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: TimelineLikeTableViewController<TimelineEntry> {
    
    let timeline: Timeline
    weak var mastodonController: MastodonController!
    
    private var newer: RequestRange?
    private var older: RequestRange?
    
    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 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(_:)
        for section in sections {
            for (id, _) in section {
                persistentContainer.status(for: id)?.decrementReferenceCount()
            }
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        tableView.register(UINib(nibName: "TimelineStatusTableViewCell", bundle: .main), forCellReuseIdentifier: "statusCell")
    }
    
    override class func refreshCommandTitle() -> String {
        return NSLocalizedString("Refresh Statuses", comment: "refresh status command discoverability title")
    }
    
    override func willRemoveRows(at indexPaths: [IndexPath]) {
        for indexPath in indexPaths {
            let id = item(for: indexPath).id
            mastodonController.persistentContainer.status(for: id)?.decrementReferenceCount()
        }
    }
    
    override func loadInitialItems(completion: @escaping ([TimelineEntry]) -> Void) {
        let request = Client.getStatuses(timeline: timeline)
        
        mastodonController?.run(request) { (response) in
            guard case let .success(statuses, pagination) = response else { fatalError() }
            
            self.newer = pagination?.newer
            self.older = pagination?.older
            
            self.mastodonController?.persistentContainer.addAll(statuses: statuses) {
                completion(statuses.map { ($0.id, .unknown) })
            }
        }
    }
    
    override func loadOlder(completion: @escaping ([TimelineEntry]) -> Void) {
        guard let older = older else {
            completion([])
            return
        }
        
        let request = Client.getStatuses(timeline: timeline, range: older)
        
        mastodonController.run(request) { (response) in
            guard case let .success(statuses, pagination) = response else { fatalError() }
            
            self.older = pagination?.older
            
            self.mastodonController?.persistentContainer.addAll(statuses: statuses) {
                completion(statuses.map { ($0.id, .unknown) })
            }
        }
    }
    
    override func loadNewer(completion: @escaping ([TimelineEntry]) -> Void) {
        guard let newer = newer else {
            completion([])
            return
        }
        
        let request = Client.getStatuses(timeline: timeline, range: newer)
        
        mastodonController.run(request) { (response) in
            guard case let .success(statuses, pagination) = response else { fatalError() }
            
            // if there are no new statuses, pagination is nil
            // if we were to then overwrite self.newer, future refreshes would fail
            if let newer = pagination?.newer {
                self.newer = newer
            }
            
            self.mastodonController?.persistentContainer.addAll(statuses: statuses) {
                completion(statuses.map { ($0.id, .unknown) })
            }
        }
    }
    
    // MARK: - UITableViewDataSource
    
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        guard let cell = tableView.dequeueReusableCell(withIdentifier: "statusCell", for: indexPath) as? TimelineStatusTableViewCell else { fatalError() }

        let (id, state) = item(for: indexPath)
        cell.delegate = self

        cell.updateUI(statusID: id, state: state)

        return cell
    }
    
}

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

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

extension TimelineTableViewController: UITableViewDataSourcePrefetching {
    func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
        for indexPath in indexPaths {
            guard let status = mastodonController.persistentContainer.status(for: item(for: indexPath).id) else {
                continue
            }
            _ = ImageCache.avatars.get(status.account.avatar, completion: nil)
            for attachment in status.attachments where attachment.kind == .image {
                _ = ImageCache.attachments.get(attachment.url, completion: nil)
            }
        }
    }
    
    func tableView(_ tableView: UITableView, cancelPrefetchingForRowsAt indexPaths: [IndexPath]) {
        for indexPath in indexPaths {
            // todo: this means when removing cells, we can't cancel prefetching
            // is this an issue?
            guard indexPath.section < sections.count,
                  indexPath.row < sections[indexPath.section].count,
                  let status = mastodonController.persistentContainer.status(for: item(for: indexPath).id) else {
                continue
            }
            ImageCache.avatars.cancelWithoutCallback(status.account.avatar)
            for attachment in status.attachments where attachment.kind == .image {
                ImageCache.attachments.cancelWithoutCallback(attachment.url)
            }
        }
    }
}