Tusker/Tusker/Screens/Conversation/ConversationViewController.swift

//
//  ConversationViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 1/17/23.
//  Copyright © 2023 Shadowfacts. All rights reserved.
//

import UIKit
import Pachyderm

class ConversationViewController: UIViewController {
    
    weak var mastodonController: MastodonController!
    
    let mainStatusID: String
    let mainStatusState: CollapseState
    var statusIDToScrollToOnLoad: String {
        didSet {
            if case .displaying(let vc) = state {
                vc.statusIDToScrollToOnLoad = statusIDToScrollToOnLoad
            }
        }
    }
    var showStatusesAutomatically = false {
        didSet {
            if case .displaying(let vc) = state {
                vc.showStatusesAutomatically = showStatusesAutomatically
            }
        }
    }
    
    private var collapseBarButtonItem: UIBarButtonItem!
    
    private var state: State = .unloaded {
        didSet {
            switch oldValue {
            case .loading(let indicator):
                indicator.removeFromSuperview()
            case .displaying(let vc):
                vc.removeViewAndController()
            default:
                break
            }
            
            switch state {
            case .unloaded:
                break
            case .loading(let indicator):
                indicator.translatesAutoresizingMaskIntoConstraints = false
                view.addSubview(indicator)
                NSLayoutConstraint.activate([
                    indicator.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor),
                    indicator.centerYAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerYAnchor),
                ])
            case .displaying(let vc):
                embedChild(vc)
            case .notFound:
                showMainStatusNotFound()
            }
            
            updateVisibilityBarButtonItem()
        }
    }
    
    init(for mainStatusID: String, state mainStatusState: CollapseState, mastodonController: MastodonController) {
        self.mainStatusID = mainStatusID
        self.mainStatusState = mainStatusState
        self.statusIDToScrollToOnLoad = mainStatusID
        self.mastodonController = mastodonController
        
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        title = NSLocalizedString("Conversation", comment: "conversation screen title")

        view.backgroundColor = .secondarySystemBackground
        
        collapseBarButtonItem = UIBarButtonItem(image: UIImage(systemName: "eye.fill")!, style: .plain, target: self, action: #selector(toggleCollapseButtonPressed))
        updateVisibilityBarButtonItem()
        navigationItem.rightBarButtonItem = collapseBarButtonItem
        // disable transparent background when scroll to top because it looks weird when items earlier in the thread load in
        // (it remains transparent slightly too long, resulting in a flash of the content under the transparent bar)
        let appearance = UINavigationBarAppearance()
        appearance.configureWithDefaultBackground()
        navigationItem.scrollEdgeAppearance = appearance
    }
    
    private func updateVisibilityBarButtonItem() {
        switch state {
        case .loading(_), .displaying(_):
            collapseBarButtonItem.isEnabled = true
        default:
            collapseBarButtonItem.isEnabled = false
        }
        
        collapseBarButtonItem.isSelected = showStatusesAutomatically
        collapseBarButtonItem.accessibilityLabel = showStatusesAutomatically ? "Collapse All" : "Expand All"
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        Task {
            await loadMainStatus()
        }
    }
    
    // MARK: Loading
    
    private func loadMainStatus() async {
        @MainActor
        func doLoadMainStatus() async -> StatusMO? {
            switch await FetchStatusService(statusID: mainStatusID, mastodonController: mastodonController).run() {
            case .loaded(let status):
                return mastodonController.persistentContainer.addOrUpdateOnViewContext(status: status)
            case .notFound:
                state = .notFound
                showMainStatusNotFound()
                return nil
            case .error(let error):
                self.showMainStatusError(error)
                return nil
            }
        }
        
        
        if let cached = mastodonController.persistentContainer.status(for: mainStatusID) {
            // if we have a cached copy, display it immediately but still try to refresh it
            Task {
                await doLoadMainStatus()
            }
            await mainStatusLoaded(cached)
        } else {
            // otherwise, show a loading indicator while loading the main status
            let indicator = UIActivityIndicatorView(style: .medium)
            indicator.startAnimating()
            state = .loading(indicator)
            
            if let status = await doLoadMainStatus() {
                await mainStatusLoaded(status)
            }
        }
    }
    
    @MainActor
    private func mainStatusLoaded(_ mainStatus: StatusMO) async {
        let vc = ConversationTableViewController(for: mainStatusID, state: mainStatusState, mastodonController: mastodonController)
        vc.statusIDToScrollToOnLoad = statusIDToScrollToOnLoad
        vc.showStatusesAutomatically = showStatusesAutomatically
        vc.addMainStatus(mainStatus)
        state = .displaying(vc)
        
        await loadContext(for: mainStatus)
    }
    
    @MainActor
    private func loadContext(for mainStatus: StatusMO) async {
        guard case .displaying(_) = state else {
            return
        }
        
        let request = Status.getContext(mainStatus.id)
        do {
            let (context, _) = try await mastodonController.run(request)
            guard case .displaying(let vc) = state else {
                return
            }
            
            await vc.addContext(context, for: mainStatus)
        } catch {
            guard case .displaying(_) = state else {
                return
            }
            let error = error as! Client.Error
            
            let config = ToastConfiguration(from: error, with: "Error Loading Context", in: self) { [weak self] toast in
                toast.dismissToast(animated: true)
                await self?.loadContext(for: mainStatus)
            }
            self.showToast(configuration: config, animated: true)
        }
    }
    
    private func showMainStatusNotFound() {
        let emoji = UILabel()
        emoji.font = .systemFont(ofSize: 64)
        emoji.text = "🤷"
        
        let title = UILabel()
        title.textColor = .secondaryLabel
        title.font = .preferredFont(forTextStyle: .title1).withTraits(.traitBold)!
        title.adjustsFontForContentSizeCategory = true
        title.text = "Not Found"
        
        let subtitle = UILabel()
        subtitle.textColor = .secondaryLabel
        subtitle.font = .preferredFont(forTextStyle: .body)
        subtitle.adjustsFontForContentSizeCategory = true
        subtitle.text = "The post you are looking for may have been deleted, or may not be visible to you."
        subtitle.numberOfLines = 0
        subtitle.textAlignment = .center
        
        let stack = UIStackView(arrangedSubviews: [
            emoji,
            title,
            subtitle,
        ])
        stack.axis = .vertical
        stack.alignment = .center
        stack.spacing = 8
        stack.isAccessibilityElement = true
        stack.accessibilityLabel = "\(title.text!). \(subtitle.text!)"
        
        stack.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(stack)
        NSLayoutConstraint.activate([
            stack.leadingAnchor.constraint(equalToSystemSpacingAfter: view.safeAreaLayoutGuide.leadingAnchor, multiplier: 1),
            view.safeAreaLayoutGuide.trailingAnchor.constraint(equalToSystemSpacingAfter: stack.trailingAnchor, multiplier: 1),
            stack.centerYAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerYAnchor),
        ])
    }
    
    private func showMainStatusError(_ error: Client.Error) {
        let config = ToastConfiguration(from: error, with: "Error Loading Status", in: self) { [weak self] toast in
            toast.dismissToast(animated: true)
            await self?.loadMainStatus()
        }
        self.showToast(configuration: config, animated: true)
    }
    
    // MARK: Interaction
    
    @objc func toggleCollapseButtonPressed() {
        guard case .displaying(let vc) = state else {
            return
        }
        showStatusesAutomatically = !showStatusesAutomatically
        vc.updateVisibleCellCollapseState()
        updateVisibilityBarButtonItem()
    }

}

extension ConversationViewController {
    enum State {
        case unloaded
        case loading(UIActivityIndicatorView)
        case displaying(ConversationTableViewController)
        case notFound
    }
}

extension ConversationViewController: ToastableViewController {
}