Refactor encryption trust level

Riot/Modules/Encryption/EncryptionTrustLevel.swift

@@ -0,0 +1,49 @@
+// 
+// Copyright 2023 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+
+/// Object responsible for calculating user and room trust level
+@objc class EncryptionTrustLevel: NSObject {
+    
+    /// Calculate trust level for a single user given their cross-signing info
+    @objc func userTrustLevel(
+        crossSigning: MXCrossSigningInfo?,
+        devicesTrust: MXTrustSummary
+    ) -> UserEncryptionTrustLevel {
+        
+        // If we could cross-sign but we haven't, the user is simply not verified
+        if let crossSigning, !crossSigning.isVerified {
+            return .notVerified
+        
+        // If we cannot cross-sign the user (legacy behaviour) and have not signed
+        // any devices manually, the user is not verified
+        } else if crossSigning == nil && devicesTrust.trustedCount == 0 {
+            return .notVerified
+        }
+        
+        // In all other cases we check devices for trust level
+        return devicesTrust.areAllTrusted ? .trusted : .warning
+    }
+    
+    /// Calculate trust level for a room given trust level of users and their devices
+    @objc func roomTrustLevel(summary: MXUsersTrustLevelSummary) -> RoomEncryptionTrustLevel {
+        guard summary.usersTrust.totalCount > 0 && summary.usersTrust.areAllTrusted else {
+            return .normal
+        }
+        return summary.devicesTrust.areAllTrusted ? .trusted : .warning
+    }
+}