//
//  FeedDetailViewController.swift
//  NewsBlur
//
//  Created by David Sinclair on 2020-08-27.
//  Copyright © 2020 NewsBlur. All rights reserved.
//

import UIKit
import SwiftUI

/// List of stories for a feed.
class FeedDetailViewController: FeedDetailObjCViewController {
    lazy var gridViewController = makeGridViewController()
    
    lazy var storyCache = StoryCache()
    
    enum SectionLayoutKind: Int, CaseIterable {
        /// Feed cells before the story.
        case feedBeforeStory
        
        /// The selected story.
        case selectedStory
        
        /// Feed cells after the story.
        case feedAfterStory
        
        /// Loading cell at the end.
        case loading
    }
    
    var isGrid: Bool {
        return appDelegate.detailViewController.layout == .grid
    }
    
    var feedColumns: Int {
        guard let pref = UserDefaults.standard.string(forKey: "grid_columns"), let columns = Int(pref) else {
            return 4
        }
        
        return columns
    }
    
    var gridHeight: CGFloat {
        guard let pref = UserDefaults.standard.string(forKey: "grid_height") else {
            return 400
        }
        
        switch pref {
        case "xs":
            return 250
        case "short":
            return 300
        case "tall":
            return 400
        case "xl":
            return 450
        default:
            return 350
        }
    }
    
//    var storyHeight: CGFloat {
//        if let pagesController = appDelegate.storyPagesViewController, let webView = pagesController.currentPage.webView {
//            let frame = pagesController.view.frame
//
//            print("Story pages frame: \(pagesController.view.frame), web height \(webView.scrollView.contentSize.height)")
//
//            pagesController.view.frame = CGRect(x: frame.origin.x, y: frame.origin.y, width: frame.size.width, height: 500)
//            pagesController.currentPage.view.frame = CGRect(x: frame.origin.x, y: frame.origin.y, width: frame.size.width, height: 500)
//            pagesController.view.layoutIfNeeded()
//
//            let height = webView.scrollView.contentSize.height + 50
//
//            print("... frame now: \(pagesController.view.frame), height: \(height)")
//
//            return height
//        } else {
//            return 1000
//        }
//    }
    
    var dataSource: UICollectionViewDiffableDataSource<SectionLayoutKind, Int>! = nil
    
    private func makeGridViewController() -> UIHostingController<FeedDetailGridView> {
//        let headerView = FeedDetailGridView(isGrid: isGrid, storyCache: storyCache)
        let gridView = FeedDetailGridView(feedDetailInteraction: self, cache: storyCache)
        let gridViewController = UIHostingController(rootView: gridView)
        gridViewController.view.translatesAutoresizingMaskIntoConstraints = false
        
        return gridViewController
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        changedLayout()
        configureDataSource()
        
        feedCollectionView.isHidden = true
        
        addChild(gridViewController)
        view.addSubview(gridViewController.view)
        gridViewController.didMove(toParent: self)
        
        NSLayoutConstraint.activate([
            gridViewController.view.topAnchor.constraint(equalTo: view.topAnchor),
            gridViewController.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            gridViewController.view.widthAnchor.constraint(equalTo: view.widthAnchor),
            gridViewController.view.heightAnchor.constraint(equalTo: view.heightAnchor)
        ])
    }
    
//    @objc override func changedStoryHeight(_ storyHeight: CGFloat) {
//        guard isGrid else {
//            return
//        }
//        
//        self.storyHeight = storyHeight
//        
//        changedLayout()
//    }
    
    @objc override func changedLayout() {
//        if isGrid {
//            feedCollectionView.collectionViewLayout = createGridLayout()
//        } else {
//            feedCollectionView.collectionViewLayout = createListLayout()
//        }
//
//        feedCollectionView.setNeedsLayout()
        
        deferredReload()
    }
    
    var reloadWorkItem: DispatchWorkItem?
    
    func deferredReload() {
        reloadWorkItem?.cancel()
        
        let workItem = DispatchWorkItem { [weak self] in
            guard let self else {
                return
            }
            
            self.configureDataSource()
        }
        
        reloadWorkItem = workItem
        DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(100), execute: workItem)
    }
    
    @objc override func reload() {
        deferredReload()
    }
    
    @objc override func reload(_ indexPath: IndexPath) {
        deferredReload()
    }
}

extension FeedDetailViewController {
//    func accessoriesForListCellItem(_ item: Int) -> [UICellAccessory] {
//        let isStarred = false //self.starredEmojis.contains(item)
//        var accessories = [UICellAccessory.disclosureIndicator()]
//        if isStarred {
//            let star = UIImageView(image: UIImage(systemName: "star.fill"))
//            accessories.append(.customView(configuration: .init(customView: star, placement: .trailing())))
//        }
//        return accessories
//    }
    
//    func leadingSwipeActionConfigurationForListCellItem(_ item: Int) -> UISwipeActionsConfiguration? {
//        let isStarred = false //self.starredEmojis.contains(item)
//        let starAction = UIContextualAction(style: .normal, title: nil) {
//            [weak self] (_, _, completion) in
//            guard let self = self else {
//                completion(false)
//                return
//            }
//
//            // Don't check again for the starred state. We promised in the UI what this action will do.
//            // If the starred state has changed by now, we do nothing, as the set will not change.
////            if isStarred {
////                self.starredEmojis.remove(item)
////            } else {
////                self.starredEmojis.insert(item)
////            }
//
//            // Reconfigure the cell of this item
//            // Make sure we get the current index path of the item.
//            if let currentIndexPath = self.dataSource.indexPath(for: item) {
//                if let cell = self.feedCollectionView.cellForItem(at: currentIndexPath) as? UICollectionViewListCell {
//                    UIView.animate(withDuration: 0.2) {
//                        cell.accessories = self.accessoriesForListCellItem(item)
//                    }
//                }
//            }
//
//            completion(true)
//        }
//        starAction.image = UIImage(systemName: isStarred ? "star.slash" : "star.fill")
//        starAction.backgroundColor = .systemBlue
//        return UISwipeActionsConfiguration(actions: [starAction])
//    }
    
    func createListLayout() -> UICollectionViewLayout {
//        let size = NSCollectionLayoutSize(
//            widthDimension: NSCollectionLayoutDimension.fractionalWidth(1),
//            heightDimension: NSCollectionLayoutDimension.estimated(200)
//        )
//        let item = NSCollectionLayoutItem(layoutSize: size)
//        let group = NSCollectionLayoutGroup.horizontal(layoutSize: size, subitem: item, count: 1)
//
//        let section = NSCollectionLayoutSection(group: group)
//        section.interGroupSpacing = 0
//
//        return UICollectionViewCompositionalLayout(section: section)
        
        
        
        var configuration = UICollectionLayoutListConfiguration(appearance: .plain)
        
//        configuration.leadingSwipeActionsConfigurationProvider = { [weak self] (indexPath) in
//            guard let self else { return nil }
//            guard let item = self.dataSource.itemIdentifier(for: indexPath) else { return nil }
//            return self.leadingSwipeActionConfigurationForListCellItem(item)
//        }
        
        return UICollectionViewCompositionalLayout.list(using: configuration)
    }
    
    func createGridLayout() -> UICollectionViewLayout {
        let layout = UICollectionViewCompositionalLayout { (sectionIndex: Int,
                                                            layoutEnvironment: NSCollectionLayoutEnvironment) -> NSCollectionLayoutSection? in
            
            guard let sectionLayoutKind = SectionLayoutKind(rawValue: sectionIndex) else {
                return nil
            }
            
            let isStory = sectionLayoutKind == .selectedStory
            let isLoading = sectionLayoutKind == .loading
            let columns = isStory || isLoading ? 1 : self.feedColumns
            
            let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0),
                                                  heightDimension: .fractionalHeight(1.0))
            let item = NSCollectionLayoutItem(layoutSize: itemSize)
            item.contentInsets = NSDirectionalEdgeInsets(top: 10, leading: 10, bottom: 10, trailing: 10)
            
            let groupHeight = isStory ? NSCollectionLayoutDimension.absolute(self.storyHeight) : isLoading ? NSCollectionLayoutDimension.absolute(100) : NSCollectionLayoutDimension.absolute(self.gridHeight)
            let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0),
                                                   heightDimension: groupHeight)
            let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitem: item, count: columns)
            
            let section = NSCollectionLayoutSection(group: group)
            section.contentInsets = NSDirectionalEdgeInsets(top: 10, leading: 10, bottom: 0, trailing: 10)
            
            return section
        }
        
        return layout
    }
}

extension FeedDetailViewController {
    func configureDataSource() {
        storyCache.reload()
        
        
//        let feedCellRegistration = UICollectionView.CellRegistration<FeedDetailCollectionCell, Int> { (cell, indexPath, identifier) in
//
////            cell.frame.size.height = self.heightForRow(at: indexPath)
//
//            self.prepareFeedCell(cell, indexPath: indexPath)
//            cell.setNeedsUpdateConfiguration()
//        }
//
//        let storyCellRegistration = UICollectionView.CellRegistration<StoryPagesCollectionCell, Int> { (cell, indexPath, identifier) in
//            self.prepareStoryCell(cell, indexPath: indexPath)
//            cell.setNeedsUpdateConfiguration()
//        }
//
//        let loadingCellRegistration = UICollectionView.CellRegistration<UICollectionViewCell, Int> { (cell, indexPath, identifier) in
//            self.prepareLoading(cell, indexPath: indexPath)
//            cell.setNeedsUpdateConfiguration()
//        }
//
//        dataSource = UICollectionViewDiffableDataSource<SectionLayoutKind, Int>(collectionView: feedCollectionView) {
//            (collectionView: UICollectionView, indexPath: IndexPath, identifier: Int) -> UICollectionViewCell? in
//            guard let sectionKind = SectionLayoutKind(rawValue: indexPath.section) else {
//                return nil
//            }
//
//            switch sectionKind {
//            case .feedBeforeStory, .feedAfterStory:
//                return collectionView.dequeueConfiguredReusableCell(using: feedCellRegistration, for: indexPath, item: identifier)
//            case .selectedStory:
//                if self.isGrid {
//                    return collectionView.dequeueConfiguredReusableCell(using: storyCellRegistration, for: indexPath, item: identifier)
//                } else {
//                    return collectionView.dequeueConfiguredReusableCell(using: feedCellRegistration, for: indexPath, item: identifier)
//                }
//            case .loading:
//                return collectionView.dequeueConfiguredReusableCell(using: loadingCellRegistration, for: indexPath, item: identifier)
//            }
//        }
//
//        var snapshot = NSDiffableDataSourceSnapshot<SectionLayoutKind, Int>()
//
//        let storyCount = Int(appDelegate.storiesCollection.storyLocationsCount)
//        var beforeSelection = [Int]()
//        var selectedIndex = -999
//        var afterSelection = [Int]()
//
//        snapshot.appendSections(SectionLayoutKind.allCases)
//
//        if self.messageView.isHidden {
//            if storyCount > 0 {
//                selectedIndex = appDelegate.storiesCollection.indexOfActiveStory()
//
//                if selectedIndex < 0 {
//                    beforeSelection = Array(0..<storyCount)
//                    snapshot.appendItems(beforeSelection, toSection: .feedBeforeStory)
//                } else {
//                    beforeSelection = Array(0..<selectedIndex)
//
//                    snapshot.appendItems(beforeSelection, toSection: .feedBeforeStory)
//                    snapshot.appendItems([selectedIndex], toSection: .selectedStory)
//
//                    if selectedIndex + 1 < storyCount {
//                        afterSelection = Array(selectedIndex + 1..<storyCount)
//                        snapshot.appendItems(afterSelection, toSection: .feedAfterStory)
//                    }
//                }
//            }
//
//            snapshot.appendItems([-1], toSection: .loading)
//
//            print("✨ configureDataSource selectedIndex: \(selectedIndex)")
//
//            //TODO: 🚧 move the above logic into StoryCache
//            storyCache.appendStories(beforeSelection: beforeSelection, selectedIndex: selectedIndex, afterSelection: afterSelection)
//        }
//
//        dataSource.apply(snapshot, animatingDifferences: false)
    }
}

extension FeedDetailViewController: FeedDetailInteraction {
    func visible(story: Story) {
        print("\(story.title) appeared")
        
        if story.index >= storyCache.before.count + storyCache.after.count - 5 {
            if storiesCollection.isRiverView, storiesCollection.activeFolder != nil {
                fetchRiverPage(storiesCollection.feedPage + 1, withCallback: nil)
            } else {
                fetchFeedDetail(storiesCollection.feedPage + 1, withCallback: nil)
            }
        }
    }
    
    func tapped(story: Story) {
        print("tapped \(story.title)")
        
        let indexPath = IndexPath(row: story.index, section: 0)
        
        didSelectItem(at: indexPath)
    }
    
    func reading(story: Story) {
        print("reading \(story.title)")
    }
    
    func read(story: Story) {
        let dict = story.dictionary
        
        if storiesCollection.isStoryUnread(dict) {
            print("marking as read '\(story.title)'")
            
            storiesCollection.markStoryRead(dict)
            storiesCollection.syncStory(asRead: dict)
            
            story.load()
            
            deferredReload()
        }
    }
    
    func hid(story: Story) {
        print("hiding \(story.title)")
        
        appDelegate.activeStory = nil
        reload()
    }
}