Tusker/Tusker/Screens/Local Predicate Statuses List/LocalPredicateStatusesViewController.swift

//
//  LocalPredicateStatusesViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 2/4/23.
//  Copyright © 2023 Shadowfacts. All rights reserved.
//

import UIKit
import Pachyderm
import CoreData

class LocalPredicateStatusesViewController: UIViewController, CollectionViewController, RefreshableViewController {
    
    private static let pageSize = 40
    
    let mastodonController: MastodonController
    private let predicate: (StatusMO) -> Bool
    private let predicateTitle: String
    private let request: (RequestRange) -> Request<[Status]>
    
    var collectionView: UICollectionView! {
        view as? UICollectionView
    }
    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
    
    private var state = State.unloaded
    private var newer: RequestRange?
    private var older: RequestRange?
    
    init(predicate: @escaping (StatusMO) -> Bool, predicateTitle: String, request: @escaping (RequestRange) -> Request<[Status]>, mastodonController: MastodonController) {
        self.mastodonController = mastodonController
        self.predicate = predicate
        self.predicateTitle = predicateTitle
        self.request = request
        
        super.init(nibName: nil, bundle: nil)
        
        self.title = predicateTitle
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func loadView() {
        var config = UICollectionLayoutListConfiguration(appearance: .plain)
        config.backgroundColor = .appBackground
        config.leadingSwipeActionsConfigurationProvider = { [unowned self] in
            (collectionView.cellForItem(at: $0) as? TimelineStatusCollectionViewCell)?.leadingSwipeActions()
        }
        config.trailingSwipeActionsConfigurationProvider = { [unowned self] in
            (collectionView.cellForItem(at: $0) as? TimelineStatusCollectionViewCell)?.trailingSwipeActions()
        }
        config.itemSeparatorHandler = { [unowned self] indexPath, sectionConfig in
            guard let item = dataSource.itemIdentifier(for: indexPath) else {
                return sectionConfig
            }
            var config = sectionConfig
            if item.hideSeparators {
                config.topSeparatorVisibility = .hidden
                config.bottomSeparatorVisibility = .hidden
            } else {
                config.topSeparatorInsets = TimelineStatusCollectionViewCell.separatorInsets
                config.bottomSeparatorInsets = TimelineStatusCollectionViewCell.separatorInsets
            }
            return config
        }
        let layout = UICollectionViewCompositionalLayout { sectionIndex, environment in
            let section = NSCollectionLayoutSection.list(using: config, layoutEnvironment: environment)
            section.readableContentInset(in: environment)
            return section
        }
        view = UICollectionView(frame: .zero, collectionViewLayout: layout)
        collectionView.delegate = self
        collectionView.dragDelegate = self
        collectionView.allowsFocus = true
        
        dataSource = createDataSource()
    }
    
    private func createDataSource() -> UICollectionViewDiffableDataSource<Section, Item> {
        let statusCell = UICollectionView.CellRegistration<TimelineStatusCollectionViewCell, (String, CollapseState)> { [unowned self] cell, indexPath, item in
            cell.delegate = self
            cell.updateUI(statusID: item.0, state: item.1, filterResult: .allow, precomputedContent: nil)
        }
        let loadingCell = UICollectionView.CellRegistration<LoadingCollectionViewCell, Void> { cell, indexPath, itemIdentifier in
            cell.indicator.startAnimating()
        }
        return UICollectionViewDiffableDataSource(collectionView: collectionView) { collectionView, indexPath, itemIdentifier in
            switch itemIdentifier {
            case .status(id: let id, state: let state, addedLocally: _):
                return collectionView.dequeueConfiguredReusableCell(using: statusCell, for: indexPath, item: (id, state))
            case .loadingIndicator:
                return collectionView.dequeueConfiguredReusableCell(using: loadingCell, for: indexPath, item: ())
            }
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        #if !targetEnvironment(macCatalyst)
        collectionView.refreshControl = UIRefreshControl()
        collectionView.refreshControl!.addTarget(self, action: #selector(refresh), for: .valueChanged)
        #endif
        
        addKeyCommand(MenuController.refreshCommand(discoverabilityTitle: "Refresh \(predicateTitle)"))
        
        NotificationCenter.default.addObserver(self, selector: #selector(handleStatusDeleted), name: .statusDeleted, object: mastodonController)
        NotificationCenter.default.addObserver(self, selector: #selector(managedObjectsDidChange), name: .NSManagedObjectContextObjectsDidChange, object: mastodonController.persistentContainer.viewContext)
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        clearSelectionOnAppear(animated: animated)
        
        if case .unloaded = state {
            Task {
                await loadInitial()
            }
        }
    }
    
    private func apply(snapshot: NSDiffableDataSourceSnapshot<Section, Item>, animatingDifferences: Bool) async {
        await Task { @MainActor in
            self.dataSource.apply(snapshot, animatingDifferences: animatingDifferences)
        }.value
    }
    
    @MainActor
    private func loadInitial() async {
        state = .loadingInitial
        
        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
        snapshot.appendSections([.statuses])
        snapshot.appendItems([.loadingIndicator])
        await apply(snapshot: snapshot, animatingDifferences: false)
        
        do {
            let req = request(.count(Self.pageSize))
            let (statuses, pagination) = try await mastodonController.run(req)
            newer = pagination?.newer
            older = pagination?.older
            
            await mastodonController.persistentContainer.addAll(statuses: statuses)
            
            var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
            snapshot.appendSections([.statuses])
            snapshot.appendItems(statuses.map { .status(id: $0.id, state: .unknown, addedLocally: false) })
            await apply(snapshot: snapshot, animatingDifferences: true)
            
            state = .loaded
            
        } catch {
            let config = ToastConfiguration(from: error, with: "Error Loading \(predicateTitle)", in: self) { [weak self] toast in
                toast.dismissToast(animated: true)
                await self?.loadInitial()
            }
            showToast(configuration: config, animated: true)
            
            await apply(snapshot: NSDiffableDataSourceSnapshot(), animatingDifferences: false)
            
            state = .unloaded
        }
    }
    
    @MainActor
    private func loadOlder() async {
        guard case .loaded = state,
              let older else {
            return
        }
        state = .loadingOlder
        
        var snapshot = dataSource.snapshot()
        snapshot.appendItems([.loadingIndicator])
        await apply(snapshot: snapshot, animatingDifferences: false)
        
        do {
            let req = request(older.withCount(Self.pageSize))
            let (statuses, pagination) = try await mastodonController.run(req)
            self.older = pagination?.older
            
            await mastodonController.persistentContainer.addAll(statuses: statuses)
            
            snapshot.deleteItems([.loadingIndicator])
            snapshot.appendItems(statuses.map { .status(id: $0.id, state: .unknown, addedLocally: false) })
            await apply(snapshot: snapshot, animatingDifferences: true)
        } catch {
            let config = ToastConfiguration(from: error, with: "Error Loading Older \(predicateTitle)", in: self) { [weak self] toast in
                toast.dismissToast(animated: true)
                await self?.loadOlder()
            }
            showToast(configuration: config, animated: true)
            
            var snapshot = dataSource.snapshot()
            snapshot.deleteItems([.loadingIndicator])
            await apply(snapshot: snapshot, animatingDifferences: false)
        }
        
        state = .loaded
    }
    
    @objc private func handleStatusDeleted(_ notification: Foundation.Notification) {
        guard let userInfo = notification.userInfo,
              let statusIDs = userInfo["statusIDs"] as? [String] else {
            return
        }
        var snapshot = dataSource.snapshot()
        let toDelete = statusIDs.map { id in
            Item.status(id: id, state: .unknown, addedLocally: false)
        }.filter { item in
            snapshot.itemIdentifiers.contains(item)
        }
        if !toDelete.isEmpty {
            snapshot.deleteItems(toDelete)
            Task {
                await apply(snapshot: snapshot, animatingDifferences: true)
            }
        }
    }
    
    @objc private func managedObjectsDidChange(_ notification: Foundation.Notification) {
        // only perform local updates while the vc is idle
        // otherwise loading the bookmarks ends up inserting them out of order
        guard case .loaded = state else {
            return
        }
        var snapshot = dataSource.snapshot()
        func prepend(item: Item) {
            if let first = snapshot.itemIdentifiers.first {
                snapshot.insertItems([item], beforeItem: first)
            } else {
                snapshot.appendItems([item])
            }
        }
        var hasChanges = false
        if let inserted = notification.userInfo?[NSInsertedObjectsKey] as? Set<NSManagedObject> {
            for case let status as StatusMO in inserted where predicate(status) {
                prepend(item: .status(id: status.id, state: .unknown, addedLocally: true))
                hasChanges = true
            }
        }
        if let updated = notification.userInfo?[NSUpdatedObjectsKey] as? Set<NSManagedObject> {
            for case let status as StatusMO in updated {
                let item = Item.status(id: status.id, state: .unknown, addedLocally: true)
                let exists = snapshot.itemIdentifiers.contains(item)
                if predicate(status) && !exists {
                    prepend(item: item)
                    hasChanges = true
                } else if !predicate(status) && exists {
                    snapshot.deleteItems([item])
                    hasChanges = true
                }
            }
        }
        if hasChanges {
            Task {
                await apply(snapshot: snapshot, animatingDifferences: true)
            }
        }
    }
    
    // MARK: Interaction
    
    @objc func refresh() {
        guard case .loaded = state,
              let newer else {
            #if !targetEnvironment(macCatalyst)
            collectionView.refreshControl!.endRefreshing()
            #endif
            return
        }
        state = .loadingNewer
        
        Task {
            do {
                let req = request(newer.withCount(Self.pageSize))
                let (statuses, pagination) = try await mastodonController.run(req)
                self.newer = pagination?.newer
                
                await mastodonController.persistentContainer.addAll(statuses: statuses)
                
                var snapshot = dataSource.snapshot()
                let localItems: [String: CollapseState] = Dictionary(uniqueKeysWithValues: snapshot.itemIdentifiers.compactMap {
                    if case .status(id: let id, state: let state, addedLocally: true) = $0 {
                        return (id, state)
                    } else {
                        return nil
                    }
                })
                var newItems: [Item] = []
                for status in statuses {
                    let state: CollapseState
                    if let existing = localItems[status.id] {
                        state = existing
                        snapshot.deleteItems([.status(id: status.id, state: existing, addedLocally: true)])
                    } else {
                        state = .unknown
                    }
                    newItems.append(.status(id: status.id, state: state, addedLocally: false))
                }
                if let first = snapshot.itemIdentifiers.first {
                    snapshot.insertItems(newItems, beforeItem: first)
                } else {
                    snapshot.appendItems(newItems)
                }
                await apply(snapshot: snapshot, animatingDifferences: true)
                
            } catch {
                let config = ToastConfiguration(from: error, with: "Error Refreshing \(predicateTitle)", in: self) { [weak self] toast in
                    toast.dismissToast(animated: true)
                    self?.refresh()
                }
                showToast(configuration: config, animated: true)
            }
            
            #if !targetEnvironment(macCatalyst)
            collectionView.refreshControl!.endRefreshing()
            #endif
            state = .loaded
        }
    }

}

extension LocalPredicateStatusesViewController {
    enum Section {
        case statuses
    }
    enum Item: Equatable, Hashable {
        case status(id: String, state: CollapseState, addedLocally: Bool)
        case loadingIndicator
        
        var hideSeparators: Bool {
            switch self {
            case .loadingIndicator:
                return true
            default:
                return false
            }
        }
        
        static func ==(lhs: Item, rhs: Item) -> Bool {
            switch (lhs, rhs) {
            case (.status(id: let a, _, _), .status(id: let b, _, _)):
                return a == b
            case (.loadingIndicator, .loadingIndicator):
                return true
            default:
                return false
            }
        }
        
        func hash(into hasher: inout Hasher) {
            switch self {
            case .status(id: let id, _, _):
                hasher.combine(0)
                hasher.combine(id)
            case .loadingIndicator:
                hasher.combine(1)
            }
        }
    }
}

extension LocalPredicateStatusesViewController {
    enum State {
        case unloaded
        case loadingInitial
        case loaded
        case loadingOlder
        case loadingNewer
    }
}

extension LocalPredicateStatusesViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
        if indexPath.section == 0,
           indexPath.row == collectionView.numberOfItems(inSection: indexPath.section) - 1 {
            Task {
                await self.loadOlder()
            }
        }
    }
    
    func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool {
        if case .status(_, _, _) = dataSource.itemIdentifier(for: indexPath) {
            return true
        } else {
            return false
        }
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        if case .status(id: let id, state: let state, _) = dataSource.itemIdentifier(for: indexPath) {
            selected(status: id, state: state.copy())
        }
    }
    
    func collectionView(_ collectionView: UICollectionView, contextMenuConfigurationForItemAt indexPath: IndexPath, point: CGPoint) -> UIContextMenuConfiguration? {
        return (collectionView.cellForItem(at: indexPath) as? TimelineStatusCollectionViewCell)?.contextMenuConfiguration()
    }
    
    func collectionView(_ collectionView: UICollectionView, willPerformPreviewActionForMenuWith configuration: UIContextMenuConfiguration, animator: UIContextMenuInteractionCommitAnimating) {
        MenuPreviewHelper.willPerformPreviewAction(animator: animator, presenter: self)
    }
}

extension LocalPredicateStatusesViewController: UICollectionViewDragDelegate {
    func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
        return (collectionView.cellForItem(at: indexPath) as? TimelineStatusCollectionViewCell)?.dragItemsForBeginning(session: session) ?? []
    }
}

extension LocalPredicateStatusesViewController: TuskerNavigationDelegate {
    var apiController: MastodonController! { mastodonController }
}

extension LocalPredicateStatusesViewController: StatusCollectionViewCellDelegate {
    func statusCellNeedsReconfigure(_ cell: StatusCollectionViewCell, animated: Bool, completion: (() -> Void)?) {
        if let indexPath = collectionView.indexPath(for: cell) {
            var snapshot = dataSource.snapshot()
            snapshot.reconfigureItems([dataSource.itemIdentifier(for: indexPath)!])
            dataSource.apply(snapshot, animatingDifferences: animated, completion: completion)
        }
    }
    
    func statusCellShowFiltered(_ cell: StatusCollectionViewCell) {
        // filtering isn't supported here
    }
}

extension LocalPredicateStatusesViewController: TabBarScrollableViewController {
    func tabBarScrollToTop() {
        collectionView.scrollToTop()
    }
}

extension LocalPredicateStatusesViewController: StatusBarTappableViewController {
    func handleStatusBarTapped(xPosition: CGFloat) -> StatusBarTapActionResult {
        collectionView.scrollToTop()
        return .stop
    }
}