Renaming screens returns (#829)

* Rename: StartChat -> StartChatScreen

* Rename: Login -> LoginScreen

* Rename: ServerSelection -> ServerSelectionScreen

* Rename: SoftLogout -> SoftLogoutScreen

ElementX/Sources/Screens/Authentication/LoginScreen/LoginScreenViewModel.swift

@@ -0,0 +1,79 @@
+//
+// Copyright 2022 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 SwiftUI
+
+typealias LoginScreenViewModelType = StateStoreViewModel<LoginScreenViewState, LoginScreenViewAction>
+
+class LoginScreenViewModel: LoginScreenViewModelType, LoginScreenViewModelProtocol {
+    var callback: (@MainActor (LoginScreenViewModelAction) -> Void)?
+
+    init(homeserver: LoginHomeserver) {
+        let bindings = LoginScreenBindings()
+        let viewState = LoginScreenViewState(homeserver: homeserver, bindings: bindings)
+        
+        super.init(initialViewState: viewState)
+    }
+
+    override func process(viewAction: LoginScreenViewAction) {
+        switch viewAction {
+        case .selectServer:
+            callback?(.selectServer)
+        case .parseUsername:
+            callback?(.parseUsername(state.bindings.username))
+        case .forgotPassword:
+            callback?(.forgotPassword)
+        case .next:
+            callback?(.login(username: state.bindings.username, password: state.bindings.password))
+        case .continueWithOIDC:
+            callback?(.continueWithOIDC)
+        }
+    }
+    
+    func update(isLoading: Bool) {
+        guard state.isLoading != isLoading else { return }
+        state.isLoading = isLoading
+    }
+    
+    func update(homeserver: LoginHomeserver) {
+        state.homeserver = homeserver
+    }
+    
+    func displayError(_ type: LoginScreenErrorType) {
+        switch type {
+        case .alert(let message):
+            state.bindings.alertInfo = AlertInfo(id: type,
+                                                 title: L10n.commonError,
+                                                 message: message)
+        case .invalidHomeserver:
+            state.bindings.alertInfo = AlertInfo(id: type,
+                                                 title: L10n.commonError,
+                                                 message: L10n.screenLoginErrorInvalidUserId)
+        case .slidingSyncAlert:
+            let openURL = { UIApplication.shared.open(ServiceLocator.shared.settings.slidingSyncLearnMoreURL) }
+            state.bindings.alertInfo = AlertInfo(id: .slidingSyncAlert,
+                                                 title: L10n.commonServerNotSupported,
+                                                 message: L10n.screenChangeServerErrorNoSlidingSyncMessage,
+                                                 primaryButton: .init(title: L10n.actionLearnMore, role: .cancel, action: openURL),
+                                                 secondaryButton: .init(title: L10n.actionCancel, action: nil))
+            
+            // Clear out the invalid username to avoid an attempted login to matrix.org
+            state.bindings.username = ""
+        case .unknown:
+            state.bindings.alertInfo = AlertInfo(id: type)
+        }
+    }
+}