feat: Implement stations screen with grouped airports

This commit introduces a new "Stations" screen that displays airports grouped by country.

Key changes:
- Added a new Gradle module: `ui:stations`.
- Created `StationsScreen.kt` to display a list of airports grouped by country using `LazyColumn`. Airports within each country are displayed as `AirportInfoItem` and countries as `CountryItem`.
- Implemented `StationsScreenViewModel.kt` to fetch and manage the state of airports grouped by country. It uses `ObserveAirportsGroupedByCountry` use case.
- Defined `ObserveAirportsGroupedByCountry.kt` use case in `domain:stations` module to provide a flow of airports grouped by country.
- Implemented `ObserveAirportsGroupedByCountryImpl.kt` in the repository layer, which fetches data using `AirportService`, stores it in `AirportsDatasource`, and maps it to the domain model.
- Added Hilt module `ObserveAirportsGroupedByCountryModule.kt` to provide the use case implementation.
- Added `stationsScreen()` and `navigateToStations()` to `FlightsNavGraph.kt` and `TopLevelDestination.kt` for navigation.
- Updated `settings.gradle.kts` and `app/build.gradle.kts` to include the new `ui:stations` and `domain:stations` modules.
- Updated `CacheObservers.kt` to make `mapToDomain` a suspend function.
- Added string resources for the stations screen title.

ui/stations/build.gradle.kts

@@ -0,0 +1,18 @@
+plugins {
+    alias(libs.plugins.flights.android.library.compose)
+    alias(libs.plugins.flights.android.library.hilt)
+    alias(libs.plugins.kotlin.serialization)
+}
+
+android {
+    namespace = "dev.adriankuta.flights.ui.stations"
+}
+
+dependencies {
+    implementation(projects.core.util)
+    implementation(projects.ui.designsystem)
+    implementation(projects.ui.sharedui)
+    implementation(projects.domain.stations)
+
+    implementation(libs.androidx.hilt.navigation.compose)
+}

ui/stations/src/main/kotlin/dev/adriankuta/flights/ui/home/StationsScreen.kt

@@ -0,0 +1,53 @@
+package dev.adriankuta.flights.ui.home
+
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.LazyListScope
+import androidx.compose.foundation.lazy.items
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.Modifier
+import androidx.hilt.navigation.compose.hiltViewModel
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import dev.adriankuta.flights.domain.types.AirportInfo
+import dev.adriankuta.flights.domain.types.Country
+import dev.adriankuta.flights.ui.home.components.AirportInfoItem
+import dev.adriankuta.flights.ui.home.components.CountryItem
+
+@Composable
+internal fun StationsScreen(
+    stationScreenViewModel: StationsScreenViewModel = hiltViewModel(),
+) {
+    val originAirports by stationScreenViewModel.originAirports.collectAsStateWithLifecycle()
+
+    StationsScreen(
+        originAirports = originAirports,
+    )
+}
+
+@Composable
+private fun StationsScreen(
+    originAirports: OriginAirportsUiState,
+) {
+    LazyColumn(
+        modifier = Modifier.fillMaxWidth(),
+    ) {
+        when (originAirports) {
+            is OriginAirportsUiState.Error -> item { Text("Error") }
+            is OriginAirportsUiState.Loading -> item { Text("Loading") }
+            is OriginAirportsUiState.Success -> groupedAirports(originAirports.groupedAirports)
+        }
+    }
+}
+
+private fun LazyListScope.groupedAirports(
+    data: Map<Country, List<AirportInfo>>,
+) {
+    data.keys.forEach { country ->
+        stickyHeader { CountryItem(country) }
+        items(data[country]!!) { airport ->
+            AirportInfoItem(airport)
+        }
+    }
+}

ui/stations/src/main/kotlin/dev/adriankuta/flights/ui/home/StationsScreenViewModel.kt

@@ -0,0 +1,55 @@
+package dev.adriankuta.flights.ui.home
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import dagger.hilt.android.lifecycle.HiltViewModel
+import dev.adriankuta.flights.core.util.Result
+import dev.adriankuta.flights.core.util.asResult
+import dev.adriankuta.flights.domain.stations.ObserveAirportsGroupedByCountry
+import dev.adriankuta.flights.domain.types.AirportInfo
+import dev.adriankuta.flights.domain.types.Country
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.stateIn
+import javax.inject.Inject
+
+@HiltViewModel
+internal class StationsScreenViewModel @Inject constructor(
+    observeAirportsGroupedByCountry: ObserveAirportsGroupedByCountry,
+) : ViewModel() {
+
+    val originAirports = originAirportsUiState(
+        useCase = observeAirportsGroupedByCountry,
+    ).stateIn(
+        scope = viewModelScope,
+        started = SharingStarted.WhileSubscribed(5_000),
+        initialValue = OriginAirportsUiState.Loading,
+    )
+}
+
+private fun originAirportsUiState(
+    useCase: ObserveAirportsGroupedByCountry,
+): Flow<OriginAirportsUiState> {
+    return useCase()
+        .asResult()
+        .map { result ->
+            when (result) {
+                is Result.Error -> OriginAirportsUiState.Error(result.exception)
+                is Result.Loading -> OriginAirportsUiState.Loading
+                is Result.Success -> OriginAirportsUiState.Success(result.data.orEmpty())
+            }
+        }
+}
+
+internal sealed interface OriginAirportsUiState {
+    data object Loading : OriginAirportsUiState
+    data class Success(val groupedAirports: Map<Country, List<AirportInfo>>) : OriginAirportsUiState
+    data class Error(val exception: Throwable) : OriginAirportsUiState
+}
+
+internal sealed interface DestinationAirportsUiState {
+    data object Loading : DestinationAirportsUiState
+    data class Success(val airports: List<AirportInfo>) : DestinationAirportsUiState
+    data class Error(val exception: Throwable) : DestinationAirportsUiState
+}

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

@@ -0,0 +1,72 @@
+package dev.adriankuta.flights.ui.home.components
+
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.Card
+import androidx.compose.material3.CardDefaults
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.dp
+import dev.adriankuta.flights.domain.types.AirportInfo
+
+@Composable
+internal fun AirportInfoItem(
+    data: AirportInfo,
+    modifier: Modifier = Modifier,
+) {
+    Card(
+        modifier = modifier
+            .fillMaxWidth()
+            .padding(horizontal = 16.dp, vertical = 4.dp),
+        elevation = CardDefaults.cardElevation(defaultElevation = 2.dp),
+    ) {
+        Column(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(16.dp),
+        ) {
+            Row(
+                modifier = Modifier.fillMaxWidth(),
+                verticalAlignment = Alignment.CenterVertically,
+            ) {
+                Column(modifier = Modifier.weight(1f)) {
+                    Text(
+                        text = data.name,
+                        style = MaterialTheme.typography.titleMedium,
+                        fontWeight = FontWeight.Bold,
+                    )
+                    Text(
+                        text = data.code,
+                        style = MaterialTheme.typography.bodyMedium,
+                    )
+                }
+                if (data.isBase) {
+                    Text(
+                        text = "BASE",
+                        style = MaterialTheme.typography.labelMedium,
+                        color = MaterialTheme.colorScheme.primary,
+                        fontWeight = FontWeight.Bold,
+                        modifier = Modifier.padding(start = 8.dp),
+                    )
+                }
+            }
+
+            Text(
+                text = "City: ${data.city.name}",
+                style = MaterialTheme.typography.bodySmall,
+                modifier = Modifier.padding(top = 8.dp),
+            )
+
+            Text(
+                text = "Region: ${data.region.name}",
+                style = MaterialTheme.typography.bodySmall,
+            )
+        }
+    }
+}

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

@@ -0,0 +1,48 @@
+package dev.adriankuta.flights.ui.home.components
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.dp
+import dev.adriankuta.flights.domain.types.Country
+
+@Composable
+internal fun CountryItem(
+    data: Country,
+    modifier: Modifier = Modifier,
+) {
+    Surface(
+        modifier = modifier
+            .fillMaxWidth()
+            .background(MaterialTheme.colorScheme.primaryContainer),
+        color = MaterialTheme.colorScheme.primaryContainer,
+    ) {
+        Row(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(horizontal = 16.dp, vertical = 8.dp),
+            verticalAlignment = Alignment.CenterVertically,
+        ) {
+            Column {
+                Text(
+                    text = data.name,
+                    style = MaterialTheme.typography.titleMedium,
+                    fontWeight = FontWeight.Bold,
+                )
+                Text(
+                    text = "Currency: ${data.currencyCode}",
+                    style = MaterialTheme.typography.bodySmall,
+                )
+            }
+        }
+    }
+}

ui/stations/src/main/kotlin/dev/adriankuta/flights/ui/home/navigation/StationsNavigation.kt

@@ -0,0 +1,25 @@
+@file:Suppress("MatchingDeclarationName")
+
+package dev.adriankuta.flights.ui.home.navigation
+
+import androidx.navigation.NavController
+import androidx.navigation.NavGraphBuilder
+import androidx.navigation.NavOptions
+import androidx.navigation.compose.composable
+import dev.adriankuta.flights.ui.home.StationsScreen
+import kotlinx.serialization.Serializable
+
+@Serializable
+data object StationsRoute
+
+fun NavController.navigateToStations(
+    navOptions: NavOptions,
+) {
+    navigate(route = StationsRoute, navOptions = navOptions)
+}
+
+fun NavGraphBuilder.stationsScreen() {
+    composable<StationsRoute> {
+        StationsScreen()
+    }
+}

ui/stations/src/main/res/values/strings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="stations_screen_title">Stations</string>
+</resources>