Add help command with full command guide

Author: memoflora

src/main/java/flora/command/HelpCommand.java

@@ -0,0 +1,52 @@
+package flora.command;
+
+import flora.storage.Storage;
+import flora.task.TaskList;
+
+/**
+ * Command to display a guide of all available commands.
+ */
+public class HelpCommand extends Command {
+
+    private static final String HELP_MESSAGE = """
+            Try one of these commands!
+
+            Adding tasks
+            • todo <description>
+            • deadline <description> /by <date>
+              (shortcuts: today, tomorrow, next week...)
+            • event <description> /from <start> /to <end>
+
+            Viewing tasks
+            • list
+            • find <keyword>
+
+            Managing tasks
+            • mark <task number>
+            • unmark <task number>
+            • delete <task number>
+            • edit <task number> [/desc ..] [/by ..] [/from ..] [/to ..]
+
+            Other
+            • help — show this guide
+            • bye — exit Flora
+
+            Date format: d/M/yyyy or d/M/yyyy H:mm
+            e.g. 25/12/2025 or 25/12/2025 14:00""";
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void execute(TaskList tasks, Storage storage) {
+        // No side effects needed.
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public String getMessage() {
+        return HELP_MESSAGE;
+    }
+}

src/main/java/flora/parser/Parser.java

@@ -16,6 +16,7 @@
 import flora.command.EditCommand;
 import flora.command.ExitCommand;
 import flora.command.FindCommand;
+import flora.command.HelpCommand;
 import flora.command.ListCommand;
 import flora.command.MarkCommand;
 import flora.command.UnmarkCommand;
@@ -55,9 +56,10 @@ public static Command parse(String input) throws FloraException {
         case "mark" -> new MarkCommand(getTaskIndex(input, firstSpaceIndex));
         case "unmark" -> new UnmarkCommand(getTaskIndex(input, firstSpaceIndex));
         case "list" -> new ListCommand();
+        case "help" -> new HelpCommand();
         case "bye" -> new ExitCommand();
         default -> throw new FloraException("Sorry, I don't recognize that command.\n"
-                           + "Try one of: todo, deadline, event, list, find, edit, mark, unmark, delete, bye");
+                           + "Type 'help' to see all available commands.");
         };
     }
 

src/test/java/flora/FloraTest.java

@@ -24,6 +24,7 @@
 import flora.command.EditCommand;
 import flora.command.ExitCommand;
 import flora.command.FindCommand;
+import flora.command.HelpCommand;
 import flora.command.ListCommand;
 import flora.command.MarkCommand;
 import flora.command.UnmarkCommand;
@@ -1224,6 +1225,27 @@ public void nonExitCommand_isExit_returnsFalse() throws FloraException {
         assertFalse(cmd.isExit());
     }
 
+    // ==================== Command: HelpCommand ====================
+
+    @Test
+    public void parser_parseHelp_returnsHelpCommand() throws FloraException {
+        Command cmd = Parser.parse("help");
+        assertInstanceOf(HelpCommand.class, cmd);
+    }
+
+    @Test
+    public void helpCommand_getMessage_returnsNonBlank() {
+        HelpCommand cmd = new HelpCommand();
+        cmd.execute(new TaskList(), null);
+        assertFalse(cmd.getMessage().isBlank());
+    }
+
+    @Test
+    public void helpCommand_isExit_returnsFalse() {
+        HelpCommand cmd = new HelpCommand();
+        assertFalse(cmd.isExit());
+    }
+
     // ==================== FloraException ====================
 
     @Test