tutanota/src/api/worker/offline/OfflineStorage.ts

import { ElementEntity, ListElementEntity, SomeEntity, TypeModel } from "../../common/EntityTypes.js"
import {
	elementIdPart,
	firstBiggerThanSecond,
	GENERATED_MAX_ID,
	GENERATED_MIN_ID,
	getElementId,
	listIdPart,
	timestampToGeneratedId,
} from "../../common/utils/EntityUtils.js"
import { CacheStorage, expandId, ExposedCacheStorage, LastUpdateTime } from "../rest/DefaultEntityRestCache.js"
import * as cborg from "cborg"
import { EncodeOptions, Token, Type } from "cborg"
import {
	assert,
	assertNotNull,
	DAY_IN_MILLIS,
	getTypeId,
	groupByAndMap,
	groupByAndMapUniquely,
	mapNullable,
	splitInChunks,
	TypeRef,
} from "@tutao/tutanota-utils"
import { isDesktop, isOfflineStorageAvailable, isTest } from "../../common/Env.js"
import { modelInfos, resolveTypeReference } from "../../common/EntityFunctions.js"
import { AccountType, OFFLINE_STORAGE_DEFAULT_TIME_RANGE_DAYS } from "../../common/TutanotaConstants.js"
import { DateProvider } from "../../common/DateProvider.js"
import { TokenOrNestedTokens } from "cborg/interface"
import {
	CalendarEventTypeRef,
	FileTypeRef,
	MailBodyTypeRef,
	MailDetailsBlobTypeRef,
	MailDetailsDraftTypeRef,
	MailFolderTypeRef,
	MailHeadersTypeRef,
	MailTypeRef,
} from "../../entities/tutanota/TypeRefs.js"
import { UserTypeRef } from "../../entities/sys/TypeRefs.js"
import { OfflineStorageMigrator } from "./OfflineStorageMigrator.js"
import { CustomCacheHandlerMap, CustomCalendarEventCacheHandler } from "../rest/CustomCacheHandler.js"
import { EntityRestClient } from "../rest/EntityRestClient.js"
import { InterWindowEventFacadeSendDispatcher } from "../../../native/common/generatedipc/InterWindowEventFacadeSendDispatcher.js"
import { SqlCipherFacade } from "../../../native/common/generatedipc/SqlCipherFacade.js"
import { FormattedQuery, SqlValue, TaggedSqlValue, tagSqlValue, untagSqlObject } from "./SqlValue.js"
import { FolderSystem } from "../../common/mail/FolderSystem.js"
import { isDetailsDraft, isLegacyMail } from "../../common/MailWrapper.js"
import { Type as TypeId } from "../../common/EntityConstants.js"
import { OutOfSyncError } from "../../common/error/OutOfSyncError.js"
import { isSpamOrTrashFolder } from "../../common/mail/CommonMailUtils.js"

/**
 * this is the value of SQLITE_MAX_VARIABLE_NUMBER in sqlite3.c
 * it may change if the sqlite version is updated.
 * */
const MAX_SAFE_SQL_VARS = 32766

function dateEncoder(data: Date, typ: string, options: EncodeOptions): TokenOrNestedTokens | null {
	const time = data.getTime()
	return [
		// https://datatracker.ietf.org/doc/rfc8943/
		new Token(Type.tag, 100),
		new Token(time < 0 ? Type.negint : Type.uint, time),
	]
}

function dateDecoder(bytes: number): Date {
	return new Date(bytes)
}

export const customTypeEncoders: { [typeName: string]: typeof dateEncoder } = Object.freeze({
	Date: dateEncoder,
})

type TypeDecoder = (_: any) => any
export const customTypeDecoders: Array<TypeDecoder> = (() => {
	const tags: Array<TypeDecoder> = []
	tags[100] = dateDecoder
	return tags
})()

/**
 * For each of these keys we track the current version in the database.
 * The keys are different model versions (because we need to migrate the data with certain model version changes) and "offline" key which is used to track
 * migrations that are needed for other reasons e.g. if DB structure changes or if we need to invalidate some tables.
 */
export type VersionMetadataBaseKey = keyof typeof modelInfos | "offline"

type VersionMetadataEntries = {
	// Yes this is cursed, give me a break
	[P in VersionMetadataBaseKey as `${P}-version`]: number
}

export interface OfflineDbMeta extends VersionMetadataEntries {
	lastUpdateTime: number
	timeRangeDays: number
}

const TableDefinitions = Object.freeze({
	// plus ownerGroup added in a migration
	list_entities:
		"type TEXT NOT NULL, listId TEXT NOT NULL, elementId TEXT NOT NULL, ownerGroup TEXT, entity BLOB NOT NULL, PRIMARY KEY (type, listId, elementId)",
	// plus ownerGroup added in a migration
	element_entities: "type TEXT NOT NULL, elementId TEXT NOT NULL, ownerGroup TEXT, entity BLOB NOT NULL, PRIMARY KEY (type, elementId)",
	ranges: "type TEXT NOT NULL, listId TEXT NOT NULL, lower TEXT NOT NULL, upper TEXT NOT NULL, PRIMARY KEY (type, listId)",
	lastUpdateBatchIdPerGroupId: "groupId TEXT NOT NULL, batchId TEXT NOT NULL, PRIMARY KEY (groupId)",
	metadata: "key TEXT NOT NULL, value BLOB, PRIMARY KEY (key)",
	blob_element_entities:
		"type TEXT NOT NULL, listId TEXT NOT NULL, elementId TEXT NOT NULL, ownerGroup TEXT, entity BLOB NOT NULL, PRIMARY KEY (type, listId, elementId)",
} as const)

type Range = { lower: string; upper: string }

export interface OfflineStorageInitArgs {
	userId: Id
	databaseKey: Uint8Array
	timeRangeDays: number | null
	forceNewDatabase: boolean
}

export class OfflineStorage implements CacheStorage, ExposedCacheStorage {
	private customCacheHandler: CustomCacheHandlerMap | null = null
	private userId: Id | null = null
	private timeRangeDays: number | null = null

	constructor(
		private readonly sqlCipherFacade: SqlCipherFacade,
		private readonly interWindowEventSender: InterWindowEventFacadeSendDispatcher,
		private readonly dateProvider: DateProvider,
		private readonly migrator: OfflineStorageMigrator,
	) {
		assert(isOfflineStorageAvailable() || isTest(), "Offline storage is not available.")
	}

	/**
	 * @return {boolean} whether the database was newly created or not
	 */
	async init({ userId, databaseKey, timeRangeDays, forceNewDatabase }: OfflineStorageInitArgs): Promise<boolean> {
		this.userId = userId
		this.timeRangeDays = timeRangeDays
		if (forceNewDatabase) {
			if (isDesktop()) {
				await this.interWindowEventSender.localUserDataInvalidated(userId)
			}
			await this.sqlCipherFacade.deleteDb(userId)
		}
		// We open database here, and it is closed in the native side when the window is closed or the page is reloaded
		await this.sqlCipherFacade.openDb(userId, databaseKey)
		await this.createTables()
		try {
			await this.migrator.migrate(this, this.sqlCipherFacade)
		} catch (e) {
			if (e instanceof OutOfSyncError) {
				console.warn("Offline db is out of sync!", e)
				await this.recreateDbFile(userId, databaseKey)
				await this.migrator.migrate(this, this.sqlCipherFacade)
			} else {
				throw e
			}
		}
		// if nothing is written here, it means it's a new database
		return (await this.getLastUpdateTime()).type === "never"
	}

	private async recreateDbFile(userId: string, databaseKey: Uint8Array): Promise<void> {
		console.log(`recreating DB file for userId ${userId}`)
		await this.sqlCipherFacade.closeDb()
		await this.sqlCipherFacade.deleteDb(userId)
		await this.sqlCipherFacade.openDb(userId, databaseKey)
		await this.createTables()
	}

	/**
	 * currently, we close DBs from the native side (mainly on things like reload and on android's onDestroy)
	 */
	async deinit() {
		this.userId = null
		await this.sqlCipherFacade.closeDb()
	}

	async deleteIfExists(typeRef: TypeRef<SomeEntity>, listId: Id | null, elementId: Id): Promise<void> {
		const type = getTypeId(typeRef)
		let typeModel: TypeModel
		try {
			typeModel = await resolveTypeReference(typeRef)
		} catch (e) {
			// prevent failed lookup for BlobToFileMapping - this catch block can be removed after May 2023
			console.log("couldn't resolve typeRef ", typeRef)
			return
		}
		let formattedQuery
		switch (typeModel.type) {
			case TypeId.Element:
				formattedQuery = sql`DELETE FROM element_entities WHERE type = ${type} AND elementId = ${elementId}`
				break
			case TypeId.ListElement:
				formattedQuery = sql`DELETE FROM list_entities WHERE type = ${type} AND listId = ${listId} AND elementId = ${elementId}`
				break
			case TypeId.BlobElement:
				formattedQuery = sql`DELETE FROM blob_element_entities WHERE type = ${type} AND listId = ${listId} AND elementId = ${elementId}`
				break
			default:
				throw new Error("must be a persistent type")
		}
		await this.sqlCipherFacade.run(formattedQuery.query, formattedQuery.params)
	}

	async deleteAllOfType(typeRef: TypeRef<SomeEntity>): Promise<void> {
		const type = getTypeId(typeRef)
		let typeModel: TypeModel
		try {
			typeModel = await resolveTypeReference(typeRef)
		} catch (e) {
			// prevent failed lookup for BlobToFileMapping - this catch block can be removed after May 2023
			console.log("couldn't resolve typeRef ", typeRef)
			return
		}
		let formattedQuery
		switch (typeModel.type) {
			case TypeId.Element:
				formattedQuery = sql`DELETE FROM element_entities WHERE type = ${type}`
				break
			case TypeId.ListElement:
				formattedQuery = sql`DELETE FROM list_entities WHERE type = ${type}`
				await this.sqlCipherFacade.run(formattedQuery.query, formattedQuery.params)
				await this.deleteAllRangesForType(type)
				return
			case TypeId.BlobElement:
				formattedQuery = sql`DELETE FROM blob_element_entities WHERE type = ${type}`
				break
			default:
				throw new Error("must be a persistent type")
		}
		await this.sqlCipherFacade.run(formattedQuery.query, formattedQuery.params)
	}

	private async deleteAllRangesForType(type: string): Promise<void> {
		const { query, params } = sql`DELETE FROM ranges WHERE type = ${type}`
		await this.sqlCipherFacade.run(query, params)
	}

	async get<T extends SomeEntity>(typeRef: TypeRef<T>, listId: Id | null, elementId: Id): Promise<T | null> {
		const type = getTypeId(typeRef)
		const typeModel = await resolveTypeReference(typeRef)
		let formattedQuery
		switch (typeModel.type) {
			case TypeId.Element:
				formattedQuery = sql`SELECT entity from element_entities WHERE type = ${type} AND elementId = ${elementId}`
				break
			case TypeId.ListElement:
				formattedQuery = sql`SELECT entity from list_entities WHERE type = ${type} AND listId = ${listId} AND elementId = ${elementId}`
				break
			case TypeId.BlobElement:
				formattedQuery = sql`SELECT entity from blob_element_entities WHERE type = ${type} AND listId = ${listId} AND elementId = ${elementId}`
				break
			default:
				throw new Error("must be a persistent type")
		}
		const result = await this.sqlCipherFacade.get(formattedQuery.query, formattedQuery.params)
		return result?.entity ? this.deserialize(typeRef, result.entity.value as Uint8Array) : null
	}

	async getIdsInRange<T extends ListElementEntity>(typeRef: TypeRef<T>, listId: Id): Promise<Array<Id>> {
		const type = getTypeId(typeRef)
		const range = await this.getRange(type, listId)
		if (range == null) {
			throw new Error(`no range exists for ${type} and list ${listId}`)
		}
		const { lower, upper } = range
		const { query, params } = sql`SELECT elementId FROM list_entities
WHERE type = ${type}
AND listId = ${listId}
AND (elementId = ${lower}
OR ${firstIdBigger("elementId", lower)})
AND NOT(${firstIdBigger("elementId", upper)})`
		const rows = await this.sqlCipherFacade.all(query, params)
		return rows.map((row) => row.elementId.value as string)
	}

	async getRangeForList<T extends ListElementEntity>(typeRef: TypeRef<T>, listId: Id): Promise<Range | null> {
		return this.getRange(getTypeId(typeRef), listId)
	}

	async isElementIdInCacheRange<T extends ListElementEntity>(typeRef: TypeRef<T>, listId: Id, id: Id): Promise<boolean> {
		const range = await this.getRangeForList(typeRef, listId)
		return range != null && !firstBiggerThanSecond(id, range.upper) && !firstBiggerThanSecond(range.lower, id)
	}

	async provideFromRange<T extends ListElementEntity>(typeRef: TypeRef<T>, listId: Id, start: Id, count: number, reverse: boolean): Promise<T[]> {
		const type = getTypeId(typeRef)
		let formattedQuery
		if (reverse) {
			formattedQuery = sql`SELECT entity FROM list_entities WHERE type = ${type} AND listId = ${listId} AND ${firstIdBigger(
				start,
				"elementId",
			)} ORDER BY LENGTH(elementId) DESC, elementId DESC LIMIT ${count}`
		} else {
			formattedQuery = sql`SELECT entity FROM list_entities WHERE type = ${type} AND listId = ${listId} AND ${firstIdBigger(
				"elementId",
				start,
			)} ORDER BY LENGTH(elementId) ASC, elementId ASC LIMIT ${count}`
		}
		const { query, params } = formattedQuery
		const serializedList: ReadonlyArray<Record<string, TaggedSqlValue>> = await this.sqlCipherFacade.all(query, params)
		return this.deserializeList(
			typeRef,
			serializedList.map((r) => r.entity.value as Uint8Array),
		)
	}

	async put(originalEntity: SomeEntity): Promise<void> {
		const serializedEntity = this.serialize(originalEntity)
		const { listId, elementId } = expandId(originalEntity._id)
		const type = getTypeId(originalEntity._type)
		const ownerGroup = originalEntity._ownerGroup
		const typeModel = await resolveTypeReference(originalEntity._type)
		let formattedQuery: FormattedQuery
		switch (typeModel.type) {
			case TypeId.Element:
				formattedQuery = sql`INSERT OR REPLACE INTO element_entities (type, elementId, ownerGroup, entity) VALUES (${type}, ${elementId}, ${ownerGroup}, ${serializedEntity})`
				break
			case TypeId.ListElement:
				formattedQuery = sql`INSERT OR REPLACE INTO list_entities (type, listId, elementId, ownerGroup, entity) VALUES (${type}, ${listId}, ${elementId}, ${ownerGroup}, ${serializedEntity})`
				break
			case TypeId.BlobElement:
				formattedQuery = sql`INSERT OR REPLACE INTO blob_element_entities (type, listId, elementId, ownerGroup, entity) VALUES (${type}, ${listId}, ${elementId}, ${ownerGroup}, ${serializedEntity})`
				break
			default:
				throw new Error("must be a persistent type")
		}
		await this.sqlCipherFacade.run(formattedQuery.query, formattedQuery.params)
	}

	async setLowerRangeForList<T extends ListElementEntity>(typeRef: TypeRef<T>, listId: Id, id: Id): Promise<void> {
		const type = getTypeId(typeRef)
		const { query, params } = sql`UPDATE ranges SET lower = ${id} WHERE type = ${type} AND listId = ${listId}`
		await this.sqlCipherFacade.run(query, params)
	}

	async setUpperRangeForList<T extends ListElementEntity>(typeRef: TypeRef<T>, listId: Id, id: Id): Promise<void> {
		const type = getTypeId(typeRef)
		const { query, params } = sql`UPDATE ranges SET upper = ${id} WHERE type = ${type} AND listId = ${listId}`
		await this.sqlCipherFacade.run(query, params)
	}

	async setNewRangeForList<T extends ListElementEntity>(typeRef: TypeRef<T>, listId: Id, lower: Id, upper: Id): Promise<void> {
		const type = getTypeId(typeRef)
		const { query, params } = sql`INSERT OR REPLACE INTO ranges VALUES (${type}, ${listId}, ${lower}, ${upper})`
		return this.sqlCipherFacade.run(query, params)
	}

	async getLastBatchIdForGroup(groupId: Id): Promise<Id | null> {
		const { query, params } = sql`SELECT batchId from lastUpdateBatchIdPerGroupId WHERE groupId = ${groupId}`
		const row = (await this.sqlCipherFacade.get(query, params)) as { batchId: TaggedSqlValue } | null
		return (row?.batchId?.value ?? null) as Id | null
	}

	async putLastBatchIdForGroup(groupId: Id, batchId: Id): Promise<void> {
		const { query, params } = sql`INSERT OR REPLACE INTO lastUpdateBatchIdPerGroupId VALUES (${groupId}, ${batchId})`
		await this.sqlCipherFacade.run(query, params)
	}

	async getLastUpdateTime(): Promise<LastUpdateTime> {
		const time = await this.getMetadata("lastUpdateTime")
		return time ? { type: "recorded", time } : { type: "never" }
	}

	async putLastUpdateTime(ms: number): Promise<void> {
		await this.putMetadata("lastUpdateTime", ms)
	}

	async purgeStorage(): Promise<void> {
		for (let name of Object.keys(TableDefinitions)) {
			await this.sqlCipherFacade.run(`DELETE FROM ${name}`, [])
		}
	}

	async deleteRange(typeRef: TypeRef<unknown>, listId: string): Promise<void> {
		const { query, params } = sql`DELETE FROM ranges WHERE type = ${getTypeId(typeRef)} AND listId = ${listId}`
		await this.sqlCipherFacade.run(query, params)
	}

	async getListElementsOfType<T extends ListElementEntity>(typeRef: TypeRef<T>): Promise<Array<T>> {
		const { query, params } = sql`SELECT entity from list_entities WHERE type = ${getTypeId(typeRef)}`
		const items = (await this.sqlCipherFacade.all(query, params)) ?? []
		return this.deserializeList(
			typeRef,
			items.map((row) => row.entity.value as Uint8Array),
		)
	}

	async getElementsOfType<T extends ElementEntity>(typeRef: TypeRef<T>): Promise<Array<T>> {
		const { query, params } = sql`SELECT entity from element_entities WHERE type = ${getTypeId(typeRef)}`
		const items = (await this.sqlCipherFacade.all(query, params)) ?? []
		return this.deserializeList(
			typeRef,
			items.map((row) => row.entity.value as Uint8Array),
		)
	}

	async getWholeList<T extends ListElementEntity>(typeRef: TypeRef<T>, listId: Id): Promise<Array<T>> {
		const { query, params } = sql`SELECT entity FROM list_entities WHERE type = ${getTypeId(typeRef)} AND listId = ${listId}`
		const items = (await this.sqlCipherFacade.all(query, params)) ?? []
		return this.deserializeList(
			typeRef,
			items.map((row) => row.entity.value as Uint8Array),
		)
	}

	async dumpMetadata(): Promise<Partial<OfflineDbMeta>> {
		const query = "SELECT * from metadata"
		const stored = (await this.sqlCipherFacade.all(query, [])).map((row) => [row.key.value as string, row.value.value as Uint8Array] as const)
		return Object.fromEntries(stored.map(([key, value]) => [key, cborg.decode(value)])) as OfflineDbMeta
	}

	async setStoredModelVersion(model: VersionMetadataBaseKey, version: number) {
		return this.putMetadata(`${model}-version`, version)
	}

	getCustomCacheHandlerMap(entityRestClient: EntityRestClient): CustomCacheHandlerMap {
		if (this.customCacheHandler == null) {
			this.customCacheHandler = new CustomCacheHandlerMap({ ref: CalendarEventTypeRef, handler: new CustomCalendarEventCacheHandler(entityRestClient) })
		}
		return this.customCacheHandler
	}

	getUserId(): Id {
		return assertNotNull(this.userId, "No user id, not initialized?")
	}

	async deleteAllOwnedBy(owner: Id): Promise<void> {
		{
			const { query, params } = sql`DELETE FROM element_entities WHERE ownerGroup = ${owner}`
			await this.sqlCipherFacade.run(query, params)
		}
		{
			// first, check which list Ids contain entities owned by the lost group
			const { query, params } = sql`SELECT listId, type FROM list_entities WHERE ownerGroup = ${owner}`
			const rangeRows = await this.sqlCipherFacade.all(query, params)
			const rows = rangeRows.map((row) => untagSqlObject(row) as { listId: string; type: string })
			const listIdsByType: Map<string, Set<Id>> = groupByAndMapUniquely(
				rows,
				(row) => row.type,
				(row) => row.listId,
			)
			// delete the ranges for those listIds
			for (const [type, listIds] of listIdsByType.entries()) {
				// this particular query uses one other SQL var for the type.
				const safeChunkSize = MAX_SAFE_SQL_VARS - 1
				const listIdArr = Array.from(listIds)
				await this.runChunked(safeChunkSize, listIdArr, (c) => sql`DELETE FROM ranges WHERE type = ${type} AND listId IN ${paramList(c)}`)
				await this.runChunked(safeChunkSize, listIdArr, (c) => sql`DELETE FROM list_entities WHERE type = ${type} AND listId IN ${paramList(c)}`)
			}
		}
		{
			const { query, params } = sql`DELETE FROM blob_element_entities WHERE ownerGroup = ${owner}`
			await this.sqlCipherFacade.run(query, params)
		}
		{
			const { query, params } = sql`DELETE FROM lastUpdateBatchIdPerGroupId WHERE groupId = ${owner}`
			await this.sqlCipherFacade.run(query, params)
		}
	}

	private async putMetadata<K extends keyof OfflineDbMeta>(key: K, value: OfflineDbMeta[K]): Promise<void> {
		let encodedValue
		try {
			encodedValue = cborg.encode(value)
		} catch (e) {
			console.log("[OfflineStorage] failed to encode metadata for key", key, "with value", value)
			throw e
		}
		const { query, params } = sql`INSERT OR REPLACE INTO metadata VALUES (${key}, ${encodedValue})`
		await this.sqlCipherFacade.run(query, params)
	}

	private async getMetadata<K extends keyof OfflineDbMeta>(key: K): Promise<OfflineDbMeta[K] | null> {
		const { query, params } = sql`SELECT value from metadata WHERE key = ${key}`
		const encoded = await this.sqlCipherFacade.get(query, params)
		return encoded && cborg.decode(encoded.value.value as Uint8Array)
	}

	/**
	 * Clear out unneeded data from the offline database (i.e. trash and spam lists, old data).
	 * This will be called after login (CachePostLoginActions.ts) to ensure fast login time.
	 * @param timeRangeDays: the maximum age of days that mails should be to be kept in the database. if null, will use a default value
	 * @param userId id of the current user. default, last stored userId
	 */
	async clearExcludedData(timeRangeDays: number | null = this.timeRangeDays, userId: Id = this.getUserId()): Promise<void> {
		const user = await this.get(UserTypeRef, null, userId)

		// Free users always have default time range regardless of what is stored
		const isFreeUser = user?.accountType === AccountType.FREE
		const timeRange = isFreeUser || timeRangeDays == null ? OFFLINE_STORAGE_DEFAULT_TIME_RANGE_DAYS : timeRangeDays
		const cutoffTimestamp = this.dateProvider.now() - timeRange * DAY_IN_MILLIS
		const cutoffId = timestampToGeneratedId(cutoffTimestamp)
		const folders = await this.getListElementsOfType(MailFolderTypeRef)
		const folderSystem = new FolderSystem(folders)

		for (const folder of folders) {
			if (isSpamOrTrashFolder(folderSystem, folder)) {
				await this.deleteMailList(folder.mails, GENERATED_MAX_ID)
			} else {
				await this.deleteMailList(folder.mails, cutoffId)
			}
		}
	}

	private async createTables() {
		for (let [name, definition] of Object.entries(TableDefinitions)) {
			await this.sqlCipherFacade.run(`CREATE TABLE IF NOT EXISTS ${name} (${definition})`, [])
		}
	}

	private async getRange(type: string, listId: Id): Promise<Range | null> {
		const { query, params } = sql`SELECT upper, lower FROM ranges WHERE type = ${type} AND listId = ${listId}`
		const row = (await this.sqlCipherFacade.get(query, params)) ?? null
		return mapNullable(row, untagSqlObject) as Range | null
	}

	/**
	 * This method deletes mails from {@param listId} what are older than {@param cutoffId}. as well as associated data
	 *
	 * For each mail we delete its body, headers, and all referenced attachments.
	 *
	 * When we delete the Files, we also delete the whole range for the user's File list. We need to delete the whole
	 * range because we only have one file list per mailbox, so if we delete something from the middle of it, the range
	 * will no longer be valid. (this is future proofing, because as of now there is not going to be a Range set for the
	 * File list anyway, since we currently do not do range requests for Files.
	 *
	 * 	We do not delete ConversationEntries because:
	 * 	1. They are in the same list for the whole conversation so we can't adjust the range
	 * 	2. We might need them in the future for showing the whole thread
	 */
	private async deleteMailList(listId: Id, cutoffId: Id): Promise<void> {
		// We lock access to the "ranges" db here in order to prevent race conditions when accessing the "ranges" database.
		await this.lockRangesDbAccess(listId)
		try {
			// This must be done before deleting mails to know what the new range has to be
			await this.updateRangeForList(MailTypeRef, listId, cutoffId)
		} finally {
			// We unlock access to the "ranges" db here. We lock it in order to prevent race conditions when accessing the "ranges" database.
			await this.unlockRangesDbAccess(listId)
		}

		const mailsToDelete: IdTuple[] = []
		const headersToDelete: Id[] = []
		const attachmentsTodelete: IdTuple[] = []
		const mailbodiesToDelete: Id[] = []
		const mailDetailsBlobToDelete: IdTuple[] = []
		const mailDetailsDraftToDelete: IdTuple[] = []

		const mails = await this.getWholeList(MailTypeRef, listId)
		for (let mail of mails) {
			if (firstBiggerThanSecond(cutoffId, getElementId(mail))) {
				mailsToDelete.push(mail._id)
				for (const id of mail.attachments) {
					attachmentsTodelete.push(id)
				}
				if (isLegacyMail(mail)) {
					mailbodiesToDelete.push(assertNotNull(mail.body))
				} else if (isDetailsDraft(mail)) {
					const mailDetailsId = assertNotNull(mail.mailDetailsDraft)
					mailDetailsDraftToDelete.push(mailDetailsId)
				} else {
					// mailDetailsBlob
					const mailDetailsId = assertNotNull(mail.mailDetails)
					mailDetailsBlobToDelete.push(mailDetailsId)
				}
				if (mail.headers) {
					headersToDelete.push(mail.headers)
				}
			}
		}
		await this.deleteIn(MailBodyTypeRef, null, mailbodiesToDelete)
		for (let [listId, elementIds] of groupByAndMap(mailDetailsBlobToDelete, listIdPart, elementIdPart).entries()) {
			await this.deleteIn(MailDetailsBlobTypeRef, listId, elementIds)
		}
		for (let [listId, elementIds] of groupByAndMap(mailDetailsDraftToDelete, listIdPart, elementIdPart).entries()) {
			await this.deleteIn(MailDetailsDraftTypeRef, listId, elementIds)
		}
		await this.deleteIn(MailHeadersTypeRef, null, headersToDelete)
		for (let [listId, elementIds] of groupByAndMap(attachmentsTodelete, listIdPart, elementIdPart).entries()) {
			await this.deleteIn(FileTypeRef, listId, elementIds)
			await this.deleteRange(FileTypeRef, listId)
		}

		await this.deleteIn(MailTypeRef, listId, mailsToDelete.map(elementIdPart))
	}

	private async deleteIn(typeRef: TypeRef<unknown>, listId: Id | null, elementIds: Id[]): Promise<void> {
		if (elementIds.length === 0) return
		const typeModel = await resolveTypeReference(typeRef)
		switch (typeModel.type) {
			case TypeId.Element:
				return await this.runChunked(
					MAX_SAFE_SQL_VARS - 1,
					elementIds,
					(c) => sql`DELETE FROM element_entities WHERE type = ${getTypeId(typeRef)} AND elementId IN ${paramList(c)}`,
				)
			case TypeId.ListElement:
				return await this.runChunked(
					MAX_SAFE_SQL_VARS - 2,
					elementIds,
					(c) => sql`DELETE FROM list_entities WHERE type = ${getTypeId(typeRef)} AND listId = ${listId} AND elementId IN ${paramList(c)}`,
				)
			case TypeId.BlobElement:
				return await this.runChunked(
					MAX_SAFE_SQL_VARS - 2,
					elementIds,
					(c) => sql`DELETE FROM blob_element_entities WHERE type = ${getTypeId(typeRef)} AND listId = ${listId} AND elementId IN ${paramList(c)}`,
				)
			default:
				throw new Error("must be a persistent type")
		}
	}

	/**
	 * We want to lock the access to the "ranges" db when updating / reading the
	 * offline available mail list ranges for each mail list (referenced using the listId).
	 * @param listId the mail list that we want to lock
	 */
	async lockRangesDbAccess(listId: Id) {
		await this.sqlCipherFacade.lockRangesDbAccess(listId)
	}

	/**
	 * This is the counterpart to the function "lockRangesDbAccess(listId)".
	 * @param listId the mail list that we want to unlock
	 */
	async unlockRangesDbAccess(listId: Id) {
		await this.sqlCipherFacade.unlockRangesDbAccess(listId)
	}

	private async updateRangeForList<T extends ListElementEntity>(typeRef: TypeRef<T>, listId: Id, cutoffId: Id): Promise<void> {
		const type = getTypeId(typeRef)

		const range = await this.getRange(type, listId)
		if (range == null) {
			return
		}

		// If the range for a given list is complete from the beginning (starts at GENERATED_MIN_ID), then we only want to actually modify the
		// saved range if we would be removing elements from the list, in order to not lose the information that the range is complete in storage.
		// So we have to check how old the oldest element in said range is. If it is newer than cutoffId, then we will not modify the range,
		// otherwise we will just modify it normally
		if (range.lower === GENERATED_MIN_ID) {
			const entities = await this.provideFromRange(typeRef, listId, GENERATED_MIN_ID, 1, false)
			const id = mapNullable(entities[0], getElementId)
			const rangeWontBeModified = id == null || firstBiggerThanSecond(id, cutoffId) || id === cutoffId
			if (rangeWontBeModified) {
				return
			}
		}

		if (firstBiggerThanSecond(cutoffId, range.lower)) {
			// If the upper id of the range is below the cutoff, then the entire range will be deleted from the storage
			// so we just delete the range as well
			// Otherwise, we only want to modify
			if (firstBiggerThanSecond(cutoffId, range.upper)) {
				await this.deleteRange(typeRef, listId)
			} else {
				await this.setLowerRangeForList(typeRef, listId, cutoffId)
			}
		}
	}

	private serialize(originalEntity: SomeEntity): Uint8Array {
		try {
			return cborg.encode(originalEntity, { typeEncoders: customTypeEncoders })
		} catch (e) {
			console.log("[OfflineStorage] failed to encode entity of type", originalEntity._type, "with id", originalEntity._id)
			throw e
		}
	}

	private deserialize<T extends SomeEntity>(typeRef: TypeRef<T>, loaded: Uint8Array): T {
		const deserialized = cborg.decode(loaded, { tags: customTypeDecoders })
		// TypeRef cannot be deserialized back automatically. We could write a codec for it but we don't actually
		// need to store it so we just "patch" it.
		// Some places rely on TypeRef being a class and not a plain object.
		deserialized._type = typeRef
		return deserialized
	}

	private deserializeList<T extends SomeEntity>(typeRef: TypeRef<T>, loaded: Array<Uint8Array>): Array<T> {
		return loaded.map((entity) => this.deserialize(typeRef, entity))
	}

	/**
	 * convenience method to run a potentially too large query over several chunks.
	 * chunkSize must be chosen such that the total number of SQL variables in the final query does not exceed MAX_SAFE_SQL_VARS
	 * */
	private async runChunked(chunkSize: number, originalList: SqlValue[], formatter: (chunk: SqlValue[]) => FormattedQuery): Promise<void> {
		for (const chunk of splitInChunks(chunkSize, originalList)) {
			const formattedQuery = formatter(chunk)
			await this.sqlCipherFacade.run(formattedQuery.query, formattedQuery.params)
		}
	}
}

/*
 * used to automatically create the right amount of SQL variables for selecting ids from a dynamic list.
 * must be used within sql`<query>` template string to inline the logic into the query.
 *
 * It is very important that params is kept to a size such that the total amount of SQL variables is
 * less than MAX_SAFE_SQL_VARS.
 */
function paramList(params: SqlValue[]): SqlFragment {
	const qs = params.map(() => "?").join(",")
	return new SqlFragment(`(${qs})`, params)
}

/**
 * comparison to select ids that are bigger or smaller than a parameter id
 * must be used within sql`<query>` template string to inline the logic into the query.
 *
 * will always insert 3 constants and 3 SQL variables into the query.
 */
function firstIdBigger(...args: [string, "elementId"] | ["elementId", string]): SqlFragment {
	let [l, r]: [string, string] = args
	let v
	if (l === "elementId") {
		v = r
		r = "?"
	} else {
		v = l
		l = "?"
	}
	return new SqlFragment(`(CASE WHEN length(${l}) > length(${r}) THEN 1 WHEN length(${l}) < length(${r}) THEN 0 ELSE ${l} > ${r} END)`, [v, v, v])
}

/**
 * this tagged template function exists because android doesn't allow us to define SQL functions, so we have made a way to inline
 * SQL fragments into queries.
 * to make it less error-prone, we automate the generation of the params array for the actual sql call.
 * In this way, we offload the escaping of actual user content to the SQL engine, which makes this safe from an SQLI point of view.
 *
 * usage example:
 * const type = "sys/User"
 * const listId = "someList"
 * const startId = "ABC"
 * sql`SELECT entity FROM list_entities WHERE type = ${type} AND listId = ${listId} AND ${firstIdBigger(startId, "elementId")}`
 *
 * this will result in
 * const {query, params} = {
 *     query: `SELECT entity FROM list_entities WHERE type = ? AND listId = ? AND (CASE WHEN length(?) > length(elementId) THEN 1 WHEN length(?) < length(elementId) THEN 0 ELSE ? > elementId END)`,
 *     params: [
 *     		{type: SqlType.String, value: "sys/User"},
 *     		{type: SqlType.String, value: "someList"},
 *     		{type: SqlType.String, value: "ABC"},
 *     		{type: SqlType.String, value: "ABC"},
 *     		{type: SqlType.String, value: "ABC"}
 *     ]
 * }
 *
 * which can be consumed by sql.run(query, params).
 *
 * It is important that the caller ensures that the amount of SQL variables does not exceed MAX_SAFE_SQL_VARS!
 * Violating this rule will lead to an uncaught error with bad stack traces.
 */
export function sql(queryParts: TemplateStringsArray, ...paramInstances: (SqlValue | SqlFragment)[]): FormattedQuery {
	let query = ""
	let params: TaggedSqlValue[] = []
	let i: number
	for (i = 0; i < paramInstances.length; i++) {
		query += queryParts[i]
		const param = paramInstances[i]
		if (param instanceof SqlFragment) {
			query += param.text
			params.push(...param.params.map(tagSqlValue))
		} else {
			query += "?"
			params.push(tagSqlValue(param))
		}
	}
	query += queryParts[i]
	return { query, params }
}

class SqlFragment {
	constructor(readonly text: string, readonly params: SqlValue[]) {}
}