use whirlpool premix priority slider to change mixfeetarget, display warning if chosen fee rate is much lower than normal priority

src/main/java/com/sparrowwallet/sparrow/terminal/wallet/MixPoolDialog.java

@@ -197,6 +197,7 @@ public class MixPoolDialog extends WalletDialog {
             tx0Previews = null;
             whirlpool.setScode(mixConfig.getScode());
             whirlpool.setTx0FeeTarget(tx0FeeTarget);
+            whirlpool.setMixFeeTarget(tx0FeeTarget);
 
             Whirlpool.Tx0PreviewsService tx0PreviewsService = new Whirlpool.Tx0PreviewsService(whirlpool, utxoEntries);
             tx0PreviewsService.setOnRunning(workerStateEvent -> {

src/main/java/com/sparrowwallet/sparrow/whirlpool/WhirlpoolController.java

@@ -55,6 +55,9 @@ public class WhirlpoolController {
     @FXML
     private CopyableLabel premixFeeRate;
 
+    @FXML
+    private Label lowPremixFeeRate;
+
     @FXML
     private ComboBox<Pool> pool;
 
@@ -139,9 +142,12 @@ public class WhirlpoolController {
             tx0Previews = null;
             tx0PreviewProperty.set(null);
             Tx0FeeTarget tx0FeeTarget = FEE_TARGETS.get(newValue.intValue());
-            premixFeeRate.setText(SparrowMinerFeeSupplier.getFee(Integer.parseInt(tx0FeeTarget.getFeeTarget().getValue())) + " sats/vB");
+            premixFeeRate.setText(getFeeRate(tx0FeeTarget) + " sats/vB");
+            lowPremixFeeRate.setVisible(tx0FeeTarget == Tx0FeeTarget.MIN && getFeeRate(tx0FeeTarget) * 2 < getFeeRate(Tx0FeeTarget.BLOCKS_4));
         });
         premixPriority.setValue(1);
+        lowPremixFeeRate.managedProperty().bind(lowPremixFeeRate.visibleProperty());
+        lowPremixFeeRate.setVisible(false);
 
         if(mixConfig.getScode() != null) {
             step1.setVisible(false);
@@ -218,6 +224,10 @@ public class WhirlpoolController {
         });
     }
 
+    private int getFeeRate(Tx0FeeTarget tx0FeeTarget) {
+        return SparrowMinerFeeSupplier.getFee(Integer.parseInt(tx0FeeTarget.getFeeTarget().getValue()));
+    }
+
     public boolean next() {
         if(step1.isVisible()) {
             step1.setVisible(false);
@@ -318,6 +328,7 @@ public class WhirlpoolController {
             tx0Previews = null;
             whirlpool.setScode(mixConfig.getScode());
             whirlpool.setTx0FeeTarget(FEE_TARGETS.get(premixPriority.valueProperty().intValue()));
+            whirlpool.setMixFeeTarget(FEE_TARGETS.get(premixPriority.valueProperty().intValue()));
 
             Whirlpool.Tx0PreviewsService tx0PreviewsService = new Whirlpool.Tx0PreviewsService(whirlpool, utxoEntries);
             tx0PreviewsService.setOnRunning(workerStateEvent -> {

src/main/resources/com/sparrowwallet/sparrow/whirlpool/whirlpool.css

@@ -43,4 +43,8 @@
 
 .field-control {
     -fx-pref-width: 180px;
-}
+}
+
+.low-fee-warning {
+    -fx-text-fill: rgb(238, 210, 2);
+}

src/main/resources/com/sparrowwallet/sparrow/whirlpool/whirlpool.fxml

@@ -107,6 +107,17 @@
                     </padding>
                     <Label text="Premix Fee Rate:" styleClass="field-label" />
                     <CopyableLabel fx:id="premixFeeRate" />
+                    <Label fx:id="lowPremixFeeRate">
+                        <graphic>
+                            <Glyph fontFamily="Font Awesome 5 Free Solid" fontSize="12" icon="EXCLAMATION_TRIANGLE" styleClass="low-fee-warning"/>
+                        </graphic>
+                        <padding>
+                            <Insets left="12" />
+                        </padding>
+                        <tooltip>
+                            <Tooltip text="A low fee rate may delay the first mix."/>
+                        </tooltip>
+                    </Label>
                 </HBox>
             </VBox>
             <VBox fx:id="step4" spacing="15">