PERTEMUAN 11 - Aplikasi MarketPlace Siswa

APLIKASI MARKETPLACE SISWA adalah aplikasi di mana mahasiswa bisa menjual produk.

Berikut adalah file MainActivity.kt-nya:
package com.example.marketsiswa // UBAH BARIS INI SESUAI NAMA PACKAGE PROJECT-MU!

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.foundation.text.KeyboardOptions
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.*
import androidx.compose.material3.*
import androidx.compose.runtime.*
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.text.input.KeyboardType
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.sp
import kotlinx.coroutines.delay
import kotlinx.coroutines.launch

// 1. Data Model
data class Product(
    val id: Long = System.currentTimeMillis(),
    val name: String,
    val price: String,
    val description: String
)

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MarketplaceTheme {
                // Wrapper Surface untuk mencegah crash render
                Surface(
                    modifier = Modifier.fillMaxSize(),
                    color = MaterialTheme.colorScheme.background
                ) {
                    MainScreen()
                }
            }
        }
    }
}

@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun MainScreen() {
    // State Management
    var currentScreen by remember { mutableStateOf("home") }
    val productList = remember { mutableStateListOf<Product>() }
    val snackbarHostState = remember { SnackbarHostState() }
    val scope = rememberCoroutineScope()

    // Inisialisasi data awal
    LaunchedEffect(Unit) {
        if (productList.isEmpty()) {
            productList.add(Product(name = "Brownies Lumer", price = "15000", description = "Cokelat melimpah."))
            productList.add(Product(name = "Kaos Custom", price = "85000", description = "Bahan adem."))
        }
    }

    Scaffold(
        snackbarHost = { SnackbarHost(snackbarHostState) },
        topBar = {
            CenterAlignedTopAppBar(
                title = {
                    Text(
                        text = if (currentScreen == "add") "Tambah Produk" else "MarketSiswa",
                        fontWeight = FontWeight.Bold
                    )
                },
                navigationIcon = {
                    if (currentScreen == "add") {
                        IconButton(onClick = { currentScreen = "home" }) {
                            Icon(Icons.Default.ArrowBack, contentDescription = "Back")
                        }
                    }
                }
            )
        },
        bottomBar = {
            NavigationBar {
                NavigationBarItem(
                    selected = currentScreen == "home",
                    onClick = { currentScreen = "home" },
                    label = { Text("Home") },
                    icon = { Icon(Icons.Default.Home, contentDescription = null) }
                )
                NavigationBarItem(
                    selected = currentScreen == "profile",
                    onClick = { currentScreen = "profile" },
                    label = { Text("Profile") },
                    icon = { Icon(Icons.Default.Person, contentDescription = null) }
                )
            }
        },
        floatingActionButton = {
            if (currentScreen == "home") {
                // Format FAB yang paling aman untuk semua versi Material 3
                ExtendedFloatingActionButton(
                    text = { Text("Jual") },
                    icon = { Icon(Icons.Default.Add, contentDescription = null) },
                    onClick = { currentScreen = "add" },
                    containerColor = MaterialTheme.colorScheme.primaryContainer,
                    contentColor = MaterialTheme.colorScheme.onPrimaryContainer
                )
            }
        }
    ) { innerPadding ->
        Box(modifier = Modifier.padding(innerPadding)) {
            when (currentScreen) {
                "home" -> HomeScreen(productList)
                "add" -> AddProductScreen(
                    onProductAdded = { newProduct ->
                        productList.add(0, newProduct)
                        scope.launch {
                            currentScreen = "home"
                            snackbarHostState.showSnackbar("Produk berhasil ditambahkan!")
                        }
                    }
                )
                "profile" -> ProfileScreen()
            }
        }
    }
}

@Composable
fun HomeScreen(products: List<Product>) {
    LazyColumn(
        modifier = Modifier.fillMaxSize(),
        contentPadding = PaddingValues(16.dp),
        verticalArrangement = Arrangement.spacedBy(12.dp)
    ) {
        item {
            Text("Halo, Siswa!", fontSize = 24.sp, fontWeight = FontWeight.ExtraBold)
            Text("Mau belanja apa hari ini?", color = Color.Gray, modifier = Modifier.padding(bottom = 8.dp))
        }
        items(products) { product ->
            Card(
                modifier = Modifier.fillMaxWidth(),
                shape = RoundedCornerShape(16.dp)
            ) {
                Column(modifier = Modifier.padding(16.dp)) {
                    Row(
                        modifier = Modifier.fillMaxWidth(),
                        horizontalArrangement = Arrangement.SpaceBetween
                    ) {
                        Text(product.name, fontWeight = FontWeight.Bold, fontSize = 18.sp)
                        Text(
                            text = "Rp ${product.price}",
                            color = MaterialTheme.colorScheme.primary,
                            fontWeight = FontWeight.Black
                        )
                    }
                    Spacer(Modifier.height(4.dp))
                    Text(product.description, color = Color.DarkGray, fontSize = 14.sp)
                }
            }
        }
    }
}

@Composable
fun AddProductScreen(onProductAdded: (Product) -> Unit) {
    var name by remember { mutableStateOf("") }
    var price by remember { mutableStateOf("") }
    var desc by remember { mutableStateOf("") }
    var isLoading by remember { mutableStateOf(false) }
    val scope = rememberCoroutineScope()

    Column(
        modifier = Modifier
            .fillMaxSize()
            .padding(24.dp),
        verticalArrangement = Arrangement.spacedBy(16.dp)
    ) {
        OutlinedTextField(
            value = name,
            onValueChange = { name = it },
            label = { Text("Nama Produk") },
            modifier = Modifier.fillMaxWidth(),
            shape = RoundedCornerShape(12.dp)
        )
        OutlinedTextField(
            value = price,
            onValueChange = { price = it },
            label = { Text("Harga") },
            keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Number),
            modifier = Modifier.fillMaxWidth(),
            shape = RoundedCornerShape(12.dp)
        )
        OutlinedTextField(
            value = desc,
            onValueChange = { desc = it },
            label = { Text("Deskripsi") },
            modifier = Modifier.fillMaxWidth(),
            minLines = 3,
            shape = RoundedCornerShape(12.dp)
        )
        Button(
            onClick = {
                isLoading = true
                scope.launch {
                    delay(1000) // Simulasi loading
                    onProductAdded(Product(name = name, price = price, description = desc))
                    isLoading = false
                }
            },
            modifier = Modifier.fillMaxWidth().height(56.dp),
            enabled = name.isNotBlank() && price.isNotBlank() && !isLoading,
            shape = RoundedCornerShape(12.dp)
        ) {
            if (isLoading) {
                CircularProgressIndicator(modifier = Modifier.size(24.dp), color = Color.White)
            } else {
                Text("Simpan Produk", fontWeight = FontWeight.Bold)
            }
        }
    }
}

@Composable
fun ProfileScreen() {
    Column(
        modifier = Modifier.fillMaxSize(),
        horizontalAlignment = Alignment.CenterHorizontally,
        verticalArrangement = Arrangement.Center
    ) {
        // Menggunakan ikon Person standar yang dijamin 100% jalan tanpa library tambahan
        Icon(
            imageVector = Icons.Default.Person,
            contentDescription = null,
            modifier = Modifier.size(100.dp),
            tint = Color.LightGray
        )
        Text("John Siswa", fontSize = 20.sp, fontWeight = FontWeight.Bold)
        Text("XII RPL 1", color = Color.Gray)
    }
}

@Composable
fun MarketplaceTheme(content: @Composable () -> Unit) {
    MaterialTheme(
        colorScheme = lightColorScheme(
            primary = Color(0xFF6200EE),
            secondary = Color(0xFF03DAC6)
        ),
        content = content
    )
}