//
//  EditListAccountsViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 12/17/19.
//  Copyright © 2019 Shadowfacts. All rights reserved.
//

import UIKit
import Pachyderm
import Combine

class EditListAccountsViewController: UIViewController, CollectionViewController {

    private var list: List
    private let mastodonController: MastodonController
    
    private var state = State.unloaded
    
    private(set) var changedAccounts = false
    
    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
    var collectionView: UICollectionView! { view as? UICollectionView }
    private var nextRange: RequestRange?
    
    private var searchResultsController: SearchResultsViewController!
    private var searchController: UISearchController!
    
    private var listRenamedCancellable: AnyCancellable?
    
    init(list: List, mastodonController: MastodonController) {
        self.list = list
        self.mastodonController = mastodonController
        
        super.init(nibName: nil, bundle: nil)
        
        listChanged()
        
        listRenamedCancellable = mastodonController.$lists
            .compactMap { $0.first { $0.id == list.id } }
            .sink { [unowned self] in
                self.list = $0
                self.listChanged()
            }
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemeneted")
    }
    
    override func loadView() {
        var config = UICollectionLayoutListConfiguration(appearance: .grouped)
        config.itemSeparatorHandler = { [unowned self] indexPath, sectionConfig in
            var config = sectionConfig
            switch dataSource.itemIdentifier(for: indexPath)! {
            case .loadingIndicator:
                config.topSeparatorVisibility = .hidden
                config.bottomSeparatorVisibility = .hidden
            case .account(id: _):
                config.topSeparatorInsets = TimelineStatusCollectionViewCell.separatorInsets
                config.bottomSeparatorInsets = TimelineStatusCollectionViewCell.separatorInsets
            }
            return config
        }
        config.trailingSwipeActionsConfigurationProvider = { [unowned self] indexPath in
            switch dataSource.itemIdentifier(for: indexPath) {
            case .account(id: let id):
                let remove = UIContextualAction(style: .destructive, title: "Remove") { [unowned self] _, _, completion in
                    Task {
                        await self.removeAccount(id: id)
                        completion(true)
                    }
                }
                return UISwipeActionsConfiguration(actions: [remove])
            default:
                return nil
            }
        }
        let layout = UICollectionViewCompositionalLayout.list(using: config)
        view = UICollectionView(frame: .zero, collectionViewLayout: layout)
        collectionView.delegate = self
        collectionView.allowsSelection = false
        collectionView.backgroundColor = .appGroupedBackground
        dataSource = createDataSource()
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        searchResultsController = SearchResultsViewController(mastodonController: mastodonController, scope: .people)
        searchResultsController.following = true
        searchResultsController.delegate = self
        searchController = UISearchController(searchResultsController: searchResultsController)
        searchController.hidesNavigationBarDuringPresentation = false
        searchController.searchResultsUpdater = searchResultsController
        searchController.searchBar.autocapitalizationType = .none
        searchController.searchBar.placeholder = NSLocalizedString("Search accounts you follow", comment: "edit list search field placeholder")
        searchController.searchBar.delegate = searchResultsController
        definesPresentationContext = true
        
        navigationItem.searchController = searchController
        navigationItem.hidesSearchBarWhenScrolling = false
        if #available(iOS 16.0, *) {
            navigationItem.preferredSearchBarPlacement = .stacked
            
            navigationItem.renameDelegate = self
            navigationItem.titleMenuProvider = { [unowned self] suggested in
                var children = suggested
                children.append(contentsOf: self.listSettingsMenuElements())
                return UIMenu(children: children)
            }
        } else {
            navigationItem.leftBarButtonItem = UIBarButtonItem(title: "Edit", menu: UIMenu(children: [
                // uncached so that menu always reflects the current state of the list
                UIDeferredMenuElement.uncached({ [unowned self] elementHandler in
                    var elements = self.listSettingsMenuElements()
                    elements.insert(UIAction(title: "Rename…", image: UIImage(systemName: "pencil"), handler: { [unowned self] _ in
                        RenameListService(list: self.list, mastodonController: self.mastodonController, present: {
                            self.present($0, animated: true)
                        }).run()
                    }), at: 0)
                    elementHandler(elements)
                })
            ]))
        }
    }
    
    private func createDataSource() -> UICollectionViewDiffableDataSource<Section, Item> {
        let loadingCell = UICollectionView.CellRegistration<LoadingCollectionViewCell, Void> { cell, indexPath, itemIdentifier in
            cell.indicator.startAnimating()
        }
        let accountCell = UICollectionView.CellRegistration<AccountCollectionViewCell, String> { [unowned self] cell, indexPath, itemIdentifier in
            cell.delegate = self
            cell.updateUI(accountID: itemIdentifier)
            cell.configurationUpdateHandler = { cell, state in
                cell.backgroundConfiguration = .appListGroupedCell(for: state)
            }
        }
        return UICollectionViewDiffableDataSource(collectionView: collectionView) { collectionView, indexPath, itemIdentifier in
            switch itemIdentifier {
            case .loadingIndicator:
                return collectionView.dequeueConfiguredReusableCell(using: loadingCell, for: indexPath, item: ())
            case .account(id: let id):
                return collectionView.dequeueConfiguredReusableCell(using: accountCell, for: indexPath, item: id)
            }
        }
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        clearSelectionOnAppear(animated: animated)
                
        Task {
            await loadAccounts()
        }
    }
    
    private func listChanged() {
        title = list.title
    }
    
    private func listSettingsMenuElements() -> [UIMenuElement] {
        var elements = [UIMenuElement]()
        if mastodonController.instanceFeatures.listRepliesPolicy {
            let actions = List.ReplyPolicy.allCases.map { policy in
                UIAction(title: policy.actionTitle, state: list.replyPolicy == policy ? .on : .off) { [unowned self] _ in
                    self.setReplyPolicy(policy)
                }
            }
            elements.append(UIMenu(title: "Show replies…", image: UIImage(systemName: "arrowshape.turn.up.left"), children: actions))
        }
        if mastodonController.instanceFeatures.exclusiveLists {
            let actions = [
                UIAction(title: "Hidden from Home", state: list.exclusive == true ? .on : .off) { [unowned self] _ in
                    self.setExclusive(true)
                },
                UIAction(title: "Shown on Home", state: list.exclusive == false ? .on : .off) { [unowned self] _ in
                    self.setExclusive(false)
                },
            ]
            elements.append(UIMenu(title: "Posts from this list are…", children: actions))
        }
        return elements
    }
    
    @MainActor
    private func loadAccounts() async {
        guard state == .unloaded else { return }
        
        state = .loading
        
        async let results = try await mastodonController.run(List.getAccounts(list.id))
        
        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
        snapshot.appendSections([.accounts])
        snapshot.appendItems([.loadingIndicator])
        await MainActor.run {
            dataSource.apply(snapshot)
        }
        
        do {
            let (accounts, pagination) = try await results
            self.nextRange = pagination?.older
            
            await withCheckedContinuation { continuation in
                mastodonController.persistentContainer.addAll(accounts: accounts) {
                    continuation.resume()
                }
            }
            
            var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
            snapshot.appendSections([.accounts])
            snapshot.appendItems(accounts.map { .account(id: $0.id) })
            await MainActor.run {
                dataSource.apply(snapshot)
            }
            
            state = .loaded
        } catch {
            let config = ToastConfiguration(from: error, with: "Error Loading Accounts", in: self) { [unowned self] toast in
                toast.dismissToast(animated: true)
                await self.loadAccounts()
            }
            self.showToast(configuration: config, animated: true)
            
            state = .unloaded
            await MainActor.run {
                dataSource.apply(.init())
            }
        }
    }
    
    private func loadNextPage() async {
        guard state == .loaded,
              let nextRange else { return }
        
        state = .loading
        
        async let results = try await mastodonController.run(List.getAccounts(list.id, range: nextRange))
        
        let origSnapshot = dataSource.snapshot()
        var snapshot = origSnapshot
        snapshot.appendItems([.loadingIndicator])
        await MainActor.run {
            dataSource.apply(snapshot)
        }
        
        do {
            let (accounts, pagination) = try await results
            self.nextRange = pagination?.older
            
            await withCheckedContinuation { continuation in
                mastodonController.persistentContainer.addAll(accounts: accounts) {
                    continuation.resume()
                }
            }
            
            var snapshot = origSnapshot
            snapshot.appendItems(accounts.map { .account(id: $0.id) })
            await MainActor.run {
                dataSource.apply(snapshot)
            }
            
            state = .loaded
        } catch {
            let config = ToastConfiguration(from: error, with: "Error Loading Accounts", in: self) { [unowned self] toast in
                toast.dismissToast(animated: true)
                await self.loadNextPage()
            }
            self.showToast(configuration: config, animated: true)
            
            state = .loaded
            await MainActor.run {
                dataSource.apply(origSnapshot)
            }
        }
    }
    
    private func addAccount(id: String) async {
        changedAccounts = true
        do {
            let req = List.add(list.id, accounts: [id])
            _ = try await mastodonController.run(req)
            self.searchController.isActive = false
            await self.loadAccounts()
        } catch {
            let config = ToastConfiguration(from: error, with: "Error Adding Account", in: self) { [unowned self] toast in
                toast.dismissToast(animated: true)
                await self.addAccount(id: id)
            }
            self.showToast(configuration: config, animated: true)
        }
    }
    
    private func removeAccount(id: String) async {
        changedAccounts = true
        do {
            let request = List.remove(list.id, accounts: [id])
            _ = try await mastodonController.run(request)
            await self.loadAccounts()
        } catch {
            let config = ToastConfiguration(from: error, with: "Error Removing Account", in: self) { [unowned self] toast in
                toast.dismissToast(animated: true)
                await self.removeAccount(id: id)
            }
            self.showToast(configuration: config, animated: true)
        }
    }
    
    private func setReplyPolicy(_ replyPolicy: List.ReplyPolicy) {
        Task {
            let service = EditListSettingsService(list: list, mastodonController: mastodonController, present: { self.present($0, animated: true) })
            await service.run(replyPolicy: replyPolicy)
        }
    }
    
    private func setExclusive(_ exclusive: Bool) {
        Task {
            let service = EditListSettingsService(list: list, mastodonController: mastodonController, present: { self.present($0, animated: true) })
            await service.run(exclusive: exclusive)
        }
    }

}

extension EditListAccountsViewController {
    enum State {
        case unloaded
        case loading
        case loaded
        case loadingOlder
    }
}

extension EditListAccountsViewController {
    enum Section: Hashable {
        case accounts
    }
    enum Item: Hashable {
        case loadingIndicator
        case account(id: String)
    }
}

extension EditListAccountsViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
        if state == .loaded,
        indexPath.item == collectionView.numberOfItems(inSection: indexPath.section) - 1 {
            Task {
                await loadNextPage()
            }
        }
    }
}

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

extension EditListAccountsViewController: ToastableViewController {
}

extension EditListAccountsViewController: MenuActionProvider {
}

extension EditListAccountsViewController: SearchResultsViewControllerDelegate {
    func selectedSearchResult(account accountID: String) {
        Task {
            await addAccount(id: accountID)
        }
    }
}

extension EditListAccountsViewController: UINavigationItemRenameDelegate {
    func navigationItem(_: UINavigationItem, shouldEndRenamingWith title: String) -> Bool {
        !title.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
    }
    
    func navigationItem(_: UINavigationItem, didEndRenamingWith title: String) {
        Task {
            let service = EditListSettingsService(list: list, mastodonController: mastodonController, present: { self.present($0, animated: true) })
            await service.run(title: title)
        }
    }
}

private extension List.ReplyPolicy {
    var actionTitle: String {
        switch self {
        case .followed:
            "To accounts you follow"
        case .list:
            "To other list members"
        case .none:
            "Never"
        }
    }
}