Tusker/Tusker/Screens/Explore/TrendingStatusesViewController.swift

//
//  TrendingStatusesViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 4/1/22.
//  Copyright © 2022 Shadowfacts. All rights reserved.
//

import UIKit
import Pachyderm

class TrendingStatusesViewController: UIViewController {
    
    weak var mastodonController: MastodonController!
    let filterer: Filterer
    
    private var collectionView: UICollectionView {
        view as! UICollectionView
    }
    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
    
    private var loaded = false
    
    init(mastodonController: MastodonController) {
        self.mastodonController = mastodonController
        self.filterer = Filterer(mastodonController: mastodonController, context: .public)
        self.filterer.htmlConverter.font = TimelineStatusCollectionViewCell.contentFont
        self.filterer.htmlConverter.monospaceFont = TimelineStatusCollectionViewCell.monospaceFont
        self.filterer.htmlConverter.paragraphStyle = TimelineStatusCollectionViewCell.contentParagraphStyle
        
        super.init(nibName: nil, bundle: nil)
        
        title = NSLocalizedString("Trending Posts", comment: "trending posts screen title")
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func loadView() {
        var config = UICollectionLayoutListConfiguration(appearance: .plain)
        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, sectionSeparatorConfiguration in
            guard let item = self.dataSource.itemIdentifier(for: indexPath) else {
                return sectionSeparatorConfiguration
            }
            var config = sectionSeparatorConfiguration
            if item.hideSeparators {
                config.topSeparatorVisibility = .hidden
                config.bottomSeparatorVisibility = .hidden
            }
            if case .status(_, _, _) = item {
                config.topSeparatorInsets = TimelineStatusCollectionViewCell.separatorInsets
                config.bottomSeparatorInsets = TimelineStatusCollectionViewCell.separatorInsets
            }
            return config
        }
        let layout = UICollectionViewCompositionalLayout { sectionIndex, environment in
            let section = NSCollectionLayoutSection.list(using: config, layoutEnvironment: environment)
            if UIDevice.current.userInterfaceIdiom == .pad || UIDevice.current.userInterfaceIdiom == .mac {
                section.contentInsetsReference = .readableContent
            }
            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, Filterer.Result, NSAttributedString?)> { [unowned self] cell, indexPath, item in
            cell.delegate = self
            cell.updateUI(statusID: item.0, state: item.1, filterResult: item.2, precomputedContent: item.3)
        }
        let zeroHeightCell = UICollectionView.CellRegistration<ZeroHeightCollectionViewCell, Void> { _, _, _ in
        }
        let loadingCell = UICollectionView.CellRegistration<LoadingCollectionViewCell, Void> { cell, _, _ in
            cell.indicator.startAnimating()
        }
        return UICollectionViewDiffableDataSource(collectionView: collectionView) { [unowned self] collectionView, indexPath, itemIdentifier in
            switch itemIdentifier {
            case .status(id: let id, let collapseState, let filterState):
                let (result, attributedString) = self.filterer.resolve(state: filterState, status: { (mastodonController.persistentContainer.status(for: id)!, false) })
                switch result {
                case .allow, .warn(_):
                    return collectionView.dequeueConfiguredReusableCell(using: statusCell, for: indexPath, item: (id, collapseState, result, attributedString))
                case .hide:
                    return collectionView.dequeueConfiguredReusableCell(using: zeroHeightCell, for: indexPath, item: ())
                }
            case .loadingIndicator:
                return collectionView.dequeueConfiguredReusableCell(using: loadingCell, for: indexPath, item: ())
            }
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        NotificationCenter.default.addObserver(self, selector: #selector(handleStatusDeleted), name: .statusDeleted, object: nil)
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        if !loaded {
            loaded = true
            var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
            snapshot.appendSections([.statuses])
            snapshot.appendItems([.loadingIndicator])
            dataSource.apply(snapshot, animatingDifferences: false)
            
            Task {
                await loadTrendingStatuses()
            }
        }
    }
    
    private func loadTrendingStatuses() async {
        let statuses: [Status]
        do {
            statuses = try await mastodonController.run(Client.getTrendingStatuses()).0
        } catch {
            let snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
            await dataSource.apply(snapshot)
            let config = ToastConfiguration(from: error, with: "Loading Trending Posts", in: self) { toast in
                toast.dismissToast(animated: true)
                await self.loadTrendingStatuses()
            }
            showToast(configuration: config, animated: true)
            return
        }
        await mastodonController.persistentContainer.addAll(statuses: statuses)
        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
        snapshot.appendSections([.statuses])
        snapshot.appendItems(statuses.map { .status(id: $0.id, collapseState: .unknown, filterState: .unknown) })
        await dataSource.apply(snapshot)
    }
    
    @objc private func handleStatusDeleted(_ notification: Foundation.Notification) {
        guard let userInfo = notification.userInfo,
              let accountID = mastodonController.accountInfo?.id,
              userInfo["accountID"] as? String == accountID,
              let statusIDs = userInfo["statusIDs"] as? [String] else {
            return
        }
        var snapshot = self.dataSource.snapshot()
        let toDelete = statusIDs
            .map { id in
                Item.status(id: id, collapseState: .unknown, filterState: .unknown)
            }
            .filter { item in
                snapshot.itemIdentifiers.contains(item)
            }
        if !toDelete.isEmpty {
            snapshot.deleteItems(toDelete)
            self.dataSource.apply(snapshot, animatingDifferences: true)
        }
    }
}

extension TrendingStatusesViewController {
    enum Section {
        case statuses
    }
    enum Item: Hashable {
        case status(id: String, collapseState: CollapseState, filterState: FilterState)
        case loadingIndicator
        
        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)
            }
        }
        
        var hideSeparators: Bool {
            if case .loadingIndicator = self {
                return true
            } else {
                return false
            }
        }
        
        var isSelectable: Bool {
            if case .status(id: _, _, _) = self {
                return true
            } else {
                return false
            }
        }
    }
}

extension TrendingStatusesViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool {
        return dataSource.itemIdentifier(for: indexPath)?.isSelectable ?? false
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        guard case .status(id: let id, collapseState: let state, _) = dataSource.itemIdentifier(for: indexPath) else {
            return
        }
        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 TrendingStatusesViewController: UICollectionViewDragDelegate {
    func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
        (collectionView.cellForItem(at: indexPath) as? TimelineStatusCollectionViewCell)?.dragItemsForBeginning(session: session) ?? []
    }
}

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

extension TrendingStatusesViewController: ToastableViewController {
}

extension TrendingStatusesViewController: MenuActionProvider {
}

extension TrendingStatusesViewController: 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) {
        fatalError()
    }
}

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