add url validation

app/src/main/java/de/lelehier/keeper/screens/home_screen.kt

@@ -2,8 +2,10 @@ package de.lelehier.keeper.screens
 
 import KeeperLargeFontFamily
 import android.print.PrintAttributes.Margins
+import android.util.Patterns
 import androidx.compose.animation.AnimatedContent
 import androidx.compose.animation.AnimatedContentTransitionScope
+import androidx.compose.animation.AnimatedVisibility
 import androidx.compose.animation.core.EaseIn
 import androidx.compose.animation.core.tween
 import androidx.compose.animation.fadeIn
@@ -16,6 +18,7 @@ import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.imePadding
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.text.KeyboardOptions
 import androidx.compose.material3.Button
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.OutlinedTextField
@@ -31,6 +34,7 @@ import androidx.compose.ui.graphics.Brush
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.text.TextStyle
 import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.text.input.KeyboardType
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
@@ -51,7 +55,7 @@ fun homeScreen(paddingValues: PaddingValues) {
             .imePadding(),
         horizontalAlignment = Alignment.CenterHorizontally,
         verticalArrangement = Arrangement.Center) {
-        Greeting();
+        Greeting(serverURL);
         AnimatedContent(
             targetState = currentScreen,
             transitionSpec = {
@@ -75,7 +79,7 @@ fun homeScreen(paddingValues: PaddingValues) {
 }
 
 @Composable
-fun Greeting() {
+fun Greeting(serverURL: String) {
     Column (horizontalAlignment = Alignment.CenterHorizontally, modifier = Modifier.padding(bottom = 24.dp)) {
         Text(
             text = "Welcome to",
@@ -90,6 +94,7 @@ fun Greeting() {
                 brush = Brush.linearGradient(listOf(MaterialTheme.colorScheme.onPrimaryContainer, MaterialTheme.colorScheme.onSecondaryContainer))),
             textAlign = TextAlign.Center,
         )
+
     }
 }
 
@@ -103,9 +108,27 @@ fun serverDialog(serverURL: String) {
         value = serverURL,
         onValueChange = { text ->
             serverURL = text
-        }
-
+        },
+        keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Uri),
+        supportingText = {
+                AnimatedVisibility(!isValidUrl(serverURL)) {
+                    Text(
+                        text = "No valid URL",
+                        color = MaterialTheme.colorScheme.error
                     )
+                }
+        }
+    )
+}
+
+fun isValidUrl(url: String): Boolean {
+    return try {
+        // Use Android's Patterns.WEB_URL for robust URL validation
+        // This handles various URL formats, including those without schemes.
+        Patterns.WEB_URL.matcher(url).matches()
+    } catch (e: Exception) {
+        false
+    }
 }
 
 @Composable