Account list db sync and pagination

DB/Sources/DB/Content/AccountList.swift

@@ -0,0 +1,27 @@
+// Copyright © 2020 Metabolist. All rights reserved.
+
+import Foundation
+import GRDB
+
+public struct AccountList: Codable, FetchableRecord, PersistableRecord {
+    let id: UUID
+
+    public init() {
+        id = UUID()
+    }
+}
+
+extension AccountList {
+    static let joins = hasMany(
+        AccountListJoin.self,
+        using: ForeignKey([Column("listId")]))
+        .order(Column("index"))
+    static let accounts = hasMany(
+        AccountRecord.self,
+        through: joins,
+        using: AccountListJoin.account)
+
+    var accounts: QueryInterfaceRequest<AccountResult> {
+        request(for: Self.accounts).accountResultRequest
+    }
+}

DB/Sources/DB/Content/AccountListJoin.swift

@@ -0,0 +1,12 @@
+// Copyright © 2020 Metabolist. All rights reserved.
+
+import Foundation
+import GRDB
+
+struct AccountListJoin: Codable, FetchableRecord, PersistableRecord {
+    let accountId: String
+    let listId: UUID
+    let index: Int
+
+    static let account = belongsTo(AccountRecord.self, using: ForeignKey([Column("accountId")]))
+}

DB/Sources/DB/Content/ContentDatabase.swift

@@ -115,10 +115,15 @@ public extension ContentDatabase {
         .eraseToAnyPublisher()
     }
 
-    func insert(accounts: [Account]) -> AnyPublisher<Never, Error> {
+    func append(accounts: [Account], toList list: AccountList) -> AnyPublisher<Never, Error> {
         databaseWriter.writePublisher {
-            for account in accounts {
+            try list.save($0)
+
+            let count = try list.accounts.fetchCount($0)
+
+            for (index, account) in accounts.enumerated() {
                 try account.save($0)
+                try AccountListJoin(accountId: account.id, listId: list.id, index: count + index).save($0)
             }
         }
         .ignoreOutput()
@@ -271,6 +276,14 @@ public extension ContentDatabase {
             }
             .eraseToAnyPublisher()
     }
+
+    func accountListObservation(_ list: AccountList) -> AnyPublisher<[Account], Error> {
+        ValueObservation.tracking(list.accounts.fetchAll)
+            .removeDuplicates()
+            .publisher(in: databaseWriter)
+            .map { $0.map(Account.init(result:)) }
+            .eraseToAnyPublisher()
+    }
 }
 
 private extension ContentDatabase {
@@ -390,6 +403,20 @@ private extension ContentDatabase {
 
                 t.primaryKey(["accountId", "statusId", "collection"], onConflict: .replace)
             }
+
+            try db.create(table: "accountList") { t in
+                t.column("id", .text).primaryKey(onConflict: .replace)
+            }
+
+            try db.create(table: "accountListJoin") { t in
+                t.column("accountId", .text).indexed().notNull()
+                    .references("accountRecord", column: "id", onDelete: .cascade, onUpdate: .cascade)
+                t.column("listId", .text).indexed().notNull()
+                    .references("accountList", column: "id", onDelete: .cascade, onUpdate: .cascade)
+                t.column("index", .integer).notNull()
+
+                t.primaryKey(["accountId", "listId"], onConflict: .replace)
+            }
         }
 
         return migrator
@@ -401,6 +428,7 @@ private extension ContentDatabase {
             try StatusContextJoin.deleteAll($0)
             try AccountPinnedStatusJoin.deleteAll($0)
             try AccountStatusJoin.deleteAll($0)
+            try AccountList.deleteAll($0)
         } completion: { _, _ in }
     }
 }

ServiceLayer/Sources/ServiceLayer/Services/AccountListService.swift

@@ -11,6 +11,7 @@ public struct AccountListService {
     public let nextPageMaxIDs: AnyPublisher<String?, Never>
     public let navigationService: NavigationService
 
+    private let list: AccountList
     private let mastodonAPIClient: MastodonAPIClient
     private let contentDatabase: ContentDatabase
     private let requestClosure: (_ maxID: String?, _ minID: String?) -> AnyPublisher<Never, Error>
@@ -18,27 +19,23 @@ public struct AccountListService {
 
 extension AccountListService {
     init(favoritedByStatusID statusID: String, mastodonAPIClient: MastodonAPIClient, contentDatabase: ContentDatabase) {
-        let accountSectionsSubject = PassthroughSubject<[[Account]], Error>()
+        let list = AccountList()
         let nextPageMaxIDsSubject = PassthroughSubject<String?, Never>()
 
         self.init(
-            accountSections: accountSectionsSubject.eraseToAnyPublisher(),
+            accountSections: contentDatabase.accountListObservation(list).map { [$0] }.eraseToAnyPublisher(),
             nextPageMaxIDs: nextPageMaxIDsSubject.eraseToAnyPublisher(),
             navigationService: NavigationService(
                 status: nil,
                 mastodonAPIClient: mastodonAPIClient,
                 contentDatabase: contentDatabase),
+            list: list,
             mastodonAPIClient: mastodonAPIClient,
             contentDatabase: contentDatabase) { maxID, minID -> AnyPublisher<Never, Error> in
             mastodonAPIClient.pagedRequest(
                 AccountsEndpoint.statusFavouritedBy(id: statusID), maxID: maxID, minID: minID)
-                .handleEvents(
+                .handleEvents(receiveOutput: { nextPageMaxIDsSubject.send($0.info.maxID) })
-                    receiveOutput: {
+                .flatMap { contentDatabase.append(accounts: $0.result, toList: list) }
-                        nextPageMaxIDsSubject.send($0.info.maxID)
-                        accountSectionsSubject.send([$0.result])
-                    },
-                    receiveCompletion: accountSectionsSubject.send)
-                .flatMap { contentDatabase.insert(accounts: $0.result) }
                 .eraseToAnyPublisher()
         }
     }