//
//  MainSplitViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 6/23/20.
//  Copyright © 2020 Shadowfacts. All rights reserved.
//

import UIKit

class MainSplitViewController: UISplitViewController {

    weak var mastodonController: MastodonController!
    
    private var sidebar: MainSidebarViewController!
    
    // Keep track of navigation stacks per-item so that we can only ever use a single navigation controller
    private var navigationStacks: [MainSidebarViewController.Item: [UIViewController]] = [:]
    
    private var tabBarViewController: MainTabBarViewController!
    
    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        if UIDevice.current.userInterfaceIdiom == .phone {
            return .portrait
        } else {
            return .all
        }
    }
    
    init(mastodonController: MastodonController) {
        self.mastodonController = mastodonController
        
        super.init(style: .doubleColumn)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        preferredDisplayMode = .oneBesideSecondary
        preferredSplitBehavior = .tile
        presentsWithGesture = false
        showsSecondaryOnlyButton = false
        delegate = self
        
        sidebar = MainSidebarViewController(mastodonController: mastodonController)
        sidebar.sidebarDelegate = self
        setViewController(sidebar, for: .primary)
        primaryBackgroundStyle = .sidebar

        setViewController(EnhancedNavigationViewController(), for: .secondary)
        // don't unnecesarily construct a content VC unless the we're in actually split mode
        // when we change from compact -> split for the first time, the VC will be transferred anyways
        if traitCollection.horizontalSizeClass != .compact {
            select(item: .tab(.timelines))
        }
        
        tabBarViewController = MainTabBarViewController(mastodonController: mastodonController)
        setViewController(tabBarViewController, for: .compact)
        
        addKeyCommand(MenuController.composeCommand)
        
        MenuController.sidebarItemKeyCommands.forEach(addKeyCommand(_:))
    }
    
    func select(item: MainSidebarViewController.Item) {
        let nav = viewController(for: .secondary) as! UINavigationController
        nav.viewControllers = getOrCreateNavigationStack(item: item)
    }
    
    func getOrCreateNavigationStack(item: MainSidebarViewController.Item) -> [UIViewController] {
        if let existing = navigationStacks[item], existing.count > 0 {
            return existing
        } else {
            let new = [item.createRootViewController(mastodonController)!]
            navigationStacks[item] = new
            return new
        }
    }
    
    @objc func handleSidebarItemCommand(_ command: UICommand) {
        let item: MainSidebarViewController.Item
        if let index = command.propertyList as? Int {
            item = .tab(MainTabBarViewController.Tab(rawValue: index)!)
        } else if let str = command.propertyList as? String {
            if str == "search" {
                item = .search
            } else if str == "bookmarks" {
                item = .bookmarks
            } else {
                fatalError()
            }
        } else {
            fatalError()
        }
        sidebar.select(item: item, animated: false)
        select(item: item)
    }

}

extension MainSplitViewController: UISplitViewControllerDelegate {
    /// Transfer the navigation stack for a sidebar item to a destination navgiation controller.
    /// - Parameter dropFirst: Remove the first view controller from the item's navigation stack before transferring.
    /// - Parameter append: Append the item's navigation stack to the destination nav controller's instead of replacing it.
    private func transferNavigationStack(from item: MainSidebarViewController.Item, to destination: UINavigationController, dropFirst: Bool = false, append: Bool = false) {
        var itemNavStack: [UIViewController]
        if item == sidebar.selectedItem {
            let detailNav = viewController(for: .secondary) as! UINavigationController
            itemNavStack = detailNav.viewControllers
        } else {
            itemNavStack = navigationStacks[item] ?? []
            navigationStacks.removeValue(forKey: item)
        }
        if itemNavStack.isEmpty {
            itemNavStack = [item.createRootViewController(mastodonController)!]
        }
        
        if dropFirst {
            itemNavStack.remove(at: 0)
        }
        
        if append {
            destination.viewControllers += itemNavStack
        } else {
            destination.viewControllers = itemNavStack
        }
    }
    
    func splitViewControllerDidCollapse(_ svc: UISplitViewController) {
        // on iPhones, the sidebar VC is never loaded, but since this method is still called, we can't do anything
        guard sidebar.isViewLoaded else { return }
        
        // Transfer the nav stacks for all the sidebar items that map 1 <-> 1 with tabs
        for tab in [MainTabBarViewController.Tab.timelines, .notifications, .myProfile] {
            let tabNav = tabBarViewController.viewController(for: tab) as! UINavigationController
            if tabNav.isViewLoaded {
                transferNavigationStack(from: .tab(tab), to: tabNav)
            }
        }
        
        // Since several sidebar items map to the single Explore tab, we only transfer the
        // navigation stack of the most-recently used one.
        let mostRecentExploreItem: (MainSidebarViewController.Item, Date)? =
            sidebar.exploreTabItems.compactMap {
                if let timestamp = sidebar.itemLastSelectedTimestamps[$0] {
                    return ($0, timestamp)
                } else {
                    return nil
                }
            }.min {
                $0.1 > $1.1
            }
        if let mostRecentExploreItem = mostRecentExploreItem?.0,
           mostRecentExploreItem != .search {
            let exploreNav = tabBarViewController.viewController(for: .explore) as! UINavigationController
            // Pop back to root, so we're appending to the Explore VC instead of some other VC
            exploreNav.popToRootViewController(animated: false)
            // Append so we don't replace the Explore VC
            transferNavigationStack(from: mostRecentExploreItem, to: exploreNav, append: true)
        }
        
        // Switch the tab bar to focus the same item as the sidebar has selected
        switch sidebar.selectedItem! {
        case let .tab(tab):
            // sidebar items that map 1 <-> 1 can be transferred directly
            tabBarViewController.select(tab: tab)
            
        case .search:
            // Search sidebar item maps to the Explore tab with the search controller/results visible
            // The nav stack can't be copied directly, since the split VC uses a different SearchViewController
            // so that explore items aren't shown multiple times.
            
            let exploreNav = tabBarViewController.viewController(for: .explore) as! UINavigationController
            let explore: ExploreViewController
            if let existing = exploreNav.viewControllers.first as? ExploreViewController {
                explore = existing
                exploreNav.popToRootViewController(animated: false)
            } else {
                // If the Explore tab hasn't been loaded before, it's root view controller won't be loaded yet, so create and add it manually.
                explore = ExploreViewController(mastodonController: mastodonController)
                exploreNav.viewControllers = [explore]
            }
            // Make sure viewDidLoad is called so that the searchController/resultsController have been initialized
            explore.loadViewIfNeeded()
            
            let nav = viewController(for: .secondary) as! UINavigationController
            let search = nav.viewControllers.first as! SearchViewController
            // Copy the search query from the search VC to the Explore VC's search controller.
            let query = search.searchController.searchBar.text ?? ""
            explore.searchController.searchBar.text = query
            // Instruct the explore controller to show its search controller immediately upon its first appearance.
            // explore.searchController.isActive can't be set directly, see FB7814561
            explore.searchControllerStatusOnAppearance = !query.isEmpty
            // Copy the results from the search VC's results controller to avoid the delay introduced by an extra network request
            explore.resultsController.loadResults(from: search.resultsController)
            
            // Transfer the navigation stack, dropping the search VC, to keep anything the user has opened
            transferNavigationStack(from: .search, to: exploreNav, dropFirst: true, append: true)
            
            tabBarViewController.select(tab: .explore)
            
        case .bookmarks, .list(_), .savedHashtag(_), .savedInstance(_):
            tabBarViewController.select(tab: .explore)
            // Make sure the Explore VC doesn't show it's search bar when it appears, in case the user was previously
            // in compact mode and performing a search.
            let exploreNav = tabBarViewController.viewController(for: .explore) as! UINavigationController
            let explore = exploreNav.viewControllers.first as! ExploreViewController
            explore.searchControllerStatusOnAppearance = false
            
        case .listsHeader, .addList, .savedHashtagsHeader, .addSavedHashtag, .savedInstancesHeader, .addSavedInstance:
            // These items are not selectable in the sidebar collection view, so this code is unreachable.
            fatalError("unreachable")
        }
    }
    
    /// Transfer a navigation stack from a navigation controller belonging to the tab bar VC to a sidebar item.
    /// - Parameter skipFirst:The number of view controllers that should be skipped from the source navigation controller.
    /// - Parameter prepend: An optional view controller to prepend to the beginning of the navigation stack being moved.
    private func transferNavigationStack(from navController: UINavigationController, to item: MainSidebarViewController.Item, skipFirst: Int = 0, prepend: UIViewController? = nil) {
        let viewControllersToMove = navController.viewControllers.dropFirst(skipFirst)
        navController.viewControllers.removeLast(navController.viewControllers.count - skipFirst)
        
        if let prepend = prepend {
            navigationStacks[item] = [prepend] + viewControllersToMove
        } else {
            navigationStacks[item] = Array(viewControllersToMove)
        }
    }
    
    func splitViewControllerDidExpand(_ svc: UISplitViewController) {
        // For each sidebar item, transfer the existing navigation stasck from the tab bar controller to ourself.
        var exploreItem: MainSidebarViewController.Item?
        for tab in MainTabBarViewController.Tab.allCases {
            guard let tabNavController = tabBarViewController.viewController(for: tab) as? UINavigationController,
                  tabNavController.isViewLoaded else { continue }
            let tabNavigationStack = tabNavController.viewControllers
            
            switch tab {
            case .timelines, .notifications, .myProfile:
                // Items that map 1 <-> 1 to tabs can be transferred directly.
                let item = MainSidebarViewController.Item.tab(tab)
                transferNavigationStack(from: tabNavController, to: item)
                
            case .explore:
                // The Explore tab is more complicated since it encapsulates a bunch of screens which have top-level sidebar items.
                
                var toPrepend: UIViewController? = nil
                
                // If the tab navigation stack has only one item or the search controller is active, it corresponds to the Search item
                // For other items, the 2nd VC in the nav stack determines which sidebar item they map to.
                // Search screen has special considerations, all others can be transferred directly.
                if tabNavigationStack.count == 1 || ((tabNavigationStack.first as? ExploreViewController)?.searchController?.isActive ?? false) {
                    exploreItem = .search
                    let searchVC = SearchViewController(mastodonController: mastodonController)
                    searchVC.loadViewIfNeeded()
                    let explore = tabNavigationStack.first as! ExploreViewController
                    if let exploreSearchControler = explore.searchController,
                       let query = exploreSearchControler.searchBar.text {
                        // Transfer query to search VC
                        searchVC.searchController.searchBar.text = query
                        // If there is a query, make the search VC activate itself upon appearing
                        searchVC.searchControllerStatusOnAppearance = !query.isEmpty
                        // Transfer the results from the explore VC, to avoid an extra network request
                        searchVC.resultsController.loadResults(from: explore.resultsController)
                    }
                    // Insert the new search VC at the beginning of the new search nav stack
                    toPrepend = searchVC
                } else if tabNavigationStack[1] is BookmarksTableViewController {
                    exploreItem = .bookmarks
                } else if let listVC = tabNavigationStack[1] as? ListTimelineViewController {
                    exploreItem = .list(listVC.list)
                } else if let hashtagVC = tabNavigationStack[1] as? HashtagTimelineViewController {
                    exploreItem = .savedHashtag(hashtagVC.hashtag)
                } else if let instanceVC = tabNavigationStack[1] as? InstanceTimelineViewController {
                    exploreItem = .savedInstance(instanceVC.instanceURL)
                }
                transferNavigationStack(from: tabNavController, to: exploreItem!, skipFirst: 1, prepend: toPrepend)
                
            case .compose:
                // The compose tab can't be activated, this is unreachable.
                fatalError("unreachable")
            }
        }
        
        // Transfer the selected tab from the tab bar VC to the sidebar
        switch tabBarViewController.selectedTab {
        case .timelines, .notifications, .myProfile:
            // These tabs map 1 <-> 1 with sidebar items
            let item = MainSidebarViewController.Item.tab(tabBarViewController.selectedTab)
            sidebar.select(item: item, animated: false)
            select(item: item)
            
        case .explore:
            // If the explore tab is active, the sidebar item is determined above when transferring the explore VC's nav stack
            sidebar.select(item: exploreItem!, animated: false)
            select(item: exploreItem!)
            
        default:
            return
        }
    }
}

extension MainSplitViewController: MainSidebarViewControllerDelegate {
    func sidebarRequestPresentCompose(_ sidebarViewController: MainSidebarViewController) {
        presentCompose()
    }
    
    func sidebar(_ sidebarViewController: MainSidebarViewController, didSelectItem item: MainSidebarViewController.Item) {
        let nav = viewController(for: .secondary) as! UINavigationController
        if let previous = sidebar.previouslySelectedItem {
            navigationStacks[previous] = nav.viewControllers
        }
        select(item: item)
    }
}

fileprivate extension MainSidebarViewController.Item {
    func createRootViewController(_ mastodonController: MastodonController) -> UIViewController? {
        switch self {
        case let .tab(tab):
            return tab.createViewController(mastodonController)
        case .search:
            return SearchViewController(mastodonController: mastodonController)
        case .bookmarks:
            return BookmarksTableViewController(mastodonController: mastodonController)
        case let .list(list):
            return ListTimelineViewController(for: list, mastodonController: mastodonController)
        case let .savedHashtag(hashtag):
            return HashtagTimelineViewController(for: hashtag, mastodonController: mastodonController)
        case let .savedInstance(url):
            return InstanceTimelineViewController(for: url, parentMastodonController: mastodonController)
        default:
            return nil
        }
    }
}

extension MainSplitViewController: TuskerRootViewController {
    @objc func presentCompose() {
        let vc = ComposeHostingController(mastodonController: mastodonController)
        let nav = EnhancedNavigationViewController(rootViewController: vc)
        nav.presentationController?.delegate = vc
        present(nav, animated: true)
    }
    
    func select(tab: MainTabBarViewController.Tab) {
        if traitCollection.horizontalSizeClass == .compact {
            tabBarViewController?.select(tab: tab)
        } else {
            if tab == .compose {
                presentCompose()
            } else {
                select(item: .tab(tab))
                sidebar.select(item: .tab(tab), animated: false)
            }
        }
    }
    
    func getTabController(tab: MainTabBarViewController.Tab) -> UIViewController? {
        if traitCollection.horizontalSizeClass == .compact {
            return tabBarViewController?.getTabController(tab: tab)
        } else {
            if tab == .compose {
                return nil
            } else if case .tab(tab) = sidebar.selectedItem {
                return viewController(for: .secondary)
            } else {
                return nil
            }
        }
    }
}

extension MainSplitViewController: BackgroundableViewController {
    func sceneDidEnterBackground() {
        if traitCollection.horizontalSizeClass == .compact {
            tabBarViewController.sceneDidEnterBackground()
        } else {
            // todo: should this do the same for the sidebar VC as well?
            if let contentVC = viewController(for: .secondary) as? BackgroundableViewController {
                contentVC.sceneDidEnterBackground()
            }
        }
    }
}