feat: Implement origin and destination airport selection

This commit introduces functionality for selecting origin and destination airports on the home screen.

Key changes:
- Modified `HomeScreen` to use `Column` instead of `LazyColumn` for layout.
- Added `AirportDropdown` composable component for selecting airports.
- Updated `HomeScreen` to include two `AirportDropdown` instances: one for origin and one for destination.
- Enhanced `HomeScreenViewModel`:
    - Added `selectedOriginAirport` and `selectedDestinationAirport` state flows.
    - Implemented `selectOriginAirport` and `selectDestinationAirport` functions to update selected airports.
    - Added `clearOriginAirport` and `clearDestinationAirport` functions.
    - Updated `homeUiState` to combine airport data with selected airports and filter destination airports to exclude the selected origin.
- Updated `HomeUiState.Success` to include `originAirports`, `destinationAirports`, `selectedOriginAirport`, and `selectedDestinationAirport`.
- Added new preview functions for `HomeScreen` in loading and success states with mock data.

ui/home/src/main/kotlin/dev/adriankuta/flights/ui/home/HomeScreen.kt

@@ -1,15 +1,26 @@
 package dev.adriankuta.flights.ui.home
 
-import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.layout.Column
-import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import dev.adriankuta.flights.domain.types.AirportInfo
+import dev.adriankuta.flights.domain.types.City
+import dev.adriankuta.flights.domain.types.Coordinates
+import dev.adriankuta.flights.domain.types.Country
+import dev.adriankuta.flights.domain.types.MacCity
+import dev.adriankuta.flights.domain.types.Region
 import dev.adriankuta.flights.ui.designsystem.theme.FlightsTheme
 import dev.adriankuta.flights.ui.designsystem.theme.PreviewDevices
+import dev.adriankuta.flights.ui.home.components.AirportDropdown
 
 @Composable
 internal fun HomeScreen(
@@ -19,22 +30,43 @@ internal fun HomeScreen(
 
     HomeScreen(
         uiState = homeUiState,
+        onOriginAirportSelect = viewModel::selectOriginAirport,
+        onDestinationAirportSelect = viewModel::selectDestinationAirport,
     )
 }
 
 @Composable
 private fun HomeScreen(
     uiState: HomeUiState,
+    onOriginAirportSelect: (AirportInfo) -> Unit,
+    onDestinationAirportSelect: (AirportInfo) -> Unit,
     modifier: Modifier = Modifier,
 ) {
-    LazyColumn(
+    Column(
-        modifier = modifier,
+        modifier = modifier.padding(16.dp),
     ) {
         when (uiState) {
-            is HomeUiState.Error -> item { Text("Error") }
+            is HomeUiState.Error -> Text("Error")
-            HomeUiState.Loading -> item { Text("Loading") }
+            HomeUiState.Loading -> Text("Loading")
-            is HomeUiState.Success -> items(uiState.airports) { airport ->
+            is HomeUiState.Success -> {
-                Text(airport.name)
+                AirportDropdown(
+                    label = "Origin Airport",
+                    airports = uiState.originAirports,
+                    selectedAirport = uiState.selectedOriginAirport,
+                    onAirportSelect = onOriginAirportSelect,
+                    modifier = Modifier.fillMaxWidth(),
+                )
+
+                Spacer(modifier = Modifier.height(16.dp))
+
+                AirportDropdown(
+                    label = "Destination Airport",
+                    airports = uiState.destinationAirports,
+                    selectedAirport = uiState.selectedDestinationAirport,
+                    onAirportSelect = onDestinationAirportSelect,
+                    modifier = Modifier.fillMaxWidth(),
+                    enabled = uiState.selectedOriginAirport != null,
+                )
             }
         }
     }
@@ -42,10 +74,56 @@ private fun HomeScreen(
 
 @PreviewDevices
 @Composable
-private fun HomeScreenPreview() {
+private fun HomeScreenLoadingPreview() {
     FlightsTheme {
         HomeScreen(
             uiState = HomeUiState.Loading,
+            onOriginAirportSelect = {},
+            onDestinationAirportSelect = {},
+        )
+    }
+}
+
+@PreviewDevices
+@Composable
+private fun HomeScreenSuccessPreview() {
+    FlightsTheme {
+        val mockAirports = listOf(
+            AirportInfo(
+                code = "WAW",
+                name = "Warsaw Chopin Airport",
+                seoName = "warsaw",
+                isBase = true,
+                timeZone = "Europe/Warsaw",
+                city = City("WAW", "Warsaw"),
+                macCity = MacCity("WARSAW"),
+                region = Region("WARSAW_PL", "Warsaw"),
+                country = Country("PL", "Poland", "PLN"),
+                coordinates = Coordinates(52.1657, 20.9671),
+            ),
+            AirportInfo(
+                code = "KRK",
+                name = "Krakow Airport",
+                seoName = "krakow",
+                isBase = true,
+                timeZone = "Europe/Warsaw",
+                city = City("KRK", "Krakow"),
+                macCity = MacCity("KRAKOW"),
+                region = Region("KRAKOW_PL", "Krakow"),
+                country = Country("PL", "Poland", "PLN"),
+                coordinates = Coordinates(50.0777, 19.7848),
+            ),
+        )
+
+        HomeScreen(
+            uiState = HomeUiState.Success(
+                originAirports = mockAirports,
+                destinationAirports = mockAirports,
+                selectedOriginAirport = mockAirports.first(),
+                selectedDestinationAirport = null,
+            ),
+            onOriginAirportSelect = {},
+            onDestinationAirportSelect = {},
         )
     }
 }

ui/home/src/main/kotlin/dev/adriankuta/flights/ui/home/HomeScreenViewModel.kt

@@ -8,8 +8,9 @@ import dev.adriankuta.flights.core.util.asResult
 import dev.adriankuta.flights.domain.search.ObserveAirportsUseCase
 import dev.adriankuta.flights.domain.types.AirportInfo
 import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
-import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.stateIn
 import javax.inject.Inject
 
@@ -18,32 +19,77 @@ class HomeScreenViewModel @Inject constructor(
     private val observeAirportsUseCase: ObserveAirportsUseCase,
 ) : ViewModel() {
 
+    private val selectedOriginAirport = MutableStateFlow<AirportInfo?>(null)
+    private val selectedDestinationAirport = MutableStateFlow<AirportInfo?>(null)
+
     internal val uiState = homeUiState(
         useCase = observeAirportsUseCase,
+        selectedOriginAirport = selectedOriginAirport,
+        selectedDestinationAirport = selectedDestinationAirport,
     )
         .stateIn(
             scope = viewModelScope,
             started = SharingStarted.WhileSubscribed(5_000),
             initialValue = HomeUiState.Loading,
         )
+
+    fun selectOriginAirport(airport: AirportInfo) {
+        selectedOriginAirport.value = airport
+        // If the selected destination is the same as the new origin, clear the destination
+        if (selectedDestinationAirport.value?.code == airport.code) {
+            selectedDestinationAirport.value = null
+        }
+    }
+
+    fun selectDestinationAirport(airport: AirportInfo) {
+        selectedDestinationAirport.value = airport
+    }
+
+    fun clearOriginAirport() {
+        selectedOriginAirport.value = null
+        // Clear destination as well since it depends on origin
+        selectedDestinationAirport.value = null
+    }
+
+    fun clearDestinationAirport() {
+        selectedDestinationAirport.value = null
+    }
 }
 
 private fun homeUiState(
     useCase: ObserveAirportsUseCase,
+    selectedOriginAirport: MutableStateFlow<AirportInfo?>,
+    selectedDestinationAirport: MutableStateFlow<AirportInfo?>,
 ): Flow<HomeUiState> {
-    return useCase()
+    return combine(
-        .asResult()
+        useCase().asResult(),
-        .map { result ->
+        selectedOriginAirport,
+        selectedDestinationAirport,
+    ) { result, origin, destination ->
         when (result) {
             is Result.Error -> HomeUiState.Error(result.exception)
-                Result.Loading -> HomeUiState.Loading
+            is Result.Loading -> HomeUiState.Loading
-                is Result.Success -> HomeUiState.Success(result.data.orEmpty())
+            is Result.Success -> {
+                val airports = result.data.orEmpty()
+                HomeUiState.Success(
+                    originAirports = airports,
+                    destinationAirports = airports.filter { it.code != origin?.code },
+                    selectedOriginAirport = origin,
+                    selectedDestinationAirport = destination,
+                )
+            }
         }
     }
 }
 
 internal sealed interface HomeUiState {
     data object Loading : HomeUiState
-    data class Success(val airports: List<AirportInfo>) : HomeUiState
+    data class Success(
+        val originAirports: List<AirportInfo>,
+        val destinationAirports: List<AirportInfo>,
+        val selectedOriginAirport: AirportInfo? = null,
+        val selectedDestinationAirport: AirportInfo? = null,
+    ) : HomeUiState
+
     data class Error(val exception: Throwable) : HomeUiState
 }

ui/home/src/main/kotlin/dev/adriankuta/flights/ui/home/components/AirportDropdown.kt

@@ -0,0 +1,66 @@
+package dev.adriankuta.flights.ui.home.components
+
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.material3.DropdownMenuItem
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.ExposedDropdownMenuBox
+import androidx.compose.material3.ExposedDropdownMenuDefaults
+import androidx.compose.material3.MenuAnchorType
+import androidx.compose.material3.OutlinedTextField
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import dev.adriankuta.flights.domain.types.AirportInfo
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun AirportDropdown(
+    label: String,
+    airports: List<AirportInfo>,
+    selectedAirport: AirportInfo?,
+    onAirportSelect: (AirportInfo) -> Unit,
+    modifier: Modifier = Modifier,
+    enabled: Boolean = true,
+) {
+    var expanded by remember { mutableStateOf(false) }
+
+    ExposedDropdownMenuBox(
+        expanded = expanded,
+        onExpandedChange = { if (enabled) expanded = it },
+        modifier = modifier,
+    ) {
+        OutlinedTextField(
+            value = selectedAirport?.let { "${it.name} (${it.code})" } ?: "",
+            onValueChange = {},
+            readOnly = true,
+            label = { Text(label) },
+            trailingIcon = {
+                ExposedDropdownMenuDefaults.TrailingIcon(expanded = expanded)
+            },
+            colors = ExposedDropdownMenuDefaults.outlinedTextFieldColors(),
+            modifier = Modifier
+                .fillMaxWidth()
+                .menuAnchor(MenuAnchorType.PrimaryNotEditable, enabled),
+            enabled = enabled,
+        )
+
+        ExposedDropdownMenu(
+            expanded = expanded,
+            onDismissRequest = { expanded = false },
+        ) {
+            airports.forEach { airport ->
+                DropdownMenuItem(
+                    text = { Text("${airport.name} (${airport.code})") },
+                    onClick = {
+                        onAirportSelect(airport)
+                        expanded = false
+                    },
+                )
+            }
+        }
+    }
+}