state holder instead of vm

LoginScreenExample.kt

@Composable
fun LoginScreen(
    modifier: Modifier = Modifier,
    state: LoginScreenState = rememberLoginScreenState(),
) {
 // ...
}

@Composable
fun rememberLoginScreenState(
    stateScope: CoroutineScope = rememberCoroutineScope(),
    doLogin: DoLogin = get(), // This is koin's get function.
    onSignUp: () -> Unit = {},
): LoginScreenState {
    return rememberSaveable(saver = LoginScreenState.getSaver(stateScope, doLogin, onSignUp)) {
        LoginScreenState(stateScope, doLogin, onSignUp)
    }
}

class LoginScreenState(
    private val stateScope: CoroutineScope,
    private val doLogin: DoLogin, // Use Case for login 
    val onSignUpClick: () -> Unit, // sending the event up to be handled by the parent responsible for navigation
) {

    var email: String by mutableStateOf("")
        private set

    var password: String by mutableStateOf("")
        private set

    var loading: Boolean by mutableStateOf(false)
        private set

    val loginEnabled by derivedStateOf { email.isNotEmpty() && password.isNotEmpty() }

    var loginResult by mutableStateOf<LoginResult?>(null)
        private set
    val emailError: Boolean by derivedStateOf { loginResult is LoginResult.EmailPattern }
    val passwordError: Boolean by derivedStateOf { loginResult is LoginResult.PasswordLength }

    fun onEmail(text: String) {
        email = text.trim()
    }

    fun onPassword(text: String) {
        password = text
    }

    fun onLogin() {
        stateScope.launch {
            loading = true
            loginResult = doLogin(email, password)
            loading = false
        }
    }

    fun dismissError() {
        loginResult = null
    }

    companion object {
        private const val EMAIL: String = "EMAIL"
        private const val PASS: String = "PASS"

        fun getSaver(
            stateScope: CoroutineScope,
            login: DoLogin,
            onSignUp: () -> Unit,
        ): Saver<LoginScreenState, *> = mapSaver(
            save = { mapOf(EMAIL to it.email, PASS to it.password) },
            restore = {
                LoginScreenState(stateScope, login, onSignUp).apply {
                    onEmail(it.getOrElse(EMAIL) { "" } as String)
                    onPassword(it.getOrElse(PASS) { "" } as String)
                }
            }
        )
    }
}