Tusker/Tusker/Screens/Profile/ProfileViewController.swift

//
//  ProfileViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 7/3/20.
//  Copyright © 2020 Shadowfacts. All rights reserved.
//

import UIKit
import Pachyderm
import Combine

class ProfileViewController: UIPageViewController {
    
    weak var mastodonController: MastodonController!
    
    // This property is optional because MyProfileViewController may not have the user's account ID
    // when first constructed. It should never be set to nil.
    var accountID: String? {
        willSet {
            if newValue == nil {
                fatalError("Do not set ProfileViewController.accountID to nil")
            }
        }
        didSet {
            pageControllers.forEach { $0.accountID = accountID }
            loadAccount()
        }
    }
    
    private var accountUpdater: Cancellable?
    
    private(set) var currentIndex: Int!
    let pageControllers: [ProfileStatusesViewController]
    var currentViewController: ProfileStatusesViewController {
        pageControllers[currentIndex]
    }
    
    private var headerView: ProfileHeaderView!
    
    private var hasAppeared = false
    
    init(accountID: String?, mastodonController: MastodonController) {
        self.accountID = accountID
        self.mastodonController = mastodonController
        
        self.pageControllers = [
            ProfileStatusesViewController(accountID: accountID, kind: .statuses, mastodonController: mastodonController),
            ProfileStatusesViewController(accountID: accountID, kind: .withReplies, mastodonController: mastodonController),
            ProfileStatusesViewController(accountID: accountID, kind: .onlyMedia, mastodonController: mastodonController)
        ]
        
        super.init(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    deinit {
        if let accountID = accountID {
            mastodonController.persistentContainer.account(for: accountID)?.decrementReferenceCount()
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = .systemBackground

        let composeButton = UIBarButtonItem(barButtonSystemItem: .compose, target: self, action: #selector(composeMentioning))
        if #available(iOS 14.0, *) {
            composeButton.menu = UIMenu(title: "", image: nil, identifier: nil, options: [], children: [
                UIAction(title: "Direct Message", image: UIImage(systemName: Status.Visibility.direct.unfilledImageName), identifier: nil, discoverabilityTitle: nil, attributes: [], state: .off, handler: { (_) in
                    self.composeDirectMentioning()
                })
            ])
        }
        navigationItem.rightBarButtonItem = composeButton
        
        headerView = ProfileHeaderView.create()
        headerView.delegate = self

        selectPage(at: 0, animated: false)
        
        currentViewController.tableView.tableHeaderView = headerView
        
        NSLayoutConstraint.activate([
            headerView.widthAnchor.constraint(equalTo: view.widthAnchor),
        ])
        
        accountUpdater = mastodonController.persistentContainer.accountSubject
            .filter { [weak self] in $0 == self?.accountID }
            .receive(on: DispatchQueue.main)
            .sink { [weak self] (_) in self?.updateAccountUI() }
        
        loadAccount()
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        hasAppeared = true
    }
    
    private func loadAccount() {
        guard let accountID = accountID else { return }
        if mastodonController.persistentContainer.account(for: accountID) != nil {
            updateAccountUI()
        } else {
            let req = Client.getAccount(id: accountID)
            mastodonController.run(req) { [weak self] (response) in
                guard let self = self else { return }
                guard case let .success(account, _) = response  else { fatalError() }
                self.mastodonController.persistentContainer.addOrUpdate(account: account, incrementReferenceCount: true) { (account) in
                    DispatchQueue.main.async {
                        self.updateAccountUI()
                    }
                }
            }
        }
    }
    
    private func updateAccountUI() {
        guard let accountID = accountID,
              let account = mastodonController.persistentContainer.account(for: accountID) else {
            return
        }
        
        // Optionally invoke updateUI on headerView because viewDidLoad may not have been called yet
        headerView?.updateUI(for: accountID)
        navigationItem.title = account.displayNameWithoutCustomEmoji
        
        // Only call updateUI on the individual page controllers if the account is loaded after the profile VC has appeared on screen.
        // Otherwise, fi the page view controllers do something with the table view before they appear, the table view doesn't load
        // its cells until the user begins to scroll.
        if hasAppeared {
            pageControllers.forEach {
                $0.updateUI(account: account)
            }
        }
    }
    
    private func selectPage(at index: Int, animated: Bool, completion: ((Bool) -> Void)? = nil) {
        let direction: UIPageViewController.NavigationDirection = currentIndex == nil || index - currentIndex > 0 ? .forward : .reverse
        currentIndex = index
        
        guard let old = viewControllers?.first as? ProfileStatusesViewController else {
            // if old doesn't exist, we're selecting the initial view controller, so moving the header around isn't necessary
            // since it will be added in viewDidLoad
            setViewControllers([pageControllers[index]], direction: direction, animated: animated, completion: completion)
            return
        }
        let new = pageControllers[index]
        
        let headerHeight = self.headerView.bounds.height
        
        // Store old's content offset so it can be transferred to new
        let prevOldContentOffset = old.tableView.contentOffset
        // Remove the header, inset the table content by the same amount, and adjust the offset so the cells don't move
        old.tableView.tableHeaderView = nil
        old.tableView.contentInset = UIEdgeInsets(top: headerHeight, left: 0, bottom: 0, right: 0)
        old.tableView.contentOffset.y -= headerHeight
        
        // Add the header to ourself temporarily, and constrain it to the same position it was in
        self.view.addSubview(self.headerView)
        let tempTopConstraint = self.headerView.topAnchor.constraint(equalTo: self.view.topAnchor, constant: -(prevOldContentOffset.y + old.tableView.safeAreaInsets.top))
        NSLayoutConstraint.activate([
            self.headerView.widthAnchor.constraint(equalTo: self.view.widthAnchor),
            tempTopConstraint
        ])
        
        // Setup the inset in new, in case it hasn't been already
        new.tableView.contentInset = UIEdgeInsets(top: headerHeight, left: 0, bottom: 0, right: 0)
        // Match the scroll positions
        new.tableView.contentOffset = old.tableView.contentOffset
        
        // Actually switch pages
        setViewControllers([pageControllers[index]], direction: direction, animated: animated) { (finished) in
            // Defer everything one run-loop iteration, otherwise altering the tableView's contentInset/Offset causes it to jump around during the animation
            DispatchQueue.main.async {
                // Move the header to the new table view
                new.tableView.tableHeaderView = self.headerView
                // Remove the inset, and set the offset back to old's original one, prior to removing the header
                new.tableView.contentInset = .zero
                new.tableView.contentOffset = prevOldContentOffset
        
                // Deactivate the top constraint, otherwise it sticks around
                tempTopConstraint.isActive = false
                // Re-add the width constraint since it was removed by re-parenting the view
                // Why was the width constraint removed, but the top one not? Good question, I have no idea.
                NSLayoutConstraint.activate([
                    self.headerView.widthAnchor.constraint(equalTo: self.view.widthAnchor)
                ])
                
                // Layout and update the table view, otherwise the content jumps around when first scrolling it,
                // if old was not scrolled all the way to the top
                new.tableView.layoutIfNeeded()
                UIView.performWithoutAnimation {
                    new.tableView.performBatchUpdates(nil, completion: nil)
                }
                
                completion?(finished)
            }
        }
    }
    
    // MARK: Interaction
    
    @objc private func composeMentioning() {
        if let accountID = accountID,
           let account = mastodonController.persistentContainer.account(for: accountID) {
            compose(mentioningAcct: account.acct)
        }
    }
    
    private func composeDirectMentioning() {
        if let accountID = accountID,
           let account = mastodonController.persistentContainer.account(for: accountID) {
            let draft = mastodonController.createDraft(mentioningAcct: account.acct)
            draft.visibility = .direct
            compose(editing: draft)
        }
    }

}

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

extension ProfileViewController: ProfileHeaderViewDelegate {
    func profileHeader(_ view: ProfileHeaderView, selectedPostsIndexChangedTo newIndex: Int) {
        // disable user interaction on segmented control while switching pages to prevent
        // race condition from trying to switch to multiple pages simultaneously
        view.pagesSegmentedControl.isUserInteractionEnabled = false
        selectPage(at: newIndex, animated: true) { (finished) in
            view.pagesSegmentedControl.isUserInteractionEnabled = true
        }
    }
    
    func profileHeader(_ view: ProfileHeaderView, showMoreOptionsFor accountID: String, sourceView: UIView) {
        let account = mastodonController.persistentContainer.account(for: accountID)!
        
        func showActivityController(activities: [UIActivity]) {
            let activityController = UIActivityViewController(activityItems: [account.url, AccountActivityItemSource(account)], applicationActivities: activities)
            activityController.completionWithItemsHandler = OpenInSafariActivity.completionHandler(navigator: self, url: account.url)
            activityController.popoverPresentationController?.sourceView = sourceView
            self.present(activityController, animated: true)
        }
        
        if account.id == mastodonController.account.id {
            showActivityController(activities: [OpenInSafariActivity()])
        } else {
            let request = Client.getRelationships(accounts: [account.id])
            mastodonController.run(request) { (response) in
                var customActivities: [UIActivity] = [OpenInSafariActivity()]
                if case let .success(results, _) = response, let relationship = results.first {
                    let toggleFollowActivity = relationship.following ? UnfollowAccountActivity() : FollowAccountActivity()
                    customActivities.insert(toggleFollowActivity, at: 0)
                }
                
                DispatchQueue.main.async {
                    showActivityController(activities: customActivities)
                }
            }
        }
    }
}

extension ProfileViewController: TabBarScrollableViewController {
    func tabBarScrollToTop() {
        pageControllers[currentIndex].tabBarScrollToTop()
    }
}