStatusCommand(initialArticles: selectedArticles, markingRead: true, undoManager: undoManager) else {
			return
		}
		runCommand(markReadCommand)
	}
	
	func markSelectedArticlesAsUnread() {
		guard let undoManager = undoManager, let markUnreadCommand = MarkStatusCommand(initialArticles: selectedArticles, markingRead: false, undoManager: undoManager) else {
			return
		}
		runCommand(markUnreadCommand)
	}
	
	func toggleStarredStatusForSelectedArticles() {
		guard !selectedArticles.isEmpty else {
			return
		}
		if selectedArticles.anyArticleIsUnstarred() {
			markSelectedArticlesAsStarred()
		} else {
			markSelectedArticlesAsUnstarred()
		}
	}

	func markSelectedArticlesAsStarred() {
		guard let undoManager = undoManager, let markReadCommand = MarkStatusCommand(initialArticles: selectedArticles, markingStarred: true, undoManager: undoManager) else {
			return
		}
		runCommand(markReadCommand)
	}
	
	func markSelectedArticlesAsUnstarred() {
		guard let undoManager = undoManager, let markUnreadCommand = MarkStatusCommand(initialArticles: selectedArticles, markingStarred: false, undoManager: undoManager) else {
			return
		}
		runCommand(markUnreadCommand)
	}
	
	func articleFor(_ articleID: String) -> Article? {
		return idToArticleDictionary[articleID]
	}

	func findPrevArticle(_ article: Article) -> Article? {
		guard let index = articles.firstIndex(of: article), index > 0 else {
			return nil
		}
		return articles[index - 1]
	}
	
	func findNextArticle(_ article: Article) -> Article? {
		guard let index = articles.firstIndex(of: article), index + 1 != articles.count else {
			return nil
		}
		return articles[index + 1]
	}
	
	func selectArticle(_ article: Article) {
		// TODO: Implement me!
	}
	
}

// MARK: Private

private extension TimelineModel {
	
	// MARK: Notifications

	@objc func statusesDidChange(_ note: Notification) {
		guard let articleIDs = note.userInfo?[Account.UserInfoKey.articleIDs] as? Set<String> else {
			return
		}
		for i in 0..<timelineItems.count {
			if articleIDs.contains(timelineItems[i].article.articleID) {
				timelineItems[i].updateStatus()
			}
		}
	}
	
	// MARK: Timeline Management
	
	func sortParametersDidChange() {
		performBlockAndRestoreSelection {
			let unsortedArticles = Set(articles)
			replaceArticles(with: unsortedArticles)
		}
	}
	
	func performBlockAndRestoreSelection(_ block: (() -> Void)) {
//		let savedSelection = selectedArticleIDs()
		block()
//		restoreSelection(savedSelection)
	}

	func rebuildArticleDictionaries() {
		var idDictionary = [String: Article]()
		articles.forEach { article in
			idDictionary[article.articleID] = article
		}
		_idToArticleDictionary = idDictionary
		articleDictionaryNeedsUpdate = false
	}
	
	// MARK: Article Fetching
	
	func fetchAndReplaceArticlesAsync(feeds: [Feed]) {
		var fetchers = feeds as [ArticleFetcher]
		if let fetcher = exceptionArticleFetcher {
			fetchers.append(fetcher)
			exceptionArticleFetcher = nil
		}
		
		fetchUnsortedArticlesAsync(for: fetchers) { [weak self] (articles) in
			self?.replaceArticles(with: articles)
		}
	}

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

	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 fetchOperation = FetchRequestOperation(id: fetchSerialNumber, readFilter: isReadFiltered, representedObjects: representedObjects) { [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 replaceArticles(with unsortedArticles: Set<Article>) {
		articles = Array(unsortedArticles).sortedByDate(sortDirection ? .orderedDescending : .orderedAscending, groupByFeed: groupByFeed)
		timelineItems = articles.map { TimelineItem(article: $0) }
		// TODO: Update unread counts and other item done in didSet on AppKit
	}
	
}