increase maximum gap limit, but display warning when gap limit is over 999

src/main/java/com/sparrowwallet/sparrow/wallet/AdvancedController.java

@@ -11,6 +11,7 @@ import javafx.fxml.FXML;
 import javafx.fxml.Initializable;
 import javafx.scene.control.ComboBox;
 import javafx.scene.control.DatePicker;
+import javafx.scene.control.Label;
 import javafx.util.StringConverter;
 
 import java.net.URL;
@@ -23,12 +24,18 @@ import java.util.stream.Collectors;
 public class AdvancedController implements Initializable {
     private static final List<Integer> DEFAULT_WATCH_LIST_ITEMS = List.of(-1, 100, 500, 1000, 5000, 10000);
 
+    private static final int MAX_GAP_LIMIT = 1000000;
+    private static final int WARNING_GAP_LIMIT = 1000;
+
     @FXML
     private DatePicker birthDate;
 
     @FXML
     private IntegerSpinner gapLimit;
 
+    @FXML
+    private Label gapWarning;
+
     @FXML
     private ComboBox<Integer> watchLast;
 
@@ -49,12 +56,14 @@ public class AdvancedController implements Initializable {
             }
         });
 
-        gapLimit.setValueFactory(new IntegerSpinner.ValueFactory(Wallet.DEFAULT_LOOKAHEAD, 9999, wallet.getGapLimit()));
+        gapLimit.setValueFactory(new IntegerSpinner.ValueFactory(Wallet.DEFAULT_LOOKAHEAD, MAX_GAP_LIMIT, wallet.getGapLimit()));
         gapLimit.valueProperty().addListener((observable, oldValue, newValue) -> {
-            if(newValue == null || newValue < Wallet.DEFAULT_LOOKAHEAD || newValue > 9999) {
+            if(newValue == null || newValue < Wallet.DEFAULT_LOOKAHEAD || newValue > MAX_GAP_LIMIT) {
                 return;
             }
 
+            gapWarning.setVisible(newValue >= WARNING_GAP_LIMIT);
+
             wallet.setGapLimit(newValue);
             if(!watchLast.getItems().equals(getWatchListItems(wallet))) {
                 Integer value = watchLast.getValue();
@@ -63,6 +72,17 @@ public class AdvancedController implements Initializable {
             }
             EventManager.get().post(new SettingsChangedEvent(wallet, SettingsChangedEvent.Type.GAP_LIMIT));
         });
+        gapLimit.getEditor().textProperty().addListener((observable, oldValue, newValue) -> {
+            try {
+                int gapLimit = Integer.parseInt(newValue);
+                gapWarning.setVisible(gapLimit >= WARNING_GAP_LIMIT);
+            } catch(Exception e) {
+                //ignore
+            }
+        });
+
+        gapWarning.managedProperty().bind(gapWarning.visibleProperty());
+        gapWarning.setVisible(wallet.getGapLimit() >= WARNING_GAP_LIMIT);
 
         watchLast.setItems(getWatchListItems(wallet));
         watchLast.setConverter(new StringConverter<>() {

src/main/resources/com/sparrowwallet/sparrow/wallet/advanced.css

@@ -0,0 +1,4 @@
+.gap-warning {
+    -fx-text-fill: rgb(238, 210, 2);
+    -fx-padding: 0 0 0 12;
+}

src/main/resources/com/sparrowwallet/sparrow/wallet/advanced.fxml

@@ -11,8 +11,9 @@
 <?import com.sparrowwallet.sparrow.control.HelpLabel?>
 <?import javafx.geometry.Insets?>
 <?import com.sparrowwallet.sparrow.control.IntegerSpinner?>
+<?import org.controlsfx.glyphfont.Glyph?>
 
-<BorderPane stylesheets="@../general.css" styleClass="line-border" xmlns="http://javafx.com/javafx" xmlns:fx="http://javafx.com/fxml" fx:controller="com.sparrowwallet.sparrow.wallet.AdvancedController">
+<BorderPane stylesheets="@advanced.css, @../general.css" styleClass="line-border" xmlns="http://javafx.com/javafx" xmlns:fx="http://javafx.com/fxml" fx:controller="com.sparrowwallet.sparrow.wallet.AdvancedController">
     <center>
         <GridPane hgap="10.0" vgap="10.0">
         <padding>
@@ -34,6 +35,14 @@
                 <Field text="Gap limit:">
                     <IntegerSpinner fx:id="gapLimit" editable="true" prefWidth="90" />
                     <HelpLabel helpText="Change how far ahead to look for additional transactions beyond the highest derivation with previous transaction outputs."/>
+                    <Label fx:id="gapWarning">
+                        <graphic>
+                            <Glyph fontFamily="Font Awesome 5 Free Solid" fontSize="12" icon="EXCLAMATION_TRIANGLE" styleClass="gap-warning" />
+                        </graphic>
+                        <tooltip>
+                            <Tooltip text="Large gap limits may cause wallet loading failures on some servers." />
+                        </tooltip>
+                    </Label>
                 </Field>
                 <Field text="Watch addresses:">
                     <ComboBox fx:id="watchLast" />