Merge branch 'feature/sync' into feature/nextgen

app/src/androidTest/java/org/koitharu/kotatsu/core/db/MangaDatabaseTest.kt

@@ -68,6 +68,7 @@ class MangaDatabaseTest {
 			Migration10To11(),
 			Migration11To12(),
 			Migration12To13(),
+			Migration13To14(),
 		)
 =======
 >>>>>>> devel

app/src/main/AndroidManifest.xml

@@ -10,6 +10,13 @@
 	<uses-permission android:name="android.permission.VIBRATE" />
 	<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
 	<uses-permission android:name="android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS" />
+	<uses-permission android:name="android.permission.GET_ACCOUNTS" />
+	<uses-permission android:name="android.permission.MANAGE_ACCOUNTS" />
+	<uses-permission android:name="android.permission.AUTHENTICATE_ACCOUNTS" />
+	<uses-permission android:name="android.permission.USE_CREDENTIALS" />
+	<uses-permission android:name="android.permission.READ_SYNC_STATS" />
+	<uses-permission android:name="android.permission.READ_SYNC_SETTINGS" />
+	<uses-permission android:name="android.permission.WRITE_SYNC_SETTINGS" />
 
 	<application
 		android:name="org.koitharu.kotatsu.KotatsuApp"
@@ -122,6 +129,9 @@
 		<activity
 			android:name="org.koitharu.kotatsu.favourites.ui.categories.edit.FavouritesCategoryEditActivity"
 			android:theme="@style/Theme.Kotatsu.DialogWhenLarge" />
+		<activity
+			android:name="org.koitharu.kotatsu.sync.ui.SyncAuthActivity"
+			android:label="@string/sync" />
 
 		<service
 			android:name="org.koitharu.kotatsu.download.ui.service.DownloadService"
@@ -133,6 +143,41 @@
 		<service
 			android:name="org.koitharu.kotatsu.widget.recent.RecentWidgetService"
 			android:permission="android.permission.BIND_REMOTEVIEWS" />
+		<service
+			android:name="org.koitharu.kotatsu.sync.ui.SyncAuthenticatorService"
+			android:exported="true"
+			tools:ignore="ExportedService">
+			<intent-filter>
+				<action android:name="android.accounts.AccountAuthenticator" />
+			</intent-filter>
+			<meta-data
+				android:name="android.accounts.AccountAuthenticator"
+				android:resource="@xml/authenticator_sync" />
+		</service>
+		<service
+			android:name="org.koitharu.kotatsu.sync.ui.favourites.FavouritesSyncService"
+			android:exported="false"
+			android:label="@string/favourites"
+			android:process=":sync">
+			<intent-filter>
+				<action android:name="android.content.SyncAdapter" />
+			</intent-filter>
+			<meta-data
+				android:name="android.content.SyncAdapter"
+				android:resource="@xml/sync_favourites" />
+		</service>
+		<service
+			android:name="org.koitharu.kotatsu.sync.ui.history.HistorySyncService"
+			android:exported="false"
+			android:label="@string/history"
+			android:process=":sync">
+			<intent-filter>
+				<action android:name="android.content.SyncAdapter" />
+			</intent-filter>
+			<meta-data
+				android:name="android.content.SyncAdapter"
+				android:resource="@xml/sync_history" />
+		</service>
 
 		<provider
 			android:name="org.koitharu.kotatsu.search.ui.MangaSuggestionsProvider"
@@ -147,6 +192,18 @@
 				android:name="android.support.FILE_PROVIDER_PATHS"
 				android:resource="@xml/filepaths" />
 		</provider>
+		<provider
+			android:name="org.koitharu.kotatsu.sync.ui.favourites.FavouritesSyncProvider"
+			android:authorities="org.koitharu.kotatsu.favourites"
+			android:exported="false"
+			android:label="@string/favourites"
+			android:syncable="true" />
+		<provider
+			android:name="org.koitharu.kotatsu.sync.ui.history.HistorySyncProvider"
+			android:authorities="org.koitharu.kotatsu.history"
+			android:exported="false"
+			android:label="@string/history"
+			android:syncable="true" />
 
 		<receiver
 			android:name="org.koitharu.kotatsu.widget.shelf.ShelfWidgetProvider"

app/src/main/java/org/koitharu/kotatsu/KotatsuApp.kt

@@ -38,6 +38,7 @@ import org.koitharu.kotatsu.scrobbling.shikimori.shikimoriModule
 import org.koitharu.kotatsu.search.searchModule
 import org.koitharu.kotatsu.settings.settingsModule
 import org.koitharu.kotatsu.suggestions.suggestionsModule
+import org.koitharu.kotatsu.sync.syncModule
 import org.koitharu.kotatsu.tracker.trackerModule
 import org.koitharu.kotatsu.widget.appWidgetModule
 
@@ -74,6 +75,7 @@ class KotatsuApp : Application() {
 				readerModule,
 				appWidgetModule,
 				suggestionsModule,
+				syncModule,
 				shikimoriModule,
 				bookmarksModule,
 				libraryModule,

app/src/main/java/org/koitharu/kotatsu/core/backup/JsonDeserializer.kt

@@ -19,6 +19,7 @@ class JsonDeserializer(private val json: JSONObject) {
 		categoryId = json.getLong("category_id"),
 		sortKey = json.getIntOrDefault("sort_key", 0),
 		createdAt = json.getLong("created_at"),
+		deletedAt = 0L,
 	)
 
 	fun toMangaEntity() = MangaEntity(
@@ -51,6 +52,7 @@ class JsonDeserializer(private val json: JSONObject) {
 		page = json.getInt("page"),
 		scroll = json.getDouble("scroll").toFloat(),
 		percent = json.getFloatOrDefault("percent", -1f),
+		deletedAt = 0L,
 	)
 
 	fun toFavouriteCategoryEntity() = FavouriteCategoryEntity(
@@ -61,5 +63,6 @@ class JsonDeserializer(private val json: JSONObject) {
 		order = json.getStringOrNull("order") ?: SortOrder.NEWEST.name,
 		track = json.getBooleanOrDefault("track", true),
 		isVisibleInLibrary = json.getBooleanOrDefault("show_in_lib", true),
+		deletedAt = 0L,
 	)
 }

app/src/main/java/org/koitharu/kotatsu/core/db/DatabasePrePopulateCallback.kt

@@ -10,8 +10,16 @@ class DatabasePrePopulateCallback(private val resources: Resources) : RoomDataba
 
 	override fun onCreate(db: SupportSQLiteDatabase) {
 		db.execSQL(
-			"INSERT INTO favourite_categories (created_at, sort_key, title, `order`, track, show_in_lib) VALUES (?,?,?,?,?,?)",
+			"INSERT INTO favourite_categories (created_at, sort_key, title, `order`, track, show_in_lib, `deleted_at`) VALUES (?,?,?,?,?,?,?)",
-			arrayOf(System.currentTimeMillis(), 1, resources.getString(R.string.read_later), SortOrder.NEWEST.name, 1, 1)
+			arrayOf(
+				System.currentTimeMillis(),
+				1,
+				resources.getString(R.string.read_later),
+				SortOrder.NEWEST.name,
+				1,
+				1,
+				0L,
+			)
 		)
 	}
 }

app/src/main/java/org/koitharu/kotatsu/core/db/MangaDatabase.kt

@@ -30,7 +30,7 @@ import org.koitharu.kotatsu.tracker.data.TrackEntity
 import org.koitharu.kotatsu.tracker.data.TrackLogEntity
 import org.koitharu.kotatsu.tracker.data.TracksDao
 
-const val DATABASE_VERSION = 13
+const val DATABASE_VERSION = 14
 
 @Database(
 	entities = [
@@ -80,6 +80,7 @@ val databaseMigrations: Array<Migration>
 		Migration10To11(),
 		Migration11To12(),
 		Migration12To13(),
+		Migration13To14(),
 	)
 
 fun MangaDatabase(context: Context): MangaDatabase = Room

app/src/main/java/org/koitharu/kotatsu/core/db/Tables.kt

@@ -1,6 +1,5 @@
 package org.koitharu.kotatsu.core.db
 
-
 const val TABLE_FAVOURITES = "favourites"
 const val TABLE_MANGA = "manga"
 const val TABLE_TAGS = "tags"

app/src/main/java/org/koitharu/kotatsu/core/db/entity/MangaTagsEntity.kt

@@ -13,13 +13,13 @@ import org.koitharu.kotatsu.core.db.TABLE_MANGA_TAGS
 			entity = MangaEntity::class,
 			parentColumns = ["manga_id"],
 			childColumns = ["manga_id"],
-			onDelete = ForeignKey.CASCADE
+			onDelete = ForeignKey.CASCADE,
 		),
 		ForeignKey(
 			entity = TagEntity::class,
 			parentColumns = ["tag_id"],
 			childColumns = ["tag_id"],
-			onDelete = ForeignKey.CASCADE
+			onDelete = ForeignKey.CASCADE,
 		)
 	]
 )

app/src/main/java/org/koitharu/kotatsu/core/db/migrations/Migration13To14.kt

@@ -0,0 +1,13 @@
+package org.koitharu.kotatsu.core.db.migrations
+
+import androidx.room.migration.Migration
+import androidx.sqlite.db.SupportSQLiteDatabase
+
+class Migration13To14 : Migration(13, 14) {
+
+	override fun migrate(database: SupportSQLiteDatabase) {
+		database.execSQL("ALTER TABLE favourite_categories ADD COLUMN `deleted_at` INTEGER NOT NULL DEFAULT 0")
+		database.execSQL("ALTER TABLE favourites ADD COLUMN `deleted_at` INTEGER NOT NULL DEFAULT 0")
+		database.execSQL("ALTER TABLE history ADD COLUMN `deleted_at` INTEGER NOT NULL DEFAULT 0")
+	}
+}

app/src/main/java/org/koitharu/kotatsu/core/network/CommonHeaders.kt

@@ -9,6 +9,7 @@ object CommonHeaders {
 	const val ACCEPT = "Accept"
 	const val CONTENT_DISPOSITION = "Content-Disposition"
 	const val COOKIE = "Cookie"
+	const val CONTENT_ENCODING = "Content-Encoding"
 	const val AUTHORIZATION = "Authorization"
 
 	val CACHE_CONTROL_DISABLED: CacheControl

app/src/main/java/org/koitharu/kotatsu/core/network/GZipInterceptor.kt

@@ -2,7 +2,7 @@ package org.koitharu.kotatsu.core.network
 
 import okhttp3.Interceptor
 import okhttp3.Response
-import org.jsoup.helper.HttpConnection.CONTENT_ENCODING
+import org.koitharu.kotatsu.core.network.CommonHeaders.CONTENT_ENCODING
 
 class GZipInterceptor : Interceptor {
 

app/src/main/java/org/koitharu/kotatsu/core/prefs/AppSettings.kt

@@ -315,6 +315,7 @@ class AppSettings(context: Context) {
 		const val KEY_DOH = "doh"
 		const val KEY_EXIT_CONFIRM = "exit_confirm"
 		const val KEY_INCOGNITO_MODE = "incognito"
+		const val KEY_SYNC = "sync"
 
 		// About
 		const val KEY_APP_UPDATE = "app_update"

app/src/main/java/org/koitharu/kotatsu/favourites/data/FavouriteCategoriesDao.kt

@@ -6,13 +6,13 @@ import kotlinx.coroutines.flow.Flow
 @Dao
 abstract class FavouriteCategoriesDao {
 
-	@Query("SELECT * FROM favourite_categories WHERE category_id = :id")
+	@Query("SELECT * FROM favourite_categories WHERE category_id = :id AND deleted_at = 0")
 	abstract suspend fun find(id: Int): FavouriteCategoryEntity
 
-	@Query("SELECT * FROM favourite_categories ORDER BY sort_key")
+	@Query("SELECT * FROM favourite_categories WHERE deleted_at = 0 ORDER BY sort_key")
 	abstract suspend fun findAll(): List<FavouriteCategoryEntity>
 
-	@Query("SELECT * FROM favourite_categories ORDER BY sort_key")
+	@Query("SELECT * FROM favourite_categories WHERE deleted_at = 0 ORDER BY sort_key")
 	abstract fun observeAll(): Flow<List<FavouriteCategoryEntity>>
 
 	@MapInfo(valueColumn = "cover")
@@ -26,7 +26,7 @@ abstract class FavouriteCategoriesDao {
 	)
 	abstract fun observeAllWithDetails(): Flow<Map<FavouriteCategoryEntity, List<String>>>
 
-	@Query("SELECT * FROM favourite_categories WHERE category_id = :id")
+	@Query("SELECT * FROM favourite_categories WHERE category_id = :id AND deleted_at = 0")
 	abstract fun observe(id: Long): Flow<FavouriteCategoryEntity?>
 
 	@Insert(onConflict = OnConflictStrategy.ABORT)
@@ -35,11 +35,8 @@ abstract class FavouriteCategoriesDao {
 	@Update
 	abstract suspend fun update(category: FavouriteCategoryEntity): Int
 
-	@Query("DELETE FROM favourite_categories WHERE category_id = :id")
+	@Query("UPDATE favourite_categories SET deleted_at = :now WHERE category_id = :id")
-	abstract suspend fun delete(id: Long)
+	abstract suspend fun delete(id: Long, now: Long = System.currentTimeMillis())
-
-	@Query("UPDATE favourite_categories SET title = :title WHERE category_id = :id")
-	abstract suspend fun updateTitle(id: Long, title: String)
 
 	@Query("UPDATE favourite_categories SET title = :title, `order` = :order, `track` = :tracker  WHERE category_id = :id")
 	abstract suspend fun update(id: Long, title: String, order: String, tracker: Boolean)
@@ -56,7 +53,10 @@ abstract class FavouriteCategoriesDao {
 	@Query("UPDATE favourite_categories SET sort_key = :sortKey WHERE category_id = :id")
 	abstract suspend fun updateSortKey(id: Long, sortKey: Int)
 
-	@Query("SELECT MAX(sort_key) FROM favourite_categories")
+	@Query("DELETE FROM favourite_categories WHERE deleted_at != 0 AND deleted_at < :maxDeletionTime")
+	abstract suspend fun gc(maxDeletionTime: Long)
+
+	@Query("SELECT MAX(sort_key) FROM favourite_categories WHERE deleted_at = 0")
 	protected abstract suspend fun getMaxSortKey(): Int?
 
 	suspend fun getNextSortKey(): Int {

app/src/main/java/org/koitharu/kotatsu/favourites/data/FavouriteCategoryEntity.kt

@@ -15,6 +15,7 @@ data class FavouriteCategoryEntity(
 	@ColumnInfo(name = "order") val order: String,
 	@ColumnInfo(name = "track") val track: Boolean,
 	@ColumnInfo(name = "show_in_lib") val isVisibleInLibrary: Boolean,
+	@ColumnInfo(name = "deleted_at") val deletedAt: Long,
 ) {
 
 	override fun equals(other: Any?): Boolean {

app/src/main/java/org/koitharu/kotatsu/favourites/data/FavouriteEntity.kt

@@ -29,4 +29,5 @@ data class FavouriteEntity(
 	@ColumnInfo(name = "category_id", index = true) val categoryId: Long,
 	@ColumnInfo(name = "sort_key") val sortKey: Int,
 	@ColumnInfo(name = "created_at") val createdAt: Long,
+	@ColumnInfo(name = "deleted_at") val deletedAt: Long,
 )

app/src/main/java/org/koitharu/kotatsu/favourites/data/FavouritesDao.kt

@@ -4,6 +4,7 @@ import androidx.room.*
 import androidx.sqlite.db.SimpleSQLiteQuery
 import androidx.sqlite.db.SupportSQLiteQuery
 import kotlinx.coroutines.flow.Flow
+import org.intellij.lang.annotations.Language
 import org.koitharu.kotatsu.core.db.entity.MangaEntity
 import org.koitharu.kotatsu.parsers.model.SortOrder
 
@@ -11,53 +12,67 @@ import org.koitharu.kotatsu.parsers.model.SortOrder
 abstract class FavouritesDao {
 
 	@Transaction
-	@Query("SELECT * FROM favourites GROUP BY manga_id ORDER BY created_at DESC")
+	@Query("SELECT * FROM favourites WHERE deleted_at = 0 GROUP BY manga_id ORDER BY created_at DESC")
 	abstract suspend fun findAll(): List<FavouriteManga>
 
 	fun observeAll(order: SortOrder): Flow<List<FavouriteManga>> {
 		val orderBy = getOrderBy(order)
-		val query = SimpleSQLiteQuery(
+		@Language("RoomSql") val query = SimpleSQLiteQuery(
-			"SELECT * FROM favourites LEFT JOIN manga ON favourites.manga_id = manga.manga_id GROUP BY favourites.manga_id ORDER BY $orderBy",
+			"SELECT * FROM favourites LEFT JOIN manga ON favourites.manga_id = manga.manga_id " +
+				"WHERE favourites.deleted_at = 0 GROUP BY favourites.manga_id ORDER BY $orderBy",
 		)
 		return observeAllRaw(query)
 	}
 
 	@Transaction
-	@Query("SELECT * FROM favourites GROUP BY manga_id ORDER BY created_at DESC LIMIT :limit OFFSET :offset")
+	@Query(
+		"SELECT * FROM favourites WHERE deleted_at = 0 " +
+			"GROUP BY manga_id ORDER BY created_at DESC LIMIT :limit OFFSET :offset"
+	)
 	abstract suspend fun findAll(offset: Int, limit: Int): List<FavouriteManga>
 
 	@Transaction
-	@Query("SELECT * FROM favourites WHERE category_id = :categoryId GROUP BY manga_id ORDER BY created_at DESC")
+	@Query(
+		"SELECT * FROM favourites WHERE category_id = :categoryId AND deleted_at = 0 " +
+			"GROUP BY manga_id ORDER BY created_at DESC"
+	)
 	abstract suspend fun findAll(categoryId: Long): List<FavouriteManga>
 
 	fun observeAll(categoryId: Long, order: SortOrder): Flow<List<FavouriteManga>> {
 		val orderBy = getOrderBy(order)
-		val query = SimpleSQLiteQuery(
+		@Language("RoomSql") val query = SimpleSQLiteQuery(
-			"SELECT * FROM favourites LEFT JOIN manga ON favourites.manga_id = manga.manga_id WHERE category_id = ? GROUP BY favourites.manga_id ORDER BY $orderBy",
+			"SELECT * FROM favourites LEFT JOIN manga ON favourites.manga_id = manga.manga_id " +
+				"WHERE category_id = ? AND deleted_at = 0 GROUP BY favourites.manga_id ORDER BY $orderBy",
 			arrayOf<Any>(categoryId),
 		)
 		return observeAllRaw(query)
 	}
 
 	@Transaction
-	@Query("SELECT * FROM favourites WHERE category_id = :categoryId GROUP BY manga_id ORDER BY created_at DESC LIMIT :limit OFFSET :offset")
+	@Query(
+		"SELECT * FROM favourites WHERE category_id = :categoryId AND deleted_at = 0 " +
+			"GROUP BY manga_id ORDER BY created_at DESC LIMIT :limit OFFSET :offset"
+	)
 	abstract suspend fun findAll(categoryId: Long, offset: Int, limit: Int): List<FavouriteManga>
 
-	@Query("SELECT * FROM manga WHERE manga_id IN (SELECT manga_id FROM favourites WHERE category_id = :categoryId)")
+	@Query(
+		"SELECT * FROM manga WHERE manga_id IN " +
+			"(SELECT manga_id FROM favourites WHERE category_id = :categoryId AND deleted_at = 0)"
+	)
 	abstract suspend fun findAllManga(categoryId: Int): List<MangaEntity>
 
-	@Query("SELECT * FROM manga WHERE manga_id IN (SELECT manga_id FROM favourites)")
+	@Query("SELECT * FROM manga WHERE manga_id IN (SELECT manga_id FROM favourites WHERE deleted_at = 0)")
 	abstract suspend fun findAllManga(): List<MangaEntity>
 
 	@Transaction
-	@Query("SELECT * FROM favourites WHERE manga_id = :id GROUP BY manga_id")
+	@Query("SELECT * FROM favourites WHERE manga_id = :id AND deleted_at = 0 GROUP BY manga_id")
 	abstract suspend fun find(id: Long): FavouriteManga?
 
 	@Transaction
-	@Query("SELECT * FROM favourites WHERE manga_id = :id GROUP BY manga_id")
+	@Query("SELECT * FROM favourites WHERE manga_id = :id AND deleted_at = 0 GROUP BY manga_id")
 	abstract fun observe(id: Long): Flow<FavouriteManga?>
 
-	@Query("SELECT DISTINCT category_id FROM favourites WHERE manga_id = :id")
+	@Query("SELECT DISTINCT category_id FROM favourites WHERE manga_id = :id AND deleted_at = 0")
 	abstract fun observeIds(id: Long): Flow<List<Long>>
 
 	@Insert(onConflict = OnConflictStrategy.IGNORE)
@@ -66,11 +81,18 @@ abstract class FavouritesDao {
 	@Update
 	abstract suspend fun update(favourite: FavouriteEntity): Int
 
-	@Query("DELETE FROM favourites WHERE manga_id = :mangaId")
+	@Query("UPDATE favourites SET deleted_at = :now WHERE manga_id = :mangaId")
-	abstract suspend fun delete(mangaId: Long)
+	abstract suspend fun delete(mangaId: Long, now: Long = System.currentTimeMillis())
+
+	@Query("UPDATE favourites SET deleted_at = :now WHERE manga_id = :mangaId AND category_id = :categoryId")
+	abstract suspend fun delete(categoryId: Long, mangaId: Long, now: Long = System.currentTimeMillis())
+
+	suspend fun recover(mangaId: Long) = delete(mangaId, 0L)
+
+	suspend fun recover(categoryId: Long, mangaId: Long) = delete(categoryId, mangaId, 0L)
 
-	@Query("DELETE FROM favourites WHERE manga_id = :mangaId AND category_id = :categoryId")
+	@Query("DELETE FROM favourites WHERE deleted_at != 0 AND deleted_at < :maxDeletionTime")
-	abstract suspend fun delete(categoryId: Long, mangaId: Long)
+	abstract suspend fun gc(maxDeletionTime: Long)
 
 	@Transaction
 	open suspend fun upsert(entity: FavouriteEntity) {
@@ -83,7 +105,7 @@ abstract class FavouritesDao {
 	@RawQuery(observedEntities = [FavouriteEntity::class])
 	protected abstract fun observeAllRaw(query: SupportSQLiteQuery): Flow<List<FavouriteManga>>
 
-	private fun getOrderBy(sortOrder: SortOrder) = when(sortOrder) {
+	private fun getOrderBy(sortOrder: SortOrder) = when (sortOrder) {
 		SortOrder.RATING -> "rating DESC"
 		SortOrder.NEWEST,
 		SortOrder.UPDATED -> "created_at DESC"

app/src/main/java/org/koitharu/kotatsu/favourites/domain/FavouritesRepository.kt

@@ -2,12 +2,12 @@ package org.koitharu.kotatsu.favourites.domain
 
 import androidx.room.withTransaction
 import kotlinx.coroutines.flow.*
+import org.koitharu.kotatsu.base.domain.ReversibleHandle
 import org.koitharu.kotatsu.core.db.MangaDatabase
 import org.koitharu.kotatsu.core.db.entity.*
 import org.koitharu.kotatsu.core.model.FavouriteCategory
 import org.koitharu.kotatsu.favourites.data.FavouriteCategoryEntity
 import org.koitharu.kotatsu.favourites.data.FavouriteEntity
-import org.koitharu.kotatsu.favourites.data.FavouriteManga
 import org.koitharu.kotatsu.favourites.data.toFavouriteCategory
 import org.koitharu.kotatsu.parsers.model.Manga
 import org.koitharu.kotatsu.parsers.model.SortOrder
@@ -62,12 +62,6 @@ class FavouritesRepository(
 			.map { it?.toFavouriteCategory() }
 	}
 
-	fun observeCategories(mangaId: Long): Flow<List<FavouriteCategory>> {
-		return db.favouritesDao.observe(mangaId).map { entity ->
-			entity?.categories?.map { it.toFavouriteCategory() }.orEmpty()
-		}.distinctUntilChanged()
-	}
-
 	fun observeCategoriesIds(mangaId: Long): Flow<Set<Long>> {
 		return db.favouritesDao.observeIds(mangaId).map { it.toSet() }
 	}
@@ -84,6 +78,7 @@ class FavouritesRepository(
 			categoryId = 0,
 			order = sortOrder.name,
 			track = isTrackerEnabled,
+			deletedAt = 0L,
 			isVisibleInLibrary = true,
 		)
 		val id = db.favouriteCategoriesDao.insert(entity)
@@ -100,27 +95,6 @@ class FavouritesRepository(
 		db.favouriteCategoriesDao.updateLibVisibility(id, isVisibleInLibrary)
 	}
 
-	suspend fun addCategory(title: String): FavouriteCategory {
-		val entity = FavouriteCategoryEntity(
-			title = title,
-			createdAt = System.currentTimeMillis(),
-			sortKey = db.favouriteCategoriesDao.getNextSortKey(),
-			categoryId = 0,
-			order = SortOrder.NEWEST.name,
-			track = true,
-			isVisibleInLibrary = true,
-		)
-		val id = db.favouriteCategoriesDao.insert(entity)
-		val category = entity.toFavouriteCategory(id)
-		channels.createChannel(category)
-		return category
-	}
-
-	suspend fun renameCategory(id: Long, title: String) {
-		db.favouriteCategoriesDao.updateTitle(id, title)
-		channels.renameChannel(id, title)
-	}
-
 	suspend fun removeCategory(id: Long) {
 		db.favouriteCategoriesDao.delete(id)
 		channels.deleteChannel(id)
@@ -138,10 +112,6 @@ class FavouritesRepository(
 		db.favouriteCategoriesDao.updateOrder(id, order.name)
 	}
 
-	suspend fun setCategoryTracking(id: Long, isEnabled: Boolean) {
-		db.favouriteCategoriesDao.updateTracking(id, isEnabled)
-	}
-
 	suspend fun reorderCategories(orderedIds: List<Long>) {
 		val dao = db.favouriteCategoriesDao
 		db.withTransaction {
@@ -162,26 +132,29 @@ class FavouritesRepository(
 					categoryId = categoryId,
 					createdAt = System.currentTimeMillis(),
 					sortKey = 0,
+					deletedAt = 0L,
 				)
 				db.favouritesDao.insert(entity)
 			}
 		}
 	}
 
-	suspend fun removeFromFavourites(ids: Collection<Long>) {
+	suspend fun removeFromFavourites(ids: Collection<Long>): ReversibleHandle {
 		db.withTransaction {
 			for (id in ids) {
 				db.favouritesDao.delete(id)
 			}
 		}
+		return ReversibleHandle { recoverToFavourites(ids) }
 	}
 
-	suspend fun removeFromCategory(categoryId: Long, ids: Collection<Long>) {
+	suspend fun removeFromCategory(categoryId: Long, ids: Collection<Long>): ReversibleHandle {
 		db.withTransaction {
 			for (id in ids) {
 				db.favouritesDao.delete(categoryId, id)
 			}
 		}
+		return ReversibleHandle { recoverToCategory(categoryId, ids) }
 	}
 
 	private fun observeOrder(categoryId: Long): Flow<SortOrder> {
@@ -190,4 +163,20 @@ class FavouritesRepository(
 			.map { x -> SortOrder(x.order, SortOrder.NEWEST) }
 			.distinctUntilChanged()
 	}
+
+	private suspend fun recoverToFavourites(ids: Collection<Long>) {
+		db.withTransaction {
+			for (id in ids) {
+				db.favouritesDao.recover(id)
+			}
+		}
+	}
+
+	private suspend fun recoverToCategory(categoryId: Long, ids: Collection<Long>) {
+		db.withTransaction {
+			for (id in ids) {
+				db.favouritesDao.recover(categoryId, id)
+			}
+		}
+	}
 }

app/src/main/java/org/koitharu/kotatsu/favourites/ui/list/FavouritesListFragment.kt

@@ -1,13 +1,17 @@
 package org.koitharu.kotatsu.favourites.ui.list
 
+import android.os.Bundle
 import android.view.Menu
 import android.view.MenuItem
 import android.view.View
 import androidx.appcompat.view.ActionMode
 import androidx.appcompat.widget.PopupMenu
+import com.google.android.material.snackbar.Snackbar
 import org.koin.androidx.viewmodel.ext.android.viewModel
 import org.koin.core.parameter.parametersOf
 import org.koitharu.kotatsu.R
+import org.koitharu.kotatsu.base.domain.ReversibleHandle
+import org.koitharu.kotatsu.base.domain.reverseAsync
 import org.koitharu.kotatsu.core.ui.titleRes
 import org.koitharu.kotatsu.favourites.ui.categories.FavouriteCategoriesActivity
 import org.koitharu.kotatsu.list.ui.MangaListFragment
@@ -25,6 +29,12 @@ class FavouritesListFragment : MangaListFragment(), PopupMenu.OnMenuItemClickLis
 
 	override val isSwipeRefreshEnabled = false
 
+	override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
+		super.onViewCreated(view, savedInstanceState)
+		viewModel.sortOrder.observe(viewLifecycleOwner) { activity?.invalidateOptionsMenu() }
+		viewModel.onItemsRemoved.observe(viewLifecycleOwner, ::onItemsRemoved)
+	}
+
 	override fun onScrolledToEnd() = Unit
 
 	override fun onFilterClick(view: View?) {
@@ -65,6 +75,15 @@ class FavouritesListFragment : MangaListFragment(), PopupMenu.OnMenuItemClickLis
 		}
 	}
 
+	private fun onItemsRemoved(reversibleHandle: ReversibleHandle) {
+		val message = viewModel.categoryName?.let {
+			getString(R.string.removed_from_s, it)
+		} ?: getString(R.string.removed_from_favourites)
+		Snackbar.make(binding.recyclerView, message, Snackbar.LENGTH_LONG)
+			.setAction(R.string.undo) { reversibleHandle.reverseAsync() }
+			.show()
+	}
+
 	companion object {
 
 		const val NO_ID = 0L

app/src/main/java/org/koitharu/kotatsu/favourites/ui/list/FavouritesListViewModel.kt

@@ -1,10 +1,15 @@
 package org.koitharu.kotatsu.favourites.ui.list
 
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.viewModelScope
 import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.flow.*
+import kotlinx.coroutines.flow.catch
-import kotlinx.coroutines.plus
+import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.withContext
 import org.koitharu.kotatsu.R
+import org.koitharu.kotatsu.base.domain.ReversibleHandle
 import org.koitharu.kotatsu.core.prefs.AppSettings
 import org.koitharu.kotatsu.favourites.domain.FavouritesRepository
 import org.koitharu.kotatsu.favourites.ui.list.FavouritesListFragment.Companion.NO_ID
@@ -12,9 +17,13 @@ import org.koitharu.kotatsu.history.domain.HistoryRepository
 import org.koitharu.kotatsu.history.domain.PROGRESS_NONE
 import org.koitharu.kotatsu.list.domain.ListExtraProvider
 import org.koitharu.kotatsu.list.ui.MangaListViewModel
-import org.koitharu.kotatsu.list.ui.model.*
+import org.koitharu.kotatsu.list.ui.model.EmptyState
+import org.koitharu.kotatsu.list.ui.model.LoadingState
+import org.koitharu.kotatsu.list.ui.model.toErrorState
+import org.koitharu.kotatsu.list.ui.model.toUi
 import org.koitharu.kotatsu.parsers.model.SortOrder
 import org.koitharu.kotatsu.tracker.domain.TrackingRepository
+import org.koitharu.kotatsu.utils.SingleLiveEvent
 import org.koitharu.kotatsu.utils.ext.asLiveDataDistinct
 
 class FavouritesListViewModel(
@@ -25,12 +34,15 @@ class FavouritesListViewModel(
 	private val settings: AppSettings,
 ) : MangaListViewModel(settings), ListExtraProvider {
 
-	private val sortOrder: StateFlow<SortOrder?> = if (categoryId == NO_ID) {
+	var categoryName: String? = null
-		MutableStateFlow(null)
+		private set
+
+	val sortOrder: LiveData<SortOrder?> = if (categoryId == NO_ID) {
+		MutableLiveData(null)
 	} else {
 		repository.observeCategory(categoryId)
 			.map { it?.order }
-			.stateIn(viewModelScope + Dispatchers.Default, SharingStarted.Eagerly, null)
+			.asLiveDataDistinct(viewModelScope.coroutineContext + Dispatchers.Default, null)
 	}
 
 	override val content = combine(
@@ -39,9 +51,8 @@ class FavouritesListViewModel(
 		} else {
 			repository.observeAll(categoryId)
 		},
-		sortOrder,
 		createListModeFlow()
-	) { list, order, mode ->
+	) { list, mode ->
 		when {
 			list.isEmpty() -> listOf(
 				EmptyState(
@@ -55,17 +66,26 @@ class FavouritesListViewModel(
 					actionStringRes = 0,
 				)
 			)
-			else -> buildList<ListModel>(list.size + 1) {
+			else -> list.toUi(mode, this)
-				if (order != null) {
-					add(ListHeader2(emptyList(), order, false))
-				}
-				list.toUi(this, mode, this@FavouritesListViewModel)
-			}
 		}
 	}.catch {
 		emit(listOf(it.toErrorState(canRetry = false)))
 	}.asLiveDataDistinct(viewModelScope.coroutineContext + Dispatchers.Default, listOf(LoadingState))
 
+	val onItemsRemoved = SingleLiveEvent<ReversibleHandle>()
+
+	init {
+		if (categoryId != NO_ID) {
+			launchJob {
+				categoryName = withContext(Dispatchers.Default) {
+					runCatching {
+						repository.getCategory(categoryId).title
+					}.getOrNull()
+				}
+			}
+		}
+	}
+
 	override fun onRefresh() = Unit
 
 	override fun onRetry() = Unit
@@ -74,12 +94,13 @@ class FavouritesListViewModel(
 		if (ids.isEmpty()) {
 			return
 		}
-		launchJob {
+		launchJob(Dispatchers.Default) {
-			if (categoryId == NO_ID) {
+			val handle = if (categoryId == NO_ID) {
 				repository.removeFromFavourites(ids)
 			} else {
 				repository.removeFromCategory(categoryId, ids)
 			}
+			onItemsRemoved.postCall(handle)
 		}
 	}
 

app/src/main/java/org/koitharu/kotatsu/history/data/HistoryDao.kt

@@ -8,48 +8,46 @@ import org.koitharu.kotatsu.core.db.entity.TagEntity
 @Dao
 abstract class HistoryDao {
 
-	/**
-	 * @hide
-	 */
 	@Transaction
-	@Query("SELECT * FROM history ORDER BY updated_at DESC LIMIT :limit OFFSET :offset")
+	@Query("SELECT * FROM history WHERE deleted_at = 0 ORDER BY updated_at DESC LIMIT :limit OFFSET :offset")
 	abstract suspend fun findAll(offset: Int, limit: Int): List<HistoryWithManga>
 
 	@Transaction
-	@Query("SELECT * FROM history WHERE manga_id IN (:ids)")
+	@Query("SELECT * FROM history WHERE deleted_at = 0 AND manga_id IN (:ids)")
 	abstract suspend fun findAll(ids: Collection<Long>): List<HistoryEntity?>
 
 	@Transaction
-	@Query("SELECT * FROM history ORDER BY updated_at DESC")
+	@Query("SELECT * FROM history WHERE deleted_at = 0 ORDER BY updated_at DESC")
 	abstract fun observeAll(): Flow<List<HistoryWithManga>>
 
-	@Query("SELECT * FROM manga WHERE manga_id IN (SELECT manga_id FROM history)")
+	@Query("SELECT * FROM manga WHERE manga_id IN (SELECT manga_id FROM history WHERE deleted_at = 0)")
 	abstract suspend fun findAllManga(): List<MangaEntity>
 
 	@Query(
 		"""SELECT tags.* FROM tags
 		LEFT JOIN manga_tags ON tags.tag_id = manga_tags.tag_id
 		INNER JOIN history ON history.manga_id = manga_tags.manga_id
+		WHERE history.deleted_at = 0
 		GROUP BY manga_tags.tag_id 
 		ORDER BY COUNT(manga_tags.manga_id) DESC 
 		LIMIT :limit"""
 	)
 	abstract suspend fun findPopularTags(limit: Int): List<TagEntity>
 
-	@Query("SELECT * FROM history WHERE manga_id = :id")
+	@Query("SELECT * FROM history WHERE manga_id = :id AND deleted_at = 0")
 	abstract suspend fun find(id: Long): HistoryEntity?
 
-	@Query("SELECT * FROM history WHERE manga_id = :id")
+	@Query("SELECT * FROM history WHERE manga_id = :id AND deleted_at = 0")
 	abstract fun observe(id: Long): Flow<HistoryEntity?>
 
-	@Query("SELECT COUNT(*) FROM history")
+	@Query("SELECT COUNT(*) FROM history WHERE deleted_at = 0")
 	abstract fun observeCount(): Flow<Int>
 
-	@Query("SELECT percent FROM history WHERE manga_id = :id")
+	@Query("UPDATE history SET deleted_at = :now WHERE deleted_at = 0")
-	abstract suspend fun findProgress(id: Long): Float?
+	abstract suspend fun clear(now: Long = System.currentTimeMillis())
 
-	@Query("DELETE FROM history")
+	@Query("SELECT percent FROM history WHERE manga_id = :id AND deleted_at = 0")
-	abstract suspend fun clear()
+	abstract suspend fun findProgress(id: Long): Float?
 
 	@Insert(onConflict = OnConflictStrategy.IGNORE)
 	abstract suspend fun insert(entity: HistoryEntity): Long
@@ -64,8 +62,13 @@ abstract class HistoryDao {
 		updatedAt: Long,
 	): Int
 
-	@Query("DELETE FROM history WHERE manga_id = :mangaId")
+	@Query("UPDATE history SET deleted_at = :now WHERE manga_id = :mangaId")
-	abstract suspend fun delete(mangaId: Long)
+	abstract suspend fun delete(mangaId: Long, now: Long = System.currentTimeMillis())
+
+	suspend fun recover(mangaId: Long) = delete(mangaId, 0L)
+
+	@Query("DELETE FROM history WHERE deleted_at != 0 AND deleted_at < :maxDeletionTime")
+	abstract suspend fun gc(maxDeletionTime: Long)
 
 	@Query("DELETE FROM history WHERE created_at >= :minDate")
 	abstract suspend fun deleteAfter(minDate: Long)

app/src/main/java/org/koitharu/kotatsu/history/data/HistoryEntity.kt

@@ -27,4 +27,5 @@ data class HistoryEntity(
 	@ColumnInfo(name = "page") val page: Int,
 	@ColumnInfo(name = "scroll") val scroll: Float,
 	@ColumnInfo(name = "percent") val percent: Float,
+	@ColumnInfo(name = "deleted_at") val deletedAt: Long,
 )

app/src/main/java/org/koitharu/kotatsu/history/domain/HistoryRepository.kt

@@ -81,6 +81,7 @@ class HistoryRepository(
 					page = page,
 					scroll = scroll.toFloat(), // we migrate to int, but decide to not update database
 					percent = percent,
+					deletedAt = 0L,
 				)
 			)
 			trackingRepository.syncWithHistory(manga, chapterId)
@@ -107,28 +108,18 @@ class HistoryRepository(
 		db.historyDao.delete(manga.id)
 	}
 
-	suspend fun delete(ids: Collection<Long>) {
-		db.withTransaction {
-			for (id in ids) {
-				db.historyDao.delete(id)
-			}
-		}
-	}
-
 	suspend fun deleteAfter(minDate: Long) {
 		db.historyDao.delete(minDate)
 	}
 
-	suspend fun deleteReversible(ids: Collection<Long>): ReversibleHandle {
+	suspend fun delete(ids: Collection<Long>): ReversibleHandle {
-		val entities = db.withTransaction {
+		db.withTransaction {
-			val entities = db.historyDao.findAll(ids.toList()).filterNotNull()
 			for (id in ids) {
 				db.historyDao.delete(id)
 			}
-			entities
 		}
 		return ReversibleHandle {
-			db.historyDao.upsert(entities)
+			recover(ids)
 		}
 	}
 
@@ -145,4 +136,12 @@ class HistoryRepository(
 	suspend fun getPopularTags(limit: Int): List<MangaTag> {
 		return db.historyDao.findPopularTags(limit).map { x -> x.toMangaTag() }
 	}
+
+	private suspend fun recover(ids: Collection<Long>) {
+		db.withTransaction {
+			for (id in ids) {
+				db.historyDao.recover(id)
+			}
+		}
+	}
 }

app/src/main/java/org/koitharu/kotatsu/history/ui/HistoryListViewModel.kt

@@ -77,7 +77,7 @@ class HistoryListViewModel(
 			return
 		}
 		launchJob(Dispatchers.Default) {
-			val handle = repository.deleteReversible(ids)
+			val handle = repository.delete(ids)
 			onItemsRemoved.postCall(handle)
 		}
 	}
@@ -94,9 +94,6 @@ class HistoryListViewModel(
 		val result = ArrayList<ListModel>(if (grouped) (list.size * 1.4).toInt() else list.size + 1)
 		val showPercent = settings.isReadingIndicatorsEnabled
 		var prevDate: DateTimeAgo? = null
-		if (!grouped) {
-			result += ListHeader(null, R.string.history, null)
-		}
 		for ((manga, history) in list) {
 			if (grouped) {
 				val date = timeAgo(history.updatedAt)

app/src/main/java/org/koitharu/kotatsu/library/ui/LibraryViewModel.kt

@@ -84,7 +84,7 @@ class LibraryViewModel(
 			return
 		}
 		launchJob(Dispatchers.Default) {
-			val handle = historyRepository.deleteReversible(ids)
+			val handle = historyRepository.delete(ids)
 			onActionDone.postCall(ReversibleAction(R.string.removed_from_history, handle))
 		}
 	}

app/src/main/java/org/koitharu/kotatsu/main/ui/MainActivity.kt

@@ -21,6 +21,7 @@ import com.google.android.material.navigation.NavigationBarView
 import com.google.android.material.snackbar.Snackbar
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
+import kotlinx.coroutines.yield
 import org.koin.android.ext.android.get
 import org.koin.androidx.viewmodel.ext.android.viewModel
 import org.koitharu.kotatsu.R
@@ -44,6 +45,7 @@ import org.koitharu.kotatsu.settings.newsources.NewSourcesDialogFragment
 import org.koitharu.kotatsu.settings.onboard.OnboardDialogFragment
 import org.koitharu.kotatsu.settings.tools.ToolsFragment
 import org.koitharu.kotatsu.suggestions.ui.SuggestionsWorker
+import org.koitharu.kotatsu.sync.domain.SyncController
 import org.koitharu.kotatsu.tracker.ui.FeedFragment
 import org.koitharu.kotatsu.tracker.work.TrackWorker
 import org.koitharu.kotatsu.utils.VoiceInputContract
@@ -341,6 +343,8 @@ class MainActivity :
 				!settings.isSourcesSelected -> OnboardDialogFragment.showWelcome(supportFragmentManager)
 				settings.newSources.isNotEmpty() -> NewSourcesDialogFragment.show(supportFragmentManager)
 			}
+			yield()
+			get<SyncController>().requestFullSyncAndGc(get())
 		}
 	}
 

app/src/main/java/org/koitharu/kotatsu/settings/ContentSettingsFragment.kt

@@ -1,11 +1,19 @@
 package org.koitharu.kotatsu.settings
 
+import android.accounts.Account
+import android.accounts.AccountManager
+import android.content.ActivityNotFoundException
+import android.content.Intent
 import android.content.SharedPreferences
 import android.os.Bundle
+import android.preference.PreferenceActivity.EXTRA_SHOW_FRAGMENT_ARGUMENTS
 import android.view.View
 import androidx.preference.ListPreference
 import androidx.preference.Preference
+import com.google.android.material.snackbar.Snackbar
+import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
 import org.koin.android.ext.android.inject
 import org.koitharu.kotatsu.R
 import org.koitharu.kotatsu.base.ui.BasePreferenceFragment
@@ -58,6 +66,11 @@ class ContentSettingsFragment :
 		settings.subscribe(this)
 	}
 
+	override fun onResume() {
+		super.onResume()
+		bindSyncSummary()
+	}
+
 	override fun onDestroyView() {
 		settings.unsubscribe(this)
 		super.onDestroyView()
@@ -90,6 +103,21 @@ class ContentSettingsFragment :
 					.show()
 				true
 			}
+			AppSettings.KEY_SYNC -> {
+				val am = AccountManager.get(requireContext())
+				val accountType = getString(R.string.account_type_sync)
+				val account = am.getAccountsByType(accountType).firstOrNull()
+				if (account == null) {
+					am.addAccount(accountType, accountType, null, null, requireActivity(), null, null)
+				} else {
+					try {
+						startActivity(getSyncSettingsIntent(account))
+					} catch (_: ActivityNotFoundException) {
+						Snackbar.make(listView, R.string.operation_not_supported, Snackbar.LENGTH_SHORT).show()
+					}
+				}
+				true
+			}
 			else -> super.onPreferenceTreeClick(preference)
 		}
 	}
@@ -111,4 +139,28 @@ class ContentSettingsFragment :
 			summary = getString(R.string.enabled_d_of_d, total - settings.hiddenSources.size, total)
 		}
 	}
+
+	private fun bindSyncSummary() {
+		viewLifecycleScope.launch {
+			val account = withContext(Dispatchers.Default) {
+				val type = getString(R.string.account_type_sync)
+				AccountManager.get(requireContext()).getAccountsByType(type).firstOrNull()
+			}
+			findPreference<Preference>(AppSettings.KEY_SYNC)?.run {
+				summary = account?.name ?: getString(R.string.sync_title)
+			}
+		}
+	}
+
+	/**
+	 * Some magic
+	 */
+	private fun getSyncSettingsIntent(account: Account): Intent {
+		val args = Bundle(1)
+		args.putParcelable("account", account)
+		val intent = Intent("android.settings.ACCOUNT_SYNC_SETTINGS")
+		@Suppress("DEPRECATION")
+		intent.putExtra(EXTRA_SHOW_FRAGMENT_ARGUMENTS, args)
+		return intent
+	}
 }

app/src/main/java/org/koitharu/kotatsu/sync/SyncModule.kt

@@ -0,0 +1,20 @@
+package org.koitharu.kotatsu.sync
+
+import androidx.room.InvalidationTracker
+import org.koin.android.ext.koin.androidContext
+import org.koin.androidx.viewmodel.dsl.viewModel
+import org.koin.dsl.bind
+import org.koin.dsl.module
+import org.koitharu.kotatsu.sync.data.SyncAuthApi
+import org.koitharu.kotatsu.sync.domain.SyncController
+import org.koitharu.kotatsu.sync.ui.SyncAuthViewModel
+
+val syncModule
+	get() = module {
+
+		single { SyncController(androidContext()) } bind InvalidationTracker.Observer::class
+
+		factory { SyncAuthApi(androidContext(), get()) }
+
+		viewModel { SyncAuthViewModel(get()) }
+	}

app/src/main/java/org/koitharu/kotatsu/sync/data/SyncAuthApi.kt

@@ -0,0 +1,30 @@
+package org.koitharu.kotatsu.sync.data
+
+import android.content.Context
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import org.json.JSONObject
+import org.koitharu.kotatsu.R
+import org.koitharu.kotatsu.parsers.util.await
+import org.koitharu.kotatsu.parsers.util.parseJson
+import org.koitharu.kotatsu.utils.ext.toRequestBody
+
+class SyncAuthApi(
+	context: Context,
+	private val okHttpClient: OkHttpClient,
+) {
+
+	private val baseUrl = context.getString(R.string.url_sync_server)
+
+	suspend fun authenticate(email: String, password: String): String {
+		val body = JSONObject(
+			mapOf("email" to email, "password" to password)
+		).toRequestBody()
+		val request = Request.Builder()
+			.url("$baseUrl/auth")
+			.post(body)
+			.build()
+		val response = okHttpClient.newCall(request).await().parseJson()
+		return response.getString("token")
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/data/SyncAuthenticator.kt

@@ -0,0 +1,38 @@
+package org.koitharu.kotatsu.sync.data
+
+import android.accounts.Account
+import android.accounts.AccountManager
+import android.content.Context
+import kotlinx.coroutines.runBlocking
+import okhttp3.Authenticator
+import okhttp3.Request
+import okhttp3.Response
+import okhttp3.Route
+import org.koitharu.kotatsu.R
+
+class SyncAuthenticator(
+	context: Context,
+	private val account: Account,
+	private val authApi: SyncAuthApi,
+) : Authenticator {
+
+	private val accountManager = AccountManager.get(context)
+	private val tokenType = context.getString(R.string.account_type_sync)
+
+	override fun authenticate(route: Route?, response: Response): Request? {
+		val newToken = tryRefreshToken() ?: return null
+		accountManager.setAuthToken(account, tokenType, newToken)
+		return response.request.newBuilder()
+			.header("Authorization", "Bearer $newToken")
+			.build()
+	}
+
+	private fun tryRefreshToken() = runCatching {
+		runBlocking {
+			authApi.authenticate(
+				account.name,
+				accountManager.getPassword(account),
+			)
+		}
+	}.getOrNull()
+}

app/src/main/java/org/koitharu/kotatsu/sync/data/SyncInterceptor.kt

@@ -0,0 +1,30 @@
+package org.koitharu.kotatsu.sync.data
+
+import android.accounts.Account
+import android.accounts.AccountManager
+import android.content.Context
+import okhttp3.Interceptor
+import okhttp3.Response
+import org.koitharu.kotatsu.BuildConfig
+import org.koitharu.kotatsu.R
+import org.koitharu.kotatsu.core.db.DATABASE_VERSION
+
+class SyncInterceptor(
+	context: Context,
+	private val account: Account,
+) : Interceptor {
+
+	private val accountManager = AccountManager.get(context)
+	private val tokenType = context.getString(R.string.account_type_sync)
+
+	override fun intercept(chain: Interceptor.Chain): Response {
+		val token = accountManager.peekAuthToken(account, tokenType)
+		val requestBuilder = chain.request().newBuilder()
+		if (token != null) {
+			requestBuilder.header("Authorization", "Bearer $token")
+		}
+		requestBuilder.header("X-App-Version", BuildConfig.VERSION_CODE.toString())
+		requestBuilder.header("X-Db-Version", DATABASE_VERSION.toString())
+		return chain.proceed(requestBuilder.build())
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/domain/SyncAuthResult.kt

@@ -0,0 +1,28 @@
+package org.koitharu.kotatsu.sync.domain
+
+class SyncAuthResult(
+	val email: String,
+	val password: String,
+	val token: String,
+) {
+
+	override fun equals(other: Any?): Boolean {
+		if (this === other) return true
+		if (javaClass != other?.javaClass) return false
+
+		other as SyncAuthResult
+
+		if (email != other.email) return false
+		if (password != other.password) return false
+		if (token != other.token) return false
+
+		return true
+	}
+
+	override fun hashCode(): Int {
+		var result = email.hashCode()
+		result = 31 * result + password.hashCode()
+		result = 31 * result + token.hashCode()
+		return result
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/domain/SyncController.kt

@@ -0,0 +1,139 @@
+package org.koitharu.kotatsu.sync.domain
+
+import android.accounts.Account
+import android.accounts.AccountManager
+import android.content.ContentResolver
+import android.content.Context
+import android.os.Bundle
+import android.util.ArrayMap
+import androidx.room.InvalidationTracker
+import androidx.room.withTransaction
+import kotlinx.coroutines.*
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+import org.koitharu.kotatsu.BuildConfig
+import org.koitharu.kotatsu.R
+import org.koitharu.kotatsu.core.db.MangaDatabase
+import org.koitharu.kotatsu.core.db.TABLE_FAVOURITES
+import org.koitharu.kotatsu.core.db.TABLE_FAVOURITE_CATEGORIES
+import org.koitharu.kotatsu.core.db.TABLE_HISTORY
+import org.koitharu.kotatsu.utils.ext.processLifecycleScope
+import java.util.concurrent.TimeUnit
+
+class SyncController(
+	context: Context,
+) : InvalidationTracker.Observer(arrayOf(TABLE_HISTORY, TABLE_FAVOURITES, TABLE_FAVOURITE_CATEGORIES)) {
+
+	private val am = AccountManager.get(context)
+	private val accountType = context.getString(R.string.account_type_sync)
+	private val minSyncInterval = if (BuildConfig.DEBUG) {
+		TimeUnit.SECONDS.toMillis(5)
+	} else {
+		TimeUnit.MINUTES.toMillis(4)
+	}
+	private val mutex = Mutex()
+	private val jobs = ArrayMap<String, Job>(2)
+	private val defaultGcPeriod: Long // gc period if sync disabled
+		get() = TimeUnit.HOURS.toMillis(2)
+
+	override fun onInvalidated(tables: MutableSet<String>) {
+		requestSync(
+			favourites = TABLE_FAVOURITES in tables || TABLE_FAVOURITE_CATEGORIES in tables,
+			history = TABLE_HISTORY in tables,
+		)
+	}
+
+	fun getLastSync(account: Account, authority: String): Long {
+		val key = "last_sync_" + authority.substringAfterLast('.')
+		val rawValue = am.getUserData(account, key) ?: return 0L
+		return rawValue.toLongOrNull() ?: 0L
+	}
+
+	fun setLastSync(account: Account, authority: String, time: Long) {
+		val key = "last_sync_" + authority.substringAfterLast('.')
+		am.setUserData(account, key, time.toString())
+	}
+
+	suspend fun requestFullSync() = withContext(Dispatchers.Default) {
+		requestSyncImpl(favourites = true, history = true, db = null)
+	}
+
+	suspend fun requestFullSyncAndGc(database: MangaDatabase) = withContext(Dispatchers.Default) {
+		requestSyncImpl(favourites = true, history = true, db = database)
+	}
+
+	private fun requestSync(favourites: Boolean, history: Boolean) = processLifecycleScope.launch(Dispatchers.Default) {
+		requestSyncImpl(favourites = favourites, history = history, db = null)
+	}
+
+	private suspend fun requestSyncImpl(favourites: Boolean, history: Boolean, db: MangaDatabase?) = mutex.withLock {
+		if (!favourites && !history) {
+			return
+		}
+		val account = peekAccount()
+		if (account == null || !ContentResolver.getMasterSyncAutomatically()) {
+			db?.gc(favourites, history)
+			return
+		}
+		var gcHistory = false
+		var gcFavourites = false
+		if (favourites) {
+			if (ContentResolver.getSyncAutomatically(account, AUTHORITY_FAVOURITES)) {
+				scheduleSync(account, AUTHORITY_FAVOURITES)
+			} else {
+				gcFavourites = true
+			}
+		}
+		if (history) {
+			if (ContentResolver.getSyncAutomatically(account, AUTHORITY_HISTORY)) {
+				scheduleSync(account, AUTHORITY_HISTORY)
+			} else {
+				gcHistory = true
+			}
+		}
+		if (db != null && (gcHistory || gcFavourites)) {
+			db.gc(gcFavourites, gcHistory)
+		}
+	}
+
+	private fun scheduleSync(account: Account, authority: String) {
+		if (ContentResolver.isSyncActive(account, authority) || ContentResolver.isSyncPending(account, authority)) {
+			return
+		}
+		val job = jobs[authority]
+		if (job?.isActive == true) {
+			// already scheduled
+			return
+		}
+		val lastSyncTime = getLastSync(account, authority)
+		val timeLeft = System.currentTimeMillis() - lastSyncTime + minSyncInterval
+		if (timeLeft <= 0) {
+			jobs.remove(authority)
+			ContentResolver.requestSync(account, authority, Bundle.EMPTY)
+		} else {
+			jobs[authority] = processLifecycleScope.launch(Dispatchers.Default) {
+				try {
+					delay(timeLeft)
+				} finally {
+					// run even if scope cancelled
+					ContentResolver.requestSync(account, authority, Bundle.EMPTY)
+				}
+			}
+		}
+	}
+
+	private fun peekAccount(): Account? {
+		return am.getAccountsByType(accountType).firstOrNull()
+	}
+
+	private suspend fun MangaDatabase.gc(favourites: Boolean, history: Boolean) = withTransaction {
+		val deletedAt = System.currentTimeMillis() - defaultGcPeriod
+		if (history) {
+			historyDao.gc(deletedAt)
+		}
+		if (favourites) {
+			favouritesDao.gc(deletedAt)
+			favouriteCategoriesDao.gc(deletedAt)
+		}
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/domain/SyncHelper.kt

@@ -0,0 +1,272 @@
+package org.koitharu.kotatsu.sync.domain
+
+import android.accounts.Account
+import android.content.*
+import android.database.Cursor
+import android.net.Uri
+import androidx.annotation.WorkerThread
+import androidx.core.content.contentValuesOf
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import org.json.JSONArray
+import org.json.JSONObject
+import org.koitharu.kotatsu.R
+import org.koitharu.kotatsu.core.db.*
+import org.koitharu.kotatsu.parsers.util.json.mapJSONTo
+import org.koitharu.kotatsu.sync.data.SyncAuthApi
+import org.koitharu.kotatsu.sync.data.SyncAuthenticator
+import org.koitharu.kotatsu.sync.data.SyncInterceptor
+import org.koitharu.kotatsu.utils.GZipInterceptor
+import org.koitharu.kotatsu.utils.ext.parseJsonOrNull
+import org.koitharu.kotatsu.utils.ext.toContentValues
+import org.koitharu.kotatsu.utils.ext.toJson
+import org.koitharu.kotatsu.utils.ext.toRequestBody
+import java.util.concurrent.TimeUnit
+
+const val AUTHORITY_HISTORY = "org.koitharu.kotatsu.history"
+const val AUTHORITY_FAVOURITES = "org.koitharu.kotatsu.favourites"
+
+private const val FIELD_TIMESTAMP = "timestamp"
+
+/**
+ * Warning! This class may be used in another process
+ */
+@WorkerThread
+class SyncHelper(
+	context: Context,
+	account: Account,
+	private val provider: ContentProviderClient,
+) {
+
+	private val httpClient = OkHttpClient.Builder()
+		.authenticator(SyncAuthenticator(context, account, SyncAuthApi(context, OkHttpClient())))
+		.addInterceptor(SyncInterceptor(context, account))
+		.addInterceptor(GZipInterceptor())
+		.build()
+	private val baseUrl = context.getString(R.string.url_sync_server)
+	private val defaultGcPeriod: Long // gc period if sync enabled
+		get() = TimeUnit.DAYS.toMillis(4)
+
+	fun syncFavourites(syncResult: SyncResult) {
+		val data = JSONObject()
+		data.put(TABLE_FAVOURITE_CATEGORIES, getFavouriteCategories())
+		data.put(TABLE_FAVOURITES, getFavourites())
+		data.put(FIELD_TIMESTAMP, System.currentTimeMillis())
+		val request = Request.Builder()
+			.url("$baseUrl/resource/$TABLE_FAVOURITES")
+			.post(data.toRequestBody())
+			.build()
+		val response = httpClient.newCall(request).execute().parseJsonOrNull() ?: return
+		val timestamp = response.getLong(FIELD_TIMESTAMP)
+		val categoriesResult = upsertFavouriteCategories(response.getJSONArray(TABLE_FAVOURITE_CATEGORIES), timestamp)
+		syncResult.stats.numDeletes += categoriesResult.first().count?.toLong() ?: 0L
+		syncResult.stats.numInserts += categoriesResult.drop(1).sumOf { it.count?.toLong() ?: 0L }
+		val favouritesResult = upsertFavourites(response.getJSONArray(TABLE_FAVOURITES), timestamp)
+		syncResult.stats.numDeletes += favouritesResult.first().count?.toLong() ?: 0L
+		syncResult.stats.numInserts += favouritesResult.drop(1).sumOf { it.count?.toLong() ?: 0L }
+		gcFavourites()
+	}
+
+	fun syncHistory(syncResult: SyncResult) {
+		val data = JSONObject()
+		data.put(TABLE_HISTORY, getHistory())
+		data.put(FIELD_TIMESTAMP, System.currentTimeMillis())
+		val request = Request.Builder()
+			.url("$baseUrl/resource/$TABLE_HISTORY")
+			.post(data.toRequestBody())
+			.build()
+		val response = httpClient.newCall(request).execute().parseJsonOrNull() ?: return
+		val result = upsertHistory(
+			json = response.getJSONArray(TABLE_HISTORY),
+			timestamp = response.getLong(FIELD_TIMESTAMP),
+		)
+		syncResult.stats.numDeletes += result.first().count?.toLong() ?: 0L
+		syncResult.stats.numInserts += result.drop(1).sumOf { it.count?.toLong() ?: 0L }
+		gcHistory()
+	}
+
+	private fun upsertHistory(json: JSONArray, timestamp: Long): Array<ContentProviderResult> {
+		val uri = uri(AUTHORITY_HISTORY, TABLE_HISTORY)
+		val operations = ArrayList<ContentProviderOperation>()
+		operations += ContentProviderOperation.newDelete(uri)
+			.withSelection("updated_at < ?", arrayOf(timestamp.toString()))
+			.build()
+		json.mapJSONTo(operations) { jo ->
+			operations.addAll(upsertManga(jo.removeJSONObject("manga"), AUTHORITY_HISTORY))
+			ContentProviderOperation.newInsert(uri)
+				.withValues(jo.toContentValues())
+				.build()
+		}
+		return provider.applyBatch(operations)
+	}
+
+	private fun upsertFavouriteCategories(json: JSONArray, timestamp: Long): Array<ContentProviderResult> {
+		val uri = uri(AUTHORITY_FAVOURITES, TABLE_FAVOURITE_CATEGORIES)
+		val operations = ArrayList<ContentProviderOperation>()
+		operations += ContentProviderOperation.newDelete(uri)
+			.withSelection("created_at < ?", arrayOf(timestamp.toString()))
+			.build()
+		json.mapJSONTo(operations) { jo ->
+			ContentProviderOperation.newInsert(uri)
+				.withValues(jo.toContentValues())
+				.build()
+		}
+		return provider.applyBatch(operations)
+	}
+
+	private fun upsertFavourites(json: JSONArray, timestamp: Long): Array<ContentProviderResult> {
+		val uri = uri(AUTHORITY_FAVOURITES, TABLE_FAVOURITES)
+		val operations = ArrayList<ContentProviderOperation>()
+		operations += ContentProviderOperation.newDelete(uri)
+			.withSelection("created_at < ?", arrayOf(timestamp.toString()))
+			.build()
+		json.mapJSONTo(operations) { jo ->
+			operations.addAll(upsertManga(jo.removeJSONObject("manga"), AUTHORITY_FAVOURITES))
+			ContentProviderOperation.newInsert(uri)
+				.withValues(jo.toContentValues())
+				.build()
+		}
+		return provider.applyBatch(operations)
+	}
+
+	private fun upsertManga(json: JSONObject, authority: String): List<ContentProviderOperation> {
+		val tags = json.removeJSONArray(TABLE_TAGS)
+		val result = ArrayList<ContentProviderOperation>(tags.length() * 2 + 1)
+		for (i in 0 until tags.length()) {
+			val tag = tags.getJSONObject(i)
+			result += ContentProviderOperation.newInsert(uri(authority, TABLE_TAGS))
+				.withValues(tag.toContentValues())
+				.build()
+			result += ContentProviderOperation.newInsert(uri(authority, TABLE_MANGA_TAGS))
+				.withValues(
+					contentValuesOf(
+						"manga_id" to json.getLong("manga_id"),
+						"tag_id" to tag.getLong("tag_id"),
+					)
+				).build()
+		}
+		result.add(
+			0,
+			ContentProviderOperation.newInsert(uri(authority, TABLE_MANGA))
+				.withValues(json.toContentValues())
+				.build()
+		)
+		return result
+	}
+
+	private fun getHistory(): JSONArray {
+		return provider.query(AUTHORITY_HISTORY, TABLE_HISTORY).use { cursor ->
+			val json = JSONArray()
+			if (cursor.moveToFirst()) {
+				do {
+					val jo = cursor.toJson()
+					jo.put("manga", getManga(AUTHORITY_HISTORY, jo.getLong("manga_id")))
+					json.put(jo)
+				} while (cursor.moveToNext())
+			}
+			json
+		}
+	}
+
+	private fun getFavourites(): JSONArray {
+		return provider.query(AUTHORITY_FAVOURITES, TABLE_FAVOURITES).use { cursor ->
+			val json = JSONArray()
+			if (cursor.moveToFirst()) {
+				do {
+					val jo = cursor.toJson()
+					jo.put("manga", getManga(AUTHORITY_FAVOURITES, jo.getLong("manga_id")))
+					json.put(jo)
+				} while (cursor.moveToNext())
+			}
+			json
+		}
+	}
+
+	private fun getFavouriteCategories(): JSONArray {
+		return provider.query(AUTHORITY_FAVOURITES, TABLE_FAVOURITE_CATEGORIES).use { cursor ->
+			val json = JSONArray()
+			if (cursor.moveToFirst()) {
+				do {
+					json.put(cursor.toJson())
+				} while (cursor.moveToNext())
+			}
+			json
+		}
+	}
+
+	private fun getManga(authority: String, id: Long): JSONObject {
+		val manga = provider.query(
+			uri(authority, TABLE_MANGA),
+			null,
+			"manga_id = ?",
+			arrayOf(id.toString()),
+			null,
+		)?.use { cursor ->
+			cursor.moveToFirst()
+			cursor.toJson()
+		}
+		requireNotNull(manga)
+		val tags = provider.query(
+			uri(authority, TABLE_MANGA_TAGS),
+			arrayOf("tag_id"),
+			"manga_id = ?",
+			arrayOf(id.toString()),
+			null,
+		)?.use { cursor ->
+			val json = JSONArray()
+			if (cursor.moveToFirst()) {
+				do {
+					val tagId = cursor.getLong(0)
+					json.put(getTag(authority, tagId))
+				} while (cursor.moveToNext())
+			}
+			json
+		}
+		manga.put("tags", requireNotNull(tags))
+		return manga
+	}
+
+	private fun getTag(authority: String, tagId: Long): JSONObject {
+		val tag = provider.query(
+			uri(authority, TABLE_TAGS),
+			null,
+			"tag_id = ?",
+			arrayOf(tagId.toString()),
+			null,
+		)?.use { cursor ->
+			if (cursor.moveToFirst()) {
+				cursor.toJson()
+			} else {
+				null
+			}
+		}
+		return requireNotNull(tag)
+	}
+
+	private fun gcFavourites() {
+		val deletedAt = System.currentTimeMillis() - defaultGcPeriod
+		val selection = "deleted_at != 0 AND deleted_at < ?"
+		val args = arrayOf(deletedAt.toString())
+		provider.delete(uri(AUTHORITY_FAVOURITES, TABLE_FAVOURITES), selection, args)
+		provider.delete(uri(AUTHORITY_FAVOURITES, TABLE_FAVOURITE_CATEGORIES), selection, args)
+	}
+
+	private fun gcHistory() {
+		val deletedAt = System.currentTimeMillis() - defaultGcPeriod
+		val selection = "deleted_at != 0 AND deleted_at < ?"
+		val args = arrayOf(deletedAt.toString())
+		provider.delete(uri(AUTHORITY_HISTORY, TABLE_HISTORY), selection, args)
+	}
+
+	private fun ContentProviderClient.query(authority: String, table: String): Cursor {
+		val uri = uri(authority, table)
+		return query(uri, null, null, null, null)
+			?: throw OperationApplicationException("Query failed: $uri")
+	}
+
+	private fun uri(authority: String, table: String) = Uri.parse("content://$authority/$table")
+
+	private fun JSONObject.removeJSONObject(name: String) = remove(name) as JSONObject
+
+	private fun JSONObject.removeJSONArray(name: String) = remove(name) as JSONArray
+}

app/src/main/java/org/koitharu/kotatsu/sync/ui/SyncAccountAuthenticator.kt

@@ -0,0 +1,78 @@
+package org.koitharu.kotatsu.sync.ui
+
+import android.accounts.AbstractAccountAuthenticator
+import android.accounts.Account
+import android.accounts.AccountAuthenticatorResponse
+import android.accounts.AccountManager
+import android.content.Context
+import android.content.Intent
+import android.os.Bundle
+import android.text.TextUtils
+
+class SyncAccountAuthenticator(private val context: Context) : AbstractAccountAuthenticator(context) {
+
+	override fun editProperties(response: AccountAuthenticatorResponse?, accountType: String?): Bundle? = null
+
+	override fun addAccount(
+		response: AccountAuthenticatorResponse?,
+		accountType: String?,
+		authTokenType: String?,
+		requiredFeatures: Array<out String>?,
+		options: Bundle?,
+	): Bundle {
+		val intent = Intent(context, SyncAuthActivity::class.java)
+		intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response)
+		val bundle = Bundle()
+		if (options != null) {
+			bundle.putAll(options)
+		}
+		bundle.putParcelable(AccountManager.KEY_INTENT, intent)
+		return bundle
+	}
+
+	override fun confirmCredentials(
+		response: AccountAuthenticatorResponse?,
+		account: Account?,
+		options: Bundle?,
+	): Bundle? = null
+
+	override fun getAuthToken(
+		response: AccountAuthenticatorResponse?,
+		account: Account,
+		authTokenType: String?,
+		options: Bundle?,
+	): Bundle {
+		val result = Bundle()
+		val am = AccountManager.get(context.applicationContext)
+		val authToken = am.peekAuthToken(account, authTokenType)
+		if (!TextUtils.isEmpty(authToken)) {
+			result.putString(AccountManager.KEY_ACCOUNT_NAME, account.name)
+			result.putString(AccountManager.KEY_ACCOUNT_TYPE, account.type)
+			result.putString(AccountManager.KEY_AUTHTOKEN, authToken)
+		} else {
+			val intent = Intent(context, SyncAuthActivity::class.java)
+			intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response)
+			val bundle = Bundle()
+			if (options != null) {
+				bundle.putAll(options)
+			}
+			bundle.putParcelable(AccountManager.KEY_INTENT, intent)
+		}
+		return result
+	}
+
+	override fun getAuthTokenLabel(authTokenType: String?): String? = null
+
+	override fun updateCredentials(
+		response: AccountAuthenticatorResponse?,
+		account: Account?,
+		authTokenType: String?,
+		options: Bundle?,
+	): Bundle? = null
+
+	override fun hasFeatures(
+		response: AccountAuthenticatorResponse?,
+		account: Account?,
+		features: Array<out String>?,
+	): Bundle? = null
+}

app/src/main/java/org/koitharu/kotatsu/sync/ui/SyncAuthActivity.kt

@@ -0,0 +1,159 @@
+package org.koitharu.kotatsu.sync.ui
+
+import android.accounts.Account
+import android.accounts.AccountAuthenticatorResponse
+import android.accounts.AccountManager
+import android.os.Bundle
+import android.text.Editable
+import android.text.TextWatcher
+import android.view.View
+import android.widget.Button
+import androidx.core.graphics.Insets
+import androidx.core.view.isGone
+import androidx.core.view.isVisible
+import androidx.transition.Fade
+import androidx.transition.TransitionManager
+import com.google.android.material.dialog.MaterialAlertDialogBuilder
+import org.koin.androidx.viewmodel.ext.android.viewModel
+import org.koitharu.kotatsu.R
+import org.koitharu.kotatsu.base.ui.BaseActivity
+import org.koitharu.kotatsu.databinding.ActivitySyncAuthBinding
+import org.koitharu.kotatsu.sync.domain.SyncAuthResult
+import org.koitharu.kotatsu.utils.ext.getDisplayMessage
+
+class SyncAuthActivity : BaseActivity<ActivitySyncAuthBinding>(), View.OnClickListener {
+
+	private var accountAuthenticatorResponse: AccountAuthenticatorResponse? = null
+	private var resultBundle: Bundle? = null
+
+	private val viewModel by viewModel<SyncAuthViewModel>()
+
+	override fun onCreate(savedInstanceState: Bundle?) {
+		super.onCreate(savedInstanceState)
+		setContentView(ActivitySyncAuthBinding.inflate(layoutInflater))
+		accountAuthenticatorResponse = intent.getParcelableExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE)
+		accountAuthenticatorResponse?.onRequestContinued()
+		binding.buttonCancel.setOnClickListener(this)
+		binding.buttonNext.setOnClickListener(this)
+		binding.buttonBack.setOnClickListener(this)
+		binding.buttonDone.setOnClickListener(this)
+		binding.editEmail.addTextChangedListener(EmailTextWatcher(binding.buttonNext))
+		binding.editPassword.addTextChangedListener(PasswordTextWatcher(binding.buttonDone))
+
+		viewModel.onTokenObtained.observe(this, ::onTokenReceived)
+		viewModel.onError.observe(this, ::onError)
+		viewModel.isLoading.observe(this, ::onLoadingStateChanged)
+	}
+
+	override fun onWindowInsetsChanged(insets: Insets) {
+		val basePadding = resources.getDimensionPixelOffset(R.dimen.screen_padding)
+		binding.root.setPadding(
+			basePadding + insets.left,
+			basePadding + insets.top,
+			basePadding + insets.right,
+			basePadding + insets.bottom,
+		)
+	}
+
+	override fun onBackPressed() {
+		if (binding.switcher.isVisible && binding.switcher.displayedChild > 0) {
+			binding.switcher.showPrevious()
+		} else {
+			super.onBackPressed()
+		}
+	}
+
+	override fun onClick(v: View) {
+		when (v.id) {
+			R.id.button_cancel -> {
+				setResult(RESULT_CANCELED)
+				finish()
+			}
+			R.id.button_next -> {
+				binding.switcher.showNext()
+			}
+			R.id.button_back -> {
+				binding.switcher.showPrevious()
+			}
+			R.id.button_done -> {
+				viewModel.obtainToken(
+					email = binding.editEmail.text.toString(),
+					password = binding.editPassword.text.toString(),
+				)
+			}
+		}
+	}
+
+	override fun finish() {
+		accountAuthenticatorResponse?.let { response ->
+			resultBundle?.also {
+				response.onResult(it)
+			} ?: response.onError(AccountManager.ERROR_CODE_CANCELED, getString(R.string.canceled))
+		}
+		super.finish()
+	}
+
+	private fun onLoadingStateChanged(isLoading: Boolean) {
+		if (isLoading == binding.layoutProgress.isVisible) {
+			return
+		}
+		TransitionManager.beginDelayedTransition(binding.root, Fade())
+		binding.switcher.isGone = isLoading
+		binding.layoutProgress.isVisible = isLoading
+	}
+
+	private fun onError(error: Throwable) {
+		MaterialAlertDialogBuilder(this)
+			.setTitle(R.string.error)
+			.setMessage(error.getDisplayMessage(resources))
+			.setNegativeButton(R.string.close, null)
+			.show()
+	}
+
+	private fun onTokenReceived(authResult: SyncAuthResult) {
+		val am = AccountManager.get(this)
+		val account = Account(authResult.email, getString(R.string.account_type_sync))
+		val result = Bundle()
+		if (am.addAccountExplicitly(account, authResult.password, Bundle())) {
+			result.putString(AccountManager.KEY_ACCOUNT_NAME, account.name)
+			result.putString(AccountManager.KEY_ACCOUNT_TYPE, account.type)
+			result.putString(AccountManager.KEY_AUTHTOKEN, authResult.token)
+			am.setAuthToken(account, account.type, authResult.token)
+		} else {
+			result.putString(AccountManager.KEY_ERROR_MESSAGE, getString(R.string.account_already_exists))
+		}
+		resultBundle = result
+		setResult(RESULT_OK)
+		finish()
+	}
+
+	private class EmailTextWatcher(
+		private val button: Button,
+	) : TextWatcher {
+
+		private val regexEmail = Regex("^[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,6}$", RegexOption.IGNORE_CASE)
+
+		override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) = Unit
+
+		override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) = Unit
+
+		override fun afterTextChanged(s: Editable?) {
+			val text = s?.toString()
+			button.isEnabled = !text.isNullOrEmpty() && regexEmail.matches(text)
+		}
+	}
+
+	private class PasswordTextWatcher(
+		private val button: Button,
+	) : TextWatcher {
+
+		override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) = Unit
+
+		override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) = Unit
+
+		override fun afterTextChanged(s: Editable?) {
+			val text = s?.toString()
+			button.isEnabled = text != null && text.length >= 4
+		}
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/ui/SyncAuthViewModel.kt

@@ -0,0 +1,22 @@
+package org.koitharu.kotatsu.sync.ui
+
+import kotlinx.coroutines.Dispatchers
+import org.koitharu.kotatsu.base.ui.BaseViewModel
+import org.koitharu.kotatsu.sync.data.SyncAuthApi
+import org.koitharu.kotatsu.sync.domain.SyncAuthResult
+import org.koitharu.kotatsu.utils.SingleLiveEvent
+
+class SyncAuthViewModel(
+	private val api: SyncAuthApi,
+) : BaseViewModel() {
+
+	val onTokenObtained = SingleLiveEvent<SyncAuthResult>()
+
+	fun obtainToken(email: String, password: String) {
+		launchLoadingJob(Dispatchers.Default) {
+			val token = api.authenticate(email, password)
+			val result = SyncAuthResult(email, password, token)
+			onTokenObtained.postCall(result)
+		}
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/ui/SyncAuthenticatorService.kt

@@ -0,0 +1,19 @@
+package org.koitharu.kotatsu.sync.ui
+
+import android.app.Service
+import android.content.Intent
+import android.os.IBinder
+
+class SyncAuthenticatorService : Service() {
+
+	private lateinit var authenticator: SyncAccountAuthenticator
+
+	override fun onCreate() {
+		super.onCreate()
+		authenticator = SyncAccountAuthenticator(this)
+	}
+
+	override fun onBind(intent: Intent?): IBinder? {
+		return authenticator.iBinder
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/ui/SyncProvider.kt

@@ -0,0 +1,111 @@
+package org.koitharu.kotatsu.sync.ui
+
+import android.content.ContentProvider
+import android.content.ContentProviderOperation
+import android.content.ContentProviderResult
+import android.content.ContentValues
+import android.database.Cursor
+import android.database.sqlite.SQLiteDatabase
+import android.net.Uri
+import androidx.sqlite.db.SupportSQLiteDatabase
+import androidx.sqlite.db.SupportSQLiteQueryBuilder
+import java.util.concurrent.Callable
+import org.koin.android.ext.android.inject
+import org.koitharu.kotatsu.core.db.*
+
+abstract class SyncProvider : ContentProvider() {
+
+	private val database by inject<MangaDatabase>()
+	private val supportedTables = setOf(
+		TABLE_FAVOURITES,
+		TABLE_MANGA,
+		TABLE_TAGS,
+		TABLE_FAVOURITE_CATEGORIES,
+		TABLE_HISTORY,
+		TABLE_MANGA_TAGS,
+	)
+
+	override fun onCreate(): Boolean {
+		return true
+	}
+
+	override fun query(
+		uri: Uri,
+		projection: Array<out String>?,
+		selection: String?,
+		selectionArgs: Array<out String>?,
+		sortOrder: String?
+	): Cursor? = if (getTableName(uri) != null) {
+		val sqlQuery = SupportSQLiteQueryBuilder.builder(uri.lastPathSegment)
+			.columns(projection)
+			.selection(selection, selectionArgs)
+			.orderBy(sortOrder)
+			.create()
+		database.openHelper.readableDatabase.query(sqlQuery)
+	} else {
+		null
+	}
+
+	override fun getType(uri: Uri): String? {
+		return getTableName(uri)?.let { "vnd.android.cursor.dir/" }
+	}
+
+	override fun insert(uri: Uri, values: ContentValues?): Uri? {
+		val table = getTableName(uri)
+		if (values == null || table == null) {
+			return null
+		}
+		val db = database.openHelper.writableDatabase
+		if (db.insert(table, SQLiteDatabase.CONFLICT_IGNORE, values) < 0) {
+			db.update(table, values)
+		}
+		return uri
+	}
+
+	override fun delete(uri: Uri, selection: String?, selectionArgs: Array<out String>?): Int {
+		val table = getTableName(uri) ?: return 0
+		return database.openHelper.writableDatabase.delete(table, selection, selectionArgs)
+	}
+
+	override fun update(uri: Uri, values: ContentValues?, selection: String?, selectionArgs: Array<out String>?): Int {
+		val table = getTableName(uri)
+		if (values == null || table == null) {
+			return 0
+		}
+		return database.openHelper.writableDatabase
+			.update(table, SQLiteDatabase.CONFLICT_IGNORE, values, selection, selectionArgs)
+	}
+
+	override fun applyBatch(operations: ArrayList<ContentProviderOperation>): Array<ContentProviderResult> {
+		return runAtomicTransaction { super.applyBatch(operations) }
+	}
+
+	override fun bulkInsert(uri: Uri, values: Array<out ContentValues>): Int {
+		return runAtomicTransaction { super.bulkInsert(uri, values) }
+	}
+
+	private fun getTableName(uri: Uri): String? {
+		return uri.pathSegments.singleOrNull()?.takeIf { it in supportedTables }
+	}
+
+	private fun <R> runAtomicTransaction(callable: Callable<R>): R {
+		return synchronized(database) {
+			database.runInTransaction(callable)
+		}
+	}
+
+	private fun SupportSQLiteDatabase.update(table: String, values: ContentValues) {
+		val keys = when (table) {
+			TABLE_TAGS -> listOf("tag_id")
+			TABLE_MANGA_TAGS -> listOf("tag_id", "manga_id")
+			TABLE_MANGA -> listOf("manga_id")
+			TABLE_FAVOURITES -> listOf("manga_id", "category_id")
+			TABLE_FAVOURITE_CATEGORIES -> listOf("category_id")
+			TABLE_HISTORY -> listOf("manga_id")
+			else -> throw IllegalArgumentException("Update for $table is not supported")
+		}
+		val whereClause = keys.joinToString(" AND ") { "`$it` = ?" }
+		val whereArgs = Array<Any>(keys.size) { i -> values.get("`${keys[i]}`") ?: values.get(keys[i]) }
+		this.update(table, SQLiteDatabase.CONFLICT_IGNORE, values, whereClause, whereArgs)
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/ui/favourites/FavouritesSyncAdapter.kt

@@ -0,0 +1,28 @@
+package org.koitharu.kotatsu.sync.ui.favourites
+
+import android.accounts.Account
+import android.content.AbstractThreadedSyncAdapter
+import android.content.ContentProviderClient
+import android.content.Context
+import android.content.SyncResult
+import android.os.Bundle
+import org.koitharu.kotatsu.sync.domain.SyncController
+import org.koitharu.kotatsu.sync.domain.SyncHelper
+import org.koitharu.kotatsu.utils.ext.onError
+
+class FavouritesSyncAdapter(context: Context) : AbstractThreadedSyncAdapter(context, true) {
+
+	override fun onPerformSync(
+		account: Account,
+		extras: Bundle,
+		authority: String,
+		provider: ContentProviderClient,
+		syncResult: SyncResult,
+	) {
+		val syncHelper = SyncHelper(context, account, provider)
+		runCatching {
+			syncHelper.syncFavourites(syncResult)
+			SyncController(context).setLastSync(account, authority, System.currentTimeMillis())
+		}.onFailure(syncResult::onError)
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/ui/favourites/FavouritesSyncProvider.kt

@@ -0,0 +1,5 @@
+package org.koitharu.kotatsu.sync.ui.favourites
+
+import org.koitharu.kotatsu.sync.ui.SyncProvider
+
+class FavouritesSyncProvider : SyncProvider()

app/src/main/java/org/koitharu/kotatsu/sync/ui/favourites/FavouritesSyncService.kt

@@ -0,0 +1,19 @@
+package org.koitharu.kotatsu.sync.ui.favourites
+
+import android.app.Service
+import android.content.Intent
+import android.os.IBinder
+
+class FavouritesSyncService : Service() {
+
+	private lateinit var syncAdapter: FavouritesSyncAdapter
+
+	override fun onCreate() {
+		super.onCreate()
+		syncAdapter = FavouritesSyncAdapter(applicationContext)
+	}
+
+	override fun onBind(intent: Intent?): IBinder {
+		return syncAdapter.syncAdapterBinder
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/ui/history/HistorySyncAdapter.kt

@@ -0,0 +1,28 @@
+package org.koitharu.kotatsu.sync.ui.history
+
+import android.accounts.Account
+import android.content.AbstractThreadedSyncAdapter
+import android.content.ContentProviderClient
+import android.content.Context
+import android.content.SyncResult
+import android.os.Bundle
+import org.koitharu.kotatsu.sync.domain.SyncController
+import org.koitharu.kotatsu.sync.domain.SyncHelper
+import org.koitharu.kotatsu.utils.ext.onError
+
+class HistorySyncAdapter(context: Context) : AbstractThreadedSyncAdapter(context, true) {
+
+	override fun onPerformSync(
+		account: Account,
+		extras: Bundle,
+		authority: String,
+		provider: ContentProviderClient,
+		syncResult: SyncResult,
+	) {
+		val syncHelper = SyncHelper(context, account, provider)
+		runCatching {
+			syncHelper.syncHistory(syncResult)
+			SyncController(context).setLastSync(account, authority, System.currentTimeMillis())
+		}.onFailure(syncResult::onError)
+	}
+}

app/src/main/java/org/koitharu/kotatsu/sync/ui/history/HistorySyncProvider.kt

@@ -0,0 +1,5 @@
+package org.koitharu.kotatsu.sync.ui.history
+
+import org.koitharu.kotatsu.sync.ui.SyncProvider
+
+class HistorySyncProvider : SyncProvider()

app/src/main/java/org/koitharu/kotatsu/sync/ui/history/HistorySyncService.kt

@@ -0,0 +1,19 @@
+package org.koitharu.kotatsu.sync.ui.history
+
+import android.app.Service
+import android.content.Intent
+import android.os.IBinder
+
+class HistorySyncService : Service() {
+
+	private lateinit var syncAdapter: HistorySyncAdapter
+
+	override fun onCreate() {
+		super.onCreate()
+		syncAdapter = HistorySyncAdapter(applicationContext)
+	}
+
+	override fun onBind(intent: Intent?): IBinder {
+		return syncAdapter.syncAdapterBinder
+	}
+}

app/src/main/java/org/koitharu/kotatsu/utils/CompositeMutex.kt

@@ -1,5 +1,6 @@
 package org.koitharu.kotatsu.utils
 
+import android.util.ArrayMap
 import kotlinx.coroutines.CancellableContinuation
 import kotlinx.coroutines.currentCoroutineContext
 import kotlinx.coroutines.isActive
@@ -11,7 +12,7 @@ import kotlin.coroutines.resume
 
 class CompositeMutex<T : Any> : Set<T> {
 
-	private val data = HashMap<T, MutableList<CancellableContinuation<Unit>>>()
+	private val data = ArrayMap<T, MutableList<CancellableContinuation<Unit>>>()
 	private val mutex = Mutex()
 
 	override val size: Int

app/src/main/java/org/koitharu/kotatsu/utils/GZipInterceptor.kt

@@ -0,0 +1,14 @@
+package org.koitharu.kotatsu.utils
+
+import okhttp3.Interceptor
+import okhttp3.Response
+import org.koitharu.kotatsu.core.network.CommonHeaders.CONTENT_ENCODING
+
+class GZipInterceptor : Interceptor {
+
+	override fun intercept(chain: Interceptor.Chain): Response {
+		val newRequest = chain.request().newBuilder()
+		newRequest.addHeader(CONTENT_ENCODING, "gzip")
+		return chain.proceed(newRequest.build())
+	}
+}

app/src/main/java/org/koitharu/kotatsu/utils/ext/AndroidExt.kt

@@ -4,9 +4,13 @@ import android.app.ActivityManager
 import android.app.ActivityOptions
 import android.content.Context
 import android.content.Context.ACTIVITY_SERVICE
+import android.content.OperationApplicationException
 import android.content.SharedPreferences
+import android.content.SyncResult
 import android.content.pm.ResolveInfo
+import android.database.SQLException
 import android.graphics.Color
+
 import android.net.ConnectivityManager
 import android.net.Network
 import android.net.NetworkRequest
@@ -35,6 +39,9 @@ import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.flow
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.suspendCancellableCoroutine
+import okio.IOException
+import org.json.JSONException
+import org.koitharu.kotatsu.BuildConfig
 import org.koitharu.kotatsu.utils.InternalResourceHelper
 import kotlin.coroutines.resume
 
@@ -111,6 +118,17 @@ fun Lifecycle.postDelayed(runnable: Runnable, delay: Long) {
 	}
 }
 
+fun SyncResult.onError(error: Throwable) {
+	when (error) {
+		is IOException -> stats.numIoExceptions++
+		is OperationApplicationException,
+		is SQLException -> databaseError = true
+		is JSONException -> stats.numParseExceptions++
+		else -> if (BuildConfig.DEBUG) throw error
+	}
+	error.printStackTraceDebug()
+}
+
 fun Window.setNavigationBarTransparentCompat(context: Context, elevation: Float = 0F) {
 	navigationBarColor = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q &&
 		!InternalResourceHelper.getBoolean(context, "config_navBarNeedsScrim", true)

app/src/main/java/org/koitharu/kotatsu/utils/ext/CursorExt.kt

@@ -0,0 +1,39 @@
+package org.koitharu.kotatsu.utils.ext
+
+import android.content.ContentValues
+import android.database.Cursor
+import org.json.JSONObject
+
+fun Cursor.toJson(): JSONObject {
+	val jo = JSONObject()
+	for (i in 0 until columnCount) {
+		val name = getColumnName(i)
+		when (getType(i)) {
+			Cursor.FIELD_TYPE_STRING -> jo.put(name, getString(i))
+			Cursor.FIELD_TYPE_FLOAT -> jo.put(name, getDouble(i))
+			Cursor.FIELD_TYPE_INTEGER -> jo.put(name, getLong(i))
+			Cursor.FIELD_TYPE_NULL -> jo.put(name, null)
+			Cursor.FIELD_TYPE_BLOB -> jo.put(name, getBlob(i))
+		}
+	}
+	return jo
+}
+
+fun JSONObject.toContentValues(): ContentValues {
+	val cv = ContentValues(length())
+	for (key in keys()) {
+		val name = key.escapeName()
+		when (val value = get(key)) {
+			JSONObject.NULL, "null", null -> cv.putNull(name)
+			is String -> cv.put(name, value)
+			is Float -> cv.put(name, value)
+			is Double -> cv.put(name, value)
+			is Int -> cv.put(name, value)
+			is Long -> cv.put(name, value)
+			else -> throw IllegalArgumentException("Value $value cannot be putted in ContentValues")
+		}
+	}
+	return cv
+}
+
+private fun String.escapeName() = "`$this`"

app/src/main/java/org/koitharu/kotatsu/utils/ext/HttpExt.kt

@@ -1,10 +1,20 @@
-
 package org.koitharu.kotatsu.utils.ext
 
 import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.RequestBody.Companion.toRequestBody
+import okhttp3.Response
 import org.json.JSONObject
+import org.koitharu.kotatsu.parsers.util.parseJson
+import java.net.HttpURLConnection
 
 private val TYPE_JSON = "application/json".toMediaType()
 
 fun JSONObject.toRequestBody() = toString().toRequestBody(TYPE_JSON)
+
+fun Response.parseJsonOrNull(): JSONObject? {
+	return if (code == HttpURLConnection.HTTP_NO_CONTENT) {
+		null
+	} else {
+		parseJson()
+	}
+}

app/src/main/java/org/koitharu/kotatsu/widget/WidgetUpdater.kt

@@ -10,7 +10,9 @@ import org.koitharu.kotatsu.core.db.TABLE_HISTORY
 import org.koitharu.kotatsu.widget.recent.RecentWidgetProvider
 import org.koitharu.kotatsu.widget.shelf.ShelfWidgetProvider
 
-class WidgetUpdater(private val context: Context) : InvalidationTracker.Observer(TABLE_HISTORY, TABLE_FAVOURITES) {
+class WidgetUpdater(
+	private val context: Context
+) : InvalidationTracker.Observer(TABLE_HISTORY, TABLE_FAVOURITES) {
 
 	override fun onInvalidated(tables: MutableSet<String>) {
 		if (TABLE_HISTORY in tables) {

app/src/main/res/drawable/ic_sync.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector
+	xmlns:android="http://schemas.android.com/apk/res/android"
+	android:width="24dp"
+	android:height="24dp"
+	android:tint="?colorControlNormal"
+	android:viewportWidth="24"
+	android:viewportHeight="24">
+	<path
+		android:fillColor="#000"
+		android:pathData="M12,18A6,6 0 0,1 6,12C6,11 6.25,10.03 6.7,9.2L5.24,7.74C4.46,8.97 4,10.43 4,12A8,8 0 0,0 12,20V23L16,19L12,15M12,4V1L8,5L12,9V6A6,6 0 0,1 18,12C18,13 17.75,13.97 17.3,14.8L18.76,16.26C19.54,15.03 20,13.57 20,12A8,8 0 0,0 12,4Z" />
+</vector>

app/src/main/res/layout/activity_sync_auth.xml

@@ -0,0 +1,178 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+	xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:orientation="vertical"
+	android:padding="@dimen/screen_padding">
+
+	<TextView
+		android:id="@+id/textView_title"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="8dp"
+		android:drawablePadding="16dp"
+		android:gravity="center_horizontal"
+		android:text="@string/sync_title"
+		android:textAppearance="?textAppearanceHeadline5"
+		app:drawableTint="?colorPrimary"
+		app:drawableTopCompat="@drawable/ic_sync"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toTopOf="parent" />
+
+	<ViewSwitcher
+		android:id="@+id/switcher"
+		android:layout_width="match_parent"
+		android:layout_height="match_parent">
+
+		<RelativeLayout
+			android:id="@+id/page_email"
+			android:layout_width="match_parent"
+			android:layout_height="match_parent">
+
+			<TextView
+				android:id="@+id/textView_subtitle"
+				android:layout_width="0dp"
+				android:layout_height="wrap_content"
+				android:layout_alignParentStart="true"
+				android:layout_alignParentTop="true"
+				android:layout_alignParentEnd="true"
+				android:layout_marginTop="12dp"
+				android:gravity="center_horizontal"
+				android:text="@string/email_enter_hint"
+				android:textAppearance="?textAppearanceSubtitle1" />
+
+			<com.google.android.material.textfield.TextInputLayout
+				android:id="@+id/layout_email"
+				style="@style/Widget.MaterialComponents.TextInputLayout.OutlinedBox"
+				android:layout_width="0dp"
+				android:layout_height="wrap_content"
+				android:layout_below="@id/textView_subtitle"
+				android:layout_alignParentStart="true"
+				android:layout_alignParentEnd="true"
+				android:layout_marginTop="30dp"
+				app:errorIconDrawable="@null"
+				app:helperText="You can sign in into an existing account or create a new one"
+				app:hintEnabled="false">
+
+				<com.google.android.material.textfield.TextInputEditText
+					android:id="@+id/edit_email"
+					android:layout_width="match_parent"
+					android:layout_height="wrap_content"
+					android:autofillHints="emailAddress"
+					android:imeOptions="actionDone"
+					android:inputType="textEmailAddress"
+					android:singleLine="true"
+					android:textSize="16sp"
+					tools:text="test@mail.com" />
+
+			</com.google.android.material.textfield.TextInputLayout>
+
+			<Button
+				android:id="@+id/button_cancel"
+				style="@style/Widget.Material3.Button.OutlinedButton"
+				android:layout_width="wrap_content"
+				android:layout_height="wrap_content"
+				android:layout_alignParentStart="true"
+				android:layout_alignParentBottom="true"
+				android:text="@android:string/cancel" />
+
+			<Button
+				android:id="@+id/button_next"
+				style="@style/Widget.Material3.Button.TonalButton"
+				android:layout_width="wrap_content"
+				android:layout_height="wrap_content"
+				android:layout_alignParentEnd="true"
+				android:layout_alignParentBottom="true"
+				android:enabled="false"
+				android:text="@string/next"
+				tools:ignore="RelativeOverlap" />
+
+		</RelativeLayout>
+
+		<RelativeLayout
+			android:id="@+id/page_password"
+			android:layout_width="match_parent"
+			android:layout_height="match_parent">
+
+			<TextView
+				android:id="@+id/textView_subtitle_2"
+				android:layout_width="0dp"
+				android:layout_height="wrap_content"
+				android:layout_alignParentStart="true"
+				android:layout_alignParentTop="true"
+				android:layout_alignParentEnd="true"
+				android:layout_marginTop="12dp"
+				android:gravity="center_horizontal"
+				android:text="@string/enter_email_text"
+				android:textAppearance="?textAppearanceSubtitle1" />
+
+			<com.google.android.material.textfield.TextInputLayout
+				android:id="@+id/layout_password"
+				style="@style/Widget.MaterialComponents.TextInputLayout.OutlinedBox"
+				android:layout_width="0dp"
+				android:layout_height="wrap_content"
+				android:layout_below="@id/textView_subtitle_2"
+				android:layout_alignParentStart="true"
+				android:layout_alignParentEnd="true"
+				android:layout_marginTop="30dp"
+				app:endIconMode="password_toggle"
+				app:errorIconDrawable="@null"
+				app:helperText="You can sign in into an existing account or create a new one"
+				app:hintEnabled="false">
+
+				<com.google.android.material.textfield.TextInputEditText
+					android:id="@+id/edit_password"
+					android:layout_width="match_parent"
+					android:layout_height="wrap_content"
+					android:autofillHints="password"
+					android:imeOptions="actionDone"
+					android:inputType="textPassword"
+					android:maxLength="24"
+					android:singleLine="true"
+					android:textSize="16sp"
+					tools:text="qwerty" />
+
+			</com.google.android.material.textfield.TextInputLayout>
+
+			<Button
+				android:id="@+id/button_back"
+				style="@style/Widget.Material3.Button.OutlinedButton"
+				android:layout_width="wrap_content"
+				android:layout_height="wrap_content"
+				android:layout_alignParentStart="true"
+				android:layout_alignParentBottom="true"
+				android:text="@string/back" />
+
+			<Button
+				android:id="@+id/button_done"
+				style="@style/Widget.Material3.Button.TonalButton"
+				android:layout_width="wrap_content"
+				android:layout_height="wrap_content"
+				android:layout_alignParentEnd="true"
+				android:layout_alignParentBottom="true"
+				android:enabled="false"
+				android:text="@string/done"
+				tools:ignore="RelativeOverlap" />
+
+		</RelativeLayout>
+	</ViewSwitcher>
+
+	<FrameLayout
+		android:id="@+id/layout_progress"
+		android:layout_width="match_parent"
+		android:layout_height="match_parent"
+		android:visibility="gone">
+
+		<com.google.android.material.progressindicator.CircularProgressIndicator
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:layout_gravity="center"
+			android:indeterminate="true" />
+
+	</FrameLayout>
+
+</LinearLayout>

app/src/main/res/values/constants.xml

@@ -1,12 +1,14 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-	<string name="url_github">https://github.com/KotatsuApp/Kotatsu</string>
+	<string name="url_github" translatable="false">https://github.com/KotatsuApp/Kotatsu</string>
-	<string name="url_discord">https://discord.gg/NNJ5RgVBC5</string>
+	<string name="url_discord" translatable="false">https://discord.gg/NNJ5RgVBC5</string>
-	<string name="url_forpda">https://4pda.to/forum/index.php?showtopic=697669</string>
+	<string name="url_forpda" translatable="false">https://4pda.to/forum/index.php?showtopic=697669</string>
-	<string name="url_twitter">https://twitter.com/kotatsuapp</string>
+	<string name="url_twitter" translatable="false">https://twitter.com/kotatsuapp</string>
-	<string name="url_reddit">https://reddit.com/user/kotatsuapp</string>
+	<string name="url_reddit" translatable="false">https://reddit.com/user/kotatsuapp</string>
-	<string name="url_weblate">https://hosted.weblate.org/engage/kotatsu</string>
+	<string name="url_weblate" translatable="false">https://hosted.weblate.org/engage/kotatsu</string>
-	<string name="email_error_report">kotatsu@waifu.club</string>
+	<string name="email_error_report" translatable="false">kotatsu@waifu.club</string>
+	<string name="account_type_sync" translatable="false">org.kotatsu.sync</string>
+	<string name="url_sync_server" translatable="false">http://95.216.215.49:8055</string>
 	<string-array name="values_theme" translatable="false">
 		<item>-1</item>
 		<item>1</item>

app/src/main/res/values/strings.xml

@@ -276,6 +276,12 @@
 	<string name="download_slowdown_summary">Helps avoid blocking your IP address</string>
 	<string name="local_manga_processing">Saved manga processing</string>
 	<string name="chapters_will_removed_background">Chapters will be removed in the background. It can take some time</string>
+	<string name="canceled">Canceled</string>
+	<string name="account_already_exists">Account already exists</string>
+	<string name="back">Back</string>
+	<string name="sync">Synchronization</string>
+	<string name="sync_title">Sync your data</string>
+	<string name="email_enter_hint">Enter your email to continue</string>
 	<string name="hide">Hide</string>
 	<string name="new_sources_text">New manga sources are available</string>
 	<string name="check_new_chapters_title">Check for new chapters and notify about it</string>
@@ -347,4 +353,7 @@
 	<string name="storage_usage">Storage usage</string>
 	<string name="available">Available</string>
 	<string name="memory_usage_pattern">%s - %s</string>
+	<string name="enter_email_text">Enter your email to continue</string>
+	<string name="removed_from_favourites">Removed from favourites</string>
+	<string name="removed_from_s">Removed from \"%s\"</string>
 </resources>

app/src/main/res/xml/authenticator_sync.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<account-authenticator
+	xmlns:android="http://schemas.android.com/apk/res/android"
+	android:accountPreferences="@xml/pref_sync"
+	android:accountType="@string/account_type_sync"
+	android:icon="@mipmap/ic_launcher"
+	android:label="@string/app_name" />

app/src/main/res/xml/pref_content.xml

@@ -39,9 +39,15 @@
 		android:valueTo="5"
 		app:defaultValue="2" />
 
+	<Preference
+		android:key="sync"
+		android:persistent="false"
+		android:summary="@string/sync_title"
+		android:title="@string/sync"
+		app:allowDividerAbove="true" />
+
 	<PreferenceScreen
 		android:fragment="org.koitharu.kotatsu.settings.backup.BackupSettingsFragment"
-		android:title="@string/backup_restore"
+		android:title="@string/backup_restore" />
-		app:allowDividerAbove="true" />
 
 </PreferenceScreen>

app/src/main/res/xml/pref_sync.xml

@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="utf-8"?>
+<PreferenceScreen />

app/src/main/res/xml/sync_favourites.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<sync-adapter xmlns:android="http://schemas.android.com/apk/res/android"
+	android:accountType="@string/account_type_sync"
+	android:allowParallelSyncs="false"
+	android:contentAuthority="org.koitharu.kotatsu.favourites"
+	android:isAlwaysSyncable="true"
+	android:supportsUploading="true"
+	android:userVisible="true" />

app/src/main/res/xml/sync_history.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<sync-adapter xmlns:android="http://schemas.android.com/apk/res/android"
+	android:accountType="@string/account_type_sync"
+	android:allowParallelSyncs="false"
+	android:contentAuthority="org.koitharu.kotatsu.history"
+	android:isAlwaysSyncable="true"
+	android:supportsUploading="true"
+	android:userVisible="true" />