//
//  ExploreViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 12/14/19.
//  Copyright © 2019 Shadowfacts. All rights reserved.
//

import UIKit
import Combine
import Pachyderm

class ExploreViewController: UIViewController, UICollectionViewDelegate {

    weak var mastodonController: MastodonController!
    
    private var collectionView: UICollectionView!
    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
    
    private(set) var resultsController: SearchResultsViewController!
    private(set) var searchController: UISearchController!
    
    var searchControllerStatusOnAppearance: Bool? = nil
    
    init(mastodonController: MastodonController) {
        self.mastodonController = mastodonController
        
        super.init(nibName: nil, bundle: nil)
        
        title = NSLocalizedString("Explore", comment: "explore tab title")
        tabBarItem.image = UIImage(systemName: "magnifyingglass")
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()

        var configuration = UICollectionLayoutListConfiguration(appearance: .insetGrouped)
        configuration.trailingSwipeActionsConfigurationProvider = self.trailingSwipeActionsForCell(at:)
        configuration.headerMode = .supplementary
        let layout = UICollectionViewCompositionalLayout.list(using: configuration)
        collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
        collectionView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        collectionView.delegate = self
        collectionView.dragDelegate = self
        view.addSubview(collectionView)
        
        dataSource = createDataSource()
        applyInitialSnapshot()
        
        resultsController = SearchResultsViewController(mastodonController: mastodonController)
        resultsController.exploreNavigationController = self.navigationController!
        searchController = UISearchController(searchResultsController: resultsController)
        searchController.searchResultsUpdater = resultsController
        searchController.searchBar.autocapitalizationType = .none
        searchController.searchBar.delegate = resultsController
        definesPresentationContext = true
        
        navigationItem.searchController = searchController
        navigationItem.hidesSearchBarWhenScrolling = false
        
        NotificationCenter.default.addObserver(self, selector: #selector(savedHashtagsChanged), name: .savedHashtagsChanged, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(savedInstancesChanged), name: .savedInstancesChanged, object: nil)
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        // Can't use UICollectionViewController's builtin version of this because it requires
        // the collection view layout be passed into the constructor. Swipe actions for list collection views
        // are created by passing a closure to the layout's configuration. This closure needs to capture
        // `self`, so it can't be passed into the super constructor.
        if let indexPaths = collectionView.indexPathsForSelectedItems {
            for indexPath in indexPaths {
                collectionView.deselectItem(at: indexPath, animated: true)
            }
        }
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        // this is a workaround for the issue that setting isActive on a search controller that is not visible
        // does not cause it to automatically become active once it becomes visible
        // see FB7814561
        if let active = searchControllerStatusOnAppearance {
            searchController.isActive = active
            searchControllerStatusOnAppearance = nil
        }
    }
    
    private func createDataSource() -> UICollectionViewDiffableDataSource<Section, Item> {
        let sectionHeaderCell = UICollectionView.SupplementaryRegistration<UICollectionViewListCell>(elementKind: UICollectionView.elementKindSectionHeader) { (headerView, collectionView, indexPath) in
            let section = self.dataSource.snapshot().sectionIdentifiers[indexPath.section]
            
            var config = headerView.defaultContentConfiguration()
            config.text = section.label
            headerView.contentConfiguration = config
        }
        
        let listCell = UICollectionView.CellRegistration<UICollectionViewListCell, Item> { (cell, indexPath, item) in
            var config = cell.defaultContentConfiguration()
            config.text = item.label
            config.image = item.image
            cell.contentConfiguration = config

            switch item {
            case .addList, .addSavedHashtag, .findInstance:
                cell.accessories = []
            default:
                cell.accessories = [.disclosureIndicator()]
            }
        }
        
        let dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: collectionView) { (collectionView, indexPath, item) in
            return collectionView.dequeueConfiguredReusableCell(using: listCell, for: indexPath, item: item)
        }
        dataSource.supplementaryViewProvider = { (collectionView, elementKind, indexPath) in
            if elementKind == UICollectionView.elementKindSectionHeader {
                return collectionView.dequeueConfiguredReusableSupplementary(using: sectionHeaderCell, for: indexPath)
            } else {
                return nil
            }
        }
        return dataSource
    }

    private func applyInitialSnapshot() {
        let account = mastodonController.accountInfo!
        
        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
        snapshot.appendSections(Section.allCases)
        snapshot.appendItems([.bookmarks], toSection: .bookmarks)
        snapshot.appendItems([.trendingTags], toSection: .discover)
        snapshot.appendItems([.addList], toSection: .lists)
        snapshot.appendItems(SavedDataManager.shared.sortedHashtags(for: account).map { .savedHashtag($0) }, toSection: .savedHashtags)
        snapshot.appendItems([.addSavedHashtag], toSection: .savedHashtags)
        snapshot.appendItems(SavedDataManager.shared.savedInstances(for: account).map { .savedInstance($0) }, toSection: .savedInstances)
        snapshot.appendItems([.findInstance], toSection: .savedInstances)
        dataSource.apply(snapshot, animatingDifferences: false)
        
        reloadLists()
    }
    
    private func reloadLists() {
        let request = Client.getLists()
        mastodonController.run(request) { (response) in
            guard case let .success(lists, _) = response else {
                return
            }
            
            var snapshot = self.dataSource.snapshot()
            snapshot.deleteItems(snapshot.itemIdentifiers(inSection: .lists))
            snapshot.appendItems(lists.map { .list($0) }, toSection: .lists)
            snapshot.appendItems([.addList], toSection: .lists)
            
            DispatchQueue.main.async {
                self.dataSource.apply(snapshot)
            }
        }
    }
    
    @objc private func savedHashtagsChanged() {
        let account = mastodonController.accountInfo!
        var snapshot = dataSource.snapshot()
        snapshot.deleteItems(snapshot.itemIdentifiers(inSection: .savedHashtags))
        snapshot.appendItems(SavedDataManager.shared.sortedHashtags(for: account).map { .savedHashtag($0) }, toSection: .savedHashtags)
        snapshot.appendItems([.addSavedHashtag], toSection: .savedHashtags)
        dataSource.apply(snapshot)
    }
    
    @objc private func savedInstancesChanged() {
        let account = mastodonController.accountInfo!
        var snapshot = dataSource.snapshot()
        snapshot.deleteItems(snapshot.itemIdentifiers(inSection: .savedInstances))
        snapshot.appendItems(SavedDataManager.shared.savedInstances(for: account).map { .savedInstance($0) }, toSection: .savedInstances)
        snapshot.appendItems([.findInstance], toSection: .savedInstances)
        dataSource.apply(snapshot)
    }
    
    private func deleteList(_ list: List, completion: @escaping (Bool) -> Void) {
        let titleFormat = NSLocalizedString("Are you sure you want to delete the '%@' list?", comment: "delete list alert title")
        let title = String(format: titleFormat, list.title)
        let alert = UIAlertController(title: title, message: nil, preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: NSLocalizedString("Cancel", comment: "delete list alert cancel button"), style: .cancel, handler: { (_) in
            completion(false)
        }))
        alert.addAction(UIAlertAction(title: NSLocalizedString("Delete List", comment: "delete list alert confirm button"), style: .destructive, handler: { (_) in
            
            let request = List.delete(list)
            self.mastodonController.run(request) { (response) in
                guard case .success(_, _) = response else {
                    fatalError()
                }
                
                var snapshot = self.dataSource.snapshot()
                snapshot.deleteItems([.list(list)])
                DispatchQueue.main.async {
                    self.dataSource.apply(snapshot)
                    completion(true)
                }
            }
        }))
        present(alert, animated: true)
    }
    
    func removeSavedHashtag(_ hashtag: Hashtag) {
        let account = mastodonController.accountInfo!
        SavedDataManager.shared.remove(hashtag: hashtag, for: account)
    }
    
    func removeSavedInstance(_ instanceURL: URL) {
        let account = mastodonController.accountInfo!
        SavedDataManager.shared.remove(instance: instanceURL, for: account)
    }
    
    private func trailingSwipeActionsForCell(at indexPath: IndexPath) -> UISwipeActionsConfiguration? {
        let handler: UIContextualAction.Handler
        switch dataSource.itemIdentifier(for: indexPath) {
        case let .list(list):
            handler = { (_, _, completion) in
                self.deleteList(list, completion: completion)
            }
            
        case let .savedHashtag(hashtag):
            handler = { (_, _, completion) in
                self.removeSavedHashtag(hashtag)
                completion(true)
            }
            
        case let .savedInstance(url):
            handler = { (_, _, completion) in
                self.removeSavedInstance(url)
                completion(true)
            }
        
        default:
            return nil
        }
        
        return UISwipeActionsConfiguration(actions: [
            UIContextualAction(style: .destructive, title: NSLocalizedString("Delete", comment: "delete swipe action title"), handler: handler)
        ])
    }
    
    // MARK: - Collection View Delegate
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        switch dataSource.itemIdentifier(for: indexPath) {
        case nil:
            return
            
        case .bookmarks:
            show(BookmarksTableViewController(mastodonController: mastodonController), sender: nil)
            
        case .trendingTags:
            show(TrendingHashtagsViewController(mastodonController: mastodonController), sender: nil)
            
        case let .list(list):
            show(ListTimelineViewController(for: list, mastodonController: mastodonController), sender: nil)
            
        case .addList:
            collectionView.deselectItem(at: indexPath, animated: true)
            let alert = UIAlertController(title: NSLocalizedString("New List", comment: "new list alert title"), message: NSLocalizedString("Choose a title for your new list", comment: "new list alert message"), preferredStyle: .alert)
            alert.addTextField(configurationHandler: nil)
            alert.addAction(UIAlertAction(title: NSLocalizedString("Cancel", comment: "new list alert cancel button"), style: .cancel, handler: nil))
            alert.addAction(UIAlertAction(title: NSLocalizedString("Create List", comment: "new list create button"), style: .default, handler: { (_) in
                guard let title = alert.textFields?.first?.text else {
                    fatalError()
                }
                
                let request = Client.createList(title: title)
                self.mastodonController.run(request) { (response) in
                    guard case let .success(list, _) = response else { fatalError() }
                    
                    self.reloadLists()
                    
                    DispatchQueue.main.async {
                        let listTimelineController = ListTimelineViewController(for: list, mastodonController: self.mastodonController)
                        listTimelineController.presentEditOnAppear = true
                        self.show(listTimelineController, sender: nil)
                    }
                }
            }))
            present(alert, animated: true)
            
        case let .savedHashtag(hashtag):
            show(HashtagTimelineViewController(for: hashtag, mastodonController: mastodonController), sender: nil)
            
        case .addSavedHashtag:
            collectionView.deselectItem(at: indexPath, animated: true)
            let navController = UINavigationController(rootViewController: AddSavedHashtagViewController(mastodonController: mastodonController))
            present(navController, animated: true)
            
        case let .savedInstance(url):
            show(InstanceTimelineViewController(for: url, parentMastodonController: mastodonController), sender: nil)
            
        case .findInstance:
            collectionView.deselectItem(at: indexPath, animated: true)
            let findController = FindInstanceViewController(parentMastodonController: mastodonController)
            findController.instanceTimelineDelegate = self
            let navController = UINavigationController(rootViewController: findController)
            present(navController, animated: true)
        }
    }
    
}

extension ExploreViewController {
    enum Section: CaseIterable {
        case bookmarks
        case discover
        case lists
        case savedHashtags
        case savedInstances
        
        var label: String? {
            switch self {
            case .bookmarks:
                return  nil
            case .discover:
                return NSLocalizedString("Discover", comment: "discover section title")
            case .lists:
                return NSLocalizedString("Lists", comment: "explore lists section title")
            case .savedHashtags:
                return NSLocalizedString("Saved Hashtags", comment: "explore saved hashtags section title")
            case .savedInstances:
                return NSLocalizedString("Instance Timelines", comment: "explore instance timelines section title")
            }
        }
    }
    
    enum Item: Hashable {
        case bookmarks
        case trendingTags
        case list(List)
        case addList
        case savedHashtag(Hashtag)
        case addSavedHashtag
        case savedInstance(URL)
        case findInstance
        
        var label: String {
            switch self {
            case .bookmarks:
                return NSLocalizedString("Bookmarks", comment: "bookmarks nav item title")
            case .trendingTags:
                return NSLocalizedString("Trending Hashtags", comment: "trending hashtags nav item title")
            case let .list(list):
                return list.title
            case .addList:
                return NSLocalizedString("New List...", comment: "new list nav item title")
            case let .savedHashtag(hashtag):
                return hashtag.name
            case .addSavedHashtag:
                return NSLocalizedString("Save Hashtag...", comment: "save hashtag nav item title")
            case let .savedInstance(url):
                return url.host!
            case .findInstance:
                return NSLocalizedString("Find An Instance...", comment: "find instance nav item title")
            }
        }
        
        var image: UIImage {
            let name: String
            switch self {
            case .bookmarks:
                name = "bookmark.fill"
            case .trendingTags:
                name = "arrow.up.arrow.down"
            case .list(_):
                name = "list.bullet"
            case .addList, .addSavedHashtag:
                name = "plus"
            case .savedHashtag(_):
                name = "number"
            case .savedInstance(_):
                name = "globe"
            case .findInstance:
                name = "magnifyingglass"
            }
            return UIImage(systemName: name)!
        }
        
        static func == (lhs: Item, rhs: Item) -> Bool {
            switch (lhs, rhs) {
            case (.bookmarks, .bookmarks):
                return true
            case (.trendingTags, .trendingTags):
                return true
            case let (.list(a), .list(b)):
                return a.id == b.id
            case (.addList, .addList):
                return true
            case let (.savedHashtag(a), .savedHashtag(b)):
                return a == b
            case (.addSavedHashtag, .addSavedHashtag):
                return true
            case let (.savedInstance(a), .savedInstance(b)):
                return a == b
            case (.findInstance, .findInstance):
                return true
            default:
                return false
            }
        }
        
        func hash(into hasher: inout Hasher) {
            switch self {
            case .bookmarks:
                hasher.combine("bookmarks")
            case .trendingTags:
                hasher.combine("trendingTags")
            case let .list(list):
                hasher.combine("list")
                hasher.combine(list.id)
            case .addList:
                hasher.combine("addList")
            case let .savedHashtag(hashtag):
                hasher.combine("savedHashtag")
                hasher.combine(hashtag.name)
            case .addSavedHashtag:
                hasher.combine("addSavedHashtag")
            case let .savedInstance(url):
                hasher.combine("savedInstance")
                hasher.combine(url)
            case .findInstance:
                hasher.combine("findInstance")
            }
        }
    }
}

extension ExploreViewController: InstanceTimelineViewControllerDelegate {
    func didSaveInstance(url: URL) {
        dismiss(animated: true) {
            self.show(InstanceTimelineViewController(for: url, parentMastodonController: self.mastodonController), sender: nil)
        }
    }
    
    func didUnsaveInstance(url: URL) {
        dismiss(animated: true)
    }
}

extension ExploreViewController: UICollectionViewDragDelegate {
    func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
        guard let item = dataSource.itemIdentifier(for: indexPath),
              let accountID = mastodonController.accountInfo?.id else {
            return []
        }
        
        let provider: NSItemProvider
        switch item {
        case .bookmarks:
            provider = NSItemProvider(object: UserActivityManager.bookmarksActivity())
        case let .list(list):
            guard let activity = UserActivityManager.showTimelineActivity(timeline: .list(id: list.id), accountID: accountID) else { return [] }
            provider = NSItemProvider(object: activity)
        case let .savedHashtag(hashtag):
            provider = NSItemProvider(object: hashtag.url as NSURL)
            if let activity = UserActivityManager.showTimelineActivity(timeline: .tag(hashtag: hashtag.name), accountID: accountID) {
                provider.registerObject(activity, visibility: .all)
            }
        case let .savedInstance(url):
            provider = NSItemProvider(object: url as NSURL)
            // todo: should dragging public timelines into new windows be supported?
        case .trendingTags, .addList, .addSavedHashtag, .findInstance:
            return []
        }
        return [UIDragItem(itemProvider: provider)]
    }
}