Refactor: Improve flight search UI and logic

This commit introduces several enhancements to the flight search user interface and underlying logic.

Key changes:
- Added an extension function `Flight.hasFlights()` to check if a flight object contains any actual flight data. This is located in `ui/home/src/main/kotlin/dev/adriankuta/flights/ui/home/extensions/FlightExt.kt`.
- In `StationsScreen.kt`:
    - The origin airport display now includes a "Origin airport" label.
    - The search input field placeholder text dynamically changes based on whether an origin airport has been selected (e.g., "Search origin airport" vs. "Search destination airport").
- In `StationsScreenViewModel.kt`:
    - When an airport is selected, the search query is now automatically cleared.
- Added new string resources in `ui/stations/src/main/res/values/strings.xml` for the dynamic placeholder text: `search_origin_airport` and `search_destination_airport`.
- In `SearchResults.kt`:
    - Implemented an `EmptyListComponent` to display a user-friendly message with an icon when no flights are found for the given search criteria.
    - The `SearchResults` composable now utilizes `itemsIndexed` for better handling of dividers between trip cards.
    - Dividers are no longer shown after the last item in the list of trips or trip dates.
    - Added previews for the empty list state (`EmptyListPreview` and `SearchResultsEmptyPreview`).

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

@@ -1,22 +1,28 @@
 package dev.adriankuta.flights.ui.home.components
 
+import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.lazy.LazyColumn
-import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.lazy.itemsIndexed
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Search
 import androidx.compose.material3.Card
 import androidx.compose.material3.CardDefaults
 import androidx.compose.material3.HorizontalDivider
+import androidx.compose.material3.Icon
 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.text.style.TextAlign
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.tooling.preview.PreviewParameter
 import androidx.compose.ui.unit.dp
@@ -25,6 +31,7 @@ import dev.adriankuta.flights.domain.types.Trip
 import dev.adriankuta.flights.domain.types.TripDate
 import dev.adriankuta.flights.domain.types.TripFlight
 import dev.adriankuta.flights.ui.home.SearchResultUiState
+import dev.adriankuta.flights.ui.home.extensions.hasFlights
 import dev.adriankuta.flights.ui.home.sample.FlightPreviewParameterProvider
 
 @Composable
@@ -48,9 +55,17 @@ internal fun SearchResults(
             is SearchResultUiState.Error -> item { Text("Error") }
             SearchResultUiState.Idle -> Unit
             SearchResultUiState.Loading -> item { Text("Loading") }
-            is SearchResultUiState.Success -> items(uiState.flight.trips) { trip ->
+            is SearchResultUiState.Success -> {
-                TripCard(trip = trip, currency = uiState.flight.currency)
+                if (uiState.flight.hasFlights()) {
-                Spacer(modifier = Modifier.height(16.dp))
+                    itemsIndexed(uiState.flight.trips) { index, trip ->
+                        TripCard(trip = trip, currency = uiState.flight.currency)
+                        if (index < uiState.flight.trips.lastIndex) {
+                            Spacer(modifier = Modifier.height(16.dp))
+                        }
+                    }
+                } else {
+                    item { EmptyListComponent() }
+                }
             }
         }
     }
@@ -78,9 +93,11 @@ private fun TripCard(
             Spacer(modifier = Modifier.height(8.dp))
 
             Column {
-                trip.dates.forEach { tripDate ->
+                trip.dates.forEachIndexed { index, tripDate ->
                     TripDateItem(tripDate = tripDate, currency = currency)
-                    HorizontalDivider(modifier = Modifier.padding(vertical = 8.dp))
+                    if (index != trip.dates.lastIndex) {
+                        HorizontalDivider(modifier = Modifier.padding(vertical = 8.dp))
+                    }
                 }
             }
         }
@@ -163,8 +180,63 @@ private fun FlightItem(
     }
 }
 
+@Composable
+private fun EmptyListComponent(
+    modifier: Modifier = Modifier,
+) {
+    Box(
+        modifier = modifier
+            .fillMaxSize()
+            .padding(16.dp),
+        contentAlignment = Alignment.Center,
+    ) {
+        Column(
+            horizontalAlignment = Alignment.CenterHorizontally,
+        ) {
+            Icon(
+                imageVector = Icons.Default.Search,
+                contentDescription = null,
+                modifier = Modifier.padding(bottom = 16.dp),
+                tint = MaterialTheme.colorScheme.primary,
+            )
+            Text(
+                text = "No flights found",
+                style = MaterialTheme.typography.titleMedium,
+                fontWeight = FontWeight.Bold,
+                textAlign = TextAlign.Center,
+            )
+            Spacer(modifier = Modifier.height(8.dp))
+            Text(
+                text = "Try changing your search criteria",
+                style = MaterialTheme.typography.bodyMedium,
+                textAlign = TextAlign.Center,
+            )
+        }
+    }
+}
+
+@Preview(showBackground = true)
+@Composable
+private fun EmptyListPreview() {
+    EmptyListComponent()
+}
+
 @Preview(showBackground = true)
 @Composable
 private fun SearchResultsPreview(@PreviewParameter(FlightPreviewParameterProvider::class) flight: Flight) {
     SearchResults(uiState = SearchResultUiState.Success(flight))
 }
+
+@Preview(showBackground = true)
+@Composable
+private fun SearchResultsEmptyPreview() {
+    SearchResults(
+        uiState = SearchResultUiState.Success(
+            Flight(
+                currency = "EUR",
+                currPrecision = 2,
+                trips = emptyList(),
+            ),
+        ),
+    )
+}

ui/home/src/main/kotlin/dev/adriankuta/flights/ui/home/extensions/FlightExt.kt

@@ -0,0 +1,6 @@
+package dev.adriankuta.flights.ui.home.extensions
+
+import dev.adriankuta.flights.domain.types.Flight
+
+internal fun Flight.hasFlights(): Boolean =
+    trips.firstOrNull()?.dates?.firstOrNull()?.flights?.isNotEmpty() == true

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

@@ -71,9 +71,21 @@ private fun StationsScreen(
             LaunchedEffect(selectedOriginAirport) {
                 selectedOriginAirport?.let { airportInfo = it }
             }
-            AirportInfoCompact(
+            Column {
-                data = airportInfo,
+                Text(
-            )
+                    text = "Origin airport",
+                    modifier = Modifier.padding(horizontal = 16.dp),
+                )
+                AirportInfoCompact(
+                    data = airportInfo,
+                )
+            }
+        }
+
+        val hintRes = if (selectedOriginAirport == null) {
+            R.string.search_origin_airport
+        } else {
+            R.string.search_destination_airport
         }
 
         OutlinedTextField(
@@ -82,7 +94,7 @@ private fun StationsScreen(
             modifier = Modifier
                 .fillMaxWidth()
                 .padding(16.dp),
-            placeholder = { Text(text = stringResource(R.string.search_airports)) },
+            placeholder = { Text(text = stringResource(hintRes)) },
             leadingIcon = { Icon(Icons.Default.Search, contentDescription = null) },
             singleLine = true,
         )

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

@@ -45,6 +45,7 @@ internal class StationsScreenViewModel @Inject constructor(
 
     fun onAirportSelected(airport: AirportInfo) {
         _selectedOriginAirport.value = airport
+        _searchQuery.value = ""
     }
 
     fun clearSelectedAirport() {

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

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
     <string name="stations_screen_title">Stations</string>
-    <string name="search_airports">Search airports</string>
+    <string name="search_origin_airport">Search origin airport</string>
+    <string name="search_destination_airport">Search destination airport</string>
 </resources>