Merge pull request #47 from jiewei98/undo-command

Add a check if previous command was undoable

src/main/java/seedu/address/model/ModelManager.java

@@ -11,6 +11,7 @@
 import javafx.collections.transformation.FilteredList;
 import seedu.address.commons.core.GuiSettings;
 import seedu.address.commons.core.LogsCenter;
+import seedu.address.logic.commands.exceptions.CommandException;
 import seedu.address.model.person.Person;
 
 /**
@@ -26,6 +27,7 @@ public class ModelManager implements Model {
     private final FilteredList<Person> filteredPersons;
 
     private AddressBook backup;
+    private boolean undoable = false;
 
     /**
      * Initializes a ModelManager with the given addressBook and userPrefs.
@@ -100,27 +102,39 @@ public boolean hasPerson(Person person) {
 
     @Override
     public void deletePerson(Person target) {
+        undoable = true;
         backup = copyAddressBook();
         addressBook.removePerson(target);
+        undoable = false;
     }
 
     @Override
     public void addPerson(Person person) {
+        undoable = true;
         backup = copyAddressBook();
         addressBook.addPerson(person);
         updateFilteredPersonList(PREDICATE_SHOW_ALL_PERSONS);
+        undoable = false;
     }
 
     @Override
     public void setPerson(Person target, Person editedPerson) {
+        undoable = true;
         backup = copyAddressBook();
         requireAllNonNull(target, editedPerson);
         addressBook.setPerson(target, editedPerson);
+        undoable = false;
     }
 
     @Override
-    public void undoCommand() {
-        setAddressBook(backup);
+    public void undoCommand() throws CommandException {
+        if (undoable) {
+            setAddressBook(backup);
+            backup = copyAddressBook();
+        } else {
+            throw new CommandException(UNABLE_TO_UNDO);
+        }
+
     }
 
     /**

src/test/java/seedu/address/logic/commands/UndoCommandTest.java

@@ -0,0 +1,27 @@
+package seedu.address.logic.commands;
+
+import static seedu.address.logic.commands.CommandTestUtil.assertCommandFailure;
+import static seedu.address.testutil.TypicalPersons.getTypicalAddressBook;
+
+import org.junit.jupiter.api.Test;
+
+import seedu.address.model.Model;
+import seedu.address.model.ModelManager;
+import seedu.address.model.UserPrefs;
+
+/**
+ * Contains integration tests (interaction with the Model) and unit tests for
+ * {@code UndoCommand}.
+ */
+public class UndoCommandTest {
+
+    private Model model = new ModelManager(getTypicalAddressBook(), new UserPrefs());
+
+    @Test
+    public void execute_undoCommand_throwsCommandException() {
+        UndoCommand undoCommand = new UndoCommand();
+
+        assertCommandFailure(undoCommand, model, "Command cannot be undone");
+    }
+
+}