//
// Copyright 2023 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only
//

import Foundation

public extension MessageBackup {
    enum EncryptionMode {
        /// Export/Import an encrypted backup to/from the remote server.
        /// The encryption key used derives entirely from the local account keychain.
        case remote
        /// Export/Import an encrypted backup used to link a new device.
        /// The encryption key used is derived from the aci and a 32-byte "ephemeral" backup key.
        case linknsync(EphemeralBackupKey)

        // TODO: [LocalBackups] introduce local mode with its own key scheme.
    }
}

public protocol MessageBackupManager {

    // MARK: - Interact with remotes

    /// Download the encrypted backup for the current user to a local file.
    func downloadEncryptedBackup(localIdentifiers: LocalIdentifiers, auth: ChatServiceAuth) async throws -> URL

    /// Upload the local encrypted backup identified by the given metadata for
    /// the current user.
    func uploadEncryptedBackup(
        metadata: Upload.EncryptedBackupUploadMetadata,
        localIdentifiers: LocalIdentifiers,
        auth: ChatServiceAuth
    ) async throws -> Upload.Result<Upload.EncryptedBackupUploadMetadata>

    // MARK: - Export

    /// Export an encrypted backup binary to a local file.
    /// - SeeAlso ``uploadEncryptedBackup(metadata:localIdentifiers:auth:)``
    func exportEncryptedBackup(
        localIdentifiers: LocalIdentifiers,
        mode: MessageBackup.EncryptionMode
    ) async throws -> Upload.EncryptedBackupUploadMetadata

    /// Export a plaintext backup binary at the returned file URL.
    func exportPlaintextBackup(localIdentifiers: LocalIdentifiers) async throws -> URL

    // MARK: - Import

    /// Import a backup from the encrypted binary file at the given local URL.
    /// - SeeAlso ``downloadEncryptedBackup(localIdentifiers:auth:)``
    func importEncryptedBackup(
        fileUrl: URL,
        localIdentifiers: LocalIdentifiers,
        mode: MessageBackup.EncryptionMode
    ) async throws

    /// Import a backup from the plaintext binary file at the given local URL.
    func importPlaintextBackup(fileUrl: URL, localIdentifiers: LocalIdentifiers) async throws

    // MARK: -

    /// Validate the encrypted backup file located at the given local URL.
    func validateEncryptedBackup(
        fileUrl: URL,
        localIdentifiers: LocalIdentifiers,
        mode: MessageBackup.EncryptionMode
    ) async throws
}