Show an alert when entering an account provider that requires Element Pro. (#4326)

ElementX/Sources/AppHooks/AppHooks.swift

@@ -33,6 +33,11 @@ class AppHooks: AppHooksProtocol {
         certificateValidatorHook = hook
     }
     
+    private(set) var elementWellKnownHook: ElementWellKnownHookProtocol = DefaultElementWellKnownHook()
+    func registerElementWellKnownHook(_ hook: ElementWellKnownHookProtocol) {
+        elementWellKnownHook = hook
+    }
+    
     private(set) var roomScreenHook: RoomScreenHookProtocol = DefaultRoomScreenHook()
     func registerRoomScreenHook(_ hook: RoomScreenHookProtocol) {
         roomScreenHook = hook

ElementX/Sources/AppHooks/Hooks/ElementWellKnownHook.swift

@@ -0,0 +1,53 @@
+//
+// Copyright 2025 New Vector Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+// Please see LICENSE files in the repository root for full details.
+//
+
+import Foundation
+import MatrixRustSDK
+
+protocol ElementWellKnownHookProtocol {
+    func validate(using client: ClientProtocol) async -> Result<Void, ElementWellKnownError>
+}
+
+struct DefaultElementWellKnownHook: ElementWellKnownHookProtocol {
+    /// A best effort implementation to let Element X advertise to users when they should be using
+    /// Element Pro. In an ideal world the backend would be able to validate the client's requests
+    /// instead of relying on it to check a well-known file for this.
+    func validate(using client: ClientProtocol) async -> Result<Void, ElementWellKnownError> {
+        guard case let .success(wellKnownData) = await client.elementWellKnown() else {
+            // Nothing to check, carry on as normal.
+            return .success(())
+        }
+        
+        do {
+            let wellKnown = try JSONDecoder().decode(ElementWellKnown.self, from: wellKnownData)
+            if wellKnown.enforceElementPro == true {
+                let serverName = client.server() ?? client.homeserver()
+                let displayableServerName = LoginHomeserver(address: serverName, loginMode: .unknown).address
+                return .failure(.elementProRequired(serverName: displayableServerName))
+            } else {
+                return .success(())
+            }
+        } catch {
+            // If it doesn't decode we have to assume it's a 404 page or similar.
+            return .success(())
+        }
+    }
+}
+
+private struct ElementWellKnown: Decodable {
+    var version: Int
+    var enforceElementPro: Bool?
+    
+    enum CodingKeys: String, CodingKey {
+        case version
+        case enforceElementPro = "enforce_element_pro"
+    }
+}
+
+enum ElementWellKnownError: Error {
+    case elementProRequired(serverName: String)
+}