Trends in explore

DB/Sources/DB/Content/ContentDatabase+Migration.swift

@@ -202,6 +202,24 @@ extension ContentDatabase {
                 t.column("statusId").references("statusRecord", onDelete: .cascade)
             }
 
+            try db.create(table: "instanceRecord") { t in
+                t.column("uri", .text).primaryKey(onConflict: .replace)
+                t.column("title", .text).notNull()
+                t.column("description", .text).notNull()
+                t.column("shortDescription", .text)
+                t.column("email", .text).notNull()
+                t.column("version", .text).notNull()
+                t.column("languages", .blob).notNull()
+                t.column("registrations", .boolean).notNull()
+                t.column("approvalRequired", .boolean).notNull()
+                t.column("invitesEnabled", .boolean).notNull()
+                t.column("urls", .blob).notNull()
+                t.column("stats", .blob).notNull()
+                t.column("thumbnail", .text)
+                t.column("contactAccountId", .text).references("accountRecord", onDelete: .cascade)
+                t.column("maxTootChars", .integer)
+            }
+
             try db.create(table: "statusAncestorJoin") { t in
                 t.column("parentId", .text).indexed().notNull()
                     .references("statusRecord", onDelete: .cascade)

DB/Sources/DB/Content/ContentDatabase.swift

@@ -439,6 +439,12 @@ public extension ContentDatabase {
         .eraseToAnyPublisher()
     }
 
+    func insert(instance: Instance) -> AnyPublisher<Never, Error> {
+        databaseWriter.writePublisher(updates: instance.save)
+            .ignoreOutput()
+            .eraseToAnyPublisher()
+    }
+
     func timelinePublisher(_ timeline: Timeline) -> AnyPublisher<[CollectionSection], Error> {
         ValueObservation.tracking(
             TimelineItemsInfo.request(TimelineRecord.filter(TimelineRecord.Columns.id == timeline.id)).fetchOne)
@@ -611,6 +617,16 @@ public extension ContentDatabase {
             .eraseToAnyPublisher()
     }
 
+    func instancePublisher(uri: String) -> AnyPublisher<Instance, Error> {
+        ValueObservation.tracking(
+            InstanceInfo.request(InstanceRecord.filter(InstanceRecord.Columns.uri == uri)).fetchOne)
+            .removeDuplicates()
+            .publisher(in: databaseWriter)
+            .compactMap { $0 }
+            .map(Instance.init(info:))
+            .eraseToAnyPublisher()
+    }
+
     func pickerEmojisPublisher() -> AnyPublisher<[Emoji], Error> {
         ValueObservation.tracking(
             Emoji.filter(Emoji.Columns.visibleInPicker == true)

DB/Sources/DB/Content/InstanceInfo.swift

@@ -0,0 +1,20 @@
+// Copyright © 2020 Metabolist. All rights reserved.
+
+import Foundation
+import GRDB
+
+struct InstanceInfo: Codable, Hashable, FetchableRecord {
+    let record: InstanceRecord
+    let contactAccountInfo: AccountInfo?
+}
+
+extension InstanceInfo {
+    static func addingIncludes<T: DerivableRequest>(_ request: T) -> T where T.RowDecoder == InstanceRecord {
+        request.including(optional: AccountInfo.addingIncludes(InstanceRecord.contactAccount)
+                            .forKey(CodingKeys.contactAccountInfo))
+    }
+
+    static func request(_ request: QueryInterfaceRequest<InstanceRecord>) -> QueryInterfaceRequest<Self> {
+        addingIncludes(request).asRequest(of: self)
+    }
+}

DB/Sources/DB/Content/InstanceRecord.swift

@@ -0,0 +1,63 @@
+// Copyright © 2020 Metabolist. All rights reserved.
+
+import Foundation
+import GRDB
+import Mastodon
+
+struct InstanceRecord: ContentDatabaseRecord, Hashable {
+    let uri: String
+    let title: String
+    let description: String
+    let shortDescription: String?
+    let email: String
+    let version: String
+    let languages: [String]
+    let registrations: Bool
+    let approvalRequired: Bool
+    let invitesEnabled: Bool
+    let urls: Instance.URLs
+    let stats: Instance.Stats
+    let thumbnail: URL?
+    let contactAccountId: Account.Id?
+    let maxTootChars: Int?
+}
+
+extension InstanceRecord {
+    enum Columns {
+        static let uri = Column(CodingKeys.uri)
+        static let title = Column(CodingKeys.title)
+        static let description = Column(CodingKeys.description)
+        static let shortDescription = Column(CodingKeys.shortDescription)
+        static let email = Column(CodingKeys.email)
+        static let version = Column(CodingKeys.version)
+        static let languages = Column(CodingKeys.languages)
+        static let registrations = Column(CodingKeys.registrations)
+        static let approvalRequired = Column(CodingKeys.approvalRequired)
+        static let invitesEnabled = Column(CodingKeys.invitesEnabled)
+        static let urls = Column(CodingKeys.urls)
+        static let stats = Column(CodingKeys.stats)
+        static let thumbnail = Column(CodingKeys.thumbnail)
+        static let contactAccountId = Column(CodingKeys.contactAccountId)
+        static let maxTootChars = Column(CodingKeys.maxTootChars)
+    }
+
+    static let contactAccount = belongsTo(AccountRecord.self)
+
+    init(instance: Instance) {
+        self.uri = instance.uri
+        self.title = instance.title
+        self.description = instance.description
+        self.shortDescription = instance.shortDescription
+        self.email = instance.email
+        self.version = instance.version
+        self.languages = instance.languages
+        self.registrations = instance.registrations
+        self.approvalRequired = instance.approvalRequired
+        self.invitesEnabled = instance.invitesEnabled
+        self.urls = instance.urls
+        self.stats = instance.stats
+        self.thumbnail = instance.thumbnail
+        self.contactAccountId = instance.contactAccount?.id
+        self.maxTootChars = instance.maxTootChars
+    }
+}

DB/Sources/DB/Extensions/Instance+Extensions.swift

@@ -0,0 +1,41 @@
+// Copyright © 2020 Metabolist. All rights reserved.
+
+import Foundation
+import GRDB
+import Mastodon
+
+extension Instance {
+    func save(_ db: Database) throws {
+        if let contactAccount = contactAccount {
+            try AccountRecord(account: contactAccount).save(db)
+        }
+
+        try InstanceRecord(instance: self).save(db)
+    }
+
+    init(info: InstanceInfo) {
+        var contactAccount: Account?
+
+        if let contactAccountInfo = info.contactAccountInfo {
+            contactAccount = Account(info: contactAccountInfo)
+        }
+
+        self.init(record: info.record, contactAccount: contactAccount)
+    }
+}
+
+private extension Instance {
+    init(record: InstanceRecord, contactAccount: Account?) {
+        self.init(uri: record.uri,
+                  title: record.title,
+                  description: record.description,
+                  shortDescription: record.shortDescription,
+                  email: record.email,
+                  version: record.version,
+                  urls: record.urls,
+                  stats: record.stats,
+                  thumbnail: record.thumbnail,
+                  contactAccount: contactAccount,
+                  maxTootChars: record.maxTootChars)
+    }
+}

Data Sources/ExploreDataSource.swift

@@ -0,0 +1,70 @@
+// Copyright © 2021 Metabolist. All rights reserved.
+
+import Combine
+import Mastodon
+import UIKit
+import ViewModels
+
+final class ExploreDataSource: UICollectionViewDiffableDataSource<ExploreViewModel.Section, ExploreViewModel.Item> {
+    private let updateQueue =
+        DispatchQueue(label: "com.metabolist.metatext.explore-data-source.update-queue")
+    private var cancellables = Set<AnyCancellable>()
+
+    init(collectionView: UICollectionView, viewModel: ExploreViewModel) {
+        let tagRegistration = UICollectionView.CellRegistration<TagCollectionViewCell, TagViewModel> {
+            $0.viewModel = $2
+        }
+
+        super.init(collectionView: collectionView) {
+            switch $2 {
+            case let .tag(tag):
+                return $0.dequeueConfiguredReusableCell(
+                    using: tagRegistration,
+                    for: $1,
+                    item: viewModel.viewModel(tag: tag))
+            }
+        }
+
+        let headerRegistration = UICollectionView.SupplementaryRegistration
+        <ExploreSectionHeaderView>(elementKind: "Header") { [weak self] in
+            $0.label.text = self?.snapshot().sectionIdentifiers[$2.section].displayName
+        }
+
+        supplementaryViewProvider = {
+            $0.dequeueConfiguredReusableSupplementary(using: headerRegistration, for: $2)
+        }
+
+        viewModel.$trends.sink { [weak self] tags in
+            guard let self = self else { return }
+
+            var snapshot = NSDiffableDataSourceSnapshot<ExploreViewModel.Section, ExploreViewModel.Item>()
+
+            if !tags.isEmpty {
+                snapshot.appendSections([.trending])
+                snapshot.appendItems(tags.map(ExploreViewModel.Item.tag), toSection: .trending)
+            }
+
+            self.apply(snapshot, animatingDifferences: false)
+        }
+        .store(in: &cancellables)
+    }
+
+    override func apply(_ snapshot: NSDiffableDataSourceSnapshot<ExploreViewModel.Section, ExploreViewModel.Item>,
+                        animatingDifferences: Bool = true,
+                        completion: (() -> Void)? = nil) {
+        updateQueue.async {
+            super.apply(snapshot, animatingDifferences: animatingDifferences, completion: completion)
+        }
+    }
+}
+
+private extension ExploreViewModel.Section {
+    var displayName: String {
+        switch self {
+        case .trending:
+            return NSLocalizedString("explore.trending", comment: "")
+        case .instance:
+            return NSLocalizedString("explore.instance", comment: "")
+        }
+    }
+}

Localizations/Localizable.strings

@@ -74,6 +74,8 @@
 "emoji.system-group.objects" = "Objects";
 "emoji.system-group.symbols" = "Symbols";
 "emoji.system-group.flags" = "Flags";
+"explore.trending" = "Trending Now";
+"explore.instance" = "Instance";
 "error" = "Error";
 "favorites" = "Favorites";
 "follow-requests" = "Follow Requests";

Mastodon/Sources/Mastodon/Entities/Instance.swift

@@ -28,4 +28,28 @@ public struct Instance: Codable, Hashable {
     public let thumbnail: URL?
     public let contactAccount: Account?
     public let maxTootChars: Int?
+
+    public init(uri: String,
+                title: String,
+                description: String,
+                shortDescription: String?,
+                email: String,
+                version: String,
+                urls: Instance.URLs,
+                stats: Instance.Stats,
+                thumbnail: URL?,
+                contactAccount: Account?,
+                maxTootChars: Int?) {
+        self.uri = uri
+        self.title = title
+        self.description = description
+        self.shortDescription = shortDescription
+        self.email = email
+        self.version = version
+        self.urls = urls
+        self.stats = stats
+        self.thumbnail = thumbnail
+        self.contactAccount = contactAccount
+        self.maxTootChars = maxTootChars
+    }
 }

MastodonAPI/Sources/MastodonAPI/Endpoints/TagsEndpoint.swift

@@ -0,0 +1,25 @@
+// Copyright © 2020 Metabolist. All rights reserved.
+
+import Foundation
+import HTTP
+import Mastodon
+
+public enum TagsEndpoint {
+    case trends
+}
+
+extension TagsEndpoint: Endpoint {
+    public typealias ResultType = [Tag]
+
+    public var pathComponentsInContext: [String] {
+        switch self {
+        case .trends: return ["trends"]
+        }
+    }
+
+    public var method: HTTPMethod {
+        switch self {
+        case .trends: return .get
+        }
+    }
+}

Metatext.xcodeproj/project.pbxproj

@@ -145,6 +145,9 @@
 		D0D2AC5325BCD2BA003D5DF2 /* TagContentConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0D2AC5225BCD2BA003D5DF2 /* TagContentConfiguration.swift */; };
 		D0D2AC6725BD0484003D5DF2 /* LineChartView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0D2AC6625BD0484003D5DF2 /* LineChartView.swift */; };
 		D0DD50CB256B1F24004A04F7 /* ReportView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0DD50CA256B1F24004A04F7 /* ReportView.swift */; };
+		D0DDA76B25C5F20800FA0F91 /* ExploreDataSource.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0DDA76A25C5F20800FA0F91 /* ExploreDataSource.swift */; };
+		D0DDA77525C5F73F00FA0F91 /* TagCollectionViewCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0DDA77425C5F73F00FA0F91 /* TagCollectionViewCell.swift */; };
+		D0DDA77F25C6058300FA0F91 /* ExploreSectionHeaderView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0DDA77E25C6058300FA0F91 /* ExploreSectionHeaderView.swift */; };
 		D0E1F583251F13EC00D45315 /* WebfingerIndicatorView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0E1F582251F13EC00D45315 /* WebfingerIndicatorView.swift */; };
 		D0E2C1D124FD97F000854680 /* ViewModels in Frameworks */ = {isa = PBXBuildFile; productRef = D0E2C1D024FD97F000854680 /* ViewModels */; };
 		D0E5361C24E3EB4D00FB1CE1 /* NotificationService.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0E5361B24E3EB4D00FB1CE1 /* NotificationService.swift */; };
@@ -332,6 +335,9 @@
 		D0D2AC6625BD0484003D5DF2 /* LineChartView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LineChartView.swift; sourceTree = "<group>"; };
 		D0D7C013250440610039AD6F /* CodableBloomFilter */ = {isa = PBXFileReference; lastKnownFileType = folder; path = CodableBloomFilter; sourceTree = "<group>"; };
 		D0DD50CA256B1F24004A04F7 /* ReportView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ReportView.swift; sourceTree = "<group>"; };
+		D0DDA76A25C5F20800FA0F91 /* ExploreDataSource.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ExploreDataSource.swift; sourceTree = "<group>"; };
+		D0DDA77425C5F73F00FA0F91 /* TagCollectionViewCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TagCollectionViewCell.swift; sourceTree = "<group>"; };
+		D0DDA77E25C6058300FA0F91 /* ExploreSectionHeaderView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ExploreSectionHeaderView.swift; sourceTree = "<group>"; };
 		D0E0F1E424FC49FC002C04BF /* Mastodon */ = {isa = PBXFileReference; lastKnownFileType = folder; path = Mastodon; sourceTree = "<group>"; };
 		D0E1F582251F13EC00D45315 /* WebfingerIndicatorView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = WebfingerIndicatorView.swift; sourceTree = "<group>"; };
 		D0E2C1CF24FD8BA400854680 /* ViewModels */ = {isa = PBXFileReference; lastKnownFileType = folder; path = ViewModels; sourceTree = "<group>"; };
@@ -415,6 +421,7 @@
 				D007023D25562A2800F38136 /* ConversationAvatarsView.swift */,
 				D05936DD25A937EC00754FDF /* EditThumbnailView.swift */,
 				D07EC7FC25B16994006DF726 /* EmojiCategoryHeaderView.swift */,
+				D0DDA77E25C6058300FA0F91 /* ExploreSectionHeaderView.swift */,
 				D0D2AC6625BD0484003D5DF2 /* LineChartView.swift */,
 				D0BEB1F624F9A84B001B0F04 /* LoadingTableFooterView.swift */,
 				D05936FE25AA94EA00754FDF /* MarkAttachmentsSensitiveView.swift */,
@@ -485,6 +492,7 @@
 			isa = PBXGroup;
 			children = (
 				D07EC7DB25B13DBB006DF726 /* EmojiCollectionViewCell.swift */,
+				D0DDA77425C5F73F00FA0F91 /* TagCollectionViewCell.swift */,
 			);
 			path = "Collection View Cells";
 			sourceTree = "<group>";
@@ -610,6 +618,7 @@
 		D0A1F4F5252E7D2A004435BF /* Data Sources */ = {
 			isa = PBXGroup;
 			children = (
+				D0DDA76A25C5F20800FA0F91 /* ExploreDataSource.swift */,
 				D021A5FF25C3478F008A0C0D /* IdentitiesDataSource.swift */,
 				D0A1F4F6252E7D4B004435BF /* TableViewDataSource.swift */,
 			);
@@ -934,6 +943,7 @@
 				D036AA07254B6118009094DF /* NotificationView.swift in Sources */,
 				D08E52EE257D757100FA2C5F /* CompositionView.swift in Sources */,
 				D0E569E0252931B100FA1D72 /* LoadMoreContentConfiguration.swift in Sources */,
+				D0DDA77525C5F73F00FA0F91 /* TagCollectionViewCell.swift in Sources */,
 				D0FE1C9825368A9D003EF1EB /* PlayerCache.swift in Sources */,
 				D05936DE25A937EC00754FDF /* EditThumbnailView.swift in Sources */,
 				D0F0B136251AA12700942152 /* CollectionItem+Extensions.swift in Sources */,
@@ -1021,6 +1031,7 @@
 				D025B17E25C500BC001C69A8 /* CapsuleButton.swift in Sources */,
 				D0C7D4C424F7616A001EBDBB /* AppDelegate.swift in Sources */,
 				D0C7D49924F7616A001EBDBB /* AddIdentityView.swift in Sources */,
+				D0DDA77F25C6058300FA0F91 /* ExploreSectionHeaderView.swift in Sources */,
 				D0FCC105259C4E61000B67DF /* NewStatusViewController.swift in Sources */,
 				D087671625BAA8C0001FDD43 /* ExploreViewController.swift in Sources */,
 				D0D2AC6725BD0484003D5DF2 /* LineChartView.swift in Sources */,
@@ -1029,6 +1040,7 @@
 				D097F4C125BFA04C00859F2C /* NotificationsViewController.swift in Sources */,
 				D0E1F583251F13EC00D45315 /* WebfingerIndicatorView.swift in Sources */,
 				D0BEB20524FA1107001B0F04 /* FiltersView.swift in Sources */,
+				D0DDA76B25C5F20800FA0F91 /* ExploreDataSource.swift in Sources */,
 				D035F88725B8016000DC75ED /* NavigationViewModel+Extensions.swift in Sources */,
 				D0C7D49B24F7616A001EBDBB /* PreferencesView.swift in Sources */,
 				D088406D25AFBBE200BB749B /* EmojiPickerViewController.swift in Sources */,

ServiceLayer/Sources/ServiceLayer/Services/ExploreService.swift

@@ -7,12 +7,15 @@ import Mastodon
 import MastodonAPI
 
 public struct ExploreService {
+    public let navigationService: NavigationService
+
     private let mastodonAPIClient: MastodonAPIClient
     private let contentDatabase: ContentDatabase
 
     init(mastodonAPIClient: MastodonAPIClient, contentDatabase: ContentDatabase) {
         self.mastodonAPIClient = mastodonAPIClient
         self.contentDatabase = contentDatabase
+        navigationService = NavigationService(mastodonAPIClient: mastodonAPIClient, contentDatabase: contentDatabase)
     }
 }
 
@@ -20,4 +23,14 @@ public extension ExploreService {
     func searchService() -> SearchService {
         SearchService(mastodonAPIClient: mastodonAPIClient, contentDatabase: contentDatabase)
     }
+
+    func instanceServicePublisher(uri: String) -> AnyPublisher<InstanceService, Error> {
+        contentDatabase.instancePublisher(uri: uri)
+            .map { InstanceService(instance: $0, mastodonAPIClient: mastodonAPIClient) }
+            .eraseToAnyPublisher()
+    }
+
+    func fetchTrends() -> AnyPublisher<[Tag], Error> {
+        mastodonAPIClient.request(TagsEndpoint.trends)
+    }
 }

ServiceLayer/Sources/ServiceLayer/Services/IdentityService.swift

@@ -64,7 +64,10 @@ public extension IdentityService {
 
     func refreshInstance() -> AnyPublisher<Never, Error> {
         mastodonAPIClient.request(InstanceEndpoint.instance)
-            .flatMap { identityDatabase.updateInstance($0, id: id) }
+            .flatMap {
+                identityDatabase.updateInstance($0, id: id)
+                    .merge(with: contentDatabase.insert(instance: $0))
+            }
             .eraseToAnyPublisher()
     }
 

ServiceLayer/Sources/ServiceLayer/Services/InstanceService.swift

@@ -0,0 +1,17 @@
+// Copyright © 2021 Metabolist. All rights reserved.
+
+import Combine
+import Foundation
+import Mastodon
+import MastodonAPI
+
+public struct InstanceService {
+    public let instance: Instance
+
+    private let mastodonAPIClient: MastodonAPIClient
+
+    init(instance: Instance, mastodonAPIClient: MastodonAPIClient) {
+        self.instance = instance
+        self.mastodonAPIClient = mastodonAPIClient
+    }
+}

View Controllers/ExploreViewController.swift

@@ -9,11 +9,15 @@ final class ExploreViewController: UICollectionViewController {
     private let rootViewModel: RootViewModel
     private var cancellables = Set<AnyCancellable>()
 
+    private lazy var dataSource: ExploreDataSource = {
+        .init(collectionView: collectionView, viewModel: viewModel)
+    }()
+
     init(viewModel: ExploreViewModel, rootViewModel: RootViewModel) {
         self.viewModel = viewModel
         self.rootViewModel = rootViewModel
 
-        super.init(collectionViewLayout: UICollectionViewFlowLayout())
+        super.init(collectionViewLayout: Self.layout())
 
         tabBarItem = UITabBarItem(
             title: NSLocalizedString("main-navigation.explore", comment: ""),
@@ -29,6 +33,16 @@ final class ExploreViewController: UICollectionViewController {
     override func viewDidLoad() {
         super.viewDidLoad()
 
+        collectionView.dataSource = dataSource
+        collectionView.backgroundColor = .systemBackground
+        clearsSelectionOnViewWillAppear = true
+
+        collectionView.refreshControl = UIRefreshControl()
+        collectionView.refreshControl?.addAction(
+            UIAction { [weak self] _ in
+                self?.viewModel.refresh() },
+            for: .valueChanged)
+
         navigationItem.title = NSLocalizedString("main-navigation.explore", comment: "")
 
         let searchResultsController = TableViewController(
@@ -43,6 +57,19 @@ final class ExploreViewController: UICollectionViewController {
         searchController.searchResultsUpdater = self
         navigationItem.searchController = searchController
 
+        viewModel.events.sink { [weak self] in self?.handle(event: $0) }.store(in: &cancellables)
+
+        viewModel.$loading.sink { [weak self] in
+            guard let self = self else { return }
+
+            let refreshControlVisibile = self.collectionView.refreshControl?.isRefreshing ?? false
+
+            if !$0, refreshControlVisibile {
+                self.collectionView.refreshControl?.endRefreshing()
+            }
+        }
+        .store(in: &cancellables)
+
         viewModel.searchViewModel.events.sink { [weak self] in
             if case let .navigation(navigation) = $0,
                case let .searchScope(scope) = navigation {
@@ -52,6 +79,18 @@ final class ExploreViewController: UICollectionViewController {
         }
         .store(in: &cancellables)
     }
+
+    override func viewWillAppear(_ animated: Bool) {
+        super.viewWillAppear(animated)
+
+        viewModel.refresh()
+    }
+
+    override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
+        guard let item = dataSource.itemIdentifier(for: indexPath) else { return }
+
+        viewModel.select(item: item)
+    }
 }
 
 extension ExploreViewController: UISearchResultsUpdating {
@@ -68,3 +107,36 @@ extension ExploreViewController: UISearchResultsUpdating {
         viewModel.searchViewModel.query = searchController.searchBar.text ?? ""
     }
 }
+
+private extension ExploreViewController {
+    static func layout() -> UICollectionViewLayout {
+        var config = UICollectionLayoutListConfiguration(appearance: .plain)
+
+        config.headerMode = .supplementary
+
+        return UICollectionViewCompositionalLayout.list(using: config)
+    }
+
+    func handle(event: ExploreViewModel.Event) {
+        switch event {
+        case let .navigation(navigation):
+            handle(navigation: navigation)
+        }
+    }
+
+    func handle(navigation: Navigation) {
+        switch navigation {
+        case let .collection(collectionService):
+            let vc = TableViewController(
+                viewModel: CollectionItemsViewModel(
+                    collectionService: collectionService,
+                    identityContext: viewModel.identityContext),
+                rootViewModel: rootViewModel,
+                parentNavigationController: nil)
+
+                show(vc, sender: self)
+        default:
+            break
+        }
+    }
+}

ViewModels/Sources/ViewModels/View Models/ExploreViewModel.swift

@@ -1,13 +1,22 @@
 // Copyright © 2020 Metabolist. All rights reserved.
 
+import Combine
 import Foundation
+import Mastodon
 import ServiceLayer
 
 public final class ExploreViewModel: ObservableObject {
     public let searchViewModel: SearchViewModel
+    public let events: AnyPublisher<Event, Never>
+    @Published public var instanceViewModel: InstanceViewModel?
+    @Published public var trends = [Tag]()
+    @Published public private(set) var loading = false
+    @Published public var alertItem: AlertItem?
     public let identityContext: IdentityContext
 
     private let exploreService: ExploreService
+    private let eventsSubject = PassthroughSubject<Event, Never>()
+    private var cancellables = Set<AnyCancellable>()
 
     init(service: ExploreService, identityContext: IdentityContext) {
         exploreService = service
@@ -15,5 +24,60 @@ public final class ExploreViewModel: ObservableObject {
         searchViewModel = SearchViewModel(
             searchService: exploreService.searchService(),
             identityContext: identityContext)
+        events = eventsSubject.eraseToAnyPublisher()
+
+        identityContext.$identity
+            .compactMap { $0.instance?.uri }
+            .removeDuplicates()
+            .flatMap { service.instanceServicePublisher(uri: $0) }
+            .map { InstanceViewModel(instanceService: $0) }
+            .receive(on: DispatchQueue.main)
+            .assignErrorsToAlertItem(to: \.alertItem, on: self)
+            .assign(to: &$instanceViewModel)
+    }
+}
+
+public extension ExploreViewModel {
+    enum Event {
+        case navigation(Navigation)
+    }
+
+    enum Section: Hashable {
+        case trending
+        case instance
+    }
+
+    enum Item: Hashable {
+        case tag(Tag)
+    }
+
+    func refresh() {
+        exploreService.fetchTrends()
+            .handleEvents(receiveOutput: { [weak self] trends in
+                DispatchQueue.main.async {
+                    self?.trends = trends
+                }
+            })
+            .ignoreOutput()
+            .merge(with: identityContext.service.refreshInstance())
+            .receive(on: DispatchQueue.main)
+            .handleEvents(receiveSubscription: { [weak self] _ in self?.loading = true },
+                          receiveCompletion: { [weak self] _ in self?.loading = false })
+            .sink { _ in } receiveValue: { _ in }
+            .store(in: &cancellables)
+    }
+
+    func viewModel(tag: Tag) -> TagViewModel {
+        .init(tag: tag)
+    }
+
+    func select(item: ExploreViewModel.Item) {
+        switch item {
+        case let .tag(tag):
+            eventsSubject.send(
+                .navigation(.collection(exploreService
+                                            .navigationService
+                                            .timelineService(timeline: .tag(tag.name)))))
+        }
     }
 }

ViewModels/Sources/ViewModels/View Models/InstanceViewModel.swift

@@ -0,0 +1,12 @@
+// Copyright © 2021 Metabolist. All rights reserved.
+
+import Foundation
+import ServiceLayer
+
+public final class InstanceViewModel: ObservableObject {
+    private let instanceService: InstanceService
+
+    init(instanceService: InstanceService) {
+        self.instanceService = instanceService
+    }
+}

ViewModels/Sources/ViewModels/View Models/NavigationViewModel.swift

@@ -121,7 +121,7 @@ public extension NavigationViewModel {
             service: identityContext.service.exploreService(),
             identityContext: identityContext)
 
-        // TODO: initial request
+        exploreViewModel.refresh()
 
         return exploreViewModel
     }

Views/UIKit/Collection View Cells/TagCollectionViewCell.swift

@@ -0,0 +1,35 @@
+// Copyright © 2021 Metabolist. All rights reserved.
+
+import UIKit
+import ViewModels
+
+final class TagCollectionViewCell: UICollectionViewListCell {
+    var viewModel: TagViewModel?
+
+    override func updateConfiguration(using state: UICellConfigurationState) {
+        guard let viewModel = viewModel else { return }
+
+        contentConfiguration = TagContentConfiguration(viewModel: viewModel).updated(for: state)
+        updateConstraintsIfNeeded()
+    }
+
+    override func updateConstraints() {
+        super.updateConstraints()
+
+        let separatorLeadingAnchor: NSLayoutXAxisAnchor
+        let separatorTrailingAnchor: NSLayoutXAxisAnchor
+
+        if UIDevice.current.userInterfaceIdiom == .pad {
+            separatorLeadingAnchor = readableContentGuide.leadingAnchor
+            separatorTrailingAnchor = readableContentGuide.trailingAnchor
+        } else {
+            separatorLeadingAnchor = leadingAnchor
+            separatorTrailingAnchor = trailingAnchor
+        }
+
+        NSLayoutConstraint.activate([
+            separatorLayoutGuide.leadingAnchor.constraint(equalTo: separatorLeadingAnchor),
+            separatorLayoutGuide.trailingAnchor.constraint(equalTo: separatorTrailingAnchor)
+        ])
+    }
+}

Views/UIKit/ExploreSectionHeaderView.swift

@@ -0,0 +1,44 @@
+// Copyright © 2021 Metabolist. All rights reserved.
+
+import UIKit
+
+final class ExploreSectionHeaderView: UICollectionReusableView {
+    let label = UILabel()
+
+    override init(frame: CGRect) {
+        super.init(frame: frame)
+
+        initialSetup()
+    }
+
+    @available(*, unavailable)
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+}
+
+private extension ExploreSectionHeaderView {
+    func initialSetup() {
+        backgroundColor = .systemBackground
+
+        addSubview(label)
+        label.translatesAutoresizingMaskIntoConstraints = false
+        label.adjustsFontForContentSizeCategory = true
+        label.font = .preferredFont(forTextStyle: .headline)
+
+        let layoutGuide: UILayoutGuide
+
+        if UIDevice.current.userInterfaceIdiom == .pad {
+            layoutGuide = readableContentGuide
+        } else {
+            layoutGuide = layoutMarginsGuide
+        }
+
+        NSLayoutConstraint.activate([
+            label.leadingAnchor.constraint(equalTo: layoutGuide.leadingAnchor),
+            label.topAnchor.constraint(equalTo: layoutGuide.topAnchor),
+            label.trailingAnchor.constraint(equalTo: layoutGuide.trailingAnchor),
+            label.bottomAnchor.constraint(equalTo: layoutGuide.bottomAnchor)
+        ])
+    }
+}