Verify Element X with an existing Element Classic account. (#5374)

* Read and import the secrets from ClassicAppAccounts.

* Record snapshots.

* Add some documentation, tidy up tests and fix the dismissal of the backup instructions.

* Workaround flakey tests (the fulfilments weren't always firing).

* Allow a custom Classic App deep link URL to be configured.

ElementX/Sources/Services/Authentication/ClassicApp/ClassicAppManager.swift

@@ -11,13 +11,19 @@ import MatrixRustSDK
 
 // sourcery: AutoMockable
 protocol ClassicAppManagerProtocol {
+    /// Loads all of the accounts found in the Classic app's file store.
     func loadAccounts() throws -> [ClassicAppAccount]
+    /// Determines which secrets will be available when loading the secrets bundle for a given account.
+    func availableSecrets(for account: ClassicAppAccount) async throws -> ClassicAppAccount.AvailableSecrets
+    /// Loads the secrets bundle for a given account.
+    func secretsBundle(for account: ClassicAppAccount) async throws -> SecretsBundleWithUserId
 }
 
 enum ClassicAppManagerError: Error {
     case invalidAppGroupIdentifier(String)
     case missingAccountKeys
     case missingCryptoStorePassphrase
+    case missingKeyBackupVersion
 }
 
 /// Reads accounts from Element Classic's shared storage.
@@ -45,7 +51,6 @@ final class ClassicAppManager: ClassicAppManagerProtocol {
         keychain = Keychain(service: classicAppKeychainServiceIdentifier, accessGroup: classicAppKeychainAccessGroupIdentifier)
     }
     
-    /// Loads all of the active accounts from the Classic app.
     func loadAccounts() throws -> [ClassicAppAccount] {
         // The account data is stored in the App Group container.
         guard let url = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: classicAppGroupIdentifier) else {
@@ -69,4 +74,41 @@ final class ClassicAppManager: ClassicAppManagerProtocol {
         accountManager.loadAccounts()
         return accountManager.accounts
     }
+    
+    func availableSecrets(for account: ClassicAppAccount) async throws -> ClassicAppAccount.AvailableSecrets {
+        switch try await databaseContainsSecretsBundle(databasePath: account.cryptoStoreURL.path(percentEncoded: false),
+                                                       passphrase: account.cryptoStorePassphrase,
+                                                       backupInfo: keyBackupVersion(for: account)) {
+        case .complete: .complete
+        case .none: .unavailable
+        case .withoutBackup, .unusedBackup: .requiresBackup
+        }
+    }
+    
+    func secretsBundle(for account: ClassicAppAccount) async throws -> SecretsBundleWithUserId {
+        guard let keyBackupVersion = try await keyBackupVersion(for: account) else {
+            throw ClassicAppManagerError.missingKeyBackupVersion
+        }
+        
+        return try await SecretsBundleWithUserId.fromDatabase(databasePath: account.cryptoStoreURL.path(percentEncoded: false),
+                                                              passphrase: account.cryptoStorePassphrase,
+                                                              backupInfo: keyBackupVersion)
+    }
+    
+    /// Fetches the current key backup version from the homeserver. This is needed to determine whether
+    /// the backup key from the crypto store is for the backup currently being used by the account.
+    private func keyBackupVersion(for account: ClassicAppAccount) async throws -> String? {
+        let url = account.homeserverURL.appending(path: "_matrix/client/v3/room_keys/version")
+        var request = URLRequest(url: url)
+        request.setValue("Bearer \(account.accessToken)", forHTTPHeaderField: "Authorization")
+        
+        let (data, response) = try await URLSession.shared.data(for: request)
+        
+        if let httpResponse = response as? HTTPURLResponse,
+           httpResponse.statusCode != 200 {
+            return nil
+        }
+        
+        return String(data: data, encoding: .utf8)
+    }
 }