Signal-iOS/SignalServiceKit/MessageBackup/MessageBackupRequestManager.swift

//
// Copyright 2024 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only
//

import Foundation
import LibSignalClient

public protocol MessageBackupRequestManager {

    func fetchBackupServiceAuth(localAci: Aci, auth: ChatServiceAuth) async throws -> MessageBackupServiceAuth

    func reserveBackupId(localAci: Aci, auth: ChatServiceAuth) async throws

    func registerBackupKeys(auth: MessageBackupServiceAuth) async throws

    func fetchBackupUploadForm(auth: MessageBackupServiceAuth) async throws -> Upload.Form

    func fetchBackupMediaAttachmentUploadForm(auth: MessageBackupServiceAuth) async throws -> Upload.Form

    func fetchBackupInfo(auth: MessageBackupServiceAuth) async throws -> MessageBackupRemoteInfo

    func refreshBackupInfo(auth: MessageBackupServiceAuth) async throws

    func fetchCDNReadCredentials(cdn: Int32, auth: MessageBackupServiceAuth) async throws -> CDNReadCredential

    // TODO: [Backups] Batched backup media
    // TODO: [Backups] Backup media
    // TODO: [Backups] List media objects
    // TODO: [Backups] Delete media objects
    // TODO: [Backups] Redeem receipt
}

public struct MessageBackupRequestManagerImpl: MessageBackupRequestManager {

    private let db: DB
    private let messageBackupAuthCredentialManager: MessageBackupAuthCredentialManager
    private let messageBackupKeyMaterial: MessageBackupKeyMaterial
    private let networkManager: NetworkManager

    init(
        db: DB,
        messageBackupAuthCredentialManager: MessageBackupAuthCredentialManager,
        messageBackupKeyMaterial: MessageBackupKeyMaterial,
        networkManager: NetworkManager
    ) {
        self.db = db
        self.messageBackupAuthCredentialManager = messageBackupAuthCredentialManager
        self.messageBackupKeyMaterial = messageBackupKeyMaterial
        self.networkManager = networkManager
    }

    // MARK: - Reserve Backup

    /// Onetime request to reserve this backup ID.
    public func reserveBackupId(localAci: Aci, auth: ChatServiceAuth) async throws {
        let backupRequestContext = try db.read { tx in
            return try messageBackupKeyMaterial.backupAuthRequestContext(localAci: localAci, tx: tx)
        }
        let base64RequestContext = Data(backupRequestContext.getRequest().serialize()).base64EncodedString()
        let request = try OWSRequestFactory.reserveBackupId(backupId: base64RequestContext, auth: auth)
        _ = try await networkManager.makePromise(
            request: request,
            canUseWebSocket: false // TODO[Backups]: Switch this back to true when reg supports websockets
        ).awaitable()
    }

    // MARK: - Backup Auth

    /// Create a `MessageBackupAuthCredential` from local ACI and the current valid backup credential. This
    /// `MessageBackupAuthCredential` is used to authenticate all further `/v1/archive` operations.
    public func fetchBackupServiceAuth(localAci: Aci, auth: ChatServiceAuth) async throws -> MessageBackupServiceAuth {
        let (backupKey, privateKey) = try db.read { tx in
            let backupKey = try messageBackupKeyMaterial.backupID(localAci: localAci, tx: tx)
            let privateKey = try messageBackupKeyMaterial.backupPrivateKey(localAci: localAci, tx: tx)
            return (backupKey, privateKey)
        }
        let authCredential = try await messageBackupAuthCredentialManager.fetchBackupCredential(
            localAci: localAci,
            auth: auth
        )
        return try MessageBackupServiceAuth(backupKey: backupKey, privateKey: privateKey, authCredential: authCredential)
    }

    // MARK: - Register Backup

    /// Onetime request to register the backup public key.
    public func registerBackupKeys(auth: MessageBackupServiceAuth) async throws {
        _ = try await executeBackupServiceRequest(
            auth: auth,
            requestFactory: OWSRequestFactory.backupSetPublicKeyRequest(auth:)
        )
    }

    // MARK: - Upload Forms

    /// CDN upload form for uploading a backup
    public func fetchBackupUploadForm(auth: MessageBackupServiceAuth) async throws -> Upload.Form {
        return try await executeBackupService(
            auth: auth,
            requestFactory: OWSRequestFactory.backupUploadFormRequest(auth:)
        )
    }

    /// CDN upload form for uploading backup media
    public func fetchBackupMediaAttachmentUploadForm(auth: MessageBackupServiceAuth) async throws -> Upload.Form {
        return try await executeBackupService(
            auth: auth,
            requestFactory: OWSRequestFactory.backupMediaUploadFormRequest(auth:)
        )
    }

    // MARK: - Backup Info

    /// Fetch details about the current backup
    public func fetchBackupInfo(auth: MessageBackupServiceAuth) async throws -> MessageBackupRemoteInfo {
        return try await executeBackupService(
            auth: auth,
            requestFactory: OWSRequestFactory.backupInfoRequest(auth:)
        )
    }

    /// Backup keep-alive request.  If not called, the backup may be deleted after 30 days.
    public func refreshBackupInfo(auth: MessageBackupServiceAuth) async throws {
        _ = try await executeBackupServiceRequest(
            auth: auth,
            requestFactory: OWSRequestFactory.backupRefreshInfoRequest(auth:)
        )
    }

    /// Delete the current backup
    public func deleteBackup(auth: MessageBackupServiceAuth) async throws {
        _ = try await executeBackupServiceRequest(
            auth: auth,
            requestFactory: OWSRequestFactory.deleteBackupRequest(auth:)
        )
    }

    // MARK: - Media

    /// Retrieve credentials used for reading from the CDN
    public func fetchCDNReadCredentials(cdn: Int32, auth: MessageBackupServiceAuth) async throws -> CDNReadCredential {
        return try await executeBackupService(
            auth: auth,
            requestFactory: { OWSRequestFactory.fetchCDNCredentials(auth: $0, cdn: cdn) }
        )
    }

    // MARK: - Private utility methods

    private func executeBackupServiceRequest(
        auth: MessageBackupServiceAuth,
        requestFactory: (MessageBackupServiceAuth) -> TSRequest
    ) async throws -> HTTPResponse {
        return try await networkManager.makePromise(
            request: requestFactory(auth),
            canUseWebSocket: false // TODO[Backups]: Switch this back to true when reg supports websockets
        ).awaitable()
    }

    private func executeBackupService<T: Decodable>(
        auth: MessageBackupServiceAuth,
        requestFactory: (MessageBackupServiceAuth) -> TSRequest
    ) async throws -> T {
        let response = try await executeBackupServiceRequest(
            auth: auth,
            requestFactory: requestFactory
        )
        guard let bodyData = response.responseBodyData else {
            throw OWSAssertionError("Missing body data")
        }
        return try JSONDecoder().decode(T.self, from: bodyData)
    }
}

public struct CDNReadCredential: Decodable {
    let headers: [String: String]
}