//
//  HomeViewController.swift
//  Reader
//
//  Created by Shadowfacts on 11/25/21.
//

import UIKit
import CoreData
import Combine
import Persistence

protocol HomeViewControllerDelegate: AnyObject {
    func switchToAccount(_ account: LocalData.Account)
}

class HomeViewController: UIViewController {
    
    weak var delegate: HomeViewControllerDelegate?
    weak var itemsDelegate: ItemsViewControllerDelegate?
    
    let fervorController: FervorController
    
    var enableStretchyMenu = true
    
    private var collectionView: UICollectionView!
    private var dataSource: UICollectionViewDiffableDataSource<Section, ItemListType>!
    private var groupResultsController: NSFetchedResultsController<Group>!
    private var feedResultsController: NSFetchedResultsController<Feed>!
    
    private var lastSyncState = FervorController.SyncState.done
    // weak so that when it's removed from the superview, this becomes nil
    private weak var syncStateView: SyncStateView?
    private var cancellables = Set<AnyCancellable>()
    
    init(fervorController: FervorController) {
        self.fervorController = fervorController
        
        super.init(nibName: nil, bundle: nil)
        
        fervorController.syncState
            .buffer(size: 25, prefetch: .byRequest, whenFull: .dropOldest)
            .receive(on: RunLoop.main)
            .sink { [unowned self] in
                self.syncStateChanged($0)
            }
            .store(in: &cancellables)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // todo: account info
        title = "Reader"
        
        if enableStretchyMenu {
            view.addInteraction(StretchyMenuInteraction(delegate: self))
        }
        
        if UIDevice.current.userInterfaceIdiom != .mac {
            view.backgroundColor = .appBackground
        }
        
        var config = UICollectionLayoutListConfiguration(appearance: UIDevice.current.userInterfaceIdiom == .mac ? .sidebar : .grouped)
        config.headerMode = .supplementary
        config.backgroundColor = .clear
        config.separatorConfiguration.topSeparatorVisibility = .visible
        config.separatorConfiguration.topSeparatorInsets = NSDirectionalEdgeInsets(top: 0, leading: 20, bottom: 0, trailing: 0)
        config.separatorConfiguration.bottomSeparatorVisibility = .hidden
        config.itemSeparatorHandler = { indexPath, defaultConfig in
            var config = defaultConfig
            if indexPath.section == 0 && indexPath.row == 0 {
                config.topSeparatorVisibility = .hidden
            }
            return config
        }
        let layout = UICollectionViewCompositionalLayout.list(using: config)
        collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
        collectionView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        collectionView.delegate = self
        view.addSubview(collectionView)
        
        dataSource = createDataSource()
        
        var snapshot = NSDiffableDataSourceSnapshot<Section, ItemListType>()
        snapshot.appendSections([.all, .groups, .feeds])
        snapshot.appendItems([.unread, .all], toSection: .all)
        dataSource.apply(snapshot, animatingDifferences: false)
        
        let groupReq = Group.fetchRequest()
        groupReq.sortDescriptors = [NSSortDescriptor(key: "title", ascending: true)]
        groupResultsController = NSFetchedResultsController(fetchRequest: groupReq, managedObjectContext: fervorController.persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil)
        groupResultsController.delegate = self
        try! groupResultsController.performFetch()
        
        let feedReq = Feed.fetchRequest()
        feedReq.sortDescriptors = [NSSortDescriptor(key: "title", ascending: true)]
        feedResultsController = NSFetchedResultsController(fetchRequest: feedReq, managedObjectContext: fervorController.persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil)
        feedResultsController.delegate = self
        try! feedResultsController.performFetch()
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        if let indexPaths = collectionView.indexPathsForSelectedItems {
            for indexPath in indexPaths {
                collectionView.deselectItem(at: indexPath, animated: true)
            }
        }
        
        var snapshot = dataSource.snapshot()
        // reconfigure so that unread counts update
        snapshot.reconfigureItems(snapshot.itemIdentifiers)
        dataSource.apply(snapshot)
    }
    
    private func createDataSource() -> UICollectionViewDiffableDataSource<Section, ItemListType> {
        let sectionHeaderCell = UICollectionView.SupplementaryRegistration<UICollectionViewListCell>(elementKind: UICollectionView.elementKindSectionHeader) { supplementaryView, elementKind, indexPath in
            let section = self.dataSource.sectionIdentifier(for: indexPath.section)!
            var config = supplementaryView.defaultContentConfiguration()
            config.text = section.title
            supplementaryView.contentConfiguration = config
        }
        let listCell = UICollectionView.CellRegistration<HomeCollectionViewCell, ItemListType> { cell, indexPath, item in
            var config = UIListContentConfiguration.valueCell()
            config.text = item.title
            if let req = item.countFetchRequest,
               let count = try? self.fervorController.persistentContainer.viewContext.count(for: req) {
                config.secondaryText = "\(count)"
                config.secondaryTextProperties.color = .tintColor
            }
            cell.contentConfiguration = config
            
            cell.accessories = [.disclosureIndicator()]
        }
        let dataSource = UICollectionViewDiffableDataSource<Section, ItemListType>(collectionView: collectionView) { collectionView, indexPath, item in
            return collectionView.dequeueConfiguredReusableCell(using: listCell, for: indexPath, item: item)
        }
        dataSource.supplementaryViewProvider = { collectionView, elementKind, indexPath in
            if elementKind == UICollectionView.elementKindSectionHeader {
                return collectionView.dequeueConfiguredReusableSupplementary(using: sectionHeaderCell, for: indexPath)
            } else {
                return nil
            }
        }
        return dataSource
    }
    
    private func syncStateChanged(_ newState: FervorController.SyncState) {
        if case .done = newState {
            // update unread counts for visible items
            var snapshot = dataSource.snapshot()
            snapshot.reconfigureItems(snapshot.itemIdentifiers)
            dataSource.apply(snapshot, animatingDifferences: false)
            
            if syncStateView == nil {
                // no sync state view, nothing further to update
                return
            }
        }
        
        func updateView(_ syncStateView: SyncStateView, isFirstUpdate: Bool) {
            switch newState {
            case .groupsAndFeeds:
                syncStateView.label.text = "Syncing groups and feeds"
            case .items:
                syncStateView.label.text = "Syncing items"
            case .updateItems(current: let current, total: let total):
                syncStateView.label.text = "Updating \(current + 1) of \(total) item\(total == 1 ? "" : "s")"
            case .excerpts(current: let current, total: let total):
                syncStateView.label.text = "Generating \(current) of \(total) excerpt\(total == 1 ? "" : "s")"
            case .error(let error):
                syncStateView.label.text = "Error syncing"
                syncStateView.subtitleLabel.isHidden = false
                syncStateView.subtitleLabel.text = error.localizedDescription
                
                syncStateView.removeAfterDelay(delay: isFirstUpdate ? 2 : 1)
                
            case .done:
                syncStateView.label.text = "Done syncing"

                syncStateView.removeAfterDelay(delay: isFirstUpdate ? 2 : 1)
            }
        }
        
        if let syncStateView = self.syncStateView {
            updateView(syncStateView, isFirstUpdate: false)
        } else {
            let syncStateView = SyncStateView()
            self.syncStateView = syncStateView
            syncStateView.translatesAutoresizingMaskIntoConstraints = false
            view.addSubview(syncStateView)
            NSLayoutConstraint.activate([
                syncStateView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
                syncStateView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
                syncStateView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            ])
            
            updateView(syncStateView, isFirstUpdate: true)
            
            view.layoutIfNeeded()
            syncStateView.transform = CGAffineTransform(translationX: 0, y: syncStateView.bounds.height)
           
            UIView.animate(withDuration: 0.25, delay: 0, options: .curveEaseOut) {
                syncStateView.transform = .identity
            }
        }
    }
    
    private func itemsViewController(for item: ItemListType) -> ItemsViewController {
        let vc = ItemsViewController(type: item, fervorController: fervorController)
        vc.delegate = itemsDelegate
        return vc
    }
    
    func selectItem(_ item: ItemListType) {
        guard let navigationController = navigationController else {
            return
        }
        if navigationController.viewControllers.count >= 2,
           let second = navigationController.viewControllers[1] as? ItemsViewController,
           second.type == item {
            while navigationController.viewControllers.count > 2 {
                navigationController.popViewController(animated: false)
            }
        } else {
            navigationController.popToRootViewController(animated: false)
            navigationController.pushViewController(itemsViewController(for: item), animated: false)
        }
    }
    
}

extension HomeViewController {
    enum Section: Hashable {
        case all
        case groups
        case feeds
        
        var title: String {
            switch self {
            case .all:
                return ""
            case .groups:
                return "Groups"
            case .feeds:
                return "Feeds"
            }
        }
    }
}

extension HomeViewController: NSFetchedResultsControllerDelegate {
    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith snapshot: NSDiffableDataSourceSnapshotReference) {
        var snapshot = dataSource.snapshot()
        if controller == groupResultsController {
            if snapshot.sectionIdentifiers.contains(.groups) {
                snapshot.deleteItems(snapshot.itemIdentifiers(inSection: .groups))
            }
            snapshot.appendItems(controller.fetchedObjects!.map { .group($0 as! Group) }, toSection: .groups)
        } else if controller == feedResultsController {
            if snapshot.sectionIdentifiers.contains(.feeds) {
                snapshot.deleteItems(snapshot.itemIdentifiers(inSection: .feeds))
            }
            snapshot.appendItems(controller.fetchedObjects!.map { .feed($0 as! Feed) }, toSection: .feeds)
        }
        dataSource.apply(snapshot, animatingDifferences: false)
    }
}

extension HomeViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        guard let item = dataSource.itemIdentifier(for: indexPath) else {
            return
        }
        show(itemsViewController(for: item), sender: nil)
        UISelectionFeedbackGenerator().selectionChanged()
    }
    
    func collectionView(_ collectionView: UICollectionView, contextMenuConfigurationForItemAt indexPath: IndexPath, point: CGPoint) -> UIContextMenuConfiguration? {
        guard let item = dataSource.itemIdentifier(for: indexPath) else {
            return nil
        }
        return UIContextMenuConfiguration(identifier: nil, previewProvider: { [unowned self] in
            return self.itemsViewController(for: item)
        }, actionProvider: nil)
    }
    
    func collectionView(_ collectionView: UICollectionView, willPerformPreviewActionForMenuWith configuration: UIContextMenuConfiguration, animator: UIContextMenuInteractionCommitAnimating) {
        guard let vc = animator.previewViewController else {
            return
        }
        animator.preferredCommitStyle = .pop
        animator.addCompletion {
            self.show(vc, sender: nil)
        }
    }
}

extension HomeViewController: StretchyMenuInteractionDelegate {
    func stretchyMenuTitle() -> String? {
        return "Switch Accounts"
    }
    func stretchyMenuItems() -> [StretchyMenuItem] {
        var items: [StretchyMenuItem] = LocalData.accounts.map { account in
            var title = account.instanceURL.host!
            if let port = account.instanceURL.port, port != 80 && port != 443 {
                title += ":\(port)"
            }
            let subtitle = account.id == fervorController.account!.id ? "Currently logged in" : nil
            return StretchyMenuItem(title: title, subtitle: subtitle) { [unowned self] in
                guard account.id != self.fervorController.account!.id else { return }
                self.delegate?.switchToAccount(account)
            }
        }
        items.append(StretchyMenuItem(title: "Add Account", subtitle: nil, action: { [unowned self] in
            let login = LoginViewController()
            login.delegate = self
            login.navigationItem.leftBarButtonItem = UIBarButtonItem(systemItem: .cancel, primaryAction: UIAction(handler: { (_) in
                self.dismiss(animated: true)
            }), menu: nil)
            let nav = UINavigationController(rootViewController: login)
            self.present(nav, animated: true)
        }))
        return items
    }
}

extension HomeViewController: LoginViewControllerDelegate {
    func didLogin(with controller: FervorController) {
        self.dismiss(animated: true)
        (view.window!.windowScene!.delegate as! SceneDelegate).didLogin(with: controller)
    }
}

private class SyncStateView: UIView {
    let label = UILabel()
    let subtitleLabel = UILabel()
    
    init() {
        super.init(frame: .zero)
        
        let blur = UIBlurEffect(style: .regular)
        let blurView = UIVisualEffectView(effect: blur)
        blurView.translatesAutoresizingMaskIntoConstraints = false
        addSubview(blurView)
        
        label.font = .preferredFont(forTextStyle: .callout)
        subtitleLabel.font = .preferredFont(forTextStyle: .caption1)
        subtitleLabel.isHidden = true
        subtitleLabel.numberOfLines = 2
        
        let stack = UIStackView(arrangedSubviews: [
            label,
            subtitleLabel,
        ])
        stack.translatesAutoresizingMaskIntoConstraints = false
        stack.axis = .vertical
        stack.alignment = .center
        stack.spacing = 4
        addSubview(stack)
        
        NSLayoutConstraint.activate([
            blurView.leadingAnchor.constraint(equalTo: leadingAnchor),
            blurView.trailingAnchor.constraint(equalTo: trailingAnchor),
            blurView.topAnchor.constraint(equalTo: topAnchor),
            blurView.bottomAnchor.constraint(equalTo: bottomAnchor),
            
            stack.centerXAnchor.constraint(equalTo: safeAreaLayoutGuide.centerXAnchor),
            stack.topAnchor.constraint(greaterThanOrEqualToSystemSpacingBelow: safeAreaLayoutGuide.topAnchor, multiplier: 1),
            stack.bottomAnchor.constraint(lessThanOrEqualToSystemSpacingBelow: safeAreaLayoutGuide.bottomAnchor, multiplier: 1),
            stack.centerYAnchor.constraint(equalTo: safeAreaLayoutGuide.centerYAnchor),
            
            topAnchor.constraint(lessThanOrEqualTo: safeAreaLayoutGuide.bottomAnchor, constant: -50),
        ])
        
        layer.shadowColor = UIColor.black.cgColor
        layer.shadowOpacity = 0.1
        layer.shadowRadius = 10
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    func removeAfterDelay(delay: Int) {
        // can't use UIView.animate's delay b/c it may clash with the appearance animation
        DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(delay)) {
            UIView.animate(withDuration: 0.25, delay: 0, options: .curveEaseIn) {
                self.transform = CGAffineTransform(translationX: 0, y: self.bounds.height)
            } completion: { _ in
                self.removeFromSuperview()
            }
        }
    }
}