Add Undo and Redo commands

src/main/java/seedu/address/MainApp.java

@@ -79,7 +79,7 @@ private Model initModelManager(Storage storage, ReadOnlyUserPrefs userPrefs) {
         ReadOnlyAddressBook initialData;
         try {
             addressBookOptional = storage.readAddressBook();
-            if (!addressBookOptional.isPresent()) {
+            if (addressBookOptional.isEmpty()) {
                 logger.info("Creating a new data file " + storage.getAddressBookFilePath()
                         + " populated with a sample AddressBook.");
             }
@@ -89,7 +89,6 @@ private Model initModelManager(Storage storage, ReadOnlyUserPrefs userPrefs) {
                     + " Will be starting with an empty AddressBook.");
             initialData = new AddressBook();
         }
-
         return new ModelManager(initialData, userPrefs);
     }
 

src/main/java/seedu/address/history/History.java

@@ -0,0 +1,36 @@
+package seedu.address.history;
+
+import seedu.address.history.exceptions.HistoryException;
+
+/**
+ * The `History` class manages the history of states in the ConnectCare application.
+ * It allows for rolling back and rolling forward to previous states.
+ */
+public interface History {
+    /**
+     * Rolls back to the previous state in the history.
+     *
+     */
+    void rollBackState() throws HistoryException;
+
+    /**
+     * Rolls forward to the next state in the history.
+     *
+     * @throws Exception If there are no more future states to roll forward to.
+     */
+    void rollForwardState() throws HistoryException;
+
+    /**
+     * Adds a new state to the history, removing subsequent states.
+     *
+     * @param state The state to add to the history.
+     */
+    void addState(State state);
+
+    /**
+     * Gets the current state from the history.
+     *
+     * @return The current state.
+     */
+    State getCurrState();
+}

src/main/java/seedu/address/history/HistoryManager.java

@@ -0,0 +1,80 @@
+package seedu.address.history;
+
+import java.util.ArrayList;
+
+import seedu.address.history.exceptions.HistoryException;
+
+
+/**
+ * The `HistoryManager` class manages the history of commands used in the ConnectCare application.
+ * It facilitates the undoing and redoing commands and updating the command history.
+ */
+public class HistoryManager implements History {
+    private int currStateIdx;
+    private final ArrayList<State> states;
+
+    /**
+     * Constructs a new HistoryManager with a starting state.
+     *
+     * @param startState The initial state of the history.
+     */
+    public HistoryManager(State startState) {
+        states = new ArrayList<>();
+        states.add(startState);
+        currStateIdx = 0;
+    }
+
+    /**
+     * Removes states after the current state, effectively truncating the history.
+     */
+    private void truncate() {
+        assert (currStateIdx >= 0 && currStateIdx < states.size());
+        states.subList(currStateIdx + 1, states.size()).clear();
+    }
+
+    /**
+     * Rolls back to the previous state in the history.
+     */
+    @Override
+    public void rollBackState() throws HistoryException {
+        if (currStateIdx == 0) {
+            throw new HistoryException("You can't rollback the state anymore!");
+        }
+        currStateIdx -= 1;
+    }
+
+    /**
+     * Rolls forward to the next state in the history.
+     *
+     * @throws Exception If there are no more future states to roll forward to.
+     */
+    @Override
+    public void rollForwardState() throws HistoryException {
+        if (currStateIdx == states.size() - 1) {
+            throw new HistoryException("You can't roll forward the state anymore!");
+        }
+        currStateIdx += 1;
+    }
+
+    /**
+     * Adds a new state to the history, removing subsequent states.
+     *
+     * @param state The state to add to the history.
+     */
+    @Override
+    public void addState(State state) {
+        truncate();
+        states.add(state);
+        currStateIdx += 1;
+    }
+
+    /**
+     * Gets the current state from the history.
+     *
+     * @return The current state.
+     */
+    @Override
+    public State getCurrState() {
+        return states.get(currStateIdx);
+    }
+}

src/main/java/seedu/address/history/State.java

@@ -0,0 +1,86 @@
+package seedu.address.history;
+
+import java.util.function.Predicate;
+
+import javafx.collections.transformation.FilteredList;
+import seedu.address.logic.commands.Command;
+import seedu.address.model.ReadOnlyAddressBook;
+import seedu.address.model.person.Person;
+
+
+
+/**
+ * The `State` class represents a snapshot of the ConnectCare application's state at a specific point in time.
+ * It contains information about the executed command and the list of tasks at that time.
+ */
+public class State {
+    private final Command command;
+    private final ReadOnlyAddressBook addressBook;
+    private final Predicate<? super Person> filteredPersonsListPredicate;
+
+    /**
+     * Constructs a new State object with the given command and task list.
+     *
+     * @param command                      The command executed to reach this state.
+     * @param addressBook                  The list of tasks at this state.
+     * @param filteredPersonsListPredicate The predicate of the filtered list
+     */
+    public State(Command command, ReadOnlyAddressBook addressBook,
+                 Predicate<? super Person> filteredPersonsListPredicate) {
+        this.command = command;
+        this.addressBook = addressBook;
+        this.filteredPersonsListPredicate = filteredPersonsListPredicate;
+    }
+
+    /**
+     * Gets the list of tasks at this state.
+     *
+     * @return The list of tasks.
+     */
+    public ReadOnlyAddressBook getAddressBook() {
+        return addressBook;
+    }
+
+    /**
+     * Gets the command executed to reach this state.
+     *
+     * @return The command.
+     */
+    public Command getCommand() {
+        return command;
+    }
+
+    /**
+     * Gets the command executed to reach this state.
+     *
+     * @return The command.
+     */
+    public Predicate<? super Person> getFilteredPersonsListPredicate() {
+        return filteredPersonsListPredicate;
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        if (other == this) {
+            return true;
+        }
+
+        // instanceof handles nulls
+        if (!(other instanceof State)) {
+            return false;
+        }
+
+        State otherState = (State) other;
+
+        FilteredList<Person> filteredListOther = new FilteredList<>(otherState.addressBook.getPersonList());
+        filteredListOther.setPredicate(otherState.filteredPersonsListPredicate);
+
+        FilteredList<Person> filteredList = new FilteredList<>(otherState.addressBook.getPersonList());
+        filteredList.setPredicate(filteredPersonsListPredicate);
+
+        return addressBook.equals(otherState.addressBook)
+                && command.equals(otherState.command)
+                && filteredList.equals(filteredListOther);
+
+    }
+}

src/main/java/seedu/address/history/exceptions/HistoryException.java

@@ -0,0 +1,18 @@
+package seedu.address.history.exceptions;
+
+/**
+ * Represents an error which occurs during execution of an invalid history rollback/roll-forward
+ */
+public class HistoryException extends Exception {
+
+    public HistoryException(String message) {
+        super(message);
+    }
+
+    /**
+     * Constructs a new {@code HistoryException} with the specified detail {@code message} and {@code cause}.
+     */
+    public HistoryException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

src/main/java/seedu/address/logic/LogicManager.java

@@ -8,6 +8,7 @@
 import javafx.collections.ObservableList;
 import seedu.address.commons.core.GuiSettings;
 import seedu.address.commons.core.LogsCenter;
+import seedu.address.history.exceptions.HistoryException;
 import seedu.address.logic.commands.Command;
 import seedu.address.logic.commands.CommandResult;
 import seedu.address.logic.commands.exceptions.CommandException;
@@ -26,7 +27,8 @@ public class LogicManager implements Logic {
 
     public static final String FILE_OPS_PERMISSION_ERROR_FORMAT =
             "Could not save data to file %s due to insufficient permissions to write to the file or the folder.";
-
+    public static final String HISTORY_SAVE_ERROR_FORMAT =
+            "Could not save state to history due to encoding errors. %s";
     private final Logger logger = LogsCenter.getLogger(LogicManager.class);
 
     private final Model model;
@@ -58,6 +60,14 @@ public CommandResult execute(String commandText) throws CommandException, ParseE
             throw new CommandException(String.format(FILE_OPS_ERROR_FORMAT, ioe.getMessage()), ioe);
         }
 
+        try {
+            model.updateState(command);
+        } catch (HistoryException e) {
+            model.restoreState(model.getCurrentState()); //Revert the command if there are issues updating state
+            throw new CommandException(String.format(HISTORY_SAVE_ERROR_FORMAT, e.getMessage()), e);
+        }
+
+
         return commandResult;
     }
 

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

@@ -51,6 +51,8 @@ public class AddCommand extends Command {
      */
     public AddCommand(Person person) {
         requireNonNull(person);
+
+        super.setReversible(true);
         toAdd = person;
     }
 
@@ -87,4 +89,8 @@ public String toString() {
                 .add("toAdd", toAdd)
                 .toString();
     }
+    @Override
+    public String getCommandString() {
+        return COMMAND_WORD;
+    }
 }

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

@@ -12,12 +12,17 @@ public class ClearCommand extends Command {
 
     public static final String COMMAND_WORD = "clear";
     public static final String MESSAGE_SUCCESS = "Address book has been cleared!";
-
-
+    public ClearCommand() {
+        super.setReversible(true);
+    }
     @Override
     public CommandResult execute(Model model) {
         requireNonNull(model);
         model.setAddressBook(new AddressBook());
         return new CommandResult(MESSAGE_SUCCESS);
     }
+    @Override
+    public String getCommandString() {
+        return COMMAND_WORD;
+    }
 }

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

@@ -7,6 +7,7 @@
  * Represents a command with hidden internal logic and the ability to be executed.
  */
 public abstract class Command {
+    private boolean isReversible;
 
     /**
      * Executes the command and returns the result message.
@@ -16,5 +17,11 @@ public abstract class Command {
      * @throws CommandException If an error occurs during command execution.
      */
     public abstract CommandResult execute(Model model) throws CommandException;
-
+    public abstract String getCommandString();
+    public boolean isReversible() {
+        return isReversible;
+    }
+    public void setReversible(boolean setValue) {
+        isReversible = setValue;
+    }
 }

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

@@ -27,7 +27,11 @@ public class DeleteCommand extends Command {
 
     private final Index targetIndex;
 
+    /**
+     * @param targetIndex Index to be deleted
+     */
     public DeleteCommand(Index targetIndex) {
+        super.setReversible(true);
         this.targetIndex = targetIndex;
     }
 
@@ -66,4 +70,8 @@ public String toString() {
                 .add("targetIndex", targetIndex)
                 .toString();
     }
+    @Override
+    public String getCommandString() {
+        return COMMAND_WORD;
+    }
 }

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

@@ -10,10 +10,15 @@ public class ExitCommand extends Command {
     public static final String COMMAND_WORD = "exit";
 
     public static final String MESSAGE_EXIT_ACKNOWLEDGEMENT = "Exiting Address Book as requested ...";
-
+    public ExitCommand() {
+        super.setReversible(false);
+    }
     @Override
     public CommandResult execute(Model model) {
         return new CommandResult(MESSAGE_EXIT_ACKNOWLEDGEMENT, false, true);
     }
-
+    @Override
+    public String getCommandString() {
+        return COMMAND_WORD;
+    }
 }