Implement Undo command

src/main/java/seedu/address/logic/commands/UndoCommand.java

@@ -0,0 +1,27 @@
+package seedu.address.logic.commands;
+
+import static java.util.Objects.requireNonNull;
+
+import seedu.address.logic.commands.exceptions.CommandException;
+import seedu.address.model.Model;
+
+/**
+ * Clears the address book.
+ */
+public class UndoCommand extends Command {
+
+    public static final String COMMAND_WORD = "undo";
+    public static final String MESSAGE_SUCCESS = "Your latest command has been undone.";
+    public static final String MESSAGE_NO_COMMAND_TO_UNDO = "Please input a command first in order to undo it.";
+
+    @Override
+    protected CommandResult execute(Model model) throws CommandException {
+        requireNonNull(model);
+        if (!model.hasPreviousCommand()) {
+            throw new CommandException(MESSAGE_NO_COMMAND_TO_UNDO);
+        }
+        model.undoCommand();
+        return new CommandResult(MESSAGE_SUCCESS);
+    }
+
+}

src/main/java/seedu/address/logic/parser/AgentAssistParser.java

@@ -18,6 +18,7 @@
 import seedu.address.logic.commands.FilterCommand;
 import seedu.address.logic.commands.HelpCommand;
 import seedu.address.logic.commands.ListCommand;
+import seedu.address.logic.commands.UndoCommand;
 import seedu.address.logic.commands.ViewCommand;
 import seedu.address.logic.parser.exceptions.ParseException;
 
@@ -86,6 +87,9 @@ public Command parseCommand(String userInput) throws ParseException {
         case CloseCommand.COMMAND_WORD:
             return new CloseCommand();
 
+        case UndoCommand.COMMAND_WORD:
+            return new UndoCommand();
+
         default:
             logger.finer("This user input caused a ParseException: " + userInput);
             throw new ParseException(MESSAGE_UNKNOWN_COMMAND);

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

@@ -94,6 +94,15 @@ public void removePerson(Person key) {
         persons.remove(key);
     }
 
+    /**
+     * Gets a copy of the current AgentAssist.
+     */
+    public AgentAssist getCopy() {
+        AgentAssist newAgentAssist = new AgentAssist();
+        newAgentAssist.setPersons(this.getPersonList());
+        return newAgentAssist;
+    }
+
     //// util methods
 
     @Override

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

@@ -77,6 +77,16 @@ public interface Model {
      */
     void setPerson(Person target, Person editedPerson);
 
+    /**
+     * Undos previous command by setting currentAddressBook to historyAddressBook.
+     */
+    void undoCommand();
+
+    /**
+     * Returns true if a command has been executed before.
+     */
+    boolean hasPreviousCommand();
+
     /** Returns an unmodifiable view of the filtered person list */
     ObservableList<Person> getFilteredPersonList();
 

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

@@ -23,7 +23,8 @@
 public class ModelManager implements Model {
     private static final Logger logger = LogsCenter.getLogger(ModelManager.class);
 
-    private final AgentAssist agentAssist;
+    private AgentAssist historyAgentAssist = null;
+    private AgentAssist currentAgentAssist;
     private final UserPrefs userPrefs;
     private final FilteredList<Person> filteredPersons;
     private final SimpleObjectProperty<Person> selectedPerson = new SimpleObjectProperty<>();
@@ -37,15 +38,22 @@ public ModelManager(ReadOnlyAgentAssist agentAssist, ReadOnlyUserPrefs userPrefs
 
         logger.fine("Initializing with address book: " + agentAssist + " and user prefs " + userPrefs);
 
-        this.agentAssist = new AgentAssist(agentAssist);
+        this.currentAgentAssist = new AgentAssist(agentAssist);
         this.userPrefs = new UserPrefs(userPrefs);
-        filteredPersons = new FilteredList<>(this.agentAssist.getPersonList());
+        filteredPersons = new FilteredList<>(this.currentAgentAssist.getPersonList());
     }
 
     public ModelManager() {
         this(new AgentAssist(), new UserPrefs());
     }
 
+    /**
+     * Save the history of the AgentAssist.
+     */
+    private void safeHistory() {
+        historyAgentAssist = currentAgentAssist.getCopy();
+    }
+
 
     //=========== UserPrefs ==================================================================================
 
@@ -86,36 +94,50 @@ public void setAgentAssistFilePath(Path agentAssistFilePath) {
 
     @Override
     public void setAgentAssist(ReadOnlyAgentAssist agentAssist) {
-        this.agentAssist.resetData(agentAssist);
+        safeHistory();
+        this.currentAgentAssist.resetData(agentAssist);
     }
 
     @Override
     public ReadOnlyAgentAssist getAgentAssist() {
-        return agentAssist;
+        return currentAgentAssist;
     }
 
     @Override
     public boolean hasPerson(Person person) {
         requireNonNull(person);
-        return agentAssist.hasPerson(person);
+        return currentAgentAssist.hasPerson(person);
     }
 
     @Override
     public void deletePerson(Person target) {
-        agentAssist.removePerson(target);
+        safeHistory();
+        currentAgentAssist.removePerson(target);
     }
 
     @Override
     public void addPerson(Person person) {
-        agentAssist.addPerson(person);
+        safeHistory();
+        currentAgentAssist.addPerson(person);
         updateFilteredPersonList(PREDICATE_SHOW_ALL_PERSONS);
     }
 
     @Override
     public void setPerson(Person target, Person editedPerson) {
         requireAllNonNull(target, editedPerson);
+        safeHistory();
+        currentAgentAssist.setPerson(target, editedPerson);
+    }
 
-        agentAssist.setPerson(target, editedPerson);
+    @Override
+    public void undoCommand() {
+        requireNonNull(this.historyAgentAssist);
+        this.setAgentAssist(this.historyAgentAssist);
+    }
+
+    @Override
+    public boolean hasPreviousCommand() {
+        return this.historyAgentAssist != null;
     }
 
     //=========== Selected Person ===========================================================================
@@ -185,7 +207,7 @@ public boolean equals(Object other) {
         }
 
         ModelManager otherModelManager = (ModelManager) other;
-        return agentAssist.equals(otherModelManager.agentAssist)
+        return currentAgentAssist.equals(otherModelManager.currentAgentAssist)
                 && userPrefs.equals(otherModelManager.userPrefs)
                 && filteredPersons.equals(otherModelManager.filteredPersons);
     }

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

@@ -149,6 +149,16 @@ public void setPerson(Person target, Person editedPerson) {
             throw new AssertionError("This method should not be called.");
         }
 
+        @Override
+        public void undoCommand() {
+            throw new AssertionError("This method should not be called.");
+        }
+
+        @Override
+        public boolean hasPreviousCommand() {
+            throw new AssertionError("This method should not be called.");
+        }
+
         @Override
         public ObservableList<Person> getFilteredPersonList() {
             throw new AssertionError("This method should not be called.");

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

@@ -0,0 +1,45 @@
+package seedu.address.logic.commands;
+
+import static seedu.address.logic.commands.CommandTestUtil.assertCommandFailure;
+import static seedu.address.logic.commands.CommandTestUtil.assertCommandSuccess;
+import static seedu.address.testutil.TypicalIndexes.INDEX_FIRST_PERSON;
+import static seedu.address.testutil.TypicalPersons.getTypicalAgentAssist;
+
+import org.junit.jupiter.api.Test;
+
+import seedu.address.logic.commands.exceptions.CommandException;
+import seedu.address.model.Model;
+import seedu.address.model.ModelManager;
+import seedu.address.model.UserPrefs;
+import seedu.address.model.person.Person;
+import seedu.address.testutil.EditPersonDescriptorBuilder;
+import seedu.address.testutil.PersonBuilder;
+
+public class UndoCommandTest {
+
+    private Model model = new ModelManager(getTypicalAgentAssist(), new UserPrefs());
+
+    @Test
+    public void execute_undo_success() {
+        Person editedPerson = new PersonBuilder().build();
+        EditCommand.EditPersonDescriptor descriptor = new EditPersonDescriptorBuilder(editedPerson).build();
+        EditCommand editCommand = new EditCommand(INDEX_FIRST_PERSON, descriptor);
+        try {
+            CommandResult result = editCommand.execute(model);
+        } catch (CommandException ce) {
+            throw new AssertionError("Execution of command should not fail.", ce);
+        }
+
+        UndoCommand undoCommand = new UndoCommand();
+        Model expectedModel = new ModelManager(getTypicalAgentAssist(), new UserPrefs());
+
+        assertCommandSuccess(undoCommand, model, UndoCommand.MESSAGE_SUCCESS, expectedModel);
+    }
+
+    @Test
+    public void execute_noPreviousCommand_failure() {
+        Model model = new ModelManager();
+        assertCommandFailure(new UndoCommand(), model, UndoCommand.MESSAGE_NO_COMMAND_TO_UNDO);
+    }
+
+}