Move command argument checking out of ctor into a dedicated method and check prior to execution.

app/src/main/java/de/jotomo/ruffyscripter/RuffyScripter.java

@@ -4,6 +4,8 @@ import android.os.DeadObjectException;
 import android.os.RemoteException;
 import android.os.SystemClock;
 
+import com.google.common.base.Joiner;
+
 import org.monkey.d.ruffy.ruffy.driver.IRTHandler;
 import org.monkey.d.ruffy.ruffy.driver.IRuffyService;
 import org.monkey.d.ruffy.ruffy.driver.display.Menu;
@@ -13,6 +15,8 @@ import org.monkey.d.ruffy.ruffy.driver.display.menu.MenuTime;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.util.List;
+
 import de.jotomo.ruffyscripter.commands.Command;
 import de.jotomo.ruffyscripter.commands.CommandException;
 import de.jotomo.ruffyscripter.commands.CommandResult;
@@ -156,6 +160,12 @@ public class RuffyScripter {
         if (unrecoverableError != null) {
             return new CommandResult().success(false).enacted(false).message(unrecoverableError);
         }
+
+        List<String> violations = cmd.validateArguments();
+        if (!violations.isEmpty()) {
+            return new CommandResult().message(Joiner.on("\n").join(violations));
+        }
+
         synchronized (RuffyScripter.class) {
             try {
                 final RuffyScripter scripter = this;

app/src/main/java/de/jotomo/ruffyscripter/commands/BolusCommand.java

@@ -7,6 +7,8 @@ import org.monkey.d.ruffy.ruffy.driver.display.MenuType;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Locale;
 
 import de.jotomo.ruffyscripter.RuffyScripter;
@@ -20,6 +22,17 @@ public class BolusCommand implements Command {
         this.bolus = bolus;
     }
 
+    @Override
+    public List<String> validateArguments() {
+        List<String> violations = new ArrayList<>();
+
+        if (bolus > 0 && bolus < 25) {
+            violations.add("Requested bolus " + bolus + " out of limits (0-25)");
+        }
+
+        return violations;
+    }
+
     @Override
     public CommandResult execute(RuffyScripter scripter) {
         try {

app/src/main/java/de/jotomo/ruffyscripter/commands/CancelTbrCommand.java

@@ -5,6 +5,9 @@ import org.monkey.d.ruffy.ruffy.driver.display.MenuType;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.util.Collections;
+import java.util.List;
+
 import de.jotomo.ruffyscripter.RuffyScripter;
 
 // TODO robustness: can a TBR run out, whilst we're trying to cancel it?
@@ -13,6 +16,11 @@ import de.jotomo.ruffyscripter.RuffyScripter;
 public class CancelTbrCommand implements Command {
     private static final Logger log = LoggerFactory.getLogger(CancelTbrCommand.class);
 
+    @Override
+    public List<String> validateArguments() {
+        return Collections.emptyList();
+    }
+
     @Override
     public CommandResult execute(RuffyScripter scripter) {
         try {

app/src/main/java/de/jotomo/ruffyscripter/commands/Command.java

@@ -1,7 +1,10 @@
 package de.jotomo.ruffyscripter.commands;
 
+import java.util.List;
+
 import de.jotomo.ruffyscripter.RuffyScripter;
 
 public interface Command {
     CommandResult execute(RuffyScripter ruffyScripter);
+    List<String> validateArguments();
 }

app/src/main/java/de/jotomo/ruffyscripter/commands/ReadPumpStateCommand.java

@@ -1,5 +1,8 @@
 package de.jotomo.ruffyscripter.commands;
 
+import java.util.Collections;
+import java.util.List;
+
 import de.jotomo.ruffyscripter.RuffyScripter;
 
 public class ReadPumpStateCommand implements Command {
@@ -8,6 +11,11 @@ public class ReadPumpStateCommand implements Command {
         return new CommandResult().success(true).enacted(false).message("Returning pump state only");
     }
 
+    @Override
+    public List<String> validateArguments() {
+        return Collections.emptyList();
+    }
+
     @Override
     public String toString() {
         return "ReadPumpStateCommand{}";

app/src/main/java/de/jotomo/ruffyscripter/commands/SetTbrCommand.java

@@ -8,8 +8,9 @@ import org.monkey.d.ruffy.ruffy.driver.display.menu.MenuTime;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Locale;
-import java.util.Objects;
 
 import de.jotomo.ruffyscripter.RuffyScripter;
 
@@ -22,26 +23,33 @@ public class SetTbrCommand implements Command {
     public SetTbrCommand(long percentage, long duration) {
         this.percentage = percentage;
         this.duration = duration;
+    }
+
+    @Override
+    public List<String> validateArguments() {
+        List<String> violations = new ArrayList<>();
 
         if (percentage % 10 != 0) {
-            throw new IllegalArgumentException("TBR percentage must be set in 10% steps");
+            violations.add("TBR percentage must be set in 10% steps");
         }
         if (percentage < 0 || percentage > 500) {
-            throw new IllegalArgumentException("TBR percentage must be within 0-500%");
+            violations.add("TBR percentage must be within 0-500%");
         }
 
         if (percentage != 100) {
             if (duration % 15 != 0) {
-                throw new IllegalArgumentException("TBR duration can only be set in 15 minute steps");
+                violations.add("TBR duration can only be set in 15 minute steps");
             }
             if (duration > 60 * 24) {
-                throw new IllegalArgumentException("Maximum TBR duration is 24 hours");
+                violations.add("Maximum TBR duration is 24 hours");
             }
         }
 
         if (percentage == 0 && duration > 120) {
-            throw new IllegalArgumentException("Max allowed zero-temp duration is 2h");
+            violations.add("Max allowed zero-temp duration is 2h");
         }
+
+        return  violations;
     }
 
     @Override