/**
 * State, Navigation & ViewModel — Practical Exercises
 * Mobile Application Development | SUZA | Semester II 2025/2026
 *
 * Copy into an Android Studio project with:
 *   implementation("androidx.navigation:navigation-compose:2.7.7")
 *   implementation("androidx.lifecycle:lifecycle-viewmodel-compose:2.7.0")
 */

import androidx.compose.foundation.layout.*
import androidx.compose.material3.*
import androidx.compose.runtime.*
import androidx.compose.ui.Modifier
import androidx.compose.ui.tooling.preview.Preview
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewmodel.compose.viewModel
import androidx.navigation.NavHostController
import androidx.navigation.NavType
import androidx.navigation.compose.NavHost
import androidx.navigation.compose.composable
import androidx.navigation.compose.rememberNavController
import androidx.navigation.navArgument
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.asStateFlow

// 1. A ViewModel with counter + reset
class CounterViewModel : ViewModel() {
    private val _count = MutableStateFlow(0)
    val count: StateFlow<Int> = _count.asStateFlow()
    fun inc() { _count.value++ }
    fun reset() { _count.value = 0 }
}

@Composable
fun CounterScreen1(vm: CounterViewModel = viewModel()) {
    val count by vm.count.collectAsState()
    Column(Modifier.padding(16.dp)) {
        Text("Count: $count")
        Button(onClick = vm::inc) { Text("Increment") }
        Button(onClick = vm::reset) { Text("Reset") }
    }
}

// 2. Navigation — two screens with argument passing
@Composable
fun App2() {
    val nav = rememberNavController()
    NavHost(nav, startDestination = "home") {
        composable("home") { HomeScreen2(nav) }
        composable(
            route = "greet/{name}",
            arguments = listOf(navArgument("name") { type = NavType.StringType })
        ) { entry ->
            GreetScreen2(
                name = entry.arguments?.getString("name") ?: "Guest",
                onBack = { nav.popBackStack() }
            )
        }
    }
}

@Composable
fun HomeScreen2(nav: NavHostController) {
    var name by remember { mutableStateOf("") }
    Column(Modifier.padding(16.dp)) {
        OutlinedTextField(value = name, onValueChange = { name = it }, label = { Text("Name") })
        Button(
            onClick = { nav.navigate("greet/${name.ifBlank { "Guest" }}") },
            enabled = name.isNotBlank()
        ) { Text("Greet") }
    }
}

@Composable
fun GreetScreen2(name: String, onBack: () -> Unit) {
    Column(Modifier.padding(16.dp)) {
        Text("Hello, $name!")
        Button(onClick = onBack) { Text("Back") }
    }
}

// 3. Shared ViewModel across screens — Cupcake-style UDF
data class OrderUiState(
    val quantity: Int = 0,
    val flavor: String = "",
    val pickupDate: String = "",
    val price: Double = 0.0
)

class OrderViewModel : ViewModel() {
    private val _state = MutableStateFlow(OrderUiState())
    val state: StateFlow<OrderUiState> = _state.asStateFlow()

    fun setQuantity(q: Int) {
        _state.value = _state.value.copy(quantity = q, price = q * 2.00)
    }
    fun setFlavor(f: String) { _state.value = _state.value.copy(flavor = f) }
    fun setDate(d: String)   { _state.value = _state.value.copy(pickupDate = d) }
    fun reset() { _state.value = OrderUiState() }
}

// 4. rememberSaveable vs remember
@Composable
fun SaveableDemo4() {
    var a by remember { mutableStateOf(0) }               // lost on rotation
    var b by rememberSaveable { mutableStateOf(0) }       // survives rotation
    Column(Modifier.padding(16.dp)) {
        Button(onClick = { a++; b++ }) { Text("A=$a  B=$b  (click then rotate)") }
    }
}

// 5. Form state hoisting — LoginForm
data class LoginState(val email: String = "", val password: String = "") {
    val isValid: Boolean get() = "@" in email && password.length >= 6
}
@Composable
fun LoginForm5(state: LoginState, onChange: (LoginState) -> Unit, onSubmit: () -> Unit) {
    Column(Modifier.padding(16.dp)) {
        OutlinedTextField(
            value = state.email, onValueChange = { onChange(state.copy(email = it)) },
            label = { Text("Email") }
        )
        OutlinedTextField(
            value = state.password, onValueChange = { onChange(state.copy(password = it)) },
            label = { Text("Password") }
        )
        Button(onClick = onSubmit, enabled = state.isValid) { Text("Login") }
    }
}
@Preview @Composable fun LoginForm5Preview() {
    var s by remember { mutableStateOf(LoginState()) }
    LoginForm5(state = s, onChange = { s = it }, onSubmit = { })
}