Refactor: Update package structure and implement bottom navigation

This commit refactors the package structure for Gradle convention plugins and introduces bottom navigation to the application.

Key changes:
- Moved Gradle convention plugin files from `dev.adriankuta.partymania` to `dev.adriankuta.flights`.
- Added `TopLevelDestination.kt` to define top-level navigation destinations with icons, titles, and routes.
- Implemented `FlightsBottomBar` Composable in `FlightsApp.kt` to display a `NavigationBar` with items for each `TopLevelDestination`.
- Updated `FlightsNavGraph.kt`:
    - Renamed from `FlightsNavGraph.kt` to `navigation/FlightsNavGraph.kt`.
    - Added `navigateToTopLevelDestination` extension function for `NavController` to handle navigation to top-level destinations with appropriate `NavOptions`.
- Updated `HomeNavigation.kt`:
    - Added `navigateToHome` extension function for `NavController`.
- Added `strings.xml` for `ui:home` module with `home_screen_title`.
- Ensured Kotlin serialization plugin is correctly applied in `app/build.gradle.kts`.

app/build.gradle.kts

@@ -1,7 +1,7 @@
 plugins {
-    alias(libs.plugins.kotlin.serialization)
     alias(libs.plugins.flights.android.application.compose)
     alias(libs.plugins.flights.android.application.hilt)
+    alias(libs.plugins.kotlin.serialization)
 }
 
 android {

app/src/main/kotlin/dev/adriankuta/flights/FlightsNavGraph.kt

@@ -1,23 +0,0 @@
-package dev.adriankuta.flights
-
-import androidx.compose.runtime.Composable
-import androidx.compose.ui.Modifier
-import androidx.navigation.NavHostController
-import androidx.navigation.compose.NavHost
-import androidx.navigation.compose.rememberNavController
-import dev.adriankuta.flights.ui.home.navigation.HomeRoute
-import dev.adriankuta.flights.ui.home.navigation.homeScreen
-
-@Composable
-fun FlightsNavGraph(
-    modifier: Modifier = Modifier,
-    navController: NavHostController = rememberNavController(),
-) {
-    NavHost(
-        navController = navController,
-        startDestination = HomeRoute,
-        modifier = modifier,
-    ) {
-        homeScreen()
-    }
-}

app/src/main/kotlin/dev/adriankuta/flights/navigation/FlightsNavGraph.kt

@@ -0,0 +1,51 @@
+package dev.adriankuta.flights.navigation
+
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.util.trace
+import androidx.navigation.NavController
+import androidx.navigation.NavGraph.Companion.findStartDestination
+import androidx.navigation.NavHostController
+import androidx.navigation.compose.NavHost
+import androidx.navigation.compose.rememberNavController
+import androidx.navigation.navOptions
+import dev.adriankuta.flights.ui.home.navigation.HomeRoute
+import dev.adriankuta.flights.ui.home.navigation.homeScreen
+import dev.adriankuta.flights.ui.home.navigation.navigateToHome
+
+@Composable
+fun FlightsNavGraph(
+    modifier: Modifier = Modifier,
+    navController: NavHostController = rememberNavController(),
+) {
+    NavHost(
+        navController = navController,
+        startDestination = HomeRoute,
+        modifier = modifier,
+    ) {
+        homeScreen()
+    }
+}
+
+fun NavController.navigateToTopLevelDestination(topLevelDestination: TopLevelDestination) {
+    trace("Navigation: ${topLevelDestination.name}") {
+        val topLevelNavOptions = navOptions {
+            // Pop up to the start destination of the graph to
+            // avoid building up a large stack of destinations
+            // on the back stack as users select items
+            popUpTo(graph.findStartDestination().id) {
+                saveState = true
+            }
+            // Avoid multiple copies of the same destination when
+            // reselecting the same item
+            launchSingleTop = true
+            // Restore state when reselecting a previously selected item
+            restoreState = true
+        }
+
+        when (topLevelDestination) {
+            TopLevelDestination.HOME -> navigateToHome(topLevelNavOptions)
+            TopLevelDestination.STATIONS -> navigateToHome(topLevelNavOptions)
+        }
+    }
+}

app/src/main/kotlin/dev/adriankuta/flights/navigation/TopLevelDestination.kt

@@ -0,0 +1,28 @@
+package dev.adriankuta.flights.navigation
+
+import androidx.annotation.StringRes
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.outlined.Place
+import androidx.compose.material.icons.outlined.Search
+import androidx.compose.ui.graphics.vector.ImageVector
+import dev.adriankuta.flights.ui.home.navigation.HomeRoute
+import kotlin.reflect.KClass
+import dev.adriankuta.flights.ui.home.R as homeR
+
+enum class TopLevelDestination(
+    val icon: ImageVector,
+    @StringRes val titleTextId: Int,
+    val route: KClass<*>,
+    val baseRoute: KClass<*> = route,
+) {
+    HOME(
+        icon = Icons.Outlined.Search,
+        titleTextId = homeR.string.home_screen_title,
+        route = HomeRoute::class,
+    ),
+    STATIONS(
+        icon = Icons.Outlined.Place,
+        titleTextId = homeR.string.home_screen_title,
+        route = HomeRoute::class,
+    ),
+}

app/src/main/kotlin/dev/adriankuta/flights/ui/FlightsApp.kt

@@ -1,25 +1,75 @@
 package dev.adriankuta.flights.ui
 
 import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.Icon
+import androidx.compose.material3.NavigationBar
+import androidx.compose.material3.NavigationBarDefaults
+import androidx.compose.material3.NavigationBarItem
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableIntStateOf
+import androidx.compose.runtime.saveable.rememberSaveable
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
-import dev.adriankuta.flights.FlightsNavGraph
+import androidx.compose.ui.res.stringResource
+import androidx.navigation.NavHostController
+import androidx.navigation.compose.rememberNavController
+import dev.adriankuta.flights.navigation.FlightsNavGraph
+import dev.adriankuta.flights.navigation.TopLevelDestination
+import dev.adriankuta.flights.navigation.navigateToTopLevelDestination
 import dev.adriankuta.flights.ui.designsystem.theme.Elevation
 
 @Composable
 fun FlightsApp(
     modifier: Modifier = Modifier,
 ) {
+    val navController = rememberNavController()
+
     Surface(
         tonalElevation = Elevation.Surface,
         modifier = modifier,
     ) {
         Scaffold(
             snackbarHost = { InAppUpdates() },
+            bottomBar = {
+                FlightsBottomBar(
+                    navController = navController,
+                )
+            },
         ) { paddingValues ->
-            FlightsNavGraph(Modifier.padding(paddingValues))
+            FlightsNavGraph(
+                navController = navController,
+                modifier = Modifier.padding(paddingValues),
+            )
+        }
+    }
+}
+
+@Composable
+internal fun FlightsBottomBar(
+    navController: NavHostController = rememberNavController(),
+) {
+    var selectedDestination by rememberSaveable { mutableIntStateOf(0) }
+
+    NavigationBar(windowInsets = NavigationBarDefaults.windowInsets) {
+        TopLevelDestination.entries.forEachIndexed { index, destination ->
+            NavigationBarItem(
+                selected = selectedDestination == index,
+                onClick = {
+                    selectedDestination = index
+                    navController.navigateToTopLevelDestination(TopLevelDestination.HOME)
+                },
+                icon = {
+                    Icon(
+                        destination.icon,
+                        contentDescription = null,
+                    )
+                },
+                label = { Text(stringResource(destination.titleTextId)) },
+            )
         }
     }
 }

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

@@ -2,7 +2,9 @@
 
 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.HomeScreen
 import kotlinx.serialization.Serializable
@@ -10,6 +12,12 @@ import kotlinx.serialization.Serializable
 @Serializable
 data object HomeRoute
 
+fun NavController.navigateToHome(
+    navOptions: NavOptions,
+) {
+    navigate(route = HomeRoute, navOptions = navOptions)
+}
+
 fun NavGraphBuilder.homeScreen() {
     composable<HomeRoute> {
         HomeScreen()

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

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