//
//  SearchViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 6/24/20.
//  Copyright © 2020 Shadowfacts. All rights reserved.
//

import UIKit
import Pachyderm
import SafariServices
import WebURLFoundationExtras

class SearchViewController: UIViewController {

    weak var mastodonController: MastodonController!
    
    private var collectionView: UICollectionView!
    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
    
    var resultsController: SearchResultsViewController!
    var searchController: UISearchController!
    
    var searchControllerStatusOnAppearance: Bool? = nil
    
    init(mastodonController: MastodonController) {
        self.mastodonController = mastodonController
        
        super.init(nibName: nil, bundle: nil)
        
        title = NSLocalizedString("Explore", comment: "explore tab title")
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()

        let layout = UICollectionViewCompositionalLayout { [unowned self] sectionIndex, environment in
            let sectionIdentifier = self.dataSource.snapshot().sectionIdentifiers[sectionIndex]
            switch sectionIdentifier {
            case .trendingHashtags:
                var listConfig = UICollectionLayoutListConfiguration(appearance: .grouped)
                listConfig.headerMode = .supplementary
                return .list(using: listConfig, layoutEnvironment: environment)
                
            case .trendingLinks:
                let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1))
                let item = NSCollectionLayoutItem(layoutSize: itemSize)
                // todo: i really wish i could just say the height is automatic and let autolayout figure out what it needs to be
                // using .estimated(whatever) constrains the height to exactly whatever
                let groupSize = NSCollectionLayoutSize(widthDimension: .absolute(250), heightDimension: .estimated(280))
                let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item])
                group.edgeSpacing = NSCollectionLayoutEdgeSpacing(leading: .fixed(8), top: nil, trailing: .fixed(8), bottom: nil)
                let section = NSCollectionLayoutSection(group: group)
                section.orthogonalScrollingBehavior = .continuousGroupLeadingBoundary
                section.boundarySupplementaryItems = [
                    NSCollectionLayoutBoundarySupplementaryItem(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .estimated(12)), elementKind: UICollectionView.elementKindSectionHeader, alignment: .topLeading)
                ]
                return section

            default:
                fatalError("unimplemented")
            }
        }
        collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
        collectionView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        collectionView.delegate = self
        collectionView.dragDelegate = self
        collectionView.backgroundColor = .secondarySystemBackground
        view.addSubview(collectionView)
        
        dataSource = createDataSource()
        
        resultsController = SearchResultsViewController(mastodonController: mastodonController)
        resultsController.exploreNavigationController = self.navigationController
        searchController = UISearchController(searchResultsController: resultsController)
        searchController.obscuresBackgroundDuringPresentation = true
        searchController.searchBar.autocapitalizationType = .none
        searchController.searchBar.delegate = resultsController
        searchController.hidesNavigationBarDuringPresentation = false
        definesPresentationContext = true
        
        navigationItem.searchController = searchController
        navigationItem.hidesSearchBarWhenScrolling = false
        if #available(iOS 16.0, *) {
            navigationItem.preferredSearchBarPlacement = .stacked
        }
        
        NotificationCenter.default.addObserver(self, selector: #selector(preferencesChanged), name: .preferencesChanged, object: nil)
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        Task(priority: .userInitiated) {
            if (try? await mastodonController.getOwnInstance()) != nil {
                await applySnapshot()
            }
        }
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        // this is a workaround for the issue that setting isActive on a search controller that is not visible
        // does not cause it to automatically become active once it becomes visible
        // see FB7814561
        if let active = searchControllerStatusOnAppearance {
            searchController.isActive = active
            searchControllerStatusOnAppearance = nil
        }
    }
    
    private func createDataSource() -> UICollectionViewDiffableDataSource<Section, Item> {
        let sectionHeaderCell = UICollectionView.SupplementaryRegistration<UICollectionViewListCell>(elementKind: UICollectionView.elementKindSectionHeader) { [unowned self] (headerView, collectionView, indexPath) in
            let section = self.dataSource.snapshot().sectionIdentifiers[indexPath.section]
            var config = UIListContentConfiguration.groupedHeader()
            config.text = section.title
            headerView.contentConfiguration = config
        }
        
        let trendingHashtagCell = UICollectionView.CellRegistration<TrendingHashtagCollectionViewCell, Hashtag> { (cell, indexPath, hashtag) in
            cell.updateUI(hashtag: hashtag)
        }
        let trendingLinkCell = UICollectionView.CellRegistration<TrendingLinkCardCollectionViewCell, Card>(cellNib: UINib(nibName: "TrendingLinkCardCollectionViewCell", bundle: .main)) { (cell, indexPath, card) in
            cell.updateUI(card: card)
        }
        
        let dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: collectionView) { collectionView, indexPath, item in
            switch item {
            case let .tag(hashtag):
                return collectionView.dequeueConfiguredReusableCell(using: trendingHashtagCell, for: indexPath, item: hashtag)
                
            case let .link(card):
                return collectionView.dequeueConfiguredReusableCell(using: trendingLinkCell, for: indexPath, item: card)
                
            default:
                fatalError("todo")
            }
        }
        dataSource.supplementaryViewProvider = { (collectionView, elementKind, indexPath) in
            if elementKind == UICollectionView.elementKindSectionHeader {
                return collectionView.dequeueConfiguredReusableSupplementary(using: sectionHeaderCell, for: indexPath)
            } else {
                return nil
            }
        }
        return dataSource
    }
    
    @MainActor
    private func applySnapshot() async {
        guard mastodonController.instanceFeatures.trends,
              !Preferences.shared.hideDiscover else {
            await dataSource.apply(NSDiffableDataSourceSnapshot())
            return
        }
        
        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
        
        let hashtagsReq = Client.getTrendingHashtags(limit: 5)
        async let hashtags = try? mastodonController.run(hashtagsReq).0
        let linksReq = Client.getTrendingLinks(limit: 10)
        async let links = try? mastodonController.run(linksReq).0
        
        if let hashtags = await hashtags {
            snapshot.appendSections([.trendingHashtags])
            snapshot.appendItems(hashtags.map { .tag($0) }, toSection: .trendingHashtags)
        }
        
        if let links = await links {
            snapshot.appendSections([.trendingLinks])
            snapshot.appendItems(links.map { .link($0) }, toSection: .trendingLinks)
        }
        
        await dataSource.apply(snapshot)
    }
    
    @objc private func preferencesChanged() {
        Task {
            await applySnapshot()
        }
    }

}

extension SearchViewController {
    enum Section {
        case trendingHashtags
        case trendingLinks
        case trendingStatuses
        case profileSuggestions
        
        var title: String {
            switch self {
            case .trendingHashtags:
                return "Trending Hashtags"
            case .trendingLinks:
                return "Trending Links"
            case .trendingStatuses:
                return "Trending Statuses"
            case .profileSuggestions:
                return "Suggested Accounts"
            }
        }
    }
    enum Item: Equatable, Hashable {
        case status(String)
        case tag(Hashtag)
        case link(Card)
        
        static func == (lhs: SearchViewController.Item, rhs: SearchViewController.Item) -> Bool {
            switch (lhs, rhs) {
            case let (.status(a), .status(b)):
                return a == b
            case let (.tag(a), .tag(b)):
                return a == b
            case let (.link(a), .link(b)):
                return a.url == b.url
            default:
                return false
            }
        }
        
        func hash(into hasher: inout Hasher) {
            switch self {
            case let .status(id):
                hasher.combine("status")
                hasher.combine(id)
            case let .tag(tag):
                hasher.combine("tag")
                hasher.combine(tag.name)
            case let .link(card):
                hasher.combine("link")
                hasher.combine(card.url)
            }
        }
    }
}

extension SearchViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        guard let item = dataSource.itemIdentifier(for: indexPath) else {
            return
        }
        switch item {
        case let .tag(hashtag):
            show(HashtagTimelineViewController(for: hashtag, mastodonController: mastodonController), sender: nil)
            
        case let .link(card):
            if let url = URL(card.url) {
                selected(url: url)
            }
            
        default:
            fatalError("todo")
        }
    }
    
    func collectionView(_ collectionView: UICollectionView, contextMenuConfigurationForItemAt indexPath: IndexPath, point: CGPoint) -> UIContextMenuConfiguration? {
        guard let item = dataSource.itemIdentifier(for: indexPath) else {
            return nil
        }
        
        switch item {
        case let .tag(hashtag):
            return UIContextMenuConfiguration(identifier: nil) {
                HashtagTimelineViewController(for: hashtag, mastodonController: self.mastodonController)
            } actionProvider: { (_) in
                UIMenu(children: self.actionsForHashtag(hashtag, source: .view(self.collectionView.cellForItem(at: indexPath))))
            }
            
        case let .link(card):
            guard let url = URL(card.url) else {
                return nil
            }
            return UIContextMenuConfiguration {
                SFSafariViewController(url: url)
            } actionProvider: { _ in
                UIMenu(children: self.actionsForTrendingLink(card: card))
            }
            
        default:
            fatalError("todo")
        }
    }
}

extension SearchViewController: UICollectionViewDragDelegate {
    func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
        guard let item = dataSource.itemIdentifier(for: indexPath) else {
                  return []
              }
        switch item {
        case let .tag(hashtag):
            guard let url = URL(hashtag.url) else {
                return []
            }
            let provider = NSItemProvider(object: url as NSURL)
            if let activity = UserActivityManager.showTimelineActivity(timeline: .tag(hashtag: hashtag.name), accountID: mastodonController.accountInfo!.id) {
                activity.displaysAuxiliaryScene = true
                provider.registerObject(activity, visibility: .all)
            }
            return [UIDragItem(itemProvider: provider)]
            
        case let .link(card):
            guard let url = URL(card.url) else {
                return []
            }
            return [UIDragItem(itemProvider: NSItemProvider(object: url as NSURL))]
            
        default:
            fatalError("todo")
        }
    }
}

extension SearchViewController: TuskerNavigationDelegate {
    var apiController: MastodonController! { mastodonController }
}

extension SearchViewController: ToastableViewController {
}

extension SearchViewController: MenuActionProvider {
}