Tusker/Tusker/Screens/Timeline/TimelineTableViewController.swift

//
//  TimelineTableViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 8/15/18.
//  Copyright © 2018 Shadowfacts. All rights reserved.
//

import UIKit
import Pachyderm

typealias TimelineEntry = (id: String, state: StatusState)

class TimelineTableViewController: DiffableTimelineLikeTableViewController<TimelineTableViewController.Section, TimelineTableViewController.Item> {
    
    let timeline: Timeline
    weak var mastodonController: MastodonController!
    
    private var newer: RequestRange?
    private var older: RequestRange?
    
    private var didConfirmLoadMore = false
    
    init(for timeline: Timeline, mastodonController: MastodonController) {
        self.timeline = timeline
        self.mastodonController = mastodonController
        
        super.init()
        
        dragEnabled = true
        
        title = timeline.title
        tabBarItem.image = timeline.tabBarImage
        
        if let id = mastodonController.accountInfo?.id {
            userActivity = UserActivityManager.showTimelineActivity(timeline: timeline, accountID: id)
        }
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    deinit {
        guard let persistentContainer = mastodonController?.persistentContainer,
              let dataSource = dataSource else { return }
        // decrement reference counts of any statuses we still have
        // if the app is currently being quit, this will not affect the persisted data because
        // the persistent container would already have been saved in SceneDelegate.sceneDidEnterBackground(_:)
        // todo: remove the whole reference count system
        for case let .status(id: id, state: _) in dataSource.snapshot().itemIdentifiers {
            persistentContainer.status(for: id)?.decrementReferenceCount()
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        tableView.register(UINib(nibName: "TimelineStatusTableViewCell", bundle: .main), forCellReuseIdentifier: "statusCell")
        tableView.register(UINib(nibName: "ConfirmLoadMoreTableViewCell", bundle: .main), forCellReuseIdentifier: "confirmLoadMoreCell")
    }
    
    // MARK: - DiffableTimelineLikeTableViewController
    
    override class func refreshCommandTitle() -> String {
        return NSLocalizedString("Refresh Statuses", comment: "refresh status command discoverability title")
    }
    
    override func timelineContentSections() -> [Section] {
        return [.statuses]
    }

    override func cellProvider(_ tableView: UITableView, _ indexPath: IndexPath, _ item: Item) -> UITableViewCell? {
        switch item {
        case let .status(id: id, state: state):
            let cell = tableView.dequeueReusableCell(withIdentifier: "statusCell", for: indexPath) as! TimelineStatusTableViewCell
            
            cell.delegate = self
            cell.updateUI(statusID: id, state: state)
            return cell
            
        case .confirmLoadMore:
            let cell = tableView.dequeueReusableCell(withIdentifier: "confirmLoadMoreCell", for: indexPath) as! ConfirmLoadMoreTableViewCell
            cell.confirmLoadMore = {
                self.didConfirmLoadMore = true
                self.loadOlder()
                self.didConfirmLoadMore = false
            }
            return cell
        }
    }
    
    override func loadInitialItems(completion: @escaping (LoadResult) -> Void) {
        guard let mastodonController = mastodonController else {
            completion(.failure(.noClient))
            return
        }
        
        let request = Client.getStatuses(timeline: timeline)
        
        mastodonController.run(request) { response in
            switch response {
            case let .failure(error):
                completion(.failure(.client(error)))
                
            case let .success(statuses, pagination):
                self.newer = pagination?.newer
                self.older = pagination?.older
                
                self.mastodonController.persistentContainer.addAll(statuses: statuses) {
                    var snapshot = Snapshot()
                    snapshot.appendSections([.statuses, .footer])
                    snapshot.appendItems(statuses.map { .status(id: $0.id, state: .unknown) }, toSection: .statuses)
                    completion(.success(snapshot))
                }
            }
        }
    }
    
    override func loadOlderItems(currentSnapshot: Snapshot, completion: @escaping (LoadResult) -> Void) {
        guard let older = older else {
            completion(.failure(.noOlder))
            return
        }
        
        guard !Preferences.shared.disableInfiniteScrolling || didConfirmLoadMore else {
            guard !currentSnapshot.itemIdentifiers(inSection: .footer).contains(.confirmLoadMore) else {
                // todo: need something more accurate than "success"/"failure"
                completion(.success(currentSnapshot))
                return
            }
            var snapshot = currentSnapshot
            snapshot.appendItems([.confirmLoadMore], toSection: .footer)
            self.dataSource.apply(snapshot)
            completion(.success(snapshot))
            return
        }
        
        let request = Client.getStatuses(timeline: timeline, range: older)
        
        mastodonController.run(request) { response in
            switch response {
            case let .failure(error):
                completion(.failure(.client(error)))
                
            case let .success(statuses, pagination):
                self.older = pagination?.older
                
                self.mastodonController.persistentContainer.addAll(statuses: statuses) {
                    var snapshot = currentSnapshot
                    snapshot.appendItems(statuses.map { .status(id: $0.id, state: .unknown) }, toSection: .statuses)
                    snapshot.deleteItems([.confirmLoadMore])
                    completion(.success(snapshot))
                }
            }
        }
    }
    
    override func loadNewerItems(currentSnapshot: Snapshot, completion: @escaping (LoadResult) -> Void) {
        guard let newer = newer else {
            completion(.failure(.noNewer))
            return
        }
        
        let request = Client.getStatuses(timeline: timeline, range: newer)
        mastodonController.run(request) { response in
            switch response {
            case let .failure(error):
                completion(.failure(.client(error)))
                
            case let .success(statuses, pagination):
                // if there are no new statuses, pagination is nil
                // if we were to then overwrite self.newer, future refresh would fail
                if let newer = pagination?.newer {
                    self.newer = newer
                }
                
                self.mastodonController.persistentContainer.addAll(statuses: statuses) {
                    var snapshot = currentSnapshot
                    let identifiers = statuses.map { Item.status(id: $0.id, state: .unknown) }
                    if let first = snapshot.itemIdentifiers(inSection: .statuses).first {
                        snapshot.insertItems(identifiers, beforeItem: first)
                    } else {
                        snapshot.appendItems(identifiers, toSection: .statuses)
                    }
                    completion(.success(snapshot))
                }
            }
        }
    }
    
    override func willRemoveItems(_ items: [Item]) {
        for case let .status(id: id, state: _) in items {
            mastodonController.persistentContainer.status(for: id)?.decrementReferenceCount()
        }
    }
    
}

extension TimelineTableViewController {
    enum Section: Hashable, CaseIterable {
        case statuses
        case footer
    }
    enum Item: Hashable {
        case status(id: String, state: StatusState)
        case confirmLoadMore
    }
}

extension TimelineTableViewController: TuskerNavigationDelegate {
    var apiController: MastodonController { mastodonController }
}

extension TimelineTableViewController: StatusTableViewCellDelegate {
    func statusCellCollapsedStateChanged(_ cell: BaseStatusTableViewCell) {
        cellHeightChanged()
    }
}

extension TimelineTableViewController: UITableViewDataSourcePrefetching, StatusTablePrefetching {
    func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
        let ids: [String] = indexPaths.compactMap {
            if case let .status(id: id, state: _) = dataSource.itemIdentifier(for: $0) {
                return id
            } else {
                return nil
            }
        }
        prefetchStatuses(with: ids)
    }

    func tableView(_ tableView: UITableView, cancelPrefetchingForRowsAt indexPaths: [IndexPath]) {
        let ids: [String] = indexPaths.compactMap {
            if case let .status(id: id, state: _) = dataSource.itemIdentifier(for: $0) {
                return id
            } else {
                return nil
            }
        }
        cancelPrefetchingStatuses(with: ids)
    }
}