Sources/SophaxChatCore/Group/GroupCryptoMigration.swift

1// GroupCryptoMigration.swift
2// SophaxChatCore
3//
4// Phase 5: Opt-in migration from Sender Keys v2 to MLS for existing groups.
5//
6// Design:
7//   - Only the group creator can initiate migration (they are the MLS coordinator).
8//   - All current members must have an MLS KeyPackage available (from their Hello bundle).
9//   - A new MLS group is created with the same name and members; the old SKv2 group is
10//     left in place so existing message history remains accessible.
11//   - SKv2 Keychain state for the old group expires naturally (7-day rotation window).
12//   - The UI flow for presenting migration to users is a future sprint concern.
13
14import Foundation
15
16// MARK: - Result type
17
18public enum GroupMigrationResult: Sendable {
19    /// The group is already running MLS — nothing to do.
20    case notNeeded
21    /// One or more members lack an MLS KeyPackage; wait until they reconnect.
22    case requiresAllOnline([String])   // peerIDs that are missing a KeyPackage
23    /// Migration initiated — new MLS group was created and Welcomes are being distributed.
24    case initiated(newGroup: GroupInfo)
25}
26
27// MARK: - Migration entry point
28
29/// Attempt to migrate `group` from Sender Keys v2 to MLS.
30///
31/// - Parameters:
32///   - group:       The existing SKv2 GroupInfo to migrate.
33///   - chatManager: The active ChatManager instance (must be the group creator's).
34/// - Returns: A `GroupMigrationResult` describing the outcome.
35/// - Throws: If the local identity's signing key is unavailable.
36@discardableResult
37public func migrateGroupToMLS(
38    _ group: GroupInfo,
39    in chatManager: ChatManager
40) throws -> GroupMigrationResult {
41
42    // Already MLS — nothing to do.
43    guard group.cryptoVersion == .senderKeysV2 else { return .notNeeded }
44
45    // Only the coordinator (creator) may initiate MLS migration.
46    let myID = chatManager.identity.publicIdentity.peerID
47    guard group.creatorID == myID else {
48        throw SophaxError.invalidMessageFormat("Only the group creator can initiate MLS migration")
49    }
50
51    // Verify every non-self member has a KeyPackage in their stored PreKeyBundle.
52    let otherMembers = group.memberIDs.filter { $0 != myID }
53    let missing = otherMembers.filter { peerID in
54        chatManager.peerBundles[peerID]?.mlsKeyPackage == nil
55    }
56    guard missing.isEmpty else { return .requiresAllOnline(missing) }
57
58    // Create the new MLS group (same name, same members, new groupID).
59    guard let newGroup = chatManager.createMLSGroup(
60        name: group.name,
61        memberPeerIDs: otherMembers
62    ) else {
63        throw SophaxError.encryptionFailed("MLS group creation failed during migration")
64    }
65
66    return .initiated(newGroup: newGroup)
67}